i am not suprised although i am disapointed for the car occupants, the control arm mountings and the control arms themselves have always been a point of contention in an impact.
the "brackets" are to be honest, pathetic for what people are doing with their cars and the speeds now being achieved, it has been well known that the rear mounting points are suseptable to failure under braking.
the 3/4" cds or dom used for control arms is to me just down right dangerous as there is insufficient circumfrence on the ends of the tubes to get a good weld..
the two point attachment is also a problem in a competition car that will go off course any number of times, and suffering the forces of impact repeatedly.
see its like this, i don't know about you but i look at every part of a car i am building, if someone has designed a particular part or system for that car, they are not responsable for making or using that part, there may be floors in its design that are not obvious at first glance, the builder should take all reasonable care when building to build the best, not just that he can, but better!
Attachment:
diagonals.jpg
in the above picture you can see the lugs for my front suspension, they point in the direction that the force is pulling on them, in my case straight up, thus loading the weld joint equally end to end as oppose to from one end in a tearing motion.
note also their thickness 3/16" and that the load is spread across 6 lugs for each lower control arm that makes 12 weld beads approimately 1/8" thick and they are 1-1/2' wide brackets that an area of 2.25" per side.
the tubes they are attached to are two pieces of 1" x 1" welded togetherto make a 2" x 1" rectangular box but with the added advantage that in the center of the box are two1/16" uprights, this would prevent tear out of the tube wall.
note also that there are three mounting points for the control arm so should one fail, it will remain in position although i suspect there may be a slight change in alignment.
the chassis is painted white so that any cracks are easier to detect not just at the mounting points but in general.
my arms are constructed if 1" x 1/8" wall erw, and although not as strong as cds or dom for the same size tube, the increase in both wall thickness and cross sectional area make them much stronger than the 3/4" dom or cds arms and again, three point fixing.
i am not a genius, this is just practical engineering folks, if someone is selling you a car then don't accept that they have engineered the thing, it may be a case that everybody makes their arms the same so we did too, so clearly they are all under engineered for the environment they are living in.
i must admit that when i built my first locost from Ron's book, i made it as the book said, that was about 18 years ago, almost immediatly i was made aware of the short commings of the lower control arms and associated brackets, i might add that this system has been in use since the 40's for race cars and the first thing to go were the brackets in favor of a tube type mount alas in single shear, remember that race cars have a very short life span in general.
i am sorry for the driver, not only for his injuries but now he can't do what he obviously loves doing, i wish him a speedy recovery and hope like his careful analasys of the accident, he does the same to his car.