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Metals - Generated by Foxit PDF Creator © Foxit Software...

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This file is to be used strictly for personal reading and non-commercial teaching purposes. Not for circulation. The file contains images from recent journal papers. Biomaterials Metals and Applications Metals definition Materials having the metallic bond and used in the biological context Presence of free electrons that account for the electrical and thermal conductivity Crystal structure determines mechanical properties Alloys: Mixtures of two or more metals Mostly used for hard tissue replacements or as structural supports to implants Mechanical properties Mechanical properties by the stress strain curve Stress: force per unit cross sectional area Strain: Change in length per original length Hooke’s law Modulus of elasticity : stiffness Ultimate tensile strength Elastic and plastic deformation Toughness: area under the curve Weak and ductile materials: polymers Metals have high tensile strength and are ductile Ceramics are characterized by their brittle nature Yield stress: 0.2% plastic strain Polymer Metal Ceramic WEAK DUCTILE TOUGH STRONG DUCTILE BRITTLE STRONG Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.
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Fracture Tensile test: tension, compression, torsion, bending Fracture occurs in tension when the local stress concentration is more than the ultimate tensile strength Stress concentration occurs at the root of any defect and the stress is 2-10 times higher than average local stress Wear Wear: mechanical degradation of the biomaterial surfaces due to close contact Can lead to loosening of implant and failure Can lead to biological responses to the wear particles Volume of wear debris directly proportional to force applied, distance between biomaterial surfaces and Archard’s constant Inversely proportional to hardness of biomaterial Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.
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Metals and ceramics are stiffer and have larger strength than biologic hard tissues Composite materials can be used to mimic biological tissues Hardness Resistance of material to plastic deformation usually by indentation Tests determine depth to which a non-deformable ball will sink into the metal under a given load and within a specific period of time Different relative scales with unitless hardness numbers, higher value implies harder materials Stainless steel 316 L commonly used stainless steel for implants L: low carbon 0.03% carbon
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