Statistical micromechanical damage model for SH-SFRC under tensile load considering the interfacial slip-softening and matrix spalling effects

Strain hardening behavior can be observed in steel fiber reinforced concretes under tensile loads. In this paper, a statistical micromechanical damage framework is presented for the strain hardening steel fiber reinforced concrete (SH-SFRC) considering the interfacial slip-softening and matrix spalling effects. With a linear slip-softening interface law, an analytical model is developed for the single steel fiber pullout behavior. The crack bridging effects are reached by averaging the contribution of the fibers with different inclined angles. Afterwards, the traditional snubbing factor is modified by considering the fiber snubbing and the matrix spalling effects. By adopting the Weibull distribution, a statistical micromechanical damage model is established with the fracture mechanics based cracking criteria and the stress transfer distance. The comparison with the experimental results demonstrates that the proposed framework is capable of reproducing the SH-SFRC’s uniaxial tensile behavior well. Moreover, the impact of the interfacial slip-softening and matrix spalling effects are further discussed with the presented framework.

A chemo-micromechanical damage model of concrete under sulfate attack

It is essential to explore the corrosion cracking of concrete under sulfate attack to predict the service performance and durability of concrete structures. The damage degree of concrete caused by sulfate attack is quantitatively investigated. Based on the damage mechanism of the local cracking stage, a chemo-micromechanical damage model of sulfate attack of concrete is established by elasto-damage mechanics. The progressive degradation behavior of concrete under sulfate attack is divided into three zones, including the chemical corrosion zone, the damaged concrete zone by expansive stress, and the intact concrete zone. The proposed chemo-micromechanical damage model can quantitatively determine the effects of chemical sulfate corrosion on mechanical properties of concrete. In addition, the present model considers the interaction among corrosion products, the damaged concrete, the intact concrete and uncorrupted hydration products. The comparison between the calculation results and the available experimental data shows that the proposed model is feasible for corrosion cracking analysis. Based on the proposed model, the influencing factors of concrete damage are discussed. With the increase of corrosion degree, the content of corrosion products, the expansion coefficient of corrosion products and the initial radius of corrosion products, the elastic moduli of concrete decrease after sulfate attack. When the tensile strength and rigidity of concrete matrix reduce, the effective elastic moduli of concrete after sulfate attack also deteriorate. The numerical results exhibit that the proposed chemo-micromechanical model is of notable significance to the application of the chemo-mechanical coupling problems of cementitious composite materials.

Experimental and numerical study of the interaction between dynamically loaded cracks and pre-existing flaws in edge loaded PMMA specimens

Dynamic fracture tests are carried out for four groups of hole-containing edge loaded specimens. The crack growth velocity, crack path, and dynamic toughness are extracted from the experiments using high-speed photography and digital image correlation. The importance of the interaction between the in-coming stress wave and the pre-existing hole is revealed and analyzed. A micromechanical damage model is calibrated to the experimental data from two of the specimens' designs and evaluated for its predictive capabilities using the other experimental configurations. The studied model is shown to be in reasonable agreement with the experimental data, and its limits are discussed

Rock Failure Analysis under Dynamic Loading Based on a Micromechanical Damage Model

A micromechanical constitutive damage model accounting for micro-crack interactions was developed for brittle failure of rock materials under compressive dynamic loading. The proposed model incorporates pre-existing flaws and micro-cracks that have same size with specific orientation. Frictional sliding on micro-cracks leading to inelastic deformation is very influential mechanism resulting in damage occurrence due to nucleation of wing-crack from both sides of pre-existing micro-cracks. Several homogenization schemes including dilute, Mori-Tanaka, self-consistence, Ponte-Castandea & Willis are usually implemented for up-scaling of micro-cracks interactions. In this study the Self-Consistent homogenization Scheme (SCS) was used in the developed damage model in which each micro-crack inside the elliptical inclusion surrounded by homogenized matrix experiences a stress field different from that acts on isolated cracks. Therefore, the difference between global stresses acting on rock material and local stresses experienced by micro-crack inside inclusion yields stress intensity factor (SIF) at the cracks tips which are utilized in the formulation of the dynamic crack growth criterion. Also the damage parameter was defined in term of crack density parameter. The developed model was programmed and used as a separate and new constitutive model in the commercial finite difference software (FLAC). The dynamic uniaxial compressive strength test of a brittle rock was simulated numerically and the simulated stress-strain curves under different imposed strain rates were compared each other. The analysis results show a very good strain rate dependency especially in peak and post-elastic region. The proposed model predicts a macroscopic stress-strain relation and a peak stress (compressive strength) with an associated transition strain rate beyond which the compressive strength of the material becomes highly strain rate sensitive. Also the damage growth process was studied by using the proposed micromechanical damage model and scale law was plotted to distinguish the dynamic and quasi-dynamic loading boundary. Results also show that as the applied strain rate increases, the simulated peak strength increases and the damage evolution becomes slower with strain increment.