Question

A three-point bending test is performed on a glass specimen having a rectangular cross section of height 5.3 mm and width 11.6 mm; the distance between support points is 50 mm.
Required:
a. Calculate the flexural strength (in MPa) if the load at fracture is 283 N. (Round up the final number to integer-no decimal please.)
b. What is the deflection, Δy=__________ mm, for a load of 265 N if the elastic modulus if the glass is 66 GPa?

Answer 1

Answer:

a) 65.139 MPa

b) 17490 GPa

Explanation:

a) calculate the flexural strength

we now that for a three-point bending test the bending moment will occur at the midsection

Max stress ( flexural strength ) = MY / I

Max stress can be expressed as ;  3/2 * ( F*l / b*d^2 )  ------- ( 1 )

F ( load at fracture ) = 283

l (distance between support point ) = 50

b = 11.6

d = 5.3

substitute given data into equation 1 above

= 3/2 * (( 283 * 50) /( 11.6 * 5.3^2) )

= 3/2 * ( 14150 / 325.844 )

=  3/2 * 43.425  =  65.139 MPa

B ) Determine deflection ( Δ y )

   load = 265 N

   elastic modulus = 66 GPa

elastic modulus = tensile stress / tensile strain

Tensile stress = Δ y

 strain = load = 66 GPa

therefore Δ y = 265 * 66 = 17490 GPa