Uniaxial compression of calcite single crystals at room temperature: insights into twinning activation and development
Uniaxial compression of calcite single crystals at room temperature: insights into twinning activation and development
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DOI：
10.5194/se-10-307-2019
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发表时间：
2018-08
期刊：
影响因子：
3.4
通讯作者：
Camille Parlangeau;A. Dimanov;O. Lacombe;S. Hallais;J. Daniel
中科院分区：
文献类型：
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作者：
Camille Parlangeau;A. Dimanov;O. Lacombe;S. Hallais;J. Daniel
抽象的。 E孪晶是方解石在低温下变形时常见的塑性变形机制。应变率、温度和围压对孪生激活的影响可以忽略不计，孪生激活主要取决于应力差。孪晶激活所需的临界分辨剪切应力 (CRSS) 取决于晶粒尺寸和应变硬化。该 CRSS 值可能遵循 Hall-Petch 关系，但由于实验数据稀疏，其随晶粒尺寸和应变的实际演变仍然存在争议。为了对孪生激活和发展提供额外的限制，在室温下对具有不同尺寸和晶体取向的无约束方解石单晶进行了新的机械测试。单轴变形以受控的位移速率进行，同时使用光学显微镜和高分辨率 CCD（电荷耦合器件）相机监测样品表面。检索到的晶体宏观应力应变行为与变形过程的表面观察结果相关。结果表明：(1) 在应变硬化阶段，随着第一个孤立的机械孪晶的激活，晶体塑性开始出现；(2) 在稳态流动应力阶段，孪晶片层致密化和增厚。室温下孪晶片层的这种增厚强调了方解石孪晶形态不仅仅受温度控制。为孤立孪晶的激活以及孪晶致密化和增厚的开始而获得的 CRSS 的不同值引发了有关在使用方解石孪晶数据进行应力反演时应考虑的适当值的问题。
Abstract. E-twinning is a common plastic deformation mechanism in calcite deformed at low temperature. Strain rate, temperature and confining pressure have negligible effects on twinning activation which is mainly dependent on differential stress. The critical resolved shear stress (CRSS) required for twinning activation is dependent on grain size and strain hardening. This CRSS value may obey the Hall–Petch relation, but due to sparse experimental data its actual evolution with grain size and strain still remains a matter of debate. In order to provide additional constraints on twinning activation and development, new mechanical tests were carried out at room temperature on unconfined single crystals of calcite, with different sizes and crystallographic orientations. Uniaxial deformation was performed at a controlled displacement rate, while the sample surface was monitored using optical microscopy and a high-resolution CCD (charge-coupled device) camera. The retrieved macroscopic stress–strain behavior of the crystals was correlated with the surface observations of the deformation process. Results show (1) the onset of crystal plasticity with the activation of the first isolated mechanical twins during the strain hardening stage, and (2) the densification and thickening of twin lamellae during the steady-state flow stress stage. Such thickening of twin lamellae at room temperature emphasizes that calcite twin morphology is not controlled solely by temperature. The different values for the CRSS obtained for the activation of isolated twins and for the onset of twin densification and thickening raises questions regarding the appropriate value to be considered when using calcite twin data for stress inversion purposes.