单轴拉伸下HTPB推进剂细观损伤演化实验研究

Experimental Study on Meso-Damage Evolution of HTPB Propellant under Uniaxial Tensile Load

为了研究HTPB固体推进剂在单轴拉伸载荷下的细观损伤机理,采用高精度微CT对拉伸过程中的HTPB推进剂进行了扫描实验,获取了不同拉伸应变下推进剂的细观损伤形貌以及孔隙率变化规律,分析了推进剂细观损伤对宏观力学性能的影响。结果表明:初始损伤的存在使得推进剂在受到载荷作用时AP颗粒就开始脱湿,AP颗粒脱湿形成的孔洞是推进剂细观损伤的主要形式。拉伸应变较小时,相对小尺寸AP颗粒而言,大尺寸AP颗粒附近的缺陷更容易发展成孔洞。随着拉伸应变的增大,绝大多数AP颗粒都开始脱湿,在推进剂宏观断裂前,大量AP颗粒脱湿形成的孔洞发生汇合,最终使推进剂断裂。加载过程中推进剂孔隙率随拉伸应变呈指数变化,初始孔隙率为1.8%,60%拉伸应变时孔隙率为19.1%。推进剂宏观力学性能处于线弹性段时,其内部细观损伤依旧在不断增加,当细观损伤累积到一定程度时推进剂的承载能力下降,宏观力学性能进入非线性段;由于AP颗粒仍具有一定的增强作用,且HTPB基体也具备承载能力,所以推进剂的应力随拉伸应变呈缓慢增加的趋势。

In order to study the meso-damage mechanism of HTPB solid propellant under uniaxial tensile load,a high-precision micro-CT was used to scan the HTPB propellant during the tensile process. The mesomorphology and porosity change law of the propellant under different tensile strains were obtained,and the effects of propellant meso-damage on macro-mechanical properties were analyzed. The results indicate that AP particles start dewetting when the propellant is loaded because of initial defects. The pores left by the dewetting of AP particles are the main form of propellant mesoscopic damage. Compared with small-sized AP particles,the defects around large-sized AP particles are more likely to develop into pores under low strain values. As the tensile strain increases,most of AP particles begin to dewet gradually. When the propellant is about to break,a large number of pores formed by the dewetting start merging,and finally the propellant is broken. During the loading process,the porosity of the propellant changes exponentially with the tensile strain,the initial porosities is 1.8% and the porosity at 60% tensile strain is 19.1%. When the macro-mechanical properties of the propellant is in the linear elastic stage,the meso-damage is still increasing. The propellant’s ability to withstand loads begins to decline when the meso-damage accumulates to a certain threshold,and the propellant’s macro-mechanical properties change nonlinearly. Because AP particles still have a certain reinforcing effect and the HTPB matrix also has the ability to withstand loads,the stress of the propellant tends to increase slowly with the tensile strain.