Tham khảo tài liệu 'biomedical engineering trends in materials science part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 Biomedical Engineering Trends in Materials Science Strain Fig. 6. Elastic softening during prestrain and recovery durign ambient temperature ageing of the as hot-rolled TÍ2448. Solid dash-dot and dash curves are respectively single step loading-unloading Fig. 4 the sixth cycle stress-strain curve in Fig. 5 and stress-strain curve of the same tensile sample tested 6 days after the cyclic deformation experiment demonstrating partial recovery of incipient Youngs modulus Hao Li Sun Zheng Yang 2007 . Even more striking is the recovery of the softened elastic modulus during ageing at room temperature which is unusual for titanium alloys Fig. 6 . The cyclic tensile tested sample was subjected to straining experiment again after 6 days to a strain of see Fig. 6 and it was observed that the incipient Youngs modulus increased from 18 GPa to 33 GPa. The same experiment after 6 month on the same sample showed that the incipient Youngs modulus is stabilized at about 33 GPa and does not recover in a signicant way any further. The above elastic softening due to prestrain and recovery behaviour appear to mimic the biological characteristics of human bone. With sport or movement induced strain the incipient Youngs modulus of the implant would progressively decrease to fall to the modulus range of human bone to allow complete elastic matching. During rest the implant would gradually recover its modulus to a value slightly above that of human hard tissue. Understanding of the elastic softening and recovery of TÍ2448 is incomplete but some clues to this extraordinary behaviour will be discussed in the next section. The effects of different heat treatment on the mechanical properties of TÍ2448 have been systematically investigated Hao Li Sun Zheng Yang 2007 . Solution treatment at high temperature has weak effect on superelasticity but causes the decrease of strength and slight increase of the incipient Youngs modulus by about 8 GPa . Slower cooling such as air cooling causes
