The Tensile Breaking Progress Simulation And Strength Prediction Of Woven Fabric

Tensile strength is one of the most important properties of woven fabrics. However, during product design processes, it is practically decided from experiences rather than prediction models, namely, it is obtained by time-consuming tests on real fabrics. Therefore it is essential to establish a model to predict tensile properties of fabrics directly from those of yarns, which is of low cost and high efficiency.The objective of this thesis is to develop a chain-of-bundles model, both one- and two-dimensional, for prediction of tensile strengths of woven fabrics. For this reason, the tested tensile strength data of yarns are firstly analyzed and fitted statistically to decide strength probability distribution and the relationship between the length of specimen and test strength is determined. Then fabric critical length is defined and calculated according to different types of yarn and fabric structures. Furthermore, a chain-of-bundles model is established that is combined with Monte Carlo method to predict tensile strength of fabrics.The study begins with the analysis of the dispersibility of yarn strength. The tensile strength of the constituent yarns of woven fabric is tested and the results are fitted by Weibull distribution functions. The analysis shows that the strength distributions of all the tested yarns are fitted in two-parameter Weibull type.The transfer relationship among tested results of different specimen lengths is decided based on statistical analysis of yarn strengths. It is found that, in addition to specimen length, such relationship is relative to the shape parameter of the Weibull distribution. The influence of specimen length on the tested strength shows some relation to the shape parameter. the greater the shape parameter, the smaller the effect. In another word, the smaller the dispersibility of the specimen tensile strength, the smaller the influence of its length on the tested value.The concept of woven fabric critical length is defined subsequently and geometrical and mechanical models are presented according to fabric structural changes during tensile testing process. The effect of the constituent yarn and fabric parameters on critical length is studied quantitatively. Results show that the factors influencing woven fabric critical length include yarn parameters (such as yarn count, twist, tensile strength and young's modulus, etc.) and fabric parameters (such as the density of yarns of the fabric, friction of yarns at interlacing points, etc.).The critical length determines the stress distribution in the loading direction of woven fabrics, while, as we know, the load distribution rule deals with the stress concentration problem in transverse direction. A chain-of-bundles model for woven fabric is proposed in terms of the critical length and load distribution rule (the Local Load Sharing rule or the Shear-Lag Analysis principle) and is used to simulate one- and two-dimensional stretching and breaking process as well as fabric strength prediction. The fundamental difference between both models is that in the one-dimension case the break of yarns in fabric is assumed to occur at a certain cross-section, while in the two-dimension case, the break position are allowed to occur within different critical lengths covering the whole range of the specimen length.The chain-of-bundles model is combined with a Monte Carlo method on a computer for simulation. It is found that because of the over-concentration effect of the Local Load Sharing rule, both the two models with this rule give a result which is far from the tested results, while with the Shear-Lag Analysis principle the simulation results from both models (one- and two-dimension) agree well with the test ones. So in both cases the Shear-Lag Analysis principle seems to be a better choice as compared to the local distribution one.Woven fabric critical length reflects the ratio of tensile strength of yarn to the fabric. The shorter the critical length, the higher the effective strength of the fabric comprised of yarns with same strength, in which lies the practical significance of the concept of the critical length.The proposed model here offers theoretical basis of prediction of woven fabric tensile strength. The conclusions in this thesis could further be applied to other kinds of textiles such as knitting fabrics and nonwovens.