Hencky应力方程与主剪应力迹线上正应力方程的比较

众所周知 ,沿滑移线上正应力的变化规律可以用 Hencky应力方程描述 ,该方程仅适用于刚塑性平面应变问题。本文给出沿主剪应力迹线上的正应力方程 ,它不限于平面应变问题 ,也不限于最大剪应力迹线 ,并指出 Hencky应力方程仅为其特例。本文还给出利用主剪应力迹线上的正应力方程求解锥模薄壁管缩颈应力的实例。     

车门外板轮廓翻边R角锐化及回弹控制方案

针对车门外板轮廓翻边R角(后门C柱侧)、车门外板轮廓整形R角(后门B柱侧)锐化进行工艺方案分析及实物论证,并针对车门外板单件刚性差,回弹控制难度大的特点,调整冲压工艺方案,利用AutoFrom软件进行回弹模拟分析验算,并在模具开发中进行应用,经实物验证调整方案有效。     

New technique of precision necking for long tubes with variable wall thickness

Frontiers of Mechanical Engineering - This study analyzed the deformation law of rear axles with variable wall thickness under bidirectional horizontal extrusion and found that necking was...     

薄壁圆筒件旋转椭球面型冲压缩口的应力分析

应用金属塑性成形理论中的轴对称薄壳理论 ,对薄壁圆筒工件旋转椭球面型冲压缩口成形过程的应力进行了分析 ,得出了缩口系数k≥ 0 71时此类工件缩口段经向应力的变化规律及其与其他参数之间的关系 ,推出了这种情况下工件最大轴向压应力及缩口力的计算公式 ,为工艺设计人员研究、制定相应缩口工艺提供了依据。     

A prediction of bursting failure in tube hydroforming process based on plastic instability

Based on plastic instability, an analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is an irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria – diffuse necking criteria for a sheet, and a tube, and a local necking criterion for a sheet – are introduced. The incremental theory of plasticity for an anisotropic material is adopted and the hydroforming limit, as well as a diagram of bursting failure with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of material properties such as anisotropy parameter, strain hardening exponent and strength coefficient on plastic instability and bursting pressure are investigated. As a result of the above approach, the hydroforming limit with respect to bursting failure is verified with experimental results.     

Forming limit of electrodeposited nickel coating in the left region

A uniform nickel (Ni) coating was bilaterally electrodeposited on the low-carbon steel substrate for the application of advanced battery shells. Its forming limit was investigated by Hill localized necking theory coupled with finite element simulation and scanning electron microscopy. The effective stress and effective strain in the Ni coating and steel substrate are deduced using Hill’s anisotropic yield function. The localized necking condition is derived by sandwich sheet analysis, and the forming limit strains are obtained by solving the nonlinear equation of the localized necking condition. Extensive calculations are carried out using the proposed model. This study exhibits the nickel coating thickness and the normal anisotropic coefficients of the coating and substrate have little influence on the forming limit curve (FLC) in the left region of the coated sheet, but the strain hardening exponents of the coating and substrate have much effect on it. The calculated result matches well with the measured data in uniaxial tension. This investigation is useful for the preparation of the electrodeposited Ni coating and helpful for the forming operation of the battery shells.     

波形套复合缩径—胀形变形分析及应力场求解

提出汽车波形套成形的复合缩径—胀形工艺 ,设计了成形模具 ;建立了波形套复合缩径—胀形力学模型 ,推导出各变形区的应力平衡方程 ,基于实验研究求解了变形区的应变场及应力场     

Superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under critical necking tension

The superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under a critical necking tension (σ_c) were studied. σ_c was defined as the minimum tension needed to generate a neck at a given drawing temperature (T_d) and was measured over a temperature range of 70–120°C. The σ_c value increased rapidly with decreasing T_d in the temperature range below 85°C, but the temperature dependence of σ_c was small above 85°C. The neck profile relied on T_d, becoming more shapely with decreasing T_d. A neck with a gradual decrease in diameter was observed in the fibers drawn at 100°C and above. The draw ratio increased significantly with increasing T_d above 90°C, but birefringence decreased. Density decreased gradually with increasing T_d, and fiber drawn at 120°C had a density of 1.347 g/cc. Wide‐angle X‐ray diffraction photographs of the fibers drawn at 100°C and below showed reflections due to crystallites, but a photograph of the fiber obtained at 120°C showed a ring‐like amorphous halo. The storage modulus (E′) at 25°C increased progressively with decreasing T_d, and the fiber drawn at 70°C had the maximum E′ value among the fibers drawn at a series of T_d's. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 179–185, 2002     

PET张力纺丝成形研究

在ＰＯＹ设备纺程上，增设一个张力和温度的调节装置．用张力纺丝（ＴＦＳ）．一步法制取ＰＥＴ纤维。通过试验和测试揭示了张力纺丝颈缩拉伸、应力和取向诱导结晶的内在联系。     

Creep rupture of a linear polyethylene: 1. Rupture and pre-rupture phenomena

The creep rupture behaviour of a high-density polyethylene was studied for material prepared at two different cooling rates. The rupture phenomena were dependent upon the morphology. The slow-cooled specimens had a degenerated spherulitic structure and all underwent brittle rupture. The fast-cooled specimens had a banded spherulitic structure and exhibited either ductile or brittle rupture depending upon the applied stress. Ductile creep rupture was associated with a large tertiary creep strain, with macro-necking and a stress whitening which corresponded to an increase in volumetric strain. Brittle creep rupture was associated with an absence of macro-necking, and either an absence or a small amount of tertiary creep. Stress whitening corresponding to a decrease in volumetric strain was a feature of both forms of failure above a threshold value of stress.