Papers by Keyword: Damage Tolerance

Abstract: The effect of Friction Stir Welding joining process on the damage tolerance behaviour of friction stir welded aluminium alloys is experimentally investigated. Fatigue crack propagation tests for different aluminium alloys and welding configurations have been performed. The main conclusion arising from the experimental study is that the damage tolerance behaviour of the welded material is in most cases comparable to the base material. Furthermore, the most critical area of the joint was identified to be the weld interface, i.e. the area between the nugget and the thermo-mechanically affected zone

Abstract: Combined strengthening-toughening technologies of several high property titanium alloys, such as TC4-DT, TC6, TC18, TC21 for aviation uses, have been studied via purification, quasi-b heat treatment, quasi-b forging and grain refinement. The effects of microstructure parameters of lamellar structure, basket-weave structure, refined grain structure etc. on the comprehensive mechanical properties of titanium alloys have been analyzed. The results have shown that, to acquire highly comprehensive static mechanical properties and excellent damage tolerance properties, quasi-b treatment and purification processing should be used for medium strength titanium alloys to get high ductility lamellar structure, while quasi-b forging processing be utilized for high strength titanium alloys to obtain high ductility basket-weave structure. Grain refinement processing is very necessary for both the strength levels of titanium alloys.

Abstract: The latest R&D of new-type titanium alloys and their aviation applications as well as the newly developed processing technologies in China have been reviewed in this paper. To meet the requirements of high performance and low cost design of aviation-oriented titanium alloys, great efforts and achievements have been made in establishing a system with Chinese characteristics, in which the low-strength-and-high-toughness titanium alloy (such as Ti45Nb alloy used for fasteners and TA18 for tubes & pipes), the medium-strength and high-damage-tolerance titanium alloy (such as TC4-DT used for large-integral airframe structures), the high-strength and high-toughness damage tolerance titanium alloy (such as TC21 used for large-integral airframe structures), and the ultra-high strength titanium alloy (such as TB8) are included. Some new processing technologies such as quasi-β forging and quasi-β heat treatment, integral isothermal forging and electron beam welding, have been demonstrated to be able to markedly enhance the properties of titanium alloys, which is regarded to be very important in increasing the application amount and level of titanium in aviation industry.

Abstract: By means of computation and analysis of damage tolerance of composite laminates with hole or crack, the conclusion is brought forth that crack on laminates can’t be cut into hole to improve the residual strength; otherwise the damage will become more serious. The method and conclusion can be reference and basis for battle damage repair of airplane composite component.

Abstract: Focus on the problem that traditional aircraft design thought can’t meet the security and economy requirement of modern aircraft, studying the optimum design method based on damage tolerance for overall beam. For example with aircraft overall beam, constructed the optimization model based on support vector machine agent model with the lightest weight of the structure as the optimization objective, the minimum residual strength value as the constraint, section parameters as the design variables, through mathematical programming, get the optimization results under different residual strength requirement value, and calculate the crack growth life.

Abstract: High performance components such as gear wheels shall be resistant to rolling-contact fatigue. This type of failure is usually caused by effects occurring on a microscopic scale, such as crack initiation at non-metallic inclusions. Much effort has been invested so far in improving the steel cleanliness. However, these high performance components often do not reach the desired service life. Preliminary failure within the guarantee terms still occurs which leads to high warranty costs. Alternative to improving steel cleanliness, the damage tolerance of high performance components could be increased by inducing the TRIP-effect around the crack tip. Due to high local strain hardening, martensite transformation occurs. The high compressive stresses related to it could delay or stop crack propagation by reducing stress concentrations via plastic deformation. In part II of this study, the microstructures and mechanical properties of the steels modified via Al-alloying and heat treated in process routes according to part I are compared to conventional 18CrNiMo7-6. Special interest is paid to the stability of the residual austenite as well as to the change in strain hardening rate under tension.

Abstract: High performance components such as gear wheels shall be resistant to rolling-contactfatigue. This type of failure is usually caused by effects occurring on a microscopic scale, such ascrack initiation at non-metallic inclusions. Much effort has been invested so far in improving thesteel cleanliness. However, these high performance components often do not reach the desiredservice life. Preliminary failure within the guarantee terms still occurs which leads to high warrantycosts. Alternative to improving steel cleanliness, the damage tolerance of high performancecomponents could be increased by inducing the TRIP-effect around the crack tip. Due to high localstrain hardening, martensite transformation occurs. The high compressive stresses related to it coulddelay or stop crack propagation by reducing stress concentrations via plastic deformation. As aresult, rolling-contact fatigue resistance of carburized steels may be increased and preliminaryfailure may be avoided. Part I of this study focuses on modifying the chemical composition ofconventional 18CrNiMo7-6 steel with Al to develop a high-strength, yet ductile matrix with a highwork hardening potential. Dilatometric tests on laboratory melts analyze the possibility of adjustinga microstructure able to produce a TRIP-effect. Both isothermal annealing and Quenching andPartitioning (Q&P) are used to stabilize residual austenite and optimum process routes areidentified.

Abstract: The certification of scarf repairs requires that the repair is capable of handling flight loads in the presence of disbonds. This paper presents a study of the fatigue disbond growth behaviour of scarf joints. By determining the strain energy release rates of a disbond in a scarf joint subjected to a unit load, a predictive model based on linear elastic fracture mechanics is presented, which is shown to correlate well with experimental results. This method offers a promising technique of predicting the fatigue life of composite scarf joints with disbonds.

Abstract: Over the past 50 years, mitigating cracks from holes has been a major focus of aerospace research, design, and stress engineers. Technology and design philosophies were developed to focus on predicting and increasing fatigue life of metal aircraft structure. One of the innovations to have the biggest impact to slow or arrest crack growth was to induce beneficial residual stresses around a hole. The zone of residual compressive stresses shields the hole from the effects of cyclic loads. The split sleeve cold expansion method was pioneered in the early 1970s by Boeing and Fatigue Technology. The split sleeve cold expansion process has become the bench mark method in mitigating fatigue cracks and enhancing durability and damage tolerance of aerospace metal structures. This paper will review the history of cold expansion methods and the evolution of this technology to the controlled and widely accepted methods used by industry today.

Abstract: The overview of the fatigue and damage tolerance substantiation approach for a 70-90 seat class regional aircraft named Mitsubishi Regional Jet, which is now under development by Mitsubishi Aircraft Corporation, is presented. To comply with the new regulatory requirement for prevention from widespread fatigue damage, full-scale airplane fatigue test will be performed with simulating actual airplane structural configuration and typical loading spectra expected in service. In addition to widespread fatigue damage, damage tolerance evaluations assuming manufacturing defect or in-service damage are being performed. Hundreds of structural tests from coupon level to sub-component level are to be used to verify the material properties and analysis methodology.