1,721,063 research outputs found
Identification of kissing defects in adhesive bonds using infrared thermography
Full text linkA carbon fibre reinforced plastic (CFRP) adhesively bonded single lap joint sample is used for comparing the detection of different defect types using pulsed phase thermography (PPT). Firstly, a polytetrafluoroethene (PTFE) insert, of the type widely used to simulate defects in composite materials, was added to the bond line of the joint. Liquid layer kissing defects were simulated using silicon grease. PPT clearly identified the PTFE but not the silicon grease contamination. The PPT identified the silicon grease defect when the joint was loaded. It is postulated that kissing defects can be detected using thermography if a small load is applied to the joint, as loading opens the defect and produces a gap that provides sufficient thermal contrast for detection. Thermoelastic stress analysis (TSA) is used to validate the approach. On-site application is addressed both in terms of the load application and the use of low cost infrared (IR) detectors
Identification of lightning strike damage using Pulse Thermography through integration of thermal data
Full text linkPulse Thermography (PT) is based on the use of infrared imaging systems to detect thermal decay from a pulsed energy source as it passes through a component or sample. Carbon Fiber Reinforced Polymer (CFRP) composite materials damaged by simulated lightning strike are inspected using PT. A new damage detection approach is proposed which exploits the integral of the difference in temperature data over time between each pixel and a reference non-damaged pixel. The resulting integration provides a value for the thermal decay pixel-by-pixel relative to a non-damaged region, which provides a quantitative damage severity parameter. The proposed data processing method is evaluated using calibrated plate sample made from Glass Fiber Reinforced Polymer (GFRP) composite with known defects, and also to investigate CFRP samples damaged by lightning strikes. The calibrated GFRP plates are 4-ply stitched bi-axial E-glass fibers with a total laminate thickness of 2.4 mm. The known defects are 20 mm square PTFE inserts placed between plies to simulate a delamination. The resulting colormap correctly identifies the known defects and displays constant severity over the PTFE insert region. The same method is applied to the lightning damaged CFRP sample made of 5-ply stitched dry fabric. The resulting integration reveals the full extent of the damage, which cannot be identified by visual inspection
Damage in CFRP composites subjected to simulated lighting strike
No full textCarbon fibre composite materials are increasingly being used in the wind turbine, aerospace, and automotive industries to reduce the structural weight of components due to their high strength to weight and stiffness to weight ratios. However, the anisotropic material properties of Carbon Fibre Reinforced Polymers (CFRP), specifically their electrical and thermal conductivities, create challenges when protecting structures from lightning strike. Moreover, the exposure of CFRP structures/components to electric currents from lightning discharges can cause significant damage. This work investigates the damage inflicted and residual mechanical properties of a CFRP composite material that has been exposed to simulated lightning strike. Seven different CFRP laminate specimens were struck with simulated lightning strike using three different waveforms: the so-called 10/350 μs waveform, which simulates the first return stroke during a direct strike according to IEC 61400-24 Ed1.0, the second was a unipolar long stroke component, and the third was a combination of the first return stroke and the long stroke. Test specimens were prepared from CFRP panels that were damaged due to the lightning strike. The test specimens were subsequently subjected to compression and shear loading to determine the post-strike mechanical properties. The compression tests were conducted using uniaxial coupons and loaded in accordance with ASTM standard D6641. The shear tests were conducted using V-notch specimens utilizing an Iosipescu test rig in accordance with ASTM standard D5379. Digital Image Correlation was used to capture the strain fields on the specimens. The test results were compared against data obtained for pristine CFRP coupon samples that were not exposed to electrical current. The shear and compression strengths, compressive and shear stress-strain curves, compressive and shear moduli, and the maximum temperature captured in the specimens during the tests are presented and discussed. Key results include that the largest reduction of strength occurred in the specimens that were subjected to the largest current and specific energy, and further that damaged specimens respond with a higher degree of nonlinear behaviour than the pristine specimens
The manufacturing procedure for aerospace secondary sandwich structure panels
No full textThis study provides a detailed consideration of five manufacturing options that are used to produce aerospace sandwich panels used in secondary structure. The structural performance of each of the manufacturing options is considered along with a cost analysis. By considering the traditional preimpregnated (prepreg), autoclave-cured process, the sources of cost have been investigated, and it has been shown that by removing a portion of the large labor content and the autoclave cure, in favor of an oven-only cure, it would be possible to make significant savings. Monitoring the time to manufacture representative full-scale sandwich panels using the five manufacturing options has shown that by using a resin film infusion (RFI) oven cure, a 30% reduction in time to production is possible. To make an initial assessment of the comparative structural performance of laminates produced using the five manufacturing options, this article also presents results of material quality, in-plane and out-of-plane loading tests. The results of these tests show that the laminates produced using RFI are comparable in quality and performance to laminates produced using the current aerospace industry standard prepreg/autoclave process. <br/
Identification of the strain rate dependence of the elastic properties of CFRP using digital image correlation
No full textEnhancement of the electrical and thermal properties of unidirectional carbon fibre/epoxy laminates through the addition of graphene oxide
Full text linkA means of enhancing electrical and thermal conductivities of carbon fibre reinforced polymer (CFRP) composites is investigated for the purpose of reducing damage when electric current and/or heat is introduced into a CFRP structure. The addition of commercially available graphene oxide (GO) nano-flakes dispersed into an epoxy resin is studied; quantities up to 6.3 vol% are used in a vacuum infusion process with carbon fibre fabric to form CFRP laminates. Measurements of the anisotropic electrical and thermal conductivity of the laminate were conducted on CFRP specimens with and without the GO nano-flakes. It is shown that the electrical conductivity in the through-thickness direction increased markedly, reaching values up to 0.18 S/cm, when 6.3 vol% of GO was added into the epoxy, showing a threefold increase compared to the neat CFRP. Similar improvement was also found in the thermal through-thickness conductivity for the same filler content, where the laminate exhibited identical values in both transverse and through-thickness directions. However, the properties transverse to the fibres were not greatly affected by the GO addition. To assess the effect of the GO on the mechanical properties, interlaminar shear strength tests were conducted that showed that the addition of the GO significantly enhanced the through-thickness shear strength
Delamination prediction on CFRP materials subjected to a lightning strike
Full text linkThis paper presents a coupled thermal-electric-mechanical model to predict the delamination damage of a Carbon Fiber Reinforced Polymer (CFRP) material when subjected to a lightning strike. A Finite Element Model (FEM) is used to predict the heat response of the CFRP material by solving the Joule heating governing equations. The results of the heat response are coupled with thermal stresses to predicte interlaminar stresses. A bilinear traction law is used to predict the delamination of the laminate. Solutions to the model are developed using a time dependent simulation with the 10/350µs standard waveform to mimic a typical lightning strike on a wind turbine blade in accordance to IEC61400 section 24 Ed 1.0. The time dependent model implements damage criteria and is able to identify damaged elements. The COMSOL software engine was used to derive the results from the thermal-electrical-mechanical model. The final result is a delamination map of the CFRP panel subjected to a lightning discharge
Analysis of full-scale aerospace sandwich panels under pressure loading
No full textThis study provides a detailed consideration of five manufacturing options that are used to produce aerospace sandwich panels used in secondary structure. The structural performance of each of the manufacturing options is considered along with a cost analysis. A means of using optical strain analysis techniques on full scale panels is devised through the design of a test rig that is capable of applying uniform static and cyclic pressure to the panels
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