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We put stiffness and strength of ultrafine-grained metals under scrutiny by means of experimental and analytical mechanics. Samples of Al 1050 were processed by Accumulative Roll Bonding (ARB) at different cycles to give ultrafine-grained microstructures. The microstructure, strength, and stiffness of the processed Al were analyzed by XRD and SEM. An analytical micromechanical model was developed to explain the predicted changes in the mechanical properties of the ultrafine-grained Al. It was revealed that an ultrafine-grained pure metal (e.g., Al) possesses a heterogeneous microstructure with the grain boundary stiffness lower than the grain/subgrain stiffness. This heterogeneous microstructure gave a decrease-after-increase behavior of the overall stiffness of Al during ARB. The grain boundary fraction of the microstructure increased from 1.9% after 2 cycles to 13.4% after 9 cycles of ARB. The stiffness decreased to 0.73 of its maximum value obtained after 2 cycles. With the aim of changing the stiffness and strength of the grain boundary, other samples were processed such that 4% SiC particles were added to Al sheets during the 1st-ARB cycle. The addition of SiC particles gave stiffer and stronger grain boundaries, which enhanced the overall stiffness and strength during ARB. Both the stiffness and strength were observed continuously increasing during ARB up to 484% and 793% after 9 cycles compared to the unprocessed Al, respectively.

International audience; High values for the work of separation have been reported in peel tests on fibrillating interfacial systems. The exact origin of these high values is not properly understood, since it remains unclear which dissipative mechanisms related to fibrillation cause a significant increase in the work of separation. In this paper, the contribution of fibril mechanics to the work of separation is quantified. To this end, a micromechanical model of a single fibril is used, in which the growth of a nucleated fibril up to the moment of fracture is described. The initial geometry is varied to reflect the variability in the substrate profile. It is observed that the stresses and strains that occur in the model are well beyond typical bulk values. Given the large variation in measured stress–strain curves for rubber materials reported in literature, a small scale single fibril experiment is performed to assess the applicability of reported bulk material parameters to this problem. The obtained experimental response falls well within the model bandwidth for the range of material parameters from literature. Furthermore, the fibril fracture stress, which serves as the failure criterion in the model, is extracted from the experiment. From the micromechanical model results, it appears that, for the considered range of material properties, the work of separation is mainly influenced by the fracture stress. Furthermore the initial geometry has a profound influence on the obtained work of separation. It is concluded that the work of separation determined from the micro-model is significantly larger than the intrinsic adhesion energy, yet it remains still an order of magnitude smaller than the values reported in literature. For the considered system this indicates that, although it has a significant contribution, fibril deformation is not the only contribution to the high work of separation.

The use of reinforcing fibres has shown to be an effective, simple and economic way to enhance the mechanical characteristics of brittle materials; in particular tensile strength, fracture and fatigue resistance, wear resistance and durability are usually noticeably higher in fibre-reinforced materials (FRC) with respect to unreinforced ones. For the above mentioned reasons composite materials today can replace or compliment other traditional structural materials. On the other hand the extensive use of brittle matrix composite materials requires appropriate computational models to describe, with adequate accuracy, their mechanical behaviour. In the present paper a mechanical-based computational model for the description of the macroscopic behaviour of such a class of materials, composed by a matrix phase and a fibre-reinforcing phase, is formulated. By considering a micromechanical-based model, the macro constitutive equations of unidirectional or randomly distributed fibres reinforced materials are obtained by taking into account the possibility of crack formation and propagation in the matrix as well as fibre debonding and breaking. The developed computational model is finally used in some numerical simulations in order to outline its reliability in the assessment of both the fibre–matrix interaction phenomenon as well as the fracture failure prediction capability in brittle matrix FRC materials.

Based on the crystallographic slip theory, a micromechanical model for polycrystal elasto–inelasticity is proposed and applied to describe the mechanical behavior of a such structure under monotonic and cyclic loading paths. Small strain theory and isotropic elasticity are assumed. Biaxial cyclic loading is of particular interest in proposed work. The kinematic hardening of the polycrystal is naturally obtained from the averaging scheme. In this scheme, we use a self-consistent interaction law. The proposed modeling effort is tested for a FCC metal under different loading situations in order to elucidate its capability. The obtained results show that this model reproduces appropriately the principle cyclic features such as Bauschinger effect, strain memory effect, ratcheting and additional hardening and other effects.

A simplified micromechanical model adapted to martensitic transformation is applied to describe transformation induced plasticity (TRIP) in steel. The accommodation of the transformation volume and shape change is performed by plastification considering Hill's anisotropic yield condition. Both a uniaxial and a triaxial loadstress state are investigated. A generalized TRIP-term is developed in the sense of an “extended” Greenwood and Johnson (1965, Proc. R. Soc. London A 283, 430-422) relation.

In the original formulation of the micromechanical method of cells, designated for the analysis of fibrous composites with periodic structure, the repeating volume element consists of four interacting subcells. The various capabilities and reability of the micromechanical model were verified in a recent review paper and a monograph. The present investigation offers a generalization of the method to an arbitrary number of subcells for the modeling of multiphase periodic composites. Such a generalization is particularly advantageous when dealing with elastic-plastic composites, since yielding and plastic flow of a metallic phase may take place at different locations. Effective constitutive laws that govern overall behavior of the elastic-viscoplastic composite material are established. These laws are given in terms of relationships between the average stress-rate and strain-rate of the inelastic multiphase composite. Comparisons between the response of boron/aluminum composite obtained by the present model and a finite element solution are given.

The problem of crack growth along the interface of two immiscible homopolymers is studied where the interface is strengthened by the addition of a small amount of diblock copolymer. A micromechanical model of the interface is proposed and a time-dependent Dugdale—Barenblatt model based on this model is used to predict the fracture toughness of the interface as a function of the applied loading, the crack growth rate and the underlying interface properties.

The paper presents a simple micromechanical model for the time-dependent deformation of polycrystalline vitreous alumina. The inelastic strain is attributed to the grain boundary sliding and growth of intergranular microcracks.

On the basis of a simple micromechanical model, expressions are developed for the overall stress and deformation rate measures in a granular mass which carries the applied loads through contact friction. Various measures of the granular fabric are examined, and explicit connections between a fabric measure and the stress and the deformation rate tensors are obtained. Then, from the balance of energy, a general stress-dilatancy equation is deduced, which includes the effect of fabric. Several other published dilatancy equations are discussed and compared with the new equation.