a lot of bolts were received with an incorrect certificate of compliance , field failures were numerous

1. Boat Trailer winch main bolt failure
FEA damage analysis
Solidworks Simulation 2019
3/30/2019 rev B
Don Blanchet
3B Associates
dwb3298@outlook.com
Prepared for: National Boat Certification Association Washington, DC

2. Solidworks 2019 model
Main bolt
½ inch

3. Failure summary
◼ A production lot of winches exhibited a
very high rate of warranty claims for
failures of the main bolt.
◼ Upon examination the failed bolts all
came from the same purchase lot from
an off-shore vendor.
◼ Metallurgical tests revealed that the
bolts did not meet the winch
manufacturers specs.

4. Purchase order specified
SAE grade 5 bolts
strength 120,000 psi
Testing of the lot of received bolts revealed an average
Strength of less than 50,000 psi
Winches had been assembled and inspected using a
Certificate of Compliance from the off-shore vendor.

5. Qualification test proof loading
performed once a year
no lot testing
Design proof load = 6000lb
Maximum recommended
use load = 3000lb
FIXED BASE

6. Max calculated distortion
under a 6000 lb load = .014 inches
Solidworks FEA simulation 2019
STATIC
LOADING

7. Max calculated bolt stress with
6000 lb load = 58,000 psi
BOLT FAILURE PREDICTED FOR
50,000 PSI BOLT MATERIAL STRENGTH

8. Max calculated bolt stress with
6000 lb load = 58,000 psi
BOLT SAFE FOR the SPECIFIED
120,000 PSI GRADE 5 BOLT MATERIAL STRENGTH
Factor of safety
120,000/58,000= 2.1

9. Analysis Summary
6000 lb
design
Load
Resulting
peak
Stress
psi
Strength
psi
Factor
Of
Safety
Low
Strength
Bolt
58,000 50,000 0.86
High
Strength
Bolt
58,000 120,000 2.01

10. Conclusion - recommendations
◼ The bolt material certificate of
compliance was not correct or
fraudulent.
◼ Remove the vendor from the Qualified
Parts List.
◼ Demand recertification or change
vendor.
◼ Perform a recall to cover liability.