30CrMnSiN钢板表面塑性损伤的激光检测

本文根据激光衍射谱谱面光强度随塑性损伤的变化规律，用３０ＣｒＭｎＳｉＡ材料进行了实测，给出了应变与损伤变量Ｄ（Ｋ）的关系曲线，并对加载和卸载条件下的Ｄ（Ｋ）￣ε曲线进行了比较，结果再次表明，用衍射光强比来定义损伤变量是可行的，该方法检测方便，计算简单、具有较高的精度，可望成为塑性损伤检测的一种有效方法，３０ＣｒＭｎＳｉＡ材料沿垂直于轧制方向拉伸的力学性能及损伤状态优于平行轧制方向，且用空穴面积百分     

30CrMnSiA材料疲劳损伤的激光检测及其细观机理

利用激光反射衍射谱面光强随疲劳损伤试样表面逐步粗糙化而变化的原理，用一种非接触、非破坏的间接疲劳损伤检测方法，对３０ＣｒＭｎＳｉＡ材料轴线平行于轧制方向（Ｌ）和垂直于轧制方向（Ｔ）两种不同试样进行拉——拉非对称循环疲劳损伤检测，证明谱面光强比Ｋ对疲劳损伤是敏感的；损伤变量Ｄ（Ｋ）和疲劳循环次数Ｎ的关系曲线大致可以分为疲劳损伤的减速、线性和加速损失区，从而对材料进行疲劳损伤检测并对其疲劳寿命进行估计；同时对扫描电镜图像分析得出衍射光强比变化所对应的疲劳损伤细观机理。     

30CrMnSiA钢板表面塑性损伤的激光检测

本文根据激光衍射谱谱面光强分布随塑性损伤的变化规律，用３０ＣｒＭｎＳｉＡ材料进行了实测，给出了应变与损伤变量Ｄ（Ｋ）的关系曲线，并对加载和卸载条件下的Ｄ（Ｋ）～ε曲线进行了比较。结果再次表明，用衍射光强比来定义损伤变量是可行的；该方法检测方便，计算简单，具有较高的精度，可望成为塑性损伤检测的一种有效方法；３０ＣｒＭｎＳｉＡ材料沿垂直于轧制方向拉伸的力学性能及损伤状态优于平行轧制方向，且用空穴面积百分数Ｆ＿Ａ得到验证；弹性变形对塑性损伤的影响可以忽略不计。     

利用激光衍射谱的变化测量金属表面的塑性变形并确定其弹塑性区交界

本文首先分析了相干光被粗糙表面散射时,其平均散射光强的空间分布与反射表面微观轮廓的统计参数的关系;进而讨论了弹性和塑性变形对金属表面轮廓统计参数影响的不同特征及与之相应的激光衍射谱的不同变化。据此,提出了一种根据衍射谱强度分布变化来测量塑性变形的方法。用实验对理论分析的结论进行了验证,并给出了一个用上述方法勾画变形物体塑性区形状及测量塑性变形程度的例子。实验表明,这种方法可以分辨不小于2×10~2με的塑性应变。     

低碳钢试件弹塑性边界的白光相关检测

金属试件的弹塑性边界检测对判断该试件是否失效有着重要意义,因此一直是研究人员较感兴趣的研究课题。利用激光和白光作为照明光源的方法都曾被提出以检测金属试件的弹塑性边界以及塑性变形。为避免激光测量的诸多缺点,本文提出一种用白光作为照明光源并结合数字图像处理来检测低碳钢试件弹塑性边界的方法。该方法将数字图像相关和低碳钢试件表面弹塑性变形前后对照明光强的反射特性结合起来以判断试件是否进入塑性屈服。文中通过对加载过程中低碳钢试件表面序列图像的处理,准确地判断了该试件是否进入塑性屈服,验证了该方法的可行性。     

用于X射线衍射测量的静高压装置及发展趋势

侧重介绍了国外静高压装置的发展和在各种装置上进行X射线衍射测量的方法，以及用各种X射线衍射装置测量材料物性参数的优缺点。各种装置中，X光源由普通的X射线管，单色X光源发展到同步辐射光源，而光子能量从数十keV到几GeV；高压下材料物性的X射线衍射测量经历了底片记录，光子计数器到自动化的原位光强测量的发展过程，测量时间从几减少到几分钟。这些实验装置和测量技术可以实现从1GPa到数百GPa压力范围，并适合于各种材料的高温高压物性和状态方程研究，它们在材料科学，地球科学等研究领域中有广阔的应用前景。     

低碳钢塑性变形量磁评定法研究

针对塑性变形量评定的局限问题,基于铁磁材料塑性变形致位错在不同方向分布不同的现象,研究了磁测法在定量评定低碳钢塑性变形量方面的应用前景。实验以工程中常用的低碳钢Q195钢板为测试材料,制作了形状尺寸一致的一批试件,并对其进行了不同程度的塑性变形量加载。通过搭建的磁化检测系统,采用相同强度及频率的正弦波激励,对所有样品进行了不同方向的磁化;同时经线圈及隧道磁敏电阻(TMR)采集了每次磁化的磁化曲线,提取了磁化曲线特征参数,对比了其与塑性变形量的定量关系。结果表明:随着塑性变形量的增加,铁磁钢材在同一磁场强度下产生的磁感应强度也会变大;沿主塑性变形方向磁化时,磁滞消耗能量最少,沿主塑性变形垂直方向磁化时,磁滞消耗的能量最多;磁路内磁场在主塑性变形方向上对塑变量的变化最敏感,而磁路外磁场在主塑变垂直方向上对塑变量的变化最敏感。实现了铁磁材料磁特征参数与塑性变形量的定量关联。本研究为开发简捷的铁磁材料塑性变形量无损评定磁方法奠定了基础。     

激光陀螺光路稳定技术的研究

为了稳定激光陀螺的光路，在陀螺控制系统中增设了角度控制。提供了一种分时控制系统，实现对角度控制器的各控制组件的分别控制和动态控制。实验结果表明，激光陀螺加上角度控制后，光强均值增大，均方差减小，曲线平坦，尤其在高低温情况下，角度控制能够改善陀螺掉光严重和无光的状态，使陀螺在任何温变下光强变化不超过15％，提高了陀螺耐高低温冲击的能力。     

NGY－2型纳米级润滑膜厚度测量仪

近３０年来，人们在利用光学方法测量润滑膜的厚度方面进行了许多研究，并且提出了一些膜厚测量方法。但是，这些方法在测量纳米级润滑薄膜时却都不同程度地存在着分辨率和精度都低等缺点。因此，根据光干涉法测量膜厚的基本原理提出了相对光强原理，并且经过特定的光路设计，研制了一种ＮＧＹ－２型纳米级润滑膜厚度测量仪．在给定条件下的测试结果表明，这种测量仪具有膜厚测量分辨率和精度都高，以及抗外界光场变化能力强等优点．关键词     

塑性变形及疲劳损伤对304奥氏体不锈钢电磁特性的影响研究

利用MTS双轴试验机制作了具有不同塑性变形及不同疲劳损伤的试样,采用四端子直流电位法考察塑性变形和疲劳损伤对304奥氏体不锈钢材料电导率的影响,并利用极软磁磁滞回线仪测量塑性变形和疲劳损伤对材料磁性特性的影响。结果表明:首先基于实验研究发现塑性变形会导致材料电导率下降,磁特性升高;并通过微观分析得到塑性变形引起材料位错、滑移、孪晶的产生是导致材料电磁属性变化的诱因。其次,考察了疲劳损伤对304奥氏体不锈钢电磁特性的影响,表明疲劳损伤也可使材料电导率下降,磁特性升高。最后,实验研究发现塑性变形与疲劳损伤的复合作用增强了对304奥氏体不锈钢电磁特性的影响。     

利用纳米硬度试验法确定Cr/Cu梯度材料的变形特性

利用纳米硬度仪研究了在Cu基底上的Cu／Cr梯度膜的机械性能。梯度膜是通过将Cu靶和Cr靶同时溅射到Cu基底材料上，但两个靶的相对溅射功率随溅射时间变化而制备。利用Oliver and Pharr方法得到了膜随其厚度变化的硬度和弹性模量。然后利用加载／卸载／再加载的方法得到了在不同深度(即膜的厚度)压头平均压力与相对压人深度之间的关系曲线，在此曲线上可以明显反映出材料的屈服特性。     

基于中间构形的大变形弹塑性模型

在大变形弹塑性本构理论中,一个基本的问题是弹性变形和塑性变形的分解.通常采用两种分解方式,一是将变形率(或应变率)加法分解为弹性和塑性两部分,其中,弹性变形率与Kirchhoff应力的客观率通过弹性张量联系起来构成所谓的次弹性模型,而塑性变形率与Kirchhoff应力使用流动法则建立联系;另一种是基于中间构形将变形梯度进行乘法分解,它假定通过虚拟的卸载过程得到一个无应力的中间构形,建立所谓超弹性-塑性模型.研究了基于变形梯度乘法分解并且基于中间构形的大变形弹塑性模型所具有的若干性质,包括:在不同的构形上,塑性旋率的存在性、背应力的对称性、塑性变形率与屈服面的正交性以及它们之间的关系.首先,使用张量函数表示理论,建立了各向同性函数的若干特殊性质,并导出了张量的张量值函数在中间构形到当前构形之间进行前推后拉的简单关系式.然后,基于这些特殊性质和关系式,从热力学定律出发,建立模型在不同构形上的数学表达,包括客观率表示的率形式和连续切向刚度等,从而获得模型所具有的若干性质.最后,将模型与4种其他模型进行了比较分析.      

Research note on a reexamination of neutral loading experiments

In the examination of the published results from neutral loading experiments, the question as to whether plastic deformation occurs is found to depend on both the material and initial loading strain. Provided that initial loading is elastic, then a subsequent stress path that follows the boundary of the initial yield surface for a hardening material is truly neutral with a wholly elastic response. However, when initial loading is elastic-plastic, then further plastic deformation is produced from a subsequent stress path that follows an isotropic expansion of the initial yield surface. These results enable the appropriateness of the kinematic hardening rule and more recent developments in plasticity theory to be appraised. Neutral loading of a non-hardening material produces plastic flow. Whether the absence of hardening is inherent or induced by plastic prestrain, it is shown that the Prandtl-Reuss theory then represents the observed behavior. In general, the purely elastic and nonhardening solutions provide respectively lower and upper bounds on the deformation.     

Investigation of Near-Surface Mechanical Properties of Materials Using Atomic Force Microscopy

As ultra-thin films or small-scale structures become widely used in electronics and biology, knowledge concerning their near-surface mechanical properties of the materials is increasingly important. Atomic force microscopy (AFM) is employed to determine near-surface elastic modulus via force-penetration curves acquired during indentation. Samples include polydimethylsiloxane (PDMS), parylene, mica, and single-crystal silicon, and indentations are performed with single-crystal silicon and silicon nitride AFM tips. An analysis algorithm based on the secant modulus method is proposed to extract the true penetration curves from the experimental displacement curves. The penetration data is then analyzed in terms of Hertzian model to estimate the elastic modulus. Three concerns in applying nanoscale AFM indentation to the measurement of the elastic modulus of an ultra-thin material are addressed. First, the effect of the lateral force caused by the inclined angle of the cantilevered probe is investigated theoretically and by numerical simulation. A second concern is local plastic deformation induced by a sharp probe tip. In this case, numerical results show a relatively small effect on the force-penetration curves if the plastic deformation is limited to the central area below the probe tip. The deviation of the elastic-plastic simulation from the elastic estimation depends on the yield strength of the material. Finally, the effect of stiffness matching between the AFM probe and the sample is a key issue that is studied numerically, and appropriate stiffness matching criteria are suggested.     

An analytical elastic-perfectly plastic contact model

A new formulation for elastic-perfectly plastic contact in the normal direction between two round surfaces that is solely based on material properties and contact geometries is developed. The problem is formulated as three separate domains: the elastic regime, mixed elastic–plastic behavior, and unconstrained (fully plastic) flow. Solutions for the force–displacement relationship in the elastic regime follow from Hertz’s classical solution. In the fully plastic regime, two well supported assumptions are made: that there is a uniform pressure distribution and there is a linear force–deflection relationship. The force–displacement relationship in the intermediate, mixed elastic–plastic regime is approximated by enforcing continuity between the elastic and fully plastic regimes. Transitions between the three regimes are determined based on empirical quantities: the von Mises yield criterion is used to determine the initiation of mixed elastic–plastic deformation, and Brinell’s hardness for the onset of unconstrained flow. Unloading from each of these three regimes is modeled as an elastic process with different radii of curvature based on the regime in which the maximum force occurred. Simulation results explore the relationship between the impact velocity and coefficient of restitution. Further comparisons are made between the model, experimental results found in the literature, and other existing elastic–plastic models. The new model is well supported by the experimental measurements of compliance curves for elastic–plastic materials and of coefficients of restitution from impact studies, and in elastic-perfectly plastic regimes is demonstrated to be more accurate than existing models found in the literature.     

粗糙峰微接触及其对润滑的影响

根据椭圆弹塑性接触模型,提出了流量因子影响模型,给出了几个该模型的应用计算实例．计算结果表明,该模型与粗糙表面的实际润滑状况有较好的一致性．通过算例分析,发现粗糙峰弹塑性变形对流量因子的影响主要决定于表面综合属性、弹性和塑性变形量．     

Numerical simulations of 3D open cell structures – influence of structural irregularities on elasto-plasticity and deformation localization

The mechanical properties of open cell structures made from an elastic–plastic bulk material are investigated by Finite Element simulations. The influence of structural irregularities on elasto-plasticity and deformation localization of open cell structures is analyzed. Six regular three-dimensional generic structures with a relative density of 12.5% are modeled by a unit cell approach for predicting the entire tensors of elasticity. From these six structures the two structures with the lowest and the highest elastic anisotropy are selected for further studies, introducing various degrees of structural irregularities. The effect of these irregularities on the linear and nonlinear behavior as well as the influence on the deformation localization is studied employing finite sample models. Results are presented by means of the direction dependent Young’s moduli, deformation plots, overall stress–strain curves, and histograms of the energy distribution.     

弹塑性微凸体侧向接触相互作用能耗

传统的结合面研究多基于光滑刚性平面与等效粗糙表面接触假设,忽略了结合面上微凸体侧向接触及相邻微凸体之间的相互作用,这导致理论模型与实际结合面存在较大出入.针对承受法向静、动态力的机械结合面,从微观上研究了微凸体侧向接触及相互作用的接触能耗.将法向静、动态力分解为法向分力和切向分力,获取弹性/弹塑性/塑性阶段考虑微凸体侧接触及相互作用的加、卸载法向分力-变形和切向分力-位移的关系.通过力的合成定理,从而获取加、卸载法向合力与总变形之间的关系,由于法向分力产生的塑性变形及切向分力产生的摩擦,导致加载、卸载法向合力-总变形曲线存在迟滞回线.通过对一个加、卸载周期内的法向合力-总变形曲线积分,获得一个周期的微凸体接触能耗,包括应变能耗及摩擦能耗.仿真分析表明:微凸体在3个阶段的能耗均随变形的增大而非线性增大.微凸体侧向接触角度越大,能耗越大,且在弹性阶段最为明显.在弹性阶段,仅存在侧向的摩擦能耗,故结合面在低载荷作用下必须采用双粗糙表面假设.在塑性阶段,由于微凸体接触能耗为应变能耗,且接触角对其能耗影响甚微,故结合面在大载荷作用下可采用单平面假设对其进行研究.相对于KE和Etsion模型,本文提出的模型与Bartier的实验结果更吻合.     

Nondestructive evaluation of plastic deformation in AA6061 aluminum alloy by electromagnetic discharge image

The electromagnetic discharge imaging (EDI) technique is combined with image analysis methods and used as a nondestructive method to evaluate the amount of plastic deformation of AA6061 aluminum alloy. Various amounts of plastic deformation was introduced mechanically by cold rolling on specimens having identical surface conditions to the specimen. Since the EDI discharge characteristics and intensity are affected by plastic deformation, the results can be used as a correlation. It is shown that the EDI discharge intensity increases with increasing rolling ratio up to 25% and reaches a saturation limit, beyond which the discharge intensity is inversely proportional to the rolling ratio. Since the changes of the internal energy and the electrical properties of the specimen caused by cold rolling has opposing effects on the EDI discharge intensity. That would eventually be saturated. Further analysis shows that the high intensity region of EDI discharge pattern is increased from 0–10% rolling ratio and then from 30% and up. As the AC frequency increased, the discharge intensity becomes proportional to the increase rolling ratio.