Search Results for crack test

Coaxial cable connectors made of brass were failing at a high rate after less than one year of service in an outdoor industrial environonment. The observed failures, which consisted of cracks in the body and end cap, were analyzed and found to be brittle fractures due to stress-corrosion cracking. Two common stress-corrosion cracking tests for copper materials were conducted on new connectors from the same manufacturing lot, confirming the initial determination of the fracture mode. Additional testing as was done in the investigation is often helpful when analyzing corrosion failures.

In TAKR 300 (Bob Hope) Class transport ships, the builder observed cracking of steel cloverleaf vehicle tie-down deck sockets following installation. Sockets were made from AH36 steel plate by flame cutting and cold coining, then submerged-arc welded to the shop deck. Cracks initiated from the tip of the cloverleaf pattern in >300 cases aboard several cargo vessels in various stages of construction. Consultants who analyzed the situation concluded that the problem may have been corrosion and hydrogen embrittlement. Three possible mechanisms of failure were considered: overload failure; fatigue fracture; and, environmentally-assisted cracking. Testing indicated overload failure was the cause. Remedial actions were taken to improve the fracture properties of the deck socket. A modified manufacturing process was developed involving milling and cutting instead of coining to round the comers of the flame-cut cloverleaf lobe. This new manufacturing process solved the problem.

A type 321 stainless steel downcomer expansion joint that handled process gases was found to be leaking approximately 2 to 3 weeks after installation. The expansion joint was the second such coupling placed in the plant after failure of the original bellows. The failed joint was disassembled and examined to determine the cause of failure. Energy-dispersive x-ray analysis revealed significant peaks for chlorine and phosphorus, indicating failure by chloride stress-corrosion cracking (SCC). Cracks in the liner and bellows exhibited a branched pattern also typical of SCC. Cracks through the inner liner initiated on the outer surface of the liner and propagated inward, whereas cracks in the bellows originated on the inner surface and propagated outward. Stress-corrosion cracking of the assembly was caused by chloride contaminants trapped inside the bellows following hydrostatic testing. Checking the test fluid for chloride and removing all fluids after hydrostatic testing were recommended to prevent further failure.

A connecting rod from a motor boat was broken in two places at the small end. At position I there was a fatigue fracture brought about by operational stress, whereas the fibrous fracture surface II was a secondary tensile fracture. Furthermore the transition on the other side of the rod was cracked symmetrically to the fatigue fracture (position III). Magnetic inspection showed indications of cracking at the transition between the rod and small end in six other connecting rods from the same batch. Metallographic investigation showed the connecting rods were rendered susceptible to fatigue by the notch effect of coarse scale-filled folds formed during forging.