OBJECTIVES  

After completing this module, you should be able to:  

• Define the key terms shown below;

• Explain the relationship stress and strain;

• Explain the relationship between modulus and strength;

• Interpret a stress-strain diagram;

• Calculate stress in tension, compression, shear, and torsion;

• Calculate change in deformation;

• Calculate modulus of elasticity;

• Rank Various materials by strength and modulus of elasticity values.

KEY TERMS  
  

          TENSION  
          COMPRESSION  
          SHEAR  
          TORSION  
          STRESS  
          STRAIN  
          MODULUS OF ELASTICITY  
          YIELD STRENGTH  
          PLASTIC DEFORMATION  
          ULTIMATE STRENGTH  

Mechanical properties deal with the way materials behave when external loads and forces are applied.  Sometimes the material stretches ( when loaded in tension), bulges (when loaded in compression),  or twists (when loaded in torsion).  Anytime a load is applied to a material it will undergo some change in shape.  This change is called deformation.  Deformation may be a temporary condition if the material is not loaded beyond its yield strength.  In other words the material is elastic up to this point, and can return to its original shape if the load is removed.  However if the load increases and exceeds the yield point, the material is now in a plastic state.  It will be permanently changed, even if the load is removed.  If the loading continues the material will shortly reach its ultimate strength, followed by failure if the load is not removed.