两端弹性约束时点焊箱型薄壁构件的翘曲扭转特性研究

主要研究了在两端受到弹性约束时,点焊双帽箱型横截面薄壁构件的扭转特性,并得到一些有用的结论:当对杆端的翘曲进行约束时,剪力主要会通过构件中部的焊点来承受;扭转刚度比会随着焊点间距的增加而增加;扭转刚度与截面形状(有焊点边长与无焊点边长的尺寸比b/a)有关,具有焊点的边长大于没有焊点的边长的构件时,其扭转刚度较大。另外,刚度比与弹性翘曲约束系数具有一定的关系,弹性约束系数越大,其刚度比也越大。在对实际点焊薄壁结构进行设计时,圣维南扭转刚度和翘曲扭转刚度是点焊薄壁构件的两个重要指标,对它的研究会对此类构件的设计和利用打下理论基础。     

点焊薄壁构件受集中载荷或均布载荷作用时的翘曲扭转研究

基于点焊薄壁构件翘曲扭转理论，分析和研究点焊双帽箱型横截面薄壁构件中部有集中载荷和整个构件长度上有均匀分布载荷作用时的扭转变形特性。进行数值仿真发现，在构件中部受集中力偶作用时，扭转刚度比与载荷作用点有关，在集中力偶作用附近流过焊点的剪应力很小，并作用点左右两侧的剪应力方向相反；在整个构件长度上受均匀分布力偶作用时，只要两端不约束翘曲，扭转刚度比保持不变等。     

双帽箱型点焊薄壁构件的局部翘曲分析

针对汽车上广泛使用的箱型点焊薄壁构件，研究在考虑焊点处的弹性特性基础上，对箱型点焊薄壁构件受扭矩时焊点处的局部翘曲变形进行分析研究，提出一种计算局部变形的近似方法。把扭矩转换成通过焊点的剪力，此剪力又由置换剪力和置换力偶矩代替，然后计算相应的局部翘曲。计算结果与运用平面薄板理论的平面应力问题和平面弯曲问题的弹性力学解之间具有较好的对应关系和精度。     

异壁厚点焊箱形截面薄壁梁的局部翘曲和扭转刚度分析

针对在汽车车体结构中广泛使用的、具有不同壁厚（也即异壁厚）的单帽和双帽对口型点焊箱形截面薄壁构件进行一系列的研究.当点焊薄壁构件受到转矩作用时,把转矩在焊点处用置换剪力与置换力偶矩进行替换,然后对异壁厚构件的局部翘曲和扭转刚度特性进行详细研究分析.当对口型点焊薄壁构件为异壁厚时,为得到具有一定扭转刚度的点焊构件,其焊点间隔和板材厚度的选择范围比相同壁厚时具有较大的提高;当质量保持不变而只改变板材厚度时,可以得到不同扭转刚度的板材厚度最大值组合,它会随着翼缘板材的位置而变化.这些结论在实际工程中可以根据不同要求有选择地加以利用.     

类椭圆截面吊臂的约束扭转特性研究

综合分析常见椭圆截面和大圆角矩形截面大吨位起重机吊臂结构力学性能,提出了一种类椭圆截面起重机吊臂结构。根据吊臂旋转平面受力状态,可将基本臂简化为闭口曲边截面悬臂薄壁梁力学模型。然后基于乌曼斯基理论,推导了该力学模型的约束扭转特性计算公式。并基于MSC.PATRAN/NASTRAN有限元数值分析验证了理论计算公式的正确性。通过算例分析,获取了一类椭圆截面吊臂的约束扭转翘曲正应力和翘曲位移等重要分析参数。研究表明,推导的理论公式可为类椭圆起重机吊臂的约束扭转分析提供一种简便可行的计算方法。     

考虑翘曲影响的Bernoulli-Euler薄壁梁的弯扭耦合振动

通过直接求解均匀薄壁梁单元弯扭耦合振动的运动偏微分方程，推导其自由振动时的精确动态传递矩阵。采用考虑翘曲影响的Bernoulli-Euler梁理论，且假定薄壁梁单元的横截面是单对称的。动态传递矩阵可以用于计算薄壁梁集合体的精确固有频率和模态形状。针对两个薄壁梁算例，采用自动Muller法和结合频率扫描法的二分法求解频率特征方程，并讨论翘曲刚度对弯扭耦合：Bernoulli-Euler薄壁梁固有频率的影响。数值结果验证了本文方法的精确性和有效性，并指出翘曲刚度可以显著改变薄壁开口截面梁的固有频率。     

扭转梁扭转刚度的理论计算方法研究

基于约束扭转理论对汽车后扭转梁的扭转刚度进行了计算,并采用线刚度,即单位外力作用下的轮心位移作为评价指标。在横梁几乎提供全部刚度的前提下,根据受力分析和几何关系,得到了横梁所受扭转力矩和轮心位移的计算公式。总结了典型的横梁截面形式,并给出了常用的扭转截面常数算式,针对简化后的主梁截面,利用薄壁结构力学推导了翘曲截面常数的计算公式。根据薄壁件的约束扭转理论,对主梁端面扭转角进行了推导,从而得出了不带扭杆扭转梁的刚度计算公式,并推广到了带扭杆的扭转梁,且对各个因子的影响程度进行了对比。和试验结果相比,考虑约束扭转时的计算结果与测量值的偏差在7.4%~10.4%之间,远优于考虑自由扭转时的计算结果。在零件概念设计阶段,利用扭转梁的外阔尺寸参数和截面特性参数,可以尽早地预测设计结果,显著缩短开发周期。     

基于Moldflow的薄壁件翘曲变形研究

翘曲变形是注塑件的主要缺陷,利用电器后盖对薄壁成型工艺进行研究。采用Moldflow软件对塑件成型过程进行数值模拟,研究了保压压力、塑件材料对注塑件翘曲变形的影响。对薄壁注塑件的数值仿真模拟结果进行统计分析,并且对影响注塑翘曲变形量的工艺参数进行综合分析,得到最优的工艺参数组合。研究结果表明:最佳的工艺参数组合可以使得塑件翘曲量变得最小。     

汽车纵梁冲压回弹的数值模拟研究

载重汽车车架纵梁是汽车最重要的承载部件之一,纵梁在压弯过程中,由于所用钢板强度较高,制件很长,冲压成形卸载后发生的U型截面侧壁的外扩和内缩(横向回弹)、U型截面的扭转以及纵向端头翘曲(纵向回弹)等问题,造成车架铆接后,整体形位尺寸超差,车架的对角线尺寸超差.这些超差严重影响了生产效率和汽车的整车可靠性.为消除以上问题,保证汽车装配的顺利进行,提高产品品质、提高产品的可靠性,针对上述问题利用DYNAFORM数值模拟软件进行了研究分析,找出了纵梁的回弹规律,并根据计算结果提出了模具改进方案.     

集装箱船扭转强度分析

纵向构件的设计不仅需要满足总纵强度的要求,更需要能承受扭转载荷的作用。本集装箱船型甲板大开口的特点导致了船体扭转刚度较低,同时,随着其主尺度的不断增加,船体各种载荷也急剧增大。因此,船体的主要文利用圣维南扭转理论(Saint Venant Torsion)去解决任意截面棱柱的扭转问题的弹性理论方法,并利用BV MARS 2000来进行集装箱船总体边界条件的比较研究,在对生成的扭转翘曲应力与合成翘曲应力图进行相关分析,从而得出距尾部不同距离的翘曲应力分布情况,从而为船体的主要纵向构件的设计不仅需要满足总纵强度的要求,更需要能承受扭转载荷的作用而提供一定的参考价值,为减少船体抗扭能力削弱而设计出较佳的船型主尺度提供设计的相关依据。     

Secondary torsional moment deformation effect by BEM

In this paper, a boundary element method is developed for the nonuniform torsion of simply or multiply connected bars of doubly symmetrical arbitrary constant cross section, taking into account secondary torsional moment deformation effect. The bar is subjected to arbitrarily distributed or concentrated twisting and warping moments, while its edges are restrained by the most general torsional boundary conditions. To account for secondary shear deformations, the concept of shear deformation coefficient is used leading to a secondary torsion constant. Four boundary value problems with respect to the variable along the bar primary and secondary angles of twist and to the primary and secondary warping functions are formulated and solved employing a pure BEM approach, that is only boundary discretization is used. The warping and the primary torsion constants are evaluated employing the aforementioned primary and secondary warping functions using only boundary integration, while the secondary torsion constant is computed employing an effective automatic domain integration. Numerical examples with great practical interest are worked out to illustrate the efficiency and the range of applications of the developed method. The influence of the secondary torsional moment deformation effect of closed shaped cross sections is verified, while the accuracy of the proposed numerical procedure for the calculation of the secondary torsion constant compared with a FEM one is noteworthy.     

A hybrid formulation for determining torsion and warping constants

Theoretically, the torsion constant of a bar subjected to a torque can be calculated irrespective of its cross-sectional shape, either with a potential energy (displacement) or with a complementary energy (stress function) formulation. The potential energy formulation, however, also provides the so-called warping constant, which may be important in the case of thin-walled sections, but the complementary energy formulation does not. On the other hand, the complementary energy formulation leads to simple analytical expressions for the torsion constant of thin-walled sections, while a finite element calculation based on potential energy requires a relatively large number of elements to obtain comparable results.Since hybrid formulations combine some potential energy features with complementary ones, a hybrid formulation was derived for the torsion problem, with the purpose of combining the advantages of both—i.e. an ultimate displacement formulation and possibly greater accuracy. Both the torsion and warping constants can be calculated consistently with this formulation.The hybrid variational formulation that was derived, together with the general discretization procedure, can be used to formulate finite elements for calculating the torsional constants for all kinds of cross-section, whether solid or thin-walled, open or closed, symmetrical or unsymmetrical. The initial application, to rectangular solid cross-sections, resulted in an improved warping constant.     

Aeroelastic stability analysis of hingeless rotor blades with composite flexures

The flap-lag-torsion coupled aeroelastic behavior of a hingeless rotor blade with composite flexures in hovering flight has been investigated by using the finite element method. The quasi-steady strip theory with dynamic inflow effects is used to obtain the aerodynamic loads acting on the blade. The governing differential equations of motion undergoing moderately large displacements and rotations are derived using the Hamilton’s principle. The flexures used in the present model are composed of two composite plates which are rigidly attached together. The lead-lag flexure is located inboard of the flap flexure. A mixed warping model that combines the St. Venant torsion and the Vlasov torsion is developed to describe the twist behavior of the composite flexure. Numerical simulations are carried out to correlate the present results with experimental test data and also to identify the effects of structural couplings of the composite flexures on the aeroelastic stability of the blade. The prediction results agree well with other experimental data. The effects of elastic coupling such as pitch-flap, pitch-lag, and flap-lag couplings on the stability behavior of the composite blades are also investigated.     

Fatigue strength assessment of spot-welded lap joint using strain energy density factor

One of the recent issues in design of the spot-welded structure such as the automobile body is to develop an economical prediction method of the fatigue design criterion without additional fatigue test. In this paper, as one of basic investigation for developing such methods, fracture mechanical approach was investigated. First, the Mode I, Mode II and Mode III, stress intensity factors were analyzed. Second, strain energy density factor (S) synthetically including them was calculated. And finally, in order to decide the systematic fatigue design criterion by using this strain energy density factor, fatigue data of the δP-N _f obtained on the various in-plane bending type spot-welded lap joints were systematically re-arranged in the °S-N _f relation. And its utility and reliability were verified by the theory of Weibull probability distribution function. The reliability of the proposed fatigue life prediction value at 10⁷ cycles by the strain energy density factor was estimated by 85%. Therefore, it is possible to decide the fatigue design criterion of spot-welded lap joint instead of the δP-N _f relation.     

钢板点焊翘曲缺陷对平均应力强度因子的影响

车身焊接易造成翘曲缺陷,显著影响其疲劳寿命。针对翘曲缺陷对平均应力强度因子的影响,基于力学理论和有限元法,将焊点模型模块化,对比分析仿真得出的合格焊点平均应力强度因子ΔKqua与翘曲缺陷焊点平均应力强度因子ΔKdef。通过寻找影响因素及影响规律,提出翘曲因子C的概念并通过仿真验证其适用性。仿真分析与理论推导得出的平均应力强度因子间的平均误差小于6%。试验结果表明,经翘曲因子修正的翘曲缺陷焊点ΔKdef的平均准确率为84.6%。     

基于动态响应有限元模拟的点焊接头疲劳寿命预测

利用三维有限元模拟和动态响应试验对点焊接头疲劳裂纹萌生和扩展特性进行了研究。利用所模拟的裂纹长度和固有频率的关系,定义了点焊疲劳裂纹扩展的三个阶段。根据所定义的裂纹萌生阶段的定义,利用局部应力应变法预测了点焊接头的疲劳裂纹萌生寿命。结果表明,所预测的疲劳萌生寿命与试验结果相吻合。