Over-the-road trailers are transportation workhorses designed to handle maximum payload day in and day out. And while the bulk of their service hours are spent on the nation’s highways, these trailers are often subjected to less than ideal terrain and driving conditions.
Over an extended period of time (and use) it’s not uncommon for trailers to exhibit signs of metal fatigue. However, a number of trailers from a leading manufacturer were reporting premature metal cracks. Because of their reputation and experience, SixD Testing & Analysis (6D) was called in to help identify and correct the problem.
Weld Cracking
Commercial trailers are partially supported on draft arms which in turn are attached to jacks supporting freestanding unattached trailers. Welds bonding these support jacks to draft arms were failing. Over time, the resulting cracks propagated into the adjoining parent material severely compromising the structural integrity of the trailer.
Testing & Analysis
6D engineers were dispatched to the field to obtain test data. Trailers were instrumented with data collection equipment and put through their usual paces. While one might assume that excessive forces on the weld were a result of the dumping activity, testing pointed to another direction.
“Testing showed that the highest stresses were seen when transporting an empty trailer,” said 6D Test Engineer, Likith Nagaraja. “Driving the empty trailer across potholes (and similar terrain hazards) caused the draft arm to bend and twist significantly.”
Testing revealed that the support jack welds were not strong enough to withstand the measured stresses. Once the crack was formed it invaded the parent material leading to failure.
Engineering a Solution
6D recommended design alternatives to dampen the impact and help relieve stress levels. Finite Element Analysis (FEA) confirmed that the modifications would reduce stress on the weld area to a safe range. Testing measurements were again taken to validate the results. A Finite Element model was used as a guide for additional gauge locations along with the previous crack location.
Results
Today the manufacturer is moving ahead confident in the new design’s ability to meet and exceed the lofty expectations of its customers. Testing and analysis again were shown to work hand-in-hand to identify the problem and engineer the most effective and practical solution.