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Finite element analysis of indentation tests on pyrolytic carbon
C B Gilpin1, A D Haubold, J L Ely
1Department of Mechanical Engineering, California State University, Long Beach 90840, USA.
The Journal of Heart Valve Disease
|June 1, 1996
Summary
Failure in pyrolytic carbon heart valves originates at the graphite interface, not the surface. Understanding these interface stresses is key to designing more durable artificial heart valves.
Area of Science:
- Biomaterials Engineering
- Mechanical Engineering
- Cardiovascular Research
Background:
- Pyrolytic carbon heart valves are crucial medical devices.
- Traditional analysis uses Hertzian crack models for monolithic materials.
- Layered pyrolytic carbon on graphite structures exhibit different failure mechanisms.
Purpose of the Study:
- To evaluate contact stresses causing failure in layered pyrolytic carbon heart valves.
- To differentiate failure modes in monolithic vs. layered materials.
- To develop a failure criterion for designing contact regions.
Main Methods:
- Simulated contact loading using a 5.1 mm diameter ball on a layered sample.
- Finite element analysis to calculate stresses under varying loads.
- Correlation of simulated stresses with laboratory experiments.
Main Results:
- Initial cracks form at the pyrolytic carbon-graphite interface due to tensile stress in pyrolytic carbon (207-276 MPa) and compression in graphite (414-483 MPa).
- Surface cracks occur at higher loads, requiring shear stress (~241 MPa) and tensile components.
- Interface cracks are initially arrested by a triaxial compression stress field.
Conclusions:
- Failure in layered pyrolytic carbon heart valves initiates at the interface, not the surface.
- A distinct failure criterion for layered structures has been established.
- These findings are critical for improving the design and longevity of pyrolytic carbon heart valves.