Accession Number : ADA266342


Title :   Non-Uniqueness in Dynamic Rate-Independent Non-Associated Plasticity


Descriptive Note : Technical rept. 15 Jun 1989-31 Mar 1992


Corporate Author : WEIDLINGER ASSOCIATES NEW YORK


Personal Author(s) : Sandler, Ivan S ; Pucik, Thomas A


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a266342.pdf


Report Date : 01 Jun 1993


Pagination or Media Count : 41


Abstract : Ground shock calculations often use rate-independent plasticity models with non-associated flow. By means of a 'constructive' mathematical proof, it is demonstrated here that this approach leads to multiple (and therefore spurious) solutions for dynamic initial/boundary value problems; in other words, uniqueness is lost. Although a simple class of multiple solutions is presented, the results are shown to be generally valid, implying that normality of flow is a necessary (as well as a sufficient) condition for uniqueness in dynamic applications of rate-independent plasticity. This finding implies an inherent lack of robustness in numerical analyses utilizing models based on non-associated flow. Because the use of such models is widespread in ground shock (and structural) calculations, the fact that uniqueness breaks down is significant; it casts serious doubt on any (and every) calculation based on these constitutive representations. It is strongly recommended that all ground shock calculators promptly abandon their reliance on such models. To describe the situation most bluntly, these models do not provide a rational basis for the computations needed for prediction, design and/or analysis applications. In all cases for which an associated flow rule is deemed inadequate to fit observed material behavior, an approach other than rate-independent plasticity must be sought in order to represent such behavior in a reliable, self-consistent and rational manner.


Descriptors :   *GROUND SHOCK , *PLASTIC PROPERTIES , PLASTIC DEFORMATION , PROPAGATION , COMPUTATIONS , RATES , GEOLOGY , WAVE PROPAGATION , BOUNDARY VALUE PROBLEMS , NORMALITY , ELASTOPLASTICITY , VALUE , SHEAR STRESSES , SHOCK , STRAIN RATE , STRAIN(MECHANICS) , PREDICTIONS , MODELS , TENSILE STRESS


Subject Categories : Nuclear Weapons


Distribution Statement : APPROVED FOR PUBLIC RELEASE