Study of the Mechanical Properties of Near-Space Airship Envelope Material Based on an Optimization Method

Round 1

Reviewer 1 Report

The authors studied biaxial nonlinear stress-strain relations of a plain weave membrane fabric and compared them with classic linear models. An experiment was used for the model optimization. The results shows pretty good error reached for the simulation.

Specific comments:

1) missing space before units (lines 213, 317, 324)

2) DIC method parameters not mentioned, especially the camera resolution.

3) There is no picture of DIC measured strain of the whole middle area to be compared with Figure 12.

4) Figure 11 is too dark.

5) The differences between data, simulation and traditional method are not visible in Fig. 13. Use rather 2D graphs.

Author Response

Response to the reviewer

Dear Reviewer:

  Thank you for your comments concerning our manuscript entitled “Study of the Mechanical Properties of Near-Space Airship Envelope Material Based on an Optimization Method” (ID: aerospace-1883807). We have studied comments carefully and have made revisions according to your comments. The revisions in this paper and the answers to the reviewers’ comments are as follows:

 

1) Missing space before units (lines 213, 317, 324)

[Answer1] The space have been added before units in lines 213,317,324.

2) DIC method parameters not mentioned, especially the camera resolution.

[Answer2] The camera is equipped with a new 24.2-megapixel CMOS sensor and EXPEED 3 digital image processor, the camera is set to take a picture of the flash spot region every 10 seconds.

Above have been added in section 4.1.

3) There is no picture of DIC measured strain of the whole middle area to be compared with Figure 12.

[Answer3] FIG. 12 shows the stress distribution diagram, the strain and deformation cloud diagram is shown in Fig.9. The strain obtained by camera and DIC technology analysis is sensitive to environmental factors and surface structure of materials, and the cloud image distribution is relatively scattered. Therefore, during data acquisition, the central area of the flash was valued and the average value was taken, while DIC strain was not measured.

(a)    Displacement map in x-direction	(b)    Map of strain in x-direction
Figure. 9 Displacement and strain nephogram in x directions

4) Figure 11 is too dark.

[Answer4] Figure 11 has been updated.

5) The differences between data, simulation and traditional method are not visible in Fig. 13. Use rather 2D graphs.

[Answer5]  Since the stress-strain relationship in latitude and longitude is nonlinear in space. The 3-D image can show the trend more clearly and better represent the stress-strain relationship, while a lot of 2-D image were needed to present the relationship of the data. As shown in the 3-D image (Fig. 13), according to the distribution trend of tests and simulation, the method proposed in this study is feasible.

Besides, figure 13 has been modified to be more clearer.

Above has been added in section 4.3.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript is focused on a specific optimization procedure for correlating experimental wowen behavior with numerical one.  The subject seems more oriented to material sciences or experimental mechanics rather than an aerospace journal, but the content is however interesting for scientific readers .

Following this observation a change in title should be requested in order to focus immediately to the content of the manuscript. The “airship” infact is just an application, but not fundamental . Something like :” Mechanical properties optimal correlation method for airship material envelope simulation and application”.

 other comments: 

1) The near -airship application needs a short indication : what altitude ? 20km?  this is not exactly orbiting site…

2) The motivation related to envelope is not enough for engineering readers. Please discuss better the introduction at line 31-33 ..

3) In the discussion of numerical/theoreticasl procedure used by literature no critical observation is reported: why the micro mechanical representation with unit-representative cell is not valid? Etc….

4) The cited standard have to be connected to the wlee-known and whole-accepted reference to ASTM standard. Please provide a sort equivalence evaluation.

5) Please indicate if The variation in properties with load level has a specific origin or it is just an observed phenomenon. Please indicate if variation in fiber orientation under loading could cause such a non-linear representation of the mechanical behavior.

6) Eq.1 and Eq. 2 are not connected each other. Please indicate why in eq.2 there are considered only some specific terms . Which is the rationale for eq.2-3 etc…

7) The same for the explanation of the representative squares : why only some of the parameters represent the effect of warp? And so on..

8) Figure 1 and figure2 are doubled ..

9) Please cite NSGA-II in reference list . It seems not derived by the authors

10) Table 4 represents values from the three loading ratio, but there are not three values. The valueas seem  averaged. Please clarify.

 11) Figure 13 is not clear. Please clarify the origin of data: experimental, numerical etcc…difficult to read.

 

MAJOR REVISION IS REQUESTED.

Author Response

Response to the reviewer

Dear Reviewer:

  Thank you for your comments concerning our manuscript entitled “Study of the Mechanical Properties of Near-Space Airship Envelope Material Based on an Optimization Method” (ID: aerospace-1883807). We have studied comments carefully and have made revisions according to your comments. The revisions in this paper and the answers to the reviewers’ comments are as follows:

 

• The near -airship application needs a short indication : what altitude ? 20km? this is not exactly orbiting site…

[Answer1] A near-space airship is a cost-effective alternative to Earth orbiting satellites for sightseeing, aerial photography, communication, and weapon transport, and has become a strategic platform for many countries, which is operating at an altitude of 20-100km.

    Above has been added in Section 1.

2) The motivation related to envelope is not enough for engineering readers. Please discuss better the introduction at line 31-33 ..

[Answer2] According to the different main structure materials of envelope materials, the structure of aerosols envelope material can be roughly divided into two categories: fabric material and polymer flexible film material. Fabric materials are also called textile composites. Compared with traditional composites, textile composites have uniform mechanical properties, higher strength and modulus. Compared with polymer flexible film materials, its strength is also more suitable for the special environment of stratospheric airships. Fabric materials used on airships are generally divided into thermal bonding layer, structural layer and helium barrier layer. Therefore, the airship envelope is a kind of high performance material, and its mechanical properties directly affect the appearance and safety of near-space airship.

    Above has been added in Section 1.

3) In the discussion of numerical/theoretical procedure used by literature no critical observation is reported: why the micro mechanical representation with unit-representative cell is not valid? Etc….

[Answer3] The relevant content has been changed to: “ Generally, the mechanical properties of envelope material can be regarded as elastic, nonlinear-elastic [10], viscoelastic [11], or viscoplastic [12] in analysis models. The choice of models is determined by the type of coated fabric, but it is always open to question. In 1997, Nayfed proposed a nonlinear constitutive model for plain woven fabrics based on the meso-mechanical behavior of representative elements [13]. In 2007, B.Nedjar proposed a fully three-dimensional constitutive model for anisotropic viscoelastic suitable for the macroscopic desxcription of fiber reinforced composites that experience finite strains [14]. In 2017, Meng Junhui obtained several parameters reflecting the material properties of the capsule based on the invariant theory [15].”

 

4) The cited standard have to be connected to the wlee-known and whole-accepted reference to ASTM standard. Please provide a sort equivalence evaluation.

[Answer4] The MSAJ standard is a widely accepted standard for the biaxial testing of woven fabrics and is recommended by American Standard ASCE1852 (1996). The MSAJ standard recommends the minimum strain residual method, the minimum stress residual method, and the best approximation method to calculate the mechanical property parameters of plain weaves. All three approaches lead to the same result. The standard’s principle is based on the least square method to find mechanical properties’ parameters.

5) Please indicate if The variation in properties with load level has a specific origin or it is just an observed phenomenon. Please indicate if variation in fiber orientation under loading could cause such a non-linear representation of the mechanical behavior.

[Answer5] The variation of material properties with load is an observed phenomenon. The materials used in this experiment are plain weave composites (see in section 3.1), including warp and weft directions, which are actually different in yarn size, bundle number, and arrangement. The joint force of yarn in both directions leads to nonlinear mechanical behavior.

6) Eq.1 and Eq. 2 are not connected each other. Please indicate why in eq.2 there are considered only some specific terms . Which is the rationale for eq.2-3 etc…

[Answer6] Eq.1 is a general mechanical property formula of near-space airship plain weave composites. Eq.2 is a fitting formula for the assumption of stress and strain in warp and weft direction according to the mechanical performance of the test. Eq.2-3: the elastic modulus in the warp or weft direction is affected by the tension in the warp and weft direction, and also exhibits nonlinear phenomena. Therefore, a quadratic term equation is used to express the elastic modulus.

7) The same for the explanation of the representative squares : why only some of the parameters represent the effect of warp? And so on..

[Answer7] Subscripts x and y denote the warp and weft directions, respectively. The parameter used for the zonal stress, such as  in , represents the influence of the warp stress on the elastic modulus. We can measure the degree of influence of the warp stress on the nonlinearity of the elastic modulus by the final magnitude of .

8) Figure 1 and figure2 are doubled ..

[Answer8] Figure 2 is doubled, one of the pictures now has been deleted.

9) Please cite NSGA-II in reference list . It seems not derived by the authors

[Answer9] There was a problem with the display due to formatting and it has been corrected, reference 27 has been cited.

10) Table 4 represents values from the three loading ratio, but there are not three values. The values seem averaged. Please clarify.

[Answer10] The three loading ratio of 1:1,1:2,2:1 are all belong to the low stress ratio, the test data under these stress ratios were processed together. The values show in table 4 is a range of elastic modulus and Poisson's ratio under these loading ratios.

11) Figure 13 is not clear. Please clarify the origin of data: experimental, numerical etcc…difficult to read.

[Answer11]

• Experimental data: Data obtained by biaxial tensile test.
• Simulation surface: The surface which was simulated by parameters obtained by the calculation method proposed in this study and the finite element software.
• Value of optimization theory: Values obtained using experimental data and the calculation method proposed in this study.

Above has been added in section 4.3.

Figure 13 has been modified to be more clearer.

Round 2

Reviewer 2 Report

Several points have been considered in the right manner, but there are some of them to be improve: 

1) the expression for the modulus in bivariate polinomial  is not justified : some short discussion or specific refrence describing the significance of the several constants reported selection should improve the manuscript. 

2)  the nonlinear representation of the stress-strain curve cannot be connected to the definition of " elastic modulus " in the nominal meaning. It is just a modulus . A short description should help . The " elastic modulus" is related to linear part of stress-strain curve. 

3) the equations of the muduli is not connected to the equation 2 . add short discussion. 

4) there are several similarities with the paper: 

"Xie, W., Wang, X., Duan, D., Tang, J., & Wei, Y. (2021). Mechanical properties of UN-5100 envelope material for stratospheric airship. The Aeronautical Journal, 125(1285), 472-488. doi:10.1017/aer.2020.92"

Please insert some discussion related to novelty content , new findings, improvements and so on... Cite the papper in reference list is not enouhg .

Author Response

Response to the reviewer

Dear Reviewer:

  Thank you for your comments concerning our manuscript entitled “Study of the Mechanical Properties of Near-Space Airship Envelope Material Based on an Optimization Method” (ID: aerospace-1883807). We have studied comments carefully and have made revisions according to your comments. The revisions in this paper and the answers to the reviewers’ comments are as follows:

 

• the expression for the modulus in bivariate polinomial  is not justified : some short discussion or specific refrence describing the significance of the several constants reported selection should improve the manuscript. 

[Answer1] A reference (Reference 28) on elastic modulus has been added to this paper. The univariate quadratic polynomial (Eq.2) is based on the stress–strain curve of the biaxial tensile test, which can be used to fit the curve. However, the elastic modulus obtained by this method only considers the effect of the stress in one direction. In fact, the stress in warp and weft directions will both affect the elastic modulus of the material. Therefore, the bivariate quadratic polynomial (Eq.3) can be obtained.

• the nonlinear representation of the stress-strain curve cannot be connected to the definition of " elastic modulus " in the nominal meaning. It is just a modulus . A short description should help . The " elastic modulus" is related to linear part of stress-strain curve.

[Answer2] The general definition of "elastic modulus" is the stress in a unidirectional stress state divided by the strain in that direction. Elastic modulus is a physical quantity describing the elasticity of a material, which is a general term. In this test, the elastic modulus is constantly changing, consistent with nonlinear results. However, if in a very short period of time, the relationship between stress and strain can be regarded as linear, which satisfies the general definition of elastic modulus.

  Above has been added in section 1.

• the equations of the muduli is not connected to the equation 2 . add short discussion. 

[Answer3] By definition, "elastic modulus" is the stress in a unidirectional stress state divided by the strain in that direction. Eq.2 in this paper defines the relationship between stress and strain from the curve results of the test, describes the nonlinear relationship between stress and strain, and is a fitting formula.

• there are several similarities with the paper: 

"Xie, W., Wang, X., Duan, D., Tang, J., & Wei, Y. (2021). Mechanical properties of UN-5100 envelope material for stratospheric airship. The Aeronautical Journal, 125(1285), 472-488. doi:10.1017/aer.2020.92"

Please insert some discussion related to novelty content , new findings, improvements and so on... Cite the papper in reference list is not enouhg .

[Answer4] The research content of this paper is fundamentally different from the above literature, which mainly describes the experiment and an approximate model method. This paper mainly uses an optimization algorithm to solve the calculation problem of elastic modulus variation, which is a further study of the mentioned literature.

Above has been added in section 1.

 

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

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