Search for: All records

Abstract We investigate shock propagation in confined, frictionless granular media using discrete element simulations with an elastoplastic contact law. Depending on the level of confinement and loading, elastoplastic systems exhibit a weak or strong shock propagation response similar to an elastic Hertzian system although the details of the shock development differ markedly from the elastic case. Two modes of dynamic stress propagation are observed based on the shock intensity regime: weak shocks carry the stresses via the initial contact path while strong shocks form new contact networks behind the front. However, unlike for elastic shock propagation, there is an upper bound to the front velocity of strong shocks that depends on the maximum intergranular contact stiffness. Since elastoplastic contact is a dissipative process, results show that dissipation is enhanced with confining pressure in the weak shock regime. 

A computational framework is developed to model and optimize the nonlinear multiscale response of three‐dimensional particulate composites using an interface‐enriched generalized finite element method. The material nonlinearities are associated with interfacial debonding of inclusions from a surrounding matrix which is modeled usingC⁻¹continuous enrichment functions and a cohesive failure model. Analytic material and shape sensitivities of the homogenized constitutive response are derived and used to drive a nonlinear inverse homogenization problem using gradient‐based optimization methods. Spherical and ellipsoidal particulate microstructures are designed to match a component of the homogenized stress‐strain response to a desired constructed macroscopic stress‐strain behavior.

 

This note presents approximate analytical expressions for the velocity of the self‐propagating reaction front in the frontal polymerization of thermoset polymers and composites. Prior estimates available in the literature for the front velocity have been limited by their applicability to simple reaction kinetics. The improved estimates provided in this work are shown to be applicable to complex reaction kinetics encountered in the frontal polymerization of neat thermoset polymers or fiber‐reinforced polymer‐matrix composites with a wide range of polymer chemistries, including dicyclopentadiene, cyclooctadiene, acrylates, and epoxies. They are also shown to be applicable to wide range of values of the initial temperature and initial degree of cure of the resin, and of the volume fraction of the reinforcing phase.

 

Frontal polymerization provides a rapid, economic, and environmentally friendly methodology to manufacture thermoset polymers and composites. Despite its efficiency and reduced environmental impact, the manufacturing method is underutilized due to the limited fundamental understanding of its dynamic control. This work reports the control and patterning of the front propagation in a dicyclopentadiene resin by immersion of phase‐changing polycaprolactone particles. Predictive and designed patterning is enabled by multiphysical numerical analyses, which reveal that the interplay between endothermic phase transition, exothermic chemical reaction, and heat exchange govern the temperature, velocity, and propagation path of the front via two different interaction regimes. To pattern the front, one can vary the size and spacing between the particles and increase the number of propagating fronts, resulting in tunable physical patterns formed due to front separation and merging near the particles. Both single‐ and double‐frontal polymerization experiments in an open mold are performed. The results confirm the front–particle interaction mechanisms and the shapes of the patterns explored numerically. The present study offers a fundamental understanding of frontal polymerization in the presence of heat‐absorbing second‐phase materials and proposes a potential one‐step manufacturing method for precisely patterned polymeric and composite materials without masks, molds, or printers.