Biomimetic Study Of Flexural Characteristics Of Tarsometatarsus Of The Pelvic Limb In The Ostrich

Based on the high load-bearing capacity of tarsometatarsus of the pelvic limb during ostrich running, we investigated the cross-section variation of the diaphysis along the tarsometatarsus and the loading characteristic during mid-stance of running. Using engineering bionic technology, we designed a bionic bar, and with finite element method based simulation, we analyzed the anti-bending performance.By CT scanning and Mimics processing the medical image data, we obtained the pixel three-dimensional coordinates and CT value(HU) of tarsometatarsus. According to the calculation formulas of the plane figure geometric parameters, we calculated cross-section parameters along the longitudinal of tarsometatarsus by programming using the software of Excel VBA. Results showed that, whether or not considering material properties, tarsometatarsus cross-sectional flexural coefficient(the second moment of area) had the same linear longitudinal variation trend with a high linearity. At the same time, we found that second moment of areain the frontal plane(Ifrontal) was larger than in the sagittal plane(Isagittal). This indicated that tarsometatarsus had a good performance when cantilever loading was applied in the frontal plane(the medial-lateral direction).The diaphysis of tarsometatarsus was divided into three parts(up,middle,down), and samples were made from four azimuth(anterior, posterior, medial, lateral) in the transverse section. Using scanning electron microscope(SEM), we observed the microstructure of tarsometatarsus in different locations. It was not found that there were significant differences in different location. By cutting and grinding, we obtained mechanical compression specimens of different regions of tarsometatarsus. Compressive strength was obtained by using the mechanical testing machine. The results showed that compressive strength was lower in medial-lateral location than in anterior-posterior location.Using CT scanning, combined with Mimics(medical image data processing software) and reverse engineering software(Geomagic Studio), we obtained 3D model of tarsometatarsus. Finite element model was established using finite element software(Hypermesh and ABAQUS). Actual stress distribution simulation was performed respectively in vitro tarsometatarsus of ostrich leg in simple loading(bending, torsion) and tarsometatarsus of living ostrich outfield experiment. Results showed that stress distribution along the longitudinal cross-section was similar to beam structure. By analyzing the acceleration, it was found that there was an inertial impact on the tarsometatarsus in medial-lateral direction. This was consistent with that bending coefficient in medial-lateral direction was larger(Ifrontal>Isagittal).Morphological structure of tarsometatarsus and good ability of resisting bending moments were consistent. It was found that the morphological structure concrete were radial distance of cross section and the center coordinates of cross section. For each cross section of tarsometatarsus, both inner and outside contour were simplified as concentric ellipses, whose length of long axis and short axis were respectively equal to radial distance in medial and lateral directions of each cross section. z was the longitudinal distance and elliptic parameter equation were obtained:outside ellipse semi-major axis(A):2A =-0.05287z+37.88, R2=0.895;outside ellipse semi-minor axis(B):2B =-0.05713z+33.21, R2=0.968;inner ellipse semi-major axis(a):2a =-0.08316z+33.36, R2=0.941;inner ellipse semi- minor axis(b):2b =-0.06844z+27.13, R2=0.995. The overall shape of tarsometatarsus was curved at some level. The curvature in medial-lateral direction(frontal plane) was larger than in anterior-posterior direction(sagittal plane). The center of midsection in frontal plane was eccentric to the outside(IV toe of ostrich foot).The equations between cross-section center(x, y) and the longitudinal distance z were:x =-0.000234z2+0.05387z-3.400, R2=0.922;y = 0.0527z-6.240, R2=0.968.According to the characteristics of the morphological structure of tarsometatarsus of ostrich and ellipse parameters and cross section center coordinates equations, we designed the bionic type bar(Ⅰ, variable cross-section oval ring) using the powerful three-dimensional modeling software Catia. We also designed three kinds of bars(Ⅱ, variable cross-section circle ring; Ⅲ, uniform cross-section ellipse ring; Ⅳ, uniform cross-section circle ring) as comparison. The bending properties of the four bar were simulated with FEA. Considering mass and stiffness factors, the results indicated that the mass ofⅠbar(bionic bar) was smaller and its specific stiffness was higher. The bionic bar can be applied to the design of the legged lander and walking mechanism.