轴对称超塑充模胀形件轮廓厚度分布的影响因素及其内部空洞发展

On Factors Affecting Non-uniformity in Thickness of Contour of Specimen in Superplastic Bulging with an Axisymmetric Die

轴对称超塑充模胀形件轮廓厚度分布的影响因素及其内部空洞发展李园春，刘马宝，吴诗惇关于超塑充模胀形的有限元模拟研究极少，这与充模过程中动态边界条件难于处理和计算过程不稳定有关．且它们没有研究降低胀形件厚度分布不均匀性问题，而厚度分布不均是超塑胀形走向实...

The authors have seen only two papers on superplastic bulging with a die, and they lid not dcal with how to reduce non-uniformity in thickness. In this researcn summary,the autbors deal with this problem for the case of axisymmetric conical die with arbitrary vertex angle (including cylindrical one)shown in Fig.1. Symbols Ho, Ro, ro and θ are clearly defined in Fig.1.The authors divide the specimen into small clements whose sizes are fixed in accordance with precision required. Our cxpcrimcntal findings are:(1) When several neighboring elements fill the die in succession, and then several neighboring elements at another portion of specimen do likewise, the non-uniformity in thickness is reduced. It is inadvisible to have one clement fill the die and then another element belonging to a different portion of it fill the die.(2) The greater Ho/ Ro is, the greater is the thinning at top and corner of die due to stretching,and the greater is the non--uniformity in thickness.(3) The smaller ro is, the greater is the thinning at die corner due to stretching, and the greater is the non--uniformity in thickness.(4) The greater θis, the earlier is side--wall of die filled, the greater is the thinning of top and corner of specimen compared with its side--wall,and the greater is the non--uniformity in thickress.(5) The smaller the frictional factor Am is,the better is the uniformity in thickness.(6) The greater the strain rate sensitivity index m or the work--hardening index n is, the better is the uniformity in thickness. m has a much greater of Toot than n.(7) The greater the normal anisotropy parameter R is, the better is the uniformity in thickness.For each of the findings above, there are curves to quantify the effect. In this Research summary,only the three curves for m arc given in Fig.2.We employ large deformation rigid-viscoplastic finite element method. We employ updatedLagrangian formula to formulate the functional. We introduce arc--tangential frictional vector modeland the functional correspondingly includes friction term; then, after variational process and usingNewton--Raphson method, We obtain the needed FEM iteration formulas.