Effects of lateral confinement on the static and dynamic strength of brittle materials

Douglas Scott Adams, Purdue University

Abstract

Filament wound advanced composite materials are used to produce a self induced lateral confinement of cylindrical Pyrex glass and Macor machinable glass ceramic specimens. The confining stress is shown to be a result of the composite wrap restricting the Poisson's expansion of the core when it is placed under an applied axial load. The lateral stress is therefore found to maintain a constant ratio to the axial stress, or a constant biaxiality ratio, for an elastic core material. These specimens are subjected to both quasi-static and dynamic high strain rate loading in order to measure the change in strength of the base material as a function of the confining stress. The experimental results are used to demonstrate the potential performance and weight savings of this confinement technique over traditional mechanical or heat shrink methods. An analysis is performed to identify the role of key core and wrap parameters that determine the ultimate strength of brittle materials confined in this fashion and to identify an accurate means of estimating the confined state of stress. The Mohr-Coulomb criterion is evaluated as a possible option for modeling the observed strength but is shown to have some deficiencies in reproducing portions of the experimental data. A fracture mechanics based model is then presented which empirically relates the observed ultimate strength data to the estimated confining stress. This model is shown to accurately reproduce the confined strength data for all the combinations of core and wrap materials tested and over a wide variety of specimen sizes and wrap thicknesses.

Degree

Ph.D.

Advisors

Sun, Purdue University.

Subject Area

Mechanics|Civil engineering|Geotechnology

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