New developments in fracture of rubbers: Predictive tools and influence of thermal aging

In this work, the influence of thermal oxidative aging on the ultimate mechanical properties of rubbers is investigated. Two new approaches to predict failure properties are proposed. The first one is the stress limiter approach that uses a “damage” parameter allowing determination of the failure stress and strain of an aged material knowing both the mechanical properties and macromolecular network characteristics of an as-received material. The second one is an extension of the energy limiter approach that suggests capturing the drop of the stress at failure by replacing the strain energy density function of an as-received elastomeric material by a function expressed in terms of an energy limiter. The predictive capabilities of these two approaches are validated using experimental results for two elastomeric materials: an EPDM and a polychloroprene (CR), both of which exhibit a largely predominant post-crosslinking (over chain scissions) during aging. Comparison between the predictions and the experimental results in terms of failure stresses and strains under uniaxial tension showed a good agreement. Consequently, these two approaches are promising tools for designing elastomeric parts subjected to thermal oxidative aging

On slip pulses at a sheared frictional viscoelastic/ non deformable interface

We study the possibility for a semi-infinite block of linear viscoelastic material, in homogeneous frictional contact with a non-deformable one, to slide under shear via a periodic set of ``self-healing pulses'', i.e. a set of drifting slip regions separated by stick ones. We show that, contrary to existing experimental indications, such a mode of frictional sliding is impossible for an interface obeying a simple local Coulomb law of solid friction. We then discuss possible physical improvements of the friction model which might open the possibility of such dynamics, among which slip weakening of the friction coefficient, and stress the interest of developing systematic experimental investigations of this question.Comment: 23 pages, 3 figures. submitted to PR

Analytical and numerical investigation using limit analysis on the ductile failure of pipes containing surface cracks

International audienceUsing cracked pipes design standards and finite element analysis, the limit load analysis for pipes containing surface cracks was determined. The study was performed on five pipes of different diameters with a constant crack length and depth. The crack geometry is a semi-elliptical surface crack. The cracked pipes are subjected to internal pressures which are obtained from formulas of cracked pipes design standards. Due to the ductile behavior of polyethylene pipes, the failure occurs when the critical stress reaches a value equal to the ultimate tensile strength multiplied by a constraint factor. In this work, the constraint factor was calculated and its evolution with the pipe diameter was analyzed. Three different definitions of a constraint factor based on global or local approaches were also compared, so that a new failure criterion can be obtained. The new failure criterion makes the prediction of the pipe residual life possible which, in turn, facilitates a systematic approach to maintenance and replacement of pipes