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Displaying 1 - 25 of 98

Shoulder fillet effects in strength distributions of MEMS components

November 6, 2020
Author(s)
Frank W. DelRio, Brad L. Boyce, Jake T. Benzing, Lawrence H. Friedman, Robert F. Cook
The failure forces and fracture strengths of polysilicon MEMS components in the form of stepped tensile bars with shoulder fillets were measured using a sequential failure chain methodology. Approximately 150 specimens for each of four fillet geometries

Microscale Mapping of Structure and Stress in Barium Titanate

April 19, 2020
Author(s)
Jane A. Howell, Mark D. Vaudin, Lawrence Henry Friedman, Robert F. Cook
Cross-correlation of electron backscatter diffraction (EBSD) patterns was used to generate rotation, strain, and stress maps of single-crystal tetragonal barium titanate (BaTiO3) containing isolated, small, sub-micrometer a domains separated from a c-

A critical evaluation of indentation crack lengths in air

November 13, 2019
Author(s)
Robert F. Cook
A extensive overview is presented of Vickers indentation crack lengths in ceramics in air. Measurement of such crack lengths is one of the most common and powerful assessments of the fracture properties of ceramics and the overview provides a critical

Stress measurements in alumina by optical fluorescence: revisited

August 27, 2019
Author(s)
Robert F. Cook, Chris A. Michaels
Stress measurements in single crystal and polycrystalline alumina are revisited using a recently-developed optical fluorescence energy shift method. The method simultaneously utilizes the R1 and R2 Cr-related ruby line shifts in alumina to determine two

Determination of Ceramic Flaw Populations from Component Strengths

June 3, 2019
Author(s)
Robert F. Cook, Frank W. DelRio
A procedure is outlined for determining the population of flaws in manufactured ceramics from strength measurements of sampled components. The broad applicability of the procedure is demonstrated in a quantitative manner, using strength measurements from a

Fracture Sequences During Elastic-Plastic Indentation of Brittle Materials

April 12, 2019
Author(s)
Robert F. Cook
A fracture analysis is developed for crack initiation sequences occurring during sharp indentation of brittle materials. Such indentations, generated by pyramidal or conical loading, generate elastic and plastic deformation. The analysis uses a non-linear

Lamellar and bundled domain rotations in barium titanate

August 27, 2018
Author(s)
Jane A. Howell, Mark D. Vaudin, Lawrence Henry Friedman, Robert F. Cook
Cross-correlation of electron backscatter diffraction patterns has been used to generate rotation maps of single crystals of tetragonal barium titanate (BaTiO3) containing multiple lamellae and bundles of  90 domains. Rotation measurement angular

Two-Dimensional Strain-Mapping by Electron Backscatter Diffraction and Confocal Raman Spectroscopy

November 27, 2017
Author(s)
Andrew J. Gayle, Lawrence Henry Friedman, Ryan Beams, Brian G. Bush, Yvonne B. Gerbig, Chris A. Michaels, Mark D. Vaudin, Robert F. Cook
The strain field surrounding a spherical indentation in silicon is mapped in two dimensions (2- D) using electron backscatter diffraction (EBSD) cross-correlation and confocal Raman spectroscopy techniques. The 200 mN indentation created a 4 m diameter

Strength of Brittle Materials in Moderately Corrosive Environments

October 30, 2017
Author(s)
Robert F. Cook
The strengths of four brittle materials―cordierite glass ceramic, fused silica, silicon, and polycrystalline alumina were measured after exposure to weakly-corrosive water and moderately- corrosive buffered HF (BHF) solution. Exposure to water did not

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics

August 22, 2017
Author(s)
Frank W. DelRio, Robert F. Cook
Scanning probe microscopy techniques—in particular atomic force microscopy (AFM)—provide a means for imaging objects and measuring mechanical properties at the nano- and micro-scales in a non-destructive manner. In this paper, the previous use of AFM in

Blunt scratch strength of polycrystalline alumina

August 21, 2017
Author(s)
Robert F. Cook
A model for the fracture strength of brittle materials controlled by blunt (spherical) scratches is developed and compared with measurements on a polycrystalline alumina. The model is based on a residual stress-intensity factor for median cracks at

Near-theoretical fracture strengths in native and oxidized silicon nanowires

June 21, 2016
Author(s)
Frank W. DelRio, Ryan M. White, Sergiy Krylyuk, Albert Davydov, Lawrence H. Friedman, Robert F. Cook
In this letter, fracture strengths σf of native and oxidized silicon nanowires (SiNWs) were determined via atomic force microscopy bending experiments and nonlinear finite element analysis. In the native SiNWs, σf in the Si was comparable to the

Stochastic behavior of nanoscale dielectric wall buckling

March 16, 2016
Author(s)
Lawrence H. Friedman, Igor Levin, Robert F. Cook
The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of