Micromechanics

About: Micromechanics is a research topic. Over the lifetime, 6000 publications have been published within this topic receiving 162635 citations.

Crack bridging in fiber reinforced cementitious composites with slip-hardening interfaces

Abstract: A new crack bridging model accounting for slip-hardening interfacial shear stress is derived for randomly oriented discontinuous flexible fibers in cement-based composites, based on a micromechanics analysis of single fiber pull-out. The complete composite bridging stress versus crack opening curve (σB − δ relation) and associated fracture energy are theoretically determined. A micromechanics-based criterion which governs the existence of post-debonding rising branch of the σB − δ curve is obtained. Implications of the present model on various composite properties, including uniaxial tensile strength, flexural strength, ductility and critical fiber volume fraction for strain-hardening, are discussed together with an example of a 2% polyethylene fiber reinforced cement composite. It is found that the present model can very well describe the slip-hardening behavior during fiber pull-out which originates from fiber surface abrasion at fiber/matrix interface. In addition, the new model predicts accurately the enhanced toughness in terms of both ultimate tensile strain and fracture energy of the composite and resolves the deficiency of constant interface shear stress model in predicting the crack opening and ultimate strain, which are critical for material design of pseudo strain hardening engineered cementitious composites (ECCs).

Micromechanics of crack bridging in fibre-reinforced concrete

Abstract: The stress-crack width relationship has been determined experimentally for concretes reinforced with two types of fibres, steel and polypropylene, of various fibre volume fractions. A micromechanics-based theoretical model is proposed which captures the essential features of the stress-crack width relationships at small crack widths (less than 0.3 mm). Micromechanisms accounted for include the bridging actions due to aggregates and fibres, Cook-Gordon interface debonding and fibre pre-stress. The fibre bridging action involves interface slip-dependent friction as well as snubbing friction for fibres bridging at inclined angles. Theoretical predictions based on independent parametric inputs compare favourably with experimental measurements of the stress-crack width relationship. Findings in this research provide confidence in the use of the proposed model for materials engineering targeted at prescribed structural performance.

Cell model for nonlinear fracture analysis – I. Micromechanics calibration

Abstract: A computational approach based on a cell model of material offers real promise as a predictive tool for nonlinear fracture analysis A key feature of the computational model is the modeling of the material in front of the crack by a layer of similarly-sized cubic cells Each cell of size D contains a spherical void of initial volume fraction f 0 The microseparation characteristics of the material in a cell, a result of void growth and coalescence, is described by the Gurson–Tvergaard constitutive relation; the material outside the layer of cells can be modelled as an elastic- plastic continuum The success of this computational model hinges on developing a robust calibration scheme of the model parameters Such a scheme is proposed in this study The material-specific parameters are calibrated by a two-step micromechanics/fracture-process scheme This article describes the micromechanics calibration of void growth taking into account both the strain hardening and the strength of the material The fracture-process calibration is addressed in a companion paper