CONCLUSIONS
An analysis of the experimental data on spalling failure has allowed us to reveal several tests in which the failure delay phenomenon was observed. This effect can be explained by the structural–temporal criterion that also makes it possible to calculate threshold stresses for different loading rates. The strength parameters of the tested material have been determined using the incubation-time criterion. It has been shown that the method of treatment of steel may significantly affect its dynamic strength. The study has enabled us to draw a conclusion that, in order to observe the failure-delay effect, all experimental conditions must be precisely controlled and certain balance must be kept between parameters like the duration and amplitude of action and the sample thickness.
Based on the above results, the following can be concluded. In order to study the strength properties of a material, it should preferably be subjected not only to high-rate overloaded pulses with a high density of supplied energy, but also to threshold actions. In this case, temporal effects that are only typical of the dynamic failure mode can be observed. If loading is performed by high-intensity post-threshold actions, the material will have no time to manifest certain characteristic structural–temporal failure effects due to the high rate of load growth.
