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Mpact details
CEMAP
MPACT SPHINX MPAVE | Verified and Validated Virtual Reality The basis of nonlinear Finite Element Analysis was developed by Marcal and co-workers and other early researchers who discovered that the nonlinear problems resulted in linear incremental equations for elastic-plastic material as well as large displacement behavior. See for example Zienkiewicz, O. C. and Taylor, R. L.,"The Finite Element Method, Solid Mechanics", Vol. 2, Butterworth and Heinemann, 2000
In a study of a test on a strip with a hole, Marcal and King obtained the following comparison for load vs displacement for a work-hardening material..
Such analysis may now be performed for more complex structures with the aid of general purpose FEA programs such as the MPAVE pre and post Processor and the MPACT solver. In the context of component integrity, high temperature effects of creep can also be combined. Low Cycle Fatigue Much work has been done on low cycle fatigue since the early fifties with the spectacular failure of the Comet commercial Jets. Early research showed the importance of elastic-plastic cycling in low cycle fatigue. Specimen tests clearly showed this. Benham,P.P. 'Fatigue of metals caused by a relatively few cycles of high load or strain amplitude', Metallurgical Reviews 1958, 3 ,203. Langer , B. F. 'Design of pressure vessels for low cycle fatigue', Trans. Amer. Soc. Mech Engnrs. 1962 84D, 389 Coffin, L. F. 'A study of the effects of cyclic thermal stresses in ductile materials', Trans. ASME, 1954 76, 931 The next step in design was obvious. It required the development of elastic-plastic analysis. Mendelson, A. and Manson, S.S. 'Practical solution of plastic deformation problems in elastic-plastic range', NASA R-28, 1959 Marcal , P. V. and Turner, C. E. 'Limited life of shells of revolution subjected to severe local bending.' J. Mech Eng Sci., 1965, 7, 4. These authors considered the problem of limited life of shells of revolution. An elastic-plastic solution was developed for the axisymmetric shells of revolution. Good correlation was found between theory and experiment. The low cycle fatigue circle was completed by comparison tests of life prediction between theory and experiment. Some general conclusions were drawn concerning low cycle fatigue. Early tests showed the importance of avoiding general collapse during cyclic loading especially in load controlled situations. This boils down to a general rule on incremental collapse, that is that it occurs in the presence of one directional loading and continued plastic straining. Sometimes incremental collapse can also be induced by small follower loads. Once avoidance of incremental collapse is assured, the cyclic elastic-plastic calculations result in strain predictions that may be used for estimating low cycle fatigue from a strain based fatigue data. Some results from that work is shown here. First we show the bellows tested, the uniaxial loading rig and the low-cycle fatigue testing rig respectively.
The next diagrams show comparisons of theory and experiment
The next diagram shows the effects of early cycling and shakedown due to cyclic work-hardening.
The results for cycling are summarized in the next few diagrams
Collapse Loads The collapse loads of these shells are also of much interest. In general the large changes in geometry have a significant effect on the post collapse loads. In this case the axisymmetric behavior can often become asymmetric.
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