A sad little "secret" about aluminum is that it has NO ENDURANCE LIMIT.
In other words, it has no Endurance Strength, which is the maximum stress level that can be tolerated while still exhibiting infinite cycle life.
In other words, given enough cycles, aluminum will fail at any stress level no matter how small.
There are 2 recent exceptions to this characteristic: Cast 319 (a modern block alloy) and Hypereutectic (as used in pistons.)
It is possible Cast 319 was used.
____________________________
To make matters worse, I don't care what the stress analyst said, those sections look too thin.
It reads as if you are referring to fatigue. The words such as endurance strength are uncommon.
For anyone new to this.. Stress is a measure of how material can fail under high compression or tension. Strain is stretch, measured inch per inch or mm per mm, etc.. basically how much can the material stretch before failing. Fatigue is a cycle of stress and / or strain.
Hypereutectic contains silicon, upwards of 19% content.
The deceiving part of an alloy (which is mix of material) is that you will get different results, either in stress or strain. There are many, many mixes of material in castings and forgings which should not be referred to as simply aluminum. Some examples of mechanical properties of cast aluminum alloys inc. 319 are..
You must be registered for see images
Please don't take any offense to this next comment.. As you mentioned "I don't care what the stress analyst said, those sections look too thin", this can be extremely challenging. Many times in my career it was thought to beef up a part, increase material thickness, yet this caused too much stiffness and transferred the stress into another part of the component / part. It is very tricky and it is an ignorant statement to simply say that you don't care what an analyst says. In the world of engineering and design, modelling a component is extremely complex.
Best regards,
Mike
