1985 Ford Aerostar rear axle fatigue failures

Welded rear axle of HSLA steel, designed assuming fatigue strength proportional to tensile strength. Brackets welded onto axle; field failures in first six months. Big product recall. Triggered industry-wide work on fatigue of welded HSLA sheet.

To give you an example, in 1985 Ford came up with the Aerostar van, and they were using high-strength low-alloy steel for the first time instead of plain carbon sheet steel. They designed the rear axle to have a fatigue strength proportional to the tensile strength of the better steel — that's what their designers knew. That would be true if it weren't welded, but the rear axle had brackets welded onto it, and they found people throwing axles, fatigue-failing them in the first six months. This was not a great day for Ford. Big product recall. There was a tremendous amount of work done after that on the fatigue strength of sheet metal welds in high-strength low-alloy steels.