| With the rapid development of our economy, polymer material and its products can be seen everywhere in modern life, especially the plastic products. The replacing of steel by plastics has become the inevitable trend. The research about modifier of UPVC has been more thorough by both at home and abroad, while the research on fracture properties especially the mixed-mode fracture properties was ignored. So the further use of UPVC materials was impeded in engineering applications. Therefore, it is necessary to research the mixed-mode fracture properties of UPVC.In this paper, the sensitive fracture factors of UPVC were studied under mode I mode Ⅱ, modeⅢ, mixed-mode Ⅰ/Ⅱ and mixed-mode Ⅰ/Ⅲ by fracture mechanics, digital image correlation and mixed-mode fracture test, It was tried to use the critical COD at steable crack extension to describe the fracture toughness of UPVC, and it is probed that COD criterion can be used to the UPVC material.The main contents and conclusions of this paper are as follows:1. The stress-strain curve and modulus of elasticity and Poisson’s ratio of UPVC material are obtained by monoaxially stretching test.2. By the fracture test of UPVC under thickness of3mm and5mm at1-2and2-1directions, combined with digital image correlation technique, it is measured for the real time crack propagation length△a and critical COD, analyzed for the fracture properties of materials at different thickness and different direction under stable crack extension(1) The curve of load and crack extension length (F-△a curve) are obtained. The results show that:Under the same boundary conditions, among all the different kinds of fracture tests completed, the maximum load-carrying capacity of UPVC is under mode Ⅱ loading conditions, and mode Ⅲ is the minimum. So mode Ⅲ loading conditions is most dangerous for UPVC. Of the important is that mode Ⅱ fracture is different from the common metal materials, and it maybe explained as the UPVC unique frcture properties. (2) The critical COD and δ-△a curve are measured and calculated for thickness3mm and5mm at different directionst. It is suggested that:The value of δC1tends to be stable when the distance of crack extension is approximately equal to the thickness of the material, so δC1can reflect the fracture toughness of UPVC under stable crack extension. Components δC1,1and δC1,n of δC1can reflect the degree of mixed-mode crack extension. Therefore, the value of δC1can be used as a fracture toughness parameter of UPVC polymer under stable crack extension.(3) For mode Ⅱ or mixed-mode Ⅰ/Ⅱ loading conditions, the propagation of the crack is mainly affected by mode Ⅰ. But with the increasing of loading angle, leading role of mode Ⅰ is gradually reduced, while mode Ⅱ is gradually increased.3. In mode Ⅰ, mode Ⅱ, modeⅢ, mixed-mode Ⅰ/Ⅱ and mixed-mode Ⅰ/Ⅲ rupture test, the worst fracture properties of crack body is under mode Ⅲ loading conditons, that is modeⅢ (out-of-plane tear) is the best way to shred UPVC that we used, for1-2direction, when the loading angle is30°and45°, the load-carrying capacity of mixed-mode Ⅰ/Ⅲ is better than mixed-mode ⅠI/Ⅱ,while the load-carrying capacity is similar to mixed-mode Ⅰ/Ⅱ when60°, for2-1direction, when the loading angle is45°and60°, the load-carrying capacity of mixed-mode Ⅰ/Ⅲ is better than mixed-mode Ⅰ/Ⅱ, while the load-carrying capacity is poorer than mixed-mode Ⅰ/Ⅱ when30°4.The fracture of UPVC material should be ductile fracture under glass state through SEM analysis of the fracture surface. |
PDF Full Text Request