Study On Dynamic Fracture Of UPVC

UPVC material is widely used in the key structural engineering. But the literature is seldom reported for the fatigue and mixed-mode fracture properties of UPVC, especially for high speed propagation mechanism of the crack under impact loading. The research on the mechanisms can help us to predict some fracture properties and fracture parameters under quasi-static crack extension and high speed crack propagation and establish the fracture criteria of the material under quasi-static and dynamic loading. The research on the mechanisms is important both on theory and engineering in the aspects of anti-fracture design, structural failure estimation and the remaining life of the structure.As the singularity on the crack tip is existed, the propagation process of the crack under quasi-static or high speed loading is extremely complex. So it is difficult for theoretical, experimental and numerical analyses. The basic research method in this paper is the fractural experiment. The fracture properties of UPVC under quasi-static and impact loading conditions are studied by fracture mechanics, digital image correlation and fracture test.The main contents and conclusions of this paper are as follows:1. Combined with the digital image correlation technology, the main mechanical properties of UPVC are studied based on the quasi-static fracture test.1) The crack extension paths of UPVC under mode Ⅰ and mixed-mode loading conditions are obtained. The relationship between load F and crack extension△a and the fracture properties under two loading conditions are obtained. And the crack tip opening displacement δc1and its component δ1,c1、δ11,c1are obtained.2) By using Vic2D, the crack tip displacement field and strain filed under mode I and mixed-mode loading conditions are calculated for both stages of the initiation crack and crack extension. And the feasibility is analyzed.2. Combined with the digital image correlation technology, the main mechanics properties under impact loading are studied based on the impact fracture test of UPVC plate.1) The crack propagation paths of UPVC under mode I and mixed-mode loading conditions are obtained. The relationships among the crack extension speed v, time t and the length of crack extension Δa under two loading conditions are obtained.2) The crack tip displacement field and strain filed for the initiation crack under pure mode I and mixed-mode loading conditions are calculated by Vic2D. And the feasibility is analyzed.3. Fractural morphology is used to analyze the micro-structure on both of the UPVC plate fracture section and the fatigue section of the crack-tip.1) The fracture mode of UPVC under fatigue stage, quasi-static loading condition and impact loading condition is obtained.2) The fatigue crack extension type of UPVC under fatigue loading conditions is obtained.