Dynamic (600–1000 s) and quasi-static (0.001–0.01 s) compression experiments are conducted on a high-purity alumina ceramic using a split Hopkinson pressure bar and a material test system, respectively. The postmortem fragments of ceramic samples at different strain rates are then characterized via synchrotron micro computed tomography (CT). The three-dimensional (3D) morphologies of fragments are quantified using the gyration tensor analysis after proper segmentation of CT images. The mean fragment size decreases in a power-law form while the mean shape indices (sphericity, elongation index and flatness index) increase in a logarithmic-linear form, with increasing strain rates. In addition, the fragment size and shape distributions are all found to follow the Weibull probability distribution. To reveal the underlying mechanisms of such strain rate effects, high-speed optical and X-ray imaging are implemented to capture the fracture process of ceramic samples under quasi-static and dynamic compression. Primary and secondary wing cracks (PWCs/SWCs) control the fracture and fragmentation of the ceramic under both loading conditions. Compared to quasi-static loading, a considerably larger number of SWCs are produced under dynamic loading, and pronounced branching and bridging occur among the PWCs, which prevent the PWCs from coalescing into axial splitting cracks. Consequently, crack networks composed of high-density wing cracks break the sample into finer and more isotropic fragments, consistent with CT characterizations. Scanning electron microscopy is utilized to analyze the micro damage modes of ceramic samples. Transgranular fracture dominates the grain-scale damage and contributes to the higher dynamic fracture resistance of the alumina under dynamic loading, as a result of more homogeneous nucleation and growth of micro cracks.

中文翻译：

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应变率对陶瓷氧化铝碎片形态的影响：基于同步加速器的研究


分别使用分体式霍普金森压力棒和材料测试系统对高纯氧化铝陶瓷进行动态（600-1000 s）和准静态（0.001-0.01 s）压缩实验。然后通过同步加速器微型计算机断层扫描 (CT) 对不同应变率下陶瓷样品的死后碎片进行表征。在正确分割 CT 图像后，使用回转张量分析对碎片的三维 (3D) 形态进行量化。随着应变率的增加，平均碎片尺寸以幂律形式减小，而平均形状指数（球形度、伸长率指数和平坦度指数）以对数线性形式增加。此外，片段大小和形状分布均遵循威布尔概率分布。为了揭示这种应变率效应的潜在机制，采用高速光学和 X 射线成像来捕获陶瓷样品在准静态和动态压缩下的断裂过程。初级和次级翼形裂纹 (PWC/SWC) 控制陶瓷在两种载荷条件下的断裂和破碎。与准静态加载相比，动态加载下会产生大量的 SWC，并且 PWC 之间会出现明显的分支和桥接，从而防止 PWC 聚结成轴向劈裂裂纹。因此，由高密度翼状裂纹组成的裂纹网络将样品破碎成更细、更各向同性的碎片，这与 CT 表征一致。利用扫描电子显微镜分析陶瓷样品的微观损伤模式。 穿晶断裂在晶粒尺度损伤中占主导地位，并且由于微裂纹的成核和生长更加均匀，导致氧化铝在动态载荷下具有更高的动态断裂抗力。