The Experts below are selected from a list of 1110 Experts worldwide ranked by ideXlab platform
B Masserey - One of the best experts on this subject based on the ideXlab platform.
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Analysis of high frequency guided wave scattering at a fastener hole with a view to fatigue crack detection.
2016Co-Authors: B Masserey, Paul FrommeAbstract:The scattering of high frequency guided ultrasonic waves by a fatigue crack at the side of a fastener hole has been studied. The guided wave pulse consists of the superposition of the two fundamental Lamb modes A0 and S0 above the cut-off frequencies of the higher modes. The scattered field was simulated using a three-dimensional finite difference algorithm with a staggered, Cartesian grid for the limited area of interest around the hole and an analytical phase angle correction for the additional, variable propagation distance. Experimentally, the modes were selectively excited using a standard ultrasonic wedge transducer and measured using a laser interferometer, resulting in good spatial resolution. The scattered field was measured and simulated for an undamaged hole, a small, part-thickness quarter-elliptical fatigue crack, and a through-thickness fatigue crack. Good agreement was found and a significant influence of the fatigue cracks on the scattered field was observed. The complex difference of the scattered field due to additional scattered waves at the fatigue cracks of variable depth and length was evaluated. This allows for the prediction of high frequency guided wave sensitivity for fatigue crack detection at fastener holes, a significant maintenance problem for Ageing Aircraft.
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High frequency guided ultrasonic waves for hidden fatigue crack growth monitoring in multi-layer model aerospace structures
2015Co-Authors: B MassereyAbstract:Especially for Ageing Aircraft the development of fatigue cracks at fastener holes due to stress concentration and varying loading conditions constitutes a significant maintenance problem. High frequency guided waves offer a potential compromise between the capabilities of local bulk ultrasonic measurements with proven defect detection sensitivity and the large area coverage of lower frequency guided ultrasonic waves. High frequency guided waves have energy distributed through all layers of the specimen thickness, allowing in principle hidden (2nd layer) fatigue damage monitoring. For the integration into structural health monitoring systems the sensitivity for the detection of hidden fatigue damage in inaccessible locations of the multi-layered components from a stand-off distance has to be ascertained. The multi-layered model structure investigated consists of two aluminium plate-strips with an epoxy sealant layer. During cyclic loading fatigue crack growth at a fastener hole was monitored. Specific guided wave modes (combination of fundamental A and S Lamb modes) were selectively excited above the cut-off frequencies of higher modes using a standard ultrasonic wedge transducer. Non-contact laser measurements close to the defect were performed to qualify the influence of a fatigue crack in one aluminium layer on the guided wave scattering. Fatigue crack growth monitoring using laser interferometry showed good sensitivity and repeatability for the reliable detection of small, quarter-elliptical cracks. Standard ultrasonic pulse-echo equipment was employed to monitor hidden fatigue damage from a stand-off distance without access to the damaged specimen layer. Sufficient sensitivity for the detection of fatigue cracks located in the inaccessible aluminium layer was verified, allowing in principle practical in situ ultrasonic monitoring of fatigue crack growth.
Bringmann Philipp - One of the best experts on this subject based on the ideXlab platform.
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Atmospheric pressure plasma jet deposition of Si-based coupling films as surface preparation for structural adhesive bonding inthe Aircraft industry: Comparison of joint durability after APPJ-CVD and solution derived silane treatments
2016Co-Authors: Bringmann PhilippAbstract:Damages of metallic Aircraft structures that occur during manufacturing, assembly and in service require local repair. Especially with current service-life extensions of Ageing Aircraft fleets, the importance of such repair methods is increasing. Typically, the repair of smaller damages on aluminium fuselage or wing skins is done by riveting a patch onto the flawed structure. However, the use of rivets reduces the strength of the structure and promotes fatigue. Joining the patch by adhesive bonding would not only offer more homogenous load distribution and weight savings, but even an increase of structural integrity. Metal adhesive bonding is commonly used in aeronautics, but requires elaborated surface treatments of the adherends, employing hazardous chemicals like chromates, due to the high durability demands. Furthermore, these treatments are usually tank processes that are not suitable for local repairs. Hence, there is a strong need for locally applicable surface preparation methods that allow safe and reliable adhesive bonding of primary Aircraft structures. The aim of this thesis is to assess the – still emerging – method of atmospheric pressure plasma deposition of silicon (Si) containing compounds concerning its suitability as surface preparation for adhesive bonding of aluminium aerostructures. Atmospheric plasma deposition is not yet used in the Aircraft industry, and the knowledge on functionality of this technology concerning bonding of aluminium parts is limited. Moreover, the durability requirements of the Aircraft industry greatly exceed the standards in other industries. Hence, special attention is paid to a thorough analysis of the key characteristics of the deposited coupling films and their effectiveness in terms of adhesion promotion as well as joint durability under particularly hostile conditions. In order to do so, the altering mechanisms of the treated joints and the behaviour of the coupling films during accelerated Ageing will be investigated in detail for the first time in this thesis. Furthermore, the influence of the aluminium surface pre-treatment (i.e. topography and oxide properties of the substrate) on the overall joint performance after coupling film deposition is thoroughly examined. Based on these findings, the surface preparation is optimised, and a process is developed to achieve maximal joint performance. As alternative local surface treatments prior to adhesive bonding, solution derived deposition of silane and sol-gel films have already been widely investigated and can be considered as reference, even though these techniques are rarely used in civil aeronautics. The knowledge on their effectiveness and capabilities in corrosive atmosphere is still very limited. Therefore, all analyses of degradation mechanisms are conducted for both plasma deposition and wet-chemical reference treatments to reveal the differences and communalities of the two Si-based coupling films. Physical and chemical analysis of the films, the oxides and the interfaces reveal differing, but interdependent failure mechanisms that are inhibited differently by the individual coupling films. Using the optimum deposition parameters, plasma films of only several nanometres in thickness significantly enlarge the corrosion resistance of bonded joints, reaching almost the level of anodising treatments with several micrometres thick oxides and strongly outperforming solution derived silane treatments. However, plasma film performance is found to be largely dependent on the precursor selection. With plasma deposition of 3-glycidoxypropyltrimethoxysilane, which has not been reported before, highest joint stability is achieved. Moreover, it is discovered that the properties of plasma and solution derived silane based films are complementary. It is shown that an optimised combined plasma and wet-chemical treatment process provides even superior resistance to bondline corrosion than state-of-the-art anodising techniques
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Atmospheric pressure plasma jet deposition of Si-based coupling films as surface preparation for structural adhesive bonding in the Aircraft industry: Comparison of joint durability after APPJ-CVD and solution derived silane treatments
2016Co-Authors: Bringmann PhilippAbstract:Damages of metallic Aircraft structures that occur during manufacturing, assembly and in service require local repair. Especially with current service-life extensions of Ageing Aircraft fleets, the importance of such repair methods is increasing. Typically, the repair of smaller damages on aluminium fuselage or wing skins is done by riveting a patch onto the flawed structure. However, the use of rivets reduces the strength of the structure and promotes fatigue. Joining the patch by adhesive bonding would not only offer more homogenous load distribution and weight savings, but even an increase of structural integrity. Metal adhesive bonding is commonly used in aeronautics, but requires elaborated surface treatments of the adherends, employing hazardous chemicals like chromates, due to the high durability demands. Furthermore, these treatments are usually tank processes that are not suitable for local repairs. Hence, there is a strong need for locally applicable surface preparation methods that allow safe and reliable adhesive bonding of primary Aircraft structures. / The aim of this thesis is to assess the – still emerging – method of atmospheric pressure plasma deposition of silicon (Si) containing compounds concerning its suitability as surface preparation for adhesive bonding of aluminium aerostructures. Atmospheric plasma deposition is not yet used in the Aircraft industry, and the knowledge on functionality of this technology concerning bonding of aluminium parts is limited. / Moreover, the durability requirements of the Aircraft industry greatly exceed the standards in other industries. Hence, special attention is paid to a thorough analysis of the key characteristics of the deposited coupling films and their effectiveness in terms of adhesion promotion as well as joint durability under particularly hostile conditions. In order to do so, the altering mechanisms of the treated joints and the behaviour of the coupling films during accelerated Ageing will be investigated in detail for the first time in this thesis. Furthermore, the influence of the aluminium surface pre-treatment (i.e. topography and oxide properties of the substrate) on the overall joint performance after coupling film deposition is thoroughly examined. Based on these findings, the surface preparation is optimised, and a process is developed to achieve maximal joint performance. / As alternative local surface treatments prior to adhesive bonding, solution derived deposition of silane and sol-gel films have already been widely investigated and can be considered as reference, even though these techniques are rarely used in civil aeronautics. The knowledge on their effectiveness and capabilities in corrosive atmosphere is still very limited. Therefore, all analyses of degradation mechanisms are conducted for both plasma deposition and wet-chemical reference treatments to reveal the differences and communalities of the two Si-based coupling films. Physical and chemical analysis of the films, the oxides and the interfaces reveal differing, but interdependent failure mechanisms that are inhibited differently by the individual coupling films. / Using the optimum deposition parameters, plasma films of only several nanometres in thickness significantly enlarge the corrosion resistance of bonded joints, reaching almost the level of anodising treatments with several micrometres thick oxides and strongly outperforming solution derived silane treatments. However, plasma film performance is found to be largely dependent on the precursor selection. With plasma deposition of 3-glycidoxypropyltrimethoxysilane, which has not been reported before, highest joint stability is achieved. Moreover, it is discovered that the properties of plasma and solution derived silane based films are complementary. It is shown that an optimised combined plasma and wet-chemical treatment process provides even superior resistance to bondline corrosion than state-of-the-art anodising techniques
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Atmospheric pressure plasma jet deposition of Si-based coupling films as surface preparation for structural adhesive bonding in the Aircraft industry Atmospheric pressure plasma jet deposition of Si-based coupling films as surface preparation for structural adhesive bonding in the Aircraft industry: Comparison of joint durability after APPJ-CVD and solution derived silane treatments
2015Co-Authors: Bringmann PhilippAbstract:Damages of metallic Aircraft structures that occur during manufacturing, assembly and in service require local repair. Especially with current service-life extensions of Ageing Aircraft fleets, the importance of such repair methods is increasing. Typically, the repair of smaller damages on aluminium fuselage or wing skins is done by riveting a patch onto the flawed structure. However, the use of rivets reduces the strength of the structure and promotes fatigue. Joining the patch by adhesive bonding would not only offer more homogenous load distribution and weight savings, but even an increase of structural integrity. Metal adhesive bonding is commonly used in aeronautics, but requires elaborated surface treatments of the adherends, employing hazardous chemicals like chromates, due to the high durability demands. Furthermore, these treatments are usually tank processes that are not suitable for local repairs. Hence, there is a strong need for locally applicable surface preparation methods that allow safe and reliable adhesive bonding of primary Aircraft structures. The aim of this thesis is to assess the – still emerging – method of atmospheric pressure plasma deposition of silicon (Si) containing compounds concerning its suitability as surface preparation for adhesive bonding of aluminium aerostructures. Atmospheric plasma deposition is not yet used in the Aircraft industry, and the knowledge on functionality of this technology concerning bonding of aluminium parts is limited. Moreover, the durability requirements of the Aircraft industry greatly exceed the standards in other industries. Hence, special attention is paid to a thorough analysis of the key characteristics of the deposited coupling films and their effectiveness in terms of adhesion promotion as well as joint durability under particularly hostile conditions. In order to do so, the altering mechanisms of the treated joints and the behaviour of the coupling films during accelerated Ageing will be investigated in detail for the first time in this thesis. Furthermore, the influence of the aluminium surface pre-treatment (i.e. topography and oxide properties of the substrate) on the overall joint performance after coupling film deposition is thoroughly examined. Based on these findings, the surface preparation is optimised, and a process is developed to achieve maximal joint performance. As alternative local surface treatments prior to adhesive bonding, solution derived deposition of silane and sol-gel films have already been widely investigated and can be considered as reference, even though these techniques are rarely used in civil aeronautics. The knowledge on their effectiveness and capabilities in corrosive atmosphere is still very limited. Therefore, all analyses of degradation mechanisms are conducted for both plasma deposition and wet-chemical reference treatments to reveal the differences and communalities of the two Si-based coupling films. Physical and chemical analysis of the films, the oxides and the interfaces reveal differing, but interdependent failure mechanisms that are inhibited differently by the individual coupling films. Using the optimum deposition parameters, plasma films of only several nanometres in thickness significantly enlarge the corrosion resistance of bonded joints, reaching almost the level of anodising treatments with several micrometres thick oxides and strongly outperforming solution derived silane treatments. However, plasma film performance is found to be largely dependent on the precursor selection. With plasma deposition of 3-glycidoxypropyltrimethoxysilane, which has not been reported before, highest joint stability is achieved. Moreover, it is discovered that the properties of plasma and solution derived silane based films are complementary. It is shown that an optimised combined plasma and wet-chemical treatment process provides even superior resistance to bondline corrosion than state-of-the-art anodising techniques
Matthias Buderath - One of the best experts on this subject based on the ideXlab platform.
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Fatigue in aerostructures - Where structural health monitoring can contribute to a complex subject
2007Co-Authors: Christian Boller, Matthias BuderathAbstract:An overview of the Aircraft design and maintenance process is given with specific emphasis on the fatigue design as well as the phenomenon of the Ageing Aircraft observed over the life cycle. The different measures taken to guarantee structural integrity along the maintenance process are addressed. The impact of structural health monitoring as a means of possibly revolutionizing the current Aircraft structural monitoring and design process is emphasized and comparison is made to jet engines and helicopters, where health monitoring has already found the respective breakthrough.
Paul Fromme - One of the best experts on this subject based on the ideXlab platform.
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Analysis of high frequency guided wave scattering at a fastener hole with a view to fatigue crack detection.
2016Co-Authors: B Masserey, Paul FrommeAbstract:The scattering of high frequency guided ultrasonic waves by a fatigue crack at the side of a fastener hole has been studied. The guided wave pulse consists of the superposition of the two fundamental Lamb modes A0 and S0 above the cut-off frequencies of the higher modes. The scattered field was simulated using a three-dimensional finite difference algorithm with a staggered, Cartesian grid for the limited area of interest around the hole and an analytical phase angle correction for the additional, variable propagation distance. Experimentally, the modes were selectively excited using a standard ultrasonic wedge transducer and measured using a laser interferometer, resulting in good spatial resolution. The scattered field was measured and simulated for an undamaged hole, a small, part-thickness quarter-elliptical fatigue crack, and a through-thickness fatigue crack. Good agreement was found and a significant influence of the fatigue cracks on the scattered field was observed. The complex difference of the scattered field due to additional scattered waves at the fatigue cracks of variable depth and length was evaluated. This allows for the prediction of high frequency guided wave sensitivity for fatigue crack detection at fastener holes, a significant maintenance problem for Ageing Aircraft.
Christian Boller - One of the best experts on this subject based on the ideXlab platform.
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Fatigue in aerostructures - Where structural health monitoring can contribute to a complex subject
2007Co-Authors: Christian Boller, Matthias BuderathAbstract:An overview of the Aircraft design and maintenance process is given with specific emphasis on the fatigue design as well as the phenomenon of the Ageing Aircraft observed over the life cycle. The different measures taken to guarantee structural integrity along the maintenance process are addressed. The impact of structural health monitoring as a means of possibly revolutionizing the current Aircraft structural monitoring and design process is emphasized and comparison is made to jet engines and helicopters, where health monitoring has already found the respective breakthrough.