Environmental Effects On Mechanical Properties Of Glass Fiber Mat,Kenaf Fiber Mat And Paper Mat Reinforced Thermosetting Resin Composites

Glass fiber mat and kenaf fiber mat reinforced thermosetting composites are usually post cured at an elevated temperature and then cooled to room temperature. Because of their dissimilarity in nature and expansion-contraction behavior and different mechanical properties of the two components(fiber and resin), thermal stresses and strain can be easily generated. These effects are elevated by environmental agents like moisture, temperature variation and thermal cycling, which can be occurred in a working environment. The aim of the present work is to investigate the influence of thermal cycling fatigue with open air moisture on mechanical properties of glass fiber mat unsaturated polyester(UP) resin composites and comparing with kenaf fiber mat UP composites, although thermal cycling effects on mechanical properties of different types of paper mat / UP were described briefly at the end of this study. For this purpose, notched and unnotched tensile test, low cycle tensile fatigue tests were performed to the both types of specimens, which have previously been subjected to a certain number of thermal cycles(from +58 oC to-25 oC). The influence and maximum changes of notched and un-notched tensile strength, modulus are delineated in this work. And different phenomena of low cycle fatigue(LCF) are described graphically after experiencing thermal cycling of both types of composites. Scanning electron microscopy(SEM) was used to monitor the potential changes in the microstructure due to the degradation caused by the thermal cycles.In case of tensile properties, in this study after definite number of thermal cycling kenaf mat composites suffered much than the glass mat composites. But notched kenaf mat compositesdropped off same percentage of their notched strength compared to glass mat composites. In this case kenaf mat showed a sharp better notched strength property considered to glass mat composites. From the finite element analysis(FEA) we also get the corresponding results, that was after thermal cycling kenaf mat / UP showed longer characteristic distances and better resistance properties against hole effect.After definite number thermal cycles except 100 cycles in LCF tests there was almost same type of modulus variation in every LCF cycles, these indicate the better performance properties of kenaf mat / UP compared to glass mat / UP in loading application of environmental service life. But after 100 thermal cycles, the kenaf mat / UP become weakened in case of modulus drop, although tensile strength changing rate was little bit less than that of glass mat /UP.Although glass fiber / UP composite had superior mechanical properties considering the volume fraction and fiber strength but after thermal cycling kenaf mat / UP showed better energy absorption properties, better tensile notched strength properties and better resistance properties against the hole effect. This phenomena happened probably because of the difference in fiber molecular structure and fiber matrix interfacial adhesion.Only un-notched tensile properties of three different type paper mat / UP composite were discussed in this study, where C type(package paper of milk and wine) paper mat composite showed highest strength property due to higher density than others.