Papers by Keyword: Fibrillar Structure

Abstract: Fibrillar structure adhesives can adhere strongly to surfaces as a gecko does. The adhesion and detachment of each fiber has significant effects on the adhesion enhancement. In the present study, we report the adhesion effect of a single fiber. Based on the JKR (Johnson-Kendall-Roberts) theory, nonlinear mechanical models are built to formulate the process of adhesion and detachment between a fiber and substrate. Comparisons of the experimental and simulative results reveal consistent process trend of adhesion and detachment, which suggests the potential applicability of the present model.

Abstract: The effect of ultrasonic etching on the crystalline structure, fibrillar structure, skin-core structure of stabilized PAN fibers was studied by XRD and SEM. It has been found various degree of decrease occurs in the crystallite size and crystallinity of fibers heated at different temperatures after ultrasonic etching. Fibrillar structure of fibers heated at 195°C~245°C appear after ultrasonic etching in 90wt% DMSO solution for 6h. When the stabilization temperature is over 245°C, no separated fibrils or macrofibrils are found. When stabilized fibers were etched in pure DMSO, skin-core morphology was observed for the fibers heated at 235°C~265°C. The method of ultrasonic etching using pure DMSO confirms the structural difference between the skin and the core, also makes the difference visual.

Abstract: The cyclic fatigue threshold value (Kth) of PVC materials with (PVC-M) and without (PVC-U) impact modifier was determined and compared in air and water environments. The PVCM specimens contain 6 pphr of chlorinated polyethylene (CPE) impact modifier. The testing was undertaken at a stress ratio of R=0.1 and fatigue threshold was evaluated at 3 different frequencies: 1Hz, 7Hz and 20Hz. Frequency noticeably affected the fatigue threshold value; regardless of the testing environment; at low frequency the fatigue threshold of PVC-M was below PVC-U, however, this difference gradually decreased with increasing frequency as Kth of PVC-M increased but Kth of PVC-U remained constant. This trend was accelerated in water where a higher of fatigue threshold, Kth, was also observed. A lower fatigue threshold of PVC-M than PVC-U is associated with the presence of CPE particles. The absorption of water into the PVC matrix was evident with the formation of nodular structures observed on the fracture surface. The presence of the nodular structures (at regions close to the threshold) has retarded the fibrillation of crazes, which then blunted the crack propagation.