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Casting and welding processes introduce defects which can grow to failure under fatigue loading. It is necessary to analyze such defects to estimate fatigue lifetimes or strength loss from uninspectable flaws. An accurate analysis should include stress gradients, singular crack stress fields, and multiple flaw interactions. It must also be easily applicable to irregularly shaped mechanical components. However, it is not feasible to mesh defects due to the tedium involved, and the need to evaluate several “what if” damage scenarios. The finite element alternating method addresses these issues conveniently and accurately. It models defects by means of analytical crack stress functions, which are superimposed on systematic uncracked finite element meshes to achieve true stress fields. Functions are available for embedded or surface elliptic flaws, and other defect shapes.

Prediction of fatigue performance of large structures and components is generally done through the use of a fatigue analysis software, FEA stress/strain analysis, load spectra, and materials properties generated from laboratory tests with small specimens. Prior experience and test data has shown that a specimen size effect exists, i.e. the fatigue strength or endurance limit of large members is lower than that of small specimens made of same material. Obviously, the size effect is an important issue in fatigue design of large components. However a precise experimental study of the size effect is very difficult for several reasons. It is difficult to prepare geometrically similar specimens with increased volume which have the same microstructures and residual stress distributions throughout the entire material volume to be tested. Fatigue testing of large samples can also be a problem due to the limitation of load capacity of the test systems available.

Problems of bore distortion, combustion blowby and gasket fatigue in lightweight engine blocks are ultimately related to the gasket sealing pressure distribution. For both conventional embossed steel gaskets and composite ones this distribution can be modified by suitable local changes in gasket stiffness. Current methods of gasket optimization concentrate on large scale iterative finite element analysis of the head/gasket/block system, with major computational costs. We present a more economical alternative in which condensed compliance matrices are obtained either from elementary NASTRAN runs or by experimental means. The algorithm enables the gasket engineer to ‘tune’ the gasket to the desired sealing pressure profile with acceptable stiffness variations.