There are a combination of factors not mentioned in the article:
One, encountering terrain with unexpectedly sharp, immovable rocks.
Two, a suspension arm design that happens to put increased force on certain wheels when they encounter immovable rocks.
Three, the wheels have a tread pattern with a sharp, angular geometry, causing stress risers at the points of the pattern, where the thin metal meets the thicker raised treads. The thinner metal thus tends to crack more readily at these points.
(BTW, it is only this last point that I consider to be a legitimate design flaw, given the innumerable constraints the engineers had to work within. The rover is a marvel of engineering on every level.)
One, encountering terrain with unexpectedly sharp, immovable rocks.
Two, a suspension arm design that happens to put increased force on certain wheels when they encounter immovable rocks.
Three, the wheels have a tread pattern with a sharp, angular geometry, causing stress risers at the points of the pattern, where the thin metal meets the thicker raised treads. The thinner metal thus tends to crack more readily at these points.
(BTW, it is only this last point that I consider to be a legitimate design flaw, given the innumerable constraints the engineers had to work within. The rover is a marvel of engineering on every level.)
An article for reference.[1]
[1] http://www.planetary.org/blogs/emily-lakdawalla/2014/0819063...