MECHANICAL PROP. & TESTING Flashcards
Engineering STRESS?
Eng. Stress= F/Ao [N/m^2]
Engineering STRAIN?
Eng. Strain= change in length/ original length
Explain the TENSILE TEST
Apply a tensile force/load slowly to a sample until fracture occurs.
Is the ELASTIC deformation reversible?
Yes
How do you find Young’s Modulus(E)?
Slope of Elastic Region of Stress vs Strain curve
What information does E give us?
The Stiffness of a material.
Give exemple of materials with HIGH E VALUE (very stiff)
Ceramics (300GPa) & Steel (207GPa)
True or False plastic has a medium E value
False (3GPa not stiff)
Stiffness depends directly on ______ and therefore
on ______ .
The Temperature + The bonds of the atoms
Hooke’s Law?
Stress=E*Strain
Explain PLASTIC deformation.
When bonds have broken and reformed with different atoms.
Yielding is when ____ changes from _____ to _____.
Deformation + Elastic + Plastic
What do we define as the maximum stress an object can take before permanent deformation?
Yield Strength
What happens at tensile strength of a POLYMER?
When polymer backbone chains are aligned and about to break.
Once TS is reached deformation becomes more ____.
Localized
True or False: In Alloys, TS happens right when we have passed the elastic region of a stress vs strain curve.
False, it’s with CERAMICS
Define Ductility.
Amount of plastic deformation before fracture
When we have little to no deformation we say that the material is _____.
Brittle
When we have some plastic deformation we say that the material is _____.
Ductile
What does a material require to be TOUGH?
Strength and Ductility
What is defined as the ability to absorb energy before fracture?
Toughness
How can we find the toughness of a material in the Stress vs Strain curve?
Area under the curve
What is Resilience?
The ability to absorbs energy on elastic loading and release on unloading.
When describing PLASTIC deformation, use ____ and ____.
True stress + True strain
True or false: True stress is ALWAYS higher than engineering stress.
True
If yielding has occurred and the load is released, the material recovers _______ only.
ELASTIC STRAIN
True or False: PLASTIC deformation has both elastic and plastic strain components.
True
Explain the phenomena of elastic strain recovery and strain hardening.
The elastic region is higher when we reload after unloading for the first time.
The _____ the indent, the harder the material.
Smaller
What is N?
Factor of Safety
