Late after the pioneer work of Cadwell, 1940 cf. The equivalent stress used as damage parameters established rubber fatigue life prediction model. From an engineering point of view, prediction of fatigue crack nucleation in automotive rubber parts is an essential prerequisite for the design of new components. The present paper deals with the specificities of the thermal response of rubber under cyclic mechanical loading at constant ambient temperature. This criterion involves a characteristic energy for tearing which is independent of the shape of the test-piece and of the disposition of the cut.
Since then, many researchers have studied this type of instability in metals. Results showed that the increased thermal stability of blends with Si69 is highly related to the formation of crosslinks between the filler. It studies the rate of development of cracks after initiation. This has subsequently led to a demand for the investigation of fatigue behaviour of rubber components, especially in conditions of multi-axial loading. It seems to me completely unrelated!! The process considered is that occurring in the absence of appreciable temperature rise as a result of the development of one or more cracks. Individual stress-strain response for the axial and shear loading is shown below. This is due to the appearance of higher stress amplitudes in the flex member during operation.
Tensile crack growth Smith et al. A prerequisite for substantiual growth of a cavity in a material is that the material is capable of large deformation before fracture. Therefore, many studies were realized to estimate fatigue lives of rubber parts, in the fatigue crack nucleation frame. A fatigue life criterion is proposed. . Both c and r are obtained by selecting a series of stress strain pairs along the material cyclic stress strain curve and describe the shape of the curve.
A full factorial experiment, whereby interactions between all the factors are investigated, would demand 729 experiments. Ratcheting rate is controlled by X which is set at a fixed value of 5. The effects of the percentage of SiO2 particles and the impact cyclic loading frequency on the impact fatigue strength was investigated. The stress term in this model makes it suitable for describing mean stresses during multiaxial loading and nonproportional hardening effects. Also, a complete literature review and explanation of fundamentals are included concerning different features these materials exhibit from the mechanical point of view: elasticity, inelasticity, fatigue, and tribology behavior.
The loading history is repeated in compression. In preparing this brief historical review, I have been led to some elementary conclusions about research itself. The other characterization is to measure the stress vs. Any stress concentration effects must be included in the input loading data. Impact fatigue tests were carried out on epoxy resin filled with SiO2 particles. The effects of the loading type, loading value and stress ratio on the crack growth behaviour are discussed. Indeed, the stabilized mean value between the maximum and minimum temperature variations during fatigue tests does not reflect only fatigue damage, since the entropic coupling also leads to a value different from zero.
On the existence of mimimizers with prescribed singular points in nonlinear elasticity. However, for the case I suggested, self-similar indentation which is vaguely more similar to a self-similar situation in a crack you get obviously only geometrical definition of strain, which is or a cone connected to the angle of the cone. First, the fact that a theory appears to work does not mean that it is true. Yet this idealization has proved in some cases to be a fair representation of actual defects. Lang, Influence of crack tip sharpness and radius on the strain distribution in rubbers analyzed by finite element simulation and experiments, in P. The main difference which is actually an interesting challenge between cavitation in elastomeric solids and cavitation in metals and gels is that of accounting for plasticity and nonlinear viscoelasticity effects.
The crystallization growth is elucidated by diffusion of chain segments into crystal nuclei. Of course, it would be great to have the experiments as well. The cracking energy density is the portion of the total elastic strain energy density that is available to be released on a given material plane. Brown and Miller Brown and Miller Brown, M. A theory of oriented crystallization in elongated polymers having network structures e. The prepared solid model has been transferred to the Ansys Static Structural Programmer in.
This multi- initiation followed by a slow propagation and cracks coalescence could explain the low scattering of the fatigue results of natural rubber. Thus, no precise values of these quantities will be given in the following discussion. The simplest hypothesis is to consider that they are vacuous i. Scanning electron microscopy analysis showed that fatigue failure is related to ligaments breakage for material B, while cavitation induced by the decohesion between zinc oxides and rubber matrix is the main cause of the fatigue damage for material A. The ability to predict the effects of complex strain histories on fatigue life is a critical need. Stress relaxation tests show that the thermal signatures of crystallization and of crystallite melting are different. Une méthode d'optimisation des différents paramètres du critère est présentée.