This work investigates hygrothermal aging degradation of unidirectional glass/epoxy composite specimens through a combination of experiments and numerical modeling. Aging is performed through immersion in demineralized water. Interlaminar shear testes are performed after multiple conditioning times and after single immersion/redrying cycles. Degradation of the fiber-matrix interface is estimated using single-fiber fragmentation tests and reverse modeling combining analytical and numerical models. A fractographic analysis of specimens aged at 50°C and 65°C is performed through X-ray computed tomography. The aging process is modeled using a numerical framework combining a diffusion analysis with a concurrent multiscale model with embedded hyper-reduced micromodels. At the microscale, a pressure-dependent viscoelastic/viscoplastic model with damage is used for the resin and fiber-matrix debonding is modeled with a cohesive-zone model including friction. A comparison between numerical and experimental results is performed.

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This paper investigates the viscoelastic/viscoplastic/fracture behavior of an epoxy resin. A state-of-the-art pressure-dependent elastoplastic constitutive model (Melro et al. 2013) is expanded to include viscoelasticity, viscoplasticity and a modified damage formulation with linear softening and shrinking pressure-dependent fracture surface. A water plasticization model with a single degradation factor is proposed. A set of new quasi-static and fatigue experiments is used to calibrate the model and assess its predictive capabilities. The model correctly represents the rate dependent plasticity and fracture initiation behavior of the studied epoxy. The stiffness and strength degradations after plasticization are also accurately captured. The model is found to be less suitable in reproducing the measured loading-unloading behavior, which displayed strong nonlinearity in combination with limited permanent deformation. Nevertheless, reasonably accurate fatigue life predictions in the low-cycle regime are obtained.@en

Mechanical properties of glass fibre reinforced polymers are dependent on the manufacturing curing cycles. During the laminate manufacturing process, each thickness position experiences a different local curing cycle. Therefore, it can be expected that mechanical properties vary through the thickness, particularly for thick laminates. To study the through-thickness variation of static and fatigue mechanical properties, thick laminates were divided into sub-laminates and these sub-laminates were separately tested. The present work reports temperature profiles through the thickness recorded during the manufacturing of thick laminates, as well as experimental data from static and fatigue tests (S-N curves) of sub-laminates obtained at different thickness positions. The variation of the mechanical properties through the thickness is discussed and related to the local curing temperatures experienced by each sub-laminate.

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In this paper, a method has been developed to use thermography for the quantitative analysis of a delamination area under dynamic loading. To demonstrate this method, a coupon was developed with double shear configuration and an initial delamination consisting of a PTFE insert. The coupon was tested under fatigue loading and an infrared (IR) camera was used to monitor the thermal response and delamination growth of the coupon during loading. The data from the thermal camera was processed in 2 steps, firstly a fast Fourier transform (FFT) was used to transform the raw data from time domain to frequency domain. In the second step, FFT thermographs were further processed using an image segmentation algorithm. Here, the thermal plots are segmented to separate the delaminated and un-delaminated areas. By computing the number of pixels in the delaminated region, the area of delamination was obtained at each cycle and has been plotted against the cycles to failure. The strain energy was computed with the help of force and displacement data from the test machine. Such signals allowed computing the fatigue propagation curves and understanding the fatigue behaviour of the test samples. This method looks promising and can be extended to test samples that cannot be tested by conventional testing methods@en

The aim of this work is to study the thickness effect in static and fatigue tests of glass-fibre unidirectional compression coupons. For this purpose, the self-heating effect, the effect of specimen geometry, and the influence of the manufacturing processes have been minimized. A scaled thickness compression coupon has been designed with the intention of reducing the influence of geometrical differences and of the manufacturing process as the thickness is scaled. In addition the self-heating effect was controlled by tuning the test frequency. The coupon design was based on a finite element analysis. The development of the manufacturing process and the design of the gripping configuration are reported in the present work. Experimental data from static and fatigue tests are reported for 4, 10 and 20 mm thick coupons where the static allowables, elastic modulus, Poisson ratios and the R=10 S-N curves are compared in order to evaluate the thickness effect.@en