Marcus Rutner

Duality of energy absorption and inertial effects: Optimized structural design for blast loading

This article provides insights into the dynamic response and protection capacity of sacrificial structures mounted on a structural member and subjected to close standoff blast loading. The three main objectives of this study are: (a) exploration of key parameters governing the failure modes of a structural member protected by a sacrificial structure; (b) quantification of blast resistance and protection capacity of the sacrificial structure and underlying structure; and (c) conducting comparative single-degree-of-freedom system analysis and high-resolution explicit finite element analysis aiming at improving current single-degree-of-freedom analysis approaches. Energy absorption and momentum resistance are identified and quantified as the main contributing mechanisms controlling the dynamic response of structural members subjected to high-speed dynamic loading. The displacement of the structural member in the blast direction, the mass per length of the structural member, and the maximum impulse are found to be parameters governing the nonlinear response. The article also presents a response surface approach which might have value for time-efficient optimized structural member design and prediction of nonlinear structural member response to blast loading. This study includes validation of the numerical data through free-air blast test data from the literature.

Internal Defect Detection in Composite Plates on Demand

The motivation for this research is a lack of accurate, efficient and costeffective methodology to detect internal defects in composite plates. A micro-size network of strings is interwoven into the composites. Each string consists of a pair of tubes, containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in the direct contact of the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. Our preliminary investigation shows that a polar product, when exposed to a microwave energy source, heats up dramatically in comparison to the ambient composite material or the non-polar reactants. Our proposed structure-health monitoring approach builds upon this finding by using a short term low-power microwave exposure, causing a local high-thermal signature along potential internal defects. The elevated temperature regions are visualized with an infrared camera. The research presented in this paper has the following objectives: (a) We introduce adequate non-polar reactants and quantify the temperature sensitivity of the polar product. (b) We investigate the optimized microstructure and material of the double-cell tube and fine-tune the design to enable fracturing of the cell walls under certain strain and ease embedment into the composites. (c) The paper sheds light on potential manufacturing processes of the micro-size sensing network per se as well as the embedment into the composites. The clear advantages of this methodology over others are that it provides large area coverage, has no requirement for an internal power source and wiring and hence does not compromise the structural integrity of the composites. doi: 10.12783/SHM2015/214

Control of the dynamic properties of nano cantilevers with structural imperfections

Acoustic metamaterials can be made out of micro/nano size structures employing various structural elements such as cantilever oscillators [JASA, 132(4), 2866–2872]. Natural frequencies and eigenmodes depend on stiffness and mass distribution which should be reflected in macro as well as micro (nano) structure analysis. This study comprises three parallel approaches to model nano cantilever beams, i.e., the analytical method, the finite element analysis, and the molecular/atomic dynamics analysis, to identify how material imperfections influence the dynamic response of the nanocantilever. The study explores to what extent and under what circumstances macrostructure mechanics differs from nanostructure molecular/atomistic mechanics and how the built-in imperfection can be used to control structural dynamic properties at various scales.