Chapter 8- Mechanical Failure

Chapter 8- Mechanical Failure - Chapter 8: Mechanical...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 8: Mechanical Failure ISSUES TO ADDRESS. .. Chapter 8 - 1 • How do flaws in a material initiate failure? • How is fracture resistance quantified; how do different material classes compare? • How do we estimate the stress to fracture? • How do loading rate, loading history, and temperature affect the failure stress? Ship-cyclic loading from waves. Computer chip-cyclic thermal loading. Hip implant-cyclic loading from walking. Adapted from Fig. 22.30(b), Callister 7e. (Fig. 22.30(b) is courtesy of National Semiconductor Corporation.) Adapted from Fig. 22.26(b), Callister 7e. Adapted from chapter-opening photograph, Chapter 8, Callister 7e. (by Neil Boenzi, The New York Times .)
Background image of page 1

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

View Full DocumentRight Arrow Icon
Ductility x 100 L L L EL % o o f = • Plastic tensile strain at failure: tensile strain, ε tensile stress, σ Brittle ( smaller % EL ) Ductile ( larger % EL ) Brittle materials: % EL<5% • Another ductility measure: 100 x A A A RA % o f o - = Chapter 8 - 2 Adapted from Fig. 6.13, Callister 7e.
Background image of page 2
Chapter 8 - 3 Ideal vs Real Materials • Stress-strain behavior (Room T ): 0.1 σ ε E /10 E /100 perfect mat’l-no flaws carefully produced glass fiber typical ceramic typical strengthened metal typical polymer • DaVinci (500 yrs ago!) observed. .. -- the longer the wire, the smaller the load for failure. • Reasons: -- flaws cause premature failure -- larger samples contain more flaws Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.4. John Wiley and Sons, Inc., 1996. TS << TS engineering materials perfect materials σ y << y engineering materials perfect materials ΕΕ engineering materials perfect materials
Background image of page 3

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

View Full DocumentRight Arrow Icon
Fracture mechanisms Fracture involves two steps: crack formation and propagation • Ductile fracture – Occurs with plastic deformation – Proceeds slowly – Characterized by stable cracks • Brittle fracture – Little or no plastic deformation – Proceeds quickly – Characterized by unstable cracks Chapter 8 - 4
Background image of page 4
Ductile vs Brittle Failure Chapter 8 - 5 Very Ductile Moderately Ductile Brittle Fracture behavior: Large Moderate % AR or % EL=> Small • Ductile fracture is usually desirable! Adapted from Fig. 8.1, Callister 7e. • Classification: Ductile: warning before fracture; More energy is required to induce Brittle: No warning
Background image of page 5

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

View Full DocumentRight Arrow Icon
Moderately Ductile Failure Chapter 8 - 6 • Evolution to failure: • Resulting fracture surfaces (steel) 50 mm particles serve as void nucleation sites. 50 mm From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 11.28, p. 294, John Wiley and Sons, Inc., 1987. (Orig. source: P. Thornton, J. Mater. Sci ., Vol. 6, 1971, pp. 347-56.) 100 mm Fracture surface of tire cord wire loaded in tension. Courtesy of F. Roehrig, CC Technologies, Dublin, OH. Used with permission. necking σ void nucleation void growth and linkage shearing at surface fracture
Background image of page 6
Ductile vs. Brittle Failure cup-and-cone fracture brittle fracture Adapted from Fig. 8.3, Callister 7e.
Background image of page 7

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

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 34

Chapter 8- Mechanical Failure - Chapter 8: Mechanical...

This preview shows document pages 1 - 8. Sign up to view the full document.

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