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09.2008 - Dr. Pawel Woelke Co-Authors Book on Shell Structures

Elasto-Plastic and Damage Analysis of Plates and Shells advances the field of shell structures and creates new analytical tools to assess damage caused by multiple hazards.

NEW YORK, NY - Weidlinger engineer Dr. Pawel Woelke and Dr. George Z. Voyiadjis, professor of Civil Engineering at Louisiana State University, have authored a new book, Elasto-Plastic and Damage Analysis of Plates and Shells. Motivated in part by deficiencies in analyses based on classical theory, which can lead to large computational errors, Voyiadjis and Woelke have developed a new comprehensive theory that predicts failure and applies to a wide range of structures modeled as shells, plates, and beams. Their approach leads to a more reliable evaluation of structural integrity and maximum permissible loads, as they are based on accurate assessments of the material and structural behavior.

Domes, silos, storage tanks (for water, gas, oil), submarines, and airplanes, even lampposts and most stadium roofs, are shells or contain shells. Increasingly, engineers are required to predict the behavior of these structures, because they are at risk of global and/or local failure from extreme loads. A prime example are the significant hull and deck fractures that developed in American Liberty ships built quickly during WWII (luckily, few ships were lost to these defects).

Voyiadjis and Woelke demonstrate that a good theory is necessary but insufficient without the appropriate analysis tools. Shell mechanics are complicated, because behavior is affected not only by geometric properties, but also by function, boundary conditions, load type, and other factors. Some factors, material properties and loads for instance, influence the amount of nonlinear behavior. Finite element modeling (FEM), which builds a facsimile of the structure out of small discrete elements (as many as a million in some cases), is used by the authors to secure an accurate analysis of the linear elastic, inelastic and softening behaviors as well as large rotations, and to describe the accumulation of damage leading to failure.

Most failure theories focus on structural details at the micro scale, which can be used to describe only local failure; the authors, in contrast, describe failure in both isotropic and composite layered shells on a macro scale that encompasses local failure. Recent increases in computer power allow for the performance of these large-scale calculations, but a brute-force approach would be prohibitively time-consuming. The challenge was to be as efficient as possible and streamline the number of operations so that engineers and researchers in the fields of civil, mechanical, and aerospace engineering; materials science; and applied mechanics could solve problems in a reasonable time frame by following the recommended procedures.

The book is dedicated to Maciej P. Bieniek, a Polish scientist and engineer who for many years taught at Columbia University (retiring as Renwick Professor Emeritus in 1993), where he was Dr. Voyiadjis’s advisor. As a consultant to Weidlinger, Dr. Bieniek developed two dynamic finite element codes, TRANAL to analyze buried structures and EPSA to analyze shells, especially underwater shells.

Pawel Woelke received a PhD from Louisiana State University, Baton Rouge, MSc from Imperial College, London, and MEng from Poznan University of Technology, Poland. Dr. Woelke specializes in computational mechanics and constitutive modeling of solids and structures. His recent work encompasses vulnerability studies and analysis and design to mitigate the effects of impact and blast on bridges, tunnels, public buildings, and other structures. He is also involved in the prediction of environmental and mechanical damage to composite materials for military and commercial applications.

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