Determine the number of cycles - crack propagation, Mechanical Engineering

Determine the number of cycles - crack propagation:

The plate of above Example  contained a crack of 50 mm length in the centre before it was subjected to cyclic stress. Determine the number of cycles the plate would undergo when final fracture occurs.smax = 100 MPa, smin = 30 MPa and law of crack propagation for material of plate is

         da  / dN  = 10-8 (Δ K I )2.25 mm/cycle

Solution

The half crack length at which fracture will occur was calculated as ac = 57.17 mm.

924_Determine the number of cycles.png

553_Determine the number of cycles1.png

∴          Δ K I =  K I max  - K I min

1315_Determine the number of cycles2.png

Using this value of Δ KI in law of fatigue crack propagation, i.e. the plate is likely to fracture under smax = 100 MPa,smin = 30 MPa if plate contains a central crack of 50 mm length, after 1048 cycles.

1764_Determine the number of cycles3.png

da / dN  = 10-8 (124)2.25 (a)2.25 / 2

= 0.51´10- 3 (a)1.125

Posted Date: 1/22/2013 2:06:43 AM | Location : United States







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