采用分离式霍普金森压杆(SHPB)系统进行了一系列常规动态单轴压缩(CDUC)试验和耦合静态动态加载(CSDL)试验,以探索实验室微观尺度下中粉砂岩的可变动态力学行为和断裂特征。在CDUC测试中,中砂岩的动态单轴强度在17.5至96.8s-1范围内与速率相关,而动态弹性模量与应变速率无关。然后,本文提出了一个广义模型来表征17.5到96.8s-1的速率依赖强度。在CSDL测试中,随着初始预压应力的增加,动态弹性模量和动态强度先非线性增加后减小。结果表明,两种经典形态类型(即,在CDUC和CSDL测试的动态应力-应变响应中观察到I型和II型)。通过扫描电子显微镜(SEM),识别了I型和II型行为中加载后微裂纹特征的微观差异。在I类行为中,晶间断裂(IF)通常始于晶粒处或附近,大多数裂纹沿晶界偏转,产生尖锐的棱角,然后聚结到沿应力波传播方向分裂试样的主断裂面上。相比之下,II类行为起因于组合的IF和经颗粒骨折(TF)。
A series of conventional dynamic uniaxial compressive (CDUC) tests and coupled static dynamic loading (CSDL) tests were performed using a split Hopkinson compression bar (
SHPB) system to explore the variable dynamic mechanical behavior and fracture characteristics of medium siltstone at a microscopic scale in the laboratory. In the CDUC tests, the dynamic uniaxial strength of the medium sandstone is rate-dependent in the range of 17.5 to 96.8 s-1, while the dynamic elastic modulus is not dependent on the strain rate. Then, this paper proposes a generalized model to characterize the rate-dependent strength from 17.5 to 96.8 s-1. In the CSDL tests, with increasing initial prestatic stress, the dynamic elastic modulus and dynamic strength increase nonlinearly at first and then decrease. The results show that two classical morphological types (i.e., Type I and Type II) are observed in the dynamic stress-strain response from the CDUC and CSDL tests. By scanning electron microscopy (SEM), microscopic differences in the post-loading microcrack characteristics in the behavior of Type I and Type II are identified. In Class I behavior, intergranular fracture (IF) usually initiates at or near the grains, with most cracks deflected along the grain boundaries, resulting in a sharp angular edge, and then coalesces to the main fracture surface that splits the specimen along the direction of stress wave propagation. In contrast, Class II behavior results from the combined IF and transgranular fracture (TF).