| Metal material is widely applied in various engineering fields with its superior performance.The study on the fracture toughness of metal material is the premise behind the guarantee of safe service. The quasi-static and dynamic fracture toughness of 2A12-T4 aluminum alloy compact tension specimens were studied in this paper through digital image correlation method, test and numerical simulation method. Also, the accuracy of digital image correlation method in quasi-static and dynamic fracture toughness test was verified by comparing the calculating results of digital image correlation method, national standard and strain gage embedment method. Besides, this paper has studied the influence of crack form and length on 2A12-T4 aluminum alloy dynamic fracture toughness, and analyzed the mechanism of crack initiation and extension with J integral theory.The main contents of this paper are as follows:Decompose the calculation formula of quasi-static and dynamic J integral. According to the features of data obtained by digital image correlation method,this paper has reasonably selected the integral path, deducing the calculation formula of J integral under quasi-static and dynamic loading and programming with MATLAB.The basic material parameters were tested to provide parameter setting basis to fracture toughness test and simulation. After that,quasi-static fracture test was conducted using 2A12-T4 aluminum alloy compact tension specimens for studying the path selection area of J integral path, verifying the conservation of J integral and calculating the quasi-static fracture toughness through digital image correlation method, then contrasting the accuracy of results through comparing with national standard of GB/T-21143-2007, and verifying the accuracy of these results.The compact tension specimens with two different forms of cracks were tested with Hopkinson tension bar. The dynamic fracture toughness of 2A12-T4 aluminum alloy was calculated by strain gauge method and digital image correlation method. The accuracy of results was verified by the comparison of result obtained before. Meanwhile, this paper calculated the inertial influence coefficient and studied the influence of the inertial effect on dynamic fracture toughness value. Furthermore, the dynamic fracture toughness of two different forms of cracks were compared and analyzed.Simulation has been done on the dynamic fracture of pre-flawed specimens with finite element method for calculating the dynamic fracture toughness value, verifying the accuracy of the simulation through comparing test results. Combining the relations of J integral on different plains from specimen symmetry plain to surface and the stretched form of cracks,this paper has also analyzed the fracture initiation and propagation mechanism. The influence of crack length on dynamic fracture toughness was studied eventually. |
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