Development of Bend Fixtures for In Situ SEM Fracture Testing at Elevated Temperatures, 18-R8122

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Principal Investigator
Kwai S. Chan

Inclusive Dates:  12/08/09 – 04/08/10

Background - SwRI has a unique capability of performing fatigue and fracture tests using a cyclic loading stage inside a scanning electron microscope (SEM). A client is interested in extending this unique capability to fatigue and fracture testing of hydrided and irradiated alloys at elevated temperatures for nuclear energy applications.

Approach - The objective of this project was to develop a set of three-point and four-point bend fixtures and the corresponding procedure for performing elastic-plastic fracture tests (J-tests) inside a SEM. The test fixtures were designed to (1) fit within the limited space available in the existing SEM loading stage, (2) provide J-resistance curves with about 0.5- to 1-mm crack extensions, and (3) allow easy placement and removal of the test specimens.

Accomplishments - A set of three-point bend and four-point bend test fixtures was designed and fabricated. The three-point bend fixture was used to demonstrate the feasibility of performing in situ J-testing inside a scanning electron microscope, as shown in Figure 1, by measuring the crack mouth opening displacements as a function of the applied load and crack extension for Zircaloy-4 at 25 °C and 316 °C. Figure 2 presents the J-resistance (J-R) curves generated using the in situ SEM testing technique for Zircaloy-4 specimens with three different combinations of width and thickness at 25 °C. The J-R curves generated by in situ fracture testing technique are not sensitive to the specimen geometry and measure the actual fracture resistance of the material.

Set-Up of the Three-Point Bend Fixture and Specimen Inside a Scanning Electron Microscope


Figure 1. Setup of the Three-Point Bend Fixture and Specimen Inside a Scanning Electron Microscope


Fracture-Resistance (J-R) Curves of Zircaloy-4 Specimens with Three Different Ratios (T/W) of Thickness to Width Tested at 25 C


Figure 2. Fracture-Resistance (J-R) Curves of Zircaloy-4 Specimens with Three Different Ratios of Thickness to Width (T/W) Tested at 25 °C


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