Tuesday, 12 October 2004 - 3:30 PM

This presentation is part of : Micromechanics and Physics of Materials

On the Physical Basis of the Zerilli-Armstrong Model Parameters

George Z. Voyiadjis and Farid H. Abed. Louisiana State University, Department of Civil & Environmental Engineering, Baton Rouge, LA 70803

The physical interpretation for the material parameters of the Zerilli-Armstrong (Z-A) constitutive relations for both bcc and fcc metals is scrutinized in this work. The Z-A model is derived based on the activation energy analysis as well as the dislocation interaction mechanisms. Despite these physical bases, the material parameters are found to be inappropriately related to the physical quantities in the microstructural scale. The inaccuracy of these parameter definitions is mainly attributed to the use of the expansion ln(1+x)~x in the final step of the model derivation. This expansion, however, is valid only for values x<<1 which is not the case at elevated temperatures. A number of modifications are, therefore, incorporated from which new relations are suggested for each particular metal structure taking into consideration the exact value of the aforementioned expansion which makes the material parameters precisely related to the microstructure physical quantities. The proposed modified relations along with the Z-A relations are evaluated using the experimental results for different bcc and fcc metals such as Tantalum, Niobium, Vanadium, and OFHC Copper. Comparisons with these experimental results are made at low and high strain rates and over a wide range of temperatures. The proposed model simulations, in general, show better correlation than the Z-A model particularly at temperatures values above 300K. Numerical identification for the physical quantities used in the definition of the proposed model parameters is also presented.

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