Elastoplastic Interaction Research Articles

Local and overall interactive instability of thin-walled box-section columns

A beam-column model has been presented on the analysis of the elasto-plastic interaction buckling behaviour between local and overall flexural buckling modes in a cold-formed thin-walled box beam-column with plate (local) and column (overall) imperfections. The beam-column is modelled as an assemblage of a series of locally buckled short struts, each being equal to half the local buckle wavelength of the perfect column. A material and geometric nonlinear finite strip method developed by the author 1–5 is employed to calculate the moment-curvature-thrust relationships of the locally buckled short strut in the elasto-plastic range. With the help of the developed M- P- θ relationships of the short strut, the strength of the locally buckled beam-column is predicted by employing Little's beam-column approach. An experimental program on the cold-formed thin-walled box columns was carried out. The comparison of the experimental and theoretical results is satisfactory.

Numerical-experimental study of the elastoplastic interaction of a striker with an obstacle

Numerical-experimental study of the elastoplastic interaction of a striker with an obstacle

Grain shape effects on the slip system activity and on the lattice rotations

Eshelby's calculation of the elastic interaction between matrix and inclusion is carried out and extended to ellipsoidal inclusions of a general shape. This analysis leads to an extended Kröner formula. It shows that the shape can significantly influence the reaction stress of the inclusion with its surroundings, allowing therefore some additional freedom of certain plastic strain components. The influence of the grain shape on the lattice rotations is also analysed in that framework, showing again the large differences compared to the case of a spherical inclusion. A comparison between the FC (Full Constraints/ Taylor/Bishop and Hill) theory and the Kröner theory has already been done in the past. The analogous similarity is here presented between the extended Kröner case and the RC (Relaxed Constraints) theory. It is shown that the latter theory is consistent with the extended Kröner approach, even for the lattice rotation calculations, for infinitely distorted grain shapes. Although the grain shape effects alter significantly the texture results, the present analyses are limited to elastic interactions. The importance of the elastoplastic interactions between inclusion and matrix is here pointed out by means of phenomena like grain curling in uniaxial compression of f.c.c. polycrystals. It is shown that those types of events cannot be correctly described by RC or extended Kröner schemes.

Introduction to tribology

The science of tribology is the study of the interaction of engineering surfaces. Although the name implies interfacial sliding (tribology derives from the Greek word for rubbing), the discipline considers static contact as well. Lubrication to reduce friction and wear has been intimately involved with the empirical development of machinery through the ages. Tribology, therefore, has been basically a ’’catch-up’’ science; trying to explain physical phenomena which were known phenomenogically for decades. The pervasive concept in all tribology is the elastoplastic interaction at the microscopic irregularities on engineering surfaces. Some of the major advances in tribology in the past ten years have been the definition of engineering surfaces on this microscopic scale and the analysis of the thermo-mechanical situation which develops when such surfaces are slid against each other under load. This paper identifies the important parameters of mechanical surface interactions on both macro and micro scales in dry contact and under elastohydrodynamic lubrication.