Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

Patterned Growth of Boron Nitride Nanotubes by Catalytic Chemical Vapor Deposition

Abstract: For the first time, patterned growth of boron nitride nanotubes is achieved by catalytic chemical vapor deposition (CCVD) at 1200 °C using MgO, Ni, or Fe as the catalysts, and an Al2O3 diffusion barrier as underlayer. The as-grown BNNTs are clean, vertically aligned, and have high crystallinity. Near band-edge absorption ∼6.0 eV is detected, without significant sub-band absorption centers. Electronic transport measurement confirms that these BNNTs are perfect insulators, applicable for future deep-UV photoelectronic devices and high-power electronics.

Fracture analysis of cellular materials: A strain gradient model

Abstract: A generalized continuum model is developed for cellular materials based on the equivalence of strain energy at the macro- and microscale. It is rather similar to the strain gradient theory, but has a well-defined characteristic length, namely, the cell size. The continuum model enables one to use powerful analytical methods to investigate fracture of cellular materials. The near-tip asymptotic fields and full-field solutions are obtained for cellular materials with hexagonal, triangular, or square lattice. Using the same strain-energy equivalence at the macro- and microscale, displacements and rotation of discrete cell walls are estimated from the continuum near-tip asymptotic fields. By postulating a maximum-tensile-stress failure criterion of cell walls, the fracture toughness of cellular materials is estimated to be proportional to the thickness h of cell walls and inversely proportional to √L, where L is the cell size. Moreover, the mixed-mode fracture toughness can be simply obtained from the fracture toughness in pure mode 1 and mode II, once the mode mixity is known. It is established that, with the same mass density, the hexagonal or triangular lattice in a cellular material can provide much higher fracture toughness than the square lattice.

Gradient elasticity and flexural wave dispersion in carbon nanotubes

Abstract: Higher-order elasticity theories have recently been used to predict the dispersion characteristics of flexural waves in carbon nanotubes (CNTs). In particular, nonlocal elasticity and gradient elasticity (with unstable strain gradients) have been employed within the framework of classical Euler-Bernoulli or improved Timoshenko beam theory to capture the dynamical behavior of CNTs. Qualitative agreement with the predictions of related molecular-dynamics (MD) simulations was observed, whereas the MD results departed significantly from those obtained with classical elasticity calculations. The present contribution aims to alert that the aforementioned higher-order models may yield questionable results for the higher wave numbers. As an alternative, gradient elasticity (with stable strain gradients), by also incorporating inertia gradients for dynamical applications, is used in combination with both Euler-Bernoulli and Timoshenko beam theories and shown to describe flexural wave dispersion in CNTs realistically for the small-to-medium range of wave numbers, i.e., the range for which MD results are available.