Pbxs Effective Mechanical Properties And Constitutive Relations Research

The main work of the dissertation is as follows:1. In the first chapter of this dissertation, the effective mechanical properties and the constitutive relations of PBX were reviewed. On the basis of many references, we take PBX into consideration as main work of this dissertation. This dissertation composed of two parts: one is the elastic properties of PBX by micromechanics-based methods, the other is the mechanical behavior and the constitutive relations in quasi-static and dynamic (means in various strain rate)state are explored.2. It is focused on the study of TATB-based PBX, the effective elastic properties of PBX can be obtained by three classical micromechanical models if the elastic properties of the components are known. The bulk modulus and shear modulus of PBX-2 are computed by these theoretical models. The results show that "Hashin-Shtrikman" model and "Third-order bounds"model are better than "Reuss-Voigt bounds" model.3. The samples with different densities were prepared to conduct compressive tests to measure elastic modulus. On the basis of the micromechanics, A new term named "interface bonding parameter" which contains the density of the bulk PBXs was promoted and a modified model of Hashin-Shtrikman model was obtained. The elastic modulus were calculated by classical Hashin-Shtrikman model and by modified model respectively. The results show that the modified model with "interface bonding parameter" can give much more accurate estimates compared to classical hashin-shtrikman model. It proves that the modified Hashin-Shtrikman can be used to predict well the effective modulus of double-composition PBXs.4. The stress-strain relations of two TATB-based PBX are measured by experiment in quasi-static state. And the elastic modulus and compress strength with the strain rate are investigated respectively. As a result, the two parameters, that can characterize the rate denpendency of matrerials, have been obtained. The results show that PBX-2 has less dependency of strain rate than that of PBX-1。5. On the basis of Lemaitre damage evolution laws , the modified damage evolution laws which is applicable for various strain rate of PBX are derived. Consideration that strain rate effect, the nonlinear damage evolution constitutive equations at low strain rate are obtained. The results show that the constitutive equations can describe the mechanical behavior of PBX at low strain rate. 6. By the help of Hopkinson bar, the dynamic stress-strain relations of HMX-based PBX with fresh and aged samples are measured respectively. The relationship between fresh and aged samples of dynamic compress strength and rate-dependency laws are explored respectively. At last, the stress-strain relations with fresh and aged samples are compared also.By using the simplified ZWT model, which be ignored the item of low strain rate -that is include five parameters, the constitutive relations are fitted with fresh and aged samples. The results show that "simplified ZWT model" can describe the mechanical behavior of HMX-based PBX at high strain rate. The results also show that the five fit parameters are not constants, but related to the strain rate.