Showing papers in "Applied Mechanics Reviews in 1986"

Buckling and Postbuckling of Imperfect Cylindrical Shells: A Review

Abstract: Thin-walled cylinders of various constructions are widely used in simple or complex structural configurations. The round cylinder is commonly found in tubing and piping, and in offshore platforms. Depending on their use, these cylinders are subjected (in service) to individual and combined application of external loads. In resisting these loads the system is subject to buckling, a failure mode which is closely associated with the establishment of its load-carrying capacity. Therefore, the system buckling and postbuckling behavior have been the subject of many researchers and investigators both analytical and experimental. The paper is a state-of-the-art survey of the general area of buckling and postbuckling of thin-walled, geometrically imperfect, cylinders of various constructions, when subjected to destabilizing loads. The survey includes discussion of imperfection sensitivity and of the effect of various defects on the critical conditions.

Boundary Layer Interactions With Compliant Coatings: An Overview

Abstract: During the past five years, several research programs have been conducted to reexamine the subject of boundary layer interactions with compliant coatings. One of the objectives of the research was to answer the question: Can compliant coatings delay transition and/or significantly reduce turbulence skin friction on bodies at high Reynolds numbers? Several significant developments have been achieved by the many investigators participating in these studies. The purpose of this article is to review the progress in our understanding of compliant coating interactions with laminar, transitional, and turbulent boundary layers. The paper will include some work done prior to the recent five year period and available in the open literature, but will emphasize more recent work, some of which is not as yet published.

Commentary on Flexible Fixturing

Abstract: One of the significant impediments to the evolution of truly flexible computer-integrated manufacturing systems is the absence of truly adaptable flexible fixturing systems. This article reports on research activities dedicated to synthesizing and developing viable universal flexible fixturing systems, methodologies, and technologies for fixturing parts of various shapes and sizes. Phase-change fixturing, modular fixture kits, and other innovative concepts are discussed. In addition, the article not only contains a state-of-the-art review of this rapidly evolving area of engineering science, but it also highlights the necessity for interdisciplinary research in order to address the frontier problems in this area. These disciplines range from the mechanics of both solids and fluids through dynamics and vibrations to artificial intelligence. This research philosophy is essential for developing viable solutions which can be successfully implemented in the factory-of-the-future.

Hidden (A)Symmetries of Elastic and Plastic Bifurcation

Abstract: Buckling at a distinct bifurcation point is more often than not symmetric, in the sense that equal and opposite amplitudes of the single buckling mode give identical physical shapes and hence energy levels. It is also commonly the case that combinations of modes break such symmetries, so that when critical loads are close (and sometimes when they are not), the preferred buckling involves a strong interaction between more than one mode. A single cubic cross-term of potential energy, readily identifiable from certain symmetry tests, then dominates the early (unstable) post-buckling, which later may be restabilized by positive quartic terms. In such instances the equilibrium paths over large deflections frequently exhibit a specific looping form, with an accompanying remote bifurcation, which was first predicted from a specialized application of the theorems underlying catastrophe theory. A number of well-known, and quite different, structural examples are given. A simple spring and link model due to Budiansky and Hutchinson, with a close similarity to the well-known Shanley model, shows that the latter can be interpreted in this manner, despite its being a problem of plastic bifurcation. Interactive buckling in sandwich panels, and in the long axially-loaded cylinder, provide two practical examples, others also being identified. A pilot scheme of perturbation analysis specifically designed to handle such problems is described, and used with considerable accuracy on the two link models, as demonstrated by comparison with exact solutions.

Dynamic Simulation of Flexible Manufacturing Systems (FMS)

Abstract: The simulation method to be used in FMS should be multilevel and dynamic and should incorporate solid modeling techniques. This means that operation control simulation in FMS should rely on information sources provided from different levels of the organization; thus there should be an overall planning level and a dynamic, or real-time, level. One should also conclude from this article that, without understanding the design principles and operating rules of FMS, the simulation model created will be inadequate and in most cases misleading. Because of this, FMS simulation should be performed by a team, incorporating the manufacturing system designers as well as the simulation experts.

Control of Machine Tools and Robots

Abstract: The principal control structure of CNC machine tools and industrial robots is similar, since in both systems each axis of motion is separately controlled with a position feedback loop. Nevertheless, the control of robots is more complex, since they include more degrees of freedom and the motion of each joint is not independent of other joints. This paper compares the conventional control schemes of both systems, and summarizes recent developments in adaptive control of machine tools and robots.