Caoutchouc

The thermal lag associated with the temperature ramping experiment in a dynamic mechanical analysis is demonstrated on carbon black filled vulcanised rubber samples by using a DMTA MkIII from Rheometric Scientific. The importance of achieving thermal equilibrium on the sample before starting the measurement is emphasised. By running a combination of isothermal and ramping steps, the impact of thermal lag

Understanding phenomenon induced by complex fatigue loadings is an important issue for the conception of industrial components. Rubber materials, thanks to their abilities to withstand high deformations, are more and more used in industry. In an ongoing study, an experimental investigation is being carried out to study the effect of multiaxial loadings on the fatigue life of polychloroprene rubber. This material is used for pulleys. Specimen used is a dumbbell type, axisymetric geometry with a reduced section at mid-height. The experimental results indicate that under uniaxial tensile loading a kink in the conventional Haigh diagrams is observed leading to high lives at high R-ratio loading as compared to low R-ratios. Fractographic studies indicate the presence of crystallographic tongues under high R-ratio loading. To reproduce multiaxial conditions on this specimen, combined axial displacements and torsion rotation fatigue tests are performed, according to three different paths, depending on the phase angle between the two axes. Different multiaxial fatigue criteria are used to analyze experimental results.

This paper deals with modeling of the interaction in overlapping cracks that the authors have earlier identified to be generic to a wide range of polymeric systems (Ramasamy and Lesser, J Polym Sci B Phys, 2003). A complex stress function method is used for evaluating stress intensity factors for interacting cracks. The interaction between two parallel overlapping cracks is considered first. It is shown for this case that the stress intensity factor can fall below the threshold value when there is sufficient overlap, leading to arrest of crack growth at the overlapping tip. Then the interaction in a doubly periodic infinite array of cracks is considered. The interaction in the array is found to be non-linear. However, at a given stress level, the highest density of stable cracks is related to the threshold value for crack propagation Kth though a simple set of equations. It is also shown that in an infinite array of cracks, the energy release rate criterion for crack growth is different from the stress intensity factor criterion due to a reduced stiffness of the material.

Biofuel production from vegetable oil is potentially a good alternative to conventional fossil derived fuels. Moreover, liquid biofuel offers many environmental benefits since it is free from nitrogen and sulfur compounds. Biofuel can be obtained from biomass (eg pyrolysis, gasification) ...

In this contribution, a new innovative isolation system for structures in earthquake regions is presented. The system consists of high damping rubber bearings strengthened with glass fibre fabrics. A wide parametric numerical investigation through Finite Element Analysis is carried out in order to develop and verify analytical models for these new isolation devices. Experimental investigations provided useful information for numerical

McKibben actuators are pneumatic actuators with very high force to weight ratios. Their ability to match the behavior of biological muscles better than any other actuators has motivated much research into the characterization and modeling of these actuators. The purpose of this paper is to experimentally characterize the behavior of McKibben artificial muscles with basic geometric parameters, and present a model that is able to predict the static behavior accurately in terms of blocked force and free displacement. A series of experiments aimed at understanding the static behavior of the actuators was conducted. The results for three different lengths (4 in., 6 in., and 8 in.), three diameters (1/8 in., 1/4 in., and 3/8 in.), and one wall thickness (1/16 in.) at pressures ranging from 10 psi to 60 psi illustrate the key design trends seen in McKibben actuator geometry. While existing models predict this static behavior, there are varying degrees of accuarcy, which motivates the prese...

The objective of this research is to investigate the potential of using crumb rubber as a partial substitute for coarse sand in the production of concrete paving block (CPB). Laboratory trials were conducted to investigate the effect of crumb rubber particle size. A comparison was also made between CPB mixtures containing various percentages of crumb rubber to determine the optimum crumb rubber content and water-cement (w/c) ratio. Styrene-butadiene rubber (SBR) latex was added to the mixtures of crumb rubber CPB and mechanical properties were evaluated. A total of 276 CPB were fabricated and tested in laboratory to determine the density, skid resistance and the compressive strength. The design strength level ranging from 31 to 43 MPa was achieved using w/c ratios of 0.45 to 0.55. The test results indicated that there was a systematic reduction in the strength with the increase in rubber content. Scanning electron micrograph showed that inclusion of SBR latex into the matrix did not improve the mechanical properties of the CPB. Results also revealed that a w/c ratio of as high as 0.55 without any SBR latex at 15% rubber content by total sand volume might be practically used to produce crumb rubber CPB which achieve the target compressive strength of 30 MPa.