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Fracture Mechanics Investigation of Polymeric Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Polymeric Materials".

Deadline for manuscript submissions: closed (20 March 2022) | Viewed by 21214

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Special Issue Editors

Prof. Dr. Gerald Pinter

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Guest Editor

Department of Polymer Science and Engineering, Montanuniversität Leoben, Leoben, Austria
Interests: fracture mechanics in polymers and composites; fatigue in polymers and composites; reliability of plastics and composites in structural applications

Dr. Florian Arbeiter

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Guest Editor

Materials Science and Testing of Polymers, Montanuniversitat Leoben, Leoben, Austria
Interests: fracture mechanics in polymers; application of fracture mechanics in additive manufacturing; impact fracture; fracture in multilayer systems
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Special Issue Information

Dear Colleagues,

This Special Issue on “Fracture Mechanics Investigation of Polymeric Materials” brings together scientists working at universities, research institutes, laboratories, and various industries to discuss state-of-the-art research on fracture mechanics in polymers and polymer matrix composites. This Special Issue is a timely approach to specifically survey recent progress in the development and application of fracture mechanics testing concepts and modeling and simulation strategies to reproduce the failure behavior of components under real service conditions. Typically, the lifetime of components in structural applications is dominated by the effect of defects or notches. These act as starting points of cracks that ultimately lead to failure or at least to a condition where the polymer part no longer fulfills its technical purpose. Fracture mechanics is a time-proven tool for the description of this failure process. Due to their strongly time- and temperature-dependent behavior, fracture mechanics concepts are sometimes difficult to be transferred to polymers. Therefore, there is still need for fundamental, as well as application-oriented, research regarding the limitations of fracture mechanics in polymers and composites.

In this Special Issue, all polymer classes are broadly addressed, and experimental and simulative fracture mechanics topics are dealt with. Ideally, the authors should be able to show results which fit within the context of reliability of polymeric parts.

Prof. Dr. Gerald Pinter
Dr. Florian Arbeiter
Guest Editors

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Keywords

Polymers
Composites
Notching
Crack initiation
Crack propagation
Crack tip plasticity
Experimental procedures
Modelling and simulation procedures
Quasi-static loads
Cyclic loads
Impact loads
Environmental effects
Structure–property correlations
Damage tolerance
Lifetime assessment

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Published Papers (10 papers)

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Research

23 pages, 6570 KiB

Open AccessArticle

Fatigue Analysis and Defect Size Evaluation of Filled NBR including Temperature Influence

by Jacopo Schieppati, Bernd Schrittesser, Stefano Tagliabue, Luca Andena, Armin Holzner, Jan Poduška and Gerald Pinter

Materials 2022, 15(11), 3745; https://doi.org/10.3390/ma15113745 - 24 May 2022

Cited by 2 | Viewed by 1821

Abstract

The fatigue behavior of a filled non-crystallizing elastomer was investigated on axisymmetric dumbbell specimens. By plotting relevant Wöhler curves, a power law behavior was found. In addition, temperature increases due to heat build-up were monitored. In order to distinguish between initiation and crack growth regimes, hysteresis curves, secant and dynamic moduli, dissipated and stored energies, and normalized minimum and maximum forces were analyzed. Even though indications related to material damaging were observed, a clear trend to recognize the initiation was not evident. Further details were revealed by considering a fracture mechanics. The analysis of the fracture surfaces evidenced the presence of three regions, associated to initiation, fatigue striation, and catastrophic failure. Additional fatigue tests were performed with samples in which a radial notch was introduced. This resulted in a reduction in lifetime by four orders of magnitude; nevertheless, the fracture surfaces revealed similar failure mechanisms. A fracture mechanics approach, which considered the effect of temperature, was adopted to calculate the critical defect size for fatigue, which was found to be approximately 9 μm. This value was then compared with the particle size distribution obtained through X-ray microcomputed tomography (μ-CT) of undamaged samples and it was found that the majority of the initial defects were indeed smaller than the calculated one. Finally, the evaluation of J-integral for both unnotched and notched dumbbells enabled the assessment of a geometry-independent correlation with fatigue life. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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11 pages, 1178 KiB

Open AccessArticle

Peeling of Flexible Laminates—Determination of Interlayer Adhesion of Backsheet Laminates Used for Photovoltaic Modules

by Gernot Oreski and Gerald Pinter

Materials 2022, 15(9), 3294; https://doi.org/10.3390/ma15093294 - 4 May 2022

Cited by 3 | Viewed by 1912

Abstract

Delamination is one of the most critical failure modes of a PV module during service lifetime. Delamination within a backsheet primarily imposes a safety risk, but may also accelerate various other PV module degradation modes. The main aim of this paper is to present a peel test set-up, which is more practical in sample preparation and execution than the width-tapered cantilever beam test and overcomes some issues of standard peel tests like the influence of sample geometry and energy dissipation through deformation on the peel test results. The best results with respect to accuracy and effort were achieved by using a 180° peel geometry where an additional adhesive tape is applied to the peel arm in order to avoid plastic deformation or breakage. The additional support of the adhesive tape leads to comparable peel strength values without any influence of the plastic deformation behavior of the peel arms with different thickness. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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13 pages, 3178 KiB

Open AccessArticle

Combined Crack Initiation and Crack Growth Model for Multi-Layer Polymer Materials

by Martin Pletz and Florian Josef Arbeiter

Materials 2022, 15(9), 3273; https://doi.org/10.3390/ma15093273 - 3 May 2022

Cited by 1 | Viewed by 1886

Abstract

The current publication deals with the fracture toughness of polymeric multi-layer materials. In detail, the crack initiation and growth, crack arrest, and crack re-initiation of a multi-layer material are examined. The aim is to develop a numerical model for crack initiation and incremental crack growth of a three-layer single edge notched bending specimen that features one brittle layer in a plastically deforming matrix. Crack initiation and crack propagation are modeled using the finite fracture mechanics concept and the energy concept, respectively. No delamination is accounted for and the crack grows in one plane. The experimental observation of a crack initiating in the brittle layer (at 61.4 ± 2.2 N) while the initial crack is blunting can be reproduced well with the numerical model (at 63.6 N) with a difference of <3.6%. The model is ready to be used for different layups to predict toughening mechanisms and damage tolerances in multi-layer materials. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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14 pages, 2415 KiB

Open AccessArticle

Fracture Load Predictions in Additively Manufactured ABS U-Notched Specimens Using Average Strain Energy Density Criteria

by Marcos Sánchez, Sergio Cicero, Sergio Arrieta and Victor Martínez

Materials 2022, 15(7), 2372; https://doi.org/10.3390/ma15072372 - 23 Mar 2022

Cited by 15 | Viewed by 1809

Abstract

This paper provides a methodology for the prediction of fracture loads in additively manufactured ABS material containing U-notches. The approach is based on the Average Strain Energy Density (ASED) criterion, which assumes that the material being analysed develops fully linear-elastic behaviour. Thus, in those cases where the material has a certain (non-negligible) amount of non-linear behaviour, the ASED criterion needs to be corrected. In this sense, in this paper, the ASED criterion is also combined with the Equivalent Material Concept (EMC) and the Fictitious Material Concept (FMC), both being corrections in which the non-linear real material is substituted by a linear equivalent or fictitious material, respectively. The resulting methodologies have been applied to additively manufactured ABS U-notched single-edge-notched bending (SENB) specimens combining five different notch radii (0, 0.25, 0.5, 1 and 2 mm) and three different raster orientations (0/90, 45/−45 and 30/−60). The results obtained demonstrate that both the ASED-EMC and the ASED-FMC combined criteria provide more accurate predictions than those obtained directly through the ASED criterion, with the ASED-EMC criterion generally providing safe more accurate predictions, with an average deviation from the experimental fracture loads between +1.0% (predicted loads higher than experimental loads) and −7.6% (predicted loads lower than experimental loads). Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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18 pages, 3861 KiB

Open AccessArticle

Resistance of Polymeric Laminates Reinforced with Fabrics against the Growth of Delaminations

by Piotr Czarnocki

Materials 2021, 14(23), 7367; https://doi.org/10.3390/ma14237367 - 30 Nov 2021

Cited by 1 | Viewed by 1364

Abstract

Dependence of the initiation values of the Strain Energy Release Rate, G_Ci, on the orientation of the reinforcement direction α relative to the delamination front was investigated for two laminates of different interfacial ply arrangements. In the case of the first laminate, the delamination was located at the interface of the layers reinforced with symmetric fabric and unidirectional fabric. In the case of the second laminate, the delamination was located at the interface of layers reinforced with symmetric fabric. In both laminates, the orientation of fibers in the layers separated by the delamination differed by 45° regarding the warp directions. The investigations were carried out for Mode I, Mode II, and Mixed-Mode I/II (G_II/G_I = 1 and G_II/G_I = 1.7) loadings using hybrid beam specimens. The major problem appearing in the intended tests was the inevitable lack of symmetry in the xz and xy planes of the specimens and the resulting deformation and stress–strain couplings, causing undesired loading modes. To decrease these couplings, especially designed hybrid beam specimens were used. An auxiliary finite element analysis was performed to assess the remaining effects of the reduced couplings. To ascertain whether statistically significant differences between Gci values for different α occurred, the one-way analysis of variance supplemented by Levene’s test was carried out. The dependence of Gci on α was found out for both laminates. However, it was not equally strong, and it turned out that the loading mode and the interfacial ply were arrangement sensitive. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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12 pages, 5865 KiB

Open AccessArticle

Structure-Property Relationships of Polyamide 12 Grades Exposed to Rapid Crack Extension

by Mario Messiha, Andreas Frank, Jan Heimink, Florian Arbeiter and Gerald Pinter

Materials 2021, 14(19), 5899; https://doi.org/10.3390/ma14195899 - 8 Oct 2021

Cited by 4 | Viewed by 1777

Abstract

Thermoplastic materials have established a reputation for long-term reliability in low-pressure gas and water distribution pipe systems. However, occasional Slow Crack Growth (SCG) and Rapid Crack Propagation (RCP) failures still occur. SCG may initiate only a small leak, but it has the potential to trigger RCP, which is much rarer but more catastrophic and destructive. RCP can create a long, straight or meandering axial crack path at speeds of up to hundreds of meters per second. It is driven by internal (residual) and external (pressure) loads and resisted by molecular and morphological characteristics of the polymer. The safe installation and operation of a pipe throughout its service lifetime therefore requires knowledge of its resistance to RCP, particularly when using new materials. In this context, the RCP resistance of five different polyamide (PA) 12 grades was investigated using the ISO 13477 Small-Scale Steady State (S4) test. Since these grades differed not only in molecular weight but also in their use of additives (impact modifiers and pigments), structure-property relationships could be deduced from S4 test results. A new method is proposed for correlating these results more efficiently to evaluate each grade using the crack arrest lengths from individual S4 test specimens. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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24 pages, 11465 KiB

Open AccessArticle

Crack Propagation Analysis of Compression Loaded Rolling Elements

by Pavol Dlhý, Jan Poduška, Michael Berer, Anja Gosch, Ondrej Slávik, Luboš Náhlík and Pavel Hutař

Materials 2021, 14(10), 2656; https://doi.org/10.3390/ma14102656 - 19 May 2021

Cited by 1 | Viewed by 2334

Abstract

The problem of crack propagation from internal defects in thermoplastic cylindrical bearing elements is addressed in this paper. The crack propagation in these elements takes place under mixed-mode conditions—i.e., all three possible loading modes (tensile opening mode I and shear opening modes II and III) of the crack are combined together. Moreover, their mutual relation changes during the rotation of the element. The dependency of the stress intensity factors on the crack length was described by general parametric equations. The model was then modified by adding a void to simulate the presence of a manufacturing defect. It was found that the influence of the void on the stress intensity factor values is quite high, but it fades with crack propagating further from the void. The effect of the friction between the crack faces was find negligible on stress intensity factor values. The results presented in this paper can be directly used for the calculation of bearing elements lifetime without complicated finite element simulations. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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23 pages, 7050 KiB

Open AccessEditor’s ChoiceArticle

Size-Induced Constraint Effects on Crack Initiation and Propagation Parameters in Ductile Polymers

by Anja Gosch, Florian Josef Arbeiter, Silvia Agnelli, Michael Berer and Francesco Baldi

Materials 2021, 14(8), 1945; https://doi.org/10.3390/ma14081945 - 13 Apr 2021

Cited by 3 | Viewed by 1819

Abstract

Fracture mechanics are of high interest for the engineering design and structural integrity assessment of polymeric materials; however, regarding highly ductile polymers, many open questions still remain in terms of fully understanding deformation and fracture behaviors. For example, the influence of the constraint and specimen size on the fracture behavior of polymeric materials is still not clear. In this study, a polymeric material with an elastic plastic deformation behavior (ABS, acrylonitrile butadiene styrene) is investigated with regard to the influence of constraint and specimen size. Different single-edge notched bending (SENB) specimen sizes with constant geometrical ratios were tested. The material key curve was used to investigate differences in the constraint, where changes for small and large specimen sizes were found. Based on a size-independent crack resistance curve (J–R curve), two apparent initiation parameters (J_0.2 and J_bl) were determined, namely, the initiation parameter J_ini (based on the crack propagation kinetics curve) and the initiation parameter J_I,lim (based on an ESIS TC 4 draft protocol). It was found that J_0.2 and J_bl could be used as crack initiation parameters whereby J_ini and J_I,lim are indicative of the onset of stable crack growth. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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23 pages, 70440 KiB

Open AccessArticle

Quantification Approaches for Fatigue Crack Resistance of Thermoplastic Tape Layered Composites with Multiple Delaminations

by Anastasiia Khudiakova, Andreas J. Brunner, Markus Wolfahrt and Gerald Pinter

Materials 2021, 14(6), 1476; https://doi.org/10.3390/ma14061476 - 17 Mar 2021

Cited by 17 | Viewed by 2252

Abstract

Automated tape placement with in-situ consolidation (ATPisc) is a layer-wise manufacturing process in which the achievement of proper interlayer bonding constitutes one of the most challenging aspects. In the present study, unidirectional carbon fiber reinforced thermoplastic laminates were produced following different manufacturing protocols using ATPisc. The interlayer bonding of the laminates produced was characterized by mode I fatigue fracture tests with double cantilever beam (DCB) specimens. Independent of the manufacturing approach, the laminates exhibited multiple cracking during DCB testing, which could not be evaluated simply following standard methods. Thus, various data analysis methodologies from literature were applied for the quantitative assessment of the fracture behavior of the laminate. The examination of the evolution of the damage parameter

φ

and the effective flexural modulus throughout testing enabled a better understanding of the damage accumulation. The Hartman-Schijve based approach was revealed to be a convenient method to present fatigue crack growth curves of laminates with multiple delaminations. Moreover, a preliminary attempt was made to employ a ‘zero-fiber bridging’ methodology to eliminate the effect of additional damage processes on the fatigue crack growth that resulted in large-scale, partially massive fiber bridging. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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18 pages, 14366 KiB

Open AccessArticle

Fracture of Thin-Walled Polyoxymethylene Bulk Specimens in Modes I and III

by Peer Schrader, Anja Gosch, Michael Berer and Stephan Marzi

Materials 2020, 13(22), 5096; https://doi.org/10.3390/ma13225096 - 12 Nov 2020

Cited by 6 | Viewed by 2972

Abstract

Thin-walled polymeric components are used in many applications. Hence, knowledge about their fracture behavior in bulk is beneficial in practice. Within this study, the double cantilever beam (DCB) and out-of-plane double cantilever beam (ODCB) tests are enhanced to enable the testing of such bulk specimens in mode I and mode III on the basis of the J-integral. This paper then presents and discusses the experimental results following the investigation of a semicrystalline polymer (polyoxymethylen) under quasi-static load conditions. From the experiments, fracture energies of similar magnitude in both mode I and mode III were determined. In mode III, pop-in fracture was observed. Furthermore, the fracture surfaces were investigated regarding the mode I and mode III dominant crack growth mechanisms, based on the morphology of the tested material. For specimens tested in mode I, no signs of plastic deformation were observed, and the fracture surface appears flat. In mode III, some samples display a twisted fracture surface (twisting angle close to 45

^{°}

), which indicates local mode I crack growth. A transfer of the presented methodology to other (more ductile) polymeric materials is deemed possible without further restrictions. In addition, the presented setup potentially enables an investigation of polymeric bulk specimens in mixed mode I+III. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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