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A simple, yet complete framework is introduced with the aim or modelling gram breakage in sous and crusnabie granular materials. The evolution of grain breakage is measured using a specific parameter of the grain-size distribution. The evolution of this new breakage parameter is related to the applied mechanical work, which allows the predictions to be independent of the stress paths. The correlation function proposed is trilinear, and is capable of describing the initiation, development, and stabilization of breakage. The initial state, coupled with three additional parameters, is used to calibrate this function. The three parameters are related to a grain specific quantity representing the strength of the particles that form the granular medium. The theory of fractal fragmentation is adopted, and the final state is considered to be unique and described by a single parameter: the fractal dimension. When tested against experimental results, this model was able to correctly predict the crushable behavior of a sand. Key words: particle breakage, granular media, grain crushing, fractal, particle strength, grain size distribution. Un cadre mecanique a la fois simple et complet est introduit dans le but de modeliser la rupture des grains dans les sols et autres milieux granulaires broyables. L'evolution de la rupture des grains est mesuree en utilisant un parametre caracteristique de la distribution granulometrique. L'evolution de ce nouveau parametre de rupture est reliee au travail mecanique applique, ce qui rend les predictions independantes du chemin des contraintes. La fonction de correlation proposee est trilineaire, et donc capable de decrire l'initiation, le developpement et la stabilisation de la rupture. L'etat initialainsi que trois autres parametres servent a calibrer cette fonction. Les trois parametres sont relies a une quantite propre au grain, et qui represente la resistance des particules qui forment le milieu granulaire. La theorie de la fragmentation fractale est adoptee, et l'etat final est donc suppose comme etant unique, et decrit par un seul parametre : la dimension fractale. Lorsque le modele est teste et les resultats compares a des travaux experimentaux, il devient possible d'apprecier la capacite du modele a simuler le comportement d'un sable. Mots-cles: rupture des particules, milieu granulaire, broyage des grains, fractal, resistance des particules, distribution granulometrique., Introduction Granular materials are of particular interest for civil engineers and soil mechanics specialists. Over time, the integrity of these materials varies depending on the mechanical conditions, the nature of [...]

Natural fibers such as jute fiber and biodegradable poly(lactic acid) (PLA) polymer are very good choices for environmental friendly material. Multi-gate injection is often used to meet the demand of mass production of injection moldings, therefore weld line is inevitable. The presence of weld lines not only detracts from the surface quality but also significantly reduces the mechanical strength of injection-molded parts. Although it is not always easy to completely eliminate weld lines, the weld strength could be improved through suitable adjustment of molding conditions such as melt temperature, mold temperature, hold pressure, injection speed, and so on. In this study, three kinds of pellets materials were prepared: long fiber pellets (LFT), the re-compounding pellets (RP), and LFT50:RP50 hybrid mixtures (LFT/RP). Tensile test was carried out to investigate the effect of different pellets and holding pressures on the mechanical property of welded jute/PLA specimens. And the interfacial shear strength of non-welded jute/PLA specimens was calculated with Kelly-Tyson Formula. Fiber separation and fiber dispersion in RP became better than that of LFT which resulted in a better interfacial property. Weld strength of RP and hybrid LFT/RP specimens was improved by 43.34% and 16.46% than that of LFT specimen, respectively. POLYM. ENG. SCI., 53: 1657-1666, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION As well known, most currently marketed composites are made from synthetic fibers and polymers that derive from petroleum which is unsustainable fossil fuel. They are not biodegradable and, thus, [...]

This paper describes a new testing method to examine the mechanical behavior of railroad ballast subjected to repeated train passages on ballasted track. Two types of cyclic loading tests, namely a single-point loading test and a movingwheel loading test, were performed with small-scale models of ballasted track. Next, a 'multi-ring shear apparatus' was developed as a type of torsional simple shear apparatus, and the applicability of a newly proposed multi-ring shear test to an element test of railroad ballast subjected to moving-wheel loads was examined by comparing the results of multi-ring shear tests with those of small-scale model tests. As a result, it was recognized that cumulative strain obtained from multi-ring shear tests is almost equivalent to the one derived from small-scale model tests. Moreover, it was revealed that the difference between loading methods has a considerable influence on the cyclic plastic deformation of railroad ballast because settlement in a moving-wheel loading test was much larger than the one in a single-point loading test. These results lead to the conclusion that a multi-ring shear test has an excellent applicability to the estimation of deformation behavior of granular materials subjected to moving- wheel loads. Key words: base course, cyclic load, gravel, railroad, special shear test. Cet article decrit une nouvelle methode d'essai pour etudier le comportement mecanique d'un ballast de voie ferree soumis a des passages repetitifs des trains sur le ballast de la voie. Deux types d'essais de chargement cyclique, l'essai a chargement sur un point et l'essai a chargement par une roue en deplacement, ont ete realises avec des modeles de ballast de voie a petite echelle. Ensuite, un << appareil de cisaillement multi-anneaux >> a ete developpe en tant que type d'appareil de cisaillement simple en torsion. L'applicabilite de l'essai propose en cisaillement multi-anneaux a ete evaluee sur un element de ballast de voie ferree soumis a un chargement par une roue en deplacement en comparant les resultats des essais de cisaillement multi-anneaux avec ceux des essais obtenus avec le modele a petite echelle. Il a ete observe que la deformation cumulative obtenue par les essais de cisaillement multi-anneaux est a peu pres equivalente a celle derivee des essais avec le modele a petite echelle. De plus, il a ete demontre que la difference entre les methodes de chargement a une influence considerable sur la deformation plastique cyclique d' un ballast de voie ferree, puisque le tassement subit lors de l' essai a chargement par une roue en deplacement est beaucoup plus grand que celui subit lors d' un essai a chargement sur un point unique. Ces resultats permettent de conclure que l'essai de cisaillement multi-anneaux est bien applicable a l'estimation du comportement en deformation de materiaux granulaires soumis a des chargements par une roue en deplacement. Mots-cles : assise de base, chargement cyclique, gravier, voie ferree, essai de cisaillement special. [Traduit par la Redaction], Introduction The study of 'track deterioration' is one of the principal assignments in railway engineering because track deterioration has serious consequences on the safety of train operations (Selig and Waters [...]