- #1

NeoPhysics

- 2

- 0

I am trying to understand the force and stress calculation in a cantilever beam, with point load at free end and fixed end at other.

So, Bending Force F=3EI.d/L3, E-Elastic Modulus, I Second moment of Inertia along XX axis, d deflection, L distance between point of consideration and point of force application. ...(1)

Stress = F.L.y/I, y being distance from neutral axis. .......(2)

From 1 and 2, stress = 3.E.y.d/L2............(3)

So here is my confusion. Pls help.

1. Let us say I am suspending a weight of 1kg, which is approx 10N force. From 1, L at the point of force application is zero. Does that mean F is inifinite where L=0?

2. From 2, stress is inversely proportional to Moment of Inertia. I beam has less MI than a retangular beam of same hieght and weight. So I select a 3x3 retangular beam and carve out a I beam, I reducing the MI therefore increasing the stress, Does not sound right...Pls help.

3. Materials have different tensile and compressive strengths. Let's say I have a material with compressive strength half the tensile strength. When I bend, the top portion is subject to tension and the lowest is subject to compression. From a design view, should I consider the compressive strength to decide the cross section area?

Thoroughly confused. Pls enlighten.

Neophysicist