自动扶梯梯级碰撞研究与有限元分析

为研究自动扶梯梯级碰撞失效原因及由于碰撞可能引起的梯级失效模式及危害程度,对国内典型的梯级样品进行结构分析。以铝合金材料为基础,通过对梯级装配体的三维模型和梯级的力学有限元分析,计算梯级的应力和挠度位移形变,得出梯级的屈服强度最大静应力和最大位移挠度断口可能发生的位置。为制定相应的保养和安全管理规范提供理论依据。     

某切边模最优斜刃角度的确定

斜刃冲裁可降低冲裁力及冲裁噪声,选取合理的斜刃角度是斜刃冲裁模具设计中需考虑的关键问题之一。目前,斜刃角度一般凭经验取值,为此基于优化设计思想对斜刃角度的取值加以研究。对连续表面处理线上的某切边模进行动态仿真分析,获得切边过程中斜刃角度与上模最大等效应力之间的关系,进而确定上模等效应力达到最大的阶段。然后针对该阶段,以上模斜刃角度为优化变量,以所需冲裁力最小为优化目标,以上模最大等效应力小于材料许用应力、刃口在垂直冲裁方向的形变位移小于0.01 mm为约束条件进行优化设计,得到不同材料和不同板料厚度情况下上模的最优斜刃角度。最后,对上模进行了疲劳分析并提出了相应的改进方案。     

超滤设备结构强度有限元分析与寿命估测

采用通用有限元软件ANSYS,对SFP型超滤设备进行结构强度有限元分析与寿命估测,计算了结构的应力分布、变形情况并估测其使用寿命。经分析可知,在最大进水压力下,SFP型超滤设备最大等效应力出现在封头的不锈钢抱箍上,其等效应力值小于不锈钢材料的许用应力;聚合物部件的第一主应力的值也远小于各自的最大拉伸强度。采用CPVC管材材料的应力强度与使用寿命预测曲线来估测SFP型超滤设备的使用寿命,在始终保持最大进水压力条件下,SFP型超滤设备估测使用寿命为1000小时;从估测的方法可见,若能降低进水压力,超滤设备的使用寿命将大大提高。     

平纹编织C/SiC材料复杂应力状态的力学行为试验研究

利用Arcan夹具,实现对2D平纹编织C/SiC复合材料拉剪、压剪加载试验,研究材料在复杂应力状态下的力学行为,分析材料的损伤演化和失效模式。试验结果表明,材料在拉剪复杂应力状态下不同角度的应力—应变曲线呈现非线性关系;在压剪复杂应力下,随着加载角度增大,应力—应变曲线非线性程度增大。断口分析表明纯剪切形成平齐断口,受拉应力影响材料在拉剪复杂应力状态下形成斜断口。试验分析表明,适当的压应力能提高抗剪切破坏能力。偏移型椭圆失效判据与试验值吻合较好,该失效判据能较好地描述材料在复杂应力状态下的破坏行为,能较好反映材料的强度特征。     

钢桥腹板间隙出平面变形影响因素敏感性分析

钢桥腹板间隙处的出平面变形破坏是钢桥破坏的常见形式之一。通过有限元数值模拟的方法,计算了不同腹板间隙大小,腹板厚度,以及肋板刚度的情况下,腹板间隙处范式等效应力和出平面位移量的分布规律;采用敏感性分析方法,计算了最大范式等效应力和最大出平面位移量对腹板间隙大小,腹板厚度,肋板刚度的敏感性程度。提出参数变化范围内,系统特性对影响因素平均敏感度的概念。研究表明,最大范式等效应力对腹板间隙大小最敏感,最大出平面位移量对腹板厚度最敏感。在实际应用中,采用合适的腹板间隙大小可以使最大范式等效应力最小,通过增加腹板厚度可以同时减小腹板间隙处的最大等效应力和最大出平面位移量,肋板采用较柔性的材料,能够有效减少腹板间隙处的出平面变形。     

链条式起下作业系统关键部件的有限元分析

为了研究蒸汽驱注式高温不压井修井作业机起下作业系统中链条传力部件的安全可靠性,利用有限元软件进行分析,精确模拟出链条静强度应力分布情况,得出链条最大等效应力小于材料的屈服极限,并且销轴和套筒接触部位极易磨损,而磨损后,链节距加大,链条总长度增加会降低其使用寿命;在此基础上对链条的疲劳寿命进行理论计算与模拟分析,计算结果表明,该结构在载荷工况下均完全满足工作要求。     

振动仿真分析网络交换设备加固设计

对网络交换设备进行了二次加固减振设计,同时利用ANSYS仿真分析对产品进行减振辅助设计,以缩短产品开发周期,降低设计成本。通过对网络交换设备进行合理简化,建立了其有限元网格模型。利用ANSYS对网络交换设备进行振动冲击有限元计算,分别获取了网络交换模块印制板在冲击振动下的应力及位移响应曲线。通过ANSYS有限元分析的后处理功能,得到隔振器的最大伸长量以及各部件最大位移量和最大等效应力值。结果表明,隔振器的伸长量在额定范围之内,设备结构的最大等效应力与材料的屈服强度还相差甚远,结构没有产生塑性变形,验证了结构设计的合理性。为网络交换设备的抗振动冲击设计提供了一定的理论参考依据。     

双材料界面裂纹应力强度因子计算

建立不同裂纹长度的双材料界面裂纹模型,用有限元软件计算和分析界面裂纹尖端附近的应力场和位移场.利用裂尖前沿应力和裂纹面相对位移分别计算了界面裂纹尖端的应力强度因子K,两种方法计算的K值完全吻合.通过数值分析,给出一种计算双材料界面裂纹应力强度因子K的经验公式.     

月牙形磨损套管抗内压强度计算

将内壁磨损套管月牙模型简化为偏心圆筒模型,通过直角坐标向双极坐标的转换和选取曲线坐标中表示应力的复势,得出了偏心磨损套管等效应力和剩余抗内压强度计算方法。磨损套管等效应力解析解和数值解对比分析表明,随着磨损深度的增加和作用在内表面压力的增大,磨损套管危险截面内、外表面的等效应力呈指数增大;磨损套管抗内压强度随磨损深度线性减少。采用双极坐标公式计算偏心磨损套管等效应力与有限元分析结果相差小于0.9%。偏心磨损套管抗内压强度理论解和月牙形磨损套管抗内压强度试验值之间相对误差小于10%。将月牙形磨损套管简化为偏心圆筒模型,采用偏心磨损套管抗内压强度公式计算月牙形磨损套管抗内压强度是可行的。     

基于双悬臂梁试样的柔度方法

NACE TM0177-96标准推荐的双悬臂梁DCB(double cantilever beam)试样主要用于测试硫化物腐蚀条件所产生的平衡载荷与裂纹扩展的相互关系,进而评估材料抗应力腐蚀开裂临界强度因子的优劣,但未提供确定裂纹长度的方法.文中通过有限元分析法提出计算V形裂纹长度的统一柔度公式,该公式在满足有效性条件下,与试样几何尺寸无关,可用于通过测试试样加载线和端面裂纹张开位移计算柔度,进而实现裂纹长度预测.文中采用30CrMo钢DCB试样和已有文献的试验数据对统一公式进行有限元模拟和试验结果对比.研究表明,所提出的柔度公式对不同V形裂纹DCB试样的裂纹长度预测结果与有限元分析结果之间的相对误差不超过2％,与试验结果之间的相对误差不大于5％.     

Finite element analysis of planar twist channel angular extrusion (PTCAE) as a novel severe plastic deformation method

A new severe plastic deformation (SPD) method based on equal channel angular pressing (ECAP) is introduced for producing ultrafine grains in bulk alloys, entitled as “Planar twist channel angular extrusion (PTCAE)”. In PTCAE method, there is additional angle, α, (plus φ and ψ angles in ECAP method) which represents angle associated with the lateral reversal arc of curvature in deformation zone. Three dimensional finite element method (FEM) simulations of both ECAP and PTCAE processes were performed in order to investigate the plastic deformation state of processed samples and, moreover, the effect of different die geometry (in terms of variation of planar twist angle) on plastic strain distribution and magnitude. Results revealed that PTCAE process related with ECAP process can impose higher strain values in different shear planes simultaneously in one deformation zone. Therefore, PTCAE can produce UFG or nanostructured materials better than ECAP method which has simpler design and significantly higher efficiency compared with other new SPD processes.     

摩擦对大型等通道转角压最大挤压载荷的影响

采用Deform-3D有限元软件对大型等通道转角压(Equal channel angular pressing,ECAP)进行动态计算仿真模拟,并进行试验研究,重点考察变形体与模具间摩擦因数和模具水平通道扩口直径对挤压载荷的影响。模拟结果表明,剪切摩擦模型适合用于ECAP变形仿真模拟计算,摩擦因数对大型ECAP的最大挤压载荷具有很大影响,随着摩擦因数的增加,最大挤压载荷急剧增加;摩擦因数μ=0.6(近似于铝和钢干摩擦)时的挤压载荷是摩擦因数为0时挤压载荷的5.1倍;增加出口通道扩口端的直径,当μ<0.6时,对最大挤压载荷几乎没有影响,而当μ>0.6时,可以明显降低最大载荷值,但也不是出口通道扩口直径越大其对应的挤压载荷就越小。试验研究表明,大型ECAP必须想办法降低摩擦才能实现批量化生产,试验和仿真的最大挤压载荷吻合。     

Effects of solution treatment and sheath on mechanical properties of Al7075 processed by ECAP

Al7075 as a hard-to-work alloy is processed difficultly by Equal channel angular pressing (ECAP) at room temperature. In this paper, experiments were conducted at several heat treatment conditions and also with a new developing strategy using sheath copper to process this alloy at room temperature. Mechanical properties were evaluated by tensile and micro hardness tests. The results demonstrated that the ultimate and yield strength of ECAPed aged samples improved. Tensile test of 4 pass processed samples with copper sheath indicated an increase in the strength in comparison with samples without sheath. The hardness test results showed more uniform distribution of hardness in their cross section for copper sheath casing samples. It was found that by increasing the copper sheath thickness, the hardness variation decreased while the average hardness increased. By considering the time limitation for the process, only solid solution samples without sheath could be successfully ECAPed in 2 passes and samples with sheath could be ECAPed only in one pass.     

Fatigue properties of fine grained magnesium alloys after severe plastic deformation

Fine grained AZ31 and AZ61 magnesium alloys produced by equal channel angular pressing (ECAP) were tested for investigating tensile and fatigue properties, including microstructure, monotonic tensile flow, fatigue life and crack growth rate. For the two alloys, the yield stress of the ECAPed sample was lower than that of the unECAPed (=as received) sample, because of the fact that the softening effect due to texture anisotropy overwhelmed the strengthening effect due to grain refinement. Grain refinement of the AZ31 and AZ61 alloys through ECAP was found not to be significantly effective in increasing fatigue strength.     

韧性材料的几种断裂形式及判据讨论

考察几种韧性材料的复合型断裂试验过程，用传统强度理论思想认定启裂位置与启裂方向，通过对不同物理机制的断裂形式变化规律的研究，判定韧性材料的主要断裂形式有三类，以空穴成核、扩张、聚合为主导机制的正拉断，和以局部剪切带形成、发展为主导机制的两种不同类型的剪切断裂。局部大塑性变形的出现在材料内引起损伤，空穴的聚合或局部剪切带的出现仅发生在载荷达到某一临界值时。导致材料断裂发生的根本因素，是危险点上某应力参数达到了材料的断裂临界值，以此对不同断裂形式的断裂判据进行讨论，提出新的韧性断裂判据。     

凸凹模零件的疲劳有限元分析

落料拉深复合模的凸凹模是模具工作时的主要受力部件.凸凹模零件的强度、刚度以及疲劳寿命校核是模具设计时必须考虑的问题.在拉深件受力分析的基础上,建立了凸凹模的受力模型,通过对凸凹模零件进行有限元分析,计算了该零件的应力、位移分布和疲劳寿命.分析结果显示:凸凹模在工作时,可能出现问题的部位为拉深孔口处,出现的主要问题是凸凹模工作时孔口的磨损;而由于该零件在交变载荷作用下疲劳寿命较大,孔口出现局部剥落的可能性小.     

Simulation and analysis of single fiber pull-out tests through ANSYS and VC++

The aim of this study was to simulate the traditional investigation process of single fiber pull-out tests on quantificational basis, with an estimation of the critical length of embedded fiber and interfacial shear strength while comparing the stimulation results with empirical results. A finite element method (FEM) model of single fiber pull-out tests was established by using ANSYS parametric design language (APDL) program flow. Interfacial average shear strength was calculated and process of interfacial debonding was simulated. Single fiber pull-out tests were implemented to validate the FEM model. Results reveal that the maximum load estimated by the FEM varied as a function of both the length and critical length of the embedded fiber, and the calculated interfacial shear strength through FEM analysis is basically in agreement with the experimental results with a trivial difference of no more than 4.5%. A software was designed to simplify the simulation with respect to the analysis system of single fiber pull-out tests.     

金属简支圆板在边缘均布载荷作用下的塑性极限解

采用双剪统一屈服准则首次对金属类材料的简支圆板在边缘均布载荷作用下的塑性极限进行求解，得出相应的统一解形式。已有的Tresca准则、vonMises准则、双剪应力准则的解答是文中解答的特例或逼近。并得到圆板的极限载荷随不同屈服准则以及边缘载荷内半径的变化曲线。     

Structure and microstructure evolution of Al–Mg–Si alloy processed by equal-channel angular pressing

An ultrafine grained Al–Mg–Si alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of Φ = 90° and outer arc of curvature of ψ = 37° from 1 to 12 ECAP passes at room temperature following route B_c. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the Al–Mg–Si alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.     

等通道弯角多道次挤压工艺累积变形均匀性研究

通过等通道弯角挤压(Equal channel angular pressing,ECAP)工艺累积足够的变形制备块状超细晶粒材料(亚微米或纳米微观结构材料)。采用节点映射法将前一次有限元分析终了结果准确映射到下一次挤压初始阶段的相应节点,实现等通道弯角多道次挤压过程有限元分析。通过有限元模拟不同模具拐角的等通道弯角多道次挤压工艺,获得相应挤压件累积等效应变分布及其规律,为ECAP挤压件晶粒均匀细化提供合理的模具设计与工艺路线。