ROVER WHEELS: Monitoring changes over time, NOTE: Read back through the thread to avoid repeating misconceptions Options

[DeanM]

[MOD NOTE: This thread follows on a post by Ed Truthan containing a MAHLI mosaic of MSL wheels taken on sol 275.]

Ed: zooming in on that marvellous underbelly MAHLI montage, there appears to be further (and previously noted) deformation of the wheel surfaces.

Damage is most evident in the view of the front-left wheel inner surface.

Such wear has previously been discussed and concerns allayed.

Nevertheless, the front left wheel surface *appears* to have been punctured.



We've only done 700 meters, and have 7000 more to get to Mt Sharp.....

Given that more odometry has now accumulated, is any (re-)new(ed) concern valid?

DeanM

[Jimbo1955]

What surprises me about the wheel damage isn't the dents. That would be expected in thin aluminum. But the gaping holes are surprising to me. It's like the alloy is very brittle.

[mcaplinger]

It's like the alloy is very brittle.

I assume (with no evidence to support it) that the wheels are 7075 alloy, which is somewhere near the upper end of aluminum alloys for fracture toughness -- http://en.wikipedia.org/wiki/Brittle_strength . http://en.wikipedia.org/wiki/Fracture is a useful intro to various types of fracture; see "ductile fracture". I'm not a mechanical engineer or a materials scientist and a hole is a little surprising to me too, but I'd rather see a clean hole than a big propagating rip.

To anticipate a question, aluminum is less subject than say, steel, to low-temperature embrittlement. See http://www.keytometals.com/page.aspx?ID=Ch...e=ktn&NM=23 -- "Below zero, most aluminum alloys show little change in properties; yield and tensile strengths may increase; elongation may decrease slightly; impact strength remains approximately constant. Consequently, aluminum is useful material for many low-temperature applications."

To sum up (note that this is all my opinion derived from public information because I've intentionally not looked at any project-internal sources on this): yes, there are holes in the wheels. Some level of wheel damage was clearly anticipated by the designers. There are a lot of tradeoffs in the MSL wheel design and it may well have not been feasible to make wheels that were impervious to puncture. Imaging the wheels is being done, presumably to assess the amount and evolution of damage. Exactly what the level of concern is, if any, is something for the project to say.