【作者】 李晓雷；

【导师】 亢一澜；

【作者基本信息】 天津大学 ， 固体力学， 2006， 博士

【摘要】 数字云纹技术是分析软材料大变形力学问题的有效实验方法。结合新的数学方法和图像处理技术,本文着重开展了两个方面的工作:一方面是深入地研究了适用于大变形测量的数字云纹测量技术;另一方面系统地研究了橡胶类材料大变形力学场的分区模型和各力学参量的分布特征。在橡胶类材料大变形测量的实验技术方面,首次提出了圆环栅数字云纹技术,实现了对实验位移场极坐标分布的直接测量。采用坐标变换及其逆变换技术,解决了对圆环变形栅和射线变形栅进行数字图像处理过程中遇到的困难,可以方便地实现变形栅线图和计算结果在两个坐标系统下的分析与转换。本文将数字云纹技术应用于橡胶类材料裂尖附近的大变形位移场与应变场的实验测量,系统地分析了裂尖附近区域大变形场的分布特征,首次从实验的角度证明了橡胶类材料大变形断裂问题裂尖场分区模型的存在。在变形过程中裂尖场确实存在有以θ=0为中心的扩张区和以θ=π/2为中心的收缩区。通过对应变场的分析,给出了收缩区与扩张区的边界线位置,讨论了各力学参量在不同扇区的一些分布特征:如极值方向、零线位置等。本文研究了不同载荷情况对分区模型的影响。本文对比分析了两种不同橡胶材料的裂尖场分区特征,结果表明材料性质变化对分区模型没有明显的影响。本文还分析了裂尖场的应变奇异性问题,分别得到了扩张区和收缩区的主应变奇异性指数。本文研制了一种适用于大变形测量的制栅技术,将这种简便的制栅技术与埋入法相结合,发展了测量物体内部截面变形场的体内栅数字云纹技术。本文利用小波变换对逻辑云纹进行图像处理,通过小波重构模拟出数字云纹条纹,将相移技术、条纹倍增和还原技术应用于数字云纹法,提高了大变形数字云纹技术的测量灵敏度,实现了对实验数据的自动化处理。这些数字云纹方法的提出,拓宽了云纹测量技术的应用范围。此外,本文还通过实验验证了这些方法的可行性。更多还原

【Abstract】 Digital moirémethods are effective experimental techniques in analyzing mechanical problems of soft materials which can endure large deformation. Introducing some novel mathematical theories and advanced image-processing techniques, this paper puts emphasis on the following aspects: study of digital moirémethods which adapt to large deformation measurement; systematically analysis of the mechanical parameters distributions near the crack tip of rubber-like material.A circular digital moirémethod which is feasible in measuring circular and radial displacements is proposed in this paper. Using coordinate transformation and its inverse operation, deformed gratings and experimental results can be easily analyzed both in Cartesian coordinate system and polar coordinate system by image-processing.The distributions of displacement near the crack tip of rubber-like materials are measured with the proposed digital moirémethod. The sector division model and the distribution rules are systematically investigated. The experimental results indicate that there are both expanding sector and shrinking sector near the crack tip. The boundary lines of sectors and strain distributions are also given. And the effect factors to sector division model near the crack tip are analyzed in detail. The strain singularity near the crack tip is also studied, and the result indicates that the singularity order of strain in the expanding sector is different from that of the shrinking sector.An easy method to prepare specimen gratings for large deformation measurement is presented. The specimen gratings are printed on the specimen and can eliminate the layer effect, which make it possible for gratings to endure large deformation with specimen. Combined the gratings preparing method with the inner-gratings moirétechnique, an inner grating digital moirémethod is proposed in this paper. Using wavelet transform in simulating moiréfringes, the digital fringes are reconstructed by the wavelet decomposition of logical moiré. Further more, phase-shifting technique and multiplied fringes technique are combined with the digital moirémethod to improve the sensitivity and accuracy of the measurement for large deformation. The validity of digital moirémethods presented in this paper is verified by typical experiments.更多还原