The effects of damage and microcracking on the impact strength of bone

Microcracking has been shown to occur when bone is 'damaged' as shown by a loss of stiffness. The effect on bones toughness of the types of damage pro duced at low losses of stiffness are not known. We loaded bovine bone speci mens in bending and tension to stiffness losses of up to 27%, and examined the microcracking produced. The tensile specimens had diffuse arrays of mic rocracks of 2-20 mu m in length, characteristic of tensile loading, on all surfaces. The bending specimens showed tensile microcracking on the tensile surface and characteristic long, straight, cross-hatched compression crack s on the compressive surface. Specimens were then broken in impact. Those t hat had been damaged in bending were divided into two groups, in one group the part of the specimen which had undergone compression damage was placed in tension, and in the other group the tensile damage was placed in tension . Tensile damage loaded in tension did not reduce the bone's energy-absorbi ng ability in impact until a modulus reduction of over 20%. However compres sion damage loaded in tension did severely reduce the bone's energy absorpt ion capabilities (by an average of about 40%). (C) 2000 Published by Elsevi er Science Ltd. All rights reserved.