基于六边界优化角度函数的多道次辊弯成形研究

目的 为了提高多道次辊弯成形中板材的成形质量、减少板材纵向弯曲缺陷的产生,提出一种基于新型六边界成形角度分配函数的多道次辊弯成形优化方法。方法 根据翼缘端部水平面投影五次曲线推导出最优辊弯成形角度公式,结合COPRA研究板件峰值纵向应变,以确定最佳成形角度分配区间;在相同条件下,利用Abaquse模拟与实验研究不同成形角度对帽形件辊弯成形纵向弯曲缺陷的影响,并分析辊弯成形工艺参数对板材辊弯过程中应力-应变的影响。结果 新型六边界成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷;应力随着成形角度增量的增加而增大,等效塑性应变随成形角度和成形角度增量的增加而增加;实验与模拟结果基本吻合,验证了模拟结果的正确性。结论 优化成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷,为提高辊弯工艺精度与板材质量提供一定的理论指导。     

超高强QP980钢冲压成形性能

目的研究宝钢新一代先进高强钢QP980与第一代先进高强钢DP980的冲压成形性能。方法采用单向拉伸、光学应变分析和帽型拉弯成形等试验方法,分析两种超高强钢在加工硬化、成形极限、拉弯成形侧壁减薄和回弹等性能特性。结果 QP980的伸长率达到21.6%,与DP980钢相比有更高的强塑积,在变形过程中能够维持较高的瞬时n值,进而提高了材料的成形极限。帽型拉弯试验中,在不同的流入距离条件下,QP980钢的侧壁减薄率均低于DP980钢。在不同压边力条件下,QP980(厚度1.0 mm)材料的回弹量大于DP980(厚度1.2 mm)材料。结论 QP980在梁型件成形过程中具有优良的抗减薄特性,采用QP980钢进行冲压成形时应考虑比同级别DP980钢更大的回弹补偿量,或者采用更大变形量的工艺设计。     

980 MPa先进高强钢材料在门槛加强梁上的辊压应用

目的为获得980 MPa级别不同先进高强钢材料在辊压零件上应用时的差异,研究典型980 MPa先进高强钢的辊压成形特性。方法采用调研和统计方法获得门槛辊压用材的主流强度与钢种,基于三点弯曲的实验方法,获得了980 MPa先进高强钢材料在指定角度和弯曲半径下的回弹特性,针对典型的门槛加强梁零件,采用CAE方法评估材料应用的可行性。结果门槛零件980 MPa级别所采用的主要先进刚强钢钢种为双相钢(DP)和马氏体钢(MS),在相对弯曲半径比R/t=2.5的情况下,980DP回弹角度最小,980QP次之,980MS最大;早期模具回弹补偿设计时对于90°圆角可给予11°~14°的回弹过弯角度;成形过程中有可能出现边波缺陷,需优化辊压成形变形过程。结论 980 MPa先进高强钢材料在应用于辊压零件时,应在设计阶段充分考虑材料回弹特性,同时变形过程应合理,避免产生边波等质量缺陷。     

型材拉弯的力学与回弹分析

回弹是弯曲成形中普遍存在的现象,是由卸载过程中内力重新分布引起的,回弹的存在直接影响弯曲件的成形精度.本文针对转台拉弯成形过程,对等边型材等曲率拉弯进行了应力-应变分析,并按照卸载预拉力与不卸载预拉力两种情况对工件回弹进行了研究与探讨,得到两组半径回弹率理论曲线.通过与试验结果对比,不卸载拉力计算的结果与试验值比较吻合.     

双金属复合板材辊式矫直的数值模型

将弯曲分层矫直数值计算和实验验证相结合,研究了双金属复合板材辊式矫直过程中的连续弯曲变形和力能参数。结果表明,使用弯曲分层矫直计算模型是计算双金属复合板材矫直过程的有效方法,分层算法的结果与实验数据有较好的一致性;双金属复合板材弯曲应变的中性层与几何中间层产生偏离,中性层位置随弯曲程度和材料比例而变化;同时,由于材料的力学性能不同,在同一弯曲单元内各组元材料的塑性层比例也不同;计算模型所给出的在双金属复合板材矫直过程中应力应变的演化,与单一材料有明显的不同;在不考虑原始曲率的前提下,矫后残余应力随着弯曲单元的增加而减小。     

基于成形角度分配优化函数的辊弯成形边波及纵向弯曲缺陷研究

目的 研究板材辊弯成形中弯曲角的分配方式,改善辊弯过程中出现的边波和纵向弯曲等各种缺陷,提高成形精度与质量.方法 以小截面型材帽形辊弯件为研究对象,首先提出五边界条件成形角分配函数,并进行成形角度优化,得到最优的成形角分配方法.其次研究各弯曲角度分配方式对板材产生的主要缺陷如边波及纵向弯曲的影响规律,并进行辊弯成形实验验证.结果 经过实验验证基于四边界条件的辊弯峰值纵向应变从4.15％降低到基于五边界条件的1.18％.验证了θN/3=33％×θ0时辊弯成形角度分配的合理性.结论 基于优化的弯曲角分配方式的纵向应变、翘曲波动量和偏差值、最大高度偏差都小于其他分配方式的相应值,表现出其在成形工艺上的优越性.研究结果为合理设计类似帽形件或复杂截面形件的辊弯工艺提供一定的理论指导.     

理想弹塑性材料弯曲回弹分析及回弹弯矩计算

分析了弯曲回弹应力应变变化过程,推导了矩形截面杆回弹弯矩、回弹曲率的计算公式(14)、(11);发现经典纯弯曲理论确定回弹弯矩的方法与公式(14)比较存在较大理论误差。     

铝型材构件多点变曲率拉弯制件回弹研究

目的 研究不同预拉伸量和补拉伸量对矩形变曲率构件回弹的影响,以提高柔性三维拉弯成形精度。方法 用有限元模拟了矩形变曲率铝型材三维拉弯成形过程,并用试验验证了有限元模拟的精度,设计了5组不同的预拉伸量参数和补拉伸量进行三维拉弯成形有限元模拟。结果 大曲率和小曲率段试验和有限元模拟的回弹误差小于2 mm,表明有限元模拟分析可以很好地对矩形变曲率构件进行模拟。得出的数据表明预拉伸量对于小曲率弧段回弹的影响比对大曲率弧段的影响更大,当预拉伸量增长到1.0%以后,回弹的下降幅度不再明显;随着补拉伸量的增大,变曲率拉弯制件两段的回弹均得到较好的抑制,当补拉伸量为1.4%时,制件靠近夹钳端出现了缩颈缺陷,产生了较大的质量缺陷。结论 研究证明适量增加预拉量和补拉量能有效减小柔性三维拉弯成形回弹。     

铝合金-聚合物复合层板弯曲回弹理论分析

针对铝合金-聚合物复合层板弯曲回弹问题,分析了复合层板弯曲过程表面层铝板及中心层聚合物的变形特征,建立了复合层板平面应变纯弯曲回弹理论分析模型.采用建立的模型预测了复合层板纯弯曲过程回弹角变化,并与实验结果进行了对比,分析了聚合物层厚度及铝合金板材力学性能对回弹的影响规律.结果表明:随着中心聚合物层厚度的增加,复合层板回弹角降低;随着表面层铝板强度的降低,复合层板回弹角减小.理论预测结果与实验结果一致,说明了本文推导的理论模型的可靠性.     

单向EMC层合板非线性弯曲行为

对单向形状记忆聚合物复合材料(EMC)层合板在其基体玻璃化转变温度(T_g)之上的弯曲行为进行了研究。首先介绍了EMC层合板多约束弯曲变形实验, 并依据纤维微屈曲变形特征建立其形函数; 然后分析得出弯曲层合板的各分应变能及由其组成的总应变能; 在此基础上, 依据虚功原理, 通过总应变能推导出外力偶矩与曲率、 等效弯曲应变之间的非线性关系式。结果表明: 在EMC板的弯曲过程中, 中性层很快接近板的拉伸表面, 且中性层位置及板的弯曲行为对板的面内剪切模量非常敏感; 在板的初始弯曲阶段, 弯矩与曲率遵循传统单向板的线弹性弯曲理论; 而后随着曲率的增加, 弯矩与曲率关系遵循本研究所提出的非线性关系, 所得理论结果与EMC层合板的四点纯弯曲实验现象较为吻合。      

考虑双拉耦合的复合材料编织物各向异性超弹性本构模型

为了准确描述复合材料编织物的各向异性力学特性,首先,基于纤维增强复合材料连续介质力学理论提出了一种考虑纤维双拉耦合的复合材料编织物各向异性超弹性本构模型,该模型中单位体积的应变能被解耦为便于参数识别的纤维拉伸变形能、双拉耦合引起的挤压变形能和纤维间角度变化产生的剪切变形能;然后,给出了模型参数的确定方法,并通过拟合单轴拉伸、双轴拉伸和镜框剪切实验数据得到了本构模型参数;最后,利用该模型对双轴拉伸和镜框剪切实验进行了数值仿真,并将模拟结果与实验结果对比分析。结果表明:提出的本构模型适用于表征复合材料编织物在成型过程中由于大变形引起的非线性各向异性力学行为。所得结论表明提出的本构模型具有简单、实用的优点,且材料参数容易确定,可为复合材料编织物成型的数值模拟和工艺优化奠定理论基础。      

Curvature determination in the bending test of continuous fibre reinforcements

Bending deformation is one of the main deformation modes in the forming of continuous fibre reinforcements. It is very specific compared to the classical continuous materials. In most textile material forming simulation models, bending stiffness is neglected, but taking into account it would give a more accurate predication, particularly the shape of wrinkles. In the deformation, fibres constituting the reinforcement can slide to each other, resulting in the bending stiffness of reinforcement is not directly related to its in‐plane tensile modulus as the classical continuous materials. Consequently, it is necessary to determine the bending stiffness by the experimental method. A cantilever bending stiffness test approach was proposed to measure the bending stiffness of continuous fibre reinforcements. A CCD camera was used to take the bending deflection shape. To calculate the curvature of bending deflection curve, uniform quartic B‐spline curve was chosen. A detailed process of curvature calculating of deflection curve was given in this paper. A single bending test gives the bending moment as a function of curvature from zero to the maximum value. Bending tests were conducted to validate the capacity of the proposed approach. A smooth curvature plot along the bending deflection curve was obtained for different types of reinforcements, and the non‐linear bending deformation behaviour can be identified with the proposed bending test method.     

Non-linear compression stress-strain curve of pitch-based high modulus carbon fibre composites and structural responses

The longitudinal compression behaviour of unidirectional composites is studied to understand the role of the fibre compressive property in deformation and failure by systematically varying the tensile modulus of reinforcing high modulus carbon fibre. As the composites deform, their softness increases with increasing compressive strain, and the loading path is traced back when the load is removed. The intensity of softening is correlated to the fibre's tensile modulus and possible softening mechanisms are discussed in conjunction with fibre and matrix properties. Further, it is investigated how the non-linear stress-strain relation affects the stress and strain distributions and deformation when plates fabricated from these fibres are tested by the three-point bending test.     

The effect of pre-strain on the material behaviour and the Bauschinger effect in the bending of hot rolled and aged steel

Compression and bend tests were performed on an annealed and aged carbon steel that had been pre-strained by different amounts. A bending model was developed to analyse the bending response of the material. While the bending test results agreed well with some of the material trends found in previous studies focusing on the Bauschinger effect, an overly high reduction of the bending yield with pre-strain was observed. Calculation of the moment curvature diagram for the pre-strained material based on the tensile and compression test data using the analytical model did not fit the experimental curve. In the control of yield phenomena by the industrial processes of temper rolling, skin passing, tension levelling and roller levelling, the effectiveness of the treatment is usually judged from tensile testing after treatment. However, the present work shows that where the yield phenomena have been removed by pre-processing, that the tensile test will not predict the subsequent bending behaviour and that the bending test may provide greater insight. This may have important consequences in the study of cold roll forming where shape defects in the product are believed to originate from small strain forward and reverse bending deformations that will be strongly affected by the Bauschinger and yield effects.     

QP和DP钢面内成形性能与边部成形性能对比研究

目的 以宝钢生产的QP980、QP1180、DP980、DP1180 4种典型超高强钢材料为研究对象,进行QP、DP钢种材料面内与边部成形特性对比分析。方法 采用单向拉伸设备以及成形试验机,并结合DIC分析技术,对4种材料的力学性能、面内成形性及边部成形性进行试验研究。结果 与DP钢相比,同等强度级别QP钢的均匀延伸率及加工硬化系数均明显更高。在面内成形应变状态下,同等强度级别QP钢极限成形深度均明显大于DP钢的,但主、次应变大小差异不大。在边部成形应变状态下,同等强度级别QP、DP钢极限成形深度以及主、次应变大小均差异不大。QP、DP钢面内成形最大主应变均明显大于边部成形最大主应变。结论 与同强度级别DP钢相比,QP钢具有更高的均匀延伸率及加工硬化系数。QP钢材料的加工硬化系数高,材料内部协同变形能力强,面内成形性能明显优于DP钢材料的,但两者的边部成形性能差异不大;QP、DP钢材料能承受更大的面内主应变,受边部加工硬化及毛刺的影响,冲裁后,边部应变明显降低,在QP、DP超高强钢零件设计制造过程中,应尽可能避免边部发生较大的变形。     

带筋管整体成形力学条件研究

目的掌握带筋管整体成形的工艺条件。方法实验研究了带筋管坯整体成形易出现的缺陷形式,并分析了影响筋板整体成形的力学条件。结果实验结果表明:对于一定高径比范围内的带筋管可整体成形,但当高径比超出临界值时,易发生起皱和倾倒缺陷。起皱主要发正在曲率半径增大的部位,倾倒则发生在曲率半径减小的部位。起皱发生的原因是曲率半径增大导致筋板中性层外侧形成了较大的压应力,倾倒则是非均匀分布的拉应力形成了弯矩,进而导致了失稳的发生。结论带筋管内部施加支撑压力能同时降低压应力和弯矩,避免起皱和倾倒的发生。最终成功成形出了椭圆度为1.5和2的整体带筋管件。     

Study on springback from thermal-mechanical boundary condition imposed to V-bending and L-bending processes coupled with infrared rays local heating

This paper shows differences of thermal-mechanical boundary condition and springback between V-bending and L-bending processes. Although a recently conducted study showed that an infrared (IR) local heating method substantially reduces springback of dual-phase (DP) 980 steel sheet in V-bending, its application to L-bending, which is one of widely used forming processes in industrial applications, has not been sufficiently reported. In the L-bending experiment conducted in this work, springback does not sufficiently decrease as much as it does in the V-bending test, even though the sheet is deformed under the same temperature condition. For analysis of the difference in springback, thermo-elastic-plastic simulation for both V-bending and L-bending processes were conducted. The numerical analysis shows that the V-bending and L-banding processes have significantly different thermal and mechanical boundary conditions even though both processes go through a bending deformation. The differences in the boundary conditions have a strong effect on the thermal-mechanical behavior of the blank, so that the springback results are different between the two bending processes. Finally, it is also shown that the L-bending process requires a higher temperature condition than the V-bending process in order to sufficiently reduce springback.     

Ti-Cu层状复合材料静态载荷下变形与失效机制

利用水下爆炸焊接法制备了Ti-Cu层状复合材料。为研究Ti-Cu层状复合材料静态荷载下变形和失效机制，对Ti-Cu层状复合材料进行了室温条件下单轴拉伸实验和预制裂纹的三点弯曲实验，并与Ti单层板和Cu单层板进行对比分析，采用SEM观察断口形貌。通过拉伸和三点弯曲实验后的微观分析表明:在拉伸实验中，Ti-Cu层状复合材料的破坏是由于多方向应力耦合作用，加工硬化和界面效应使其拉伸强度远高于Ti单层板和Cu单层板；在预制裂纹的三点弯曲实验中，Ti-Cu层状复合材料的断裂是多重损伤失效相互作用的结果。Cu层形成大量的滑移带和变形带，Ti层产生大量的微裂纹，Ti-Cu层状复合材料由于多种损伤累积，形成一种特有的沿基体和界面交替传播的裂纹形态；相对于均质金属，Ti-Cu层状复合材料复杂的变形和失效行为是其力学性能提高的重要原因。