Fibre failure assessment in carbon fibre reinforced polymers under fatigue loading by synchrotron X-ray computed tomography

Abstract

Please cite this article as: Garcea SC, Sinclair I, Spearing SM, Fibre failure assessment in carbon fibre reinforced polymers under fatigue loading by synchrotron X-ray computed tomography, Composites Science and Technology (2016), doi: 10.1016/j.compscitech.2016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractIn situ fatigue experiments using synchrotron X-ray computed tomography (SRCT) are used to assess the underpinning micromechanisms of fibre failure in double edge notch carbon/epoxy coupons. Observations showed fibre breaks along the 0º ply splits, associated with the presence and failure of bridging fibres, as well as fibres failed in the bulk composite within the 0º plies. A tendency for cluster formation, with multiple adjacent breaks in the bulk composite was observed when higher peak loads were applied, exceeding 70% of the ultimate tensile stress. Ex situ fatigue tests were used to assess the accumulation and distribution of fibre breaks for different loading conditions, varying peak load and number of cycles. A direct comparison with the quasi-static case for an equivalent peak load, considering the same material system and geometry, hasshown that fatigue produces a significantly higher number of fibre breaks. This supports the hypothesis that fibre breaks are indeed caused by the load cycling.

A new model for fatigue life prediction based on infrared thermography and degradation process for CFRP composite laminates

“…Two failure cycles ( = N 10 fl 6 and = N 10 fl 7 ) related to fatigue limit were considered for the determination of the failure threshold stiffness, and then the whole − S N curve corresponding to each failure cycles. Compared to the S-N curve obtained by the traditional testing method, the − S N curve corresponding to = N 10 fl 7 for UD CFRP laminates is inside the 95% confidence intervals, while the predicted results for triaxially braided CFRP laminates are higher than experimental data. The − S N curve corresponding to = N 10 fl 6 is recommended for both of the two types of composite materials because the predicted results are relatively more conservative.…”

“…A number of Non-Destructive Evaluation (NDE) methods, such as radiography [5][6][7], acoustic emission [8][9][10][11] and infrared thermography [12][13][14][15][16][17] have been employed to in situ monitor and characterize damage evolution within metals and composites under cyclic loading. Among these methods, infrared thermography is advantageous for its real-time and non-contact measurement during fatigue tests.…”

Predicting damage accumulation and fatigue life of UD composites under longitudinal tension

“…Figures 5 and 6 show a good agreement between model predictions and experimental data. Nevertheless, the model predicts a large amount of variability for the total number of fibre breaks (see Figure 5b); this means that experimental data obtained with one specimen [5,6] only is not sufficient to fully validate the model.…”

“…Figure 5 shows the accumulation and clustering of fibre breaks in a UD carbon/epoxy specimen under cyclic longitudinal tension. The experimental results were obtained by Garcea et al [6] through ex-situ high-resolution computed tomography of the same carbon/epoxy material as analysed in Figure 4, but with a slightly different specimen geometry (see Table 1). …”

A computationally-efficient micromechanical model for the fatigue life of unidirectional composites under tension-tension loading

“…Only a few micromechanical approaches to predict fatigue of UD composite under cyclic longitudinal tension can be found in the literature. Ogin [43] used an analytical approach to predict the lifetime and residual strength of both UD and cross-ply composite laminates, by taking into account the fatigue growth of fibre/matrix interface debonds, as well as the statistical distribution of flaws along the fibres; however, the model neglected the formation of clusters of fibre-breaks, which has been recently shown to affect the failure process under fatigue [44]. Qian et al [37] developed a FE fatigue model for UD composites, where the fatigue damage of unit-cells with 7 and 45 fibres was analysed and, with a multi-scale approach, the fatigue life of coupon-sized specimens were predicted; the model, besides being computationally expensive, also over-estimated the fatigue life of the coupons.…”