Study On Mechanical Properties Of Architectural Membrane Based On The Digital Speckle Measurement Technology

As a new material,membrane material is widely used in the field of constructional engineering.As the theoretical basis of membrane structure design,the mechanical properties of membrane materials have been paid more and more attention by scholars at home and abroad in recent years.Compared with traditional building materials,the mechanical properties of membrane materials are very different.In addition,because of its low stiffness,the accuracy of deformation measurement is very high,and the traditional contact measuring instruments rarely reach the standard.In order to effectively guide the design of engineering structure and reduce the accident rate of membrane structure,it is very important to measure the mechanical properties of membrane materials simply and effectively.In view of the above problems,three kinds of membrane materials,such as Sattler,Heytex and Xingyida,are used as experimental objects,on the basis of the self-made gripping device made by the team and using digital speckle measurement technology,uniaxial tensile test,trapezoid tear test and central crack tear test were designed respectively.The main research contents are as follows.On the basis of uniaxial tensile test,the tensile strength limits of three kinds of membrane materials were obtained,and the elastic modulus of three kinds of membrane materials were obtained by using the stress-strain curve of multiple cyclic tensioning in the elastic deformation range of membrane material.The deformation of membrane during tensile process was measured by digital speckle measurement technique.The Poisson’s ratio of membrane material was obtained by calculating the strain ratio of wrap and weft in elastic range.The tear strength of Sattler membrane was obtained by trapezoid tear test,and the tensile properties of different membrane materials were analyzed by comparing the tensile stress-strain curves of three kinds of membrane materials.In order to better fit the engineering practice,the crack pretreatment of membrane specimen was carried out on the basis of central crack tear test.The effects of cracks of different lengths and angles on the tensile properties of membrane were analyzed and some laws of three stages of membrane tearing were discussed.The strain cloud images of the whole process of membrane tear were collected by using digital speckle measurement technique.By comparing the main strain cloud images before,during and after the crack propagation,the tear propagation law of membrane material was analyzed.Finally,based on the least squares method,the stress-strain curve of central crack tear of membrane materials is fitted and analyzed.In addition,combined with the mechanical parameters obtained from the membrane properties testing,the tear theory of orthotropic materials in fracture mechanics is adopted,and the analytical solution of displacement of fracture theory is compared with the experimental results.The applicability of the theoretical model to orthotropic membrane materials is verified.Based on the theoretical model and the measured displacement values of the composite mode(Ⅰ,Ⅱ)stress intensity factor near the tip of the central crack,the crack propagation law of the membrane is further analyzed.