Research Plan

 

The overall research effort consists of two thrusts that are intimately related to each other

  • Discovery: studies fundamental novel nonlinear phenomena in stress wave mitigation
  • Demonstration: explores design, fabrication, and evaluation of scalable material systems with stress wave mitigating characteristics

The multidisciplinary nature of the research effort dictates that both thrusts involve effort from all of the investigators, and includes experimental, numerical, and analytical components. By necessity, there is significant overlap between the thrusts in the sense that the discovery thrust is relevant to and informed by the material design process, and the material design and fabrication process generates additional discovery topics that must be understood for the design to continue.

 

Discovery Thrust

This thrust deals with the discovery of novel fundamental phenomena in various material classes that show interesting wave propagation characteristics. In early studies of model systems, granular media have been seen to exhibit stress wave mitigation, passive shock energy redirection, and nonlinear tailoring aspects that are promising for accomplishing the goals of the present research. Thus, a significant part of the Discovery thrust is dedicated to studying stress wave propagation in nonlinear granular media, nonlinear energy redirection in preferential paths within the material, and the physics of nonlinear interactions at interfaces within the material.

Other materials of interest include phase transforming ceramics and a new class of inorganic polymer-like ceramics called geopolymers. Phase transforming ceramics have been shown to provide beneficial toughening characteristics in fracture situations. We plan to investigate their potential benefits as a stress wave mitigating material by having either transformation strengthening or weakening in the material, either before or during loading. Geopolymers could have promising uses as both adhesive materials and structural matrix materials. Little is known about them, however, and they will also be studied in some detail to discover their ability to be integrated into a stress wave mitigating material system.

The Discovery thrust involves experimental, numerical, and theoretical studies by all the investigators in a highly coupled fashion. Fundamental questions addressed include

  • What are the intrinsic wave dynamics of granular media, especially regarding their capacity to localize, focus, or redirect shock energy?
  • How is the capacity for nonlinear targeted energy transfer and shock energy redirection altered in configurations of branched granular media embedded in an elastic or plastic matrix?
  • What is the physics of intrinsically nonlinear granular interfaces between elastic layers? Can we develop a predictive capability of shock energy trapping and local dissipation in these interfaces?
  • How do the candidate materials behave over orders of magnitude of loading rate, especially regarding dynamic energy transfer (relevant at lower rates) and dissipation (relevant at lower and higher rates)? Is this response scale dependent, i.e., is it scalable both as features become smaller and larger?
  • What effect does failure (either matrix, interface/interphase, or particle) have on the wave propagation characteristics of the materials?

 

Demonstration Thrust

This thrust concentrates on the design and fabrication of material systems that posses particular wave management characteristics. The goal here is to devise a framework by which scientific advancements made in the Discovery thrust form a basis for predicting in detail the wave mitigation response of particular material system designs. The designs are then manufactured and experimentally evaluated to show whether the predicted results are indeed achieved. Redesign is then done if needed. During this design-fabrication-evaluation-redesign process, some aspects of new discovery may also be needed (for example those pertaining specifically to the materials system, rather than individual constituents), and they are pursued accordingly. The entire team of investigators interact on this thrust, proceeds in parallel with the Discovery thrust, increasing in complexity from 1D to 1.5D to 2D and eventually to 3D systems.

The Demonstration thrust involves experimental, numerical, and theoretical studies by all of the investigators in a highly coupled fashion. Fundamental questions addressed include

  • How can we integrate granular materials into a ceramic or geopolymeric surrounding 3D architecture while preserving their wave propagation characteristics?
  • How is particle contact maintained/affected during this process?
  • What designs can actually be achieved within acceptable ranges of tolerance (i.e., levels of disorder that still maintain desirable wave propagation characteristics)?
  • What effect do layer material properties in a layer plate have on global dynamic response?
  • How do temporal and spatial loading characteristics affect global dynamic response?
  • What metrics quantify stress wave management characteristics for varying temporal and spatial loading characteristics?

 

Schematic representation of multiscale design of stress wave mitigating structures. Individual constituent responses at microscale (microstructural level) are combined in synergistic fashion at mesoscale (component level) to produce desired macroscale (entire structure level) response.