Characterization of CFRP Composite to Investigate the Curing Process Parameters

Abstract

Carbon Fiber Reinforced Polymer (CFRP) composites are well known for its excellent mechanical properties along with high strength to weight ratio which makes it suitable for space and aerospace applications. On varying the proportion of constituents in a composite the properties get changed which can be determined using characterization. Characterization is the preliminary step before the actual application of a newly introduced material. Various thermal analysis techniques like Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC) and Thermo-Mechanical Analysis (TMA) are there to characterize the properties including glass transition temperature, heat of reaction, degree of cure, specific heat and coefficient of thermal expansion. These techniques are generally not practiced for in-situ cure monitoring and are only implemented in laboratories under ideal conditions. In this dissertation, commercially available HCU 200 unidirectional fiber pre-impregnated with reactive epoxy resin A45 is being used as the prepreg tape for its characterization. Two samples with unidirectional and bidirectional configurations are manufactured using the prepreg tapes as per ASTM D7028 standard. DMA tests for all the samples are performed using EXTAR DMS 6100 equipment with three point bending clamping method. The storage modulus, loss modulus and loss factor (tan delta) curves are plotted against temperature as a result of DMA test. The glass transition temperature is found from the peak values of tan delta curves for each sample. The comparative study of all the samples highlighted that the glass transition temperature is a property of epoxy alone and orientation of carbon fibers have a negligible impact on it. The DSC testing for two different samples has been performed according to ASTM D3418 and ISO 11357 to find the cure kinetic parameters. The curve fitting of the dynamic DSC testing data at five different heating rates has been done using linear least square regression method to find the activation energy and pre-exponential factor from the slope and the y-intercept value. The coefficient of thermal expansion (CTE) measurement has been done based on the ASTM D696 standard using the dilatometry technique. The simulation work in the form of a case study of an L-shaped part has been performed using COMPRO plug-in with ABAQUS software to find the effect of cure kinetic parameters on the spring-in angle of the L-shaped part. The results showed that the CTE and activation energy are playing a major role on the spring-in angle of the L-shaped part.