Age-Related Residual Stresses at Diaphyseal Surface of Bovine Femur Measured by XRD-IP System
The presence of residual stress in the diaphysis of quadrupedal extremities has been reported. Residual stress is defined as the stress that remains in bone tissue without any external forces. It is one of the stresses applied to bone tissue, as well as static stresses due to the body weight and dynamic stresses due to the movement. The bone residual stress can be measured from the deformation state of hydroxyapatite (HAp) crystals in bone tissue using X-ray diffraction. The authors proposed a sin2.. method for detecting residual stress at the diaphyseal surface of extremities. However, the previous system requires a complicated experimental setup, long irradiation time, and limitations of the sample size. Here, X-ray imaging plate (IP) can detect the two dimensional distribution of the diffracted X-rays from the HAp crystals in one irradiation. The aim of the study was to establish a simple measurement system using an X-ray diffraction technique with IP (XRD-IP) for obtaining the residual stress at the diaphyseal surface of extremities and to apply this system to residual stress measurements of young and mature bovine femurs. In the experiments, the mid-diaphysis part of femurs taken from a lessthan- 1-month-old and a 23-month-old bovine were used. The diaphysis specimens were irradiated with characteristic Mo- K.. X-rays, and the X-ray diffraction pattern was detected by an IP. A part of Debye ring of the (211) planes of HAp crystals was obtained in the pattern and the residual stress in the bone axis was calculated from the deformation state of the ring. The magnitude of residual stresses in the mature bone corresponded approximately to the results of the previous method. Further, it was demonstrated that the residual stresses at diaphyseal surface varied with age and location.