ARTIFACTUAL NONLINEARITY DUE TO WEAR GROOVES AND FRICTION IN 4-POINT BENDING EXPERIMENTS OF CORTICAL BONE

Experiments and analyses were performed to determine the cause of a no nlinear force-deflection response observed in four-point flexural fati gue of beams of cortical bone machined from the mid-diaphysis of the e quine third metacarpus. Observable grooves which formed on the beam su rface at supports and load noses were found to be the primary cause of the nonlinearity. An additional geometric nonlinearity at large defle ctions revealed by finite element modeling may be minimized by using t he smallest diameter supports and load noses recommended in ASTM 790. However, frictional constraint of the beams at the load noses and supp orts can occur at low load levels and should be avoided by using rolle r-bearing supports and load noses, or some equivalent method. Copyrigh t (C) 1996 Elsevier Science Ltd.