拉拔速度对空拉拔锌合金微管的影响

运用deform-3D软件模拟了锌合金微管(Φ2.45 mm×0.13 mm)的空拉拔成形过程。研究了拉拔速度对锌合金微管表面质量、力学性能和尺寸精度的影响。结果表明:拉拔速度对微管的应变和应力影响非常大,进而直接影响其表面质量、力学性能和尺寸精度。适当的拉拔速度可使多道次空拉拔锌合金微管的应变较均匀、最大等效应力和损伤值较低,从而减少皱缩和拉拔裂纹等缺陷,降低断裂倾向。锌合金微管具有均匀应变、较小等效应力的拉拔速度为22 mm/s。实验结果很好地验证了模拟的结论:在模拟优化的拉拔速度下,空拉拔制备的锌合金微管具有较高的尺寸精度和力学性能,并且皱缩等缺陷较少。     

刚性有限元弹塑性分析的网格相关性

本文通过理论分析模型及算例检验证明，采用刚性有限元进行弹塑性分析的计算结果与网格剖发形式相关。刚性有限元的这一缺点，可通过加密网格，采用不规则形状单元及沿可能屈服面方向划分单元交界线的方法加以改善。     

土体三维弹塑性分析中的体积闭锁分析及单元选择

在材料不可压缩或胀/缩塑性流动情况下，传统低阶单元有体积闭锁问题。以摩尔－库仑模型为例，推导了塑性剪切应变和塑性体积应变的关系，揭示闭锁产生的原因。分析8节点等参元、Wilson非协调元、EAS单元和14节点单元的闭锁性态，表明8节点单元有严重闭锁性，Wilson非协调元也有闭锁性，EAS单元和采用降阶积分的14节点单元能克服闭锁。单元测试和方形基础的承载力计算两个数值算例证实了分析的结果，为土体三维分析中选择有效可靠的单元提供依据。     

珠光体钢丝多道次拉拔成形过程中的应变路径分析

目的研究高强度珠光体钢丝冷拉大变形过程中应变路径的变化规律及其对力学性能的影响。方法运用网格重划分和场变量传递技术,建立钢丝多道次冷拉应变路径全纪录有限元模拟方法,预测钢丝由0.62 mm到0.09 mm的多道次冷拉过程应变路径的演变。结果 23道次冷拉变形后,钢丝的最大应变值可达到4.360。随着拉拔道次增加,最大与最小等效应变值之间的差值随之增大,由第1道次的0.028增大至第23道次的0.473。结论钢丝多道次拉拔过程中,各道次在心部到表层方向上的等效应变分布规律相同,均为先增大后减小;钢丝心部等效应变值最小,次表层处等效应变值最大。     

板的弹塑性弯曲有限元分析中的分层法

论述了板的弹塑性弯曲有限元分析方法,对屈服函数的选取作了分析,采用发展方法,着重分析了对板的弹塑性切性刚度矩阵的建立,所论述的分层计算方法对其它非线性板弯曲的有限元计算具有一定的参考价值。     

管材数控弯曲回弹规律的有限元分析

回弹是管材弯曲卸载后必然发生的现象,并严重影响弯曲管件的精度和管材弯曲生产的效率.成形参数对管材弯曲卸载后的回弹有重要的影响.为了研究成形参数对回弹角的影响,基于弹塑性有限元软件ANSYS建立了管材数控弯曲及回弹的有限元模型,以不锈钢管弯曲及回弹过程为典型研究对象,实验验证了所建立的有限元模型的可靠性,并分析了部分工艺和材料性能参数对管材数控弯曲回弹的影响规律.结果表明:回弹角随弯曲角、芯棒与管壁间隙及材料硬化系数的增大而增大,随材料硬化指数的增大而减小.     

板材多道次热轧的有限元连续模拟

为充分考虑各因素对板形的影响,建立了三维弹性等效空心辊模型,开发了有限元数据的参数化生成模块;自主编制了网格重划分及参数传递模块,并与有限元软件MARC相结合,显著节约了建模及计算时间,使多道次连续模拟成为可能;成功解决了计算过程中网格畸变带来的计算困难并实现了前后道次之间参数的连续性,最终实现了中厚板多道次热轧过程的...     

汽车轮胎的三维有限元结构分析

本文从轮胎内部材料微结构出发,建立三维分析模型,考虑轮胎大位移引起的几何非线性,轮胎各部位材料的物理非线性和拉压不同模量,考虑了轮胎与地面接触区域的可动性,通过一参数来提高预测接触区域的准确性,并用白光散斑干涉计量技术测定轮胎表面的大位移场,结果表明计算与实验结果是吻合的。     

顶层空旷多层砌体结构的弹塑性地震反应分析

将顶层空旷多层砌体结构简化为串并朕多质点分析模型，利用动力弹塑性时程分析方法对其进行了数值分析。系统地研究了顶层空旷多层砌体结构层数、顶层边墙与中柱刚度比和顶层横墙间距等参数变化时这种结构地震作用的一些变化规律。     

工艺参数对薄壁件多道次旋压变形均匀性的影响

目的研究成形工艺参数对薄壁件多道次旋压变形均匀性的影响。方法采用试验的方法,研究了双轮数控旋压成形铝合金薄壁件过程中,旋压间隙δ、进给率f和旋轮圆角半径R等关键工艺参数,对制件表面质量和壁厚均匀性的影响。结果 3个工艺参数都对制件表面质量和壁厚均匀性有影响。结论减小旋压间隙δ、采用较大的主轴转速S和较小的进给率f可提高零件的表面质量和尺寸精度。改善零件壁厚分布的均匀化程度,适当提高旋轮圆角半径R,也能使变形的均匀化程度提高。     

固定短芯棒拔管残余应力分布规律研究

为了研究固定短芯棒拔管残余应力的产生机理和分布规律,采用弹塑性有限元法模拟拉拔过程,讨论模具形状参数、拉拔变形参数、摩擦条件对残余应力的影响.结果表明,当模具半锥角α较小时,随着α的增加,残余应力增大;在减径率εs一定的条件下,随着减壁量ΔS的增加,钢管内外表面的残余应力逐渐减小,在ΔS一定而εs增加时,内外表面上残余应力呈先增大后减小变化趋势;同时,轴向残余应力随着拉拔速度v和摩擦系数μ的增加而增大.     

Discussion and calculation on welding residual longitudinal stress and plastic strain by finite element method

In recent years, some researchers have put forward the new viewpoint that the weld is merely formed during the cooling process, not concerned with the heating process. According to this view, it can be concluded that it is not the compressive but the tensile plastic strain that may remain in the weld. To analyze the formation mechanism of the longitudinal residual stress and plastic strain, finite element method (FEM) is employed in this paper to model the welding longitudinal residual stress and plastic strain. The calculation results show that both the residual compressive plastic strain and the tensile stress in the longitudinal direction can be found in the weld.     

Study on elastic-plastic component in indentation fatigue of sodalime glass

Fracture mechanics studies on glass by indentation has become predominant in recent times. Interest in it has become more prominent due to a large application of such materials in areas of engineering applications encountering fluctuating stresses induced thermally, mechanically or physically. However, glass subjected to repeated indentation at a point prior to crack initiation with subcritical loads phenomenological to metal fatigue has not been systematically investigated. Repeated indentation at a single point with different subcritical loads (0·1N, 0·15N, 0·25N, 0·50N, 1·0N) was performed till radial cracks occurred. The length of the diagonal was measured after each indentation, which was found to increase with indentation cycle eventually leading to crack initiation. This observation was analysed considering the elastic plastic component and the residual stress developed during each cycle. A mathematical model has been postulated to correlate the contribution of cumulative residual stress for crack initiation. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995.     

拉深比对304不锈钢圆筒件残余应力的影响

304不锈钢圆筒拉深件在其口部易发生纵向开裂,外壁残余拉应力过大是造成其纵向开裂的根本原因之一.本文结合有限元法分析不同拉深比所得圆筒拉深件的残余应力,用纳米压痕试验研究了拉深比对304不锈钢圆筒拉深件筒壁残余应力的影响.结果表明:304不锈钢圆筒拉深件外壁的残余拉应力从筒底到口部先增大后减小,最大残余应力出现在筒壁中部约60%筒壁高度处;纳米压痕测得拉深比为1.43、1.54、1.67和1.82拉深圆筒件筒壁的最大残余应力分别为391.87、745.30、793.74和1 013.1 MPa;最大残余应力随拉深比的增大而增大.与其他文献对比分析,此研究结果是正确可靠的.     

A rapid method for stress separation in two dimensional photoelastic models

Obtaining the individual stress components at internal points in a two dimensional photoelastic model is time consuming and requires considerable expertise. A rapid method has been developed for calculating the stress distribution along an axis of symmetry. An example is given to show that the results are sufficiently accurate for engineerng design purposes.     

Synchrotron diffraction measurement of residual stresses in friction stir welded 5383-H321 aluminium butt joints and their modification by fatigue cycling

This paper presents two‐dimensional information on the residual stresses in 8 mm 5383‐H321 aluminium plates joined by double pass (DP) friction stir welding (FSW). It considers the inherent variability in residual stress magnitudes along 0.5 m lengths of weld pass, and their modification under a sequence of applied fatigue loads. This represents one of a planned series of experiments aimed at illuminating the effects of fatigue cycling on residual stress fields. In this particular case, the magnitudes of the bending fatigue loads (R= 0.1) were chosen to correlate with the measured proof strengths of the weld metal (approximately 160 MPa) and the parent plate (approximately 260–270 MPa). In four‐point bend S–N tests at R= 0.1 on 40 mm wide FS welded specimens of this alloy and plate thickness, these peak stress levels correspond to lives of around 10⁵ cycles and 10⁷ cycles, respectively. Results from the work indicate that significant variability exists among welded plates in peak compressive stress magnitudes (a range of perhaps ?50 MPa to ?140 MPa), although peak tensile stresses were relatively low and more consistent (from around 0 to 30 MPa). Fatigue loading accentuates the peak‐to‐valley stress change and causes an overall translation of the stresses to become more positive. Peak tensile stresses increase several‐fold during fatigue cycling.     

Residual stress in pearlitic steel rods during progressively cold drawing measured by X-ray diffraction

This research aims to investigate the residual stress evolution in pearlitic steels during progressively cold drawing. To this end, pearlitic steel rods of 13 mm diameter are continuously cold-drawn to wires of 5.3 mm, and then the residual stresses of multi-pass drawing rods are evaluated by X-ray diffraction technique. The XRD results indicate that the residual stresses of pearlitic steel rods increase gradually with the growing of drawing strain, from stress-free of original rod to high tensile stress of 650 MPa in the last pass drawing wire.     

Rolling contact in railways: modelling, simulation and damage prediction

Various kinds of defects are induced by rolling contact on the rail track: kidney‐shaped cracking, shelling and nowadays squat and head checking, which are studied under the sponsorship of the French national railways company SNCF. Modelling of such defects requires the development of specific computational tools in order to evaluate, in the vicinity of the wheel–rail contact zone, the mechanical state (stress, plastic strain cycle and residual stress pattern), which is at the origin of the damages. Moreover, since the loadings induce multiaxial stress and strain states, it is necessary to use a multiaxial criterion to predict the occurrence of fatigue cracks. This review paper is devoted to the presentation of the main results of this research.     

三维壁板气动弹性颤振研究的微分求积方法

考虑几何非线性,采用活塞理论计算气动力,基于VonKarman薄板理论和线弹性应力应变关系,建立了三维薄板气动弹性微分方程,采用一种全新的方法即微分求积方法对方程进行了离散,并建立了气动弹性微分方程的微分求积格式,采用Lyapunov间接法确定了系统颤振边界,并分析了系统参数对颤振边界的影响,最后采用数值方法分析了各种系统参数对壁板颤振幅值的影响,得到了一些有意义的结果。     

Finite element analysis of three dimensional crack growth by the use of a boundary element sub model

A new automated method to model non-planar three dimensional crack growth is proposed which combines the advantages of both the boundary element method and the finite element method. The proposed method links the two methods by a submodelling strategy in which the solution of a global finite element model containing an approximation of the crack is interpolated to a much smaller boundary element model containing a fine discretization of the real crack. The method is validated through several numerical comparisons and by comparison to crack growth measured in a test specimen for an engineering structure.