jiangyu li, university of washington lecture 18 impact test and stress concentration mechanical...
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![Page 1: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/1.jpg)
Jiangyu Li, University of Washington
Lecture 18Impact Test and Stress Concentration
Mechanical Behavior of Materials Section 4.8, 8.1, 8.2
Jiangyu LiUniversity of Washington
Mechanics of Materials Lab
![Page 2: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/2.jpg)
Jiangyu Li, University of Washington
Strain Energy
Modulus of toughness & modulus of resilience
Increasing the strain rate increase strength, but
decrease ductility
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Jiangyu Li, University of Washington
Impact Test
• Charpy V-notch & Izod tests most common
• Energy calculated by pendulum height difference
• Charpy – metals, Izod - plastics
![Page 4: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/4.jpg)
Jiangyu Li, University of Washington
Fracture Surface
Different heat treatments of AISI 4140 steel – harder on left
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Jiangyu Li, University of Washington
Trend in Impact Behavior
• Toughness is generally proportional to ductility• Also dependent on strength, but not so strongly• Brittle Fractures
– Lower energy– Generally smooth in appearance
• Ductile Fracture– Higher energy– Rougher appearance on interior with 45° shear lips
![Page 6: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/6.jpg)
Jiangyu Li, University of Washington
Effect of Temperature
Decrease temperature increase strength, but decrease ductility
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Jiangyu Li, University of Washington
Ductile-Brittle Transition
![Page 8: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/8.jpg)
Jiangyu Li, University of Washington
Brittle Failure
![Page 9: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/9.jpg)
Jiangyu Li, University of Washington
Failure Criteria
• Materials assumed to be perfect:– Brittle Materials
• Max Normal Stress
– Ductile Materials• Max Shear Stress• Octahedral Shear
Stress
• Materials have flaw or crack in them:– Linear Elastic Fracture
Mechanics (LEFM)• Stress intensity factor (K)
describes the severity of the existing crack condition
• If K exceeds the Critical stress intensity (Kc), then failure will occur
![Page 10: Jiangyu Li, University of Washington Lecture 18 Impact Test and Stress Concentration Mechanical Behavior of Materials Section 4.8, 8.1, 8.2 Jiangyu Li](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d6b5503460f94a49f9e/html5/thumbnails/10.jpg)
Jiangyu Li, University of Washington
Stress Concentration
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Jiangyu Li, University of Washington
Crack Tip in Real Materials
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Jiangyu Li, University of Washington
Effect of Crack Length
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Jiangyu Li, University of Washington
Brittle vs. Ductile Behavior
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Jiangyu Li, University of Washington
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Jiangyu Li, University of Washington
Assignment
• Mechanical Behavior of Materials
4.34, 8.1, 8.3