Stresses and Strains Flashcards
Define Stress
Force per unit area acting on a surface
Force/Area
What’s the difference between Normal Force and Shear force
And therefore Normal Stress and Shear Stress
Normal Force is applied perpendicular to a section
Shear Force is applied parallel to a section
Stress associated with the normal force is Normal or Direct Stress
Stress associated with the shear force is Shear Stress
Explain the Method of Section
Cut the member by passing an imaginary section through it
Provided the entire member is in equilibrium, any part after the imaginary cutting must also be in equilibrium.
So The internal forces must balance the external forces on each part
+ve Normal Stresses are ________
-ve Normal stresses are ________
Equation for Normal Stress =
Tensile
Compressive
Equation for Shear Stress =
What is the unit of stress
Pa or Nm^-2
What is an allowable stress.
What is a Safety factor
A Material Property , Maximum stress a material can withhold without fracture
A multiplier that is less 1, multiplied by allowable stress. To keep the stress way below the allowable.
The maximum stress of your system cannot surpass the safety factor
Define Yield Strength
Stress at which a material starts to deform plastically
1) Find section with maximum internal stress and use that in allowable stress calculation.
Define Normal Strain, & what is the equation
ratio of the change in length of the material against its original length ε
Due to a Normal Stress acting on the body
ε = New Length/ Origional
Define Shear Strain
What’s the approximation made with this result
Shear Strain γ is the measured distortion of a body due to shear stress
It’s defined as the sum of the angles made between a side of the body in its original position and the same side of the body in its deformed position.
tan (shear strain) = Displacement between the vertex post deformation and pre deformation/ Height of the original side.
That tan(shear strain) = Shear Strain when shear strain is small.
Explain Strain hardening
Strain hardening is when a material starts to deform plastically,the stress required to continue deforming continues with increasing strain.
This is due to the formation of dislocations, imperfections in the crystal lattice. As Number of dislocations increase, they will germinate snagged on each other preventing the material to move and deform
Occurs Until the Ultimate Tensile Stress - Maximum stress a material can withstand before fracture
What is the Equation for Young’s modulus
Units?
Stress / Strain
Pa
What’s the Equation for Shear Modulus
Shear Stress/ Shear Strain
Explain what did Poission Discover
That when a bar is placed in tension, Lateral Contractions accompany the longitudinal extension
Or when a bar is placed in compression , lateral extensions accompany the longitudinal contraction
The ratio between how a material deforms laterally and longitudinally is called the Poisson Ratio.
Derive an Equation that calculates Extension in terms of length, load force, young modulus and area of cross section
P = Load force
E = Young’s modulus
L = length
A = Area
Derive an equation that calculates the strain laterally due to a longitudinal strain, in terms of Poissons ratio , Load force, Width of cross section , Height of Cross section , length of body, Youngs Modulus
P = Load force
E = Young’s modulus
L = length
b = width of cross section
d = height of cross section
What’s the equation that links Shear Modulus to Young’s modulus
Define Young’s modulus
Define Shear Modulus
Define Poissons Ratio
question with billet of steel
