Experimental Analysis Of Three-dimensional Deformation In Large Deformation Fracture

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.