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Nearly all‐natural and synthetic composites derive their characteristic attributes from a hierarchical makeup. Engineered metamaterials exhibit properties not existing in natural composites by precise patterning, often periodically on size scales smaller than the wavelength of the phenomenon they influence. Lightweight fiber‐reinforced polymer composites, comprising stiff/strong fibers embedded within a continuous matrix, offer a superior structural platform for micro‐architectured metamaterials. The emergence of microvascular fiber‐composites, originally conceived for bioinspired self‐healing via microchannels filled with functional fluids, provides a unique pathway for dynamic reconfigurable behavior. Demonstrated here is the new ability to modulate both electromagnetic and thermal responses within a single structural composite by fluid substitution within a serpentine vasculature. Liquid metal infiltration of varying density micro‐channels alters polarized radio‐frequency wave reflection, while water circulation through the same vasculature enables active‐cooling. This latest approach to control bulk property plurality by widespread vascularization exhibits minimal impact on structural performance. Detailed experimental/computational studies, presented in this paper, unravel the effects of micro‐vascular topology on macro‐mechanical behavior. The results, spanning multiple physics, provide a new benchmark for future design optimization and real‐world application of multifunctional and adaptive microvascular composite metamaterials.

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Printed Circuit Heat Exchangers (PCHEs) have high compactness and efficiency for heat transfer, which makes them an attractive option for the Very High Temperature Reactors (VHTRs). Design methodology of PCHE for non-nuclear service is well established in the ASME Code, Section VIII; however, ASME Code rules for PCHE nuclear services are yet to be developed. Towards developing the ASME Section III code rules for PCHE, the study started with the design of PCHE core specimens for testing following the ASME section VIII methodology. The failure responses of these PCHE specimens are investigated by using Finite Elements Analyses (FEA). Two dimensional isothermal plane strain analyses are performed using an uncoupled constitutive material model. Parametric studies by varying shape and size of semicircular channels, PCHE core size, and loading cases are performed to quantify the critical parameters which influence the PCHE failure responses under pressure creep and pressure burst loadings. Results indicate that the maximum creep strain and its location are dependent on the PCHE core size. Significant reduction in creep strains are observed at the channel sharp corners by considering a realistic semielliptical channel shape instead of a semicircular channel in the analysis.

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Printed Circuit Heat Exchangers (PCHEs) are well-suited for Very High Temperature Reactors (VHTRs) due to high compactness and efficiency for heat transfer. The design of PCHE must be robust enough to withstand possible failure caused by cyclic loading during high temperature operation. The current rules in ASME Code Section III Division 5 to evaluate strain limits and creep-fatigue damage based on elastic analysis method have been deemed infeasible at temperatures above 650°C. Hence, these rules are inapplicable for temperatures ranging from 760–950°C for VHTRs. A full inelastic analysis method with complex constitutive material description as an alternative, on the other hand, is time consuming; hence impracticable. Therefore, the simplified Elastic-Perfectly Plastic (EPP) analysis methodology is used as a solution in ASME Code Section III Division 5. The current literature, however, lacks any study on the performance evaluation of PCHE through EPP analysis. To address these issues, this study initiates the pathway of EPP evaluation of an actual size PCHE starting with elastic orthotropic analysis in the global scale. Subsequently, preliminary planning for analyzing intermediate and local submodels are provided to determine channel level responses to evaluate PCHE performance against strain limits and creep-fatigue damage using Code Case-N861 and N862 respectively.

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