Study On The Void Formation Mechanism In RTM Process

This thesis concerns the research which was undertaken to identify the causes of void formation during the impregnation and polymerization stages of RTM,and methods of reducing the final void content within the component. The impregnation phase of the RTM process was identified as being the stage where the majority of voids were formed. A study of resin impregnation into reinforcement was undertaken to determine the reasons for uneven flow and air entrapment. The dry reinforcements were studied to assess the microstructure of the preforms in order to determine reasons for obstruction of the resin flow. Fibre construction and resin properties were identified as potential causes of flow impediment. Fiber orientation and preform stacking were also assumed to assist in the development of uneven flow,leading to air entrapment. A major factor determining the formation of micro voids within fiber bundles was identified as the transverse impregnation of resin into fibre bundles.Systemic theoretical study was taken to analyze the injection flow. Based on the Darcy's law,a simple impregnation model was developed to assess the microscopic impregnation rates and pressure distribution between fibre bundles,in the capillary between fibres and transversely into fibre bundles. The major moulding process variables of injection pressure,injection temperature,fibre construction and resin properties have been assessed to determine their effect on the void content. A Lie(45) experiments were designed to find the better moulding process variables. The void weight content was measured in the study. It was observed that 35 and O.SMPa,UP and fabric is the better choice. By studying the density of products and the microscopic graph,it was found that the void content in the end of the mould is more than other location and it was also found that vacuum assistance during impregnation reduced void formation. This is the developing tendency of RTM processing technology in recent years.