Influence of delamination on fatigue properties of a fibreglass composite (original) (raw)
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Fatigue damage analysis of composite materials using thermography-based techniques
Procedia structural integrity, 2019
Composite materials are nowadays used in many fields of industry, especially for producing large structural components in many applications ranging from naval to aerospace. Beside to the capability and versatility of uses, the study of damage in composites is not easy due to the different failure mechanisms that can occur simultaneously or in different conditions. The characterisation of composites represents then a critical stage of assessing mechanical properties and resistance and a careful attention has to be put in the study and damage analysis. Due to this, the fatigue performances imposed by Standards have to be verified by means of experimental techniques involving experimental campaign in laboratory on samples or directly on large components. However, classical procedures for evaluating the fatigue resistance of materials present two issues: the expensive and time-consuming tests because of the high number of specimens being tested, and the totally absence of information on occurring damage. 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. Among the different techniques, for instance, thermographic methods are considered as a useful tool for the rapid evaluation of fatigue damage and fatigue resistance at specific cycles number (endurance limit). The capability of thermography, is not only, related to the experimental procedure providing specific tests capable of assessing fatigue resistance in accelerated way, but also to study the energy involved in the fatigue processes. As previously said, damage mechanisms in composite materials are difficult to be understood and even a small scale anomaly can lead the failure of the material without visible damage or visible signs of the onset of failure phenomena. For this reason, energy intrinsically dissipated can be another point of view to face up to a sudden failure. In this way, energy-related parameters assessed by the analysis of thermographic signal can be useful for assessing information related to the onset of irreversible damage. The focus of the present research is to provide an innovative method for process thermal signal from innovative composites obtained by Automated Fiber Placement process in order to understand the fatigue behaviour qualitatively and quantitatively.
Effect of delamination on the fatigue life of gfrp: a thermographic and numerical study
Composite Structures
Delamination is the major failure mechanism in composite laminates and eventually leads to material failure. An early-detection and a better understanding of this phenomenon, through non-destructive assessment, can provide a proper in situ repair and allow a better evaluation of its effects on residual strength of lightweight structural components. Here we adopt a joint numerical-experimental approach to study the effect of delamination on the fatigue life of glass/epoxy composites. To identify and monitor the evolution of the delamination during loading, we carried out stepwise cyclic tests coupled with IR-thermography on both undamaged and artificially-damaged samples. The outcome of the tests shows that IRthermography is able to identify a threshold stress, named damage stress σ D , which is correlated to the damage initiation and the fatigue performance of the composite. Additionally, we performed FE-simulations, implementing the delamination by cohesive elements. Such models, calibrated on the basis of the experimental fatigue results, can provide a tool to assess the effect of parameters, such as the delamination size and location, and composite stacking sequence, on the residual strength and fatigue life of the composite material.
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.
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.
Thermal phenomenon of glass fibre composite under tensile static and fatigue loading
JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES, 2017
The aim of this study is to understand the thermal phenomenon of unidirectional Glass Fibre Reinforced Polymer (GFRP) composite under static and fatigue (tensile) loads. This study used a rectangular shaped GFRP composite and consisted of specimens with and without a circular notch. Under static test, the constant displacement rate was applied. Under fatigue test, frequency and amplitude of stress were explored to study the fatigue properties and damage evolution of the specimen. Thermography was used in real-time observation to obtain the temperature profile on the external surface of the specimens. This experimental method showed that the thermal phenomenon gave a good detection of the damage appearance of GFRP material under static loading. Moreover, thermal phenomenon gave a good correlation with the energy dissipation under fatigue loading. Thermal phenomenon successfully determined the high cycle fatigue strength of GFRP composite. This study concluded that thermal phenomenon observed by Infra-Red (IR) camera has successfully demonstrated the damage propagation and the strength behaviour of GFRP composite due to tensile loading in both static and fatigue conditions. The IR camera can then be used to determine the damage evolution and the strength prediction based on the thermal phenomenon on the external surface of the GFRP composite.
A review of thermographic techniques for damage investigation in composites.PDF
The aim of this work is a review of scientific results in the literature, related to the application of thermographic techniques to composite materials. Thermography is the analysis of the surface temperature of a body by infrared rays detection via a thermal-camera. The use of this technique is mainly based on the modification of the surface temperature of a material, when it is stimulated by means of a thermal or mechanical external source. The presence of defects, in fact, induces a localized variation in its temperature distribution and, then, the measured values of the surface temperature can be used to localize and evaluate the dimensions and the evolution of defects. In the past, many applications of thermography were proposed on homogeneous materials, but only recently this technique has also been extended to composites. In this work several applications of thermography to fibres reinforced plastics are presented. Thermographic measurements are performed on the surface of the specimens, while undergoing static and dynamic tensile loading. The joint analysis of thermal and mechanical data allows one to assess the damage evolution and to study the damage phenomenon from both mechanical and energetic viewpoints. In particular, one of the main issues is to obtain information about the fatigue behaviour of composite materials, by following an approach successfully applied to homogenous materials. This approach is based on the application of infrared thermography on specimens subjected to static or stepwise dynamic loadings and on the definition of a damage stress, D , that is correlated to the fatigue strength of the material. A wide series of experimental fatigue tests has been carried out to verify if the value of the damage stress, D , is correlated with the fatigue strength of the material. The agreement between the different values is good, showing the reliability of the presented thermographic techniques, to the study of composite damage and their fatigue behaviour.
Delamination Detection By Thermography
Infrared thermography is a twodimensional, non-contact technique allowing surface temperature mapping by providing colourful images easy to interpret through the use of an external energy source and an infrared detector. The attention of the present study was focused on the aid provided by active thermography for non-destructive evaluation of composite material. In present work the experimental analysis was performed by testing several specimens, which were made of E glass woven with epoxy which included the most commonly encountered kinds of damage called delamination artificially created in composite laminate specimens. From the experimental investigations, the effects of delamination area on the detection were elucidated. Also the applicability of the present thermograph method depends on a relative difference of thermal property between the delamination and its surrounding was explained.
A review of thermographic techniques for damage investigation in composites
Frattura ed Integrità Strutturale
The aim of this work is a review of scientific results in the literature, related to the application of thermographic techniques to composite materials. Thermography is the analysis of the surface temperature of a body by infrared rays detection via a thermal-camera. The use of this technique is mainly based on the modification of the surface temperature of a material, when it is stimulated by means of a thermal or mechanical external source. The presence of defects, in fact, induces a localized variation in its temperature distribution and, then, the measured values of the surface temperature can be used to localize and evaluate the dimensions and the evolution of defects. In the past, many applications of thermography were proposed on homogeneous materials, but only recently this technique has also been extended to composites. In this work several applications of thermography to fibres reinforced plastics are presented. Thermographic measurements are performed on the surface of the specimens, while undergoing static and dynamic tensile loading. The joint analysis of thermal and mechanical data allows one to assess the damage evolution and to study the damage phenomenon from both mechanical and energetic viewpoints. In particular, one of the main issues is to obtain information about the fatigue behaviour of composite materials, by following an approach successfully applied to homogenous materials. This approach is based on the application of infrared thermography on specimens subjected to static or stepwise dynamic loadings and on the definition of a damage stress, D , that is correlated to the fatigue strength of the material. A wide series of experimental fatigue tests has been carried out to verify if the value of the damage stress, D , is correlated with the fatigue strength of the material. The agreement between the different values is good, showing the reliability of the presented thermographic techniques, to the study of composite damage and their fatigue behaviour.
Thermographic diagnosis of fatigue degradation of epoxy-glass composites
2007
AbstrAct Purpose: The purpose of this paper was to describe results of application of thermography to evaluate the degree of fatigue degradation of epoxy-glass composites. Design/methodology/approach: Samples of epoxy-glass composite were subjected to fatigue degradation. During fatigue test, after defined number of cycles, samples were heated using infra-red heater and at the opposite side temperature increase was evaluated with thermovision camera. Findings: Analysis of achieved results allowed to elaborate relation between number of fatigue cycles and the degree of fatigue degradation. Such relation may be applied in diagnostic procedures. Research limitations/implications: Performed tests were of preliminary character and results will be applied to prepare research programme on thermographic testing of composites. Practical implications: Results of such tests may be applied in the future in diagnostic procedures to nondestructive evaluation of the degree of fatigue degradation of high performance polymer composites. Originality/value: Thermographic methods are applied up till now to non-destructive flaws detection. Proposed in the paper method may be applied to evaluate the degree of thermal and fatigue degradation in composites without any macroscopic flaws.
Journal of Composites Technology and Research, 1994
A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TM_ cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the macroscopic coefficient of thermal expansion (CTE) to be measured and collected as functions of the TMF cycles. The specific implementation was incorporated into the commonly employed idealized in-phase and out-of-phase TMF cycles. However, the techniques discussed could be easily implemented into any form of load-controlled TMF mission cycle. By quantifying the degradations of these properties, tremendous insights are gained concerning the progression of macroscopic composite damage and often times the progression of damage within a given constituent. This information should also be useful for the characterization and essential for the verification of analytical damage modeling methodologies. Several examples utilizing this test technique are given for three different fiber lay-ups of titanium metal matrix composites.