Mechanical characterization of Ti-6Al-4V gyroids: On the systematic underestimation of their compressive stiffness

Porous biomaterials offer unique advantages compared to traditional materials. To benefit from these advantages accurate knowledge of the material’s mechanical properties is crucial. In this study, titanium skeletal and sheet-gyroid-based unit cells were mechanically characterized. To this end, porous cylindrical short and long samples were manufactured in Ti-6Al-4V ELI (grade 23), scanned and subjected to quasi-static uniaxial compression tests. Experiments were complemented with finite element simulations. Both our experimental and in silico findings, yielded offset and plateau stresses in line with most literature. They also showed that the intrinsic stiffness of titanium gyroids is substantially underestimated by studies experimentally characterizing them in compression. In most instances, these underestimations ranged from 40% to 80%. A compelling explanation for the observed underestimations was found to be a slanted contact between the compression plate and sample. We show this can lead to underestimations in the measured modulus of titanium gyroids, with limited effect on their offset and plateau stresses, when samples with lower length-diameter ratios are used. These findings carry obvious design implications, but more importantly, they raise questions regarding the general accuracy of experimentally determined compressive moduli reported in the literature for metallic porous biomaterials, and the conclusions derived from them. • Ti-6Al-4V ELI (grade 23) skeletal and sheet-gyroids with volume fractions ranging from 10% to 70% were characterized both experimentally and in silico. • Offset and plateau stresses were found to be in line with previously reported values in literature. • Elastic modulus was found to be systematically underestimated in literature, with underestimations ranging from 40% to 80% in most studies. • A slanted contact between the sample and compression plate was found to offer a compelling explanation for the observed underestimations.