Experimental Investigation Of The Contact Problem Of Large Deformation Soft Material And Rigid Wedge Indenter

Soft materials are closely related to people’s lives and widely applied in technology and manufacturing, extensively studied in mechanics, life science, chemistry, medicine, food, materials, environmental science, engineering and many other fields. In-depth study of the large deformation contact behaviour of soft material in engineering applications is not only helpful for improving material performance and optimizing structure design, but also important for developing new materials. In this thesis, a study of large deformation soft material contacting with rigid wedge is presented, and large deformation contact fields are measured and systematically analyzed through optical measurement techniques.Three techniques, including digital moiré, three-dimensional digital image correlation and thermoelastic stress analysis, are employed in this thesis for measuring large deformation contact behaviour of soft materials. Both in-plane and out-of-plane calibration procedures were conducted to establish the minimum measurement uncertainty of the DIC system, which provide confidence in the measured results. In the digital moiré experiment, embeded-gratings were used as markers in a transparent silicone rubber. This approach reduced the measurement error caused by the out-of-plane deformation, and achieved a successful non-contacting measurement of the large deformation contact field of soft material. Experimental results were processed by digital image processing technique, and the deformation field near contacting area are provided. A simple way of computing strain is also presented by extracting grid deformation parameters and the strain distribution near the contact boundary is obtained.Focusing on the large deformation contact mechanics of soft material and rigid wedge, this thesis systematically studied the influence of wedge angles and indentation depths on the deformation field. First, the deformation of a rubber-like material compressed by wedges with four different slope angles(5 °, 15 °, 45 °, 73 °) is analyzed, through the discussion of displacement field θuur, and strain fieldθθεεεrr,,, and the sector configuration varying with load and wedge angle is systematically studied. Second, the deformation fields of bionic skin contacting with sutures(parallel mode and cross mode) under tensile loading are given, the characteristics of displacement and strain fields and their impact on wound healing are discussed.Experimental results are compared with similar theoretical models, to provide experimental evidence for engineering applications of the theoretical model. The images representing experimental and theoretical fields were decomposed and reconstructed individually. The first fifty Tchebichef moments of each image were taken as image features for comparison. The uncertainties caused by experimental measurements and image reconstruction were both taken into consideration. This method is proved to be effective for the analysis of soft material in contact problems.