Fracture of elastomers under static mixed mode: the strain-energy-density factor

This work deals with the fracture of rubbers under a mixed mode loading (I + II) and it is an extension of our previous papers on that subject [Aït Hocine N, Naït Abdelaziz M, Imad A (2002) Int J Fract 117:1–23; Aït Hocine N, Naït Abdelaziz M (2004) In: Sih GC, Kermanidis B, Pantelakis G (eds) 6th international conference for mesomechanics. Patras (Greece), May 31–June 4, pp 381–385]. An experimental and a numerical analysis were carried out using a Styrene Butadiene Rubber (SBR) filled with 20 and 30% of carbon black. Sheets with an initial central crack (CCT specimens) inclined with a given angle compared to the loading direction were used. The J-integral and its critical values J _c (fracture surface energy) were determined by combining experimental data and finite element results. These critical values, determined at the onset of crack growth, were found to be quite constant for each elastomer tested, which suggests that J _c represents a reasonable fracture criterion of such materials. Then, the strain–stress field and the strain-energy-density factor S, earlier introduced by Sih [Sih GC (1974) Int J Fract 10(3):305–321; Sih GC (1991) Mechanics of fracture initiation and propagation. Kluwer Academic Publishers, Dordrecht, 428 pp] were numerically calculated around the crack tip. According to the experimental observations, the plan of crack propagation is perpendicular to the direction of the maximum principal stretch. Moreover, as suggested by Sih in the framework of linear elastic fracture mechanics (LEFM), the minimum values S ^min of the factor S are reached at the points corresponding to the crack propagation direction. These results suggest that the concept of the maximum principal stretch and the one of the strain-energy-density factor can be used as indicators of the crack propagation direction.     

Study and characterization of composites materials based on polypropylene loaded with olive husk flour

In Algeria, a significant quantities of olive husk are rejected to nature causing by the way major nuisances to environment, to give us a reason for which our work is focused on the valorization of this waste by its incorporation in a polypropylene matrix. The hydrophilic nature of natural fibers affects negatively its adhesion to hydrophobic polymeric matrix. To improve interfacial adhesion, two modes of chemical treatments were done using vinyltriacetoxysilane (VTAS) and maleic‐anhydride‐polypropylene (PPMA) compatibilisant agent. Several formulations of PP filled with 10 and 20% by mass of olive husk flour treated (OHFT) and untreated (OHFUT) were prepared. The chemical modification of olive husk flour was studied by Fourier transform infrared (FTIR) spectroscopy. The tensile properties, the water‐absorption behavior, the thermal degradation properties, and crystallinity of the composites were investigated. It was found that, the incorporation of the treated and untreated OHF improves the thermal stability of the composites. However, the use of the compatibilizer agent PPMA leads to a better thermal stability compared with the treatment of the OHF by the VTAS and the OHFUT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Removal of Cetylpyridinium Bromide by Adsorption onto Maghnite: Application to Paper Deinking

The removal of cetylpyridinium bromide (CPB) from aqueous solutions was investigated using a mineral adsorbent called Maghnite (a bentonite obtained from Maghnia, West Algeria). The adsorption kinetics of CPB on Maghnite is pseudo-second order and the adsorption isotherm follows essentially the model of Redlich–Peterson. The results obtained show that CPB is adsorbed on Maghnite with an adsorption capacity of 0.438 mmol/g (168.4 mg/g). Physical data indicate that CPB is efficient for the deinking of newspaper solutions, only when the natural Maghnite is associated to CPB. These results are of practical interest, since CPB shows a double action—to protect and to optimize aquatic environment.     

Commutation modelling and sparks reduction based on coupled circuit method

The commutating machines have a notable effect on the exchanges in brush–commutator contact area, which is particularly obvious when determining the intensity of sparks located on the brush. With time, higher current density at the descending edge promote sparks excitation, which itself increases intensity of the electrical erosion, brush temperature and thus also the wear. So in order to make an analytical study of commutation phenomenon, the coupled circuit method was developed. Therefore, a generalized mathematical model of the commutation, for brush–commutator, is established and can be extended for any other types of commutation on the basis of electromagnetic field (e.g. transformers and phase shift transformer. This model provides a greater efficiency to explain the impact of the electromagnetic fluxes surrounding brush area (or switch), specially for the current transition of the commutation process. Successful commutation is defined as operation in normal service, with no serious damages to the commutator, brushes or switches due to sparking that might require abnormal maintenance. It is recognized that some visible sparking are not evidence of unsuccessful commutation. The recommendation to improve the commutation (to achieve longer brush life) is the implementation of the proposal (slotted brush), which provides a linear and a sweet transition of currents in the coils of commutation. Copyright © 2012 John Wiley & Sons, Ltd.