Computationally implemented modeling of creep of composite materials caused by phase dissolution

Abstract

Multiphasic composites with time-evolving, transient microstructures exhibit time-dependent behavior under load. One mechanism leading to this behavior is the dissolution of loadbearing phases within such materials. When the dissolution process occurs inside one phase of the composite material, the stress transmitted by the dissolving phase transfers into the neighboring phases, resulting in additional deformation of the whole composite. This additional deformation of the macroscopic material manifests as time-dependent creep of the composite. The purpose of this paper is to provide a general kinematic framework for such dissolution induced creep for virtually any material class, and to mechanistically model the same utilizing a computationally-implemented approach that is consistent with the kinematic framework. Utilizing this modeling approach, two distinct processes are computationally simulated, namely 1) creep of a water saturated, porous, frozen body upon warming and 2) creep of cement paste due to hydration-induced dissolution of cement grains. The simulation results show that microstructure evolution induces significant creep behavior of the whole composite in these two simulated cases.

Creep and relaxation of cement paste caused by stress‐induced dissolution of hydrated solid components

“…In addition to inherent C‐S‐H viscoelasticity/viscoplasticity, some other mechanisms have also been proposed, including dissolution of load‐bearing phases and poromechanical effects, both of which manifest as time‐dependent transfer of microscale stresses among phases. Recently, a study conducted by Li and Grasley suggested that in unsaturated, early age cement paste, where poromechanical effects can be neglected, the contribution of C‐S‐H viscoelasticity/viscoplasticity to creep/relaxation of cement paste may not be as significant as the creep caused by dissolution of load‐bearing cement grains during the hydration reaction . The gradual dissolution of cement grains induces a redistribution of the stress from dissolving, load‐bearing cement grains to precipitated hydration products, increasing the elastic deformation of the remaining solid constituents, and yielding VE/VP behavior of cement paste on the bulk scale.…”

“…Its natural configuration, to which the body would return if stimuli were removed, also evolves with time. The kinematic framework of this process is summarized in Figure (for more detail see), where χ's denote the motions of the material body from one configuration to another. For any species i in the composite material, its motion is defined by x i = χ i ( X i , t), where x i is the position vector of species i in the current configuration, X i is the position vector of species i in the reference configuration, and the boldface indicates a vector (or, in general, a higher order tensor).…”

“…The computationally implemented model developed in this study is an updated version of the (hydration‐induced) cement grain dissolution prediction model introduced in ref . The cement grain dissolution prediction model has been utilized in different areas to predict the time‐dependent behavior of cement composites .…”

“…The apparent VE/VP moduli of cement paste are calculated based on the averaged stress and strain over the whole composite. A more detailed description of the FEM routine can be found in ref …”

“…To test the hypothesis that stress‐induced dissolution is a mechanism of creep of cementitious materials, a recently developed computational approach that couples a hydration microstructure evolution model and a finite element calculation model is utilized . In the original version of the model, cement grains dissolve with time following empirically derived hydration kinetics equations to simulate the hydration reaction, and the hydration products and pore solution are treated as one single thermodynamic system that steps quasi‐statically from one equilibrium state to another.…”