Real-time microdamage and strain detection during micromechanical testing of single trabeculae

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Description/Abstract

For the assessment of local deformations, we recently combined mechanical testing of trabecular bone with high-speed photography. In a previous study on cuboids of human vertebral trabecular bone we found strained trabeculae to whiten, and scanning electron microscopy showed excessive microdamage in whitened zones. In the presented study we tested single trabeculae from bovine femur and tibia in a three-point-bending geometry. Whitening was detected in the form of an ellipsoid zone on the tension side on tested trabeculae. Upon crack formation the whitening fades and a whitened zone following the propagating crack tip can be seen In addition to whitening/microdamage assessment we use ink marks applied to the samples and a modified digital image correlation to obtain the local strains involved in whitening and formation. In the presented loading case the tensile strain along the long axis of the trabecula qualitatively correlates best with the whitening zones seen. Whitening and thus microdamage initiates around a local tensile strain of 3%, whereas crack initiation occurs at strains around 13%. Our results allow for the first time to correlate microdamage and local strains directly, which is direly needed for the development of realistic damage models used in finite element analyses.