Energy Absorption Optimization Design Of Brittle Composites With Impact Loading

Ceramic, glass and other brittle materials have become important construction materials of daily life, production and scientific research. For brittle materials, impact resistance is an important subject in research field. The metal material’s energy absorption is through the plastic deformation. Instead, brittle materials absorb energy with the help of crack initiation and propagation. The dynamic fracture process of brittle materials is composed of crack initiation, propagation, branching and merging, relating to complex problems of nonlinear, transient simulation, etc. So, the classical fracture mechanics is no longer applicable. This paper introduced cohesive element method to research the dynamic crack propagation and energy absorption of two-phase brittle composite material. We use dynamic crack propagation simulation program which was based on cohesive element theory and written by professor Molinari of Enoch Pratt Free Library to simulate crack initiation, propagation and calculate energy absorption in this process. On this basis, we established the optimization model to maximize the energy absorption of brittle composite with impact loading. According to the principles of mechanics, we proposed toughness swop criteria and modified genetic algorithm to solve the above optimization problem and improve impact resistance of the structure. The research works of this paper are as follows:1. Inspired by the staggered distribution characteristic of natural biological material like shellfish, we consider three different staggered structures composed of two kinds of brittle materials. We analyze the dynamic fracture properties of the above staggered distributions under impact loading and verify the excellent dynamic fracture performance of staggered distribution.2. Based on the original dynamic crack propagation simulation program, this paper established the optimization model of energy absorption of anti impact structure. In this model, design variables are fracture toughness of grid edges; the objective function is energy absorption of dynamic crack propagation; the constraint functions are material volume fraction and the critical crack length. We propose a swop criterion to optimize the toughness distribution of two-phase brittle composite to achieve the largest energy consumption. Through two numerical examples, we study their toughness distributions and the energy absorptions and verify the effectiveness of the swop criteria. We also investigate the effects of volume fraction and the critical crack length on the optimization results.3. Swop criterion only operates on the fracture toughness of an element edge at each iteration step which may lead to low efficiency. Because of the complexity and high nonlinear of the optimization problem, swop criterion cannot guarantee the optimum solution. So the genetic algorithm is introduced to solve the optimization model of the same, In this paper, we modify the genetic algorithm. We change the traditional coding with 0 and 1 to coding with 1 and 2. Compare the optimization results of the two optimization algorithms and the application scope of the two optimization methods is given.In summary, this paper provides useful theoretical exploration and practice methods to energy absorption optimization design of brittle composites.