The effect of yield damage on the viscoelastic properties of cortical bone tissue as measured by dynamic mechanical analysis

Abstract

We have previously shown, using Dynamic Mechanical Analysis (DMA), that the presence of a defect in cortical bone tissue affects the apparent viscoelastic properties of that bone. However, mechanically induced damage is more complex than a machined defect making it difficult to predict its effect on bone viscoelasticity. We performed DMA measurements before and after introduction of yield damage into cortical bone beams from sheep radii. The specimens were placed in a DMA machine and baseline measurements of storage modulus (E1) and loss factor (tandelta) were performed using a 3-point bending configuration for a frequency range of 1-10 Hz. Measurements were done in all four bending directions (cranial, caudal, medial, and lateral) in random order. After subjecting the specimens to monotonic yield damage in a servohydraulic testing machine with the load applied to the cranial surface, oscillatory tests were repeated. To supplement results from the current experiment, additional analyses were performed on data from experiments where bone was either cut or fatigue-loaded between viscoelasticity measurements. Introduction of mechanical damage increased tan delta and frequency sensitivity of E1, consistent with the assertion that increased energy dissipation in damaged bone might contribute to its increased resistance to fatigue and fracture.

Differences in the mechanical behavior of cortical bone between compression and tension when subjected to progressive loading

“…Previous studies have shown that the viscous nature of bone depends on hydration condition of the tissue (Yamashita et al, 2002), and such viscoelastic properties as storage modulus and loss modulus of bone increase with increasing damage density (Yeni et al, 2004; Yeni et al, 2007). In this study, a much higher total stress relaxation (Δσ) and a slightly greater time constant (τ) were observed in compression than in tension (Figures 6 and 7).…”

Increased Microstructural Variability is Associated With Decreased Structural Strength But With Increased Measures of Structural Ductility in Human Vertebrae

“…In addition, ultimate displacement (Δ u ), the maximum displacement traveled by the cross-head before specimen’s failure, and work to fracture (W), the total amount of work done for fracture, were obtained as measures of structural ductility. Also, post-yield energy (W py ) was estimated as a ductility measure, where yield point was found using 5% secant stiffness method [25]. In order to assess the variation of structural ductility measures relative to strength, W py , W and Δ u were normalized with strength to produce post-yield energy to strength ratio (W py /F max ), work to fracture to strength ratio (W/F max ) and ultimate displacement to strength ratio (Δ u /F max ).…”

Progressive post-yield behavior of human cortical bone in compression for middle-aged and elderly groups

“…The post-yield behavior of bone is usually associated with microdamage accumulation (Forwood and Parker, 1989; Burr et al, 1997, 1998; Fazzalari et al, 1998a, b; Norman et al, 1998; Reilly and Currey, 1999; Timlin et al, 2000; Akkus and Rimnac, 2001), viscoelastic responses (Bredbenner and Davy, 2006; Joo et al, 2007; Yeni et al, 2007), and plastic deformation (Fondrk et al, 1988). For instance, yielding coincides with the formation of damage in bone (Zioupos et al, 1994), and the induced damages may lead to an elevated viscoelastic response of bone (Yeni et al, 2007).…”

“…For instance, yielding coincides with the formation of damage in bone (Zioupos et al, 1994), and the induced damages may lead to an elevated viscoelastic response of bone (Yeni et al, 2007). In addition, microdamage accumulation plays a significant role in energy dissipation in both fatigue and monotonic fractures of bone (Schaffler et al, 1995; Burr et al, 1997; Jepsen and Davy, 1997; Martin et al, 1997; Fazzalari et al, 1998a, b; Norman et al, 1998; Vashishth et al, 1997, 2003; Zioupos, 2001).…”