CMC-Vol. 15, No. 2, 2010

Open Access

ARTICLE

The Colossal Piezoresistive Effect in Nickel Nanostrand Polymer Composites and a Quantum Tunneling Model
Oliver K. Johnson¹, Calvin J. Gardner¹, David T. Fullwood¹, Brent L.Adams¹, Nathan Hansen², George Hansen²
CMC-Computers, Materials & Continua, Vol.15, No.2, pp. 87-112, 2010, DOI:10.3970/cmc.2010.015.087
Abstract A novel nickel nanostrand-silicone composite material at an optimized 15 vol% filler concentration demonstrates a dramatic piezoresistive effect with a negative gauge factor (ratio of percent change in resistivity to strain). The composite volume resistivity decreases in excess of three orders of magnitude at a 60% strain. The piezoresistivity does decrease slightly as a function of cycles, but not significantly as a function of time. The material's resistivity is also temperature dependent, once again with a negative dependence.
The evidence indicates that nickel strands are physically separated by matrix material even at high volume fractions, and More >

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Study of Deformation Mechanisms in Titanium by Interrupted Rolling and Channel Die Compression Tests
Lei Bao^1,2, Christophe Schuman¹, Jean-sébastien Lecomte¹, Marie-Jeanne Philippe¹, Xiang Zhao², Liang Zuo², Claude Esling¹
CMC-Computers, Materials & Continua, Vol.15, No.2, pp. 113-128, 2010, DOI:10.3970/cmc.2010.015.113
Abstract The mechanisms of small plastic deformation of titanium (T40) during cold rolling and channel die compression by means of "interrupted in situ" EBSD orientation measurements were studied. These interrupted EBSD orientation measurements allow to determine the rotation flow field which leads to the development of the crystallographic texture during the plastic deformation. Results show that during rolling, tension twins and compression twins occur and various glide systems are activated, the number of grains being larger with twins than with slip traces. In channel die compression, only tension twins are observed in some grains, whereas slip More >

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Computational Homology, Connectedness, and Structure-Property Relations
Dustin D. Gerrard¹, David T. Fullwood¹, Denise M. Halverson², Stephen R. Niezgoda³
CMC-Computers, Materials & Continua, Vol.15, No.2, pp. 129-152, 2010, DOI:10.3970/cmc.2010.015.129
Abstract The effective properties of composite materials are often strongly related to the connectivity of the material components. Many structure metrics, and related homogenization theories, do not effectively account for this connectivity. In this paper, relationships between the topology, represented via homology theory, and the effective elastic response of composite plates is investigated. The study is presented in the context of popular structure metrics such as percolation theory and correlation functions. More >

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Spectral Approaches for the Fast Computation of Yield Surfaces and First-Order Plastic Property Closures for Polycrystalline Materials with Cubic-Triclinic Textures
Hamad F. Al-Harbi¹, Marko Knezevic^1,2, Surya R. Kalidindi^1,3
CMC-Computers, Materials & Continua, Vol.15, No.2, pp. 153-172, 2010, DOI:10.3970/cmc.2010.015.153
Abstract In recent work, we have demonstrated the viability and computational advantages of DFT-based spectral databases for facilitating crystal plasticity solutions in face-centered cubic (fcc) metals subjected to arbitrary deformation paths. In this paper, we extend and validate the application of these novel ideas to body-centered cubic (bcc) metals that exhibit a much larger number of potential slip systems. It was observed that the databases for the bcc metals with a larger number of slip systems were more compact compared to those obtained previously for fcc metals with a smaller number of slip systems. Furthermore, we More >

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