The fatigue crack growth behavior of composite solid carboxyl-terminated polybutadiene (CTPB) base propellants from a two stage-rocket has been analyzed. Both motors presented similar compositional percentage of the different constituents but while the booster motor presented aluminum as fuel and fine oxidizer particles, the sustainer motor presented nitroguanidine as fuel and coarse rigid inorganic particles. The fracture characterization revealed that the critical energy release rate values obtained from the grains of the booster motor were higher than those computed from the sustainer motor. The fatigue crack growth behavior of the propellant grains under study was comparable to that shown in rubber and the fatigue crack growth curves obtained from the booster motor were below those from the sustainer motor. The micromechanism of failure in both motors was microvoid nucleation and growth till the formation of a macro-crack capable of subcritical advancement. In the grains from the booster motor, the nucleation and progression of damage occurred through the matrix with fracture surfaces plain and with no trace of oxidizer particles. Instead, in the propellant grains from the sustainer motor, the damage was generated in the particle–binder interface and the progression occurred along these interfaces leading to an abrupt fracture surface with discernible oxidizer particles. The mechanism of failure in the booster motor led to a better fatigue crack growth behavior and the irregular crack advancement in the sustainer motor implied a lower exponent of the crack growth rate to the energy release rate power law.

中文翻译：

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端羧基聚丁二烯固体火箭推进剂疲劳裂纹扩展行为

分析了两级火箭复合固体羧基封端聚丁二烯（CTPB）基推进剂的疲劳裂纹扩展行为。两种发动机的不同成分的组成百分比相似，但助推器发动机将铝作为燃料和细氧化剂颗粒，维持发动机将硝基胍作为燃料和粗硬无机颗粒。断裂表征表明，从助推器电机的颗粒获得的临界能量释放率值高于从支撑电机计算的值。所研究的推进剂药柱的疲劳裂纹扩展行为与橡胶中显示的类似，并且从助推器发动机获得的疲劳裂纹扩展曲线低于来自支撑发动机的疲劳裂纹扩展曲线。两种电机故障的微观机制都是微孔的成核和生长，直到形成能够进行亚临界推进的宏观裂纹。在来自增压马达的晶粒中，通过基体发生成核和损伤的进展，其断裂表面平坦且没有氧化剂颗粒的痕迹。取而代之的是，在来自支撑马达的推进剂药柱中，颗粒-粘合剂界面中产生了损坏，并且沿着这些界面发生了进展，导致突然断裂表面带有可辨别的氧化剂颗粒。助力电机的故障机制导致了更好的疲劳裂纹扩展行为，并且支撑电机中不规则的裂纹推进意味着裂纹扩展速率对能量释放速率幂律的指数较低。