Research Papers

Analytical Model of the Confined Compression Test Used to Characterize Brittle Materials

[+] Author and Article Information
Sidney Chocron

Engineering Dynamics Department, Southwest Research Institute, San Antonio, TX 78238schocron@swri.edu

James D. Walker, Arthur E. Nicholls, Kathryn A. Dannemann, Charles E. Anderson

Engineering Dynamics Department, Southwest Research Institute, San Antonio, TX 78238

J. Appl. Mech 75(2), 021006 (Feb 20, 2008) (7 pages) doi:10.1115/1.2775501 History: Received November 17, 2006; Revised June 26, 2007; Published February 20, 2008

Numerical and analytical simulations of projectiles penetrating brittle materials such as ceramics and glasses are a very challenging problem. The difficulty comes from the fact that the yield surface of brittle materials is not well characterized (or even defined), and the failure process may change the material properties. Recently, some works have shown that it is possible to characterize and find the constitutive equation for brittle materials using a confined compression test, i.e., a test where a cylindrical specimen, surrounded by a confining sleeve, is being compressed axially by a mechanical testing machine. This paper focuses on understanding the confined compression test by presenting an analytical model that explicitly solves for the stresses and strains in the sample and the sleeve, assuming the sleeve is elastic and the specimen is elastoplastic with a Drucker–Prager plasticity model. The first part of the paper briefly explains the experimental technique and how the stress-strain curves obtained during the test are interpreted. A simple and straightforward approach to obtain the constitutive model of the material is then presented. Finally, a full analytical model with explicit solution for displacements, strains, and stresses in the specimen and the sleeve is described. The advantage of the analytical model is that it gives a full understanding of the test, as well as information that can be useful when designing the test (e.g., displacements of the outer radius of the specimen).

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Experimental setup

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Figure 2

(a) Stress versus axial strain obtained in a typical test with many load-unload cycles. (b) Stress versus hoop-strain curve for the same test.

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Figure 3

First loading cycle in test BF-14

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Figure 4

“Idealized” stress-strain curves used for the interpretation of the results

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Figure 5

(a) Equivalent stress versus pressure plot for a typical test. (b) Envelopes for six different tests showing that sample strength is limited. All the tests shown are confined compression of predamaged samples.

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Figure 6

Stress versus strain curves for compression of unconfined-predamaged samples. Confinement pressure in these samples is zero.




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