## General Mechanical

#### Bending stress analysis

• zlsiegel
Subscriber
Hi everyone,

I have a question about a bending analysis I'm working on. The part in question is a flat glass plate with a series of holes. The glass manufacturer only provides one strength value - bending strength - which is 25 MPa. I've set up a simulation in ANSYS where I solve for maximum principal stress, which comes out to be 13 MPa inside one of the holes. My question is, is it valid to compare those values directly? I.e. can I conclude that I have a safety factor of 25/13 = ~2? Or should principal stresses only be compared to UTS, and therefore do I need to somehow convert my principal stress results into a value that can be directly compared to the vendor's bending strength?
• peteroznewman
Subscriber
Ask the manufacturer how they measure the bending strength. Do they use a 4 point bending fixture? How do they calculate the strength value? Most importantly, what is the surface quality of the glass.

Glass is a brittle material and its strength is highly dependent on the surface quality. The smoother the surface, the higher the strength. If the surface is roughened or etched so that adhesive can bond to it properly, the strength is greatly reduced.  A plate with holes in it creates a stress concentration. How are the holes created?  Microscopic examination of the edge of the holes will reveal small cracks or scratches that will lower the strength of the plate.