Papers by Keyword: Damage Tolerance

Abstract: Lugs are numerous in aircraft and most of them are key structures in aircraft, in which fracture break occurs frequently. It is necessary to improve the fatigue life level of the lugs. In this thesis, the genetic algorithm is used to optimize the crack propagation life of the lugs with or without interference bushes. The curves of optimization results with different safety margin are gained, which can guide the damage tolerance design of the lugs in engineering.

Abstract: In order to carry out the railway axle design according to the “Damage Tolerance” philosophy, reliable crack-growth models for these kind of components are necessary. Indeed, damage tolerance principles have received more and more attention from railway technical community, thanks to its ambitious task concerning the inspection intervals prevision of railway components subjected to non-stationary loading conditions. In this paper, a simple routine is exposed that is able to calculate the characteristic parameters of the Linear Elastic Fracture Mechanics (LEFM) for a generic cracked mechanical component. Such parameters are then used in a two parameters propagation law to estimate the necessary time for a crack to become critical.

Abstract: The paper presents application of damage tolerance optimisation principles to the design of industrial components. It is illustrated via design optimisation of a Fuel Flow Vent Hole (FFVH) located in the Wing Pivot Fitting (WPF) of an F-111 aircraft. The aim is to determine the shape of the cutout that will maximise its residual strength under the operating loading conditions. Damage tolerance shape optimisation is performed using a heuristic optimisation method known as the ‘Biological algorithm’. The maximum stress intensity factor (SIF) for all of the cracks around the boundary of the optimal cutout is found to be significantly lower compared to that of the initial shape. This shows that an improved residual (fracture) strength is achieved for the optimal designs. The variability in SIF around the cutout boundary is reduced, thereby making the shape more evenly fracture critical. The shapes of the residual strength optimal vent holes are found to depend on the initial crack sizes. It is also shown that a damage tolerance optimisation additionally produces a lighter WPF component design, which is highly desirable for aerospace industries.

Abstract: In this paper, the probabilistic compliance methodology for damage tolerance design of thicker composite structures were investigated, and the research results show that for the composite laminates withstanding impact energy below 90J, if it cannot produce barely visible impact damage (BVID), then using the probabilistic methodology can meet certification requirements of damage tolerance.

Abstract: Third generation Al-Li alloy 2195 and 2198 were studied. The material properties of these two Al-Li alloy were compared with traditional alloy 2024; damage tolerance properties was tested and compared with 2024 as well. Microstructure of parent material and welded sample was studied and compared. Crack growth rate was tested and compared. Some conclusions were drawn: Al-Li alloy had a great strength and damage tolerance; local inhomogeneities microstructure in welded samples, which created the difference of damage tolerance and the tendency of crack growth rate in welded samples.

Abstract: Increasing utilization of thermoplastic composites in the structural application necessitates understanding of damage tolerance characteristics. In this work, unreinforced, 20 % short, 20 % long glass fiber reinforced polypropylene were injection molded and considered. Test specimens with different notch sizes were tested under static as well as fatigue loading conditions. Under static load condition, short fiber reinforced and unreinforced test material exhibited notch strengthening effect; whereas long fiber reinforced material exhibited notch weakening effect. Failure morphology under fatigue condition exhibited the influence of notch size and length of reinforced fibers over performance. Significant difference between notched and unnotched specimens is observed at low cycle fatigue and very less difference in performance is observed at high cycle fatigue condition.

Abstract: The result shows: If probabilistic methods were used to conduct compliance analysis for composite structure damage tolerance. When the impact energy is low, calculated result should conservatively use probabilistic methods of Weibull distribution fitting; when the impact energy is high, calculated result should conservatively use probabilistic methods of logarithmic linear fitting.

Abstract: -annealed Ti-6Al-4V ELI alloy has a special chemical composition and manufacturing process, intended to optimise its fatigue and fracture properties. This alloy is used in primary fatigue-critical structures of advanced military aircraft, but little has been generally published about its properties, particularly the fatigue and crack growth behaviour under service loading. A test programme has been set up to assess the fatigue durability and damage tolerance properties of the alloy, in the context of the two most relevant analysis methods. The first is strain – life analysis, used to estimate safe lives (durability). The second is fatigue crack growth analysis, used to assess the damage tolerance behaviour. This paper presents preliminary results of the test programme.

Abstract: This paper develops a three-layer back-propagation artificial neural network model to analyze and predict the correlation between processing parameters and properties of the damage tolerance type titanium alloy TC21. The inputs of the ANN are working temperatures, deformation extent, deformation rate and heat treatment conditions. And the outputs are mechanical properties namely ultimate strength, yield strength, elongation, reduction of area, plane strain fracture toughness and microstructure concerned parameters such as β phase fraction, βphase grain size, substructure length and thickness. The ANN is trained with experimental data and achieves a very good performance, which has already been applied to the optimization of processing for forging of aero-parts.

Abstract: Two important factors in damage tolerance engineering are the damage size that can be tolerated and the use of applied nondestructive testing (NDT) technique for detection of defects. Generally, NDT of large mechanical structures, such as vessels and pipes in nuclear power plants, is carried out according to national codes, and the damaged mechanical parts detected during periodic NDT are repaired or replaced after the evaluation. However, unexpected accidents can occur if cracks in the structure grow and exceed the tolerance limit during operation. Therefore, there is a need to develop NDT techniques that can detect micro-damage in the vessels and pipes. In this paper, we propose a cylinder-type magnetic camera to fill this need. We use a cylindrically integrated Hall sensor array (CIHaS) as a magnetic sensor to create magnetic images, and we use a solenoid coil as the source of the magnetic field detected by the magnetic camera in order to achieve high crack-detection ability. The proposed method is tested with an examination of the cracks on a prepared pipe sample.