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Sub-modeling techniques implemented in commercial finite element codes were reviewed. New sub-modeling applications in structural mechanics stress analysis are presented. Sub-modeling methods based on displacement and force cut boundary application are compared. Advantages and disadvantages of these methods are discussed. The case of nested sub-models is demonstrated.

Engineering machines and components are proneto structural failures during their service time due to certaintechnical reasons and also due to some unforeseencircumstances. The technical breakdowns sometime lead tohigh economic imbalance and can also be fatal to life andproperty. Predicting the failure and evaluating the breakagecharacteristics of engineering components are crucial indetermining the life of the component and also increasetheir maintenance and safety in daily life. This research study deals with the modelling andnumerical simulations of an aluminium alloy specimen in3D stress-state and thereby predicting the fatigue failure ofthe material subjected to external cyclic loadings. Topredict the failure of a component, a specimen with aninduced crack can be evaluated through cyclic loadingprocess. It is based on the fact that the presence of a crackstends to modify the stresses present locally on thecomponent that the elastic deformation and the stressesattributed with them are totally insufficient for the designagainst fracture. It is based on the assumption that thespecimen undergoes complete fracture when the crackreaches its critical size even though the stress at the criticalcrack tip is much lower than the yield stress of thecomponent. The critical size of the crack is based on theapplication of the load and the number of load cycles itundergoes.The main aim of this research is to present andvalidate the numerical method for the study of theinfluence of cracks present in the engineering components.Finite element method was applied for numericalsimulation. In this study the tension, torsion, combined tension-torsion and fatigue loads was applied. Theexperimental testing data of mechanical properties wasused in numerical simulation as input data. This researchstudy investigates the three-dimensional stress-strain stateand fatigue prediction of D16T aluminium alloy which ispredominantly used in the aerospace and automobileindustries for their high strength-to-weight ratio and muchbetter physical properties. The different specimen modelsare then analysed and the most efficient one was selectedfor the preliminary experimental tests.