An automobile manufacturer rejected several 1035 steel stub axles because of what appeared to be short longitudinal cracks in the surfaces of the pins. The cracks were found when six axles were examined for defects by magnetic-particle inspection. However, metallographic examination showed that these lines were not cracks but slag inclusions at and immediately below the surface. Analysis (visual inspection, metallographic examination, and 100x/500x magnetic-particle inspection) supported the conclusions that the inclusions consisted of pieces of fireclay from channel brick that were flushed into the ingot mold. Although no true cracks were present, rejection of the stub axles was nevertheless justified. Slag streaks could reduce the strength of the stub axles and lead to the formation of fatigue fractures during operation. No recommendations were made.

A drive-line assembly failed during vehicle testing. The vehicle had traveled 9022 km (5606 mi) before the failure occurred. Both the intact and fractured parts of the assembly were analyzed to determine the cause and sequence of failure. Visual examination of the assembly showed three of four bearing caps, two cap screws, and one universal-joint spider had fractured. Examination of the three fractured bearing caps and the spider showed no evidence of fatigue but showed that fracture occurred in a brittle manner. The bearing cap that was not destroyed still contained portions of the two fractured cap screws. It was found that the two cap screws failed in fatigue under service stresses. The three bearing caps and the universal-joint spider broke in a brittle manner. The properties of the material in the cap screws did not fulfill the specifications. The modified 1035 steel was of insufficient alloy content. Also, the tensile strength and endurance limit were lower than specified and were inadequate for the application. The material for the cap screw was changed from modified 1035 steel to 5140 steel.

A heavy duty facing lathe failed when the tool post caught one of the jaws on the rotating chuck, causing the spline shaft that drives the main spindle to fracture. A detailed analysis of the fracture surfaces (including fractography, metallography, and analytical stress calculations) revealed areas of damage due to rubbing with evidence of cleavage fracture on the unaffected surfaces. The results of stress analysis indicated that repeated reversals of the spindle produced stresses exceeding the fatigue limit of the shaft material. These stresses led to the formation of microcracks in a retaining ring groove that were accelerated to sudden failure when the tool post and chuck collided.