Evaluation of complex time-dependent stress field and reduction of loss energy for viscoelastic laminated tires

粘弹性材料的应力/应变分析技术为设计轮胎的复合结构和减少轮胎的运行阻力提供了各种知识。采用数字全息法和数字图像相关法分析粘弹性材料的应力场和应变场。实验结果表明，数字全息测量位移精度可达30nm，应变测量精度可达7.5×10^<-6>。这些精度足以测量粘弹性材料中的位移场。通过数字图像相关法获得的实验数据表明，该方法可以实时测量粘弹性材料的全场位移，即使材料受到较大的变形。这些发展起来的技术也被应用于断裂力学，作者表明这些技术对确定应力强度因子是有用的。另一方面，由于仅从实验位移数据难以分析粘弹性材料的应力状态，作者发展了实验-数值混合技术。该方法首先建立粘弹性物体的有限元模型，然后将实测的实验位移数据输入到所建立的有限元模型的边界上。从而同时计算粘弹性物体的应力场和应变场。结果表明，该方法可以准确地分析非比例加载下粘弹性物体的应力场和应变场。

Techniques for stress/strain analysis in viscoelastic materials give the various knowledge to design composite structures of tires and to reduce running resistance of tires. In the present research, digital holography and digital image correlation method were developed to analysis the stress/strain field in viscoelastic materials. The experimental results show that the digital holography has accuracies of 30nm in displacement measurement and of 7.5×10^<-6> in strain measurement. These accuracies are enough to measure the displacement field in viscoelastic materials. And, the experimental data obtained by digital image correlation method shows that the method can measure the full field displacement in viscoelastic materials in real time, even if the materials are subjected large deformation. These developed techniques were also applied to fracture mechanics and the authors showed that the techniques are useful to determine stress intensity factors. On the other hand, the authors developed experimental-numerical hybrid technique because it is difficult to analyze stress state in viscoelastic material only from experimental displacement data. In the developed hybrid technique, finite element model of viscoelastic object is constructed, and then, the measured experimental displacement data is inputted on the boundary of the constructed finite element model. Consequently, the stress and strain fields in the viscoelastic object are simultaneously calculated. The results show that the stress and strain fields in the viscoelastic object under non-proportional loading can be analyzed exactly by the proposed technique.