Masahiro Kusaka

Study on Mechanism of Decrease in Strength of GFRP Immersed in Weak Acid Solution by SAM.

Glass fiber reinforced vinyl ester resins (GFRP) were immersed in weak acid solution (1% sulfuric acid water) at 40°C for various periods from 0 to 12 months. After drying at room temperature for one week, the tensile and the bending tests were carried out on them. The tensile strength of GFRP decreased slowly with increasing immersion time, and the bending strength was degraded rapidly with increasing immersion time in the early stage. From the test results, it was considered as follows:(1) The decrease in strength of GFRP was due to the damage of glass fibers.(2) The damage of glass fibers proceeded from the surface to the inside of GFRP.In order to confirm this mechanism of decrease in strength, the inside of GFRP was observed nondestructively with a scanning acoustic microscope (SAM). From the observation results, it was confirmed that the damage of glass fibers was caused by corrosion by weak acid solution, and the corrosion of glass fibers was produced in GFRP. Therefore, the mechanism of decrease in strength of GFRP due to immersion in weak acid solution was clarified by this study.

Effect of Insert Layer on J-integral of Dissimilar Material Joint Subjected to Temperature Changes.

In this paper, the J-integral for an interfacial crack by thermal stress that developed during the cooling of the dissimilar material joint is studied. The thermoelastic analysis of J-integral for the bonded joint with an insert layer is performed using the finite element method. The effect of insert layer on the J-integral under the thermoelastic condition is discussed. It is found that the J-integral have three types of variation with an increase of insert layer thickness. The variations of J-integral with an increase of insert layer thickness are dominated by the nondimensional parameter (αC-αB)/(αA-αB) that expressed the relation in magnitude of coefficients of linear expansion and the ratio of Youngs modulus (EA/EC). As a result, it is possible to predict the variation of J-integral with an increase of insert layer thickness by using these dominant parameters.

Evaluation of Adhesive Strength of Resin Liner Film.

In this study, a new method to evaluate the adhesive strength of the interface between resin liner film and cement mortar has been developed. The peel test for vinyl ester resin liner films on cement mortar surfaces was carried out. The critical energy release rate (Gc value) was obtained from the peel load and crack length measured during the peel test. Gc values were not affected by the crack length or the thickness of resin liner film. Therefore it was established that Gc values could be used to evaluate the adhesive strength of resin liner film. Furthermore, the effect of primer coats on the adhesive strength of resin liner film were revealed by obtaining the Gc value.