An experimental technique has been developed that is capable of (1) dynamically loading the specimen in multiaxial compression; (2) controlling the stress state in the specimen in the range from uniaxial stress to uniaxial strain; and (3) allowing the recovery of the sample after loaded by a single, well defined pulse for the characterization of the failure mode. In this technique, cylindrical ceramic specimens were loaded in the axial direction using a split Hopkinson pressure bar modified to apply a single loading pulse, and were confined laterally either by shrink fit sleeves, or by eletro-magnetic force.ududQuasi-static and dynamic multiaxial compression experiments have been performed on a machinable glass ceramic, Macor, and a monolithic engineering ceramic, sintered aluminum nitride (A1N). The cylindrical ceramic specimens were confned laterally by shrink fit sleeves: the amount of confining pressure (0-230 MPa) was varied by using different sleeve materials. The quasi-static axial load was applied by a hydraulic driven Material Test System (MTS), whereas the dynamic axial load was provided by a modified split Hopkinson (Kolsky) pressure bar (SHPB). Under both quasi-static and dynamic loading conditions, the experimental results for both materials showed that the failure mode changed from fragmentation by axial splitting under conditions of uniaxial stress (without lateral confinement) to localized deformation on faults under moderate lateral confinement. The fault initiation process was studied experimentally in detail. Based on the experimental results, a compressive brittle failure process was summarized. A transition from brittle to ductile behavior was observed in Macor under high confinement pressure which was achieved using a second sleeve around the inner sleeve. The compressive failure strengths of both materials increased with increasing confinement pressure under both quasi-static and dynamic loading conditions. The highest dynamic compressive strengths of Macor and A1N measured in the experiments were 1.35 GPa and 5.40 GPa, respectively, whereas their quasi-static compressive strength were measured to be 0.43 GPa and 2.5 GPa, respectively.ududBased on the experimental results on A1N together with available data in the literature, a failure/flow criterion was developed for ceramic materials under multiaxial loading. A Mohr-Coulomb criterion and an improved Johnson-Holmquist model were found to fit the experimental data for brittle failure, whereas the materials exhibited pressure insensitive plastic flow at high pressures. Observations made in other types of dynamic experiments (e.g., shock wave loading) were rationalized based on the postulated failure mechanisms and the possibility of plastic flow beyond the Hugoniot elastic limit (HEL). The effect of various material properties on the failure behavior was investigated using the proposed failure criterion. The applicability of the present model to a range of ceramics was also explored and the limitations of the model were outlined.ud
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机译:已经开发出一种实验技术,该技术能够(1)在多轴压缩条件下动态加载样本; (2)将试样的应力状态控制在单轴应力至单轴应变的范围内; (3)允许在加载一个明确定义的单个脉冲后回收样品,以表征失效模式。在这项技术中,使用经修改的霍普金森压力棒将圆柱形陶瓷试样轴向加载,该霍普金森压力棒经修改以施加单个加载脉冲,并通过收缩配合套筒或电磁力从侧面进行约束。在可加工的玻璃陶瓷Macor和整体式工程陶瓷烧结氮化铝(AlN)上进行了动态多轴压缩实验。圆柱形陶瓷试样通过热套套管横向约束:围压的大小(0-230 MPa)通过使用不同的套管材料而变化。准静态轴向载荷是由液压驱动的材料测试系统(MTS)施加的,而动态轴向载荷是由改进的霍普金森(Kolsky)分压式压力杆(SHPB)提供的。在准静态和动态载荷条件下,两种材料的实验结果均表明,破坏模式从在单轴应力(无侧向约束)条件下的轴向劈裂转变为在中等侧向约束下的断层局部变形。通过实验详细研究了故障启动过程。根据实验结果,总结了压缩脆性破坏过程。在高约束压力下,在Macor中观察到了从脆性到延性的转变,这是通过使用围绕内套筒的第二个套筒实现的。在准静态和动态载荷条件下,两种材料的压缩破坏强度都随围压的增加而增加。在实验中测得的Macor和A1N的最高动态抗压强度分别为1.35 GPa和5.40 GPa,而其准静态抗压强度分别为0.43 GPa和2.5 GPa。 ud ud基于实验结果AlN与文献中的可用数据一起,为陶瓷材料在多轴载荷下的破坏/流动准则制定了标准。发现Mohr-Coulomb准则和改进的Johnson-Holmquist模型符合脆性破坏的实验数据,而材料在高压下表现出对压力不敏感的塑性流动。根据假定的失效机制和塑性流动超出Hugoniot弹性极限(HEL)的可能性,合理化了其他类型的动态实验(例如冲击波载荷)中的观察结果。使用提出的失效准则研究了各种材料特性对失效行为的影响。还探讨了本模型对一系列陶瓷的适用性,并概述了该模型的局限性。 ud
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