ch7-S09 - MY2100 – Ch 7, Part 1, Slide 1 Chapter 7:...

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Unformatted text preview: MY2100 – Ch 7, Part 1, Slide 1 Chapter 7: Mechanical Properties structure processing properties Performance Mechanical properties deal with how a material responds to forces. This subject is extremely important to almost every engineer who is using materials or designing structures. MY2100 – Ch 7, Part 1, Slide 2 • Stress and strain : What are they and why are they used instead of load and deformation? • Elastic behavior: Why does it occur and how much deformation results? What materials deform least? • Plastic behavior: At what point do dislocations cause permanent deformation? What materials are most resistant to permanent deformation? 1 ISSUES TO ADDRESS... • Ceramic Materials: How do their properties differ from metals? • Polymers: How do their properties differ from metals? MY2100 – Ch 7, Part 1, Slide 3 Stress To understand and calculate the effect of forces, we define a parameter called stress which is independent of specimen dimensions . In one dimension (tension or compression), stress is defined as the applied force divided by the area it acts on. F F A F F A Compression Tension σ comp = - F/A σ tension = + F/A MY2100 – Ch 7, Part 1, Slide 4 Stress The units of stress are the same as those of pressure. English system: • lbs/in 2 , usually abbreviated psi. • kilo-lbs/in 2 , usually abbreviated ksi (1 ksi = 1,000 lbs/in 2 ) SI system: • N/m 2 , called a Pa (Pascal) • Typical stresses are in MPa (MegaPascal, 10 6 Pa) or GPa (GigaPascal, 10 9 Pa) Useful conversion: 1 ksi = 6.895 MPa MY2100 – Ch 7, Part 1, Slide 5 Engineering stress & true stress A o True Stress is calculated based on the actual area and defined as σ Τ = F/A i , where A i is the instantaneous area during deformation. At small deformations , these stresses are similar in magnitude. Engineering Stress is calculated based on the original area (A o ). So, σ = F/A o . A i During deformation, the area of a material subjected to a force changes constantly. F F MY2100 – Ch 7, Part 1, Slide 6 Strain To quantify deformation (change in shape of a material), we define a dimensionless parameter called strain ( ε )....
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This note was uploaded on 03/16/2011 for the course MY 2100 taught by Professor Staff during the Spring '08 term at Michigan Technological University.

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ch7-S09 - MY2100 – Ch 7, Part 1, Slide 1 Chapter 7:...

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