Residual life estimation of cracked aircraft structural components

Predmet ovog istraživanja je usmeren na uspostavljanje proračunske procedure za analizu čvrstoće elemenata avionskih konstrukcija sa aspekta zamora i mehanike loma. Za tu svrhu ovde će biti uspostavljena proračunska procedura za procenu preostalog veka elemenata avionskih konstrukcija tipa dela oplate krila i uški pod dejstvom cikličnih opterećenja konstantne amplitude i spektra opterećenja. Poseban aspekt istraživanja se odnosi na primenu gustine energije deformacije (GED) za procenu preostalog veka elemenata konstrukcija sa inicijalnim oštećenjima tipa prskotina. Za određivanje analitičkih izraza za faktore intenziteta napona ovde su korišćeni specijalni singularni konačni elementi. Verifikacija proračunskih procedura za procene preostalog veka je podržana sa sa analitičkim i eksperimentalnim rezultatima uključivši i testove na zamor posebno sa aspekta eksperimentalnog određivanja malociklusnih zamornih karakteristika materijala.The subject of this investigation is focused on developing computation procedure for strength analysis of damaged aircraft structural components with respect to fatigue and fracture mechanics. For that purpose, here will be defined computation procedures for residual life estimation of aircraft structural components such as wing skin and attachment lugs under cyclic loads of constant amplitude and load spectrum. A special aspect of this investigation is based on using of the Strain Energy Density (SED) method in residual life estimation of structural elements with initial cracks. To determine analytic formulae for the stress intensity factors here singular finite elements are used. Verification of computation procedures for residual life estimations will be supported with corresponding experimental tests for determination of low cyclic fatigue properties of materials and corresponding parameters of fracture mechanics, including fatigue tests of representative aircraft structural elements

Determination of Stress Intensity Factors in Low Pressure Turbine Rotor Discs

An attention in this paper is focused on the stress analysis and the determination of fracture mechanics parameters in low pressure (LP) turbine rotor discs and on developing analytic expressions for stress intensity factors at the critical location of LP steam turbine disc. Critical locations such as keyway and dovetail area experienced stress concentration leading to crack initiation. Major concerns for the power industry are determining the critical locations with one side and fracture mechanics parameters with the other side. For determination of the critical locations in LP turbine rotor disc conventional finite elements are used here. For this initial crack length and during crack growth it is necessary to determine SIFs. In fatigue crack growth process it is necessary to have analytic formulas for the stress intensity factor. To determine analytic formula for stress intensity factor (SIF) of cracked turbine rotor disc special singular finite elements are used. Using discrete values of SIFs which correspond to various crack lengths analytic formula of SIF in polynomial forms is derived here. For determination of SIF in this paper, combined J-integral approach and singular finite elements are used. The interaction of mechanical and thermal effects was correlated in terms of the fracture toughness

Buckling and post-buckling behavior of shell type structures under thermo mechanical loads

The thermo mechanical buckling and post-buckling behavior of layered composite shell type structure are considered with the finite element method under the combination of temperature load and applied mechanical loads. To account for through-thickness shear deformation effects, the thermal elastic, and higher-order shear deformation theory is used in this study. The refined higher order theories, that takes into account the effect of transverse normal deformation, is used to develop discrete finite element models for the thermal buckling analysis of composite laminates. Attention in this study is focused on analyzing the temperature effects on buckling and post-buckling behavior of thin shell structural components. Special attention in this paper is focused on studying of values of the hole in curved panel on thermal buckling behavior and consequently to expend and upgrade previously conducted investigation. Using finite element method, a broader observation of the critical temperature of loss of stability depending on the size of the hole was conducted. The presented numerical results based on higher-order shear deformation theory can be used as versatile and accurate method for buckling and post-buckling analyzes of thin-walled laminated plates under thermo mechanical loads

Fracture mechanics analysis of damaged turbine rotor discs using finite element method

This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pressure steam turbine disc

Failure analysis of jet engine turbine blade

Jet engine turbine blade cast by investment precision casting of Ni-base superalloy, which failed during exploatation, was the subject of investigation. Failure analysis was executed applying optical microscopy (OM), transmission electron microscopy (TEM) using replica technique, scaning electron microscopy (SEM) and stress rupture life tests. On the ground of obtained results it was concluded that the failure occurred as a result of structural changes caused by turbine blade overheating above the exploitation temperature

Fracture mechanics analysis of damaged turbine rotor discs using finite element method

This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pressure steam turbine disc

Buckling and post-buckling behavior of shell type structures under thermo mechanical loads

The thermo mechanical buckling and post-buckling behavior of layered composite shell type structure are considered with the finite element method under the combination of temperature load and applied mechanical loads. To account for through-thickness shear deformation effects, the thermal elastic, and higher-order shear deformation theory is used in this study. The refined higher order theories, that takes into account the effect of transverse normal deformation, is used to develop discrete finite element models for the thermal buckling analysis of composite laminates. Attention in this study is focused on analyzing the temperature effects on buckling and post-buckling behavior of thin shell structural components. Special attention in this paper is focused on studying of values of the hole in curved panel on thermal buckling behavior and consequently to expend and upgrade previously conducted investigation. Using finite element method, a broader observation of the critical temperature of loss of stability depending on the size of the hole was conducted. The presented numerical results based on higher-order shear deformation theory can be used as versatile and accurate method for buckling and post-buckling analyzes of thin-walled laminated plates under thermo mechanical loads

Fractographic analysis of the aluminum matrix composite prepared by accumulative roll bonding

Recent research in the material science field is focused on the easy-to-apply and cost-effective production of the structural components with enhanced mechanical properties. As an answer to these new trends in the present study, the inexpensive household aluminum foils are used to produce the multilayer aluminum matrix composite. The aluminum matrix composites are manufactured by hot-rolling of the sandwiched foils and afterward subjected to microstructural characterization and mechanical testing. Analysis of the produced composite microstructure and fracture surface obtained after tensile testing was performed using the scanning electron microscopy (SEM). The qualitative fractographic analysis revealed that the ductile fracture features prevail in the overall fracture mode of the investigated multilayer composite, while the quantitative fractographic investigation allowed more detailed insight into the composite failure process and depicted critical parameters that led to the composite failure