fatigue patterns in materials - aalborg universitethomes.civil.aau.dk/lda/advanced structural...
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Fatigue patterns in materials
Lars Damkilde Section for Structural MechanicsDepartment of Civil Engineering, Aalborg University
Fatigue – combined failure
Top and bottom is cracked due to fatigue.
Middle part fails due to plastic failure
Part of a cranehook
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Roller shaft failure
Photograph of fracture surface showing initiation site, beachmarks from fracture propagation, and small area of final fracture.
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Composite failures
Metal fatigue failure is characterised by slow crack propagation; cracks initiate and propagate in a series of notch blunting and crack propagation events. By contrast, composite fatigue failure is a diffuse accumulation of damage, including multiple damage modes and complex failure mechanisms.
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Tubular joints – welded details
After many years in service, aluminum trichord sign structures often develop significant cracks and event complete failures in their welded connections, as shown in this photo of a failing joint. Redundant connections in most cases prevent pieces of the structure from falling onto the highway, but signs with failing joints need to be repaired or replaced.
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