棱锥压头几何形状和试样力学性能对压入径向裂纹萌生的影响

仪器化压入测试技术,能够识别材料微区的硬度和力学性能参数,已成为微小尺度力学测试的重要手段。当被测试样为脆性材料时,压入可能在试样表面产生裂纹。压入裂纹萌生是仪器化压入测试技术研究中的关键问题。当测试断裂力学参数(如断裂韧度K_(IC))时,压入裂纹是测试的必要条件,应确保出现;当测试非断裂力学参数(如硬度H、弹性模量E等)时,压入裂纹可能引起测试误差,应避免出现。研究压入裂纹萌生,有助于区分仪器化压入测试中断裂测试和非断裂测试的实验条件,包括压头的选取。压入裂纹的萌生由裂纹驱动应力的强度和分布决定。压头几何形状和试样力学性能主要影响裂纹的驱动应力强度。仪器化压入测试通常使用棱锥形压头,测试断..

EFFECT OF STRUCTURAL RELAXATION ON THE DEFORMATION BEHAVIOR OF A Zr64.13Cu15.75Ni10.12Al10 BULK METALLIC GLASS UNDER NANOINDENTATION

Structural relaxation by isothermal annealing below the glass transition temperature is conducted on a Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass. The effect of structural relaxation on thermal and mechanical properties was investigated by differential scanning calorimetry and instrumented nanoindentation. The recovery of the enthalpy in the DSC curves indicates that thermally unstable defects were annihilated through structural relaxation. During nanoindentation, the structural relaxation did not have a significant influence on the serrated plastic flow behavior. However, Structural relaxation shows an obvious effect in increasing both the hardness and elastic modulus, which is attributed to the annihilation of thermally unstable defects that resulted from the relaxation

Spherical indentation method for estimating equibiaxial residual stress and elastic-plastic properties of metals simultaneously

For instrumented spherical indentation, the presence of equibiaxial residual stress in a material will lead the indentation load-depth curve to shift upward or downward. The load differences between the stressed and stress-free curves were used to estimate the equibiaxial residual stress. Using dimensional analysis and finite element simulations, the equibiaxial residual stress was related to the elastic-plastic parameters and the relative load difference at a fixed normalized indentation depth (h/R = 0.1). Based on these expressions, and together with the method for determining elastic-plastic parameters established in our previous work, an integrated method was proposed to estimate the equibiaxial residual stress and elastic-plastic parameters of metals simultaneously via instrumented spherical indentation. This method avoids preknowledge of the yield strength and measuring the contact area. Applications were illustrated on Al 2024, Al 7075, and Ti Grade 5 with introduced stresses. By comparing the results determined by this integrated method with the reference values, the maximum relative error is generally within +/- 10% for the yield strength, within +/- 15% for the elastic modulus, and within +/- 20% for the equibiaxial</p

Determination of shear creep compliance of linear viscoelastic solids by instrumented indentation when the contact area has a single maximum

Lee and Radok [J. Appl. Mech. 27, 438 (1960)] derived the solution for the indentation of a smooth rigid indenter on a linear viscoelastic half-space. They had pointed out that their solution was valid only for regimes where contact area did not decrease with time. In this article, a large number of finite element simulations and one typical experiment demonstrate that Lee-Radok solution is approximately valid for the case of reducing contact area. Based on this finding, three semiempirical methods, i.e., Step-Ramp method, Ramp-Ramp method and Sine-Sine method, are proposed for determination of shear creep compliance using the data of both loading and unloading segments. The reliability of these methods is acceptable within certain tolerance

棱锥压入断裂测试中裂纹萌生和扩展机制的研究

棱锥压入断裂测试中裂纹萌生和扩展机制的研

多功能硬度计

宏观尺度的仪器化压入测试(弹性模量和压入硬度)和传统硬度(维氏硬度、布氏硬度、洛氏硬度)测

多功能硬度计

宏观尺度的仪器化压入测试(弹性模量和压入硬度)和传统硬度(维氏硬度、布氏硬度、洛氏硬度)测