在役设备材料弹塑性力学参数测定方法综述--小冲杆实验力学研究进展之一

20多年以来,采用小型试件的小冲杆试验技术来测量在役设备材料的各种力学参数已经取得了很大进展,这个方法已经用来确定材料的弹性模量、屈服强度、塑性性能、抗拉强度、韧一脆转变温度、断裂韧度、蠕变性能和黏塑性性能等各种力学性能。由于从小冲杆试验的测量结果来确定材料的力学性能是一个反问题,因此,与此有关的反问题分析方法也得到了相应的发展。本文系统综述小冲杆试验的测量技术及从测量数据来确定材料弹塑性参数的各种经验方法和计算方法,例如有限元分析和参数法、反向有限元法、有限元和反方法、反向识别和人工神经网络、有限元优化和试验变形形状以及杂交反方法等。     

两种超导体的力学性质

本文测量了YBa_2Cu_3O_(7-6)和Bi_2Sr_2Ca_2Cu_30_y两种超导材料的压缩强度极限和压缩弹性模量E,指出了样品成型压力,试验温度T对σb和E的影响,研究了对超导临界转变温度T_c的影响.     

基于小冲孔试验的S30403高温力学性能研究

小冲孔试验技术(Small Punch Test,SPT)具有取样简单快捷、经济效益好、近乎无损等优势.介绍了基于弹性能量理论预测材料屈服强度的小冲孔能量法,对试验原理及步骤进行了详细的阐述.在验证试验重复性很好的基础上对S30403不锈钢进行小冲孔能量法试验,通过试验结果和常规拉伸试验结果的对比,证明了能量法的可行性.同时利用100℃、200℃、300℃温度条件下的小冲孔试验数据对已有能量法公式进行修正,使得能量法在高温条件下同样适用.     

家兔颈总动脉血管低温力学性能的实验研究

实验研究了家兔颈总动脉血管低温下的轴向和周向的力学性能．这些力学性能包括应力应变曲线和断裂强度，它们将有助于血管低温保存过程的热应力分析．结果表明，血管在低温下的力学性能与室温情况非常不同，冷冻血管的弹性模量要比未冷冻的高很多．当温度接近液氮温度时，甚至可能高几千倍．低温下，血管的轴向模量要高于周向的，但他们的断裂强度相差不大．最后，从血管组分的力学性能考虑，讨论了血管整体力学性能的变化规律．     

A New Shear-Compression-Specimen for Determining Quasistatic and Dynamic Polymer Properties

A new design of the shear compression specimen (SCS) for investigating the viscoelastic shear response of polymers is presented. The specimen consists of a polymer gage section with two metal ends that remain essentially rigid during deformation. Two closed-form analytic models are developed to predict the average stress and strain in the gage section from the deformation-load histories. This new SCS design and its analytic models are thoroughly evaluated via laboratory measurements and numerical simulations. These simulations show that the deformations in the gage section are more uniform than in the original design, and the distribution of the average shear stress and strain are highly homogenous. The simulation results yield good agreement with those of closed-form analytic results and the experiments demonstrate that the new SCS geometry and its analytic models are as reliable as other commonly employed specimens. It can also generate higher strain rates under usual loading conditions because of its smaller specimen gage length. The need for care in specimen preparation is also discussed in detail as illuminated by the experimental and simulation results.

Integrated Measurement Technique for Curing Process-Dependent Mechanical Properties of Polymeric Materials Using Fiber Bragg Grating

We propose an integrated technique to measure critical mechanical properties of polymeric materials. The method is based on a fiber Bragg grating (FBG) sensor. A polymer of interest is cured around a glass FBG and the Bragg wavelength (BW) shift is measured and documented while polymerization progresses at the curing temperature. After complete polymerization, the BW shift is monitored continuously as the temperature of the cured polymer changes. The desired material properties are then found inversely from the relationship between the Bragg wavelength shift and the deformation of the polymer caused by the changes in the material properties.     

A methodology for determining mechanical properties of freestanding thin films and MEMS materials

We have developed a novel chip-level membrane deflection experiment particularly suited for the investigation of sub-micron thin films and microelectro-mechanical systems. The experiment consists of loading a fixed-fixed membrane with a line load applied at the middle of the span using a nanoindenter. A Mirau microscope interferometer is positioned below the membrane to observe its response in real time. This is accomplished through a micromachined wafer containing a window that exposes the bottom surface of the specimen. A combined atomic force microscope/nanoindenter incorporates the interferometer to allow continuous monitoring of the membrane deflection during both loading and unloading. As the nanoindenter engages and deflects the sample downward, fringes are formed and acquired by means of a CCD camera. Digital monochromatic images are obtained and stored at periodic intervals of time to map the strain field. Stresses and strains are computed independently without recourse to mathematical assumptions or numerical calibrations. Additionally, no restrictions on the material behavior are imposed in the interpretation of the data. In fact, inelastic mechanisms including strain gradient plasticity, piezo and shape memory effects can be characterized by this technique.The test methodology, data acquisition and reduction are illustrated by investigating the response of 1-μm thick gold membranes. A Young's modulus of , a yield stress of and a residual stress of are consistently measured. The post-yield behavior leading to fracture exhibits typical statistical variations associated to plasticity and microcrack initiation.     

A New Device for Mechanical Testing of Blood Vessels at Cryogenic Temperatures

As part of an ongoing program to study the thermo-mechanical effects associated with cryopreservation via vitrification (vitreous in Latin means glassy), the current study focuses on the development of a new device for mechanical testing of blood vessels at cryogenic temperatures. This device is demonstrated on a bovine carotid artery model, permeated with the cryoprotectant cocktail VS55 and a reference solution of 7.05M DMSO, below glass transition. Results are also presented for crystallized specimens, in the absence of cryoprotectants. Results indicate that the elastic modulus of a specimen with no cryoprotectant, at about −140°C (8.6 and 15.5°C below the glass transition temperature of 7.05M DMSO and VS55, respectively), is 1038.8 ± 25.2 MPa, which is 8 and 3% higher than that of a vitrified specimen permeated with 7.05M DMSO and VS55, respectively. The elastic modulus of a crystallized material at −50°C is lower by ∼20% lower from that at −140°C.     

块石对土石混合体力学性能的影响研究

土石混合体是一种由强度较高岩块、强度较低的土体充填成分及相应孔隙等多相体系组成的复杂地质材料。我国中西部地区诸多地质灾害的发生均与其抗剪强度密切相关。影响土石混合体力学性能的因素很多。本文采用柔性边界条件下的大型剪切实验,从含石量、块石排列、块石尺寸三个方面研究了块石对土石混合体力学性能的影响。通过正交实验确定了3种因素对土石混合体抗剪强度的影响顺序及各因素的显著性水平,研究发现在这3个影响因素中,块石尺寸对土石混合体抗剪性能的影响最大,含石量次之,块石排列的影响最小。     

铝箔力学性能的实验研究

铝箔已被广泛应用于电子工业,现又被用作锂电池正极集流体,因而对于铝箔的力学性能要求也在不断提高。通过表征和研究铝箔的力学性能(弹性模量、屈服强度、断裂强度等),能够为铝箔相关技术的可靠性研究提供必要的数据支持和理论指导,从而使铝箔得到合理和可靠的使用。本文运用微拉伸、纳米压痕和动态力学分析(DMA)实验,分别研究了不同厚度的H18态和O态铝箔的力学性能。结果表明两者的弹性模量均约为30GPa,仅为块材的一半;H18态铝箔材料的断裂强度要明显强于块材,而O态铝箔材料的断裂强度则明显小于块材;此外,H18态铝箔材料的屈服强度明显大于块材,O态铝箔材料的屈服强度与块材相仿。并且,随着厚度的增加,H18态铝箔材料的延伸率显著增大,但是仍远小于块材。通过扫描电子显微镜(SEM)对铝箔材料断裂形貌进行微观分析,发现铝箔的拉伸断裂方式为脆性断裂。     

A critical review of microscale mechanical testing methods used in the design of microelectromechanical systems

Microelectromechanical systems (MEMS) technologies are evolving at a rapid rate with increasing activity in the design, fabrication, and commercialization of a wide variety of microscale systems and devices. The importance of accurate mechanical property measurement for successful design was realized early on in the development of this field. Consequently, there exist many different techniques to measure quantities such as the Young's modulus (E), yield strength (σ _Y ), fracture strength (σ _F ), residual stress (σ _F ), and residual stress gradient (∇σ _R ) of microscale structures and materials. We review and critically compare several of the important techniques including the microtension test, axisymmetric plate bend test, microbeam bend test, M-test, wafer curvature measurements, dynamic (resonant) tests, fabrication of passive strain sensors, and Raman spectroscopy. We discuss the characteristics of typical test structures, and the common sources of structure-related errors in measurement. A rational approach for the selection of test techniques for the design of microsystems is suggested.     

On-Chip Electrostatically Actuated Bending Tests for the Mechanical Characterization of Polysilicon at the Micro Scale

The issue of mechanical characterization of polysilicon used in micro electro mechanical systems (MEMS) is discussed in this paper. An innovative approach based on a fully on-chip testing procedure is described; two ad hoc designed electrostatically actuated microsystems are here used in order to determine experimentally the Young’s modulus and the rupture strength of polysilicon. The first device is based on a rotational test structure actuated by a system of comb-finger capacitors which load up to rupture a couple of tapered beams under bending in the plane parallel to the substrate. The second microsystem is based on a large plate with holes. It constitutes with the substrate a parallel plate capacitor moving in the direction orthogonal to the substrate itself. A couple of tapered beams placed at the centre of the plate is loaded up to rupture in bending in the plane orthogonal to the substrate. By means of the two devices, experimental data are obtained: they allow for a careful determination of Young’s modulus and rupture strength. The rupture values are interpreted by means of the Weibull approach; statistical size effects and stress gradient effect are taken into account thus allowing for a direct comparison between the data obtained from the two test structures.     

A New Method of Creating High-Temperature Speckle Patterns and Its Application in the Determination of the High-Temperature Mechanical Properties of Metals

Experimental Techniques - Speckle techniques, such as DIC (Digital Image Correlation) and DSP (Digital Speckle Photography), are frequently used to determine the high-temperature mechanical...     

超声波对金属材料性能影响实验研究

通过对紫铜和低碳钢在超声波作用下材料特性的实验研究，探讨此类材料的一些特殊表现诸如屈服点降低，硬化率降低和延伸率降低等．建立了一套超声波材料拉伸实验系统，给出材料特性变化的实验数据并对这些特殊现象的形成机理进行初步探讨．给出了韧性金属材料在超声波作用下的本构方程，并与实验结果相比较，结果表明理论分析与实验结果一致     

在氢环境中钢的应变速率效应

从静态、准静态直到冲击的应变速率范围内(.ε=10-7~103sec-1),研究了在氢环境中应变速率对10钢力学性能的影响。结果表明:对于10钢,应变速率在3.33×10-3~3.33×10-6sec-1范围,氢的影响最明显,随着应变速率的提高或降低,氢的影响逐渐减弱;对于渗氢和未渗氢试样,应变速率在10-4~103sec-1范围内,屈服应力都随着应变速率的增加而增加,在.ε<6.0×102sec-1区域Ⅰ内流动应力与应变速率呈线性关系,在.ε>6.0×102sec-1区域Ⅱ内流动应力对应变速率十分敏感。与准静态时相比较,高应变速率下未渗氢试样的流动应力增加了1.1倍,而渗氢试样则增加了1.5倍。文中给出了可以精确描述10钢在高应变速率下渗氢与未渗氢试样的应力应变关系表达式。     

铝-镁合金5A06在瞬态热冲击条件下的力学性能研究

通过热强度试验,测试并确定航空航天材料在复杂高速热冲击条件下的强度极限等关键参数,对于航空航天材料和结构的可靠性评定、寿命预测以及高速飞行器的安全设计具有重要的意义。针对强度设计手册中没有航空航天材料在高速热冲击环境下的强度极限等表征参数的现状,使用自行研制的高速飞行器瞬态气动热试验模拟系统,对铝-镁合金材料5A06在多种不同的瞬态热冲击条件下,进行气动加热模拟与热载联合试验研究,得到在瞬态热、力学环境的共同作用下铝-镁合金5A06材料的强度极限、承载时间等力学性能变化状况。为研究分析航空航天材料和结构在高速热冲击环境下的承载能力和结构减重提供了可靠依据。     

疲劳对比试验的可靠寿命假设检验

本文直接将疲劳对比试验的可靠寿命（安全寿命）进行对比试验，提出了可靠寿命对比的假设检验方法，通过此方法对试验结果进行判断，可以检验子样是否来自可靠寿命相同的母体，了解工艺方法或设计方案的改变对疲劳性能的影响，它为疲劳对比试验假设检验提供了一新途径。     

硬质聚氨酯泡沫力学特性的静水压力加载实验方法研究

泡沫材料在多轴载荷下的力学性能是工程中非常关心的问题。利用土壤的三轴压缩试验装置,通过试验方法的改进,提出了一种体应变测定和修正的方法,对硬质聚氨酯泡沫材料的静水压力特性进行了研究,得到了一些有价值的数据和结论。研究表明:在准静态静水压加载条件下,该材料的应力-应变曲线明显地分为弹性段、塑性段和压实段,且屈服强度比单向压缩时略大、压实应变略小。最后通过不同高度的试样对比试验,对聚氨酯泡沫材料的不均匀变形和弯曲的原因进行了分析和比较,指出了试验时应该注意的问题。     

An analytical solution for a linear viscoelastic layer loaded with a cylindrical punch: Evaluation of the rebound indentation test with application for assessing viability of articular cartilage

A general closed-form solution for the so-called rebound indentation test’ is obtained for a cylindrical flat-ended punch indenting a linear viscoelastic layer lying on a rigid substrate. Under the assumption of time-independent Poisson's ratio, we derive closed-form analytical expressions for the contact force (in a displacement controlled regime) and for the indentation displacement (in a load-controlled regime) and we consider in detail the case of standard viscoelastic solid. Our results indicate that the rebound displacement (in other words the indentation displacement in the load-controlled stage) is independent of the relaxed elastic modulus and Poisson's ratio, and also of the layer's thickness. Our analytical solution can be used for layered samples of arbitrary materials exhibiting viscoelastic properties; however, since the rebound indentation test has been recently suggested for assessing the viability of biomedical materials, we have applied our theoretical framework to the identification of materials parameters from experiments on articular cartilage. In this context, we have found a pretty good agreement for the rebound deformation, even until the strain becomes relatively large.     

结晶特性与制造工艺对炸药件力学性能的影响

通过对塑料粘结炸药(PBX)在压制、热老化及贮存中炸药HMX、TATB和粘结剂F的性能变化规律的研究,揭示了加工和贮存条件对炸药件的力学性能的影响。得出如下结论:1)随着老化温度的提高,粘结剂F结晶度增加。TATB基PBX炸药经老化后力学性能没有明显变化,说明粘结剂结晶度和炸药颗粒度的变化对炸药总体性能影响不大。2)钢模压制的TATB基PBX药柱在经历多次温度循环后,TATB与粘结剂F界面的作用有所减弱,药柱内部产生由脱粘引起的缺陷,其力学强度下降。TATB基PBX药柱的力学强度与模量均随着环境温度的升高而呈下降趋势,而等静压成型能明显改善TATB基PBX的力学性能。