In fatigue failure, the crack can initiate at any location of the element, however, cracks prefer surface discontinuities.

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Question restatement: In fatigue failure, the crack can initiate at any location of the element, however, cracks prefer surface discontinuities.

Option 1: True
- This statement aligns with the general understanding in fatigue analysis: cracks can indeed initiate at various locations depending on material defects, residual stresses, and loading, and there is a strong tendency for initiation at surface discontinuities due to stress concentration and exposure to the tensile cyclic stresses at the surface.
- The phrase 'can initiate at any location' acknowledges that internal flaws or inclusions could also serve as initiation points, which is accurate in some scenarios.
- The addition 'cracks prefer surface discontinuities' highlights a widely observed behavior that surface defects (steps, notches, cracks at surface imperfections) are common initiation sites because the local stress intensity is higher there, especially under cyclic loading.

Option 2: False
- If someone marks this as false, they would be contradicting the well-established notion that fatigue initiation is strongly influenced by surface flaws and discontinuities, which act as stress concentrators.
- This option would imply that cracks do not preferentially start at surfaces, which contradicts empirical evidence from crack initiation studies where surfaces often initiate cracks first under many fatigue loading conditions.
- It also conflicts with practical design knowledge where surface finish and surface defects are critical factors in fatigue life prediction, reinforcing the idea that surface discontinuities are preferred initiation sites.

Final reflection on the statements:
- The combined claim that cracks can start anywhere but tend to prefer surface discontinuities captures both the possible internal initiation and the common, influential role of surface flaws in fatigue behavior.
- Therefore, the statement in Option 1 is consistent with fatigue crack initiation theory, while Option 2 contradicts established understanding by denying the surface preference.

BK10A6500 Engineering Mechanics 3 - Blended teaching 6.1.2025-20.4.2025 Quiz 8.2

In fatigue failure, the crack can initiate at any location of the element, however, cracks prefer surface discontinuities.

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