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The paper addresses a compressive-failure theory for polymer-matrix nanocomposites in the case where failure onset is due to microbuckling. Two approaches based on the three-dimensional linearized theory of stability of deformable bodies are applied to laminated and fibrous nanocomposites. According to the first approach (continuum compressive-failure theory), nanocomposites are modeled by a homogeneous anisotropic medium with effective constants, including microstructural parameters. The second approach uses the piecewise-homogeneous model, three-dimensional relations for fibers (CNT) and matrix, and continuity conditions at the fiber-matrix interface. The compressive-failure theory is used to solve specific problems for laminated and fibrous nanocomposites. Some approximate failure theories based on the one-and two-dimensional applied theories of stability of rods, plates, and shells are analyzed Keywords: nanocomposites, CNT fiber, polymer matrix, compressive failure, microbuckling, three-dimensional linearized theory of stability of deformable bodiesIntroduction. Today's literature on the fracture mechanics of composites considers the paper [17] to be the first to describe, in 1960, fiber microbuckling as a compressive failure mechanism for unidirectional fibrous composites. In the years that followed, several authors set forth different approximate models for the quantitative and qualitative description of this mechanism. These models are based on a number of assumptions and hypotheses, of which the following are worth mentioning: no (neglected) subcritical stresses in the matrix, use of applied one-and two-dimensional theories of stability of rods and plates to study microbuckling, modeling of the matrix by a one-dimensional elastic object, etc.The paper [14] was apparently the first to propose, in 1965, a highly approximate model for the quantitative description of microbuckling in composites within the framework of a plane problem (in fact, the fibrous composite was modeled by a laminated composite), using the above-mentioned assumptions and hypotheses (the same results were reported in [14]). Despite the highly approximate model, the results from [14] were used in many publications, including the seven-volume collective monograph [13], and are generally recognized and widely cited. In the literature on the fracture mechanics of composites (see, e.g., [15]), these results are named the Dow-Gruntfest-Rosen-Schuerch theory, after the authors of the first publications [14,17,45,46].Thus, to describe the failure mechanism in question [17], we need a stability theory for unidirectional fibrous composites (Fig. 1) or laminated composites (Fig. 2) subjected to axial compression. The paper [17] addressed a fibrous composite; thus, it is expedient to construct a stability theory for the material represented in Fig. 1. In this connection, a stability theory for laminated composites (Fig. 2) is to be developed to attain two ends (two different cases). In the first case, a stability theory is needed to describe the f...

The paper draws on the similarities between the well-known process of whiskerization of microfibres and the recent idea of bristled nanowires. The new method for evaluation of the effective elastic properties of such materials is suggested based on the model of four-component composition. This model assumes the transverse isotropy of continuum and predicts five elastic moduli and density as independent effective constants. An example of calculation of the constants for the particular materials is given. It shows the significant increase in the shear strength of composites with whiskerized or bristled fibres.

Two types of vibratory pile driving have been identified by the Authors termed respectively ‘slow’ and ‘fast’ vibrodriving. The occurrence of slow or fast motion is determined by the initial soil density, pile diameter, displacement amplitude and acceleration of vibration. Slow vibrodriving is concluded to be the most widely encountered and the paper, therefore, concentrates on this type of motion. A theory and interactive computer simulation of the case of slow vibratory driving has been developed. The motion is considered to be that of a rigid body subject to viscous—Coulomb side and elasto—plastic end resistance under a combined sinusoidal excitation and static surcharge force. Experimental verification of the theory has been by means of tests on a fully instrumented 0·745 kW (1 hp) model in dry cohesionless soils. The need for further research work to quantify soil resistance and the dependence of this on displacement amplitude and frequency of vibration is stressed. The Authors recommend that this information is obtained from full scale tests using a prototype designed on the basis of the information provided by the present research work. Deux types de battage de pieux vibratoire ont été identifiés par les auteurs et désignés respectivement par vibrobattage ‘lent’ et vibrobattage ‘rapide’. La ‘lenteur’ ou la ‘rapidité’ du mouvement est déterminée par la densité initiale du sol, le diamètre du pieu, l'amplitude du déplacement et l'accélération des vibrations. Selon les conclusions, le type de vibrobattage ‘lent’ est celui qui se rencontre le plus fréquemment et l'article se concentre donc sur ce type de mouvement. Une théorie et une simulation interactive sur ordinateur du cas du vibrobattage ‘lent’ ont été mises au point. Le mouvement est envisagé comme étant celui d'un corps rigide soumis à une résistance visqueuse, type Coulomb et extrémité élastoplastique, sous l'action simultanée d'une surcharge statique et d'une excitation sinusoïdale. La théorie a été vérifiée expérimentalement par des essais sur un modèle 0·745 kW (1 HP) à instrumentation complète dans des sols secs sans cohésion. L'article insiste sur la nécessité d'effectuer des recherches supplémentaires pour quantifier la résistance du sol et sa dépendance avec l'amplitude du déplacement et la frequence de vibrations. Pour obtenir ces renseignements, les auteurs recommandent d'effectuer des essais a l'échelle à l'aide d'un prototype réalisé sur la base des renseignements obtenus à partir des travaux de recherches actuels.

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