Fracture toughness of bone using a compact sandwich specimen: Effects of sampling sites and crack orientations

Abstract

The energy required to propagate a crack through bone can be estimated in terms of its fracture toughness, which is an intrinsic property and an important measure of the material's susceptibility to fracture. However, in the past detailed fracture toughness characterization of bone has been limited due to specimen size limitations. To address this issue the present study used a compact sandwich specimen and examined the variation in fracture toughness of bovine femoral bone as a function of testing sites and crack orientations. Two crack orientations, radial and circumferential, and three testing sites situated along the thickness of bone were investigated. The results indicated that there were statistically significant differences in fracture toughness between the testing sites for both radial and circumferencial cracks. Crack orientation also appeared to influence the fracture toughness at two of the test sites. The microstructure of bone and its fracture surface morphology were examined using microscopy and exhibited differences corresponding to the differences in fracture toughness, thus suggesting a correlation between microstructure and fracture toughness.

The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue

“…As can be seen, dehydration causes an appreciable reduction of fracture energy, accompanied by a slight increase of elastic modulus, in agreement with earlier works (Currey, 1988a;Lucksanasombool et al, 2001;Nyman et al, 2006;Wang and Agrawal, 1996). The vascular porosity (Table 3) can be used to estimate the content of free water.…”

“…The quality of organic and mineral phases, as well as their spatial arrangement and interaction, contribute to the mechanical properties of the material. It is accepted that the mineral phase is the main contributor to the elastic and strength and Agrawal, 1996). Also, dehydration affects the viscoelastic behaviour of cortical bone: for instance, it reduces the loss factor without appreciable changes in the storage modulus (Yamashita et al, 2002), and increases the relaxation rate (Sasaki and Enyo, 1995).…”

“…The majority of the works have focused on the resistance to pre-crack starting advance under tension, both in the longitudinal (Norman et al, 1995(Norman et al, , 1996 and transverse (Phelps et al, 2000) axes of long bones. A variety of fracture test specimens has been used: the compact tension (CT) specimen (Norman et al, 1995); the chevron-notched beam specimen (Yan et al, 2006); the compact sandwich tension specimen (Wang and Agrawal, 1996); and the single-edge notched beam (SEN) specimen (Phelps et al, 2000). A wide range of critical stress intensity factors or critical energy release rates for cortical bone has been reported, for the very reason that they vary depending on the source, type and location of bone tested, as well as the testing method (Yan et al, 2006;Brown et al, 2000).…”

Small animal bone biomechanics

“…al. 23 and Wang and Agrawal24 extended the measurement of bone fracture from mode I (tensile) to mode II (in plane shear) and introduced smaller specimen designs. Zioupos and Currey25 evaluated the effectiveness of various fracture mechanics based parameters and their comparison with traditional strength and work-to-fracture parameters.…”

Mode I fracture characterization of human bone using the DCB test

“…Several fracture tests have been used in this context: compact tension (CT) [1]; chevron notched beam [2]; compact sandwich tension [3]; single edge notched beam (SEN) [4]; and double cantilever beam (DCB) [5].…”