| Tension fabric structures（TFS）have been built more and more widely in recent decades due to their novel appearance and efficient force transmission mode.However,during the manufacturing,transportation,installation and service stage,initial defects inevitably occur in architectural fabrics,and the stress concentration near the defects makes the TFS prone to tear at low stress level,thus tearing failure is the main failure mode of TFS,the tearing performance of architectural fabrics is crucial to the overall safety of TFS.However,since the unsderstanding of the tearing mechanism is not deep enough,design codes of TFS in various countries don’t have any provision about the tearing resistance of architectural fabrics.Currently,there is still no consensus on the tearing test methods,the theoretical analyses are also relatively weak,the numerical methods are not investigated in depth,and there still lack of instructive guidance for the design of TFS to resist tearing failure.Based on the above reasons,this paper establised an analytical framework for the tearing resistance of architectural fabrics,from experimental,theoretical and numerical ways based on fracture mechanics theory.Relationship between many effect factors to the tearing resistance are investigated,the tearing failure mechanism is then revealed,and the tearing resistance evaluation method is proposed.The main work includes the following aspects:（1）Central crack tearing method is adopted to study the tearing performance of PTFE and PVC coated fabrics under uniaxial and equi-biaxial loading,the experimental variables include crack length and deviate angle.Combining the tearing damage process images and the load-displacement curves,the tearing failure modes and the tearing residual strength（TRS）were obtained.For biaxial tearing test,full-field strain near the crack tip was also obtained by 2D DIC.（2）Based on linear elastic fracture mechanics（LEFM）theory,a new TRS model is proposed by further considering the damage zone near the crack tip.The proposed theoretical model overcomes the drawbacks of traditional strength-criteria-based model which highly depends emperical assumption and curve fitting,and the drawbacks of traditional LEFM model which only valid for large crack cases.Furthermore,it has the advantages of simple expressions and clear physical meaning of model parameters,thus it is very convenient for engineering applications.According to the proposed model,the applicable condition of the traditional LEFM model is given,the uniaxial and biaxial TRS evolution curves,the allowable crack length under working stress range are presented.（3）The crack band model preciously used in concrete fracture mechanics is introduced,framework of the numerical method for tearing failure simulation of architectural fabrics is proposed.Considering the characteristics of architectural fabrics,the constitutive model includes the elastic model,the damage initiation criterion,the damage evolution criterion and the fracture criterion are establised.Based on virtual crack closure technique（VCCT）,the crack-length-independent fracture energy is obtained.Adopting the self-developed user material subroutine,effect of stress softening curves,mesh dependence and parameter sensitivity are investigated.The proposed model is also compared with the CZM model implanted in Abaqus,the accuracy and efficiency of the proposed model is validated.（4）Based on the proposed numerical method,uniaxial and equi-biaxial tearing mechanism and the tearing resistance of architectural fabrics are simulated and analyzed.Verification with the experimental results and theoretical values are first conducted,and the tearing mechanism under different crack lengths,angles,specimen sizes and crack locations are analyzed from the perspectives of macroscopic load-displacement curves and local stress distribution and damage evolution.The concept of non-size-effect TRS is proposed,and the specimen size requirements for non-size-effect TRS are given.（5）For how to consider the tearing resistance performance of TFS in the design stage,it is proposed that reasonable material selection should be the main focus.Accordingly,a index constant for the tearing resistance and its detailed calculation method are proposed.Finally,based on the allowable crack length under working stress range,the grading evolution method of fabric tearing resistance is proposed,and the thereshold KIC for each tearing resistance grade are given. |
