An improved yield criterion characterizing the anisotropic and tension-compression asymmetric behavior of magnesium alloy

A novel yield criterion based on CPB06 considering anisotropic and tension-compression asymmetric behaviors of magnesium alloys was derived and proposed(called M_CPB06).This yield criterion can simultaneously predict the yield stresses and the Lankford ratios at different angles(if any)under uniaxial tension,compression,equal-biaxial and equal-compression conditions.Then,in order to further describe the anisotropic strain-hardening characteristics of magnesium alloy,the proposed M_CPB06 criterion was further evolved to the M_CPB06ev model by expressing the parameters of the M_CPB06 model as functions of the plastic strain.As the model was developed,the stresses and Lankford ratios of AZ31B and ZK61M magnesium alloys at different angles under tensile,compressive and through-thickness compressive conditions were used to calibrate the M_CPB06/M_CPB06ev and the existing CPB06ex2 model.Calibration results reveal that compared with the CPB06ex2 yield criterion with equal quantity of coefficients,the M_CPB06 criterion exhibits certain advancement,and meanwhile the M_CPB06ev model can relatively accurately predict the change of the yield locus with increase of the plastic strain.Finally,the M_CPB06ev model was developed through UMAT in LS-DYNA.Finite element simulations using the subroutine were conducted on the specimens of different angles to the rolling direction under tension and compression.Simulation results were highly consistent with the experimental results,demonstrating a good reliability and accuracy of the developed subroutine.

On an Application of the Improved Maximum Product Criterion to Inverse Acoustic Scattering in a Layered Medium

In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well known factorization method, in which a computationally effective numerical scheme for the reconstruction of the shape of the scatterer is presented. This is possible, due to a mixed reciprocity principle, which renders the computation of the Green function at the background medium unnecessary. Moreover, to further refine our inversion algorithm, an efficient Tikhonov parameter choice technique, called Improved Maximum Product Criterion (IMPC) is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no a priori knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples.

An approximate nonlinear modified Mohr-Coulomb shear strength criterion with critical state for intact rocks

In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now,leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD,and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comprehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions.

Modified Mohr-Coulomb strength criterion considering rock mass intrinsic material strength factorization

With the increase of mining depth of mineral resources,the rock mass stress state is being more and more complex.The rock mass show different features,namely,with the increase of hydrostatic pressure,rock mass failure mode turns from brittle tension failure to structure ductile failure and its limit strength also increases.The restriction of minimal principal stress on the initiation and development of microcrack and the change of micro-unit stress state by the intermediate principal stress play a decisive role in the increase of rock mass limit strength.Based on the rock mass failure behavior law under complex stress state and the σ2-dependence on the rock mass strength,we proposed a Modified Mohr-Coulomb(M-MC) strength criterion which is smooth and convex.Finally,the M-MC criterion is validated by multiaxial test data of eight kinds of rock mass.We also compared the fitting results with Mohr-Coulomb criterion(MC).It shows that the new criterion fits the test data better than the Mohr-Coulomb criterion.So the M-MC strength criterion well reveals the rock mass bearing behavior and can be widely used in the rock mass strength analysis.The results can provide theoretical foundations for stability analysis and reinforcement design of complex underground engineering.

Determination of rock resistant coefficient based on Mohr-Coulomb criterion for underwater tunnel

According to the load-structure method, the wall rock with lining can bear the load caused by the surrounding rock, and the rock resistant coefficient (RRC) is a key parameter for evaluating the capacity of this wall rock. Based on the Mohr-Coulomb yield criterion, this paper develops a formula for calculating the RRC, which has been applied to the real engi-neering project, such as Xiamen Xiang’an East Passage Underwater Tunnel Project. The fact shows that this formula is helpful for designers to determine the RRC value.

Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

Cracking Patterns of Shear Walls in Reinforced Concrete Structure due to Strong Earthquake Based on Mohr-Coulomb Criterion

A primary goal of seismic design of buildings is to protect people's life safety during strong earthquakes. Fundamentally,to predict the survived space and estimate people escape intervals during structural collapse are very important,which requires to describe the failure process more detailedly not only for structural joints but also for slabs and shear walls. In the present paper,the details of Mohr-Coulomb failure criterion with tension-cutoff together with its expression in failure surface and local coordinate system of reinforced concrete( RC) shear wall are given firstly,and then several typical cracking patterns of RC shear wall,such as tension shear crack and compression shear crack, are analyzed based on Mohr-Coulomb failure criterion with tension-cutoff.

烟火剂爆燃光谱示温反演研究

如何在高温、高压、高辐射状态下准确测温一直是一个难题,为解决该难题,以辐射光谱测温技术为基础,实现对多元烟火剂爆燃过程的非接触温度测量,为进一步明确烟火剂的反应步骤与爆燃产物提供了基础参数。通过建立多元烟火剂与示温颗粒的辐射光谱测温模型,给出基于凝聚相小灰体颗粒的发射率计算方法,开展凝聚相颗粒辐射谱线获取实验并进行连续热辐射谱线的示温反演。为提高反演的准确性,提出了一种方法以降低在多元烟火剂爆燃时出现的离子峰展宽影响,该方法采用维恩变换分析光谱曲线,使用Bisquare算法和最小二乘算法的双平方加权拟合去除非热辐射谱线,开展热辐射温度的反演。发现了烟火剂爆燃二次升温规律,温度出现升温-降温-再升温-再降温的二次放热的现象。该研究为炸药一类物质爆燃的温度场温度变化检测提供了一种新的反演思路和方法。

基于Kriging模型的某高射速自动机内抽壳滑板疲劳优化

为提高抽壳滑板的疲劳寿命,进而满足射速在1500发/min左右的某10连发高射速自动机寿命达1000发的最低寿命要求,提出一种基于Kriging回归的代理模型用于抽壳滑板的疲劳优化。在与试验结果相符的有限元模型基础上,通过拉丁超立方采样设置初始样本点,构建与样本点相对应的结构模型,并计算每一组样本的理论寿命。根据初始样本点构建Kriging代理模型的同时,采用以改善期望准则为加点准则、遗传算法为子优化求解算法的代理优化算法来对目标函数进行寻优。优化后抽壳滑板的疲劳寿命提高到1193发,且经试验验证,优化结果满足自动机战术技术指标。研究结果表明,通过基于Kriging和遗传算法的代理优化算法能够快速有效地寻优得到全局最优解,适用于高射速自动机内破断零部件的疲劳优化,对工程应用具有一定的借鉴意义。

适用于多夹层盐穴储气库的改进Mohr-Coulomb准则

考虑到多夹层盐岩在三轴压缩和拉伸应力状态下破坏强度的差别较大,对盐岩破坏的Mohr-Coulomb准则进行修正,得到改进后的Mohr-Coulomb准则,利用室内盐岩实验数据回归出相应的公式,并与已有的两种准则的计算结果进行对比。建立了多夹层盐穴储气库有限元模型,分析了储气库的埋深、顶跨、顶部盐岩厚度、顶部相邻非盐岩层厚度及弹性模量等参数对储气库最小许可运行压力的影响规律,并对比了改进Mohr-Coulomb准则与已有准则的计算结果。综合研究表明:改进Mohr-Coulomb准则与实验数据具有很好的一致性,能够反映盐岩从三轴压缩应力状态转换为三轴拉伸应力状态时破坏强度变化对储气库最小许可运行压力的影响;储气库最小许可运行压力梯度随着顶跨的增加而增加,随着顶部相邻非盐岩层弹性模量的增加而降低,而顶部盐岩和相邻非盐岩厚度对其影响不显著。

改进无模型自适应迭代学习的直线电机滑模控制

二维直线电机具有非线性、多变量及强耦合等特点,其精确模型无法获得,同时,在实际过程中由于参数摄动及扰动而造成的运行不稳定现象,致使对其跟踪控制十分困难。针对以上问题,根据无模型自适应迭代学习控制不依赖被控系统精确数学模型的特点,及滑模控制具有可设计且与对象参数和扰动无关的滑动模态,提出一种改进无模型自适应迭代学习的滑模结构复合控制策略。在无模型自适应迭代学习控制方案的准则函数中加入误差变化率,并对其收敛性进行分析论证;然后在紧格式动态线性化基础上,设计指数趋近律滑模控制,使改进无模型自适应迭代学习的滑模控制复合策略能够克服不稳定现象并具有很强的鲁棒性,从而进一步提高系统响应速度和控制精度。最后通过仿真和实物验证,控制精度稳定在1μm范围内,并与其他控制方案相比,验证了所提方法的准确性和有效性。

基于不完全退火的正态云禁忌搜索算法及应用

针对RC电路参数优化应用时的局限性,提出一种基于不完全退火的正态云禁忌搜索算法。该算法对原始禁忌搜索算法在寻优过程中出现的对寻优起点过度依赖、早熟、灵敏度不一致等问题进行了改进,首先通过引入改进的不完全模拟退火Metropolis准则作为算子,使得原始禁忌搜索不再依赖初始可行解,具备了一定逃离局部最优解能力;然后采用正态云模型,提出了一种自适应禁忌表记忆策略及遗忘机制,使得禁忌搜索算法具备更强随机性与模糊性,进一步增强其全局搜索性能;最后针对灵敏度不一致问题,提出串行多维多灵敏度混合编、解码策略,实现在同一算法框架下对不同寻优对象定义不同搜索范围,使得低灵敏度解受忽略程度大大降低。采用8个基准函数及TSP-Oliver30标准测试算例进行性能评估,并与其他6种同类型算法对比,证明该算法对原始禁忌搜索算法优化效果良好。将该算法应用于SiMOSFET加速器磁铁开关电源参数优化后,经仿真与实验,结果表明:所提改进算法能够对工程应用进行实际优化,具备优越性与可行性。

考虑突发状况下预期调配的多能工配置问题

单元分散的Seru生产系统易遭遇多能工短缺的突发状况,为了尽快恢复受损单元的运营能力,需从正常单元调配多能工。针对这种情况,文中研究了考虑未来突发状况下预期调配的多能工初始配置问题。根据初始分配人数和短缺人数,制定预期调配准则,构建以运营效率和预期调配成本为目标的多能工优化配置模型,设计改进的非支配遗传算法(NSGA-Ⅱ)获得Pareto解集。以某个大型电动汽车企业在6个城市构建生产基地为例,确定不同等级多能工的分配决策,验证了文中模型和算法的有效性,并对多能工短缺事件概率进行灵敏度分析。结果表明:多能工短缺事件概率对预期调配成本影响显著,极端追求预期调配成本最低的方案会导致部分多能工闲置,应根据实际情况合理地设定运营效率的下界约束。

基于改进切线角和变形速率的滑坡预警——以湖南省石门县雷家山滑坡为例

为了研究湖南省滑坡监测预警方法,提高预警成功率,以石门县雷家山滑坡为例展开研究。通过对灾害现场进行详细地质调查,对滑坡特征进行了描述,初步阐述了滑坡发生的成因机理。研究结果表明,独特的地形地貌、结构松散的土体是滑坡形成的内在因素,强降雨和工程切坡活动是导致滑坡的外因。基于GNSS系统获取滑坡的全过程变形-时间曲线,并对变形曲线特征进行分析,发现该滑坡具有明显的初始变形、等速变形、加速变形三阶段演化特征,属于渐变型滑坡。将切线角和变形速率阈值作为滑坡预警的重要指标,建立了预警判据,并对接群防群测信息平台,可以为相关部门展开防灾减灾工作和应急响应提供直接依据。雷家山滑坡实现成功避险,验证了该监测预警方法的实用价值。

企业的质量奖设立研究

当前我国已转向高质量发展阶段,要推动质的有效提升和量的合理增长。新时代的质量含义不仅仅是产品和服务质量,还包含了经营管理质量和发展质量,因此质量是企业持续经营和发展的重要保障,是企业的生命力。而设立和评选质量奖是国家、各级政府、组织鼓励和引导不断提升质量水平,打造质量品牌的重要手段。介绍了国内外的主要质量奖并对比了异同,分析了设立企业质量奖的意义和必要性,提出了设置奖项的思路,并给出了奖项设置和评选标准的参考。

基于辅助电压判据的柔性直流换流阀子模块旁路拒动策略

为解决柔性直流输电换流站换流阀子模块旁路开关拒动导致直流闭锁,首先,开展了旁路开关动作原理和动作过程力学分析;接着,从现场检查、故障录波和旁路开关合闸故障复现试验3个方面,深入分析某换流阀子模块旁路拒动事件的故障原因。然后,针对无转折晶闸管子模块设计的在运工程,提出基于辅助电压判据的旁路开关拒动改进设计策略;最后,根据4种不同运行工况分别开展改进设计策略试验验证。结果表明,所提改进设计策略具有可靠性和有效性,该策略实施后避免了旁路开关拒动导致换流阀子模块炸裂和换流阀闭锁,进一步提高了在运柔性直流输电工程换流阀子模块运行可靠性。

Triaxial strength behaviour of rockmass satisfying Modified Mohr-Coulomb and Generalized Hoek-Brown criteria

The triaxial strength of twenty rockmass types was predicted using two non-linear triaxial strength criteria for rockmass i.e. Modified Mohr-Coulomb(MMC) criterion and Generalized Hoek-Brown(GHB)criterion. Four different rockmass classification systems were used for the calculation of MMC criterion parameters while only GSI classification system has been used for calculation of GHB parameters. The representative value of the uniaxial compressive strength and elastic modulus of rockmass have been estimated using probabilistic approach. A hypothetical case of an unsupported tunnel has been analyzed considering both MMC and GHB criteria. The analysis was done using the convergence-confinement method with two different approaches. The first approach predicts the tunnel response using GHB criterion directly. The second approach predicts the tunnel response using equivalent Mohr-Coulomb parameters obtained by linearization of triaxial data points obtained from MMC and GHB criteria. The tunnel response has been estimated in terms of radius of plastic zone, tunnel convergence and tunnel convergence strain. For very poor rockmasses the tunnel response predicted by MMC criterion is less than that predicted by GHB criterion. For poor and fair rockmass, the tunnel response estimated considering both the criteria are comparable except for few cases. Squeezing condition in rockmass has been also evaluated.

Limit equilibrium analysis for rock slope stability using basic Hoek–Brown strength criterion

Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.

Validation of Hoek-Brown failure criterion charts for rock slopes

Although stability charts suggested by Hoek and Bray on the basis of Mohr-Coulomb criterion are used for rock slopes,but complete and precise recognition is required for distinguishing cohesive strength and Mohr-Coulomb equivalent internal friction angle for rock mass.The paper by Lia et al.[6]is the only one that introduced rock slope charts according to Hoek-Brown failure criterion.In this paper,at first,this type of charts is introduced.Then,Mohr-Coulomb failure criterion charts[2]are compared and validated with Hoek-Brown failure criterion ones[6].Next,Bishop method utilizing Slide software is compared with Hoek-Brown failure criterion stability charts.Average standard deviation(ASD),root mean square error(RMSE)and variance account for(VAF)were used for the comparison.According to the results,because of high distribution and very low correlation among the comparisons,Hoek-Brown failure criterion charts are not efficient.

Elastoplastic homogenization of particulate composites complying with the Mohr–Coulomb criterion and undergoing isotropic loading

This work aims at determining the overall response of a two-phase elastoplastic composite to isotropic loading. The composite under investigation consists of elastic particles embedded in an elastic perfectly plastic matrix governed by the Mohr-Coulomb yield criterion and a non-associated plastic flow rule. The composite sphere assemblage model is adopted, and closed-form estimates are derived for the effective elastoplastic properties of the composite either under tensile or compressive isotropic loading. In the case when elastic particles reduce to voids, the composite in question degenerates into a porous elastoplastic material. The results obtained in the present work are of interest, in particular, for soil mechanics.