ch9.2-S09 - Chapter 9 Failure structure processing...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
MY2100 – Ch 9, Part 2, Slide 1 Chapter 9 Failure structure processing properties Performance ISSUES TO ADDRESS. .. How do loading rate, loading history, and temperature affect the failure stress? Why can a cyclic or repeated load or strain cause material failure?
Background image of page 1

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

View Full DocumentRight Arrow Icon
MY2100 – Ch 9, Part 2, Slide 2 Failure without prior defects We have been discussing that if a structure contains a defect (especially a sharp crack), it can fail in a catastrophic manner at stresses substantially below the yield strength. Now we will talk about two ways that structures can fail at low stresses even without pre-existing defects .
Background image of page 2
MY2100 – Ch 9, Part 2, Slide 3 Brittle fracture Materials can undergo brittle fracture under the right conditions. Brittle fracture is favored by: 1. Low temperatures 1. High loading (straining) rates - this limits the time available for dislocation motion, viscous flow or chain sliding 3. Any phenomenon that makes permanent deformation more difficult.
Background image of page 3

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

View Full DocumentRight Arrow Icon
MY2100 – Ch 9, Part 2, Slide 4 Effect of loading rate in tensile tests Loading rate = ∆ε/∆ time = Increased loading rate. .. -- increases σ y and TS -- decreases % EL Why? An increased rate gives less time for dislocations to move past obstacles. σ ε σ y TS TS larger ε smaller ε ε
Background image of page 4
MY2100 – Ch 9, Part 2, Slide 5 Classic example of how steels can undergo brittle fracture What kind of tests can we do to prevent these kinds of failures?
Background image of page 5

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

View Full DocumentRight Arrow Icon
MY2100 – Ch 9, Part 2, Slide 6 High-rate loading of steels One test used => “Charpy Impact Test” - impose high loading rates, put a notch in the sample & test at different temperatures. measure energy absorbed by fracture. sample final height initial height (Charpy) sample
Background image of page 6
MY2100 – Ch 9, Part 2, Slide 7 Ductile/Brittle Transition If this test is conducted at different temperatures, many steels exhibit a transition temperature at which the energy absorbed goes down and the fracture becomes brittle. Different steels have different curves, and if you design with steel at low temperatures you should be aware of this.
Background image of page 7

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

View Full DocumentRight Arrow Icon
MY2100 – Ch 9, Part 2, Slide 8 Why does a ductile-to-brittle transition occur?
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

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.

Page1 / 33

ch9.2-S09 - Chapter 9 Failure structure processing...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online