Total Fatigue Life Estimation Of Aircraft Structural Components Using Strain Energy Density Method

This paper is aimed at developing a suitable computation method for estimating the fatigue life of structural elements exposed to the load spectrum. The total fatigue life can be divided into two parts, until the appearance of the initial damage and the other part represents the remaining life, i.e. until the effective fracture. The conventional approach to estimating the total life requires that low-cycle fatigue characteristics of the material be used until the initial damage occurs, and dynamic characteristics of the material for the remaining life. In order to obtain a more efficient method, the Strain Energy Density (SED) method was used in this paper. The essence of this approach is to use the same low - cycle fatigue characteristics of the material to estimate the life expectancy and the remaining life. This work is focused to developing efficient computation method and software for total fatigue life of metal aircraft structural components. To obtain efficient computation method, here the same fatigue low cyclic material properties for crack initiation and crack growth are used together with finite element method (FEM) for stress analyzes. To validate quality computation methods and in-house software for fatigue life estimations computation results are compared with experiments. The results show that the predicted results agree well with the test dat

Opremanje palube RoRo tankera po modelu "ključ u ruke"

U članku se najprije ukratko daju osnovne odrednice RoRo tankera. Potom se opisuje projektni zadatak koji se odnosi na opremanje glavne palube i način njegovog rješavanja crtanjem trodimenzionalnog modela. U nastavku se razmatra okruženje u kojem rade brodogradilišta, te se prepoznaje važnost lanaca dobave. Na koncu se analizira pristup dobavljaču po modelu „ključ u ruke“ s naglaskom na primjeni paralelnog inženjerstva u malim poduzećima i mogućnosti smanjenja troškova. Zaključak podržava pristup povezivanja između velikih subjekata-brodogradilišta koja mogu pridobiti važne poslove i manjih/malih subjekata koji odabrani segment proizvodnje mogu izraditi jeftinije, dostatno kvalitetno i na vrijeme

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

Damage tolerance analysis of structural components under general load spectrum

In this investigation fatigue behaviour of damaged structural components under cyclic loads constant amplitude and load spectrum is considered. Primary attention of this investigation is the establishment of computation procedure for the evaluation of the residual life of aircraft attachment lug type structural elements in the presence of initial cracks. In this investigation for residual life estimation and crack growth analysis Strain Energy Density ( SED) method is used. The SED method uses the low-cycle fatigue (LCF) properties of the material in crack growth analysis. In this approach experimentally obtained dynamic properties of the material such as Forman's constants are not required when this method is concerned. The complete computation procedure for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the damaged structural elements. To determine analytic expressions for stress intensity factors (SIF) singular finite elements are used. Results of numerical simulation for crack propagation based on strain density method have been compared with own experimental results

On the possibility of calibrating urban storm-water drainage models using gauge-based adjusted radar rainfall estimates

Traditionally, urban storm water drainage models have been calibrated using only raingauge data, which may result in overly conservative models due to the lack of spatial description of rainfall. With the advent of weather radars, radar rainfall estimates with higher temporal and spatial resolution have become increasingly available and have started to be used operationally for urban storm water model calibration and real time operation. Nonetheless, the insufficient accuracy of radar rainfall estimates has proven problematic and has hindered its widespread practical use. This work explores the possibility of improving the applicability of radar rainfall estimates to the calibration of urban storm-water drainage models by employing gauge-based radar rainfall adjustment techniques. Four different types of rainfall estimates were used as input to the recently verified urban storm water drainage models of the Beddington catchment in South London; these included: raingauge, block-kriged raingauge, radar (UK Met Office Nimrod) and the adjusted (or merged) radar rainfall estimates. The performance of the simulated flow and water depths was assessed using measurements from 78 gauges. Results suggest that a better calibration could be achieved by using the block-kriged raingauge and the adjusted radar estimates as input, as compared to using only radar or raingauge estimates

MATHEMATICAL MODELLING FOR DRYING OF SAWDUST IN A TRIPLE PASS ROTARY DRYER

Today, rotary dryers are often use to dry sawdust prior to their further processing, palletizing and briquetting, into commercially voluble product. This paper present mathematical model for drying process of sawdust particles in a triple pass rotary dryer. As basis for this model, we used existing mathematical models for drying of sawdust and other biological materials in a single pass rotary dryer, which are modified and extended in order to satisfy mathematical description of motion of material in the triple pass rotary dryer. Developed mathematical model is used as basis for further developing of the simulation model that predict temperature and moisture profile sawdust and drying along the dryer. In order to solve and validate developed rotary dryer model, commercial triple pass rotary dryer, installed in enterprise Panensa near town of Srbac, have been analysed, and measured sawdust drying data have been used for comparison. Comparison between predicted and the measured results were good. Mathematical model i.e. rotary dryer simulation model developed in this paper is going to enable better management and controlling of process in the mentioned commercial rotary dryer as well as in other rotary dryers for wood waste with modification of appropriate model parameters

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