Research On The Mechanical Properties Of Architectural Membranes Based On The Digital Image Correlation Method

In recent years the most common used architectural membranes are PVC film,ETFE film and PTFE film,which belong to flexible composite.Their mechanical properties are also widely studied because of their strong non-linearity,large deformation and sensitiveness to the damage.In this paper the mechanical parameters,concentration,damage and fracture of architectural membranes are studied with the digital image correlation(DIC).The main research contents and results are as follows:(1)A new spot-image making technique is developed.Two kinds of speckle patterns are designed by MATLAB and Photoshop,the quality of speckle patterns evaluated by image correlation matching and average gray gradient method.The speckle pattern is printed on the surface of the specimen with the water transfer printing technology.Compared with the common used speckle making technology,the new method is more convenient and the quality of the speckle can be guaranteed.(2)The basic mechanical properties of PTFE architectural membranes such as the tensile strength,tear strength are studied.The influence of stretching directions on the tensile strength of architectural membranes is compared and the three stages of tensile failure and the failure modes are discussed.(3)The reduction of the strength of the crease in the membrane is studied.The effect of cyclic loading number on the tensile strength of creases is investigated.(4)The double-tongue tearing,trapezoidal tearing and uni-axial slit slippage experiments are carried out on the architectural membranes,and the failure mechanisms of three different tearing methods are analyzed systematically.(5)The mechanical properties of architectural films under uni-axial tension and bi-axial tension are analyzed by digital image correlation.The distribution law of the strain field and the displacement field under the two loads is obtained.(6)For the membrane with hole,the local strain around the porous under the uni-axial and bi-directional loading are compared.The strain field index indicating the failure of the membrane is analyzed and the strain concentration coefficient at the edge of hole is obtained.(7)The mechanical properties of the membrane with the hole under cross double bi-axial stretching are studied by digital image correlation,and the strain field around the hole is analyzed.The change rule of the local strain at the hole edge with the load step is analyzed based on the hole edge characteristic curve and the the law of the local strain change with distance from the hole edge on the characteristic edge line is analyzed.The strain field index predicting the damage of membrane with hole under cross double bi-axial stretching is analyzed,and the strain concentration coefficient at the edge of hole is obtained.