Surface concentration of chlorpyrifos evaluated by electromagnetic discharge imaging technique

Image analysis is used in conjunction with the Electromagnetic Discharge Imaging (EDI) technique to evaluate the surface concentration and the characteristic discharge intensity of chlorpyrifos. Nearly identical surface condition of gypsum specimens were subjected to chlorpyrifos solutions of various concentrations. The EDI discharges were then applied to detect the changes. Experimental results show that the EDI discharge intensity increases with increasing chlorpyrifos concentration up to 0.4% where a saturation limit is reached. Since the changes of the ionization property and the dielectric property caused by the concentration variation have opposing effects on the EDI discharge intensity, saturation by the foregoing two effects occur at high concentration. Further analysis shows that three characteristic gray levels were found in the gray-level distribution curve for each chlorpyrifos concentration of 0.1%, 0.4%, and 1.6%. These characteristic gray levels can be used to rank concentration of chlorpyrifos.     

Mathematical model for cold rolling based on energy method

There is an increasing requirement for improved accuracy of the rolling models which are widely used in rolling plant in order to produce high-quality products, because this accuracy is important for rolling schedule setup and automatic control. A three-dimensional mathematical model for cold rolling using tangential velocity field and energy method is firstly proposed to investigate the deformation of the strip at the roll gap based on elastic and plastic mechanics. The field and geometrical approximation yield criterion are used to integrate the internal plastic deformation power. The friction power is analyzed using the co-line vector inner product method. Finally, the analytical expressions of roll separating force and roll torque are obtained quickly considering the effect of roll flattening on the roll separating force. The predicted roll separating forces are consistent with other researchers’ models, especially for on-line measured roll separating forces in a tandem cold rolling plant. The accurate predicted results provide valuable guidelines for optimization of rolling process.     

Lüders bands propagation of 1045 steel under multiaxial stress state

Inhomogeneous plastic deformation of 1045 steel under monotonic loading was experimentally studied. Thin-walled tubular specimens were used in the experiments and custom-made small strain gages were bonded on the specimen surface to characterize the local deformation. Experiments were conducted under tension, torsion, and combined tension–torsion. During the propagation of Lüders bands, the local deformation experienced two-stage deformation: an abrupt plastic deformation stage followed by a slower deformation process. In some area of the gage section of the specimen, a small amount of initial plastic deformation occurred before the Lüders front reached. During the propagation of Lüders bands, multiple Lüders fronts can be formed. Under tension, torsion, and combined tension–torsion with a constant axial load, the Lüders front was approximately parallel to the material plane of maximum shear stress. When the combined axial-torsion followed a proportional fashion, the stress–extensometer strain responses were dependent on the axial/torsional loading ratio, and the Lüders fronts were oriented differently and propagated along the specimen axis at a different velocity. The local strain was inhomogeneous even at the work-hardening stage. The relationships between the equivalent stress and the equivalent plastic strain were found to be practically identical for all the loading cases studied.     

An experimental study on grain deformation and interactions in an Al-0.5%Mg multicrystal

Heterogeneous plastic deformation behavior of a coarse-grained Al-0.5%Mg multicrystal was investigated experimentally at the individual grain level. A flat uniaxial tensile specimen consisting of a single layer of millimeter-sized grains was deformed quasi-statically up to an axial strain of 15% at room temperature. The initial local crystallographic orientations of the grains and their evolutions after 5, 12, and 15% plastic strains were measured by electron backscattered diffraction pattern analysis in a scanning electron microscope. The local in-plane plastic strains and rigid body rotations of the grains were measured by correlation of digital optical video images of the specimen surface acquired during the tensile test. It is found that both intergranular and intragranular plastic deformation fields in the aluminum multicrystal specimen under uniaxial tension are highly heterogeneous. Single or double sets of slip-plane traces were predominantly observed on the electro-polished surfaces of the millimeter-sized grains after deformation. The active slip systems associated with these observed slip-plane traces were identified based on the grain orientation after deformation, the Schmid factor, and grain interactions in terms of the slip-plane trace morphology at grain boundaries. It is found that the aluminum multicrystal obeys neither the Sachs nor the Taylor polycrystal deformation models but deforms heterogeneously to favor easy slip transmission and accommodation among the grains.     

A combined upper-bound and elastic-plastic finite element solution for a fastener hole subjected to internal torsion

Fastener holes used in the mechanical joints are vulnerable to failure due to development of stress concentration at their edges. Inducing compressive residual stresses by different techniques has been the most common method to reinforce the holes to date. In this work, a new reinforcement technique called internal torsion, which can be classified as a localized severe plastic deformation process, is proposed as an alternative to the cold expansion pre-stressing. A special specimen is designed to represent the behavior of a typical fastener hole during the internal torsion process. The deformation of the specimen in the vicinity of its hole surface is studied by introducing a parametric kinematically admissible velocity field (PKAVF) within the deformation affected zone (DAZ). Calibration of the parameters in relation to the deformation of the material during the process is done by an elastic-plastic finite element solution that was performed in ABAQUS for a specimen made of interstitial free (IF) steel. Numerical analysis of the deformation is carried out to understand the process and to estimate the optimum process parameters. Subsequently, the calibrated model is used in an upper-bound solution of the problem to estimate the torque–twist response of the specimen during internal torsion. Finally, the results of upper-bound solution are compared with those of finite element analysis. There is a good agreement between the upper-bound solution and finite element results, which verifies validity of the calibrated velocity field model and the upper-bound solution based on the model for the internal torsion problem.     

冻融循环和不均匀冻胀下寒区隧道的塑性解答

季冻区长期冻融循环造成围岩强度和变形性能劣化,使得寒区隧道易进入塑性状态,且寒区隧道围岩呈现以径向冻胀为主的不均匀冻胀.合理考虑寒区隧道冻融循环对围岩性能的劣化以及围岩的不均匀冻胀属性,基于Mohr-Coulomb准则推导了寒区隧道冻胀力、应力与位移的塑性解答,同时给出相应的弹性解答和冻结围岩弹-塑性状态的判定方法,对所得解答进行讨论和对比验证,最后探讨了冻融循环、不均匀冻胀与体积冻胀率对寒区隧道应力分布、塑性区半径、洞壁位移和冻胀力的影响规律.研究表明:本文解答具有广泛的适用性和良好的可比性,并得到文献塑性解答的退化验证;冻胀力、洞壁位移与塑性区半径随冻融次数增加分别增大20.3%、8.44倍、2.16倍,以量化长期冻融循环造成围岩性能的劣化效应;冻结围岩由均匀冻胀转变为不均匀冻胀时冻胀力增大42.8%,但塑性区半径几乎无变化;4种体积冻胀率参数均显著影响冻胀力,尤其是水热迁移系数可使冻胀力增大123.6%.本文结果可为季冻区隧道设计与冻害问题解决提供一定的理论依据.     

冻融循环和不均匀冻胀下寒区隧道的塑性解答

季冻区长期冻融循环造成围岩强度和变形性能劣化,使得寒区隧道易进入塑性状态,且寒区隧道围岩呈现以径向冻胀为主的不均匀冻胀.合理考虑寒区隧道冻融循环对围岩性能的劣化以及围岩的不均匀冻胀属性,基于Mohr-Coulomb准则推导了寒区隧道冻胀力、应力与位移的塑性解答,同时给出相应的弹性解答和冻结围岩弹-塑性状态的判定方法,对所得解答进行讨论和对比验证,最后探讨了冻融循环、不均匀冻胀与体积冻胀率对寒区隧道应力分布、塑性区半径、洞壁位移和冻胀力的影响规律.研究表明:本文解答具有广泛的适用性和良好的可比性,并得到文献塑性解答的退化验证;冻胀力、洞壁位移与塑性区半径随冻融次数增加分别增大20.3%、8.44倍、2.16倍,以量化长期冻融循环造成围岩性能的劣化效应;冻结围岩由均匀冻胀转变为不均匀冻胀时冻胀力增大42.8%,但塑性区半径几乎无变化;4种体积冻胀率参数均显著影响冻胀力,尤其是水热迁移系数可使冻胀力增大123.6%.本文结果可为季冻区隧道设计与冻害问题解决提供一定的理论依据.     

三种钢轨材料与车轮匹配时滚动磨损与损伤行为

利用WR-1轮轨滚动磨损试验机研究了U71Mn、PD3、PG4三种钢轨与AAR-B车轮材料匹配时的滚动磨损与损伤性能.结果表明:不同钢轨材料的微观组织结构明显不同,钢轨硬度对轮轨滚动摩擦系数基本无影响;随钢轨硬度增加,钢轨磨损率减小,车轮磨损率增大,轮轨系统总磨损率先减小后增大.随试验时间增加,不同钢轨试样的硬化率趋于一致,车轮试样硬化率随钢轨试样硬度的增加而变大,轨轮硬度比随试验时间增加趋于相同.钢轨材料对轮轨试样表面损伤形貌有一定影响,随钢轨硬度增加轮轨表面犁沟现象明显,钢轨试样表面剥落损伤减轻且塑性变形层变薄,出现了明显的疲劳裂纹损伤,钢轨硬度增加导致车轮试样表面剥落加重且塑性变形层变厚;轮轨试样表层出现明显的白层现象,且车轮试样的白层更厚.     

On the Plastic Wave Propagation Along the Specimen Length in SHPB Test

To observe the plastic wave propagation, an experimental setup is designed with a SHPB facility and a high speed digital camera. Two types of OFHC copper were selected as specimen materials: in the cold work condition and after total annealing, which represent non strain hardening and strain hardening material respectively. The rise time of incident impulse in the SHPB test is relevant to bar’s radius. A maximum allowable specimen length and a maximum allowable impact velocity (MAIV) of striker are proposed for the SHPB test. The propagation of plastic waves is observed along specimen length at the beginning of specimen’s plastic deformation in SHPB test. However, for both types of material, no plastic wave motion is caught along specimen length for large plastic strain level. Side confinement effect of friction is found to be significant, even with lubricant in the experiment.     

An experimental study of inhomogeneous cyclic plastic deformation of 1045 steel under multiaxial cyclic loading

An experimental study was conducted on the inhomogeneous cyclic plastic deformation of 1045 steel under multiaxial cyclic loading. Thin-walled tubular specimens were used and small strain gages were bonded on the specimen surface to characterize the local deformation. The controlled loading paths included cyclic tension–compression, cyclic torsion, proportional axial-torsion, 90°-out-of-phase axial-torsion, and fully reversed torsion with a constant axial stress. The maximum stress in each experiment was lower than the lower yield stress of the material. It was found that the cyclic plastic deformation within the gage section of the specimen under multiaxial stress state followed the three-stage process that was observed from uniaxial loading, namely, incubation, propagation, and saturation. The plastic deformation was significantly inhomogeneous during the propagation stage, and the inhomogeneity continued through the saturation stage. The duration of each stage and the saturated strains were dependent on the cyclic stress amplitude and the loading path. Multiaxial stress state reduced the incubation stage. With identical equivalent stress magnitude, the nonproportional loading path resulted in the shortest incubation and propagation stages, and the saturated equivalent plastic strain magnitude was the smallest. Although the deformation over the gage section was inhomogeneous, the plastic deformation in a given local area was found to be practically isotropic.     

Evolution of strain localization autowaves in a zirconium alloy and evaluation of plasticity margin in a rolling area

The stress-strain state of a zirconium alloy in a cold rolling area is studied by considering the evolution of strain localization autowaves and changes in the ultrasound velocity. It is found that in the region of transition from the upsetting zone to the reduction zone, there is a significant exhaustion of the plasticity reserve of the material, so that fracture is most likely in exactly this region. It is shown that the traditional methods of estimating the plasticity margin from mechanical characteristics cannot reveal this region; an integrated analysis of plastic deformation macrolocalization patterns and acoustic measurement results is required.     

基于声发射参量的不同深度灰岩塑性破坏识别研究

对某矿深部灰岩进行单轴压缩试验,测得试件破坏全过程的应力、应变和声发射参数。通过分析应力、应变和声发射参数之间的关系,可根据声发射振铃计数率的变化情况,将全过程分为三个阶段:第一阶段处于孔隙裂隙压密阶段,振铃计数率较多;第二阶段处于稳定变形阶段,声发射处于平静期;第三阶段岩石进入塑性变形阶段,振铃计数率明显增加。研究发现,深度越深,第一阶段终止时的应力水平越高;将声发射累计能率与累计振铃计数率的比值定义为能振比λ,λ的变化规律一定程度上反映出试件内部裂隙发展情况。研究λ的变化规律能够为识别岩体失稳提供依据,提高声发射技术监测预报的准确性。     

Vibration analysis of a circular disk tensioned by rolling using finite element method

Summary The paper proposes a method in finite element analysis for estimating natural frequencies of a disk tensioned by rolling, without the use of eigenvalue analysis. The natural frequencies of a disk vary when the localized plastic deformation caused by roll-tensioning induces residual stresses. Tensioning is used for improving the dynamic stability of circular saws; the optimal condition of rolling can be predicted from natural frequency characteristics. In the proposed method, the natural frequencies after rolling are easily estimated from the mode shapes of the disk before rolling and the stress distribution after rolling. The method is based on ideas similar to thermal stress and sensitivity analysis rather than on eigenvalue analysis. The effectiveness of the method is shown by comparing the natural frequency characteristics obtained by this method with those by eigenvalue analysis. Received 18 June 1998; accepted for publication 8 April 1999     

Effect of grain size on slow fatigue crack propagation and plastic deformation near crack tip

Fatigue crack growth and its threshold are investigated at a stress ratio of 0.5 for the three-point bend specimen made of Austenitic stainless steel. The effect of grain size on the crack tip plastic deformation is investigated. The results show that the threshold value Δk_th increases linearly with the square root of grain size d and the growth rate is slower for materials with larger grain size. The plastic zone size and ratio for different grain sizes are different at the threshold. The maximum stress intensity factor is k_max and σ_ys is the yield strength. At the same time, the characteristics of the plastic deformation development is discontinuous and anti-symmetric as the growth rate is increased from 2·10^—8 to 10⁻⁷ mm/cycle.A dimensionless relation of the form for collating fatigue crack starting growth data is proposed in which Δk_th represents the stress intensity factor range at the threshold. Based on experimental results, this relation attains the value of 0.6 for a fatigue crack to start growth in the Austenitic stainless steel investigated in this work. Metallurgical examinations were also carried out to show a transgranular shear mode of cyclic cleavage and plastic shear.     

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在重轨万能轧制过程中,首先建立了简化的三维理论模型. 然后分别给出了轨腰、轨头及轨 底的运动学许可速度场以及相应的应变速度场和剪应变速度强度,并求出了相应变形区的塑 性变形功率、速度间断面上消耗的功率以及由于摩擦产生的摩擦功率. 最后根据上限原理分 别求解了水平辊和两个立辊的轧制力上限解. 通过比较可知,二辊轧制理论公式误差很大因 此不能用于万能轧制过程,而上限法求得的轧制力近似解大于轧制现场数据但最大误差不超 过13\%, 因此根据上限原理进行轧制工艺参数设定及优化是比较可靠的.     

Experimental study of the plastic yielding of rolled sheet metals with the cruciform plate specimen

In the current paper, an experimental technique for the evaluation of the in-plane yield loci of sheet metals with the cruciform plate specimen is presented. The measurement system is shown to conform to the optimized design concept proposed by other researchers. Finite element analysis demonstrates a reasonably wide area of uniform stress distribution in the center of the cruciform specimen, which allows the measurement of in-plane strain field by using a stacked strain rosette. Based on the designed apparatus, the yield loci of the 1100-F aluminum sheets corresponding to the as-received condition, and 25% and 50% thickness reductions by further rolling, were constructed, respectively, by applying biaxial loadings along the two principal axes of the cruciform specimen. A set of uniaxial tension tests were also performed to determine the plastic properties of the aluminum sheet along different directions with respect to the rolling direction. Finally, Hill's 1990 yield criterion is examined based on the experimental data from both biaxial and uniaxial tension tests.     

基于塑性体积应变的岩石损伤变形特性实验研究

为分析岩石塑性变形与损伤的关系,在定义岩石的初始损伤和临界损伤,提出塑性体积应变分析方法,从而以塑性体积应变为损伤变量,采用归一化方法建立岩石的损伤本构模型。采用递增循环加载实验确定岩石损伤本构模型中的弹性卸载模量和弹性应变比例系数两个参数。通过实验和理论分析得出:当荷载较小时,普通单轴压缩状态下岩石损伤随荷载的增加具有减小趋势,荷载超过一定数值后,岩石损伤才开始增加;单轴递增循环压缩状态下当循环荷载大于约35%峰值强度后,卸载后岩石的损伤具有增加的趋势,小于该荷载之前具有减小的趋势。整个加载过程的理论应力-应变曲线能很好地与实验结果相吻合,在循环加载区间理论结果还能体现出岩石实验结果中的回滞环。     

Nondestructive detection of damage in aluminum: Electromagenetic discharge imaging

Electromagnetic Discharge Imaging (EDI) is applied for the nondestructive detection of imperfections and inhomogeneities in solids. These imperfections were introduced mechanically by drilling holes of different sizes and chemically by applying corrosive agents to aluminum specimens. The results are influenced by a host of variables associated with the waveform generator, the dielectric air gap and the specimen type. Correlation is thus established between the electromagnetic discharge image and the degree of material damage. Detection of material damage was also made possible even when the specimen surface was a layer of opaque insulation material.     

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从结构损伤识别的需要出发研究能够准确反映钢构件承载过程中发生的塑性变形 和损伤过程的量化测试方法. 用漫反射法测量了钢构件在变形和损伤过程中表面粗糙度变化 的图像,依据记录下来的表面图像进一步处理得到构件表面粗糙度的平均灰度值的变化,据 此寻找对构件塑性变形和损伤状态相关并且敏感的参数指标. 研究结果表明,基于漫反射法 和图像处理得到的钢构件承载过程中表面粗糙度的平均灰度值的变化可以判断金属试样是否 发生了塑性变形,并可定量描述试样在塑性变形后期的损伤程度.     

Notch sensitivity in nanoscale metallic glass specimens: Insights from continuum simulations

Recent experiments have shown that nano-sized metallic glass (MG) specimens subjected to tensile loading exhibit increased ductility and work hardening. Failure occurs by necking as opposed to shear banding which is seen in bulk samples. Also, the necking is generally observed at shallow notches present on the specimen surface. In this work, continuum finite element analysis of tensile loading of nano-sized notched MG specimens is conducted using a thermodynamically consistent non-local plasticity model to clearly understand the deformation behavior from a mechanics perspective. It is found that plastic zone size in front of the notch attains a saturation level at the stage when a dominant shear band forms extending across the specimen. This size scales with an intrinsic material length associated with the interaction stress between flow defects. A transition in deformation behavior from quasi-brittle to ductile becomes possible when this critical plastic zone size is larger than the uncracked ligament length. These observations corroborate with atomistic simulations and experimental results.