A 15 foot trailer and trailer hitch were rented and installed at a rental location. The trailer was loaded with a very light load. Shortly after leaving the rental location, the trailer became detached from the pickup truck towing the trailer. The failed combination tri-ball trailer hitch is shown in Photograph A.
Photograph A Overall view of failed tri-ball hitch.
A close-up view of the failed ball, retrieved from the hitch ball cup is shown in Photograph B.
Photograph B Close-up view of failed ball.
Visual and microscopic examinations revealed the weld attaching the ball to the hitch tube was defective. Scanning electron microscopic examination of the fracture surface revealed metal fatigue, excessive pipe porosity and cleavage fracture.
These fracture features were consistent with a long-term crack which occurred as a result of defective welding. The bottom of the failed trailer ball exhibited a threaded bolt hole to be used to bolt the trailer ball to the hitch tube prior to welding. The bottom of the hitch ball is shown in Photograph C.
Photograph C View of ball surface to be attached to trailer hitch tube.
No evidence of a hole to be used to bolt ball to hitch tube was found. (see photo A).
The cause of this trailer accident was determined to be defective assembly and defective welding.