FORMULATION, VALIDATION, AND APPLICATION OF A FINITE-ELEMENT MODEL FOR ELASTOMERIC LAG DAMPERS

A time-domain finite element model has been developed to model the dyn amic behavior of nonlinear viscoelastic elastomers. Motivated by helic opter lag damper applications, a member in pure shear (one-dimension) is analyzed. The current approach is based on the method of Anelastic Displacement Fields (ADF). This approach extends the linear ADF approa ch to model the strain-dependent behavior characteristic of elastomeri c materials. Material nonlinearities are introduced via nonlinear func tions that describe the dependence of the unrelaxed and relaxed materi al moduli, and the anelastic strain rate on the instantaneous total an d anelastic strains. The parameters that characterize the nonlinear ma terial behavior are identified through harmonic strain controlled expe rimental tests. Experimental stress data for only two strain amplitude s (10% and 100%, zero static offset) are used to determine the ADF mod el parameters. The modeling approach is validated against linearized c omplex moduli data and stress-strain hysteresis loops at various strai n amplitudes and static strain offsets. The new ADF method is used to model two elastomeric systems, a silicon based high-damping elastomer, and a black rubber low-damping, high-stiffness elastomer. Nonlinear f inite element equations are obtained in terms of the resulting ADF par ameters. The potential of the subject technique is explored through a two element two material elastomeric snubber-damper model. The combine d snubber-damper finite element equations are integrated in the time-d omain and a limit cycle scenario, in the presence of an inherent initi al instability is demonstrated.