Thermomechanical problem on vibration of a viscoelastic rubberlike rod under dynamic loading

The problem on vibration of a viscoelastic rod under dynamic load at one of its ends is considered. The external loading has a signfficant influence on the dynamic characteristics of the material. By using the complex moduli, the problem on vibration of the viscoelastic rod was solved. The complex shear and Young's moduli of a rubberlike material should exhibit the same dependence on frequency. The properties of a rubberlike material was applied. The temperature influence is associated both with the Newton boundary conditions and dissipative heating. The dissipative function is expressed in terms of deformations. The frequencies of high-damping materials occur at or near frequencies that are normally of interest in vibration problems at room temperature. For solving the problem a finite element model was applied. Using this model, qualitative analysis of the influence of dynamic load and dissipative heating on the resonant vibrations of viscoelastic rod is performed. According to the theory of viscoelasticity an analysis of the results was done. The reliability of the values of frequencies for the first resonances was checked. The numerical results qf the problem on vibration of a viscoelastic cylindrical rod under dynamic load at one of its end by the general thermomechanical laws on vibration in damped mechanical systems were obtained and investigated. Distribution of the temperature of dissipative heating along the rod axis is analyzed.

COMPARISON OF FATIGUE CRITERIA UNDER PROPORTIONAL AND NON-PROPORTIONAL MULTIAXIAL LOADING

ABSTRACTOwing to their interesting mechanical behavior and their diversity, rubberlike materials are more and more used in the industry. Previous works (Poisson et al.) presented an important experimental investigation on the multiaxial fatigue of polychloroprene rubber, with both proportional and non-proportional combinations of tension and torsion loads (with a large range of loads and three different phase angles: 0°; 90°, 180°). A fatigue criterion, based on the dissipated energy density (DED) was introduced. Comparing this parameter to the most important criteria available on literature—which are the strain energy density (SED), the cracking energy density (CED), and the Eshelby tensor—in their accuracy allows one to predict fatigue life of rubberlike material. All the predictors are computed with an analytical viscoelastic model based on the kinematics of a combined tension and torsion loading applied on a cylinder. This cylinder represents the central part of the axisymetric dumbbell specimen, and the model was identified with a polychloroprene rubber. It is finally shown that the DED and CED reach more conclusive results, provided the structure, the material, and the loads investigated.

Experimental Analysis of the Damage Zone around Crack Tip for Rubberlike Materials under Mode-I Fracture Condition

Studying the deformation and fracture properties of soft materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of rubberlike materials. In this paper, an application of the experimental digital moire method to determine the damage zone around crack tip for rubberlike material is presented. The measurement principles and the basic procedures of the method are explained in detail. The deformation of crack tip fields in the damage zones is analyzed using the sector division mode. Finally, an analysis of the damage zone is proposed to describe crack-tip fields in rubber-like materials with large deformation.

Inflation of a Thick-Walled Shell Which Exhibits Stress Softening

The Mullins effect (Mullins, 1947), also known as stress softening, is exhibited by certain rubberlike materials and refers to changes of the mechanical properties, due to prior deformation. Johnson and Beatty (1995) have investigated the Mullins effect in equibiaxial tension by performing cycles of static inflation and deflation experiments on latex balloons. These experiments show that stress softening results in a decrease in the pressure necessary to inflate a balloon, and in addition, indicate inelastic effects of hysteresis and permanent set. The objective of this paper is to investigate the finite deformation static inflation from the virgin state, followed by quasi-static removal of the internal pressure, of a thick-walled homogeneous spherical shell composed of an incompressible isotropic rubberlike material which exhibits stress softening and permanent set. Since the initial inflation of the shell, due to application of an internal pressure, does not result in a homogeneous deformation, a state of residual stress is present after complete removal of the internal pressure. A procedure is presented for the determination of the response of the shell for the first cycle of inflation and deflation from the virgin state, and the analysis includes strain softening and the inelastic effects of hysteresis and permanent set. It is assumed that, for the initial static inflation of the shell from the virgin state, the internal pressure and stress distribution for a monotonically increasing internal or external radius are the same as for a hyperelastic shell, and also that the magnitude of the permanent set of an element of the material is related monotonically to the deformation at the end of the inflation.