Expert: Jeanette A - 12/2/2008

Question
hi there i was wondering if you could guide me on how to answer this

A specimen of steel of circular cross-section, 25mm diameter, and 240mm long has been tested in axial tension.  A load of 42.674 kN produced an extension of 0.1018 mm and the specimen returned to its original length on unloading.      
     
Determine (in kN/mm2) the modulus of elasticity of the steel.


Answer
Hey Traci,

The steps you could take in order to find Young's Modulus (E) is:

1) Strain

Strain can be expressed as

   strain = dL / L (1)

   where

   strain = (m/m) (in/in)

   dL = elongation or compression (offset) of the object (m) (in)

   L = length of the object (m) (in)


2) Stress

Stress can be expressed as

   stress = F/A (2)

   where

   stress = (N/m2) (lb/in2, psi)

   F = force (N) (lb)

   A = area of object (m2) (in2)


3) Young's Modulus (Tensile Modulus)

Young's modulus or Tensile modulus can be expressed as

   E = stress / strain = (F / A) / (dL / L) (3)

   where

   E = Young's modulus (N/m2) (lb/in2, psi)


I hope this is of some help.


Warm Regards,
Jeanette