The Experts below are selected from a list of 18 Experts worldwide ranked by ideXlab platform
John Wang - One of the best experts on this subject based on the ideXlab platform.
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Proposed through-life management approaches for adhesively bonded repair of primary structures
International Journal of Adhesion and Adhesives, 2018Co-Authors: Alan R. H. Baker, John WangAbstract:Abstract The inability of current non-destructive inspection (NDI) procedures to confirm bond integrity has greatly limited the application of adhesively bonded repairs to primary aircraft structure, especially in applications where failure of the repair would lead to safety in flight concerns. Given these concerns, applications to primary structure are generally limited to situations where the residual Strength of the parent structure in the absence of the repairs can exceed the Design limit load by an acceptable factor, most conservatively as high as 1.5, which is the Design Ultimate Strength. This paper proposes technologies and associated strategies that could lead to some relaxation of the current residual Strength requirements. This makes possible the wider application of adhesively bonded repairs to primary metallic structure suffering fatigue cracks and composite airframe structure suffering visible impact damage. The detection of weak, and even absent (“Kissing”), adhesive bonds generally requires the application of a significant stress to the region of the adhesive bond which cannot be achieved by conventional NDI – ultrasonic techniques for example. Since it is generally not feasible to stress the actual repair patch, a “Proof Test” has been developed. This test requires the application of shear stress to a bonded repair coupon (BRC) made of the patch material. The BRC is bonded to the parent structure concurrently with the patch. This test can confirm both the initial and through-life structural integrity of the repair bond. However, it must be agreed by the appropriate authority that the BRC is fully representative of the patch system. In addition to the proof test more critical repairs also require through-life structural health monitoring (SHM) with a focus on detecting patch disbonding and a secondary focus in the case of repairs to metals of monitoring crack growth. It is concluded that to detect patch disbonding, a simple approach using resistance strain gauges, or more robustly optical fibre sensors, holds the most promise, at least in the short term. Disbonding is detected from measurements of reductions in strain transfer from the parent structure into the patch, an approach previously demonstrated during full-scale fatigue testing of a repaired F111 wing. Based on use of the Proof Test together with SHM, as appropriate, decision charts are presented for the management of adhesively bonded repairs to fatigue cracks in metallic structure in which the crack is not removed and to composite structure following removal of visual impact damage. A simple approach to the management of stress-reducing reinforcements for metallic components is also presented.
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on the certification of bonded repairs to primary composite aircraft components
Journal of Adhesion, 2015Co-Authors: A A Baker, Andrew J Gunnion, John WangAbstract:Airworthiness certification is required when bonded repairs are made to primary composite structure in situations where damage has reduced or has the potential to reduce residual Strength to below the Design Ultimate Strength. Generally, certification of bonded primary structure poses many difficulties. As most repairs are one-off events meeting these certification requirements is especially challenging since demonstration by testing will generally not be possible or cost-effective. This paper discusses options for addressing the two key issues relating to certification: (a) how to validate initial and enduring bond Strength of adhesive bonds, mainly given the inability of conventional non-destructive inspection to provide this assurance and (b) how to develop acceptable generic Design allowables for bonded repairs which represent actual failure modes – especially for cyclic loading, since validation by testing of simulated repairs will generally be infeasible. It is concluded that proof testing of bonded...
A A Baker - One of the best experts on this subject based on the ideXlab platform.
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on the certification of bonded repairs to primary composite aircraft components
Journal of Adhesion, 2015Co-Authors: A A Baker, Andrew J Gunnion, John WangAbstract:Airworthiness certification is required when bonded repairs are made to primary composite structure in situations where damage has reduced or has the potential to reduce residual Strength to below the Design Ultimate Strength. Generally, certification of bonded primary structure poses many difficulties. As most repairs are one-off events meeting these certification requirements is especially challenging since demonstration by testing will generally not be possible or cost-effective. This paper discusses options for addressing the two key issues relating to certification: (a) how to validate initial and enduring bond Strength of adhesive bonds, mainly given the inability of conventional non-destructive inspection to provide this assurance and (b) how to develop acceptable generic Design allowables for bonded repairs which represent actual failure modes – especially for cyclic loading, since validation by testing of simulated repairs will generally be infeasible. It is concluded that proof testing of bonded...
Alan R. H. Baker - One of the best experts on this subject based on the ideXlab platform.
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Proposed through-life management approaches for adhesively bonded repair of primary structures
International Journal of Adhesion and Adhesives, 2018Co-Authors: Alan R. H. Baker, John WangAbstract:Abstract The inability of current non-destructive inspection (NDI) procedures to confirm bond integrity has greatly limited the application of adhesively bonded repairs to primary aircraft structure, especially in applications where failure of the repair would lead to safety in flight concerns. Given these concerns, applications to primary structure are generally limited to situations where the residual Strength of the parent structure in the absence of the repairs can exceed the Design limit load by an acceptable factor, most conservatively as high as 1.5, which is the Design Ultimate Strength. This paper proposes technologies and associated strategies that could lead to some relaxation of the current residual Strength requirements. This makes possible the wider application of adhesively bonded repairs to primary metallic structure suffering fatigue cracks and composite airframe structure suffering visible impact damage. The detection of weak, and even absent (“Kissing”), adhesive bonds generally requires the application of a significant stress to the region of the adhesive bond which cannot be achieved by conventional NDI – ultrasonic techniques for example. Since it is generally not feasible to stress the actual repair patch, a “Proof Test” has been developed. This test requires the application of shear stress to a bonded repair coupon (BRC) made of the patch material. The BRC is bonded to the parent structure concurrently with the patch. This test can confirm both the initial and through-life structural integrity of the repair bond. However, it must be agreed by the appropriate authority that the BRC is fully representative of the patch system. In addition to the proof test more critical repairs also require through-life structural health monitoring (SHM) with a focus on detecting patch disbonding and a secondary focus in the case of repairs to metals of monitoring crack growth. It is concluded that to detect patch disbonding, a simple approach using resistance strain gauges, or more robustly optical fibre sensors, holds the most promise, at least in the short term. Disbonding is detected from measurements of reductions in strain transfer from the parent structure into the patch, an approach previously demonstrated during full-scale fatigue testing of a repaired F111 wing. Based on use of the Proof Test together with SHM, as appropriate, decision charts are presented for the management of adhesively bonded repairs to fatigue cracks in metallic structure in which the crack is not removed and to composite structure following removal of visual impact damage. A simple approach to the management of stress-reducing reinforcements for metallic components is also presented.
Andrew J Gunnion - One of the best experts on this subject based on the ideXlab platform.
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on the certification of bonded repairs to primary composite aircraft components
Journal of Adhesion, 2015Co-Authors: A A Baker, Andrew J Gunnion, John WangAbstract:Airworthiness certification is required when bonded repairs are made to primary composite structure in situations where damage has reduced or has the potential to reduce residual Strength to below the Design Ultimate Strength. Generally, certification of bonded primary structure poses many difficulties. As most repairs are one-off events meeting these certification requirements is especially challenging since demonstration by testing will generally not be possible or cost-effective. This paper discusses options for addressing the two key issues relating to certification: (a) how to validate initial and enduring bond Strength of adhesive bonds, mainly given the inability of conventional non-destructive inspection to provide this assurance and (b) how to develop acceptable generic Design allowables for bonded repairs which represent actual failure modes – especially for cyclic loading, since validation by testing of simulated repairs will generally be infeasible. It is concluded that proof testing of bonded...
Ahamed J - One of the best experts on this subject based on the ideXlab platform.
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Hybrid composite ply joints for integrating radiofrequency apertures in multifunctional aircraft structures
RMIT University, 2018Co-Authors: Ahamed JAbstract:Optimal utilisation of dissimilar materials is fundamental to the development of high-performance multifunctional structures, especially in lightweight aerospace applications. For multifunctional load-bearing antenna structures, utilisation of composite materials with dissimilar electrical properties enable the integration of radiofrequency transparent apertures in load-bearing aircraft structural skins. Aircraft skins are typically fabricated from advanced carbon fibre polymer composite, while the aperture requires an electrically non-conductive composite material such as quartz or glass fibre polymer composite. One method of achieving efficient load transfer between the structural skin and the aperture is to employ ply joints. Ply joints are co-cured composite joints produced by forming butt-splices and/or overlaps between individual plies while intelligently tailoring the relative positions and spatial distribution of the ply terminations. In this thesis, novel structural concepts for hybrid ply joints enabling multifunctional load-bearing antennas are developed. The load-carrying capacity of hybrid ply joints depends strongly on several Design parameters such as the distance between ply terminations (step length), overlap length, the spatial distribution of ply terminations, joint thickness and the mechanical stiffness and coefficients of thermal expansion of the dissimilar composite materials. An experimental program was created to investigate the influence of these key Design parameters on the load-carrying capacity of hybrid ply joints. Several ply-interleaved and ply-overlap joint configurations were evaluated under quasi-static uniaxial tensile and compression loading conditions. Fractographic analysis is also performed to determine the failure mechanism. The findings of the experimental program are used to guide the development of predictive capability for the structural performance of hybrid ply joints. Both analytical and high-fidelity computational models were developed; the analytical models are based on Strength of materials and linear elastic fracture mechanics methods while computational models employ continuum damage mechanics and cohesive element method. The study revealed that the principal damage mode in hybrid ply joints is delamination emanating from the vicinity of ply terminations. The loss of load-carrying capacity is caused by transverse matrix as they promote the coalesce of delaminations. Through judicious selection of the spatial distribution of ply terminations and step/overlap length, hybrid ply joints can be Designed to reach the Design Ultimate Strength of the load-bearing skin structure. The analytical and computational predictive capability developed for hybrid ply joints enable the Design optimisation of structurally integrated radiofrequency transparent apertures for multifunctional load-bearing antenna structures