Material characterisation for finite element analysis of rubber components
1998
Gough, J. | Muhr, A.H. (Tun Abdul Razak Research Centre, Brickendonbury, Hertford SG138NL (United Kingdom)) | Thomas, A.G.
Experimental determination of the strain-energy function of an elastomer is in general not simple, even if simplifying assumptions are made of isotropy, incompressibility and perfect elasticity. This is because it requires simultaneous measurement of the stresses corresponding to imposition of two orthogonal strains which need to be varied independently over the full range. The issue is often avoided; for example, many finite element packages recommended using stress-strain data from uniaxial tests to fit the constants in particular forms of strain-energy function. In consequence the usefulness of the finite element analyses can be compromised by the choice of an unsuitable strain-energy function. . In the work presented here an intermediate technique, based on measurement of two stresses corresponding to a particular state of biaxial strain (shear) is used. The technique is straightfoward, although it requires a purpose built 'split pure-shear' sraining jig. Although, it enables a more general form for the strain energy function to be derived, the results support a simplifying assumption which, if made, would permit the same information to be derived from a uniaxial test. Strain-energy functions derived using the technique are given for natural rubber compounds with a range of loadings of N330 black and good agreement is found with uniaxial data. The technique is also useful for probing multiaxial relaxation and cyclic softening behaviour, and preliminary results on these aspects are reported.
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