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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.

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Presentation on theme: "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."— Presentation transcript:

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 University of Washington Mechanics of Materials Lab

2 Jiangyu Li, University of Washington Strain Energy Modulus of toughness & modulus of resilience Increasing the strain rate increase strength, but decrease ductility

3 Jiangyu Li, University of Washington Impact Test Charpy V-notch & Izod tests most common Energy calculated by pendulum height difference Charpy – metals, Izod - plastics

4 Jiangyu Li, University of Washington Fracture Surface Different heat treatments of AISI 4140 steel – harder on left

5 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

6 Jiangyu Li, University of Washington Effect of Temperature Decrease temperature increase strength, but decrease ductility

7 Jiangyu Li, University of Washington Ductile-Brittle Transition

8 Jiangyu Li, University of Washington Brittle Failure

9 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 (K c ), then failure will occur

10 Jiangyu Li, University of Washington Stress Concentration

11 Jiangyu Li, University of Washington Crack Tip in Real Materials

12 Jiangyu Li, University of Washington Effect of Crack Length

13 Jiangyu Li, University of Washington Brittle vs. Ductile Behavior

14 Jiangyu Li, University of Washington

15 Assignment Mechanical Behavior of Materials 4.34, 8.1, 8.3


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