材料参数对高强不锈钢管数控绕弯成形失稳起皱的影响

目的研究材料参数波动对管材数控绕弯成形失稳起皱的影响规律。方法基于ABAQUS有限元平台,建立了21-6-9高强不锈钢管数控绕弯成形过程三维弹塑性有限元模型,并验证了模型的可靠性;采用该模型模拟分析了材料参数波动对其数控绕弯成形过程失稳起皱的影响规律。结果随着厚向异性指数、屈服强度的增大或弹性模量、硬化指数的减小,弯管的起皱趋势增大,泊松比和强度系数对弯管起皱趋势的影响较小。结论材料参数对弯管起皱趋势影响的大小依次为:屈服强度、弹性模量、厚向异性指数、硬化指数、强度系数和泊松比。     

飞机复杂曲面蒙皮零件充液拉深技术研究

目的研究充液拉深工艺参数对飞机复杂曲面蒙皮零件成形质量的影响规律。方法以飞机灯罩蒙皮零件为研究对象,结合材料力学特性分析了零件的工艺性。基于破裂和起皱失稳条件理论研究了零件的加载工艺窗口,利用有限元方法分析了零起皱和破裂等缺陷,通过优化工艺参数和拉延筋参数获得了合格的构件。结果基于仿真优化结果,进行了模具设计和工艺验证实验,分析了实际充液拉深过程中缺陷产生的原因,为落差较大蒙皮零件的精密制造提供参考。结论对于具有多特征的复杂零部件,过渡曲面易产生起皱缺陷,仅通过调整液室压力或毛料尺寸的方法无法在保证不发生拉裂和贴模问题的前提下消除起皱缺陷。通过设置拉延筋来增加材料流动阻力、控制材料流动,可以消除过渡区域的起皱缺陷。     

微机模拟法研究纤维增强金属基复合材料拉伸断裂过程

本研究在统计分析及材料断裂力学分析的基础上,建立了长纤维增强金属基复合材料板材拉伸断裂过程的微计算机模拟方法。用该方法得到的模拟结果与已有实测结果吻合良好,从而初步证实了分析模型及其模拟程序系统的有效性。     

1100铝合金双滚轮滚压包边模拟及实验研究

目的 研究双滚轮滚压包边工艺在1100铝合金包边成形中应用的可行性。方法 结合有限元模拟和L16(45)的正交模拟试验,研究1100铝合金双滚轮滚压包边过程中翻边高度、TCP-RTP距离、滚轮半径、圆角大小及滚压速度等因素对包边成形情况的影响规律,以及各因素对波浪起皱量及伸缩量的影响趋势,分析缺陷产生机理。结果 各工艺参数对波浪起皱量和伸缩量的影响显著性排序分别为：翻边高度＞TCP-RTP值＞滚轮半径＞圆角半径＞滚压速度;圆角半径＞滚压速度＞翻边高度＞滚轮半径＞TCP-RTP值。双滚轮滚压包边中使1100铝合金板材产生波浪起皱和伸缩量的临界应力分别为30和20 MPa。结论 根据正交试验结果选取最优参数组合进行模拟和实验,结果表明实验结果波浪起皱系数与伸缩系数分别为4.20%和4.98%,成形质量较高,证明了双滚轮滚压包边的工艺合理性。     

TA1纯钛微型杯件软模微拉深成形工艺研究

目的 提高现有微成形工艺的可成形性,解决薄板易破裂等缺陷,探究薄板软模微拉深成形工艺的工艺参数对成形性的影响,致力于制造具有更大拉深比的微型杯件。方法 采用退火后的纯钛薄板作为原始板材,设计了薄板的软模微拉深成形模具进行实验。实验中探讨了工艺参数和材料参数对微型杯件极限拉伸比的影响。工艺参数包括压边力、橡胶性能和润滑方式,材料参数主要是晶粒尺寸。结果 通过控制压边力能够避免微拉深工艺中的缺陷。压边力过低会导致法兰区域起皱,压边力过高会导致上圆角部位破裂。采用刚度系数为72 N/mm的压边弹簧能够有效避免起皱和破裂。选用硬度为65HA的聚氨酯橡胶能够成形出极限拉深比最大（为2.64）的纯钛微型杯件。软模微拉深工艺必须采用有效的润滑方式来提高板材的流动行为。采用蓖麻油润滑能够有效避免微型杯件的破裂缺陷。板材的晶粒尺寸对极限拉深比的影响是最强烈的。晶粒尺寸为8.4 μm的纯钛薄板能够制造出极限拉深比为2.64的微型杯件,而随着晶粒尺寸的增大,微型杯件的极限拉深比显著下降。结论 通过软模微拉深工艺并且采用合适的工艺参数成功制备了极限拉深比为2.64的微型杯件,与现有工艺相比,所获得的微型杯件的极限拉深比提高了20%。     

台阶盒形件起皱和开裂改善

目的 改善台阶盒形件拉深成形时凸缘区起皱和圆角区开裂的缺陷。方法 理论分析了起皱和开裂产生的原因,利用有限元模拟分析了压边力大小、凹模运行方式和板料形状对台阶盒形件拉深成形的影响,采用实验验证了有限元模拟结果的准确性。结果 长方形板料拉深成形时,4个角部相比直边部位流动阻力更大,直边部位材料过度向模具型腔内流动,造成凸缘区周向压应力过大,进而引起起皱,当零件拉深深度较大时,圆角部位材料变形剧烈且材料流动不均匀,极易产生开裂;采用20 kN的压边力、梯形的凹模向下运行方式和类椭圆形板料的工艺参数可以控制材料流动,使板料变形均匀并改善凸缘区起皱和圆角区开裂缺陷。结论 有限元模拟可为冲裁工艺参数的选取提供理论指导。     

基于响应面法的平底筒形件充液成形工艺参数优化

目的在板材充液成形过程中,压边间隙与最大液室压力的数值选取具有较大的随机性,同时由于材料的不同、坯料形状的差异,需要进行大量的仿真模拟来寻求优化结果。对于尺寸大、形状复杂的零件,模拟时间较长,工作效率较低。基于响应面法,构造压边间隙、最大液室压力与最大减薄率之间的响应面模型。方法以法兰外缘起皱高度为约束条件,通过Design-Expert软件求解最优结果,将最优结果进行了有限元模拟。结果模拟结果、响应值与试验结果相吻合。结论响应面法能够较好地用于预测和优化板材充液成形过程关键工艺参数。     

模拟参数对橡皮成形TB5钛合金凸弯边起皱模拟的影响

目的 针对高强钛合金成形时遇到的起皱问题,引入有限元模拟技术。方法 利用MATLAB对模拟结果的峰高进行量化。以橡皮成形TB5钛合金的凸弯边为考察对象,对板料初始网格、加载时间、加载方式及与橡皮接触的摩擦等模拟参数建立正交设计表L9(34),应用ABAQUS/Explicit模拟起皱,全面研究模拟参数对皱纹的影响。结果 研究全面评估了模拟参数对起皱模拟结果的影响,板料网格是影响起皱的最重要因素。结论 试验证明了TB5钛合金拥有良好的冷成形性能,但在成形过程中有起皱问题。     

2A12 铝合金平底筒形件充液拉深数值模拟研究

目的研究工艺参数对2A12铝合金平底筒形件充液拉深成形的影响规律。方法采用数值模拟方法,研究了液室压力加载路径、成形液室压力、压边力和压边间隙对板材充液拉深成形效果的影响。结果获得了充液拉深成形的失效形式,以及不同工艺参数下零件壁厚减薄率的变化规律。成形前期,液室压力不宜过大,最大液室压力在10~25 MPa之间,压边间隙在1.05~1.15mm之内,可有效避免零件过度减薄和法兰起皱。结论合理的液室压力加载路径和压边间隙,可以有效地控制零件法兰区起皱,防止凸模圆角处破裂。     

深冷处理消除铝合金板材残余应力的建模与仿真

介绍了用(热)弹塑有限元技术对铝合金板材深冷处理过程进行建模与仿真的基本原理.基于实验研究探讨了深冷处理数值模拟所需的7075铝合金材料的物性参数.运用ABAQUS6.5有限元软件,对7075铝合金板材深冷处理过程瞬态温度场与应力场进行了数值模拟.数值模拟得到的残余应力值与已发表文献的实验结果比较一致.最后分析了不同厚度铝合金板材的深冷处理应力消除效果.     

THE RANDOMNESS OF FATIGUE CRACK GROWTH UNDER CONSTANT-AMPLITUDE LOADS

An analysis of fatigue crack growth from an statistical point of view has been carried out. Eighteen pre-cracked specimens obtained from the same sheet of aluminium alloy were subjected to identical load and environmental conditions. Tests were conducted under constant-amplitude loads in order to isolate the effect of material randomness. The experimental results exhibited two different types of dispersion: one showed as a change in the mean growth rate between tests and the other as nonuniform growth in the same specimen. At a subsequent stage, the statistical distribution of the experimental results was studied and a theoretical model was developed to account for the growth pattern observed. The proposed model uses a growth law comprising random parameters to account for the low-frequency component (slow changes). The comparison of the performance of two different laws, viz. the Paris-Erdogan law and the cubic law, is presented. Both were tested on the assumption of randomness in two of their fitting parameters. In addition to the above-mentioned law, the model uses a stochastic log-normal process to model the high-frequency component (rapid changes). The parameters for this process were determined by time series analysis of fatigue crack growth rate data.     

隔声材料排布顺序对复合板材隔声特性的影响

对高速列车平顶组合结构进行隔声测试,调换其中2块隔声垫的前后位置后,平顶组合结构隔声特性发生显著改变。针对这一问题,基于统计能量法探究双层隔声复合板材中材料排布顺序对于整体结构隔声特性的影响规律,分析该现象产生的原因;接着,进一步利用基于统计能量法的隔声预测模型对三层隔声复合板材中材料排布顺序对整体隔声特性的影响进行延伸探究。结果表明:对于双层复合结构,当两种隔声材料的种类一定时,将隔声量较大的材料置于近声源端,将隔声量较小的置于远声源端,对整体结构隔声量的提升最显著,主要提升低频隔声量;对于三层复合结构,情况较为复杂,其中,将隔声量最大的材料置于近声源端,将隔声量次大的材料置于远声源端,将隔声量最小的材料置于中间时,对整体结构隔声量的提升最显著,且同时提升低频和中频隔声量。研究内容对于工程中复合材料隔声性能的进一步改善有借鉴意义。     

Image analysis of sheet metal surfaces

The analysis of a sheet metal surface is essential to describe phenomena like friction or varnishing ability. As 2D measurements are not sufficient for a full understanding of the surface performance, 3D image analysis methods are performed to characterise the topography of rough surfaces. In this paper some investigations are presented concerning the lubrication area and the material cut spots of a St14 sheet surface. To consider relevant aspects for metal forming, roughness measurements have been performed with elongated and loaded sheets. The evolution of the surface structure is essential to understand effects like the lubricated friction or the contact between the paint and rough surfaces.     

Plane strain transversely anisotropic analysis in sheet metal forming simulation using 6-component Barlat yield function

In most FEM codes, the isotropic-elastic and transversely anisotropic-elastoplastic model using Hill??s yield function has been widely adopted in 3D shell elements (modified to meet the plane stress condition) and 3D solid elements. However, when the 4-node quadrilateral plane strain or axisymmetric element is used for 2D sheet metal forming simulation, the above transversely anisotropic Hill model is not available in some FEM code like Ls-Dyna. A novel approach for explicit analysis of transversely anisotropic 2D sheet metal forming using 6-component Barlat yield function is elaborated in detail in this paper, the related formula between the material anisotropic coefficients in Barlat yield function and the Lankford parameters are derived directly. Numerical 2D results obtained from the novel approach fit well with the 3D solution.     

2024－T3铝合金包铝薄板抗疲劳特性DFR截止值的试验研究

用一种新的ＤＦＲ概念比较国产和美国产２０２４－Ｔ３铝合金包铝薄板的抗疲劳特性，试验分析认为，在相同试验条件下，两国产２０２４－Ｔ３包铝薄板抗疲劳特性相当，没有显著差异。     

Progressive damage modelling of SMC composite materials

The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation.     

Finite Element Analysis of sheet metal bending process to predict the springback

Springback remains a major concern in sheet metal forming process. Springback, shape discrepancy between fully loaded and unloaded configuration due to elastic recovery of material, is mainly affected by geometrical parameters, material properties of sheet and lubrication condition between the blank and the tool. A total-elastic–incremental-plastic (TEIP) algorithm, for large deformation and large rotational problems, was incorporated in indigenous Finite Element software. This software was used to predict the springback in a typical sheet metal bending process and to investigate the influence of these parameters on springback. The results of simulation are validated with own experiments and published experimental results.     

Experimental and finite element study on the spring back of double curved aluminum/polypropylene/aluminum sandwich sheet

The most prominent feature of sheet material forming process is an elastic recovery phenomenon during unloading which leads to spring back and side wall curl. Metal–polymer laminate sheets are emerging materials that have many potential applications. Therefore evaluation of spring back is mandatory for production of precise products from these new sheet materials. In this paper, the results of spring back evaluation of AA3105/polypropylene/AA3105 sandwich sheet materials have been presented after being subjected to double-curvature forming. Numerical simulation of double-curvature forming process has also been carried out using both implicit and explicit finite element programs. The influences of some geometrical parameters on spring back such as thickness of sandwich sheet and tool curvatures radii have been evaluated.     

Investigation of the effect of temper rolling on the texture evolution and mechanical behavior of IF steels using multiscale simulation

The main objective of this study is to simulate texture and deformation during the temper-rolling process. To this end, a rate-independent crystal plasticity model, based on the self-consistent scale-transition scheme, is adopted to predict texture evolution and deformation heterogeneity during temper-rolling process. For computational efficiency, a decoupled analysis is considered between the polycrystalline plasticity model and the finite element analysis for the temper rolling. The elasto-plastic finite element analysis is first carried out to determine the history of velocity gradient during the numerical simulation of temper rolling. The thus calculated velocity gradient history is subsequently applied to the polycrystalline plasticity model. By following some appropriately selected strain paths (i.e., streamlines) along the rolling process, one can predict the texture evolution of the material at the half thickness of the sheet metal as well as other parameters related to its microstructure. The numerical results obtained by the proposed strategy are compared with experimental data in the case of IF steels.     

A probabilistic model for spatial distribution of material properties

This paper deals with probabilistic characteristics of nonhomogeneous properties of structural materials such as structural ceramics and proposes a probabilistic model that can be used for digital-analytical simulation of such material properties. The model will be compatible with the finite element method and therefore extremely useful for the analysis and design of nonhomogeneous structural systems. A technique is also presented to consider simultaneously random variations of two material properties. A particular emphasis is placed, however, on the probabilistic model for spatial variation of material strength which results in a corresponding statistical size effect. The principal idea lies in the interpretation that the material strength is a random function of the space variables. This interpretation together with a digital simulation technique of random function makes it possible to demonstrate the statistical size effect in terms of numerical examples. Specific examples considered here correspond to hot pressed silicone nitride for whch some experimental results are available.