To provide a crack generation evaluation device that can evaluate the development of micro-cracks due to torsion fatigue.SOLUTION: A crack development evaluation method includes: a step of repeatedly applying a torsion load to a test piece (step S2-2); a step of photographing a portion of the test piece at which a crack is generated (step S2-3); a step of determining, from among a plurality of pixels of the photographed image, a pixel having a brightness lower than a predetermined threshold as a crack (step S2-4); a step of determining the coordinates of both ends of the crack (step S2-5); and a step of determining the length of the crack and an angle formed by the crack and a torsion axis of the test piece on the basis of the coordinates of both ends of the crack (step S2-6).SELECTED DRAWING: Figure 14
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