LIFE PREDICTION OF ANTI-CORROSIVE GLASSFIBER REINFORCED UNSATURATED POLYESTERIN WATER AND ACID

摘要

The demand for FRP structure having longer life, such as 50 or 100- year life hasbeen increasing. In order to guarantee the long life, two things have to be needed. One is theunderstanding the degradation behavior and the other is the development of life predictionmethod. The degradation behavior of the anti-corrosive glass fiber reinforced unsaturatedpolyester has been studied by some of the authors and it was clarified that the degradation ofinterphase was the more important factor than the resin and the reinforcement. Therefore weshould develop the life prediction method including the interphase degradation. For lifeprediction, time temperature superposition principal method using stress relaxation test isapplied. FRP in pipe configuration for sewage application was tested in water and acidenvironment. The materials used are the unsaturated polyester and ECR type glass fibers andfabricated by a filament winding method. The deformation was kept constant and the load wasmonitored for one week in a water bath at the constant temperatures. The acid solution (1NH2SO4) and the pipe were put in the polyethylene bag and then sunk in the water bath under acidconditions. The time temperature superposition principle was applied to the result of the stressrelaxation test, and the smooth master curve could be obtained in both the water and acidenvironments. The stress relaxation behaviors in water and acid were the same. The propertiesin 100 years could be predicted from the master curves. The relationship between the sift factorand reciprocal of the temperature were the Arrhenius type, and the activation energies in waterand acid were the same. It means that the stress relaxation behavior in acid could be understoodfrom that in water. Furthermore, the time needed for the test is only for one week, and it isapparently shorter than the previous method for the current life prediction which takes morethan one year. In addition, in order to understand the effect of interphase degradation on thestress relaxation behavior, the stress relaxation test for the specimens which have interphasedegradation was carried out. The stress relaxation behaviors of the virgin specimen and thedegraded specimen were different and the change of the stress of the degraded specimen waslarger. It suggests that the stress relaxation behavior would be changed at the time when theinterphase damage appears. For further life prediction, this knowledge should be included.