Post- Impact Fatigue Damage Analysis of Quasi Isotropic CFRP Laminates through Infrared Thermography
24 Jun 2019-Vol. 13, Iss: 49, pp 536-546
TL;DR: In this paper, the infrared thermography NDT technique was used for the damage analysis of these post-impact fatigue loaded carbon fiber reinforced plastic (CFRP) specimens to understand the damage distribution across the specimen.
Abstract: Carbon fiber reinforced plastic (CFRP) materials used for lightweight aircraft structures are susceptible to low velocity accidental impacts during manufacture and while in service. In this study the CFRP laminates subjected to low velocity impact conditions of three different energy levels were tested under various fatigue loading conditions till it reached the failure state. The infrared thermography NDT technique was used for the damage analysis of these post-impact fatigue loaded CFRP specimens to understand the damage distribution across the specimen. The cooling response curves obtained from the active thermography of the post impact fatigue specimens under four different combinations (transmission or reflection mode with impacted or un-impacted surface facing camera) for each of the specimens were analyzed. The rate of cooling in the temperature response curves is different for each specimens subjected with various post impact-fatigue loading conditions and it seems to be correlated with the extent of post-impact fatigue damage present in each specimen quantified through X-ray CT image processing. The temperature rise observed in the passive thermography at the fiber/ply breakage during static strength tests were proportional to corresponding load drops and the non-homogeneous spread of damage at the onset of tensile failure was seen from the thermographs.
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TL;DR: In this article , the impact resistance of carbon fiber-reinforced polyurethane (CFR-PU) was investigated with subsequent comparison of different methods for damage detection.
Abstract: With the increasing use of fiber-reinforced polymers in safety–critical applications, detailed investigations of material behavior under various mechanical loads are mandatory. Since carbon fiber-reinforced polyurethane can often be found in aerospace and automotive industries, good impact resistance is required for potential crashes and bird strikes. Besides the determination of characteristic values from impact and cyclic tests, the impact damage detection and observation in subsequent tests via non-destructive testing, is of prime importance. Thus, the impact resistance of CFR–PU was investigated with subsequent comparison of different methods for damage detection. The fatigue after impact performance was carried out by performing multiple amplitude tests. The impact tests resulted in a linear grow of damage area with increasing impact energies. Multiple amplitude tests showed a significant decrease in fatigue after impact strength, especially, if fiber failure and delamination occurred. The successive material damage could be described by evaluating dynamic stiffness and specimen temperature.
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TL;DR: In this paper, the authors experimentally tested three composite structures made of glass fiber-reinforced plastic, hybrid composite with a core made of the same material and face sheets made of aluminum alloy and a carbon fiber reinforced plastic structure extracted from the vertical stabilizer of a military aircraft.
Abstract: The application of polymeric composites as materials for structural design of vehicles and other constructions has led to maintain them in safe and effective manner. A special attention should be paid to the aircraft structures, which must be lightweight and reveal superior mechanical properties in order to fulfill growing demands in this industry. Thus, the non-destructive testing techniques applied for such materials should be evaluated in several categories: effectiveness in detection, localization and identification of damage in possible early phase of their development, complexity of application and a cost of inspection. In the following study the authors experimentally tested three composite structures made of glass fiber-reinforced plastic, hybrid composite with a core made of the same material and face sheets made of aluminum alloy and a carbon fiber-reinforced plastic structure extracted from the vertical stabilizer of a military aircraft with barely visible impact damage and delaminations. The tests were performed using various techniques including PZT sensing, ultrasonic, thermography and vibration-based inspection in order to analyze the applicability of these methods in the environmental conditions of inspection of aircraft elements. The performed analysis allows concluding about effectiveness of the applied methods and their specific applications in non-destructive testing of composite elements.
247 citations
"Post- Impact Fatigue Damage Analysi..." refers background in this paper
...In order to provide practical information on the damage state of FRP composite materials, a number of non-destructive methods that are well-established can be employed [2-4]....
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TL;DR: In this paper, the fatigue mechanisms of wind turbine blades were examined using computed tomography (CT) to identify key damage mechanisms, such as transverse matrix cracking in the surface layer, occurring predominantly at free edges.
Abstract: The fatigue mechanisms of Glass Fibre Reinforced Polymer (GFRP) used in wind turbine blades were examined using computed tomography (CT). Prior to mechanical testing, as-manufactured [+45/?45/0]3,s glass/epoxy specimens were CT scanned to provide 3-dimensional images of their internal microstructure, including voids. Voids were segmented and extracted, and individual characteristics and volumetric distributions were quantified. The coupons were then fatigue tested in uniaxial loading at R = ?1% to 40% of the nominal tensile failure stress. Some tests were conducted to failure for correlation with the initial void analysis and to establish failure modes. Other tests were stopped at various life fractions and examined using CT to identify key damage mechanisms. These scans revealed transverse matrix cracking in the surface layer, occurring predominantly at free edges. These free-edge cracks then appeared to facilitate edge delamination at the 45/?45° interface. Propagation from sub-critical, surface ply damage to critical, inner ply damage was identified with either a ?45/0° delamination, or a 0° fibre tow failure allowing a crack to propagate into the specimen bulk. Final failure occurred in compression and was characterised by total delamination between all the 45/?45° plies. A quantitative void analysis, taken from the pre-test CT scans, was also performed and compared against the specimens’ fatigue lives. This analysis, to the authors’ knowledge the first of its kind, measured and plotted approximately 10,000 voids within the gauge length of each specimen. The global void measurement parameters and distributions showed no correlation with fatigue life. A local ply-level investigation revealed a significant correlation between the largest void and fatigue life in the region of the laminate associated with the crack propagation from sub-critical to critical damage
153 citations
TL;DR: In this paper, the authors used infrared thermography and phased array ultrasonic to detect defects and impact damage in carbon fiber reinforced composites and recorded a video during the impact event.
Abstract: Infrared thermography and phased array ultrasonic are used to detect defects and impact damage in carbon fibre reinforced composites. Apart from its use as non-destructive evaluation technique, infrared thermography is also employed to record a video during the impact event. The visualization of thermal signatures, caused by local dissipation of impact energy, allows gaining information which is useful for understanding the material response to impact. In particular, the two techniques allow for estimation, in a reliable way, of the overall delamination extension which is of utmost importance for material design purposes.
143 citations
"Post- Impact Fatigue Damage Analysi..." refers background in this paper
...537 visible, effective in-situ NDT methods are important; equally important is the need to understand damage progression in such materials under fatigue loading for effective life prediction [1]....
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TL;DR: In this paper, the authors investigated the fatigue behavior of a braided carbon fiber polymeric composite plate and used a thermographic approach to rapidly determine the composite high cycle fatigue strength.
Abstract: Thermography was used to investigate the fatigue behavior of a braided carbon fiber polymeric composite plate. A thermographic approach, originally developed in an earlier study for metallic alloys, was employed to rapidly determine the composite high cycle fatigue strength. The method yielded a fatigue threshold value that was in excellent agreement with that obtained through a conventional experimental test program. The damage mechanisms responsible for the increased heat dissipation and ultimately failure were identified, which provides support for the existence of a fatigue threshold for this material. An extension of the thermographic technique to rapidly determine the entire fatigue stress-life curve for the composite plate provided a direct correlation to the stress-life curve determined through a conventional test program. Energy dissipation was also used as an indicator to determine the high cycle fatigue strength, providing support for the thermographic approach. A relationship between the dissipated heat, the intrinsic energy dissipation and the number of cycles to failure has been clearly established.
142 citations
"Post- Impact Fatigue Damage Analysi..." refers methods in this paper
...The authors state that IRT is quite successful in detecting damage initiation and growth; hence, it is an effective technique for assessing the fatigue damage progression in components made of composite materials [5]....
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...John Montesano et al. (2013) conducted fatigue studies on carbon fiber-polyimide resin composite and stated that the high cycle fatigue strength determined using the thermographic approach showed excellent correlation with that of conventional stress-life curve....
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TL;DR: In this paper, the authors assess the comparative accuracy and reliability of conventional and novel void characterisation techniques for analysing voids within carbon fiber reinforced composite (CFRC) laminates.
Abstract: Voids and porosity are critical imperfections in fibre reinforced composite materials. The aim of this study is to assess the comparative accuracy and reliability of conventional and novel void characterisation techniques for analysing voids within carbon fibre reinforced composite (CFRC) laminates. While microscopy and Archimedes density measurements can only give results of limited accuracy and reliability, micro-computed tomography (micro-CT) analysis was found to have no significant inherent errors and is able to characterise the three-dimensional size, shape and distribution of voids in CFRC laminates. The accuracy of micro-CT was also verified by analysing artificial voids of a known size and shape disbursed throughout a CFRC laminate sample.
129 citations
"Post- Impact Fatigue Damage Analysi..." refers background in this paper
...The recent advances in the X-ray CT aid the researchers in detecting and characterizing damages in the fiber reinforced composite materials in the three dimensions [7,8]....
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