MURI on Mechanics and Mechanisms of Impulse Loading, Damage and Failure of Marine Structures and Materials

Principal Investigator: G. Ravichandran
Co-Investigators: K. Bhattacharya, T. Colonius, P. E. Dimotakis, M. Gharib, M. Ortiz, A. J. Rosakis and J. E. Shepherd

Program Manager: Dr. Yapa Rajapakse, ONR

This multidisciplinary research program seeks to develop a fundamental understanding of the mechanics and mechanisms of impulse loading and the resulting damage and failure in marine structures and materials of relevance to the Navy. The current state of knowledge provides detailed understanding of individual aspects; however, impulse failure of marine structures is a highly inter-connected and highly coupled phenomenon. Therefore, an integrated multidisciplinary approach based on the comprehensive understanding of fluid/structure interactions, impulse loads arising from explosions and wave slamming, and their effects on materials and structures of marine craft, made of composites and sandwich structures forms the basis of the proposed research. This approach emphasizes the delicate interplay between the source, the fluid, the structure and the material through a collaborative effort that includes theory, large-scale simulation, and controlled and highly instrumented dynamic experimentation.

The proposed effort will be pursued in the context of three highly relevant loading conditions:
Loading due to bubble collapse and cavitation in underwater explosions (UNDEX) and their effect on fiber reinforced composite and sandwich structures;

Shock focusing phenomena in convergent geometries and their effect on composite materials/structures;

Wave slamming and the effect of repeated transient loading on sandwich structures and light-weight metals.

High-speed quantitative visualization of the interfacial conditions between the fluid and solid will be used to probe the mechanisms of impulse load creation and transmission as well as the resulting deformation and failure. The experimental geometries will include both simple (planar) and complex (curved) surfaces to emulate geometries of marine structures. Appropriate scaling laws will be used (when necessary) to infer the boundary conditions generated by the impulse loads on realistic marine structures. These loads will then be applied to the materials/structures of interest and the resulting dynamic deformation and failure modes will be characterized using a wide range of diagnostic tools based on full field, high-speed optical and infrared thermography. Comprehensive 3-D fluid dynamical (CFD) and structural/material mechanics (FEM) models will be developed. Multiscale modeling including a realistic description of cavitation, bubble collapse, wave slamming, composite materials and sandwich structures will form an integral part of this computational effort. All these results will be incorporated into comprehensive theories that can be used to design impulse loading mitigation technologies.

To pursue these ambitious goals, the proposal gathers a diverse and distinguished team with expertise spanning fluid mechanics, thermal sciences, explosion mechanics, solid and structural mechanics, materials science and computational science and engineering. This team is carefully chosen to meet the goals of this proposal, and there exist numerous connections and a proven record of collaborative research amongst team members.

The proposed research will develop novel experimental techniques, advanced diagnostics and a new generation of validated computational models. With its unprecedented attention to the solid/fluid interface under impulse conditions, this proposal is also likely to raise new questions and lead to the discovery of new phenomena. The highly resolved data from the experiments will be used to validate the computational models and codes. All these are expected to have a significant technological impact on the design of next generation light-weight and high-speed marine structures including littoral combat ships, destroyers, cruisers, and advanced sea bases. Finally, this proposal provides for unique opportunity for training of students and postdoctoral scholars in an area of importance to the national defense in an interdisciplinary setting.