TY - JOUR
T1 - Fatigue crack propagation in additively manufactured porous biomaterials
AU - Hedayati, R.
AU - Amin Yavari, S.
AU - Zadpoor, A. A.
N1 - Accepted Author Manuscript
PY - 2017
Y1 - 2017
N2 - Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 104 cycles. The test results also showed that for the same load level of 0.5 Fy, the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45° direction with respect to the notch direction.
AB - Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 104 cycles. The test results also showed that for the same load level of 0.5 Fy, the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45° direction with respect to the notch direction.
KW - Additive manufacturing
KW - Biomedical scaffolds
KW - Crack propagation
KW - Fatigue behavior
KW - Porous biomaterials
UR - http://resolver.tudelft.nl/uuid:c229afae-1e73-46f5-8936-818d24730a52
UR - http://www.scopus.com/inward/record.url?scp=85015283996&partnerID=8YFLogxK
U2 - 10.1016/j.msec.2017.03.091
DO - 10.1016/j.msec.2017.03.091
M3 - Article
AN - SCOPUS:85015283996
SN - 0928-4931
VL - 76
SP - 457
EP - 463
JO - Materials Science and Engineering C: Materials for Biological Applications
JF - Materials Science and Engineering C: Materials for Biological Applications
ER -