To comprehensively understand the fracture properties of solid propellants, the mode I tensile fracture toughness tests at different temperatures (253.15–343.15 K) and loading rates (2–500 mm/min) were conducted on the newly designed circumferentially notched cylinder sample with different initial crack sizes (4.5 and 6.5 mm) for hydroxyl-terminated polybutadiene (HTPB) propellant. Test results reveal that the shape of the tensile fracture stress-strain curves was not significantly influenced by temperature, loading rate and the initial crack size. Higher loading rate and lower temperature can lead to a rise in the tensile fracture toughness of HTPB propellant described by the stress intensity factor, however, continuously increasing loading rate cannot dramatically improve this fracture toughness beyond the rate of 250 mm/min. In addition, the fracture toughness is more sensitive to temperature. Furthermore, the variation of the initial crack size causes obvious changes in the fracture toughness with the coupled effects of low temperature and higher loading rates. At these test conditions, a higher tensile fracture toughness can be obtained with the shorter initial crack. For all the test conditions, there is a linear rise in the strain corresponding to the fracture toughness as temperature increases. Meanwhile, this strain increases with the shorter initial crack. Whereas, the effect of loading rate on this strain is complex. Based on the time-temperature superposition principle (TTSP), the master curves with a log-curvilinear form were constructed to predict the mode I tensile fracture toughness of the propellant at different initial crack sizes in a wide range of loading conditions.

中文翻译：

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HTPB推进剂周向缺口圆柱试样断裂性能试验研究

为全面了解固体推进剂的断裂特性，对新设计的具有不同初始值的周向缺口圆柱试样进行了不同温度（253.15~343.15 K）和加载速率（2~500 mm/min）下的I型拉伸断裂韧性试验。端羟基聚丁二烯 (HTPB) 推进剂的裂纹尺寸（4.5 和 6.5 毫米）。试验结果表明，拉伸断裂应力-应变曲线的形状不受温度、加载速率和初始裂纹尺寸的显着影响。较高的加载速率和较低的温度可以导致由应力强度因子描述的HTPB推进剂的拉伸断裂韧性的提高，但是，持续增加加载速率并不能显着提高超过250 mm / min的速率的断裂韧性。此外，断裂韧性对温度更敏感。此外，初始裂纹尺寸的变化在低温和较高加载速率的耦合作用下导致断裂韧性明显变化。在这些测试条件下，可以通过较短的初始裂纹获得较高的拉伸断裂韧性。对于所有的测试条件，随着温度的升高，断裂韧性对应的应变呈线性上升。同时，这种应变随着初始裂纹的缩短而增加。然而，加载速率对该应变的影响是复杂的。基于时间-温度叠加原理（TTSP），