HTPB推进剂定应变老化损伤本构特性研究

Research on Damage Constitutive Characteristic of HTPB Propellant Under Constant Strain Aging

关键词:  HTPB推进剂  定应变  加速老化试验  损伤  本构模型

Key words:  HTPB propellant  Constant strain  Accelerated aging tests  Damage  Constitutive mode

摘要:

为研究复合固体推进剂在定应变老化条件下的力学特性及本构行为，开展了HTPB推进剂方坯定应变加速老化试验。考虑到推进剂内部缺陷分布的随机性，建立了定应变老化条件下推进剂的统计损伤本构模型。在构建损伤变量方程时，通过引入初始损伤系数，将推进剂的老化过程等效看作是一种损伤过程。基于定应变加速老化试样的单轴拉伸试验数据，对模型进行了验证，结果显示理论模型与试验结果吻合较好，能准确地描述推进剂在定应变老化过程中的力学行为。通过对模型参数进一步分析发现:初始损伤系数方程能区分化学老化与定应变对推进剂的损伤作用。化学老化对推进剂的损伤效应随老化时间呈指数规律增大；同一老化时间段内，定应变对推进剂的损伤作用呈指数规律增大。化学老化不但影响本构模型曲线在损伤段强度的大小，还影响其形状特性，在55℃条件下，老化时间小于284d时，试样拉伸曲线具有明显的屈服区；老化时间大于284d时，没有明显的屈服区。定应变仅降低损伤段强度的大小，不改变其形状特性；在定应变老化过程中，损伤应变阈值随老化时间及定应变水平基本呈现线性关系下降。

Abstract:

Accelerated aging tests under constant strain were conducted on HTPB propellant with the goal of investigating its mechanical properties and constitutive behaviors. Considering the random distribution of internal defect in propellant，a statistical damage constitutive model of propellant was established. The initial damage coefficient，making aging process of propellant equivalent to a form of damage，was introduced to construct the damage variable. Based on the uniaxial tension test of propellant samples aged under constant strain，the model was validated. Results show that theoretical model has good agreement with experimental results and can accurately describe the mechanical behavior of propellant during the constant strain aging. Further analysis indicated the damage effects caused by chemical aging and constant strain can be identified from the equation of initial damage coefficient. Chemical aging can not only influence the tensile strength of propellant in damage phase，but also change the shape characteristics of stress-strain curve. There are obvious yield zones in the stress-strain curves when aging time is below 284 days while there are nonsignificant yield zones at aging time above 284 days under the aging temperature of 55 ℃. The constant strain only decreased the tensile strength in damage phase. The strain threshold value decreased linearly along with the aging time and constant strain level during aging process.