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Mechanical Behavior
Demonstrate an understanding of the basic principles of stress and strain and etc.
21
Mechanical Engineering
Undergraduate 3
05/07/2014

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Cards

Term
Mechanical properties of metals
Definition
Stress versus strain
Hardness
Creep
Term
Mechanical properties of metal is also applicable to ceramics
Definition
Ceramic (brittle fracture, creep)
Term
Tensile test is the answer
Definition
A load-versus-elongation curve
Stress-versus-stain curve
Term
Elastic deformation
Definition
Initial linear portion
Can fully recover to the initial length
Term
Plastic deformation
Definition
Permanent deformation
Cannot recover to the initial length
Nonlinear portion after the elastic limit
Term
Yield strength
Definition
intersection of the deformation curve with a strain-line parallel to the elastic portion and offset 0.2 % on the strain axis
Stress necessary to generate 0.2% of permanent deformation
Resistance of the metal to permanent deformation
Term
Yield strength
Definition
Yield strength for a low-carbon steel
Upper yield point: distinct break point from the elastic region
Ripple pattern : nonhomogeneous deformation at a point of stress concentration
Lower yield point: at the end of the ripple pattern, start of general plastic deformation
Term
Young’s modulus, E
Definition
The linearity of the stress-strain plot in the elastic region
Represents the stiffness of the material
Term
Tensile strength
Definition
The maximum stress after the yield strength
Term
Residual stress
Definition
stress remaining within a structural material after all applied loads are removed
Thermomechanical treatments (welding, machining)
Term
Strain hardening
Definition
The phenomenon of increasing strength with increasing deformation
Term
Cold working (below one-half of the melting point)
Definition
Metal shaping with the advantage of the strain hardening
Term
strain hardening
Definition
1.Engineering stress-strain: stress decreases after the tensile stress
(Area fixed)
2.Actual stress-strain: stress increases after the tensile stress
(necking-Area reduces)
Term
Ductility & Toughness
Definition
1.Failure stress varies due to complexity of the final neck down – hard to predict
2.Ductility is the percent elongation at failure

3.Formability(ductility) indicates the general ability of the metal to be plastically deformed
4.Toughness :
Strength + Ductility
Term
Ceramics and glasses
Definition
Ceramics and glasses do not demonstrate a significant amount of plastic deformation
Brittle fracture : characteristic of ceramics and glasses
Tension: relatively weak (280 Mpa)
Compression: relative strong (2100 Mpa)
Term
Elastic deformation
Definition
stretching of atomic bonds in the vicinity of the equilibrium point
Nearly straight-line of F versus a implies linear elastic behavior
Term
Plastic deformation
Definition
distortion and reformation of atomic bonds
Term
Difference between theory and practice
Definition
Theory (by atomic bonding force): 1000 Mpa (copper)
Practice (shear test): 100 Mpa (copper)
Term
Slip mechanism
Definition
becomes more difficult as the individual atomic step distances are increased
Term
Dislocation
Definition
along high atomic density plane and high-atomic density directions is much easier
Term
Slip system
Definition
combination of families of crystallographic planes and directions corresponding to dislocation motion
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