Chapter 2 Strain [MOM]

What are two types of strains in engineering mechanics?

• Muscle strain

• Normal strain,  $\epsilon$  and shear strain,  $\gamma$  

• Normal strain, $\gamma$ and shear strain,  $\epsilon$ 

Match correct strains with their physical change

[Choose ALL which applicable]

• Normal strain, $\epsilon$ : Change in SHAPE

• Normal strain, $\epsilon$ : Change in SIZE

• Shear strain, $\gamma$ : Change in SHAPE

• Shear strain, $\gamma$ : Change in SIZE

Average normal strain is expressed as: $\epsilon_{ave}=\frac{\Delta s'-\Delta s}{\Delta s}$ 
What is this ratio in simpler words?

•  $\frac{Final\ length}{Original\ length}$  

•  $\frac{Change\ of\ length}{Original\ length}$  

•  $\frac{Original\ length}{Final\ length}$  

And what is the unit of normal strain,  $\epsilon$ ?

[Choose ALL which applicable]

• Dimensionless

• mm/mm

• in/in

• kg/kg

• m/m

Average shear strain is expressed as:
 $\gamma_{nt}=\frac{\pi}{2}-\lim\theta'$  

 Explain this in simpler terms

• New angle after deformation

• Original angle before deformation

• Change of an originally perpendicular angle

And what is the unit of this shear strain, $\gamma$ ?

[Choose ALL which applicable]

• Dimensionless

• Degree

• Radian

• m/m

Match CORRECT sign of normal strain, $\pm\ \epsilon$ , with its physical change in size

•  $+\epsilon$ : Contraction; $-\epsilon$ : Elongation

•  $-\epsilon$ : Contraction; $+\epsilon$ : Elongation

• No difference between  $-\epsilon$ and $+\epsilon$ 

Match CORRECT sign of shear strain, $\pm\ \gamma$ , with its physical change in shape

•  $+\gamma$ : Angle getting smaller; $-\gamma$ : Angle getting bigger

•  $+\gamma$ : Angle getting bigger; $-\gamma$ : Angle getting smaller

• No difference between $+\gamma$ and  $-\gamma$