Temporal Characteristics of Failure in High-Speed Tests
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Temporal Characteristics of Failure in High-Speed Tests I. V. Smirnova,* and Corresponding Member of the RAS Yu. V. Petrova,b Received March 21, 2020; revised March 21, 2020; accepted April 5, 2020
Abstract—The unstable behavior of generally accepted strength characteristics of a material makes it difficult to evaluate the dynamic strength of a material in high-speed loading problems. This work reveals a new effect, which in a number of practically important cases of tests with a controlled loading rate for evaluating the dynamic strength allows us to offer a convenient time characteristic of the incubation processes of failure under high speed loads. It is shown that this time characteristic does not depend on the strain rate or loading rate and can be determined from general experiments. This makes it possible to enter a material parameter that can be used for criteria for evaluating the strength of a material under high-speed loads, including for calculating the rate and time dependence of critical failure stresses. Keywords: dynamic strength, high strain rate, incubation processes, time to failure, strength criteria DOI: 10.1134/S1028335820050109
With the development of technology, the question more often arises on forecasting the influence of highspeed and impact loads on the strength of materials and structures. A large number of works indicate the influence of the strain rate on the critical stress of failure [1, 2] or plastic flow [3, 4]. Due to the unstable behavior of the strength characteristics, it is impossible to apply the well-established approach to assessing the strength of a material [2, 5], which is based on the concept of a constant value of the critical failure stress or plastic flow. Thus, there is an urgent need to identify the strength characteristics of the material, which are independent of the history and method of application of the load. In this paper, we consider an experimentally determined temporal characteristic that is independent of the speed of a load and can be used to evaluate incubation processes in the structure of the material preceding the onset of macrofailure. Let us consider the case of uniaxial compression or splitting, when failure begins at the stage of load growth without pronounced residual deformation. Moreover, by the fact indicating the beginning of failure, we mean the beginning of a decrease in stresses in the stress–time diagram or stress–strain diagram. In this case, the maximum stress is taken as the strength of the material. The situation under consideration is a Saint
Petersburg State University, St. Petersburg, Russia for Problems in Mechanical Engineering, Russian Academy of Sciences, St. Petersburg, Russia *e-mail: [email protected] b Institute
typical of rocks, concrete, ceramics, and other brittle and quasi-brittle materials. Moreover, the fact is well known that an increase in the strain (stress) rate leads to a change in the failure stress. Therefore, the strain rate is regulated for standard or industry tests. In experiments, the change
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