This paper presents the application of anisotropic damage theory to the study of forming limit diagram of A12024T3 aluminum alloy sheet. In the prediction of limiting strains of the aluminum sheet structure, a finite ...This paper presents the application of anisotropic damage theory to the study of forming limit diagram of A12024T3 aluminum alloy sheet. In the prediction of limiting strains of the aluminum sheet structure, a finite element cell model has been constructed. The cell model consists of two phases, the aluminum alloy matrix and the intermetallic cluster. The material behavior of the aluminum alloy matrix is described with a fully coupled elasto-plastic damage constitutive equation. The intermetallic cluster is assumed to be elastic and brittle. By varying the stretching ratio, the limiting strains of the sheet under biaxial stretching have been predicted by using the necking criterion proposed. The prediction is in good agreement with the experimental findings. Moreover, the finite element cell model can provide information for understanding the microscopic damage mechanism of the aluminum alloy. Over-estimation of the limit strains may result if the effect of material damage is ignored in the sheet metal forming study.展开更多
目的:探讨针刺联合三步七法推拿对颈肩腰腿痛(neck,shoulder,waist and leg pain,NSWLP)肾虚血瘀证患者颈肩腰腿活动功能的影响。方法:将NSWLP肾虚血瘀证患者112例按照随机数字表法分为对照组和观察组各56例。对照组予西医常规干预方案...目的:探讨针刺联合三步七法推拿对颈肩腰腿痛(neck,shoulder,waist and leg pain,NSWLP)肾虚血瘀证患者颈肩腰腿活动功能的影响。方法:将NSWLP肾虚血瘀证患者112例按照随机数字表法分为对照组和观察组各56例。对照组予西医常规干预方案,观察组在对照组基础上采取针刺联合三步七法推拿治疗,连续治疗4周后比较两组患者疼痛程度,颈椎、肩关节、腰椎、膝关节功能以及临床疗效。结果:治疗4周后,两组患者视觉模拟量表(visual analogue scale,VAS)评分均降低(P<0.01),观察组降低更明显(P<0.01);两组患者颈椎病临床评价量表(cervical spondylosis clinical evaluation scale,CASCS)、Constant-Murley欧美肩关节评分法(constant-murley score,C-M)、日本骨科协会(Japanese Orthopaedic Association,JOA)评分、Lysholm评分均升高,观察组升高更明显(P<0.01);观察组总有效率为94.64%(53/56),高于对照组的80.36%(45/56)(P<0.05)。结论:西医常规治疗基础上予针刺联合三步七法推拿治疗NSWLP肾虚血痧证疗效更佳,可进一步减轻患者疼痛,改善颈肩腰腿活动功能。展开更多
表征应力状态参量的应力三轴度是控制材料断裂模式的关键因素,所以应力三轴度作为影响材料的断裂因素而被引入到众多失效模型中。利用有限元辅助测试(Finite element Aided Testing,FAT)方法来获取材料等效全程单轴本构关系,进而获取漏...表征应力状态参量的应力三轴度是控制材料断裂模式的关键因素,所以应力三轴度作为影响材料的断裂因素而被引入到众多失效模型中。利用有限元辅助测试(Finite element Aided Testing,FAT)方法来获取材料等效全程单轴本构关系,进而获取漏斗型试样在拉伸过程中根部截面上的应力三轴度演化情况,并同根据Bridgman应力修正后的单轴本构关系得到的应力三轴度分布进行了对比分析。结果表明,基于Bridgman应力修正得到的应力三轴度与有限元计算结果相差较大。基于应力三轴度分析,讨论了漏斗型试样的破断机理,给出了四种延性材料的等效全程单轴本构关系、破断应变、破断应力和漏斗根部截面的应力三轴度分布随截面中心von Mises等效应变的变化规律。展开更多
基金Project supported by the Research Committee of The Hong Kong Polytechnic University (No.G-YX34).
文摘This paper presents the application of anisotropic damage theory to the study of forming limit diagram of A12024T3 aluminum alloy sheet. In the prediction of limiting strains of the aluminum sheet structure, a finite element cell model has been constructed. The cell model consists of two phases, the aluminum alloy matrix and the intermetallic cluster. The material behavior of the aluminum alloy matrix is described with a fully coupled elasto-plastic damage constitutive equation. The intermetallic cluster is assumed to be elastic and brittle. By varying the stretching ratio, the limiting strains of the sheet under biaxial stretching have been predicted by using the necking criterion proposed. The prediction is in good agreement with the experimental findings. Moreover, the finite element cell model can provide information for understanding the microscopic damage mechanism of the aluminum alloy. Over-estimation of the limit strains may result if the effect of material damage is ignored in the sheet metal forming study.
文摘表征应力状态参量的应力三轴度是控制材料断裂模式的关键因素,所以应力三轴度作为影响材料的断裂因素而被引入到众多失效模型中。利用有限元辅助测试(Finite element Aided Testing,FAT)方法来获取材料等效全程单轴本构关系,进而获取漏斗型试样在拉伸过程中根部截面上的应力三轴度演化情况,并同根据Bridgman应力修正后的单轴本构关系得到的应力三轴度分布进行了对比分析。结果表明,基于Bridgman应力修正得到的应力三轴度与有限元计算结果相差较大。基于应力三轴度分析,讨论了漏斗型试样的破断机理,给出了四种延性材料的等效全程单轴本构关系、破断应变、破断应力和漏斗根部截面的应力三轴度分布随截面中心von Mises等效应变的变化规律。
