【作者】 肖霞；

【导师】 亢一澜；

【作者基本信息】 天津大学 ， 固体力学， 2009， 博士

【摘要】 软材料的丰富物理内涵和广泛应用范围迫切需要关于其力学性能的探究。在其大变形断裂力学的研究中,由于受到材料本构关系多样性的影响,理论和数值研究存在一些困难。而不受材料性能限制的实验测试方法,成为大变形断裂力学问题研究的有效手段,但由于受到实验技术的限制,目前工作甚少。本文针对大变形断裂力学问题的实验研究展开工作,主要包括:对大变形非均匀场变形测量实验技术的改进,和对大变形断裂裂尖区域的系统的实验测试和实验分析。本文对数字云纹实验技术进行改进,提出圆环射线栅线数字云纹法,建立有效的大变形图像的处理技术,实现了对极坐标下大变形非均匀变形场的直接测量。该方法中选用圆环和射线栅线作为变形测试的基本元件,通过对圆射栅线直接的四步相移及其相应的图像处理,实现了极坐标系下的位相场、位移场的直接测量和提取。同时,该方法以极点和射线为观测点可以对变形体的刚体平动和转动位移进行测量。圆射栅线数字云纹法集成了物体变形位移测量和刚体位移测量的功能,拓宽了数字云纹实验技术在材料和结构的力学行为分析中的应用。本文应用数字云纹变形测量技术,研究了大变形断裂裂尖区域平面变形场的特征,讨论了裂尖区域的扇形分区构形。首先,对橡胶材料不同载荷方式( 90°, 60°,45°)的裂尖区域变形场进行测试,通过对位移场ur, uθ、应变场<b疤?舝 ,εθ,εrθ、面积应变场ΔS S的分析,系统地讨论了裂尖区域的扇形分区构形,及其随着载荷方向改变的规律。并以90°载?绞轿?初步探究了裂尖区域扇形分区中的应力强度因子K和奇异性指数λ的特征。其次,对受拉仿生皮肤材料不同缝合方式下(平行缝合和交叉缝合)针口尖端区域的变形场进行测试,讨论了尖端区域的扇形分区构形特征及其对伤口愈合的影响。本文提出大变形断裂问题的三嵌套模型。文中采用三维数字散斑相关方法测量了裂尖区域沿厚度方向的离面变形场,并基于对裂尖区域平面和离面变形特征的分析,提出了大变形断裂问题的三嵌套模型,即裂尖区域由三个由内向外嵌套的区域组成,分别是:尖端的三维变形损伤区,存在扇形分区构形的中间区域,均匀变形的远场区。其中,中间区域由扇形扩张区和收缩区组成。更多还原

【Abstract】 Soft materials with abundant physical characteristics are widely applied in both engineering and biology fields, which urges the recognition on mechanical properties of the materials. At present, uncertainty of the materials’constitutive relationships on reasonability and applicability complicates the theoretical and numerical analysis of its large deformation fracture mechanics of soft materials. While, experimental method performs to be effective due to its independence on materials. Because of deficiency on the present experimental techniques, there is less experimental analysis of large deformation fracture mechanics in recent reports.In the thesis, two main contents are evolved in the experimental research on large deformation fracture mechanics, including enhancement on experimental technique and experimental measurement and analysis on crack tip field with large deformation. Direct digital moirémethod with circular and radial gratings and its phase shifting technique are proposed, for the purpose of non-uniform large deformation measurement. Circular and radial cu疤? are used as both reference and specimen gratings in the method for deformation measurement. Phase ??ting technique is directly implemented on circular and radial fringes, which facilitates obtaining displacement fields in polar coordinate system, radial ur and circumferential uθ, and strain fieldsεr ,εθ,εrθare calculated subsequently. Meanwhile, rigid translation and rotation can both be measured according to the characteristic concentric point and the radial line of the circular and radial gratings. Thus, the proposed method is capable to measure deformation displacement and rigid displacement synthetically. It extends the application of digital moirémethod in mechanical analysis of materials and structures.In-plane deformation fields near the crack tip of soft materials are measured and analyzed by applying digital moirémethod. First, deformation fields of rubber materials applied with different direction loads( 90°, 60°,45°) are measured, including displacement ur , uθand strainεr ,εθ,εrθ,ΔS S, based on which experimental sector division frame and its alteration with loading direction are discussed. Fracture parameters such as stress intensity factor K and singularity exponentλfor the 90°loading large deformation fracture are referred elementarily. Second, deformation fields of unitensioned bio-skins oversewed with different stitching formats (parallel and cross) are measured and analyzed. Also, experimental sector division frame of the sutural area and its influence on the injury recovery are discussed.A 3-nested-deformation model is proposed to describe the deformation field near the crack tip with large deformation of soft materials. Out-of-plane deformation field near the crack tip is measured by applying the three-dimensional digital speckle correlation method. Based on the measured in-plane and out-of-plane deformation distributions, the 3-nested-deformation model is proposed, which says that the crack-tip field can be described by three characteristic regions as follows: the inner region with 3D-deformation and possible damages, the interim region consisted of expanding sector and shrinking sector, and the outer region with uniform loading and deformation.更多还原