Theoretical study on loading history dependence of dynamic failure strength for brittle materials

Whether the dynamic failure strength of brittle materials is an intrinsic material property has been debated, owing to its dependence on loading history. To further study such a dependence, a characteristic time failure criterion for brittle materials is developed and introduced into the dynamic damage evolution law to establish a time-dependent dynamic uniaxial constitutive model in the pre-peak load branch. The criterion and the constitutive model are validated by the previous literature data. The results show that, the dynamic failure strength of brittle materials at high strain rates is not a material property due to its loading history dependence. But both the rate enhancement effect and loading history dependence of dynamic strength is a macroscopic mechanical behavior of the material rather than a structural response. When regarded as a mechanical behavior, it is accompanied by changes in the stress-strain curve, whereas a structural response presupposes that the stress-strain curve remains unchanged under quasi-static and dynamic loadings. The microcrack inertial effect is one of the physical mechanisms behind the strain rate enhancement effect and loading history dependence of dynamic failure strength for brittle materials. Macroscopically, the loading history dependence of dynamic strength for brittle materials results from the time-dependent dynamic stress-strain curve. The dynamic strength and stress-strain response of brittle materials should correspond to the full strain or stress history rather than an instantaneous or average rate of the history curve.