Effect of delamination on the fatigue life of gfrp: a thermographic and numerical study (original) (raw)
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Influence of delamination on fatigue properties of a fibreglass composite
Composite Structures, 2014
Residual fatigue life, stiffness and strength are directly related to presence of defects and damages in composite materials, among which delamination is one of the most diffused. This work aims to study the effect of delamination on fatigue behaviour of a glass fibre reinforced composite. Experimental tests are carried out to check fatigue life decrease of delaminated specimens, with a Teflon layer at half of its thickness, by a comparison with undamaged material. In order to evaluate defects presence and their progressive evolution, infrared thermography is taken into account, monitoring surface temperature of the damaged and undamaged samples. Static and fatigue tests are carried out, and a high cycle fatigue limit is identified for this composite material. Three approaches, based on thermal observations of static and dynamic tests at increased stress amplitude, revealed a relation between thermal response of the material and the fatigue limit. From this standpoint, thermography can be indicated as a valid tool to monitor damage initiation and its evolution during testing, and to estimate fatigue life.
Composite Structures, 2016
This paper details a study on the application of Thermoelastic Stress Analysis (TSA) for the investigation of delamination damage propagation in glass fibre reinforced composite materials. A woven Glass (0/90)/Epoxy composite sample containing a purposely created delamination was subjected to a step-cyclic loading (varying mean level) while monitoring the thermoelastic response of the sample with an infrared camera. A finite element analysis (FEA) was performed using cohesive elements to simulate the propagation of the delamination under a monotonically increasing axial load. It is shown that the delamination crack length inferred from the TSA results is consistent with microscopic analysis of the sample, and that the measured crack growth rate is in reasonable agreement with simulation results.
Journal of Theoretical and Applied Mechanics
Delamination crack growth is a major source of failure in composite laminates under static and fatigue loading conditions. In the present study, damage mechanics based failure models for both static and fatigue loadings are evaluated via UMAT subroutine to study the delamination crack growth phenomenon in Glass Fiber Reinforced Plastic (GFRP) composite laminates. A static local damage model proposed by Allix and Ladevèze is modified to an non-local damage model in order to simulate the crack growth behavior due to static loading. Next, the same classical damage model is modified to simulate fatigue delamination crack growth. The finite element analysis results obtained by the proposed models are successfully compared with the available experimental data on the delamination crack growth for GFRP composite laminates.
International Journal of Aerospace Engineering
Glass fibre-reinforced plastic (GFRP) composite laminates are used in many industries due to their excellent mechanical and thermal properties. However, these materials are prone to the initiation and propagation of delamination crack growth between different plies forming the laminate. The crack propagation may ultimately result in the failure of GFRP laminates as structural parts. In this research, a comprehensive mathematical model is presented to study the delamination crack growth in GFRP composite laminates under fatigue loading. A classical static damage model proposed by Allix and Ladevèze is modified as a fatigue damage model. Subsequently, the model is implemented in commercial finite element software via UMAT subroutine. The results obtained by the finite element simulations verify the experimental findings of Kenane and Benzeggagh for the fatigue crack growth in GFRP composite laminates.
Composite Structures, 2018
The introduction, originally in 2009, by the FAA of a 'slow growth' approach to the certification of polymer-matrix fibre composites has focused attention on the experimental data and the analytical tools needed to assess the growth of delaminations under cyclic-fatigue loads. Of direct relevance is the fact that fatigue tests on aircraft composite components and structures reveal that no, or only little, retardation of the fatigue crack growth (FCG) rate occurs as delamination/impact damage grows. Therefore, of course, the FCG data that are ascertained in laboratory tests, and then employed as a material-allowable property to design and life the structure, as well as for the development, characterisation and comparison of composite materials, must also exhibit no, or only minimal, retardation. Now, in laboratory tests the double-cantilever beam (DCB) test, using a typical carbon-fibre reinforced-plastic (CFRP) aerospace composite, is usually employed to obtain fracture-mechanics data under cyclic-fatigue Mode I loading. However, it is extremely difficult to perform such DCB fatigue tests without extensive fibre-bridging developing across the crack faces. This fibre-bridging leads to significant retardation of the FCG rate. Such fibre-bridging, and hence retardation of the FCG, is seen to arise even for the smallest values of the pre-crack extension length, a p-a 0 , that are typically employed. The results from the DCB tests also invariably exhibit a relatively large degree of inherent scatter. Thus, a methodology is proposed for predicting an 'upper-bound' FCG curve from the laboratory test data which is representative of a composite laminate exhibiting no, or only very little, retardation of the FCG rate under fatigue loading and which takes into account the inherent scatter. To achieve this we have employed a novel methodology, based on using a variant of the Hartman-Schijve equation, to access this 'upperbound' FCG rate curve, which may be thought of as a material-allowable property and which is obtained using an 'A basis' statistical approach. Therefore, a conservative 'upper-bound' FCG curve may now be calculated from the DCB laboratory test data for material development, characterision and comparative studies, and for design and lifing studies.
Damage evolution and infrared thermography in woven composite laminates under fatigue loading
International Journal of Fatigue, 2006
An analytical model based on cumulative damage has been used for predicting the damage evolution in composite materials. The model is verified with experimental data from a carbon/epoxy composite fatigued under tension-tension load. Fatigue tests of specimens have been monitored with an infra-red thermography system. By analysing the temperature of the external surface during the application of cyclic loading, it is possible to evaluate the damage evolution. The model agrees well with the experimental data, and it can be used to predict the evolution of damage in composites.
Damage assessment of composite materials by means of thermographic analyses
Composites Part B: Engineering, 2013
Composite materials are largely used for structural applications, thanks to their high strength-to-weight ratios. However, it is difficult to make accurate estimations on their mechanical behavior, as it is affected by several factors, involved both in the manufacturing process and in the experimental testing. In this study, GFRP laminates, with different stacking sequences, are tested under static loading conditions. During testing, thermal analyses are also performed by means of a thermal camera, obtaining an energetic parameter (i.e. the temperature) useful for the evaluation of damage. The thermographic method allows both qualitative and quantitative analyses to be performed in a relatively short time. Besides thermal analyses, damage is also assessed by means of static tests, interrupted at different load levels, and followed by stiffness reduction measurements and microscopic analyses, allowing for a comparison of the obtained results.
A new rapid thermographic method to assess the fatigue limit in GFRP composites
Composites Part B: Engineering, 2016
Conventional procedures and methods used for obtaining the fatigue performance of materials represent a critical aspect of mechanical characterization because of time consuming tests with a high number of specimens. In the last few years, great efforts have been made to develop a number of methods aimed at reducing testing time and, subsequently, the cost of the experimental campaign. In the process, thermographic methods have shown to be a useful tool for the rapid evaluation of fatigue damage and fatigue limit. This work deals with a new procedure for the evaluation of fatigue limit and the monitoring of damage in GFRP material by means of thermography. Although damage mechanisms in composite materials are difficult to understand, the proposed procedure allows us to obtain a number of parameters providing information relating to the onset of failure phenomena. It is worth noting that the reported procedure provides results in good agreement with those attained by the standard test methods.
Delamination analysis by damage mechanics: Some applications
Composites Engineering, 1995
Ahstraet-Delamination is a phenomenon which involves complex degradation of both layers and inter-laminar connections. To take into account these degradations, the composite laminate is modeled at a meso scale as a stacking of homogeneous layers connected by interfaces. Layers and interfaces may be damaged. Both onset of delamination and its propagation on a short distance are predicted. Two applications are presented, the numerical simulations are compared with experimental results: (i) delamination in the vicinity of a straight edge of a specimen under tension or compression, (ii) delamination near the hole of a perforated plate under tension.
Engineering Fracture Mechanics, 2013
An overview is given of the development of methods for the prediction of fatigue driven delamination growth over the past 40 years. Four categories of methods are identified: stress/strain-based models, fracture mechanics based models, cohesive-zone models, and models using the extended finite element method. It is highlighted that most models are phenomenological, based on the observed macro-scale behaviour of test specimens. It is suggested that a more physics based approach, focusing on elucidating the mechanisms involved, is needed to come to a full understanding of the problem of delamination growth.