裂纹试样尺寸对局部解理断裂应力σ_f的影响

应用弹塑性有限元计算了 3种不同尺寸COD试样裂尖前的应力分布 .在不同温度下进行了拉伸和COD试验 .通过精确测量起裂源距钝化裂尖前的距离 ,测定了局部解理断裂应力σf.结果表明 ,在一定范围内随裂纹深度a/h ,试样高度h和试验温度的增加 ,COD和断裂载荷Pf 明显变化 ,而σf 基本不变 .σf 是一个稳定的材料本质参数 ,它的值不随裂纹试样尺寸变化 .

C-Mn钢焊接接头的解理断裂行为的研究

测定不同φ(焊缝)的C-Mn钢焊接接头Charpy-V冲击试样、COD裂纹试样的低温断裂参量,φ(焊缝)小于一定值时,解理裂纹起裂于母材各区,韧性用σf/σy较小的分散带表征;当φ(焊缝)大于一定值时,解理裂纹起裂于焊缝粗晶区,韧性用相应的σf/σy较窄的分散带表征。焊接接头的解理断裂由脆性相开裂形成微裂纹,在外加主应力达到解理断裂应力σf时导致解理断裂。

两种Fe含量下铸造U-2Nb合金的拉伸塑性

实验研究了两种Fe含量下铸造U-2Nb合金的室温拉伸性能。结果表明:高Fe含量导致合金的脆性断裂,SEM分析发现脆性断裂包含沿晶和解理两种断裂机制。常规Fe含量的合金获得了高的拉伸塑性,断口呈现韧性穿晶断裂。

Anisotropic surface broken bond properties and wettability of calcite and fluorite crystals

Anisotropic surface broken bond densities of six different surfaces of calcite and three surfaces of fluorite were calculated. In terms of the calculated results, the commonly exposed surfaces of the two minerals were predicted and the relations between surface broken bonds densities and surface energies were analyzed. Then the anisotropic wettability of the commonly exposed surfaces was studied by means of contact angle measurement. The calculation results show that the （101^-4）, （213^-4）and （01 1^-8）surfaces for calcite and （111） for fluorite are the most commonly exposed surfaces and there is a good rectilinear relation between surface broken bond density and surface energy with correlation of determination （R^2） of 0.9613 and 0.9969, respectively. The anisotropic wettability of different surfaces after immersing in distilled water and sodium oleate solutions at different concentrations can be explained by anisotropic surface broken bond densities and active Ca sites densities, respectively.

Mineral cleavage nature and surface energy: Anisotropic surface broken bonds consideration

The population of surface broken bonds of some typical sulfide, oxide and salt-type minerals which may belong to cubic, tetragonal, hexagonal, or orthorhombic system, were calculated. In terms of the calculation results, the cleavage natures of these minerals were analyzed, and the relationship between surface broken bonds density and surface energy was also established. The results show that the surface broken bonds properties could be used to predict the cleavage nature of most of minerals, and the predicted cleavage planes agree well with those reported in previous literature. Moreover, this work explored a rule that, surface broken bonds density is directly related to surface energy with determination coefficient（R2） of over 0.8, indicating that the former is a dominant factor to determine the latter. Therefore, anisotropic surface broken bonds density can be used to predict the stability of mineral surface and the reactivity of surface atoms.

Atomic-scale observation of the deformation and failure of diamonds by in-situ double-tilt mechanical testing transmission electron microscope holder

In-situ transmission electron microscopy(TEM)has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects.To take advantage of the atomic resolution of advanced TEMs,a compact five-degree-of-freedom nanomanipulator was integrated with an indenter that was made of nanotwinned diamonds,for both the in-situ mechanical testing and double tilting of TEM samples.As a demonstration,in-situ bending tests were performed on the?111?,?110?and?100?single-crystal diamond needles.The tests revealed the{111}cleavage to be the dominant failure mode.The in-situ indentation on a diamond nanoplate led to curved cracks consisting of nanometer-scale steps,which were identified to be atomic flat{111}facets.The atomic-scale observation of the deformation and failure of diamonds demonstrated the stability of the entire system and the durability of the indenter.We expect that more delicate research can be carried out by means of this holder in the near future,including in-situ stimulation,atomic characterization,and tomography.