Crack Initiation and Crack Growth Behavior during Fatigue Process of the Bovine Bone

In order to clarify the fatigue process of bone, rotating bending fatigue tests and creep tests were conducted using bovine femoral compact bone in laboratory air and Ringer\u27s solution. The results obtained are summarized as follows. ( 1 ) Fatigue lives in laboratory air and Ringer\u27s solution showed little difference. ( 2 )At high stress levels above 100 MPa, creep rupture time and fatigue failure time are nearly the same, but at low stress levels below 100 MPa, the latter is shorter than the former. This indicates that fatigue damage accumulation controls the fatigue fracture process at low stress levels. ( 3 ) During the fatigue process of bovine bone, several microcracks were initiated and propagated accompanied by crack coalescences among them. The crack path was zigzagged. ( 4 ) The relation-ship between the ratio of crack initiation cycles N_i to fatigue cycles N_f and stress amplitude was investigated. The ratio N_i/N_f decreased with a decrease of the stress amplitude region. ( 5 ) There is a linear relationship between crack growth rate da/dN and stress intensity factor ΔK on the log-log plot, and the Paris equation da/dN=CΔK^m holds, where C and m are C=5. 25×10^-9 and m=1. 49, respectively