Visco-thermo-elastic Simulation Approach For Prediction of Cure-induced Residual Stresses in Fiber Reinforced Composites

Abstract

Liquid composite molding (LCM) has established as a high quality manufacturing process for fiber reinforced composite structures. In order to reduce cycle times significantly, novel fast curing matrix resins are being introduced into series production. These put high requirements on process control and part reproducibility. Problems that may be encountered in this context involve process-induced distortion and surface waviness resulting from anisotropic and cure-dependent material properties. Numerical simulations represent a powerful approach to avoid the use of costly trial-and-error methods. For this reason, a simulation approach is being developed which aims at the prediction of residual stresses and accompanying effects on different length scales. Based on a resin characterization comprising reaction kinetics, cure-dependent relaxation modulus as well as thermal expansion and pressure-dependent chemical shrinkage, a generalized MAXWELL model is selected to describe the process-related mechanical behavior of the thermoset. Taking into account the influence of the process parameters on the resin properties enables a detailed analysis of process-property-relationships. By this, the developed simulation approach offers the possibility of a comprehensive analysis of both local and global process-induced phenomena and hence prevention of flaws.

Development and verification of a cure-dependent visco-thermo-elastic simulation model for predicting the process-induced surface waviness of continuous fiber reinforced thermosets

“…After curing at different cure cycles and completed cooling process, the final glass transition temperature (Tg) values are given with 90.5°C for cure at 80°C and 108.1°C for a curing at 120°C respectively. According to relaxation experiments conducted in previous studies 42 a decreased relaxation modulus and thus an decreased surface displacement is to be expected with elevated Tg values. This correlation is confirmed based on the results of the numerical simulation.…”

“…Numerical and experimental values at the elevated curing temperature show significant differences which can be attributed to following aspects: The material data show particularly good fitting at 80°C. 42 Furthermore, fiber-matrix-interaction 60,61 is intensified through faster injection process which non-reproducibly influences fiber architecture and favors voids at elevated tooling temperatures. 62 Since impregnation defects during the impregnation process and subsequent formation of voids 63 are not taken into account in the numerical model, the surface waviness is underestimated in the numerical prediction.…”

“…46 The modelling parameters of the UD-NCF are based on the microscopic and computed -tomography analysis of the final specimen plates (Figure 2(a)). The simulation of the curing process is carried out using abaqus © 2022 combined with a subroutine of thermo-viscoelastic material model of the matrix developed in 42,43 and extensive material characterization previously published in. 12,44…”

“…To close this gap and to numerically predict the surface properties of FRP, the cure-dependent visco-thermo-elastic model introduced in 42,43 is used to predict the surface waviness of an epoxy resin composite. The underlying material data are taken from 12,44 and have previously been determined under process-specific conditions.…”

“…40 However, a comprehensive and complex experimental characterization of the resin material represents a prerequisite for the use of curedependent viscoelastic models. 41 To close this gap and to numerically predict the surface properties of FRP, the cure-dependent visco-thermo-elastic model introduced in 42,43 is used to predict the surface waviness of an epoxy resin composite. The underlying material data are taken from 12,44 and have previously been determined under process-specific conditions.…”