HMX晶体热致相变对损伤的影响

Effects of Heating-Induced Phase Transition on Damage for HMX Crystal

HMX基PBX炸药混合体系中炸药晶体在发生高温熔化和分解反应之前,会率先发生非均匀热膨胀和固相晶型转变,使材料的力学性能和安全性能发生突变。为探究HMX晶体的热致相变对材料内部损伤演化的影响机制,发展了考虑HMX晶体热膨胀和相变等变形机制的热力耦合晶体本构模型,从力学角度揭示了黏结剂包覆HMX晶体相变对体积变形、应力状态以及裂纹成核演化过程的影响机理,量化分析了升温速率对材料相变和裂纹损伤状态的影响规律。结果表明:随着加载温度升高,HMX晶体的热膨胀和β→δ相变导致体积增大,晶体内部形成拉伸应力状态,同时晶体与黏结剂相互挤压形成的局部压剪作用使晶体内部出现裂纹成核和扩展现象。相变温度附近HMX晶体内部裂纹成核和扩展数量显著增加,晶体内部发生不可逆损伤。外界升温速率对晶体内部裂纹形核扩展与损伤造成显著影响,较高的升温速率会加大晶体损伤程度,增加炸药内潜在热点源及意外点火风险。

At high temperature loading,the thermal expansion and solid-solid phase transition firstly occur in HMX-based PBXs prior to the melting and decomposition of HMX crystal,thereby inducing the abrupt change of mechanical and safety properties.A constitutive model integrating with several deformation mechanisms,including thermal expansion,and phase transition was developed to investigate the effects of heating-induced phase transition on damage evolution.The influence mechanisms of phase transition in binder-bonded HMX single crystal on the volumetric deformation,stress states and crack nucleation and growth were revealed from the viewpoint of mechanics.The effects of heating rate on phase transition and crack related damage evolution were quantitatively analyzed.The calculated results show that,as the increase of loading temperature,tension stress formed due to the thermal expansion and β→δ phase transition in unilateral-restrained HMX crystal and local shear stress formed due to mutually compression between crystal and binder,contribute to the nucleation and growth of HMX crystal.The number density of cracks exhibits a remarkable growth near the phase transition temperature,thereby inducing the irreversible damage.The heating rate has a significant influence on the nucleation and growth of cracks.Large heating rate will increase the crack related damage level of crystal,thereby increasing the number density of potential hotspots and risks of inadvertent ignition.