Study And Experimental Verification On Stress Striaxiality Fracture Criterion Of Metallic Materials

The stress triaxiality fracture criterion takes the stress triaxiality as a parameter,and the cracked body and the uncracked body are taken into consideration.From both the macroscopical and meso-mechanical aspects,the cracking problem of the metallic material and the crack-free body are well explained.Many scholars proposed that the determination of material parameters in the stress triaxiality fracture criterion in practical engineering applications is not yet clear,and whether the four fracture mechanisms are common to a certain material,and whether elastoplasticity can also be calculated when they study and use the criterion.Therefore,through the fracture test and stress field calculation of cracked and uncracked LY12 aluminum alloys,the changing rules of the four fracture mechanisms of the material:cleavage fracture,normal fracture,shear fracture with void,and shear fracture without void are clarified and then the seven parameters is determined,which answer the above questions.The main work and innovation results of this article include the following aspects:1.The stress field at the crack tip was corrected.For ductile materials,due to the passivation deformation at the crack tip,the singularity of the stress field at the crack tip does not exist,resulting in no fundamental difference between the stress field at the crack tip and the stress field of the notched specimen and the conventional specimen.On this basis,we proposed two different concepts of ideal cracks and finite size cracks.The ideal cracks are applicable to brittle materials and fatigue cracks.The finite size cracks are applicable to ductile materials.2.The stress triaxiality fracture criterion has been used to explain the relevant tests of the cracked body.The stress fields of two cracked body models are calculated,and it is concluded that it is more accurate to express the stress field at the crack tip of a ductile material with a limited size crack stress field.Through data calculation and comparison of tests,the three fracture mechanisms of LY12-CZ,LY12-M,HY130,and HY100 four kinds of material cracks3.The fracture test of LY12 aluminum alloy notch specimens and conventional specimens are completed.Through the macro and meso-analysis of the fracture,the fracture mechanisms of different fractures are obtained,and the fracture mechanism is explained by the stress triaxiality fracture criterion.The finite element method was used to calculate the stress field of the notched specimen and calculate the relevant parameters.4.Through the stress field obtained by the finite element calculation,the parameters in the stress triaxiality criterion corresponding to four different material cracks of LY12-CZ,LY12-M,HY130 and HY100 are calculated.The seven parameters of the stress triaxiality fracture criterion corresponding to the fracture of the LY12 aluminum alloy notched specimen and the conventional specimen were calculated systematically.