This paper presents a viscoelastic temperature- and degree-of-cure-dependent constitutive model for an epoxy resin. Multi-temperature relaxation tests on fully and partially cured rectangular epoxy specimens were conducted in a dynamic mechanical analysis apparatus with a three-point bending clamp. Master curves were constructed from the relaxation test results based on the time–temperature superposition hypothesis. The influence of the degree of cure was included through the cure-dependent glass transition temperature which was used as reference temperature for the shift factors. The model parameters were optimized by minimization of the differences between the model predictions and the experimental data. The model predictions were successfully validated against an independent creep-like strain history over which the temperature varied.
Adhesive bonding modelling is often realised using cohesive zone models (CZM). For pure mode I loading, these laws represent the cohesive stress versus the interface displacement evolution designated as traction-separation laws (TSL). They enable the description of the interface irreversible phenomena such as damage and/or plasticity, while permitting a refined evaluation of the cohesive stress along the overlap. However, these laws are usually chosen a priori. For brittle and ductile adhesives the TSL shapes usually chosen are respectively bilinear softening and elasto-plastic. But the development of direct CZM measurements has highlighted that the law shapes can be more complex. The wrong initial choice of the TSL shape can then have an impact on the simulation results reliability. In this article, several methods used to evaluate CZM parameters are compared in terms of TSL shape robustness. Synthetic noisy data generated from a trapezoidal CZM are used for the inverse identification of a bilinear softening TSL. By applying this procedure on different type of synthetic measurements (respectively Force-displacement, J-integral, backface strain and DIC) the ability of these techniques to capture parameters for a chosen CZM shape that is not the right one enables a rigorous evaluation the robustness to the law shape.
Adhesive bondline mechanical behaviour is frequently described with cohesive zone models (CZM). For mode I loading condition these phenomenological laws simply represent the evolution of the peel stress as a function of the two adherends relative displacement normal to the joint. Generally, these laws are identified rather than really measured using experimental data obtained from crack initiation and propagation experiments such as the Double Cantilever Beam Test (DCB). The uncertainty on parameter estimation are generally not indicated, as for a DCB test it is only the critical energy release rate that has the most influence on the results. However, the uncertainties on the other parameters prevent the use of the identified TSL for other mechanical tests where mode I solicitations are predominant. In this article, the purpose is to evaluate the methodologies reliability for the assessment of mode I CZM. To do so, several methods used to evaluate CZM parameters are compared in terms parameter estimation reliability. Synthetic noisy data are considered for a χ² function minimisation. Then, sensitivity calculations are performed to determine the estimated parameters standard deviation. By applying this procedure on different type of synthetic measurements (respectively P(), J(,), backface strain and DIC) the ability of these different techniques to capture the best parameters for a chosen CZM shape can be rigorously evaluated.
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