It is well known that metallic materials exhibit worse fatigue damage tolerance as they behave stronger in strength and softer in modulus. This raises concern on the long term safety of the recently developed biomecha...It is well known that metallic materials exhibit worse fatigue damage tolerance as they behave stronger in strength and softer in modulus. This raises concern on the long term safety of the recently developed biomechanical compatible titanium alloys with high strength and low modulus. Here we demonstrate via a model alloy, Ti-24 Nb-4 Zr-8 Sn in weight percent, that this group of multifunctional titanium alloys possessing nonlinear elastic deformation behavior is tolerant in fatigue notch damage. The results reveal that the alloy has a high strength-to-modulus（σ/E） ratio reaching2% but its fatigue notch sensitivity（q） is low, which decreases linearly from 0.45 to 0.25 as stress concentration factor increases from 2 to 4. This exceeds significantly the typical relationship between σ/E and q of other metallic materials exhibiting linear elasticity. Furthermore, fatigue damage is characterized by an extremely deflected mountain-shape fracture surface, resulting in much longer and more tortuous crack growth path as compared to these linear elastic materials. The above phenomena can be explained by the nonlinear elasticity and its induced stress relief at the notch root in an adaptive manner of higher stress stronger relief. This finding provides a new strategy to balance high strength and good damage tolerance property of metallic materials.展开更多
基金supported by the National Key Research and Development Program of China (2016YFC1102601 and 2017YFC1104901)the National Natural Science Foundation of China (51571190 and 51631007)the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (QYZDJ-SSW-JSC031)
文摘It is well known that metallic materials exhibit worse fatigue damage tolerance as they behave stronger in strength and softer in modulus. This raises concern on the long term safety of the recently developed biomechanical compatible titanium alloys with high strength and low modulus. Here we demonstrate via a model alloy, Ti-24 Nb-4 Zr-8 Sn in weight percent, that this group of multifunctional titanium alloys possessing nonlinear elastic deformation behavior is tolerant in fatigue notch damage. The results reveal that the alloy has a high strength-to-modulus（σ/E） ratio reaching2% but its fatigue notch sensitivity（q） is low, which decreases linearly from 0.45 to 0.25 as stress concentration factor increases from 2 to 4. This exceeds significantly the typical relationship between σ/E and q of other metallic materials exhibiting linear elasticity. Furthermore, fatigue damage is characterized by an extremely deflected mountain-shape fracture surface, resulting in much longer and more tortuous crack growth path as compared to these linear elastic materials. The above phenomena can be explained by the nonlinear elasticity and its induced stress relief at the notch root in an adaptive manner of higher stress stronger relief. This finding provides a new strategy to balance high strength and good damage tolerance property of metallic materials.
