# Beam shear failure

1. Sep 11, 2010

### Hockeyguy2026

I started a new job two weeks ago and I've been out of school for twenty years and have not used strength of materials knowlegde since. I had a part fail in the lab and I would like to calculate the force that would have been necessary to cause the shear failure. I have simplified the problem to a 1/2" tall tooth with a cross section area of .125". The material is 303 stainless steel. Can anyone help me with the equation to find this force. I understand that the part failure was caused by repeative stress and not a blunt force but my first step is to find that blunt force value.

2. Sep 11, 2010

### Studiot

What temperature was the component running at at failure?

3. Sep 11, 2010

### Hockeyguy2026

The temperature was below freezing - approx. -5C. The failed compent was from an ice maker.

4. Sep 11, 2010

### Studiot

OK so standard quoted materials properties would apply.

Shear stress = Force/area

So you can calculate a coarse failure load by multiplying the shear stength of your steel by the 1/8 sq inch.

However the forces on gear teeth are much more complex so this will only give you an upper bound. There are significant stress concentrations depending upon the shape of the teeth.

Also, what did the fracture surface look like? Can you describe it?
Was it crystalline and shiny or dull and smooth? or was it part crystalline and part dull?

5. Sep 11, 2010

### Hockeyguy2026

The failure looks part crystalline and part dull. The part that broke off is a stream divider that changes the flow of ice from an evaporator to a nozzle that pushes the ice through a tube. The part failed after many months of 24/7 operation.

6. Sep 11, 2010

### Studiot

The crystalline part is brittle failure, the dull part ductile failure.