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Innovative pothole patching materials reinforced with a high-toughness, low-viscosity nanomolecular resin, dicyclopentadiene (DCPD, C10H12), have been experimentally proven to be effective in repairing cracked asphalt pavements and can significantly enhance their durability and service life. In this paper, a three-dimensional micromechanical framework is proposed based on the micromechanics and continuum damage mechanics to predict the effective elastic-damage behaviors of this innovative pothole patching material under the splitting tension test (ASTM D6931). In this micromechanical model, irregular coarse aggregates are approximated and simulated by randomly allocated multi-layer-coated spherical particles in certain representative sizes. Fine aggregates, asphalt binder (PG64-10), cured DCPD (p-DCPD), and air voids are formulated into an isotropic elastic asphalt mastic matrix based on the multilevel homogenization approach. The theoretical micromechanical elastic-damage predictions are then systemically compared with properly designed laboratory experiments as well as three-dimensional finite elements numerical simulations for the innovative pothole patching materials.

A multi-scale micromechanical model is proposed to predict the damage degree of hybrid fiber-reinforced concrete under or after high temperatures. The thermal degradation of hybrid fiber-reinforced concrete is generally composed of the damage of the cement paste caused by thermal decomposition and thermal incompatibility, the deterioration of aggregates and fibers, and the interfacial damage between aggregates and the matrix. In this multi-scale model, four levels of hybrid fiber-reinforced concrete structures are considered when the thermal damage degree is derived; namely, the equivalent calcium silicate hydrate (C–S–H) product level, the cement paste level, the concrete level, and the hybrid fiber-reinforced concrete level. At the cement paste level, thermal decompositions of C–S–H product and calcium hydroxide are taken into account. In addition, a dimensionless parameter of the crack density is introduced to represent the thermal cracking of the matrix. At the concrete level, the interfacial damage of aggregates is simulated by a spring–interface model, in which the interfacial parameters are assumed to be functions of temperature. Moreover, at the cement paste level and the hybrid fiber-reinforced concrete level, a sub-stepping homogenization method is proposed to determine the effective properties. Comparisons between previously published experimental data and predictions and discussions illustrate the feasibility of the proposed multi-scale model in predicting thermal damage of concrete and hybrid fiber-reinforced concrete.

Most concrete structures repaired by the electrochemical deposition method are not fully saturated and the healing interfaces are not always perfect in reality. To demonstrate these issues, micromechanical models are presented for unsaturated concrete repaired by electrochemical deposition method with the healing interfacial transition zone based on our latest work. The repaired unsaturated concrete is represented as a multiphase composite made up of the water, unsaturated pores, intrinsic concrete, deposition products and the healing interfacial transition zone between the latter two components. The equivalent particle, matrix and composite for repaired unsaturated concrete are obtained by modifying the differential-scheme and the generalized self-consistent method. Modifications are utilized to rationalize the differential-scheme based estimations by taking into the water (including further hydration and viscosity effects), interfacial transition zone and the shapes of the pores into considerations. Furthermore, our predictions are compared with those of the existing models and available experimental results, thus illustrating the feasibility and capability of the proposed micromechanical framework.

In quasi-brittle polycrystalline materials, damage by cracking or cleavage dominates plastic and viscous deformation. This paper proposes a micromechanical model for rock-like materials, incorporating the elastic-damage accommodation of the material matrix, and presents an original method to solve the system of implicit equations involved in the formulation. A self-consistent micromechanical approach is used to predict the anisotropic behavior of a polycrystal in which grain inclusions undergo intragranular damage. Crack propagation along planes of weakness with various orientation distributions at the mineral scale is modeled by a softening damage law and results in mechanical anisotropy at the macroscopic scale. One original aspect of the formulated inclusion–matrix model is the use of an explicit expression of Hill’s tensor to account for matrix ellipsoidal anisotropy. To illustrate the model capabilities, a uniaxial compression test was simulated for a variety of polycrystals made of two types of mineral inclusions with each containing only one plane of weakness. Damage always occurred in only one mineral type: the damaging mineral was that with a smaller shear modulus (respectively higher bulk modulus) when bulk modulus (respectively shear modulus) was the same. For two minerals with the same shear moduli but different bulk moduli, the maximum damage in the polycrystal under a given load was obtained at equal mineral fractions. However, for two minerals with different shear moduli, the macroscopic damage was not always maximum when the volume fraction of two minerals was the same. When the weakness planes’ orientations in the damaging mineral laid within a narrow interval close to the loading direction, the macroscopic damage behavior was more brittle than when the orientations were distributed over a wider interval. Parametric studies show that upon proper calibration, the proposed model can be extended to understand and predict the micro–macro behavior of different types of quasi-brittle materials.

Since pullout behaviors of fibers intersecting a fracture plane of cementitious composite are similar to those in a single-fiber pullout test, micromechanical model of fracture energy for hooked-end steel fiber-reinforced cementitious composite (HSFRCC) is developed on the basis of single hooked-end steel fiber pullout test. The hooked-ends of steel fibers intersecting a fracture plane have various deformations which can be generally classified into hooked-end total deformation, partial deformation, and nondeformation. The pullout energy of steel fiber with deformed hooked-end is significantly different from that with nondeformed one; derivations of pullout energies of hooked-end steel fibers with deformed/nondeformed hooked-ends are carried out first. The fracture energy model of HSFRCC is proposed using probabilistic method accounting for energy contributions from all steel fibers intersecting the fracture plane. Experimental validation of the proposed micromechanical model is performed, and excellent agreements are observed in comparison with experimental data from uniaxial tensile tests. As the proposed fracture energy model is a function of physical and micro-geometric properties of hooked-end steel fibers and cementitious matrix, it can guide optimal design of HSFRCC.

A progressive micromechanical damage-plasticity formulation is proposed to analyze the single hooked-end steel fiber pullout energy from the surrounding cement-based matrix within the context of hooked-end steel fiber-reinforced cementitious composites (HSFRCC). As the hooked-end steel fiber has a unique fiber geometry, its fiber pullout energy from the cement-based matrix consists of the interfacial fiber-matrix debonding, the frictional sliding and pullout energy, and the elastoplastic deformation energy of the steel fiber hooked end. The aforementioned energy components are analytically derived first, and the superposition principle is subsequently employed to obtain the total energy dissipation during the fiber pullout process. Good agreement is obtained for comparisons between the experimental results of single hooked-end steel fiber pullout tests and the proposed analytical predictions. This satisfactory verification supports the validity and applicability of the proposed damage-plasticity energy prediction formulation, and suggests the applicability of this methodology to further investigation on micromechanical fracture energy prediction of HSFRCC during flexural macro-cracking.

Based on a well-established micromechanical model of damage initiation in low-cycle fatigue (LCF) already developed in Abdul-Latif (1994), a new extension is proposed for describing the damage deactivation effect. With a small strain assumption, it is assumed that the local damage variables initiate at the crystallographic slip system level. It is considered that the damage is active only if micro-cracks (MC) are open, while damage affects differently the mechanical properties of polycrystals during its closure (inactive phase). The anisotropic damaged (activation and deactivation) behavior concept is adopted only at the macroscopic level. With a fourth-order damage tensor, the deactivation damage effect under multiaxial cyclic loadings is modeled describing the related phenomenon of the induced-oriented anisotropy. Several numerical simulations are conducted describing the overall damaged behavior of polycrystals in biaxial LCF. The responses of a given grains aggregate are recorded and then discussed. As a conclusion, the model describes fairly well the damage activation and deactivation effect in plastic fatigue, notably under multiaxial complex loading paths.

Based on the slip theory, a micromechanical model of damaged-inelastic behavior, which was recently proposed for metallic polycrystalline structures (FCC), is extended in order to describe the unilateral effect in low-cycle fatigue with a small strain assumption. In this micromechanical model, the micro-damage variables initiate and then evolve on the activated crystallographic slip systems. These variables are coupled with micro-macro constitutive equations. The formulation of the unilateral character of the damage (activation and deactivation) is limited only to the macroscopic level using the isotropic damaged concept. At this point, the unilateral effect is introduced with the help of a simple phenomenological constant. It allows to appropriately describe the macro-damage parameter evolution during the closure of defects (inactive phase) with the continuity of the stress-strain response.

A theoretical micromechanical model is proposed to describe the damaged behavior of polycrystalline metals. Based on the slip theory, a local micro-damage variable representing the transgranular damage is introduced and fully coupled with micro-macro anelastic constitutive equations for FCC polycrystals proposed by Cailletaud (1987, 1992). The micro-damage is supposed to be initiated and then evolved on the activated crystallo graphic slip systems to define isotropic damage at the macroscopic level (i.e., in the Repre sentative Volume Element RVE). The coupling between damage and the behavior at both microscopic and macroscopic levels is carefully discussed. The obtained model is applied and discussed in the case of uniaxial monotonic and cyclic loading, neglecting the quasi- unilateral effect as well as the localization of the fatigue micro-cracks on the surface of the loaded medium.