Applied Sciences

Editorial

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3 pages, 169 KiB

Open AccessEditorial

Special Issue on Fatigue and Fracture of Non-Metallic Materials and Structures

by Andrea Spagnoli

Appl. Sci. 2020, 10(5), 1841; https://doi.org/10.3390/app10051841 - 7 Mar 2020

Cited by 1 | Viewed by 2038

Abstract

This Special Issue covers the broad topic of structural integrity of non-metallic materials, and it is concerned with the modelling, assessment and reliability of structural elements of any scale. In particular, the articles being contained in this issue concentrate on the mechanics of [...] Read more.

This Special Issue covers the broad topic of structural integrity of non-metallic materials, and it is concerned with the modelling, assessment and reliability of structural elements of any scale. In particular, the articles being contained in this issue concentrate on the mechanics of fracture and fatigue in relation to applications to a variety of non-metallic materials, including concrete and cementitious composites, rocks, glass, ceramics, bituminous mixtures, composites, polymers, rubber and soft matters, bones and biological materials, advanced and multifunctional materials. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

Research

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22 pages, 2992 KiB

Open AccessArticle

Comparative Fatigue Life Assessment of Wind Turbine Blades Operating with Different Regulation Schemes

by Brian Loza, Josué Pacheco-Chérrez, Diego Cárdenas, Luis I. Minchala and Oliver Probst

Appl. Sci. 2019, 9(21), 4632; https://doi.org/10.3390/app9214632 - 31 Oct 2019

Cited by 12 | Viewed by 4767

Abstract

A comparative evaluation of the fatigue damage occurring in the blades of small wind turbines, with different power regulation schemes, has been conducted for the first time. Three representative test cases were built, one based on stall regulation and two using pitch regulation. [...] Read more.

A comparative evaluation of the fatigue damage occurring in the blades of small wind turbines, with different power regulation schemes, has been conducted for the first time. Three representative test cases were built, one based on stall regulation and two using pitch regulation. The power curves were tuned to be identical in all cases, in order to allow for a direct comparison of fatigue damage. A methodology combining a dynamic simulation of a wind turbine forced by stochastic wind speed time series, with the application of the IEC 61400-2 standard, was designed and applied for two levels of turbulence intensity. The effect of the wind regime was studied by considering Weibull-distributed wind speeds with a variety of parameter sets. Not unexpectedly, in typical wind regimes, stall regulation led to a generally higher fatigue damage than pitch regulation, for similar structural blade design, but the practical implications were smaller than thought previously. Given the need for cost-effective designs for small wind turbines, stall regulation may be a viable alternative for off-grid applications. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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16 pages, 1900 KiB

Open AccessFeature PaperArticle

A Numerical Evaluation of SIFs of 2-D Functionally Graded Materials by Enriched Natural Element Method

by Jin-Rae Cho

Appl. Sci. 2019, 9(17), 3581; https://doi.org/10.3390/app9173581 - 1 Sep 2019

Cited by 14 | Viewed by 2342

Abstract

This paper presents the numerical prediction of stress intensity factors (SIFs) of 2-D inhomogeneous functionally graded materials (FGMs) by an enriched Petrov-Galerkin natural element method (PG-NEM). The overall trial displacement field was approximated in terms of Laplace interpolation functions, and the crack tip [...] Read more.

This paper presents the numerical prediction of stress intensity factors (SIFs) of 2-D inhomogeneous functionally graded materials (FGMs) by an enriched Petrov-Galerkin natural element method (PG-NEM). The overall trial displacement field was approximated in terms of Laplace interpolation functions, and the crack tip one was enhanced by the crack-tip singular displacement field. The overall stress and strain distributions, which were obtained by PG-NEM, were smoothened and improved by the stress recovery. The modified interaction integral

{\tilde{M}}^{(1, 2)}

was employed to evaluate the stress intensity factors of FGMs with spatially varying elastic moduli. The proposed method was validated through the representative numerical examples and the effectiveness was justified by comparing the numerical results with the reference solutions. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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28 pages, 2422 KiB

Open AccessArticle

An Elastic Interface Model for the Delamination of Bending-Extension Coupled Laminates

by Stefano Bennati, Paolo Fisicaro, Luca Taglialegne and Paolo S. Valvo

Appl. Sci. 2019, 9(17), 3560; https://doi.org/10.3390/app9173560 - 30 Aug 2019

Cited by 18 | Viewed by 4111 | Correction

Abstract

The paper addresses the problem of an interfacial crack in a multi-directional laminated beam with possible bending-extension coupling. A crack-tip element is considered as an assemblage of two sublaminates connected by an elastic-brittle interface of negligible thickness. Each sublaminate is modeled as an [...] Read more.

The paper addresses the problem of an interfacial crack in a multi-directional laminated beam with possible bending-extension coupling. A crack-tip element is considered as an assemblage of two sublaminates connected by an elastic-brittle interface of negligible thickness. Each sublaminate is modeled as an extensible, flexible, and shear-deformable laminated beam. The mathematical problem is reduced to a set of two differential equations in the interfacial stresses. Explicit expressions are derived for the internal forces, strain measures, and generalized displacements in the sublaminates. Then, the energy release rate and its Mode I and Mode II contributions are evaluated. As an example, the model is applied to the analysis of the double cantilever beam test with both symmetric and asymmetric laminated specimens. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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18 pages, 2787 KiB

Open AccessArticle

Failure Probability Prediction of Thermally Stable Diamond Composite Tipped Picks in the Cutting Cycle of Underground Roadway Development

by Yong Sun, Xingsheng Li and Hua Guo

Appl. Sci. 2019, 9(16), 3294; https://doi.org/10.3390/app9163294 - 11 Aug 2019

Cited by 5 | Viewed by 2531

Abstract

The Thermally Stable Diamond Composite (TSDC) tipped pick has been developed to replace Tungsten Carbide (WC) tipped picks for hard rock cutting. Due to the material properties of TSDC, a major failure mode of TSDC tipped picks during rock cutting is random failures [...] Read more.

The Thermally Stable Diamond Composite (TSDC) tipped pick has been developed to replace Tungsten Carbide (WC) tipped picks for hard rock cutting. Due to the material properties of TSDC, a major failure mode of TSDC tipped picks during rock cutting is random failures caused by excessive bending force acting on the cutting tips. A probabilistic approach has been proposed to estimate the failure probability of picks with this failure mode. However, there are two limitations in existing research: only one drum revolution is considered, and the variation of rock thickness is ignored. This study aims to extend the current approach via removing these limitations, based on the failure probability analysis of picks over a full cutting cycle in the underground coal mining roadway development process. The research results show that both drum advance direction and the variation of rock thickness have significant impacts on pick failure probability. The extended approach can be used to estimate pick failure probability for more realistic scenarios in real applications with improved accuracy. Although the study focused on TSDC tipped picks, the developed approach can also be applied to other types of picks. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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10 pages, 3825 KiB

Open AccessArticle

Wedge-Splitting Test on Carbon-Containing Refractories at High Temperatures

by Martin Stückelschweiger, Dietmar Gruber, Shengli Jin and Harald Harmuth

Appl. Sci. 2019, 9(16), 3249; https://doi.org/10.3390/app9163249 - 8 Aug 2019

Cited by 15 | Viewed by 4691

Abstract

The mode I fracture behavior of ordinary refractory materials is usually tested with the wedge-splitting test. At elevated temperatures, the optical displacement measurement is difficult because of the convection in the furnace and possible reactions of refractory components with the ambient atmosphere. The [...] Read more.

The mode I fracture behavior of ordinary refractory materials is usually tested with the wedge-splitting test. At elevated temperatures, the optical displacement measurement is difficult because of the convection in the furnace and possible reactions of refractory components with the ambient atmosphere. The present paper introduces a newly developed testing device, which is able to perform such experiments up to 1500 °C. For the testing of carbon-containing refractories a gas purging, for example, with argon, is possible. Laser speckle extensometers are applied for the displacement measurement. A carbon-containing magnesia refractory (MgO–C) was selected for a case study. Based on the results obtained from tests, fracture mechanical parameters such as the specific fracture energy and the nominal notch tensile strength were calculated. An inverse simulation procedure applying the finite element method yields tensile strength, the total specific fracture energy, and the strain-softening behavior. Additionally, the creep behavior was also considered for the evaluation. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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11 pages, 3994 KiB

Open AccessArticle

Fatigue in Concrete under Low-Cycle Tensile Loading Using a Pressure-Tension Apparatus

by Sayed M. Soleimani, Andrew J. Boyd, Andrew J.K. Komar and Sajjad S. Roudsari

Appl. Sci. 2019, 9(16), 3217; https://doi.org/10.3390/app9163217 - 7 Aug 2019

Cited by 3 | Viewed by 3007

Abstract

Fatigue due to low-cycle tensile loading in plain concrete was examined under different conditions using the pressure-tension apparatus. A total of 22 wet or dry standard concrete cylinders (100 mm × 200 mm) were tested. By definition, low-cycle loading refers to the concept [...] Read more.

Fatigue due to low-cycle tensile loading in plain concrete was examined under different conditions using the pressure-tension apparatus. A total of 22 wet or dry standard concrete cylinders (100 mm × 200 mm) were tested. By definition, low-cycle loading refers to the concept of multiple load cycles applied at high stress levels (i.e., a concrete structure subjected to seismic loading). Results suggest that concrete samples subjected to low-cycle tensile loading will fail after a relatively low number of cycles of loading and at a lower magnitude of stress compared to the maximum value applied during cyclic loading. Furthermore, non-destructive testing was employed in order to ascertain the extent of progressive damage inflicted by tensile loading in concrete specimens. It was found that ultrasonic pulse velocity is a viable technique for evaluating the damage consequential of loads applied to concrete, including that resultant from low levels of tensile stress (i.e., as low as 10% of its maximum tensile capacity). Additionally, finite element analysis was performed on a modeled version of the pressure-tension apparatus with a sample of concrete, which has yielded similar results to the experimental work. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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20 pages, 9094 KiB

Open AccessArticle

Plain and Fiber-Reinforced Concrete Subjected to Cyclic Compressive Loading: Study of the Mechanical Response and Correlations with Microstructure Using CT Scanning

by Jesús Mínguez, Laura Gutiérrez, Dorys C. González and Miguel A. Vicente

Appl. Sci. 2019, 9(15), 3030; https://doi.org/10.3390/app9153030 - 27 Jul 2019

Cited by 12 | Viewed by 2982

Abstract

The response ranges of three principal mechanical parameters were measured following cyclic compressive loading of three types of concrete specimen to a pre-defined number of cycles. Thus, compressive strength, compressive modulus of elasticity, and maximum compressive strain were studied in (i) plain, (ii) [...] Read more.

The response ranges of three principal mechanical parameters were measured following cyclic compressive loading of three types of concrete specimen to a pre-defined number of cycles. Thus, compressive strength, compressive modulus of elasticity, and maximum compressive strain were studied in (i) plain, (ii) steel-fiber-reinforced, and (iii) polypropylene-fiber-reinforced high-performance concrete specimens. A specific procedure is presented for evaluating the residual values of the three mechanical parameters. The results revealed no significant variation in the mechanical properties of the concrete mixtures within the test range, and slight improvements in the mechanical responses were, in some cases, detected. In contrast, the scatter of the mechanical parameters significantly increased with the number of cycles. In addition, all the specimens were scanned by means of high resolution computed tomography, in order to visualize the microstructure and the internal damage (i.e., internal micro cracks). Consistent with the test results, the images revealed no observable internal damage caused by the cyclic loading. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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21 pages, 11216 KiB

Open AccessArticle

Meso-Scale Simulation of Concrete Based on Fracture and Interaction Behavior

by Xueyu Xiong and Qisheng Xiao

Appl. Sci. 2019, 9(15), 2986; https://doi.org/10.3390/app9152986 - 25 Jul 2019

Cited by 27 | Viewed by 4260

Abstract

Based on the cohesive zone model, a meso-scale model is developed for numerical studies of three-phase concrete under tension and compression. The model is characterized by adopting mixed-mode fracture and interaction behavior to describe fracture, friction and collision in tension and compression processes. [...] Read more.

Based on the cohesive zone model, a meso-scale model is developed for numerical studies of three-phase concrete under tension and compression. The model is characterized by adopting mixed-mode fracture and interaction behavior to describe fracture, friction and collision in tension and compression processes. The simulation results match satisfactorily with the experimental results in both mechanical characteristics and failure mode. Whole deformation and crack propagation process analyses are conducted to reveal damage evolution of concrete. The analyses also set a foundation for the following parametric studies in which mode II fracture energy, material parameter, frictional angle and aggregates’ mechanical characteristics are considered as variables. It shows that the mixed-mode fracture accounts for a considerable proportion, even in tension failure. Under compression, the frictional stress can constrain crack propagation at the beginning of the damage and reestablish loading path during the softening stage. Aggregates’ mechanical characteristics mainly affect concrete’s performance in the mid-and-late softening stage. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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14 pages, 3257 KiB

Open AccessArticle

Numerical Investigation of Mineral Grain Shape Effects on Strength and Fracture Behaviors of Rock Material

by Zhenhua Han, Luqing Zhang and Jian Zhou

Appl. Sci. 2019, 9(14), 2855; https://doi.org/10.3390/app9142855 - 17 Jul 2019

Cited by 11 | Viewed by 3320

Abstract

Rock is an aggregate of mineral grains, and the grain shape has an obvious influence on rock mechanical behaviors. Current research on grain shape mostly focuses on loose granular materials and lacks standardized quantitative methods. Based on the CLUMP method in the two-dimensional [...] Read more.

Rock is an aggregate of mineral grains, and the grain shape has an obvious influence on rock mechanical behaviors. Current research on grain shape mostly focuses on loose granular materials and lacks standardized quantitative methods. Based on the CLUMP method in the two-dimensional particle flow code (PFC^2D), three different grain groups were generated: strip, triangle, and square. Flatness and roughness were adopted to describe the overall contour and the surface morphology of the mineral grains, respectively. Simulated results showed that the grain shape significantly affected rock porosity and further influenced the peak strength and elastic modulus. The peak strength and elastic modulus of the model with strip-shaped grains were the highest, followed by the models with triangular and square grains. The effects of flatness and roughness on rock peak strength were the opposite, and the peak strength had a significant, positive correlation with cohesion. Tensile cracking was dominant among the generated microcracks, and the percentage of tensile cracking was maximal in the model with square grains. At the postpeak stage, the interlocking between grains was enhanced along with the increased surface roughness, which led to a slower stress drop. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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16 pages, 6312 KiB

Open AccessArticle

Analytical Study of Reinforced Concrete Beams Tested under Quasi-Static and Impact Loadings

by Sayed Mohamad Soleimani and Sajjad Sayyar Roudsari

Appl. Sci. 2019, 9(14), 2838; https://doi.org/10.3390/app9142838 - 16 Jul 2019

Cited by 13 | Viewed by 4864

Abstract

During dynamic events (such as impact forces), structures fail to absorb the incoming energy and catastrophic collapse may occur. Impact and quasi-static tests were carried out on reinforced concrete beams with and without externally bounded sprayed and fabric glass fiber-reinforced polymers. For impact [...] Read more.

During dynamic events (such as impact forces), structures fail to absorb the incoming energy and catastrophic collapse may occur. Impact and quasi-static tests were carried out on reinforced concrete beams with and without externally bounded sprayed and fabric glass fiber-reinforced polymers. For impact loading, a fully instrumented drop-weight impact machine with a capacity of 14.5 kJ was used. The drop height and loading rate were varied. The load-carrying capacity of reinforced concrete beams under impact loading was obtained using instrumented anvil supports (by summing the support reactions). In quasi-static loading conditions, the beams were tested in three-point loading using a Baldwin Universal Testing Machine. ABAQUS FEA software was used to model some of the tested reinforced concrete beams. It was shown that the stiffness of reinforced concrete beams decreases with increasing drop height. It was also shown that applying sprayed glass fiber-reinforced polymers (with and without mechanical stiffeners) and fabric glass fiber-reinforced polymers on the surface of reinforced concrete beams increased the stiffness. Results obtained from the software analyses were in good agreement with the laboratory test results. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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25 pages, 4354 KiB

Open AccessArticle

A Damage Model for Concrete under Fatigue Loading

by Zhi Shan, Zhiwu Yu, Xiao Li, Xiaoyong Lv and Zhenyu Liao

Appl. Sci. 2019, 9(13), 2768; https://doi.org/10.3390/app9132768 - 9 Jul 2019

Cited by 6 | Viewed by 3879

Abstract

For concrete, fatigue is an essential mechanical behavior. Concrete structures subjected to fatigue loads usually experience a progressive degradation/damage process and even an abrupt failure. However, in the literature, certain essential damage behaviors are not well considered in the study of the mechanism [...] Read more.

For concrete, fatigue is an essential mechanical behavior. Concrete structures subjected to fatigue loads usually experience a progressive degradation/damage process and even an abrupt failure. However, in the literature, certain essential damage behaviors are not well considered in the study of the mechanism for fatigue behaviors such as the development of irreversible/residual strains. In this work, a damage model with the concept of mode-II microcracks on the crack face and nearby areas contributing to the development of irreversible strains was proposed. By using the micromechanics method, a micro-cell-based damage model under multi-axial loading was introduced to understand the damage behaviors for concrete. By a thermodynamic interpretation of the damage behaviors, a novel fatigue damage variable (irreversible deformation fatigue damage variable) was defined. This variable is able to describe irreversible strains generated by both mode-II microcracks and irreversible frictional sliding. The proposed model considered both elastic and irreversible deformation fatigue damages. It is found that the prediction by the proposed model of cyclic creep, stiffness degradation and post-fatigue stress-strain relationship of concrete agrees well with experimental results. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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15 pages, 5145 KiB

Open AccessArticle

Experimental Investigation on Chemical Grouting in a Permeated Fracture Replica with Different Roughness

by Lichuang Jin, Wanghua Sui and Jialu Xiong

Appl. Sci. 2019, 9(13), 2762; https://doi.org/10.3390/app9132762 - 9 Jul 2019

Cited by 23 | Viewed by 3416

Abstract

This paper presents an experimental investigation on chemical grouting in a permeated fracture replica considering its roughness. Tests of grouting with flowing water in the fracture replica were carried out under different Bardon’s standard roughness profiles. The interactions between influential factors were considered [...] Read more.

This paper presents an experimental investigation on chemical grouting in a permeated fracture replica considering its roughness. Tests of grouting with flowing water in the fracture replica were carried out under different Bardon’s standard roughness profiles. The interactions between influential factors were considered and an experimental platform for grouting in rough fractures with flowing water was established. The effect of chemical grouting in fractures with flowing water was investigated using orthogonal experiment. The joint roughness coefficient (JRC), the initial water flow rate, the gel time, and the fracture opening were selected as factors in the orthogonal experiment. The results show that there is a positive correlation between the water plugging rate and JRC, and negative correlations between the water plugging rate and the initial water flow rate, gel time, and fracture opening. The change curve of the water flow rate is divided into three categories: Single platform decreasing type, double platform decreasing type, and multi-peak fluctuating type. The curve of seepage pressure contains three categories: Single peak type, multi-peak type and platform type. The results provide a reference for grouting in rock fractures. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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21 pages, 9901 KiB

Open AccessArticle

Numerical–Experimental Correlation of Impact-Induced Damages in CFRP Laminates

by Andrea Sellitto, Salvatore Saputo, Francesco Di Caprio, Aniello Riccio, Angela Russo and Valerio Acanfora

Appl. Sci. 2019, 9(11), 2372; https://doi.org/10.3390/app9112372 - 11 Jun 2019

Cited by 32 | Viewed by 4665

Abstract

Composite laminates are characterized by high mechanical in-plane properties and poor out-of-plane characteristics. This issue becomes even more relevant when dealing with impact phenomena occurring in the transverse direction. In aeronautics, Low Velocity Impacts (LVIs) may occur during the service life of the [...] Read more.

Composite laminates are characterized by high mechanical in-plane properties and poor out-of-plane characteristics. This issue becomes even more relevant when dealing with impact phenomena occurring in the transverse direction. In aeronautics, Low Velocity Impacts (LVIs) may occur during the service life of the aircraft. LVI may produce damage inside the laminate, which are not easily detectable and can seriously degrade the mechanical properties of the structure. In this paper, a numerical-experimental investigation is carried out, in order to study the mechanical behavior of rectangular laminated specimens subjected to low velocity impacts. The numerical model that best represents the impact phenomenon has been chosen by numerical–analytical investigations. A user defined material model (VUMAT) has been developed in Abaqus/Explicit environment to simulate the composite intra-laminar damage behavior in solid elements. The analyses results were compared to experimental test data on a laminated specimen, performed according to ASTM D7136 standard, in order to verify the robustness of the adopted numerical model and the influence of modeling parameters on the accuracy of numerical results. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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19 pages, 3021 KiB

Open AccessArticle

Fatigue Assessment of Prestressed Concrete Slab-Between-Girder Bridges

by Eva O.L. Lantsoght, Rutger Koekkoek, Cor van der Veen and Henk Sliedrecht

Appl. Sci. 2019, 9(11), 2312; https://doi.org/10.3390/app9112312 - 5 Jun 2019

Cited by 11 | Viewed by 4539

Abstract

In the Netherlands, the assessment of existing prestressed concrete slab-between-girder bridges has revealed that the thin, transversely prestressed slabs may be critical for static and fatigue punching when evaluated using the recently introduced Eurocodes. On the other hand, compressive membrane action increases the [...] Read more.

In the Netherlands, the assessment of existing prestressed concrete slab-between-girder bridges has revealed that the thin, transversely prestressed slabs may be critical for static and fatigue punching when evaluated using the recently introduced Eurocodes. On the other hand, compressive membrane action increases the capacity of these slabs, and it changes the failure mode from bending to punching shear. To improve the assessment of the existing prestressed slab-between-girder bridges in the Netherlands, two 1:2 scale models of an existing bridge, i.e., the Van Brienenoord Bridge, were built in the laboratory and tested monotonically, as well as under cycles of loading. The result of these experiments revealed: (1) the static strength of the decks, which showed that compressive membrane action significantly enhanced the punching capacity, and (2) the Wöhler curve of the decks, showed that the compressive membrane action remains under fatigue loading. The experimental results could then be used in the assessment of the most critical existing slab-between-girder bridges. The outcome was that the bridge had sufficient punching capacity for static and fatigue loads and, therefore, the existing slab-between-girder bridges in the Netherlands fulfilled the code requirements for static and fatigue punching. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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12 pages, 2936 KiB

Open AccessArticle

Effects of Fineness and Dosage of Fly Ash on the Fracture Properties and Strength of Concrete

by Chung-Hao Wu, Chung-Ho Huang, Yu-Cheng Kan and Tsong Yen

Appl. Sci. 2019, 9(11), 2266; https://doi.org/10.3390/app9112266 - 31 May 2019

Cited by 12 | Viewed by 2839

Abstract

This study focuses on evaluating the effects of the fineness of fly ash on the strength, fracture toughness, and fracture resistance of concrete. Three fineness levels of fly ash that respectively pass sieves—no. 175, no. 250, and no. 32—were used. In addition to [...] Read more.

This study focuses on evaluating the effects of the fineness of fly ash on the strength, fracture toughness, and fracture resistance of concrete. Three fineness levels of fly ash that respectively pass sieves—no. 175, no. 250, and no. 32—were used. In addition to the control concrete mixture without fly ash, two fly ash replacement levels of 10% and 20% by weight of the cementitious material were selected for the concrete mixture. The experimental results indicate that the compressive strength of the fly ash concrete decreases with the increase in the replacement ratio of fly ash but increases in conjunction with the fineness level of fly ash. The presence of finer fly ash can have beneficial effects on the fracture energy (G_F) of concrete at an early age (14 days) and attain a higher increment of G_F at a later age (56 days). The concrete containing finer fly ash was found to present larger critical stress intensity factors (K^S_IC) at various ages, and the K^S_IC also increases in conjunction with the fineness levels of fly ash. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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14 pages, 7580 KiB

Open AccessArticle

Studies of Fracture Damage Caused by the Proppant Embedment Phenomenon in Shale Rock

by Mateusz Masłowski, Piotr Kasza, Marek Czupski, Klaudia Wilk and Rafał Moska

Appl. Sci. 2019, 9(11), 2190; https://doi.org/10.3390/app9112190 - 29 May 2019

Cited by 9 | Viewed by 3799

Abstract

This paper concerns the effect of proppant embedment related to hydraulic fracturing treatment. This phenomenon occurs if the strength of a dry reservoir rock is lower than that of proppant grains. The aim of this research was the laboratory determination of the loss [...] Read more.

This paper concerns the effect of proppant embedment related to hydraulic fracturing treatment. This phenomenon occurs if the strength of a dry reservoir rock is lower than that of proppant grains. The aim of this research was the laboratory determination of the loss of width of the proppant pack built of light ceramic grains. A laboratory simulation of the embedment phenomenon was carried out for a shale rock on a hydraulic press in a heated embedment chamber specially prepared for this purpose. Tests were conducted at high temperature and axial compressive stress conditions. The surfaces of cylindrical core plugs (fracture faces) were imaged under an optical microscope equipped with 3D software. The fracture faces were examined and compared before and after the embedment phenomenon. Analysis of the obtained images of the fracture face was done, based on a research method of the embedment phenomenon developed at the Oil and Gas Institute—National Research Institute. On the basis of the laboratory tests, the parameters characterizing the embedment phenomenon were defined and discussed. In addition, the percentage reduction in the width of the proppant pack was determined. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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10 pages, 1563 KiB

Open AccessArticle

Comprehensive Evaluation of Fatigue Performance of Modified Asphalt Mixtures in Different Fatigue Tests

by Kun Li, Ming Huang, Haobai Zhong and Benliang Li

Appl. Sci. 2019, 9(9), 1850; https://doi.org/10.3390/app9091850 - 6 May 2019

Cited by 10 | Viewed by 3395

Abstract

The four-point bending beam fatigue test (4PB), two-point bending trapezoidal beam fatigue test (Trapezoidal Beam), and Overlay Tester (OT) are used to evaluate the fatigue performance of six kinds of asphalt mixtures that are widely used in engineering, and newly developed ones. The [...] Read more.

The four-point bending beam fatigue test (4PB), two-point bending trapezoidal beam fatigue test (Trapezoidal Beam), and Overlay Tester (OT) are used to evaluate the fatigue performance of six kinds of asphalt mixtures that are widely used in engineering, and newly developed ones. The result shows that, in all three kinds of fatigue tests, the fatigue performances of the 6% SBS (styrene-butadiene-styrene block copolymer) modified asphalt mixture is the best, and those of the 10% WPE (waxed polyethylene) + 3% SBS, 4% SBS + 0.4% PA610, and 4% SBS modified asphalt mixture are good. The fatigue performances of the warm modified mixing agent and the base asphalt mixture are the worst. An increase in SBS content can effectively improve the fatigue performance of the asphalt mixture. The fatigue performance of the SBS-modified asphalt mixture can be improved by the addition of WPE and PA610. In different tests, the ranking of fatigue performance of the asphalt mixture is similar, and the specific ranking is slightly different. The three different fatigue tests can be used simultaneously to obtain a more comprehensive and objective evaluation in the R&D process for a new modified asphalt. The three fatigue tests process shows that more precise forming and cutting technology is needed, as the strain range used in the 4PB test is very wide, and the number of samples used in each group is small. The preparation of the Trapezoidal Beam test samples is complex; the amount of test data is huge and has high precision, which is suitable for scientific research instead of a field laboratory, and the strain range of the test is moderate in the three methods. The strain range of the OT test is the narrowest; the test specimen is relatively simple to prepare, and the fatigue performance of a specific modified asphalt mixture can be obtained quickly in a simple laboratory. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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14 pages, 6281 KiB

Open AccessArticle

Numerical Modeling Approach on Mining-Induced Strata Structural Behavior by Considering the Fracture-Weakening Effect on Rock Mass

by Jiaming Shu, Lishuai Jiang, Peng Kong, Pu Wang and Peipeng Zhang

Appl. Sci. 2019, 9(9), 1832; https://doi.org/10.3390/app9091832 - 3 May 2019

Cited by 16 | Viewed by 3493

Abstract

By employing the longwall mining method, a series of intensive strata structure responses and activities will be induced including stress redistribution, fracture extension and strata movement. Due to the geological stratification feature of coal mine strata, tensile failure and tension-induced fracturing play dominant [...] Read more.

By employing the longwall mining method, a series of intensive strata structure responses and activities will be induced including stress redistribution, fracture extension and strata movement. Due to the geological stratification feature of coal mine strata, tensile failure and tension-induced fracturing play dominant roles in the strata of the fractured zone. These responses induced in the strata require the consideration of the weakening effect on the rock mass behavior due to failure and fracturing in tension. In this study, a numerical modeling approach on mining-induced strata structural behaviors was proposed by considering the mechanical behaviors of the caved zone consolidation and tension-induced weakening in the fractured zone. Based on a numerical model built according to a study site, a parametric study with respect to different fracturing intensity parameters was performed to investigate the fracturing weakening effect on the mining-induced stress redistribution and strata movement. The numerical results showed that the tensile fracture intensity had a notable effect on the mining-induced stress distribution in two aspects: (1) Increase in peak and area of the front abutment stress; (2) variation in the patterns of stress recovery in the goaf. The stress data obtained from numerical simulation represent and help to back-analyze the structural behaviors (failure, movement) of the overlying strata. The high stress on the coal seam indicated that the strata lay on and transferred loads to the seam, while the low stress indicated the detachment between the seam and the suspending strata. With the increase in fracture intensity, the roof strata were more prone to breaking and caving, and the suspending length of the roof beam decreased, which made the strata sufficiently break, cave and transfer the overburden load to loose rock in the goaf; caving along the strike direction of the panel became the dominant overlying strata structure movement, while the dominant movement caved along the dip direction in the case of strong and intact overlying strata with few tensile fractures. Thus, the tensile fracturing intensity should not be ignored in studies related to the behaviors of the overlying strata. Validated by analytical studies, this study presents a novel numerical modeling approach for this topic and can be utilized for multiple studies based on proper roof fracturing estimation or back analysis. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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19 pages, 4338 KiB

Open AccessArticle

Numerical Analysis of the Mechanical Behaviors of Various Jointed Rocks under Uniaxial Tension Loading

by Jiaming Shu, Lishuai Jiang, Peng Kong and Qingbiao Wang

Appl. Sci. 2019, 9(9), 1824; https://doi.org/10.3390/app9091824 - 1 May 2019

Cited by 14 | Viewed by 3132

Abstract

In a complex stress field of underground mining or geotechnical practice, tension damage/failure in rock masses is easily triggered and dominant. Unlike metals, rocks are generally bi-modularity materials with different mechanical properties (Young’s modulus, etc.) in compression and tension. It is well established [...] Read more.

In a complex stress field of underground mining or geotechnical practice, tension damage/failure in rock masses is easily triggered and dominant. Unlike metals, rocks are generally bi-modularity materials with different mechanical properties (Young’s modulus, etc.) in compression and tension. It is well established that the Young’s modulus of a rock mass is directly related to the presence of the fracture or joint, and the Young’s modulus estimation for jointed rocks and rock masses is essential for stability analysis. In this paper, the tensile properties in joint rocks were investigated by using numerical simulations based on the discrete element method. Four influencing parameters relating to the tensile properties (joint dip angle, joint spacing, joint intersection angle, and joint density) were studied. The numerical results show that there is an approximately linear relationship between the joint dip angle (α) and the joint intersection angle (β) with the tensile strength (σ_t), however, the changes in α and β have less influence on the Young’s modulus in tension (E_t). With respect to joint spacing, the simulations show that the effects of joint spacing on σ_t and E_t are negligible. In relation to the joint density, the numerical results reveal that the joint intensity of rock mass has great effect on E_t but insignificant effect on σ_t. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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16 pages, 4082 KiB

Open AccessArticle

Experimental and DEM Analysis on Secondary Crack Types of Rock-Like Material Containing Multiple Flaws Under Uniaxial Compression

by Yong Li, Weibing Cai, Xiaojing Li, Weishen Zhu, Qiangyong Zhang and Shugang Wang

Appl. Sci. 2019, 9(9), 1749; https://doi.org/10.3390/app9091749 - 27 Apr 2019

Cited by 22 | Viewed by 3305

Abstract

To better understand the evolution of crack propagation in brittle rock mass, the particle velocity field evolution on both sides of secondary crack in rock-like materials (cement mortar specimens) with pre-existing parallel double flaws under uniaxial compression is analyzed based on the discrete [...] Read more.

To better understand the evolution of crack propagation in brittle rock mass, the particle velocity field evolution on both sides of secondary crack in rock-like materials (cement mortar specimens) with pre-existing parallel double flaws under uniaxial compression is analyzed based on the discrete element theory. By bringing in strain rate tensor, a new technique is proposed for quantifying the failure mechanism of cracks to distinguish the types and mechanical behaviors of secondary cracks between pre-existing parallel flaws. The research results show that the types and mechanical behaviors of secondary cracks are distinct at different axial loading stages and can be directly identified and captured through the presented approach. The relative motion trend between particles determines the types and mechanical behaviors of secondary cracks. Based on particles movement on both sides of secondary cracks between cracks, the velocity fields of particles can be divided into four types to further analyze the causes of different types of cracks. In different axial loading stages, the velocity field types of particles on both sides of cracks are continuously evolving. According to the particle velocity field analysis and the proposed novel way, the types of macroscopic cracks are not directly determined by the types of dominated micro-cracks. Under uniaxial compression, the particles between secondary cracks and pre-existing parallel flaws form a confined compressive member. Under the confinement of lateral particles, secondary cracks appear as shear cracks between pre-existing parallel flaws at the beginning stage of crack initiation. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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19 pages, 5409 KiB

Open AccessArticle

Triaxial Loading and Unloading Tests on Dry and Saturated Sandstone Specimens

by Diyuan Li, Zhi Sun, Quanqi Zhu and Kang Peng

Appl. Sci. 2019, 9(8), 1689; https://doi.org/10.3390/app9081689 - 24 Apr 2019

Cited by 16 | Viewed by 3867

Abstract

The brittle failure of hard rock due to the excavation unloading in deep rock engineering often causes serious problems in mining and tunneling engineering, and the failure process is always affected by groundwater. In order to investigate the effects of stress paths and [...] Read more.

The brittle failure of hard rock due to the excavation unloading in deep rock engineering often causes serious problems in mining and tunneling engineering, and the failure process is always affected by groundwater. In order to investigate the effects of stress paths and water conditions on the mechanical properties and failure behavior of rocks, a series of triaxial compression tests were conducted on dry and saturated sandstones under various loading and unloading paths. It was found that when the sandstone rock samples are saturated by water, the cohesion, the internal friction angle and the Young’s modulus will decrease but the Poisson′s ratio will increase. The fracturing characteristics of the sandstone specimens are related to the initial confining pressure, the stress paths and the water conditions from both macroscopic and microscopic viewpoints. The failure of sandstone in unloading test is more severe than that under loading test, particularly for dry sandstone samples. In unloading test, the energy is mainly consumed for the circumferential deformation and converted into kinetic energy for the rock bursts. The sandstone is more prone to produce internal cracks under the effect of water, and the absorbed energy mainly contributes to the damage of rock. It indicates that the possibility of rockburst in saturated rock is lower than the samples in dry condition. It is important to mention that water injection in rock is an effective way to prevent rockburst in deep rock engineering. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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16 pages, 10404 KiB

Open AccessArticle

Effect of Crack Orientation on Fatigue Life of Reinforced Concrete Bridge Decks

by Eissa Fathalla, Yasushi Tanaka and Koichi Maekawa

Appl. Sci. 2019, 9(8), 1644; https://doi.org/10.3390/app9081644 - 20 Apr 2019

Cited by 16 | Viewed by 5692

Abstract

In visual inspection of bridges at sites, much attention is given to the density and width of cracks of concrete, but little attention is paid to crack orientation for the diagnosis of bridge performance. In this research, the effect of crack orientation on [...] Read more.

In visual inspection of bridges at sites, much attention is given to the density and width of cracks of concrete, but little attention is paid to crack orientation for the diagnosis of bridge performance. In this research, the effect of crack orientation on the remaining fatigue life of reinforced concrete (RC) bridge decks is investigated for crack patterns with a wide range of possible crack orientations. The data assimilation technology of multi-scale simulation and the pseudo-cracking method, which are widely validated for fatigue-lifetime simulation, are utilized in this study. The impact of the crack direction on fatigue life is found to be associated with the coupled flexure-shear mode of failure, and the mechanism to arrest shear cracking by preceding cracks is quantitatively estimated. This mechanism is similar to the stop-hole to prevent fatigue cracks in steel structures, and it enables us to enhance the fatigue life of RC decks. It is demonstrated that the crack orientations that approximate the longitudinal and transverse directions of RC decks are the ones that most extend remaining fatigue life. Finally, the higher risk cracking locations on the bottom surface of RC decks are discussed, presenting information of use to site inspectors. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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18 pages, 4207 KiB

Open AccessArticle

Curable Area Substantiation of Self-Healing in Concrete Using Neutral Axis

by Choonghyun Kang and Taewan Kim

Appl. Sci. 2019, 9(8), 1537; https://doi.org/10.3390/app9081537 - 13 Apr 2019

Cited by 1 | Viewed by 2787

Abstract

The self-healing nature of concrete has been proved in many studies using various methods. However, the underlying mechanisms and the distinct area of self-healing have not been identified in detail. This study focuses on the limits of the area of self-healing. A bending [...] Read more.

The self-healing nature of concrete has been proved in many studies using various methods. However, the underlying mechanisms and the distinct area of self-healing have not been identified in detail. This study focuses on the limits of the area of self-healing. A bending specimen with a notch is used herein, and its flexural strength and stiffness before and after healing are compared and used for self-healing assessment. In addition, the neutral axis of the specimen was measured using successive strain gauges attached to the crack propagation part. Although the strength and stiffness of the concrete recovered after self-healing, the change in the location of the neutral axis before and after healing was insignificant, which indicates that physical recovery did not occur for once-opened crack areas. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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16 pages, 8894 KiB

Open AccessArticle

Three-Dimensional Physical and Numerical Modelling of Fracturing and Deformation Behaviour of Mining-Induced Rock Slopes

by Guoxiang Yang, Anthony K. Leung, Nengxiong Xu, Kunxiang Zhang and Kunpeng Gao

Appl. Sci. 2019, 9(7), 1360; https://doi.org/10.3390/app9071360 - 31 Mar 2019

Cited by 13 | Viewed by 3394

Abstract

Fracturing behaviour of jointed rock mass subjected to mining can significantly affect the stability of the rock structures and rock slopes. Ore mining within an open-pit final slope would lead to large-scale strata and surface movement of the rock slope. Rock mass structure, [...] Read more.

Fracturing behaviour of jointed rock mass subjected to mining can significantly affect the stability of the rock structures and rock slopes. Ore mining within an open-pit final slope would lead to large-scale strata and surface movement of the rock slope. Rock mass structure, or more specifically, the strength, spacing and distribution of rock joints, are the controlling factors that govern the failure and deformation mechanisms of the final slope. Two-dimensional (2-D) physical modelling tests have been conducted in the literature, but in general, most of them have simplified the geological conditions and neglected some key features of rock mass structure in the field. In this study, new three-dimensional (3-D) physical modelling methods are introduced, with realistic modelling of mechanical behaviour of rock mass as well as identified properties of predominant rock joint sets. A case study of Yanqianshan iron mine is considered and the corresponding 1:200 model rock slope was created for studying the rock joint effects on the strata movement and the subsidence mechanism of the slope. The physical model test results are subsequently verified with 3-D discrete element numerical modelling. Due to the presence of the predominant joints, the observed well-shaped strata subsidence in Yanqianshan iron mine was successfully reproduced in the 3-D physical model. The failure mechanism of rock slopes differs from the trumpet-shaped subsidence observed in unconsolidated soil. Due to the formation of an arching mechanism within the rock mass, the strata deformation transferred gradually from the roof of the goaf to the slope surface. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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20 pages, 1069 KiB

Open AccessArticle

Determination of Fracture Properties of Concrete Using Size and Boundary Effect Models

by Xiaofeng Gao, Chunfeng Liu, Yaosheng Tan, Ning Yang, Yu Qiao, Yu Hu, Qingbin Li, Georg Koval and Cyrille Chazallon

Appl. Sci. 2019, 9(7), 1337; https://doi.org/10.3390/app9071337 - 29 Mar 2019

Cited by 6 | Viewed by 3033

Abstract

Tensile strength and fracture toughness are two essential material parameters for the study of concrete fracture. The experimental procedures to measure these two fracture parameters might be complicated due to their dependence on the specimen size or test method. Alternatively, based on the [...] Read more.

Tensile strength and fracture toughness are two essential material parameters for the study of concrete fracture. The experimental procedures to measure these two fracture parameters might be complicated due to their dependence on the specimen size or test method. Alternatively, based on the fracture test results only, size and boundary effect models can determine both parameters simultaneously. In this study, different versions of boundary effect models developed by Hu et al. were summarized, and a modified Hu-Guan’s boundary effect model with a more appropriate equivalent crack length definition is proposed. The proposed model can correctly combine the contributions of material strength and linear elastic fracture mechanics on the failure of concrete material with any maximum aggregate size. Another size and boundary model developed based on the local energy concept is also introduced, and its capability to predict the fracture parameters from the fracture test results of wedge-splitting and compact tension specimens is first validated. In addition, the classical Bažant’s Type 2 size effect law is transformed to its boundary effect shape with the same equivalent crack length as Koval-Gao’s size and boundary effect model. This improvement could extend the applicability of the model to infer the material parameters from the test results of different types of specimens, including the geometrically similar specimens with constant crack-length-to-height ratios and specimens with different initial crack-length-to-height ratios. The test results of different types of specimens are adopted to verify the applicability of different size and boundary effect models for the determination of fracture toughness and tensile strength of concrete material. The quality of the extrapolated fracture parameters of the different models are compared and discussed in detail, and the corresponding recommendations for predicting the fracture parameters for dam concrete are proposed. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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17 pages, 10395 KiB

Open AccessArticle

Research on the Blow-Off Impulse Effect of a Composite Reinforced Panel Subjected to Lightning Strike

by Senqing Jia, Fusheng Wang, Weichao Huang and Bin Xu

Appl. Sci. 2019, 9(6), 1168; https://doi.org/10.3390/app9061168 - 19 Mar 2019

Cited by 12 | Viewed by 3891

Abstract

The blow-off impulse effect of a composite reinforced panel subjected to lightning strike is studied combing electric-thermal coupling with explicit dynamic methods. A finite element model of a composite reinforced panel is established under the action of 2.6/10.5 µs impulse current waveform with [...] Read more.

The blow-off impulse effect of a composite reinforced panel subjected to lightning strike is studied combing electric-thermal coupling with explicit dynamic methods. A finite element model of a composite reinforced panel is established under the action of 2.6/10.5 µs impulse current waveform with current peak 60 kA. Blow-off impulse elements are selected according to numerical results of electric-thermal coupling analysis. Elements failure, pressure, and von Mises stress distribution are discussed when blow-off impulse analysis is completed. The results show that the blow-off impulse effect can alter the damage forms of a composite reinforced panel and causes the damage distribution to deviate from the initial fiber direction in each layer. Elements failure modes around the blow-off impulse area are similar to that around the attachment area of the lightning strike. The blow-off impulse effect can well model the internal damage, concave pit, and bulge phenomenon around the attachment area. Additionally, pressure contours are not presented as an anisotropic characteristic but an isotropic characteristic under the blow-off impulse effect, which indicates that the mechanical behavior of composite materials presents as an anisotropic characteristic in low pressure while as an isotropic characteristic in high pressure. This method is suitable to evaluate shock damage of a composite reinforced panel induced by lightning strike. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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17 pages, 4550 KiB

Open AccessFeature PaperArticle

How Soft Polymers Cope with Cracks and Notches

by Andrea Spagnoli, Michele Terzano, Roberto Brighenti, Federico Artoni and Andrea Carpinteri

Appl. Sci. 2019, 9(6), 1086; https://doi.org/10.3390/app9061086 - 14 Mar 2019

Cited by 16 | Viewed by 4029

Abstract

Soft matter denotes a large category of materials showing unique properties, resulting from a low elastic modulus, a very high deformation capability, time-dependent mechanical behavior, and a peculiar mechanics of damage and fracture. The flaw tolerance, commonly understood as the ability of a [...] Read more.

Soft matter denotes a large category of materials showing unique properties, resulting from a low elastic modulus, a very high deformation capability, time-dependent mechanical behavior, and a peculiar mechanics of damage and fracture. The flaw tolerance, commonly understood as the ability of a given material to withstand external loading in the presence of a defect, is certainly one of the most noticeable attributes. This feature results from a complex and highly entangled microstructure, where the mechanical response to external loading is mainly governed by entropic-related effects. In the present paper, the flaw tolerance of soft elastomeric polymers, subjected to large deformation, is investigated experimentally. In particular, we consider the tensile response of thin plates made of different silicone rubbers, containing defects of various severity at different scales. Full-field strain maps are acquired by means of the Digital Image Correlation (DIC) technique. The experimental results are interpreted by accounting for the blunting of the defects due to large deformation in the material. The effect of blunting is interpreted in terms of reduction of the stress concentration factor generated by the defect, and failure is compared to that of traditional crystalline brittle materials. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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22 pages, 5929 KiB

Open AccessArticle

Cracking Behavior of RC Beams Strengthened with Different Amounts and Layouts of CFRP

by Muhammad Umair Saleem, Hisham Jahangir Qureshi, Muhammad Nasir Amin, Kaffayatullah Khan and Hassan Khurshid

Appl. Sci. 2019, 9(5), 1017; https://doi.org/10.3390/app9051017 - 12 Mar 2019

Cited by 20 | Viewed by 5141

Abstract

The bending and shear behavior of RC beams strengthened with Carbon Fiber-Reinforced Polymers (CFRP) is the primary objective of this paper, which is focused on the failure mechanisms and on the moment-curvature response prior-to, and post, strengthening with different amounts and layouts of [...] Read more.

The bending and shear behavior of RC beams strengthened with Carbon Fiber-Reinforced Polymers (CFRP) is the primary objective of this paper, which is focused on the failure mechanisms and on the moment-curvature response prior-to, and post, strengthening with different amounts and layouts of the CFRP reinforcement. Seven reinforced concrete beams were tested in 4-point bending, one without any CFRP reinforcement (control beam, Specimen C1), four with the same amount of CFRP in flexure but with different layouts of the reinforcement for shear (Specimens B1–B4), and two with extra reinforcement in bending, with and without reinforcement in shear (Specimens B6 and B5, respectively). During each test, the load and the mid-span deflection were monitored, as well as the crack pattern. The experimental results indicate that: (a) increasing the CFRP reinforcement above certain levels does not necessarily increase the bearing capacity; (b) the structural performance can be optimized through an appropriate combination of CFRP flexural and shear reinforcement; and (c) bond properties at the concrete–CFRP interface play a vital role, as the failure is very often triggered by the debonding of the CFRP strips. The experimental values were also verified analytically and a close agreement between the analytical and experimental values was achieved. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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12 pages, 1574 KiB

Open AccessArticle

Effect of Slag Particle Size on Fracture Toughness of Concrete

by Chung-Ho Huang, Chung-Hao Wu, Shu-Ken Lin and Tsong Yen

Appl. Sci. 2019, 9(4), 805; https://doi.org/10.3390/app9040805 - 25 Feb 2019

Cited by 10 | Viewed by 3798

Abstract

The effects of particle size of ground granulated blast furnace slag (GGBS) on the fracture energy, critical stress intensity, and strength of concrete are experimentally studied. Three fineness levels of GGBS of 4000, 5000, 6000 cm²/g were used. In addition to [...] Read more.

The effects of particle size of ground granulated blast furnace slag (GGBS) on the fracture energy, critical stress intensity, and strength of concrete are experimentally studied. Three fineness levels of GGBS of 4000, 5000, 6000 cm²/g were used. In addition to the control mixture without slag, two slag replacement levels of 20% and 40% by weight of the cementitious material were selected for preparing the concrete mixtures. The control mixture was designed to have a target compressive strength at 28 days of 62 MPa, while the water to cementitious material ratio was selected as 0.35 for all mixtures. Test results indicate that using finer slag in concrete may improve the filling effect and the reactivity of slag, resulting in a larger strength enhancement. The compressive strength of slag concrete was found to increase in conjunction with the fineness level of the slag presented in the mixture. Use of finer slag presents a beneficial effect on the fracture energy (G_F) of concrete, even at an early age, and attains a higher increment of G_F at later age (56 days). This implicates that the finer slag can have a unique effect on the enhancement of the fracture resistance of concrete. The test results of the critical stress intensity factor (K^S_IC) of the slag concretes have a similar tendency as that of the fracture energy, indicating that the finer slag may present an increase in the fracture toughness of concrete. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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17 pages, 18796 KiB

Open AccessArticle

Fatigue Life of RC Bridge Decks Affected by Non-Uniformly Dispersed Stagnant Water

by Eissa Fathalla, Yasushi Tanaka and Koichi Maekawa

Appl. Sci. 2019, 9(3), 607; https://doi.org/10.3390/app9030607 - 12 Feb 2019

Cited by 11 | Viewed by 4039

Abstract

Stagnant water on reinforced concrete (RC) decks reduces their life significantly compared to the case of dry states. Fully submerged states have been investigated as the most severe case, which is however rarely experienced in reality. Currently, it is possible to simulate concrete–water [...] Read more.

Stagnant water on reinforced concrete (RC) decks reduces their life significantly compared to the case of dry states. Fully submerged states have been investigated as the most severe case, which is however rarely experienced in reality. Currently, it is possible to simulate concrete–water interactions for lifetime prediction of RC decks. In this study, fatigue lifetime is systematically computed for various locations of stagnant water at the upper layer of RC decks. It is found that the patterns of wet and dry areas have a great influence on the remaining fatigue life even though the same magnitude of cracking develops. Then, a hazard map for the wetting locations with regard to the remaining fatigue life is presented based on the systematically arranged simulation. Finally, a nonlinear correlation is introduced for fatigue life prediction based upon site inspected wetting locations, which can be detected by non-destructive testing technology. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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15 pages, 3067 KiB

Open AccessArticle

Indices to Determine the Reliability of Rocks under Fatigue Load Based on Strain Energy Method

by Huanran Fu, Sijing Wang, Xiangjun Pei and Weichang Chen

Appl. Sci. 2019, 9(3), 360; https://doi.org/10.3390/app9030360 - 22 Jan 2019

Cited by 6 | Viewed by 3234

Abstract

Rock is a complicated material which includes randomly distributed grains and cracks. The reliability of rocks under fatigue load is very important during the construction and operation of rock engineering. In this paper, we studied the deformation and failure process of red sandstone [...] Read more.

Rock is a complicated material which includes randomly distributed grains and cracks. The reliability of rocks under fatigue load is very important during the construction and operation of rock engineering. In this paper, we studied the deformation and failure process of red sandstone under fatigue load in a laboratory based on a new division method of strain energy types. The traditional elastic strain energy density is divided into two categories: grain strain energy density and crack strain energy density. We find that the proportion of the grain strain energy density to total strain energy density can be used as an indicator of rock yield and the proportion of the crack strain energy density to total strain energy density can be used as an indicator of rock failure. Subsequently, through extensive literature research, we found that such a phenomenon is widespread. We also find the proportion of grain strain energy density to total strain energy density when yielding is affected by rock types and elastic modulus. The proportion of crack strain energy density to total strain energy density in the pre-peak stage is stable and not affected by rock types and elastic modulus, which is about 0.04~0.13. These findings should be very helpful for rock stable state judging in rock engineering. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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12 pages, 3614 KiB

Open AccessArticle

Optimization of Shape Design of Grommet through Analysis of Physical Properties of EPDM Materials

by Young Shin Kim, Eui Seob Hwang and Euy Sik Jeon

Appl. Sci. 2019, 9(1), 133; https://doi.org/10.3390/app9010133 - 2 Jan 2019

Cited by 8 | Viewed by 4503

Abstract

Ethylene propylene diene monomer (EPDM) has superior mechanical properties, water resistance, heat resistance, and ozone resistance. It can be applied to various products owing to its low hardness and high slip resistance properties. A grommet is one of the various products made using [...] Read more.

Ethylene propylene diene monomer (EPDM) has superior mechanical properties, water resistance, heat resistance, and ozone resistance. It can be applied to various products owing to its low hardness and high slip resistance properties. A grommet is one of the various products made using EPDM rubber. It is a main component of automobiles, in which it protects wires throughout the inside and outside of a vehicle body. The grommet, made of EPDM, has different mounting performance depending on the process parameters and the shape of the grommet. This study conducted optimization to improve the mounting performance of a grommet using EPDM materials. The physical properties of the main molding materials were investigated according to process parameters. A grommet was fabricated according to the process parameters of fabrication. Insertion force and separation force were examined through experiments. Nonlinear material constants were determined through uniaxial and biaxial tensile tests. The nonlinear analysis of the grommet was conducted, and a compound design that incorporated the shape parameters for the minimum load of each part was derived. Then, additional nonlinear analysis was performed. This was followed by a comparative analysis of the actual model through experimental evaluation. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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Review

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18 pages, 5514 KiB

Open AccessReview

Understanding the Fracture Behaviors of Metallic Glasses—An Overview

by Guan-Nan Yang, Yang Shao and Ke-Fu Yao

Appl. Sci. 2019, 9(20), 4277; https://doi.org/10.3390/app9204277 - 12 Oct 2019

Cited by 17 | Viewed by 4363

Abstract

Fracture properties are crucial for the applications of structural materials. The fracture behaviors of crystalline alloys have been systematically investigated and well understood. The fracture behaviors of metallic glasses (MGs) are quite different from that of conventional crystalline alloys and have drawn wide [...] Read more.

Fracture properties are crucial for the applications of structural materials. The fracture behaviors of crystalline alloys have been systematically investigated and well understood. The fracture behaviors of metallic glasses (MGs) are quite different from that of conventional crystalline alloys and have drawn wide interests. Although a few reviews on the fracture and mechanical properties of metallic glasses have been published, an overview on how and why metallic glasses fall out of the scope of the conventional fracture mechanics is still needed. This article attempts to clarify the up-to-date understanding of the question. We review the fracture behaviors of metallic glasses with the related scientific issues including the mode I fracture, brittle fracture, super ductile fracture, impact toughness, and fatigue fracture behaviors. The complex fracture mechanism of MGs is further discussed from the perspectives of discontinuous stress/strain field, plastic zone, and fracture resistance, which deviate from the classic fracture mechanics in polycrystalline alloys. Due to the special deformation mechanism, metallic glasses show a high variability in fracture toughness and other mechanical properties. The outlook presented by this review could help the further studies of metallic glasses. The review also identifies some key questions to be answered. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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Other

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2 pages, 216 KiB

Open AccessCorrection

Correction: Bennati et al. An Elastic Interface Model for the Delamination of Bending-Extension Coupled Laminates. Appl. Sci. 2019, 9, 3560

by Stefano Bennati, Paolo Fisicaro, Luca Taglialegne and Paolo S. Valvo

Appl. Sci. 2020, 10(5), 1711; https://doi.org/10.3390/app10051711 - 3 Mar 2020

Viewed by 1729

Abstract

We, the authors, wish to make the following corrections to our paper [...] Full article

(This article belongs to the Special Issue Fatigue and Fracture of Non-metallic Materials and Structures)

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