Browsing by Author "Figueroa-Gordon, Douglas J."
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Item Open Access Fail-Safe Design of Integral Metallic Aircraft Structures Reinforced by Bonded Crack Retarders(Elsevier Science B.V., Amsterdam., 2009-01-01T00:00:00Z) Zhang, Xiang; Boscolo, M.; Figueroa-Gordon, Douglas J.; Allegri, Giuliano; Irving, Phil E.This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.Item Open Access Hydrogen re-embrittlement susceptibility of ultra high strength steels(Cranfield University, 2005-09) Figueroa-Gordon, Douglas J.; Robinson, M. J.300M ultra high strength steel has been widely used for over forty years as a structural material in aerospace applications where a high strength is required. These parts are generally protected from corrosion by electroplated cadmium sacrificial coatings. However, there are concerns over this coating material due to its high toxicity and alternative coatings including Zinc-14%Nickel and SermeTel®1140/962 have been considered. It is known that applying electrodeposited coatings causes atomic hydrogen to be absorbed by the steel substrate producing delayed failure by direct hydrogen embrittlement. Hydrogen is also absorbed when a sacrificial coating undergoes corrosion in service and this process is known as re-embrittlement. The effect of electroplated Zinc-14%Nickel and aluminium based SermeTel®1140/962 sacrificial coatings in causing hydrogen embrittlement and re-embrittlement of 300M steel have been compared to that of conventional electroplated cadmium. AerMet®100 ultra high strength steel has been also considered as alternative replacement for the conventional 300M. Hence, the hydrogen embrittlement and re-embrittlement susceptibilities of AerMet®100 were studied when coated with cadmium, Zinc-14%Nickel and SermeTel®1140/962. In addition, two alternative alloys GifloM2000 and CSS-42LTM were also taken into consideration and only the extent of hydrogen re-embrittlement was assessed when coated with cadmium and SermeTel®1140/962, respectively. Slow strain rate tests, SSRT, were carried out for plated, plated and baked as well as plated, baked and corroded tensile specimens. The time to failure values were compared using a Weibull distribution, statistical ttests and embrittlement indices. Differences in hydrogen susceptibility of the high strength steels considered might depend upon their intrinsic hydrogen transport characteristics. These properties were studied and compared in terms of hydrogen diffusivity and solubility.Item Open Access Hydrogen transport and embrittlement in 300 M and AerMet100 ultra high strength steels(Elsevier Science B.V., Amsterdam., 2010-05-01T00:00:00Z) Figueroa-Gordon, Douglas J.; Robinson, M. J.This paper describes how hydrogen transport affects the severity of hydrogen embrittlement in 300 M and AerMet100 ultra high strength steels. Slow strain rate tests were carried out on specimens coated with electrodeposited cadmium and aluminium-based SermeTel 1140/962. Hydrogen diffusivities were measured using two-cell permeation and galvanostatic charging methods and values of 8.0 × 10−8 and 1.0 × 10−9 cm2 s−1 were obtained for 300 M and AerMet100, respectively. A two-dimensional diffusion model was used to predict the hydrogen distributions in the SSR specimens at the time of failure. The superior embrittlement resistance of AerMet100 was attributed to reverted austenite forming around martensite laths during teItem Open Access The response of aluminium/GLARE hybrid materials to impact and to in-plane fatigue(Elsevier Science B.V., Amsterdam., 2009-10-15T00:00:00Z) Bagnoli, F.; Bernabei, M.; Figueroa-Gordon, Douglas J.; Irving, Phil E.Fibre metal laminates (FMLs), such as glass reinforced aluminium (GLARE), are a family of materials with excellent damage tolerance and impact resistance properties. This paper presents an evaluation of the low velocity impact behaviour and the post-impact fatigue behaviour of GLARE laminate adhesively bonded to a high strength aluminium alloy substrate as a fatigue crack retarder. The damage initiation, damage progression and failure modes under impact and fatigue loading were examined and characterised using an ultrasonic phased array C-scan together with metallography and scanning electron microscopy (SEM). After impact on the substrate, internal damage to the GLARE bonded on the opposite side of the substrate occurred in the form of fibre and matrix cracking. No delamination was detected at the GLARE/substrate bond. Before impact the bonded GLARE strap caused reductions in substrate fatigue crack growth rate of up to a factor of 5. After impact the retardation was a factor of 2. The results are discussed in terms of changes to the GLARE stiffness promoted by the impact damage.