Materials in Mechanical Design

# Materials in Mechanical Design - Materials in Mechanical...

This preview shows pages 1–6. Sign up to view the full content.

1 Materials in Mechanical Design Materials taken from Chapter 2 of Mott, Machine Elements in Mechanical Design, 2003 Materials in Mechanical Design Â The designer must specify the required materials for each part of a mechanical device. Physical properties Mechanical properties Match the properties to the expectations placed on them Classes of Material Â Metals and their alloys Â Elastomers Â Plastics Â Woods Â Composites Â Ceramics and glasses

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 Properties of Metals Â Tensile tests determine strength, elastic, and ductility properties for metals, plastics, and other types of materials. Â A round or flat bar of the material is clamped between jaws and pulled slowly until it breaks in tension. Â The data from these tensile tests are shown on stress-strain diagrams. Tensile strength Â The peak of the stress-strain curve is considered the ultimate tensile strength (su). (AKA: ultimate strength, tensile strength) Â Measures the highest apparent stress on a test bar of the material Stress-Strain Diagram for Steel Mott, Machine Elements in Mechanical Design, 2003
3 Stress-Strain Diagram for Aluminum Mott, Machine Elements in Mechanical Design, 2003 Yield Strength Â Yield Strength (s y ): The portion of the stress-strain diagram where there is a large increase in strain with little or no increase in stress. Â Proportional Limit : The point on the stress-strain curve where the straight line deviates. Â Elastic Limit : The point at which a material experiences some amount of plastic strain and thus will not return to its original shape after release of the load. Modulus of Elasticity in Tension Â For part of the stress-strain diagram that is straight, stress is proportional to strain. Â There, the value of E, the modulus of elasticity, is the constant of proportionality. Â E = stress = σ strain ε

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
4 Ductility and Percent Elongation Â Ductility : The degree to which a material will deform before ultimate fracture. Antonym = brittleness Â When ductile materials are used in machine members, impending failure is detected easily, so sudden failure is unlikely. Â Percent Elongation : The usual measure of ductility. Percent Elongation = L f –L o * 100% L o Shear Strength Â Both the yield strength and the ultimate strength in shear are important properties of materials. Â s ys = s y / 2 = 0.50 s y = yield strength in shear Â s us = 0.75 s u = ultimate strength in shear Poisson’s Ratio Â During a tensile strain, the cross-sectional dimensions perpendicular to the direction of the tensile strain shorten. Â Poisson’s ratio (v): The ratio of the shortening strain to the tensile strain.
5 Illustration of Poisson’s Ratio Mott, Machine Elements in Mechanical Design, 2003 Modulus of Elasticity in Shear Â The Modulus of Elasticity in Shear (G): The ratio of shearing stress to shearing strain. Â

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 20

Materials in Mechanical Design - Materials in Mechanical...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online