切应力对牛骨蠕变变形的影响研究

骨尤其是湿骨,在恒定载荷作用下会发生蠕变变形。为了确定切应力是否影响骨的蠕变变形,采用对骨薄板试样分别施加集中载荷和均布载荷的方式,测量试样挠度实时的变化曲线。结果显示,在载荷恒定时,骨试样的挠度随时间不断增加,体现了典型的蠕变特性。集中荷载下骨的蠕变变形远大于均布荷载下骨的蠕变变形,湿骨的蠕变位移比干骨高近7倍。分析认为,对试样粘弹性性质的影响不仅有正应力的作用,也有切应力的作用;切应力产生的蠕变变形约为正应力所产生蠕变变形的0.85倍。     

Impact of Effective Stress and Matrix Deformation on the Coal Fracture Permeability

The permeability of coal is an important parameter in mine methane control and coal bed methane exploitation because it determines the practicability of methane extraction. We developed a new coal permeability model under tri-axial stress conditions. In our model, the coal matrix is compressible and Biot’s coefficient, which is considered to be 1 in existing models, varies between 0 and 1. Only a portion of the matrix deformation, which is represented by the effective coal matrix deformation factor $f_\mathrm{m}$ , contributes to fracture deformation. The factor $f_\mathrm{m}$ is a parameter of the coal structure and is a constant between 0 and 1 for a specific coal. Laboratory tests indicate that the Sulcis coal sample has an $f_\mathrm{m}$ value of 0.1794 for $\hbox {N}_{2}$ and $\hbox {CO}_{2}$ . The proposed permeability model was evaluated using published data for the Sulcis coal sample and is compared to three popular permeability models. The proposed model agrees well with the observed permeability changes and can predict the permeability of coal better than the other models. The sensitivity of the new model to changes in the physical, mechanical and adsorption deformation parameters of the coal was investigated. Biot’s coefficient and the bulk modulus mainly affect the effective stress term in the proposed model. The sorption deformation parameters and the factor $f_\mathrm{m}$ affect the coal matrix deformation term.     

粗糙面在梯度表面层上滑动接触的应力分布

对粗糙面在梯度表面层上的滑动过程进行应力分布研究,以模拟实际摩擦过程中,考虑塑性变形情况下,梯度覆层体中的应力分布规律,同时与均质体及单覆层体进行比较研究,分析了在表面载荷相同时滑动接触的应力分布。结果表明覆层体出现塑性变形后,在接触表面上的压力分布与弹性变形时有很大变化,在界面处梯度层的应力分布比单层膜更为理想,其应变梯度也较小;受相同表面载荷作用下产生塑性变形时,梯度层膜在基体产生塑性变形较小     

Study on the Effect of Scanning Strategy on Residual Stress in Laser Additive Manufacturing with the Laser Ultrasound Technique

Experimental Mechanics - During the laser additive manufacturing (LAM) process large temperature gradients can form, generating a mismatch in deformation that can lead to high level of residual...     

Incremental Computation Technique for Residual Stress Calculations Using the Integral Method

The Integral Method for determining residual stresses involves making surface deformation measurements within a sequence of small increments of material removal depth. Typically, the associated matrix equation for solving the residual stresses within each depth increment is ill-conditioned. The resulting error sensitivity of the residual stress evaluation makes it essential that data measurement errors are minimized and that the residual stress solution method be as stable as possible. These two issues are addressed in this paper. The proposed method involves using incremental deformation data instead of the total deformation data that are conventionally used. The technique is illustrated using an example ESPI hole-drilling measurement.     

On the Stress Field of a Nonlinear Elastic Solid Torus with a Toroidal Inclusion

Standard measures of local deformation such as deformation gradient, strain, elastic deformation, and plastic deformation are dimensionless. However, many macroscopic and submacroscopic geometrical changes observed in continuous bodies result in the formation of zones across whose boundaries significant changes in geometry can occur. In order to predict the sizes of such zones and their influence on material response, theories of elasticity and plasticity have been employed in which second gradients of deformation, gradients of strain, as well as gradients of elastic or of plastic deformation are taken into account. The theory of structured deformations provides additive decompositions of first deformation gradient and of second deformation gradient, valid for large deformations of any material, in which each term has a multiscale geometrical interpretation corresponding to the presence or absence of submacroscopic disarrangements (non-smooth geometrical changes such as slips and void formation). This article provides a field theory that broadens the earlier field theory, elasticity with disarrangements, by including energetic contributions from submacroscopic “gradient-disarrangements” (limits of averages of jumps in gradients of approximating deformations) and by treating particular kinematical conditions as internal constraints. An explicit formula is obtained showing the manner in which submacroscopic gradient-disarrangements determine a defectiveness density analogous to the dislocation density in theories of plasticity. A version of the new field theory incorporates this defectiveness density to obtain a counterpart of strain-gradient plasticity, while another instance of elasticity with gradient-disarrangements recovers an instance of strain-gradient elasticity with symmetric Cauchy stress. All versions of the new theory included here are compatible with the Second Law of Thermodynamics.     

基于分形理论的双渐开线齿轮接触应力研究

综合考虑接触面粗糙度、材料特性等因素对齿轮接触应力的影响，基于分形理论和经典Hertz接触理论建立双渐开线齿轮分形接触模型. 该模型中，影响载荷和实际接触面积的主要因素包括分形维数、粗糙度幅值和材料特性参数. 理论分析表明:分形维数一定时，真实接触面积随着载荷的增大而增大；载荷一定时，接触面积随着粗糙度幅值的增大而减小；随着材料特性参数值的增加，在一定程度上加强了软材料轮齿承载能力，同时会使得微凸体由弹性变形到塑性变形的临界面积减小. 对比分形接触模型和有限元模型两种计算双渐开线齿轮轮齿接触应力方法，结果证明了分形接触模型计算双渐开线齿轮接触应力的有效性.      

Sn和Si含量对Al—Sn—Si合金室温压缩变形流变应力的影响

采用Gleeble-1500试验机，在室温和恒应变速率下，测定了Al-Sn-Si系合金压缩变形的流变应力曲线。结果表明，在Sn、Si含量分别为0－20和0－8wt．％的范围内，当Sn含量恒定时，流变应力随Si含量的增加而增加，而当Si含量恒定时，流变应力则随Sn含量的增加而略有降低；从Al-Sn-Si，Al-Si及Al-Sn 合金流变应力曲线的差异，分析了Sn和Si对合金塑性变形过程的影响机制。     

基于有限元模拟的SUS304奥氏体不锈钢摩擦耦合变形过程的应力分析

采用ANSYS/LS-DYNA软件对SUS 304奥氏体不锈钢薄板的摩擦耦合变形过程进行了数值模拟.采用隐式-显式序列求解法和分段线性塑性材料模型,分析了钢带摩擦耦合变形时的应力分布规律及载荷、下压量和滑动速度等因素对钢带剪应力、主应力及等效应力的影响.结果表明:摩擦耦合变形的试验参数显著影响钢带的应力分布,验证了钢带在低于其屈服强度的应力条件下发生塑性变形的摩擦诱发效应.对奥氏体不锈钢摩擦诱发马氏体转变行为的研究及其摩擦学性能的改善具有一定的指导意义.     

Stress field of a damaged material near the crack tip

In this paper, a deformation theory of plasticity for damaged materials is proposed. An asymptotic expression forH near a crack tip is obtained. Finally, the stress and strain fields near the crack tip are presented.     

Effect of Isochronous Annealing on the Formation of Shear Bands in the Vicinity of a Stress Concentrator on the Surface of Iron-Based Amorphous Alloys

The effect of isochronous annealing on the formation of shear bands in the vicinity of a stress concentrator on the surface of an amorphous material is studied. Using the local deformation method, a parameter is introduced to determine the temperature interval in which amorphous and crystal phases coexist.     

双列直插器件(DIP)焊接过程中的应力评价

为探讨陶瓷封装双列直插器件在焊接后出现开裂的问题,应用云纹干涉法和Twyman/Green干涉法实时测试了该类型器件在焊接过程中的面内和离面变形情况,并将测试数据与有限元法相结合,评估了焊接过程中器件内部因印制板变形而产生的应力大小。由此对原先"焊接导致开裂"的说法做出了评价。同时,通过器件的变形测试,探讨了优化焊接工艺的方法。研究结果表明,焊接顺序对器件内部热应力和器件变形影响不大,而适当提高器件高度可有效减小焊接时的热应力。     

应力波穿越岩石节理时能量耗散规律的实验研究

采用材料试验机和大尺度激光表面仪对大理岩和花岗岩两种岩石进行三点弯曲和粗糙断裂面的扫描实验,详细地分析了粗糙断裂面的分形特征。通过SHPB实验,研究并提出了波能量耗散与断裂面分形维数的定量关系;分析了分形维数对波能量耗散的影响规律。研究得出以下结论:1)随着粗糙断裂面分形维数的增大,通过断裂面时应力波能耗将相应增加;2)应力波能量主要是以热能和塑性变形能耗散。分形维数越大,比表面积则越大,粗糙表面粒子相互摩擦和挤压程度相应增加,导致波的机械能转化成热能和塑性变形能部分增加,因而波动能量耗散越大。     

岩石分形节理粗糙性对应力场影响的光弹模拟研究

节理的粗糙性是影响岩体力学特性的重要因素。现有的众多的研究结果表明：不规则的节理面具有很好的自相似特征，可以用分形几何去描述，节理面的分形维数是表征节理面粗糙度（ＪＲＣ）恰当的统计量。基于以上观点，为了能够精确地控制节理面的粗糙性，本文以Ｍａｎｄｅｌｂｒｏｔｗｅｉｅｒｓｔｒａｓｓ函数生成不同分维的分形曲线来模拟实际的粗糙节理面，制成光弹实验试样进行多组的单压和压剪实验，通过光弹条纹和接触点的变化来研究不规则的节理对于岩体变形，应力场的影响，得出了一些有益的结论．     

材料的弹粘塑性本构关系和应力波的演化

试验表明，大多数工程材料在冲击载荷作用之下的变形一般都同时包含有可恢复的瞬态性弹性变形和不可恢复的粘滞性塑性变形，即其本构关系可以用弹粘塑性模型来描述。本文从内变量理论出发，探讨了时率相关材料的弹粘塑性本构关系的一般特性，建立了增量型的弹粘塑性本构关系的一般理论框架和普适的表达式，并且对两种最常用的本构模型——Bodner-Partom模型和Johnson-Cook模型给出了在一维应变条件下的具体形式。通过计算和讨论一维应变粘塑性靶板中冲击波的衰减机制和应力波的演化规律，特别是考察各种粘塑性本构模型中的材料参数对冲击波的衰减和应力波的演化的影响，得出了一些可以直接应用或具有一定借鉴价值的结果，为研究应力波的其他衰减机制以及在人防工程中智能防护层设计时新材料的选取奠定了基础。     

Stress and deformation analysis from reduced-scale plastic-model testing

The use of scale models, which are made from plastic material, for stress and deformation analysis of missile nose-cone structures is discussed. The special strain-gage application and testing techniques, which are required because of the use of plastic materials, are detailed.The utilization of relatively inexpensive simplified models for the investigation of two specific design conditions is cited. The first case is a stress and deformation study of a thin, constant-thickness, shallow spherical shell which is supported by a circumferential line reaction and subjected to uniform external pressure. Comparisons are made with a recently published theoretical analysis of the problem.The second case is a particular design problem which is concerned with the determination of the stress and deformation in a variable-thickness, shallow spherical shell with several various-size cutouts. The shell is loaded with a varying external-pressure load which is reacted by a circumferential line load at the periphery. Influence curves for both stress and deformation are given.Some limitations of plastic-model testing are reviewed, and guides to successful use of the method are given.Paper was presented at 1959 SESA Spring Meeting held in Washington, D. C. on May 20–22.     

The Constitute Law of Gas Seepage in Rock Fractures Undergoing Three-dimensional Stress

This paper is based on the research we have done in recent years of the constitute law of gas seepage in rock fractures. Both experiments and theoretical derivations will be discussed. The gases used in our experiments include methane and CO₂, both of which are highly adsorptive. The experiments were conducted mainly in coal fractures. The results reveal that the permeability coefficient of gas in rock fractures varies parabolically with respect to fracture pore pressure. When the pore pressure is below a certain value, the permeability coefficient decreases while the pore pressure increases. It is different from the water seepage law in fractures. Analysis shows that this abnormality is caused by adsorption. It is also concluded that the tangent deformation has the same effects as normal deformation on gas seepage law. The permeability of gas in fractures has a negative exponent relationship with both normal deformation and tangent deformation.     

考虑塑性和刚度不匹配的焊接残余应力估算

现有残余应力计算方法未能考虑材料塑性变形和焊接接头刚度不匹配的影响,使得焊接残余应力计算结果和实际残余应力存在较大偏差.在2219-T87铝合金钨极氩弧焊焊接头残余应力测试基础上,提出一种基于非线性有限元和材料弹性模量分区的残余应力—释放应变曲线的残余应力计算方法,研究了材料塑性变形和接头刚度不匹配对焊接残余应力计算的影响.结果表明,焊接接头中非均质材料塑性不匹配可以引起对于残余应力计算的较大误差;材料塑性变形对残余应力的影响大于接头刚度不匹配对残余应力的影响.所提出方法修正了传统方法在焊接接头的残余应力计算中由于未考虑接头非均质材料塑性不匹配而引起的误差.     

新型铝锡硅合金高温塑性变形流变应力的研究

采用高温等温压缩变形方法,在温度为373-673K范围和应变速率为0.001-1.0s^-1范围内,测定了新型Al-10Sn-4Si合金的流变应力曲线,结果表明,该合金为正应变速率敏感材料并且具有稳态流变特征;稳态流变应力随变形速率的增加而增大,随变形温度的升高而降低,通过回归分析,建立了该合金高温塑性变形时稳态流变应力的半经验方程,这种稳态流变特征与动态回复、动态再结晶及局部晶界粘滞性流动行为有关,受热激活过程控制。     

A STRESS VECTOR-BASED CONSTITUTIVE MODEL FOR COHESIONLESS SOIL (Ⅱ)-APPLICATION

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