Papers by Author: Nam Ho Kim

Abstract: Two dimensional statistical characteristics of inter particle/void distance (ID) for various particle/void and dispersion types are studied in relation with toughening of plastics using computer generated three dimensional models. Particle/void size groups adopted were of log-normal distribution. Particles/voids were dispersed at uniform-random. It was found that IDs are (a) of approximately Gaussian distribution but; (b) not of Gaussian distribution for particle/void sizes of bimodal log-normal distribution (created by mixing of two groups of articles/voids). It was also found that the degree of ID uniformity, which can be represented by the inverse of the coefficient of variation, for a single group of log-normally sized particles/voids is not sensitive to standard deviation of particle/void size. Mixing effect on ID characteristics using two groups of log-normally distributed particles/voids with similar mean particle/void diameters was simulated. It was found that, when a significant amount (36 vol %) of particles/voids of a small mean and standard deviation of ID, was mixed with a group of particles/voids of a large mean and standard deviation of ID, mean and standard deviation of ID for the mixture were not substantially lower than those of the group of particles/voids of the large mean and standard deviation of ID. It was also found that the degree of ID uniformity for the mixture of the two groups were lower than those of individual groups, indicating that the mixing has deleterious effect on toughening.

Abstract: Toughening of thermosets by creation of residual compressive stresses around microspheres is studied. Expandable hollow micro-spheres containing liquefied gas were used for the creation of residual compressive stresses. Microscopic compressive residual stresses around the micro-spheres in the vicinity of the crack tip were graphically analysed and related to macroscopic mechanical behaviour for mode I fracture. It was confirmed that toughening was due to residual compressive stresses rather post-cure effect.