Derivation of Plastic Work Rate Done per Unit Volume for Mean Yield Criterion and Its Application

In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield （MY） criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.

Investigation on the plastic work-heat conversion coefficient of 7075-T651 aluminum alloy during an impact process based on infrared temperature measurement technology

The plastic work-heat conversion coefficient is one key parameter for studying the work-heat conversion under dynamic deformation of materials. To explore this coefficient of 7075-T651 aluminum alloy under dynamic compression, dynamic compression experiments using the Hopkinson bar under four groups of strain rates were conducted, and the temperature signals were measured by constructing a transient infrared temperature measurement system. According to stress versus strain data as well as the corresponding temperature data obtained through the experiments, the influences of the strain and the strain rate on the coefficient of plastic work converted to heat were analyzed.The experimental results show that the coefficient of plastic work converted to heat of 7075-T651 aluminum alloy is not a constant at the range of 0.85–1 and is closely related to the strain and the strain rate. The change of internal structure of material under high strain rate reduces its energy storage capacity, and makes almost all plastic work convert into heat.

Deduction of plastic work rate per unit volume for unified yield criterion and its application

A unified linear expression of plastic work rate per unit volume is deduced from the unified linear yield criterion and the associated flow rule. The expression is suitable for various linear yield loci in the error triangle between Tresca’s and twin shear stress yield loci on the π-plane. It exhibits generalization in which the different value of criterion parameter b corresponds to a specific linear formula of plastic work rate per unit volume. Finally, with the unified linear expression of plastic work rate and upper-bound parallel velocity field the strip forging without bulge is successfully analyzed and an analytical result is also obtained. The comparison with traditional solutions shows that when b=1/(1+ 3 ) the result is the same as the upper bound result by Mises’ yield criterion, and it also is identical to that by slab method with m=1, σ0=0.

Equal perimeter yield criterion and its specific plastic work rate: Development, validation and application

In order to overcome the nonlinearity of Mises criterion, a new linear yield criterion with a dodecagon shape of the same perimeter as Mises criterion was derived by means of geometrical analysis. Its specific plastic work rate expressed as a linear function of the yield stress, the maximum and minimum strains was also deduced and compared with that of Mises criterion. The physical meaning of the proposed yield criterion is that yielding of materials begins when the shear yield stress τs reaches the magnitude of 0.594σs. By introducing the Lode parameter, validation of evolution expressions of the proposed yield criterion with those based on Tresca, Mises and TSS criteria as well as available classical yield experimental results of various metals shows that the present results intersect with Mises results and coincide well with experimental data. Moreover, further application to the limit analysis of circle plate as an example is performed to demonstrate the effectiveness of the proposed yield criterion, and the subsequent comparison of limit loads with the Tresca analytical solutions and Mises numerical results shows that the present results are higher than the Tresca analytical results, and are in good agreement with the Mises numerical results.

INSTANTANEOUS THERMAL EXPANSION BEHAVIOR OF HETEROGENEOUS MATERIALS WITH A WORK-HARDENING ELASTOPLASTIC MATRIX AND ELASTIC SPHEROIDAL INHOMOGENEITIES

The instantaneous thermal expansion behavior of-two-phase heterogeneous materials subjected to a uniform temperature change is explored in the present study. The matrix phase is assumed to be a work-hardening ductile metal and the dispersive phase is assumed to consist of either aligned or randomly-oriented, elastic,, spheroidal inhomogeneities. The plastic flow and decreasing stiffness of the matrix during Eshelby's transformation strain of the equivalent inclusions are accounted for by using the deformation theory of plasticity. The explicit results of the instantaneous overall thermal expansion coefficients and the critical inelastic temperature changes are presented for aligned disc- and fiber-inclusions. For the spherical and randomly-oriented spheroidal inclusion, the present study demonstrates that when the yielding of the composites is governed by the average matrix stress, the overall response is always elastic in spite of the temperature change.

THE VIRTUAL WORK PRINCIPLE AND LINEAR COMPLEMEN-TARY METHOD FOR COUPLING ANALYSIS OF ELASTO-PLASTIC DAMAGE STRUCTURE

The virtual displacement principle of elasto-plastic damage mechanics is presented. A linear complementary method for elasto-plastic damage problem is proposed by using FEM technique. This method is applicable to solving the damage structure analysis of hardened and softened nonlinear material.

Humanoid Based Intelligence Control Strategy of Plastic Cement Die Press Work-Piece Forming Process for Polymer Plastics

The plastic cement belongs to a sort of polymer material, the chemical composition is very complex, and the plastic cement work-piece is generally manufactured by die press forming. Aimed at being difficult to control in parameters of forming process, the paper explored the humanoid based intelligence control strategy. In the paper, it made the anatomy in control puzzle resulted in uncertainty such as chemical component of plastic cement etc., summarized up the characteristic of cybernetics in forming process, researched on the humanoid based intelligence control strategy, and constructed the control algorithm of forming process in plastic cement work-piece. Taking the process experiment of temperature and pressure control as an example, it validated the good dynamic and static control quality through simulation of control algorithm constructed in this paper. The experimental results show that the control algorithm explored in this paper is reasonably available.

Plastic variational principle based on the least work consumption principle

Plastic variational principles are foundation to solve the boundary-value problems of plastic mechanics with the variational method(or energy method) and finite element method.The most convenient way of establishing different kinds of variational principles is to set up the extreme principle related to the studied problem.Based on a general new extreme principle-the Least work consumption principle,the variational principles of the rigid-plastic and rigid-viscoplastic material were derived.In comparison with existing methods,the method in this paper is more clear and direct,and the physical meaning is clear-cut.This method can offer a new way for establishing other kinds of variational principles.

经颅磁声电刺激强度对小鼠前额叶皮质网络可塑性的影响

背景:经颅磁声电刺激是一种新型无创的神经调控技术,利用超声波与静磁场耦合作用产生的感应电场调节神经系统的放电活动,但其影响大脑突触可塑性的作用机制研究尚浅。目的:探讨经颅磁声电刺激强度对小鼠前额叶皮质神经网络突触可塑性的影响。方法:①动物实验:将24只C57小鼠平均且随机分为4组,对照组(接受伪刺激)、刺激6.35 W/cm^(2)组(接受0.3 T、6.35 W/cm^(2)的耦合刺激)、刺激17.36 W/cm^(2)组(接受0.3 T、17.36 W/cm^(2)组的耦合刺激)和刺激56.25 W/cm^(2)组(接受0.3 T、56.25 W/cm2的耦合刺激),记录小鼠执行T迷宫过程中局部场电位信号和行为学正确率。②建模仿真实验:构建经颅磁声电刺激小鼠前额叶皮质神经网络模型,分别比较不同刺激强度下神经网络结构连接特性。结果与结论:①经颅磁声电刺激能够有效缩短小鼠行为学习时间,工作记忆能力得到改善(P<0.05),且习得行为后继续刺激小鼠前额叶,各组小鼠T迷宫行为学实验准确度没有明显差异(P>0.1)。分析小鼠前额叶局部场电位信号发现经颅磁声电刺激促进了β节律与γ节律能量增强;而随刺激强度升高,β节律与γ节律出现了非同步性下降;通过β-γ相位幅值耦合发现,刺激增强了神经网络适应新的信息和任务要求的能力变化。②建模仿真发现,刺激使得神经网络放电水平增强,长时程突触权重水平提高而短时程突触权重仅在刺激强度较高时降低。③研究结果表明,不同的刺激强度与神经网络功能结构的影响存在复杂的非线性关系;这种神经调控技术为治疗突触功能障碍和神经网络异常等相关神经疾病方面提供新的可能。

四工作辊轧机轧制304不锈钢板件截面塑性变形分析

针对四工作辊轧机轧制304不锈钢板件存在变形量大、尺寸不稳定的问题,利用Solidworks软件建立四工作辊轧制系统有限元模型,采用Deform软件对304不锈钢板件在不同轧辊直径、轧辊转速和轧辊压下量下进行轧制仿真,分析其对轧件截面高度和等效应力分布的影响,根据轧制仿真分析结果设计制造了四工作辊轧机,并对不同压下量下仿真和生产的轧件截面高度进行对比分析。结果表明,轧件截面塑性变形可分为相互作用Ⅰ区、过渡Ⅱ区和变形Ⅲ区,等效应力、等效应变和截面高度在Ⅰ区最大,在Ⅲ区最小且变化平稳,Ⅱ区值位于两者之间并呈U型分布。

APPLICATION OF NONLOCAL FRICTION IN SEVERAL KINDS OF PLASTIC FORMING PROBLEMS

The nonlocal friction law proposed by Oden et al. was adopted in order to consider the nonlocal friction effect of the asperities on the rough contact surface between the die and the workpiece in several kinds of metal plastic forming problems. The mechanical equilibrium equations with the integral-differential form were obtained by using the engineering method or slab method, and solved approximately by using the perturbation method. The normal stress distributions on the contact surfaces in metal forming problems with nonlocal friction were obtained, and the factors which affect the nonlocal friction effect were analyzed.

五宝场硬塑性地层斧形曲面PDC齿破岩性能研究

为解决川东油气钻井中五宝场沙溪庙组硬塑性地层PDC钻头磨损严重、起下钻频繁的问题,开展了斧形曲面PDC齿在硬塑性地层破岩性能的研究。首先采用X射线衍射试验与三轴力学试验分别获取该地层岩石性质和力学参数,然后采用有限元仿真与试验相结合的方法开展斧形曲面PDC齿破岩性能研究。研究结果表明:斧形曲面PDC齿主要以剪切、挤压、犁切共同作用破岩;相较于常规PDC齿,斧形曲面PDC齿有更强的吃入岩石的能力和稳定性,能有效减小钻头异常振动,提高钻头寿命,并在不同磨损高度(0~3 mm)时,破岩比功降低2.2%~8.2%;根据试验得到斧形曲面齿较常规齿破岩性能提高了11.39%,且试验与仿真平均切削力误差仅为7.46%,验证了仿真模型的正确性。本研究表明斧形曲面PDC齿在硬塑性地层对提高破岩性能具有重要意义。

高强无磁不锈钢Cr21Ni13Mn5Mo2N的热加工特性

利用Gleeble 3800热模拟机对奥氏体不锈钢Cr21Ni13Mn5Mo2N进行热压缩实验,研究该钢种的高温变形与应变速率以及温度的关系,建立了双曲正弦本构方程,最终得到其热激活能为679.58 kJ/mol,应变速率因子Z=εexp(679580/R T)。实验结果表明,在950~1200℃,0.01~10 s^(-1)条件内,材料变形过程均发生动态再结晶,在950℃,应变速率为0.1 s^(-1)条件下,再结晶开始的变形量为10%。流变应力随温度升高及应变速率降低呈现明显下降趋势,由950℃、10 s^(-1)时的326 MPa降低至1200℃、0.01 s^(-1)时的75 MPa。结合微观组织分析及锻造试验,对压缩试样开裂问题进行深入探究,结果表明晶界处碳、氧化物的聚集恶化晶界塑性,导致热变形过程中在该处形成裂纹源并逐步扩展。通过热处理和热变形试验,确定Cr21Ni13Mn5Mo2N电渣锭在1170℃固溶6 h后晶界碳、氧化物消除,电渣锭晶界处结合力明显提升,成功消除锻造开裂问题,实现锻造成材率大幅提升。

基于Solid Works注塑模具的塑件结构设计

注塑成型方法是制造塑料制品的一个最主要途径。模具是注塑成型必需的设备。介绍了采用Solid Works软件进行模具设计的方法和相关术语,总结了注塑模具设计的过程,提出了注塑模具零件结构设计的规律和设计原则。

辛置煤矿厚硬基本顶大巷煤柱回收工作面运输巷支护设计

针对霍州煤电集团辛置煤矿厚硬基本顶大巷煤柱回收工作面运输顺槽支护难的问题,本文采用FLAC3D数值模拟研究方法,对运输顺槽进行分析设计。模拟结果显示:工作面回采稳定后,运输顺槽顶板塑性区最大发育深度为4.5 m,两帮塑性区最大发育深度为2 m,最终确定,工作面运输顺槽巷帮采用锚杆、网支护,顶板采用锚杆、锚索、锚网混合支护。现场实测结果表明,测点段巷道围岩顶板围岩变形稳定在350 mm,顶板变形量稳定在240 mm。

浅埋工作面回采对边坡稳定性的影响研究

针对下伏工作面回采造成边坡失稳问题,通过数值模拟研究了不同工作面回采位置下坡体滑动和塌陷特征,分析了采空区和坡体塑性区分布规律。结果表明:工作面位置显著影响边坡滑动和塌陷特征;工作面回采后,顶板岩层成为边坡土体的主要承载结构,若工作面位于边坡滑动侧,会进一步提高边坡土体滑动空间;当工作面位于坡脚下部时,回采后边坡稳定性最高,当工作面位于坡体下部时,回采后边坡稳定性最差;采空区上部岩层以拉伸、剪切混合破坏为主,边坡土体以剪切破坏为主。

Influence of stress path change on the resistance to plastic deformation of cold rolled sheets

Flat workpieces have been tested in order to investigate the influence of stress path change （loading mode） while keeping strain path unchanged. These investigations are pertinent to the testing of cold rolled strips and to subsequent forming. The workpieces which first compressed by plane strain compression in thickness direction were then tested in perpendicular direction in order to measure the influence of strain and stress path. The tension workpieces came from flat die compression test at different deformation histories. Two different materials were investigated： 18/8 Ti stainless steel and AW-1050 aluminium. The results show that the plastic flow by tension in lengthwise direction after pre-strain by compression in thickness direction will begin at an appreciably lower stress than that of the workpieces unloaded after pre-compression. Comparing with two materials, it can be seen that both 18/8 Ti stainless steel and AW-1050 aluminium behave similarly. The drop in yield stress is lower for AW-1050 aluminium than that for 18/8 Ti stainless steel. However, reloading in different directions than in the precious step results in significantly higher strain hardening.

Describing failure in geomaterials using second-order work approach

Geomaterials are known to be non-associated materials. Granular soils therefore exhibit a variety of failure modes, with diffuse or localized kinematical patterns. In fact, the notion of failure itself can be confusing with regard to granular soils, because it is not associated with an obvious phenomenology. In this study, we built a proper framework, using the second-order work theory, to describe some failure modes in geomaterials based on energy conservation. The occurrence of failure is defined by an abrupt increase in kinetic energy. The increase in kinetic energy from an equilibrium state, under incremental loading, is shown to be equal to the difference between the external second-order work,involving the external loading parameters, and the internal second-order work, involving the constitutive properties of the material. When a stress limit state is reached, a certain stress component passes through a maximum value and then may decrease. Under such a condition, if a certain additional external loading is applied, the system fails, sharply increasing the strain rate. The internal stress is no longer able to balance the external stress, leading to a dynamic response of the specimen. As an illustration, the theoretical framework was applied to the well-known undrained triaxial test for loose soils. The influence of the loading control mode was clearly highlighted. It is shown that the plastic limit theory appears to be a particular case of this more general second-order work theory. When the plastic limit condition is met, the internal second-order work is nil. A class of incremental external loadings causes the kinetic energy to increase dramatically, leading to the sudden collapse of the specimen, as observed in laboratory.

ELASTIC－PLASTIC CONSTITUTIVE MODELS BASED ON THE MULTIPLICATION PROCESSES OF DEFORMED GRAINS

According to the characteristics of micro-deformation of polycrystalline metal,the author divides grains intothree kinds and proposes a new conceplion of deformed grains.multiplication,from which some explicit elastic-Plastic constitutive equations can be deduced and some experimental results can be explained quantitativelv,It shows that the macro-yield,rate-correlativity work hardening and other phenomena are all closely related to the kinetic process of grains deformation.