椭圆凹模液压胀形法制作成形极限图

本文介绍了一种利用椭圆凹模液压胀形制作成形极限图的方法，与通常采用的半球形凸模和圆柱凸模刚模胀形法相比，该方法更简便易行。     

大型弯头无模整体液压胀形新工艺的实验研究

提出了一种旨在用于大型管路系统的无模整体液压胀形制造弯头新工艺，成功地获得了一个厚度3．0mm，口径531．0mm，弯曲半径1310．0mm 的45．0°弯头实验件，其材料为Q235A该弯头初始结构为截面为正六边形的焊接扇形环壳结构，成形压力约为2．5MPa，实验表明，无模整体液压胀形法制造大型弯头造价低廉，简单可行。     

椭球壳液压胀形过程焊缝建模方式的研究

为了研究焊缝区域有限元建模方式对椭球壳胀形过程轴长变化规律的影响,提出3种焊缝建模方式:即完整焊缝模型,粗略焊缝模型与无焊缝模型。首先进行初始轴长比为1.8的椭球壳的液压胀形实验研究,得到轴长随内压力的变化规律。其次进行了3种建模方式的椭球壳胀形过程的数值模拟,对比数值模拟和实验过程轴长变化规律,分析建模方式对模拟精度的影响。结果表明:在变形初期,3种建模方式的模拟精度相近,尺寸偏差均小于4%;但是在变形中后期,无焊缝模型的模拟精度较差,最大尺寸偏差达15%;粗略焊缝模型和完整焊缝模型都能较好地预测轴长的变化规律,且尺寸偏差不超过5%。综上所述,粗略焊缝模型既能简化建模方式,又能较好地预测椭球壳胀形过程轴长的变化规律。     

扁球壳体的整体无模成形理论与实验

对不同轴比和不同瓣数的不锈钢扁球壳体进行了整体无模胀形成形实验研究及理论探讨.首先介绍了壳体成形的几何调节原理和材料调节原理,讨论了扁球壳体的应力分布特点和塑性变形顺序.对实验壳体的尺寸变化、变形过程中的内外表面应变分布、变形前后的壁厚变化规律进行了测试分析,探讨了各种壳体的趋球变形过程,壳体的长短轴变化趋势及塑性变形规律.实验证明,在封闭扁球壳体内塑性趋球规律仍然起作用,扁球无模液压整体成形是一项有发展前途的新工艺.     

不锈钢球壳无模液压胀形过程的有限元模拟

用弹塑情限元对不锈钢球壳液胀形过程进行了数值模拟，给出了胀形过程中壳体外形和焊变化规律，分析了应力应变及残余应力分布规律，并与试验结果进行了比较。     

不锈钢棒材无模成形温度场有限元模拟

采用有限元法对不锈钢棒材无模成形温度场进行了研究,并利用有限元分析软件对其进行了模拟,该模拟结果很好地反映了拉伸件在整个变形过程中的温度分布规律,为无模成形的进一步研究提供了可靠的依据.     

大型弯头液压成形的理论分析与实验研究

针对现有弯头制造中存在的问题 ,提出了用环壳液压胀形工艺制造弯头的方法 ,分析了环壳的应力特点 ,并给出了其最后的成形压力 .通过实验研究了环壳胀形过程中位移、应变的变化规律及成形后壳体的几何尺寸 ,并对其成形过程中的起皱进行了分析 .研究表明用液压液压胀形工艺制作弯头是可行的 .     

特种陶瓷材料胶态无模成形技术研究进展

综述了特种陶瓷胶态无模成形技术的研究进展.按照陶瓷浆料固结方式的不同对其进行了分类,分别为通过液体排除、物理或化学胶凝及颗粒流动进行陶瓷浆料固结的无模成形技术.对基于不同固结方式的各种成形方法的原理、工艺过程及应用进行了详细的分析.最后对陶瓷胶态无模成形技术的发展前景进行了展望.     

高精度17-4PH不锈钢隔碗拉深液压胀形复合成形工艺参数优化

目的 针对17-4PH不锈钢冷成形回弹大、贴模性差等问题,研究17-4PH不锈钢隔碗零件的拉深成形和液压胀形规律,确定隔碗零件拉深液压胀形复合成形的最佳工艺及参数.方法 利用有限元方法确定并优化了拉深预成形和液压胀形中的工艺参数.基于优化后的结果设计并制造了相关的模具,最终通过试验验证了有限元方法的有效性.结果 结合数...     

胶态无模快速成形陶瓷制件的应用及发展趋势

胶态无模快速成形陶瓷制件由于具有成形精度高、可机械加工能力好、能够制备大尺寸,复杂形状陶瓷制件等特点而备受关注。本文综述了近年来发展迅速的几种陶瓷胶态无模快速成型技术。着重介绍了各种技术的成形原理和方法、工艺过程及研究现状等,通过比较分析了不同快速成型制造技术在陶瓷零件制造中的特点及其存在的问题,对于陶瓷零件成形时不同成形技术的选择提出了一些参考意见,并结合课题组研究成果展望了胶态成形的发展趋势。     

Efficient and accurate simulation of the packaging forming process

To allow for large‐scale forming applications, such as converting paperboard into package containers, efficient and reliable numerical tools are needed. In finite element simulations of thin structures, elements including structural features are required to reduce the computational cost. Solid‐shell elements based on reduced integration with hourglass stabilization is an attractive choice. One advantage of this choice is the natural inclusion of the thickness, not present in standard degenerated shells, which is especially important for many problems involving contact. Furthermore, no restrictions are imposed on the constitutive models since the solid‐shell element does not require the plane stress condition to be enforced. In this work, a recently proposed efficient solid‐shell element is implemented together with a state‐of‐the‐art continuum model for paperboard. This approach is validated by comparing the obtained numerical results with experimental results for paperboard as well as with those found by using 3D continuum elements. To show the potential of this approach, a large‐scale forming simulation of paperboard is used as a proof of concept.     

Evaluation of ductile fracture in sheet metal forming using the ellipsoidal void model

The ductile fracture in the simulation of sheet-metal-forming processes is evaluated by the ellipsoidal void model previously proposed by the author. In the present study, the simulation and experiment of the hole expansion test are performed using six types of metals. For an alloy, the relationship between prestrain and hole expansion ratio calculated using the ellipsoidal void configuration and ellipsoidal void shape and that calculated using the ellipsoidal void configuration and circular void shape agree with the relationship obtained experimentally. For a pure metal, the relationship between prestrain and hole expansion ratio calculated using the average void configuration and average void shape agrees with that obtained experimentally. Furthermore, the method of introducing prestrain to an as-rolled sheet is proposed, and the prestrain in this sheet is estimated.     

Stress concentration factors of a general triaxial ellipsoidal cavity

The equivalent inclusion method is applied to solve the stress concentration problem concerning the disturbing effect of a general triaxial ellipsoidal cavity on an otherwise uniform normal stress state. Several useful solutions in simple form for limiting cases are derived and numerical results for general cases are obtained. These findings show the general features of the stress concentration factors around the base equator of the cavity. It is found that (1) when Poisson's ratio of the material is zero, the stress concentration factor does not vary along the equator of the cavity; (2) When the aspect ratio c/b of the cavity is very small, the stress concentration factor is also constant along the equator; (3) In general, the variation of stress concentration factors around the equator is less than 0.17 regardless of Poisson's ratio of the material. Thus, it is concluded that the stress concentration factor may be treated as constant around the equator of an ellipsoidal cavity with only a slight error.     

Experimental investigations on buckling of cylindrical shells under axial compression and transverse shear

This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision forin-situ measurement of the initial geometric imperfections. The shell models are made by rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections δ_max are of the order of ±3t (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through finite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen influences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.     

模具结构对箔板电磁微成形的影响

对T2紫铜箔板进行电磁微成形实验,研究不同模具结构对材料成形性能的影响.采用激光共聚焦显微镜及轮廓仪研究不同模具结构对箔板电磁微成形的影响规律,分析模具结构对材料流动规律的影响.研究结果表明:随着电压的升高坯料出现不同程度的翘曲现象,采用凸型模具更有利于凹模内气体的排除,使得坯料能够迅速贴模;随着电压的升高材料成形性不断提高,采用凹型模具比采用凸型模具更加有利于微槽精度的提高;电磁成形制件应变分布均匀,凸型模具成形制件壁厚最小值出现在微槽侧壁,成形过程以拉深成形为主;凹型模具成形制件最小壁厚出现在微槽底部,成形过程以胀形为主.     

复合材料圆柱壳的轴压屈曲失效试验

为了研究高径比大于1的复合材料圆柱壳的轴压屈曲性能及其失效模式,对2组单向纤维圆柱壳和3组外侧环裹环向纤维圆柱壳进行了轴压试验,观察了试件的受力过程和破坏形态,获得了荷载-位移曲线和荷载-应变曲线,利用有限元模型分析了单向纤维圆柱壳两种屈曲形式的破坏机制,对比分析了两种铺层试件的轴压性能。结果表明:单向纤维复合材料圆柱壳出现先纵向劈裂后板壳屈曲和先柱壳屈曲后纵向劈裂的两种破坏模式;外侧环向纤维可改善圆柱壳的轴压性能,屈曲发展有一定的阶段性并表现出延性特征,破坏形式和承载力均较为稳定。     

Efficient implicit finite element analysis of sheet forming processes

The computation time for implicit finite element analyses tends to increase disproportionally with increasing problem size. This is due to the repeated solution of linear sets of equations, if direct solvers are used. By using iterative linear equation solvers the total analysis time can be reduced for large systems. For plate or shell element models, however, the condition of the matrix is so ill that iterative solvers do not reach the huge time‐savings that are realized with solid elements. By introducing inertial effects into the implicit finite element code the condition number can be improved and iterative solvers perform much better. An additional advantage is that the inertial effects stabilize the Newton–Raphson iterations. This also applies to quasi‐static processes, for which the inertial effects finally do not affect the results. The presented method can readily be implemented in existing implicit finite element codes. Industrial size deep drawing simulations are executed to investigate the performance of the recommended strategy. It is concluded that the computation time is decreased by a factor of 5 to 10. Copyright © 2003 John Wiley & Sons, Ltd.     

整体成型复合材料模型机翼设计方案优选与验证

采用多级优化方法,对给定外形和尺寸的复合材料模型机翼进行了设计方案优选。首先基于单因素的效能评估和灰关联度的综合效能评估对机翼进行了结构布局设计,然后采用有限元法对工字梁机翼进行结构细节优化与铺层设计,最后采用基于真空袋法的整体成型工艺制备了蒙皮-夹芯、蒙皮-加筋、C型梁和工字梁等4种典型结构的复合材料模型机翼,并利用三点弯曲试验对优选设计方案进行了验证。优化结果表明：工字梁机翼结构效能水平最高,其次是后C型梁机翼,结构效能最差的是蒙皮-腹板机翼,梁凸缘采用等厚度变宽度可获得近似等强度梁结构。试验结果验证了优化设计方案的有效性。     

Buckling and postbuckling of anisotropic laminated cylindrical shells under combined axial compression and torsion

A postbuckling analysis is presented for an anisotropic laminated cylindrical shell of finite length subjected to combined loading of axial compression and torsion. The governing equations are based on classical shell theory with von Kármán–Donnell-type of kinematic nonlinearity and including the extension–twist, extension–flexural and flexural–twist couplings. The nonlinear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine interactive buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, anisotropic laminated cylindrical shells for different values of load-proportional parameters. The results show that the postbuckling characteristics depend significantly upon the load-proportional parameter. The results reveal that in combined loading cases the postbuckling equilibrium path is unstable and the shell structure is imperfection-sensitive.