The Numerical Simulation Of Fracture Toughness Test Under High Strain Rate

With a large number use of brittle material such as concrete and rock in civil engineering, strong impact load must be considered in the design of some important protective structures such as dams, nuclear power plant containment. Brittle materials always contain a large number of native defects, it leads to a significantly difference of dynamic responses under impact loading and static load. Therefore, studying the dynamic mechanical properties, especially dynamic fracture toughness which is related to the crack propagation is very important. However, due to the difficulties of theory and experimental techniques, the research of dynamic fracture toughness of brittle materials under high strain rate has been slow.Finite element software ANSYS/LS-DYNA program was used in the numerical simulations of semi-circular bending (SCB) test with crack under static and impact loading in this article.The results of the study are as follows:(1)For semi-circular bending (SCB) test under pure I type loading, according to the simulation results of static test, fitting formula of I type stress intensity factor which applies to pure I type loading is put forward and the maximum error is less than 10%. According to the simulation results of static test, fitting formula of I type stress intensity factor which applies to mixed-mode loading is put forward and the maximum error is less than 10%.The simulation result of dynamic test shows that:for semi-circular bending (SCB) test under pure I type loading, dynamic stress intensity factor KId showed regular changes with the change of specimen radius R, bearing interval s and relative crack length a/R.When relative bearing interval s/R=1.2,a/R is in the range of 0.1 to 0.4 and when relative crack length a/R=0.4, s/R is in the range of 1.2 to 1.6,the influence of the inertial effect is relatively small and the error of KId which is calculated with static fitting formula is about 10%.(2)For semi-circular bending (SCB) test with mixed-mode crack, according to the simulation results of static test,fitting formula of Ⅰ type and Ⅱ type stress intensity factor which applies to mixed-mode loading are put forward. The simulation result of dynamic experiment shows that dynamic stress intensity factor KⅠd and KⅡd showed regular changes with t relative crack length a/R and crack angle β for semi-circular bending (SCB) test under mixed-mode loading. When relative crack length a/R is from 0.2 to 0.4 and crack angle β is in the range of 10° to 40°,the error of KId which is calculated with static fitting formula is less than 10%. When relative crack length a/R is from 0.4 to 0.6 and crack angle β is in the range of 10° to 40°, The influence of inertial effect is small and KⅡd can be calculated with static fitting formula.(3)The comparison of stress intensity factor KⅠd and KⅡd of SCB test with mixed-mode crack under static and dynamic loading shows that the change law of stress intensity factor under dynamic and static loading are similar. However, due to the influence of inertia effect of dynamic loading test, The change amplitude and trend of stress intensity factor under dynamic loading are obviously different with them under static loading.