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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。
In order to study the mechanical properties and constitutive behavior of composite solid propellants under constant strain aging conditions, the accelerated aging test of billets of HTPB propellants was carried out. Considering the randomness of the internal defect distribution of propellants, a statistical damage constitutive model of propellants under constant strain aging was established. When constructing the damage variable equation, the aging process of propellants is regarded as a kind of damage process by introducing the initial damage coefficient. Based on the uniaxial tensile test data of constant strain accelerated aging specimens, the model was verified. The results show that the theoretical model is in good agreement with the experimental results and can accurately describe the mechanical behavior of propellants in the process of constant strain aging. Through further analysis of the model parameters, it is found that the initial damage coefficient equation can distinguish the damage effect of chemical aging and constant strain on the propellant. The damage effect of chemical aging on propellants increases exponentially with the aging time. During the same aging time, the damage of propellants by constant strain increases exponentially. Chemical aging not only affects the strength of the constitutive model curve but also affects its shape characteristics. When the aging time is less than 284 d at 55 ℃, the tensile curve of the sample has obvious yield zone. When the aging time is more than 284 days, No obvious yield zone. The constant strain reduces the strength of the damaged section only and does not change its shape and properties. During the process of constant strain aging, the damage strain threshold decreases linearly with the aging time and the level of strain.