Tohru Morii

Weight changes of a randomly orientated GRP panel in hot water

Abstract This paper deals with the weight change mechanism in randomly orientated E glass fibre mat reinforced unsaturated polyester (GRP) panels immersed in hot water. GRP panels were immersed in distilled water at 60°C and 80°C, after which the wet and re-dried specimen weights were measured. In this case, the weight change mechanism was divided into three phases. In the first phase, water absorption occurred in the resin matrix, while matrix dissolution with negligible water absorption occurred in the second phase. In the third phase, once again water absorption with continual dissolution of fibre/matrix interface ensued. The delay time for matrix dissolution and water absorption was defined as the difference between the saturation time for GRP and unreinforced resin.

Weight-change analysis of the interphase in hygrothermally aged FRP: Consideration of debonding

Abstract This study deals with the experimental and analytical evaluation of weight changes in the interphase in hygrothermally aged fiber-reinforced plastics (FRP). The influence of debonding on the weight change is mainly discussed. The weight change of the interphase was evaluated by comparing the weight change of FRP with that of the plain resin. This method showed that both weight gain and weight loss occurred in the interphase, and these changes were closely related to each other. The volume of debonding at the interphase was evaluated quantitatively by microscopic observation of the aged FRP. Weight gain in the interphase was calculated from the volume of debonding, and the calculated results showed good agreement with experimental data. This result clarified that the weight gain in the interphase was caused by water penetration into debonds at the interphase. The results obtained suggested that improvement in the water resistance of the binder at the interphase is important to enhance the water resistance of glass-fiber-mat reinforced plastics.

Damage tolerance of glass mat/epoxy laminates hybridized with flexible resin under static and impact loading

This study deals with the impact property and damage tolerance of matrix hybrid composite laminates with different laminate constitution. The matrix hybrid composite laminates consisted of the laminae with a conventional epoxy resin and the laminae with a flexible epoxy resin modified from the conventional resin to avoid the interlaminar delamination. The impact energy absorption ratio greatly depended on the matrix resin placed at the impact face. The energy absorption was almost constant if the conventional resin was placed at the impact surface layer, while it increased exponentially with the increasing fraction of the flexible resin if the flexible resin was placed at the impact face. The impact energy was absorbed by the damage development and propagation in the laminate with conventional resin laminae as the impacted face, while it was absorbed by both the recoverable deformation of the flexible resin and the damage propagation in the laminate with flexible resin laminae as the impacted face.

Weight changes of the fibre/matrix interface in GRP panels immersed in hot water

Abstract The weight-change behaviour of the fibre/matrix interface in composite panels consisting of randomly orientated E-glass-fibre continuous strand mat in unsaturated polyester has been studied. Two matrix resins of different filler content were used. GRP and plain resin specimens were immersed in hot water (60°C and 80°C) and the weight of the specimens was measured as a function of time. The weight changes were evaluated in terms of three parameters: apparent weight gain, net weight gain and weight loss. The weight changes of the fibre/matrix interface were obtained from the differences in the weight changes of the GRP and the unreinforced resin. Water absorption at the interface occurred after water absorption of the matrix resin reached almost saturation level. Weight loss due to dissolution of binder from the interface occurred after water penetration into the interface. Debonding occurred at the fibre/matrix interface as a result of water penetration, and, in consequence, the binder dissolved into water at the interface. The net weight gain and weight loss of the interface increased linearly with the square root of immersion time, and the filler had little effect on these phenomena.

Nonlinear stress-strain behavior of piezoelectric ceramics under tensile loading

Fracture strength and stress-strain behavior under tensile stress in piezoelectric ceramics have been investigated with special emphasis on the effect of environmental temperature. The materials used in this work are the commercial piezoelectric ceramics, PbZrO/sub 3/-PbTiO/sub 3/ (PZT) and PLZT. An attempt was first made to evaluate the tensile strength properties at the room temperature of PZT samples having a specially designed specimen geometry. Not only fracture strength, but also elastic properties, tensile modulus and Poissons ratio, were evaluated and then the stress-strain behavior under tension was investigated. As a result, stress-strain response under tension for piezoelectric ceramics, PZT and PLZT, was confirmed to be nonlinear. The nonlinearity in the stress-strain relationship under compression loading has already been reported by some investigations. However, very little work has been done on the tensile stress-strain relationship, as studied in this paper. The results of tensile test for PZT samples at the various environmental temperatures indicated that the stress-strain response of poled and nonpoled samples was nonlinear independent of test temperature. The strength of both the poled samples and the nonpoled samples increased linearly against test temperature. Moreover, acoustic emission monitoring was performed simultaneously during tensile tests, and thus the tensile failure process in piezoelectric ceramics was discussed. It was also pointed out that the tensile strength of PLZT increased monotonically against the amount of La.

Weight change mechanism of randomly oriented GFRP panel immersed in hot water

Abstract This study deals with the weight changes of the fiber/matrix interface and the weight change mechanisms of the randomly oriented E-glass fiber continuous strand mat reinforced unsaturated polyester panels. The weight changes were evaluated by introducing the weight gain due to water absorption ( M g ) and the weight loss due to matrix dissolution ( M l ). The weight changes of the fiber/matrix interface ( M gI and M lI ) were obtained from the difference of M g and M l between GFRP and neat resin. Water absorption of the interface occurred after water absorption of matrix resin reached saturation. Weight loss due to dissolution of binder on glass-fiber mat and matrix from the interface occurred after water penetration into the interface. The debondings at the fiber/matrix interface occurred due to water penetration, and as a result, the binder and matrix dissolved easily in the water through the interface. The weight changes of the GFRP panel were classified into three phases. In phase I, only the resin matrix absorbed water. In phase II, the fiber/matrix interface absorbed water. After that phase, water absorption into the fiber/matrix interface and matrix dissolution from the interface occurred simultaneously.

Influence of molding condition on tensile properties of flat braided fabric reinforced phenolic composite

This study discusses the influence of molding conditions on the tensile properties of flat braided glass fabric reinforced phenolic composite. In addition, the influence of sizing on the tensile properties is also discussed by changing the amount of sizing of the glass fiber bundle. The tensile strength improved when longer periods of resin impregnation were allowed. A higher amount of sizing also improved the tensile strength by facilitating good resin impregnation into fiber bundles. Good resin impregnation suppressed matrix cracking at low strain levels, and it was the key issue to improve the tensile strength in braided fabric reinforced phenolic resin composite.

Damage Mechanics on Hydrothermal-Aged Fiber-Reinforced Plastics (FRP)

The elastic modulus of randomly oriented, glass fiber mat reinforced plastics after hydrothermal aging was estimated introducing finite element analyses and the damage mechanics. The debonding between fiber and matrix of the hydrothermal aged fiber-reinforced plastics (FRPs) was dealt with as the internal damage, and the damage mechanics were introduced to the finite element analyses. The damage angle around the fiber greatly affected the modulus reduction of the aged FRPs independent of the damage thickness. The internal damage of the aged FRPs was determined quantitatively by the weight loss due to water immersion, and the modulus of the aged FRPs was calculated by the finite element analysis introducing the damage parameter. The calculated results corresponded well to the experimental results, and it was analytically clarified that the modulus reduction of the aged FRPs was caused by the occurrence of the debonding between fiber and matrix.

Nonlinear Stress-Strain Behavior of PbZrO3–PbTiO3 under Various Temperatures

This study deals with the tensile stress-strain behavior of piezoelectric ceramics under various environmental temperatures. The material used is commercial piezoelectric ceramics, PbZrO 3 -PbTiO 3 (PZT). The tensile test was performed under various temperatures in the environmental chamber for poled and nonpoled samples having a specially designed specimen geometry, in order to discuss the effects of temperature on the stress-strain behavior. It was clarified that the stress-strain response of poled and nonpoled samples was nonlinear independent, of test, temperature, and the nonlinearity was stronger with the increase of test temperature. Moreover it was clarified that the stronger the nonlinearity is, the higher the fracture strength is

Effect of Water Temperature on Hygrothermal Aging of GFRP Panel

This study deals with the effect of water temperature on the hygrothermal aging of a GFRP panel. Materials used in this study are two types of continuous E-glass fibre mat reinforced polyester which have different fillers. The specimens are immersed in hot water at 60°, 80° and 95° C and then weight changes and bending properties are measured. The water temperature affects the weight changes but it never affects the changes in bending properties against weight gain. Moreover the difference in the degradation progress in the thickness direction is clear from the results of the ‘one side immersion test’.