Effects Of Fracture Energy And Damage Evolution On Toughness Fracture

Solids break into multiple fragments under impact tensile loading.The Lower Limit of the average fragment size generated during fragmentation can be predicted by the Mott-Grady model based on the linear cohesive fracture hypothesis.In fact,the damage evolution of ductile metals is diversified.Mott unloading wave also has an impact on ductile fragmentation.In this thesis,the effects of different damage evolution laws,fracture energy and Mott unloading wave on ductile fracture process are studied by numerical simulation.One-dimensional dynamic tension fragmentation experiment of 1060-O pure aluminium ring was carried out by using hydraulic expansion ring experimental device,and the experimental phenomena and results were analyzed.ABAQUS/Explicit dynamic finite element method was used to simulate the tensile fracture process of ductile metal rod(45 # steel)at high strain rate.The influence of linear and non-linear damage evolution on the ductile fracture process was analyzed.The numerical results show that the damage evolution law has a significant influence on the fracture process of ductile metals.The larger the non-linear index ? is,the less the number of fragments produced during the fracture process is;Grady-Kipp fragmentation formula can still predict the fragments size generated during the ductile fracture process in a certain range;when the non-linear index ? is much larger than 0(i.e.,the viscous property of materials),the effect of damage evolution law on ductile fracture has significant strain rate sensitivity.The lower the strain rate,the greater the deviation between numerical results and theoretical analysis,but the deviation is not obvious when the strain rate effect is not considered.The process of free expansion of 1060-O pure aluminium ring at a given initial velocity is realized by numerical simulation.The effects of different fracture energies and different constitutive relations on the tough fracture process are analyzed.The results show that fracture energy has a significant effect on ductile fragmentation.The larger the fracture energy,the more viscous the material is,and the less the number of fragments produced by metal fragmentation;the larger the fracture energy,the smaller the fragment size produced by ductile fragmentation falls near Grady-Kipp fragmentation formula;when the fracture energy is small,the fragment size falls near the brittle fracture formula.If the material constitutive model is replaced by the brittle fracture model,the fragment size falls on the brittle fracture formula.The finite element fluid-solid coupling method was used to realize the dynamic expansion and fragmentation process of 1060-O pure aluminium ring with a notch under hydraulic impact.The complete propagation process of Mott unloading wave was analyzed.The results show that the ring breaks into two segments at the notch,and the Mott unloading wave propagates into the ring first,and the rigid unloading occurs at the point through which the carrier-unloading passes.The circumferential velocity occurs rapidly at this point,the circumferential stress begins to unload immediately,and the circumferential strain tends to balance.A new unloading wave will be emitted at the necking of the ring during the expansion process and propagate to both sides of the necking.The propagation time of the Mott unloading wave calculated by the theoretical formula is not much different from that judged by the circumferential strain balance time in the simulation,and the strain rate effect of the material has little influence on the calculation results,and good data results can still be obtained in the ideal Mott theoretical model.The theoretical formulas of Mott and Grady can better calculate the propagation time of the unloading wave and location.The dynamic tensile test of 1060-O pure aluminium ring was carried out with a hydraulic expansion ring experimental device.The experimental results show that the strain changes at different locations of the Mott unloading wave in the propagation process are consistent with those in the simulation,and the fracture morphology of the recovered specimen is similar to that in the simulation.The experimental results well verify the conclusions of the simulation on the Mott unloading wave propagation.