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..

多孔和铸装高能推进剂的燃烧转爆轰

为研究多孔和铸装高能推进剂的危险性能，设计加工了燃烧转爆轰的实验装置，并建立了以光电管为主的测试系统。经实验发现，多孔装药在燃烧向爆轰的转变过程中有冲击波／爆轰波的回传现象，而铸装药则没有

Measuring the mechanical properties of micro-cantilever sensors

利用一种静态和两种动态的检测技术,对红外辐射探测微悬臂梁式传感器材料的弹性模量进行了测试研究.在静态检测实验中,利用纳米硬度计直接测出传感器材料的弹性模量;在动态实验中,分别利用谱平面光学滤波法和多普勒测振仪得到微悬臂梁传感器结构的固有频率,再结合数值模拟计算求出传感器的等效弹性模量.通过几种检测结果的分析和比较,获得了更加精确的微梁传感器单元的弹性模量值,为微梁的优化设计和评估提供了可靠的参数

Super-resolution Image Reconstruction Algorithm Based on Sub-pixel Shift

针对多帧图像超分辨率重建问题,利用一阶泰勒展式,在亚像素级上对图像退化过程进行建模,并建立极小化能量函数,选择grAPH-CuT算法进行能量极小化求解.为了验证本文算法的有效性,采用模拟图像退化过程和直接用相机拍摄两种方式获得低分辨率图像序列.从4x4倍重建结果的比较来看,本文算法不仅对模拟退化过程产生的低分辨率图像序列有效,而且在提高真实低分辨率图像的分辨能力方面也有很好的效果.此外,实验结果表明本文算法对噪声有较好的抗干扰能力.This paper studies the problem of multi-frame image super-resolution reconstruction.The process of image degradation is modeled by using the first-order Taylor expansion based on sub-pixel.Then the energy minimization function is established and the graph-cut algorithm is chosen to solve the energy minimization.In order to confirm this algorithm, we obtain the low resolution images by two ways: simulating image degradation and taking photos.By comparing the 4 × 4 times reconstruction results, it is shown that this algorithm is valid not only for simulation of low resolution images but also for real images.Besides, experimental results show that this algorithm possesses good anti-interference ability of noise.国家自然科学基金(61373077); 国防基础科研计划(B0110155); 国防科技重点实验室基金(9140C30211ZS8); 高等学校博士学科点专项科研基金(20110121110020); 福建省自然科学基金(2011J01365); 福建省重点项目(2014H0034); 航空科学基金(20125168001); 黄慧贞集美大学学科建设基金(ZC2014010)资助~

真空磁过滤电弧离子镀法制备类金刚石涂层方法及性能研究

采用真空磁过滤电弧离子镀方法，在GT35基体上沉积类金刚石膜。通过对清洗工艺及弧电流、工件所加负偏压、沉积温度等参数的研究，制定出了合理的工艺路线，并对这种膜层进行了X-射线光电子谱（XPS）分析，利用干涉仪、纳米硬度计对膜层的粗糙度、纳米硬度作了进一步检测。结果表明，采用此种方法制备的类金刚石膜层，SP^3含量约为40．1％；组织致密，无大的颗粒；镀膜后的粗糙度可以达到0．015μm；纳米硬度约为55GPa。并将膜层与TiN膜层组成摩擦副，进行了耐磨性试验。结果表明膜层的耐磨性较好

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

The characterization of plastic flow in three different bulk metallic glass systems

Plastic deformation behaviors of Zr52.5Al10Ni10Cu15Be12.5, Mg65Cu25Gd10 and Pd43Ni10Cu27P20 bulk metallic glasses (BMGs) are studied by using the depth-sensing nanoindentation, macroindentation and uniaxial compression. The significant difference in plastic deformation behavior cannot be correlated to the Poisson's ratio or the ratio of shear modulus to bulk modulus of the three BMGs, but can be explained by the free volume model. It is shown that the nucleation of local shear band is easy and multiple shear bands can be activated in the Zr52.5Al10Ni10Cu15Be12.5 alloy, which exhibits a distinct plastic strain during uniaxial compression and less serrated flow during nanoindentation. (c) 2006 Elsevier B.V. All rights reserved

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

Critical serrated flow features during nanoindentation in La-based bulk metallic glasses

La57.6Al17.5(Cu,Ni)(24.9) and La64Al14(Cu,Ni)(22) bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)(24.9) BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)(22) BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration

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