Location

La Jolla, CA

Start Date

1-1-1991 12:00 AM

Description

Scanning electron acoustic microscopy (SEAM) is one of a number of new microscopic imaging techniques using acoustic waves that have appeared during the last decade or so [1–6]. Although SEAM has been applied to the characterization of a wide variety of materials [7–15], only recently has it been applied to the assessment of brittle materials [16, 17]. We have found [17] that SEAM images of Vickers indentations of SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to assess the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the SiC whisker-reinforced alumina is heat-treated at 1000°C in order to relieve the residual stresses around the indentations. Similar studies were performed in soda-lime glass where a comparison of SEAM and reflected polarized light observations of Vickers indentations in the glass both before and after heat-treatment confirms our interpretation of the strong contrast. We develop here a mathematical model of image contrast in SEAM due to the effect of residual stresses in materials. Although the work was motivated by the experimental findings in ceramics, the theory is applicable to other materials as well.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

10B

Chapter

Chapter 7: Characterization of Materials

Section

Non-Linear Acoustic Properties

Pages

1869-1874

DOI

10.1007/978-1-4615-3742-7_95

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Microstress Contrast in Scanning Electron Acoustic Microscopy of Ceramics

La Jolla, CA

Scanning electron acoustic microscopy (SEAM) is one of a number of new microscopic imaging techniques using acoustic waves that have appeared during the last decade or so [1–6]. Although SEAM has been applied to the characterization of a wide variety of materials [7–15], only recently has it been applied to the assessment of brittle materials [16, 17]. We have found [17] that SEAM images of Vickers indentations of SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to assess the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the SiC whisker-reinforced alumina is heat-treated at 1000°C in order to relieve the residual stresses around the indentations. Similar studies were performed in soda-lime glass where a comparison of SEAM and reflected polarized light observations of Vickers indentations in the glass both before and after heat-treatment confirms our interpretation of the strong contrast. We develop here a mathematical model of image contrast in SEAM due to the effect of residual stresses in materials. Although the work was motivated by the experimental findings in ceramics, the theory is applicable to other materials as well.