Strength of Metals at High Strain Rates

Results of metal testing in impact tension–compression and indentation are analyzed. As the analysis of these data demonstrates, the strength of metals increases greatly with strain rates and at moderate indentation rates. At high indentation rates, a decrease in the specific energy (per unit volume of a displaced material) necessary for the formation of a conical cavity was observed. The account of the effects of viscosity, temperature increase upon plastic deformation and its localization can be used to explain the above phenomena.     

Hardness and Fracture Toughness of SiC-Particle-Reinforced MoSi2 Composites

The indentation technique has been used to evaluate the hardness and fracture toughness of SiC-reinforced MoSi₂ composites made by hot-pressing. It is seen that the toughness increases with increasing indentation crack length (under increasing load) and a probable mechanism responsible for this behavior is described. It is also observed that there is an optimum volume fraction of SiC particles for which the maximum fracture toughness of the composite can be achieved.     

Material surface layer damage estimation for cyclic loading conditions using the nanoindenting and nanoscratching techniques

The nanoindenting method is based on the automatic measurement and recording of the force acting on the indenter (10⁻²-5 N) and the depth of indentation (10⁻²-200 μm). The scratch hardness or nanoscratching method is based on the continuous recording of resistance forces to movement of the indenter impressed into the surface. __________ Translated from Problemy Prochnosti, No. 4, pp. 132–139, July–August, 2006.     

Generalized Deformation Curve for High-Strength Steel over a Wide Range of Strain Rates

Test results for different high-strength steel specimens in static and impact tension and compression over a wide range of strain rates were summarized. These data were used to calculate the generalized deformation curve. The calculations based on this curve were compared with the experimental data on impact indentation with the conical indenter to evaluate the applicability of this method for studying the behavior of metals at high strain rates.     

微纳米尺度压痕硬度尺寸效应的研究进展

针对微纳米尺度下,材料硬度测试中出现的正常压痕尺寸效应或逆向压痕尺寸效应,即硬度值随着压痕深度或施加载荷的增大而减小或增大的现象,目前有很多解释或描述的模型或方程,以寻求出现硬度压痕尺寸效应的根源.但由于硬度测试中所受到的影响因素众多,还没有一种方法能完全符合各种材料和测试条件的硬度测试结果,通过对现有的几种解释硬度压痕尺寸效应方法进行比较分析,对硬度压痕尺寸效应的研究方向进行了展望.     

Crack formation in metallized single crystal silicon substrates

Ball bonding of metallized silicon substrates has been simulated by microindentation, with a hemispherical diamond indentor, of (100) silicon wafers that contained aluminum film layers. The indentation loads varied up to 35N and the thickest aluminum film, composed of four layers, was 100 × 10^-6 m. The radial cracks in the silicon, beneath the aluminum film, were measured as a function of indentation load and aluminum film thickness, and compared to that of unmetallized silicon. The crack lengths have been used to determine the fracture toughness,K _c = 24.4 ± 4.9 MPam^0.5, which is twice the value obtained by Vickers indentation experiments. A model describing the relationship between the film thickness versus the radial crack length is presented.     

纳米压痕仪测试TNT单晶(100)晶面的模量与硬度

用溶剂蒸发法制备了厘米级TNT大单晶。用X-射线衍射(XRD)、差示扫描量热(DSC)方法表征了其晶型结构。结果表明,其晶体为单斜晶系,最大显露晶面为(100)。用纳米压痕仪获得TNT(100)晶面上的压入模量、压入硬度分别为(17.40±0.35)GPa和(0.81±0.05)GPa,该模量显著高于熔铸TNT炸药的压缩模量。     

Indentation deformation and cracking behavior of hydrated aluminoborate glasses

Aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation due to a highly flexible network structure. In cesium aluminoborate glasses, it has been found that the use of a simple post-treatment, namely aging in a humid atmosphere, can further improve this resistance. To better understand the mechanical properties of this glass family upon humid aging, we here study the effect of aging conditions on the structure and mechanical properties of Li,K,Cs-aluminoborate glasses. As expected, we find that higher humidity and longer aging time cause more pronounced permeation of atmospheric water into the glasses. Due to their denser structure and stronger modifier-oxygen bonds, the humid aging has a relatively smaller effect on the mechanical properties of Li- and K-containing glasses relative to Cs-containing glasses, with the latter achieving an ultrahigh crack resistance. We find that the humid aging leads to the formation of a hydration layer in the Cs-aluminoborate glass surface, with a thickness of around 26 μm upon aging at 23 °C with 40% relative humidity for 7 days. Moreover, a remarkable indentation behavior, that is, the observation of μm-sized shear bands inside the imprint of the Cs-glass upon aging at 60% relative humidity is reported. Taken as a whole, the work provides guidelines for how to control the humid aging rate as a function of relative humidity and temperature to form a hydration layer and thus achieve improved crack resistance in such glasses.     

Application of a Depth Sensing Indentation Hardness Test to Evaluate the Mechanical Properties of Food Materials

ABSTRACT: A depth sensing indentation hardness test with an associated analysis is described as a convenient and simple technique for characterizing mechanical properties of food materials, such as hardness (H), elastic modulus (E), and an elasticity index (I_E), which represents the ratio of elastic to total deformation. Storage modulus (G') and loss tangent (tan§) of the selected model food material, a whey protein concentrate (WPC) gel, have also been determined using an oscillatory dynamic testing. Fractal dimension (D) and strain rate (or frequency) exponent (n) of the WPC gels were determined using both the indentation and dynamic test results. A good correlation between the results from the indentation and the dynamic tests was established. The effects of protein concentration, deformation rate, and chemical treatment on the mechanical properties of the WPC gels were clearly illustrated using the indentation test.     

焊接挤压辊造成管体表面缺欠的处理

为了有效消除高频直缝焊管管坯外表面的压痕和划伤缺欠,结合高频焊管机组焊接挤压辊的设计特点,分析了焊接挤压辊造成管坯压痕或划伤等表面缺欠的原因,认为上挤压辊辊缘对管坯造成线状压痕或压坑、侧挤压辊辊缘对管坯造成线性压痕或月牙状划伤、下辊辊缘对管坯造成线性压痕是造成表面缺欠的主要原因。通过对焊接挤压辊造成管坯表面缺欠原因的分析,提出了相应的防止措施。