Experimental mixed-mode fracture study in the interface of vertebrae bone tissue-hydroxyapatite cement using the bi-material Brazilian disc specimen

The use of resin based cement is a common method for strengthening and retaliation the damaged bones material. However due to lack of sufficient adhesion in the interface of two materials (i.e. bone and injected cement) a crack can be initiated in the interface and consequently it can be fractured due to application of external loads to the repaired bone part. In order to investigate the load carrying capacity and reliability of bi-material joint of bone's soft tissue-hydroxyl apatite cement, a number of bi-material bone-cement specimens in the shape of circular disc containing a center crack in the interface of disc and subjected to diametral compression were tested. The bi-material specimens were load under different inclination angles of crack related to the loading direction. This results in application of different mixed mode I+II (i.e. tensile-shear deformation) in the interface of center crack. The results showed that the fracture load and fracture energy becomes more by increasing the crack inclination angle (i.e. increasing the contribution of shear mode deformation relative to mode I component). In addition the overall strength of bi-material bone-cement system was higher than the neat one material bone material. The fracture of all tested bi-material samples was extended along the interface line of Brazilian disc specimen with no kinking into any of two bone or cement materials.