Aluminum flex and yield over product life

Hi All, need some insight. Working on a small enclosure that requires aluminum to slightly flex to disengage a simple opening mechanism. The aluminum will be milled in the final product. Has anyone come across anything similar? Can aluminum flex ever so slightly and the elasticity will last many years?

Any thoughts or critiques are welcome. Product is in super early stages

This sounds like an interesting situation. It sounds like you are interested in creating something flexible but creating the object with a milling machine seems contrary – if the housing can flex as part of the mechanism will it be rigid enough to machine?

The amount of flexure will be driven by your wall thickness and wall supports. As far as remaining elastic for years, that is another ballgame. You do not often find springs made of aluminum as it is inherently prone to fatigue and will break under cyclical loading. The fatigue life is tied to many factors including material grade, purity, heat treatment, surface finish, load magnitude, and environmental conditions.

How thick are yours walls and how far do you wish to deflect the aluminum?

The word milled aluminum and elasticity don’t go together very often. You don’t want to work harden the material by having something that will flex frequently over time.

There are all kinds of spring steels and materials that are well suited for flexing. Without looking at the specifics of the design it is very hard to say.

Either way, if your enclosure is CNC’ed you can always build a prototype and perform the accelerated life testing to see how many times you can use your latch before it fails. It may good enough to last tens of thousands of cycles, but really no good way to tell without a more in depth look at the design and material.

Fatigue is defined by the number of cycles and stress.

Plenty of handbooks out there that will define the fatigue strength of most, if not all, aluminum alloys; treated, untreated, coated, uncoated, etc.

I wouldn’t advise it.
You would be better off inserting another part (spring steel or plastic) to do the job.

Can you find an example of another product doing something similar with aluminum?

Agree. Couple times flexing, tops with aluminum. Steel is your friend in this case, or titanium!

If you look at their fatigue life curves, steel flatlines- you can cyclically load it more or less forever as long as the stress is below about 1/2 of the ultimate tensile strength. With aluminum, that doesn’t happen. Aluminum will eventually fail at any stress level, if you cycle it long enough. “Eventually” is a relative term though- most airplanes are almost entirely aluminum, are subject to considerable cyclical stress, and fatigue failures are rare (partly because airplanes are inspected for cracks regularly). So what you’re proposing is certainly possible.

You also need to bear in mind that any kind of surface imperfection (scratches, notches, etc.) will have a dire effect on fatigue life. If your mechanism acts in such a way that it will mark the surface, fatigue failure will happen much more quickly at a given stress level.

Thanks you all so much for the extrmemely helpful feedback.


I would step back and ask the whys

why this material

why this design

why not an alternative material

why not a proven design that already exists

Sometimes as designers we get so focused on making a solution WORK that we forget to judge if it is the right solution…