Design,manufacturing And Experimental Study Of CFRP Specimen Under Biaxial Tensile Load

Composite plate and shell structures,such as composite high-pressure vessels,composite tanks,are often subjected to biaxial loads during service.The failure mechanism and mode obtained by the uniaxial test are not accurate enough to evaluate their strength performance,which makes it difficult to realize the precise structural design.Therefore,it is necessary to study the strength performance of composite materials under biaxial loading.In this dissertation,for the carbon fiber reinforced composite plastic(CFRP)plate and shell structure with a stiffness ratio of 2:1,a finite element analysis model of a cruciform biaxial tensile specimen was established,and the thickness ratio of its loading arm and the central test area was analyzed.The thickness ratio between the loading arm and the central test area was designed to be 4:1.Aiming at the key parameters which are prone to dimensional deviation in the manufacturing process of the specimen,the influence of parameter deviation on the stress concentration and the uniformity of stress distribution in the central test area of the specimen was discussed,and the manufacturing tolerance of the dimensional parameter was determined.A method of laying the specimen in the variable thickness area combined with "integrated paving + open paving" was designed to avoid the stress concentration in the variable thickness area and realize the uniform transition of the stress of the specimen during the loading process.Combining the three-dimensional strain optical measurement system,the strain electrical measurement system,and the acoustic emission detection system,a CFRP biaxial tensile test measurement platform was built.The unixial tensile test of CFRP was carried out,and the stress correction coefficient of the cruciform CFRP biaxial tensile specimen was obtained.The biaxial tensile test of the cruciform CFRP biaxial tensile specimen under various load ratios was carried out.The ultimate strength,strain field distribution and acoustic signal distribution of the specimen under different load ratios were obtained.The strength envelope of the composite material in the "tension-tension" quadrant was established,which revealed the failure mechanism of CFRP under biaxial tensile load,and provided data support for the performance evaluation and design of composite plate and shell structures.