The tests were performed using three-points bending specimens (3PB specimens) and compact specimens (CT specimens), an extensometer fixture surrounding the CT specimens was used for displacement measurements. Stable, unstable crack growth and local unstable crack growth were observed, plus two types of unstable crack growth in CT specimens were observed from load--displacement curves measured by the extensometer fixture. The crack extensions were measured by key-curve method, and J-resistance curves, tearing modulus curves and local crack-opening angle curves for CT specimens were determined. The tearing modulus parameter and local crack-opening angles for prediction of crack stable growth and fracture instability were employed. Tearing instability criterion gave the incorrect conclusion for the evaluations of fracture instability in the paper, but the analysis of local crack-opening angles can give some rough estimations. At last, fractography for CT specimens was described.
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