Formation of adiabatic shear band in metal matrix composites

A modified single-pulse loading split Hopkinson torsion bar (SSHTB) is introduced to investigate adiabatic shear banding behavior in SiCp particle reinforced 2024 Al composites in this work. The experimental results showed that formation of adiabatic shear band in the composite with smaller particles is more readily observed than that in the composite with larger particles. To characterize this size-dependent deformation localization behavior of particle reinforced metal matrix composites (MMCp), a strain gradient dependent shear instability analysis was performed. The result demonstrated that high strain gradient provides a deriving force for the formation of adiabatic shear banding in MMCp. (C) 2004 Elsevier Ltd. All rights reserved.

Laser-induced wavy pattern formation in metal thin films

Laser-induced well-ordered and controllable wavy patterns are constructed in the deposited metal thin film. The micrometer-sized structure and orientation of the wavy patterns can be controlled via scanning a different size of rectangle laser spot on the films. Ordered patterns such as aligned, crossed, and whirled wave structures were designed over large areas. This patterning technique may find applications in both exploring the reliability and mechanical properties of thin films, and fabricating microfluidic devices. (C) 2004 American Institute of Physics.

Anisotropic, gradient and metal-like mechanical behaviors of teeth and their implications on tooth functions

The anisotropy and gradient of the elastic modulus and the hardness of teeth were investigated by means of instrumented indentation method. Such properties are attributed to the unique microstructures of teeth based on scanning electron microscopic analysis. By comparing the relationship between the ratio of hardness to the reduced elastic modulus and the ratio of elastic unloading work to the total work of teeth in course of indentation to those of other materials, we found that the material behaviors of teeth display metal-like characteristics rather than ceramics as considered traditionally. These material behaviors and relevant functions are discussed briefly.

Characteristics of deep penetration laser welding of dissimilar metal Ni-based cast superalloy K418 and alloy steel 42CrMo

Experimental trials of autogenous deep penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 5.0 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding velocity and defocusing distance on the morphology, welding depth and width as well as quality of the welded seam were investigated. Results show that full keyhole welding is not formed on both K4.18 and 42CrMo side, simultaneously, due to the relatively low output power. Partial fusion is observed on the welded seam near 42CrMo side because of the large disparity of thermal-physical and high-temperature mechanical properties of these two materials. Tile rnicrohardness of the laser-welded joint was also examined and analyzed. It is suggested that applying negative defocusing in the range of Raylei length can increase the welding depth and improve tile coupling efficiency of the laser materials interaction. (c) 2007 Elsevier Ltd. All rights reserved.

Determination of interface properties between micron-thick metal film and ceramic substrate using peel test

Peel test measurements have been performed to estimate both the interface toughness and the separation strength between copper thin film and Al2O3 substrate with film thicknesses ranging between 1 and 15 mu m. An inverse analysis based on the artificial neural network method is adopted to determine the interface parameters. The interface parameters are characterized by the cohesive zone (CZ) model. The results of finite element simulations based on the strain gradient plasticity theory are used to train the artificial neural network. Using both the trained neural network and the experimental measurements for one test result, both the interface toughness and the separation strength are determined. Finally, the finite element predictions adopting the determined interface parameters are performed for the other film thickness cases, and are in agreement with the experimental results.

Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries

This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures. (c) 2007 American Institute of Physics.