Development of generalized yield surface of fly ash microbubble composites using nonlinear multiscale analysis

This study presents a multiscale framework to model the nonlinear constitutive behavior of particulate composites containing hollow ceramic inclusions. The composite consists of an elasto-plastic epoxy matrix, plastic in compression and linear elastic in tension, reinforced with brittle, linearly elastic fly ash microbubbles Representative volume elements (RVEs) with varying particle volume fractions (15–45%) are used to capture the micromechanical response under multiaxial loading. A structured modeling strategy is employed, including the idealization of fly ash microbubbles as hollow spheres and calibration of cohesive zone models using experimental data and SEM fracture imaging. A three-dimensional yield surface is constructed from RVE simulations, incorporating pressure sensitivity and Lode angle dependence. A custom VUMAT subroutine was developed to implement the proposed yield function which incorporates compressive hardening, tensile softening via a fracture strain limit and a viscosity-based regularization scheme enhances stability in explicit dynamic simulations, especially under small strain increments with low hardening modulus or perfect plasticity. This unified micromechanics-driven approach enables simulation of progressive failure in syntactic foams and related composites. • - A comprehensive multiscale approach is developed to model the nonlinear constitutive behavior of particulate composites containing hollow ceramic (fly ash) inclusions. • - Representative Volume Elements (RVEs) with varying particle volume fractions (15–45%) are used to capture the micromechanical response of the composite under multiaxial loading. • - A three-dimensional yield surface incorporating pressure sensitivity and Lode angle dependence is derived from RVE simulations, with compressive hardening, tensile softening, and viscosity-based regularization implemented in a custom VUMAT subroutine. • - The unified modeling framework enables realistic simulation of progressive failure in syntactic foams and similar particulate composites.