Modulus of rupture formula

mindstorm87

1. The problem statement, all variables and given/known data
Prove the formula of modulus of rupture using the third point loading test.
R = Pl/bd^2 P: load at fracture
l: length
b: width
d: depth
2. Relevant equations



3. The attempt at a solution
I don't know how to start. PLease help me.

AlephZero

Use the definition of modulus of rupture - hint, it's a stress at some point in the beam.

Set up the shear force and bending moment diagram for the loading in a 3-point test, and find the stress from the usual beam equations.