Tearing analysis of PVC coated fabric under uniaxial and biaxial central tearing tests

Abstract

In this study, detailed uniaxial and biaxial central tearing tests of a type of PVC coated polyester fiber fabric for buildings were carried out. The characteristics of the damage morphology, the formation of the triangle area at the crack tip, crack propagation, and failure modes during the entire tearing process were studied. The influence of crack orientation, crack length, and load ratio on tearing behaviors were analyzed, and it was found that the two parameters of crack orientation and length could be combined into a single variable of the number of cutting-off yarns in the direction perpendicular to crack propagation. For the uniaxial central tearing test, four widely used theoretical models were used to fit the experimental results, which led to the conclusion that Thiele’s empirical formula was the most suitable theory for predicting the tearing strength of PVC fabrics. Finally, the strain of all yarns across the crack section before and at the moment of crack propagation was recorded by the DIC equipment, and the load borne by each yarn was calculated based on the uniaxial tension curve of this material. In this way, the strain and load distributions were obtained for the first time, from which it was observed that the maximum strain almost always concentrated in the del-zone at crack tips, and the number of cutting-off yarns significantly affected the strain distribution. Specifically, the more yarns were cut off, the more difficult it was for other yarns far from the crack to exert their load-carrying capacity.

Modified stress field model for critical tearing strength of architectural coated fabrics

“…Based on the curve, the design and calculations can be conducted, such as the determination of the allowable crack size. 19,24,30,32 Therefore, if a model can employ fewer test data to obtain an effective σ c -a curve, it will reduce the amount of test work and facilitate the use of single-edge notched or uniaxial central tearing tests. Both the modified stress field model and Thiele's empirical formula have two fitting constants and their σ c -a curves can, in theory, be obtained based on only two test data.…”

Tearing behaviors of polytetrafluoroethylene coated fabric under uniaxial in-plane tearing tests

“…Furthermore, the strain distribution at the crack section, which is the most representative, has been studied extensively. 31 , 32 In the case of the acquisition of the strain distribution at the crack section when tearing initiates, by marking the central position of all the yarns on the surface before testing, according to the marking position, the strain of each yarn at the slit section can be obtained based on the photos captured using the DIC equipment during the testing. In this treatment, the strain at the center of a yarn is used as the average strain in the yarn to approximate the uneven strain in this yarn.…”

“…The spatial three-dimensional deformation can be measured. 32 As shown in Figure 3, all the tests are conducted using the universal testing machine CMT4204, the clamping fixture is adopted, and the maximum load of 20 kN can meet the requirements of all the tests. All the tests are conducted at a temperature of 20 AE 2 C and a relative humidity of 65 AE 3%.…”

“…Then, the loads of the yarns are added to calculate the total load F cal . 32 A comparison of F cal and the critical tearing load F cr is presented in Figure 24. It is apparent from Figure 24 that, for the majority of cases, F cal is slightly less than F cr , but the deviations between them are all within 10%, and they are almost consistent in the weft direction.…”

“…Current researches also commonly focus on the onset of tearing and critical tearing strength. [23][24][25][30][31][32][33][34] Therefore, although it is quite difficult to simulate the process after tearing initiates when adopting a macroscopic continuum model, attention is paid to the tearing initiation and the preceding stage, which are crucial and meaningful to real-life projects. For the onset of tearing, the stress criterion is adopted, and an assessment is introduced as the average stress inside different multiples of the yarn spacing from the crack tip reaches the uniaxial tensile strength.…”