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发表于 2007-12-4 05:48:41
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来自 加拿大
Every model has its own reason for existence. No one is best for all; it all depends on your goal and conditions for analysis.
These constitutive equations are in two distinct categories: the first assumes that the strain energy density is a polynomial functions of the principal strain invariants; in the case of incompressible materials, this material model is commonly referred to as a Rivlin material; in the second category, it is assumed that the strain energy density is a separable function of the three principal stretches; Ogden, Peng, and Peng-Landel material models are examples in this categrory.
High order strain energy functions are of little practical value, because rubber materials are not sufficiently reproducible to allow one to evaluate a large number of coefficients with any accuracy. Therefore, the extra terms only do a good job in fitting experimental errors. The Mooney-Rivlin model remains the most widely used strain energy function in FEA, and should be the first choice due to its simplicity and robustness.
A neo-Hookean Mooney-Rivlin model has a first coefficient equal to one-half of the shear modulus and a second coeffcieknt equal to zero. This material model exhibits constant shear modulus and give s good correlation with experimental data up to 40% strain in uni-axial tension and up to 90% in simple shear.
A 2-coeffcieinmt Mooney-Rivlin model shows good agreement with tensile test data up to 100% strain, but it has been found inadequate in describing the compression model of deformation. It also fails to account fot the stiffening of the material at large strains.
A 3-term, or greater Moone-Rivlin model accounts for a non-constant shear modulus. Caution needs to be exercised on inclusion of higher order terms to fit the data, since this may result in unstable energy functions yielding non-physical results outside the range of the experimental data. The Yeoh model differs from other higher order models in that it depends on the first strain invariant only. This model has been demonstrated to fit various requirements on material testing.
Only when your stress-strain curve has more than two turning points, you can consider using higher order M-R models. When your stress-strain curve has a special shape, maybe Arruda-Boyce is better for you; at this time consider the handbook or research papers for the shape of statistical mechanics based models like Arruda-Boyce and Van der Waals. |
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