金属板材无模渐进成形板厚变化仿真与实验研究

板厚变化是板材渐进成形工艺涉及的主要问题,与成形角度、层间距等工艺参数密切相关。针对成形角度分别为45°和60°的方锥件,结合数值模拟和实验结果证明余弦定理可用于预测成形零件的板材厚度,但预测值较实际值偏大。运用无模渐进成形有限元模型,分析了工具头尺寸和层间距对板材厚度变化的影响,结果表明大的工具头尺寸和小的层间距有助于提高板厚的均匀化程度,不同的工具头尺寸虽然导致板厚均匀区域大小有所差别,但最终的板厚尺寸趋于一致,随着层间距的增大,余弦定理的预测误差增大。

宽板弯曲成形过程中板厚变化精化模型

基于弹塑性力学基本理论,在考虑板材真实本构关系基础上建立了宽板板厚变化精细化模型。同时,借鉴分三层思想,较好地考虑了宽板在弯曲成形过程中部分纤维层应力反号过程,因此具有较好的精确性和较强的普适性。最后,以铝板为例进行分析,发现计算值和实验值吻合较好。本文研究成果为深入研究弯曲变形过程和科学制定弯曲成形工艺具有一定的理论价值和实用意义。

宽板弯曲成形过程中板厚变化精确解

基于弹塑性力学曲梁理论,分析宽板弯曲成形过程基本力学规律,推导了板厚变化精确解析解。在推导过程中,摒弃塑性体积不变假设,同时考虑弯曲成形过程中弹性变形过程,具有较强的精确性和普适性,研究成果为深入研究弯曲变形过程和科学制定弯曲成形工艺具有一定的理论价值和实用意义。

考虑板料厚度变化的圆孔翻边应力平衡微分方程及求解方法

考虑圆孔翻边过程中板料厚度变化,导出了一个新的圆孔翻边平衡微分方程式,并对圆孔翻边变形力计算公式进行修正。实验表明,修订后的圆孔翻边力公式的计算结果更接近于生产实际,且原理更为科学合理,具有较好的实用性。

金属板料单点渐进成形轨迹优化及模拟研究

表面质量差是金属板料渐进成形工艺的重要缺陷。针对曲面零件单点渐进成形表面质量差的问题,文章提出了一种基于零件截面曲线形状用增量弧长S0来控制增量步长Δz的方法,建立了Δz与增量弧长S0间的计算关系;以曲面零件为研究对象,与固定增量步长成形方法对比,利用有限元软件ANSYS/workbench模拟零件单点渐进成形过程,分析了S0对板料厚度变化和板料应变的影响。试验与模拟结果表明:该方法不仅有效改善了曲面零件成形后的表面质量,单件零件成形效率也明显提高,加工层数为30层时,成形效率提高19%,50层时,成形效率提高22%;优化方法得到的零件在平缓曲面处厚度更厚,该处零件厚度随着S0的增加而增加;优化方法导致的板料应变大于传统成形方法,且S0越小应变越均匀,但最终板料应变趋于一致。

数值模拟在摩托车油箱外壳体冲压成形中的应用研究

应用DYNAFORM软件对摩托车油箱外壳体冲压成形过程进行有限元数值模拟。针对实际生产中油箱外壳体材料厚度不均匀、局部变薄严重的现象,分析其变形特点及主要工艺参数对板料厚度变化的影响,确定了油箱外壳体冲压成形的三个主要工艺参数及模具调整过程中的修整原则。指出应先修整模具拉延筋高度,然后修整凹模圆角半径,再修整凸模圆角半径。生产实践表明,与传统设计的试模方法相比,采用有限元数值模拟方法,模具调试时间缩短75%,且得到的产品板料厚度均匀,刚性好,精度高。

缩口力的工程计算与试验验证

对薄壁筒形件在锥形凹模中缩口成形力的工程计算进行了分析研究,对Μ.Β.斯德洛日夫及Ε.Π.翁克索夫分别提出的圆筒形件缩口力计算方法进行了实例计算和实验。结果表明,由于两种方法都综合考虑板厚变化、加工硬化及摩擦等因素的影响,故计算结果十分接近,而且与实验数据相吻合。

缓面零件单点渐进成形刀具轨迹优化数值模拟

利用有限元软件ANSYS/workbench,以平缓曲面零件为例,模拟零件单点渐进成过程,研究了优化方法中增量角度Δθ对零件厚度、成形精度、等效应变等方面的影响,并与传统固定增量步长方法进行对比。结果表明:加工层数相同时,优化方法更有助于提高板厚,且零件壁厚随着增量角度Δθ的增加而增加;优化方法较明显的提高了零件底部成形精度,无论增量角度Δθ取值多少,零件底部都能充分成形,与实验结果相吻合;加工层数相同时,在相同区域优化方法导致的板料等效应变大于固定增量步长成形方法,Δθ越小应变越均匀,但两种方法最终的等效应变趋于一致。

Construction and solution of strain model along thickness of aluminum alloy plate under plastic deformation

A thickness strain model of aluminium alloy plate under plastic deformation,based on thin plate assumption was proposed.It is found that when ratio of stress fractions is constant during in-plane loading,ratios of strain components under various loading conditions are linearly related and these points of ratios form a η-η line.Under these simple loadings,strains in thickness direction can be easily calculated by the η-η line equation without integral and differential work.When the plate is under more complicated loading conditions,the thickness can be computed by the proposed optimization and piecewise calculation model.Validation computations indicate that the relative error of the results of the presented model is less than 0.75% compared with the proven theories and FE simulation.Therefore,the developed model can be applied to engineering calculation,e.g.pre-stretching analysis of aerospace aluminium thick plate,with acceptable accuracy.

Curling of New Concrete Pavement and Long-Term Performance

Curling results from the temperature differential across the concrete slab thickness and may induce undue stresses in newly placed slab. This study deals with the finite element （FE） analysis of curling, curling stresses, field measurement of curling on a newly built jointed plain concrete pavement, and comparison of its long-term performance using both Mechanistic-Empirical Pavement Design Guide （MEPDG） and HIPERPAVII software. The FE analysis was performed with a software program, ANSYS. The test section was modeled as a three-layer system with 300 mm concrete slab, 100 mm treated drainable base, and 150 mm lime-treated subgrade. All layers were assumed to be linear elastic. Temperature data was collected at five different depth locations across the concrete slab with digital data loggers. Curling was measured on five different days with a simple setup. The effect of temperature nonlinearities across the slab thickness was also examined. The results show that both upward and downward curling increase as the temperature differential increases. The maximum stress resulting from the combined effect of curling and traffic loading due to positive temperature differential is higher than that due to the negative temperature differential of the same magnitude. Since temperature differential has a significant influence on curling, both curling and curling stresses can be mitigated at an early age with temperature control, namely via enhanced curing. Both MEPDG and HIPERPAVII showed approximately the same performance for the PCC thickness ranging from 215 mm to 300 mm for this project. Performance prediction from HIPERPAVII is very sensitive to the change in PCC thickness less than 230 mm whereas MEPDG prediction is not as sensitive to the thickness change as with HIPERPAV 1I.

钢制车轮弯曲疲劳寿命的影响因素

弯曲疲劳寿命是钢制车轮的一项重要性能指标,但制造过程中的过盈配合和轮辐板厚变化对车轮疲劳寿命的影响规律尚不清楚。本文通过测定轮辐板厚变化规律,并建立考虑过盈配合和轮辐板厚变化的钢制车轮弯曲疲劳有限元模型,比较了是否考虑这两种因素对车轮疲劳热点位置应力水平的影响,最后采用比例双轴疲劳方法预测车轮疲劳寿命。结果表明,过盈配合及轮辐板厚变化均会带来车轮弯曲疲劳寿命的下降,在有限元分析中不可忽略。