Mechanical characterization, constitutive and finite element modelling of SMC composites with randomly oriented glass fibres
University of New Brunswick
Composite materials have recently been of particular interest to the automotive industry due to their high strength-to-weight ratio and versatility. Among different composite materials used in mass-produced cars, are sheet molded compound (SMC) composites, which consist of random fibres making them inexpensive candidates for non-structural applications in future vehicles. In this work, a constitutive and finite model describing the deformation behavior of an SMC composite was developed. Materials were prepared with varying fibre orientation and volume fraction, followed by a series of uniaxial tensile and flexural tests at varying strain rates. Tensile strength was found to increase with increasing fibre volume fraction and strain rate, but tensile strength was much less sensitive to increases in strain rate. Flexural strength was found to also increase with increasing fibre volume fraction; however, failure displacement was found to decrease. The two material orientations used, longitudinal and transverse, had vastly different results in reference to tensile strength and fracture strain, this was due the influence of the manufacturing process on the fibre orientation. Yield and ultimate tensile strengths were higher in the transverse direction. The uniaxial experimental results were used to develop a general Holloman type analytical model and to create and calibrate the finite element model, with both including the effects of strain, strain rates, and fibre volume fraction. The analytical model was found to accurately predict composite deformation in majority of cases, while some error was found in tensile properties of SMC composites with lower volume fractions and high strain rates. The finite element model, validated by the flexural results, closely predicted both SMC volume fraction samples predicting the failure force and displacement with less than 3.5% error in the lower volume fraction tests and 6.6% error in the higher volume fraction tests.