Majority of the water feeders in a new chicken house had stopped working. The water feeders were found to be operated on the principle that when the chickens pecked a plastic bowl, a compressed spring released a squirt of water. The small compression springs were made from type 302 stainless steel, and the operating stresses were safely within the design limits given by the Goodman diagram. The springs were revealed by scanning electron microscopy to contain numerous cracks on their inside surface, and these cracks were all at 45 deg to the wire axis. The solution was recommended as to select a grade of spring steel that would be more corrosion resistant than 302 stainless.

A bomb retaining ring fabricated from type 302 stainless steel unwrapped during a practice flight, causing the bomb fins to deploy. The retaining ring was able to unwrap itself because it was thinner and softer than required. Hardness testing, metallography, and tensile testing confirmed that the component was in the annealed condition and not in the required work-hardened 1/4-hard condition.

Type 302 stainless steel springs used in a printing operation failed by breaking into several pieces after two months in service. The springs were operating over a very small deflection and were regulating the flow of ink, in which they were constantly immersed. Fatigue fractures on every piece of the spring were revealed by visual examination. Each of the fractures was found to be oriented at 45 deg to the wire axis. Clear evidence of pitting corrosion at the fatigue fracture origin was also observed. Free chloride ions were revealed to be present in the ink in which the spring was operating. An alternative ink that contained no free chloride ions was recommended.

The conical helical spring sealed, within each switch enclosure, fractured to lead to the failure of several electrical toggle switches. The spring was fabricated from 0.43 mm diam AISI type 302 stainless steel wires. Appreciable amount of scale was observed on the fracture surface and tool marks were revealed on the inner surface of the broken spring. A typical fatigue fracture that originated at a tool mark on the wire surface was revealed by inspection of a fracture surface of the broken springs. Regions which displayed beach marks around the fracture origin and parallel striations within the beach-mark regions were revealed by scanning electron microscopy. As a corrective measure, the spring-winding operation was altered to eliminate the tool marks.

Life testing of cyclic loaded, miniature extension springs made of 17-7 PH stainless steel wire and AISI 302 Condition B stainless steel wire has shown end hook configuration to be a major source of weakness. To avoid cracking and subsequent fatigue failure, it was found that stress concentration depended on end hook bend sharpness. Also, interference fits are to be avoided in the end hooks of small springs. Additionally, a need for careful consideration of the stress-corrosion properties of candidate materials for spring applications has been demonstrated by stress-corrosion test results for 17-7 PH CH900 and for Custom 455 CH850 stainless steels. Laboratory testing of these two materials in the form of compression springs confirmed the superiority of the 17-7 PH over Custom 455.