Papers by Keyword: Crazing

Abstract: The advantages of structural-mechanical modification of fibers by the mechanism of crazing for obtaining bioresorbable suture materials with biological activity are shown. Optimal conditions for realization of solvent crazing of polylactide fibers are determined as the stretching rate is not more than 75% / min and the ethanol content in the water-ethanol mixture is not less than 30-40% by weight. In this case, the value of yield stress decreases by 3-5 times, and the breaking elongation increases to 400-600%. The process of uniaxial deformation of fibers under these conditions is accompanied by the formation of a highly dispersed oriented structure with a pore diameter and fibrils of about 20-30 nm and bulk porosity up to 60% by volume. Moreover, the crazing of fibers based on polylactide under these conditions is accompanied by low-temperature crystallization, reaching a degree of crystallinity of 40%. The monofilaments based on polylactide containing biologically active additives (brilliant green, fuchsine) by the crazing mechanism are obtained. Such materials are promising for use in medicine as bioresorbable sutures with antibacterial activity.

Abstract: Microscopic studies on the toughening mechanism of rubber-toughened PMMA (RTPMMA) were carried out using a polarizing optical microscope (POM) and a transmission electron microscope (TEM). POM result showed that in a typical RT-PMMA, a damage zone was developed in the vicinity of crack-tip, and therefore, it was considered that energy dissipation due to the damage zone development was the primary toughening mechanism. TEM result exhibited that the damage zone was a crowd of micro-crazes generated around rubber particles in the vicinity of notch-tip. Finite element analysis was then performed to simulate such damage formations in crack-tip region. Macro-scale and micro-scale models were developed to simulate damage zone formation and micro-crazing, respectively, with use of a damage model. It was shown that the damage model introduced was successfully applied to predict such kind of macro-damage and micro-craze formations.

Abstract: Effect of annealing on the fracture behavior of poly(lactic acid) (PLA) was investigated. Fracture toughness of PLA samples prepared under different annealing conditions was measured under static and dynamic loadings. Microstructure and crack growth behavior were characterized by polarizing microscopy (POM). Crystallinity was determined by DSC analysis. Fracture surface morphology was also studied by scanning electron microscopy. It was shown that the static fracture toughness increased with increase of crystallinity, while the dynamic toughness increased as crystallinity increased. POM exhibited that craze formation played an important role in the fracture mechanism of amorphous samples. Macroscopic fracture toughness and microscopic crack growth mechanism were correlated on the basis of these experimental results, and effect of annealing on the toughness and mechanism were discussed.