Mechanical Properties of the Caudal Fin Resulting from the Caudal Skeletal Structure of the Bluefin Tuna

The primary skeletal structure used by dolphins to generate the dorsoventral bending characteristic of cetacean swimming is the vertebral column. In the vertebral column of the saddleback dolphin Delphinus delphis, we characterize the static and dynamic mechanical properties of the intervertebral joints, describe regional variation and dorsoventral asymmetries in mechanical performance, and investigate how the mechanical properties are correlated with vertebral morphologies. Using a bending machine that applies an external load (N m) to a single intervertebral segment, we measured the resulting angular deformation (rad) of the segment in both dorsal extension and ventral flexion. Intervertebral segments from the thoracic, lumbar and caudal regions of the vertebral column were tested from five individuals. Using quasi-static bending tests, we measured the initial (low-strain) bending stiffness (N m rad-1) as a function of segment position, direction of bending (extension and flexion) and sequential cutting of intervertebral ligaments. We found that initial bending stiffness was significantly greater in the lumbar region than in adjacent thoracic and caudal regions, and all joints were stiffer in extension than is predicted (r2 = 0.554) by the length and width of the intervertebral disc and the length of the cranial vertebral body in the segment. Stiffness in flexion is predicted (r2 = 0.400) by the width of the nucleus pulposus, the length of the caudal vertebral body in the segment and the height of the transverse processes from the ventral surface of the vertebral body. We also performed dynamic bending tests on intervertebral segments from the lumbo-caudal joint and the joint between caudal vertebrae 7 and 8. Dynamic bending stiffness (N m rad-1) increases with increasing bending amplitude and is independent of bending frequency. Damping coefficient (kg m2 rad-2 s-1) decreases with increasing bending amplitude and frequency. Resilience (% energy return) increases from approximately 20% at low bending amplitudes (+/-0.6 degree) to approximately 50% at high bending amplitudes (+/-2.9 degrees). Based on these findings, the dolphin's vertebral column has the mechanical capacity to help control the body's locomotor reconfigurations, to store elastic energy and to dampen oscillations.

Download Full-text

Environmental impact on the mechanical properties of Porites spp. corals

Coral Reefs ◽

10.1007/s00338-021-02064-3 ◽

2021 ◽

Author(s):

Molly A. Moynihan ◽

Shahrouz Amini ◽

Nathalie F. Goodkin ◽

Jani T. I. Tanzil ◽

J. Q. Isaiah Chua ◽

...

Keyword(s):

Climate Change ◽

Mechanical Properties ◽

Chemical Composition ◽

Structural Integrity ◽

Organic Content ◽

Skeletal Structure ◽

Future Climate Change ◽

Geochemical Composition ◽

Wide Range ◽

Reef Environments

AbstractDespite the economic and ecological importance of corals’ skeletal structure, as well as their predicted vulnerability to future climate change, few studies have examined the skeletal mechanical properties at the nanoscale. As climate change is predicted to alter coral growth and physiology, as well as increase mechanical stress events (e.g., bioerosion, storm frequency), it is crucial to understand how skeletal mechanical properties change with environmental conditions. Moreover, while material properties are intimately linked to the chemical composition of the skeleton, no previous study has examined mechanical properties alongside carbonate geochemical composition. UsingPoritescoral cores from a wide range of reef environments (Thailand, Singapore, Taiwan), we correlated coral’s micro-mechanical properties with chemical composition. In contrast to previous mechanical measurements of reef-building corals, we document unprecedented variability in the hardness, stiffness, and micro-cracking stress ofPoritescorals across reef environments, which may significantly decrease the structural integrity of reef substrate. Corals from environments with low salinity and high sedimentation had higher organic content and fractured at lower loads, suggesting that skeletal organic content caused enhanced embrittlement. Within individual coral cores, we observed seasonal variability in skeletal stiffness, and a relationship between high sea surface temperature, increased stiffness, and high-density. Regionally, lower Sr/Ca and higher Mg/Ca coincided with decreased stiffness and hardness, which is likely driven by increased amorphous calcium carbonate and skeletal organic content. If the coral is significantly embrittled, as measured here in samples from Singapore, faster erosion is expected. A decrease in skeletal stiffness will decrease the quality of reef substrate, enhance the rate of bioerosion by predators and borers, and increase colony dislodgement, resulting in widespread loss of structural complexity.

Download Full-text

Phase Transformations in Ti-7w/oMo-3w/oMe Alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052584 ◽

1974 ◽

Vol 32 ◽

pp. 514-515

Author(s):

S. Fujishiro

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

Transmission Electron Microscopy ◽

Tensile Strength ◽

Mechanical Processing ◽

Ray Method ◽

X Ray ◽

Transmission Electron ◽

Water Quench ◽

Alpha Beta

The mechanical properties of three titanium alloys (Ti-7Mo-3Al, Ti-7Mo- 3Cu and Ti-7Mo-3Ta) were evaluated as function of: 1) Solutionizing in the beta field and aging, 2) Thermal Mechanical Processing in the beta field and aging, 3) Solutionizing in the alpha + beta field and aging. The samples were isothermally aged in the temperature range 300° to 700*C for 4 to 24 hours, followed by a water quench. Transmission electron microscopy and X-ray method were used to identify the phase formed. All three alloys solutionized at 1050°C (beta field) transformed to martensitic alpha (alpha prime) upon being water quenched. Despite this heavily strained alpha prime, which is characterized by microtwins the tensile strength of the as-quenched alloys is relatively low and the elongation is as high as 30%.

Download Full-text