Failure criteria

Failure of Fiber Composite Laminates: Progressive Damage and Polynomial Invariants - Two distinctly different failure methods are given. The first is that of progressive damage where lamina level failure criteria are used to predict the sequence of damage/failures within the laminate. The second method is that of polynomial invariants which takes t... he scale of the laminate itself and its symmetry properties as the fundamental basis for failure characterization. The two methods are carefully and thoroughly compared. Critical Experimental and Theoretical Tests for Failure Criteria - The evaluation procedure for isotropic material failure criteria involves assessing their theoretical basis followed by comparisons with critical data sets (ductile and brittle). All of the long standing commonly used failure forms are found to be fundamentally incapable of functioning as general three dimensional failure criteria. All but one (Mises) cannot even serve for just a single, restricted materials type. Only the recently developed, two property failure theory outlined in Section II correlates well with all the data cases and has complete generality, going from the ductile limit to the brittle limit. Some failure criteria for fiber composites are also evaluated. The Ductile/Brittle Transition, Gaging Ductility Levels - Under the heading Organizing Principle the isotropic material failure criterion is put into the form that is best for examining ductility and brittleness matters. Starting with the ductile/brittle transition, a failure number index is derived that gages the level of ductility (and brittleness) in failure. The failure number, Fn, is expressed in terms of the uniaxial strength ratio, T/C, and the nondimensionalized first invariant of the stress state at failure. Many examples with detailed explanations are given. Fracture Mechanics - A sharply focused examination is taken of the two major failure disciplines: fracture mechanics and failure criteria. First, the historical development of the field of fracture ...Read More