Modelling of Ratchet Growth in TATB‐Based Charge under Thermal Cycling

Abstract

AbstractThe TATB‐based explosives undergo irreversible volume growth upon a series of cyclic thermal loading known as ratchet growth and have been extensively studied. In the past, experimental elucidation of this phenomenon has focused on irreversible expansion as a function of the number of thermal excursions over a given temperature range, where growth is asymptotic with increasing cycle number. In this paper, we find that the ratchet growth of TATB‐based charge evolves associated with its dimension, and demonstrate that the growth can be modeled by a force‐thermal coupled calculation method. We have measured the strain response of four various size specimens, and the results show that irreversible strain on the smaller specimen grows more significantly and rapidly. Based on the equivalent relaxation model in which the relaxation stresses are regarded as functions of temperature and temperature gradient, we develop a force‐thermal coupled method for calculating the irreversible deformation. The relaxation model parameters were calibrated by comparing the calculations with the experimental measurements. We propose that it is the thermal expansion effect rather than thermal stress, which plays a dominant role in irreversible deformation. Further analysis indicated that the size effect of ratchet growth was not caused by temperature gradient, but was positively correlated with thermal excursions. The size effect of temperature distribution in the process of equivalent stress relaxation may be responsible for the size effect ratchet growth of TATB‐based charges. Such tests and analytical models should help to understand and predict the ratchet growth response for TATB‐based charges.