I watched this Mike Busch video concerning bolted joints in tension, which covers our Piper Cherokee wing spar joints:
Watching it toward the end, I observe that the joint isn't pure shear, but rather shear plus friction, where the friction is supplied by the clamping tension of the attach bolts. Losing that tension can cause fretting on the sides of the through holes, which can lead to fracture of the surrounding material in the same way the ERAU failure apparently occurred. So I was wondering whether it would be of value to periodically re-torque the attach bolts. Since the spar cap and carry-through are made of relatively softer material, is it possible that bolt tension is being relieved by "cold-flow" of the aluminum?
BTW, I have no relationship with Mr Busch or Savvy Aviation, but I do find his videos very informative.
Watching it toward the end, I observe that the joint isn't pure shear, but rather shear plus friction, where the friction is supplied by the clamping tension of the attach bolts. Losing that tension can cause fretting on the sides of the through holes, which can lead to fracture of the surrounding material in the same way the ERAU failure apparently occurred. So I was wondering whether it would be of value to periodically re-torque the attach bolts. Since the spar cap and carry-through are made of relatively softer material, is it possible that bolt tension is being relieved by "cold-flow" of the aluminum?
BTW, I have no relationship with Mr Busch or Savvy Aviation, but I do find his videos very informative.