A gray iron cylinder head cracked after approximately 16,000 km of service. The head was cracked on the rocker arm pan rail next to the No. 3 intake port and extended into the water jacket on the rocker-arm side of the head. Microporosity was revealed in the crack in the sections taken from the water jacket next to the plug and the area next to the No. 3 intake port. A wave of microporosity travels midway between the inner and outer surfaces of the casting was observed and was concluded to have caused the cracking. The reasons and remedies for shrinkage porosity were discussed. Controlled pouring temperatures, improved design and use of chills were recommended to avoid the casting defects.

The U-0.8wt%Ti alloy is often used in weapon applications where high strength and fairly good ductility are necessary. Components are immersion quenched in water from the gamma phase to produce a martensitic structure that is amenable to aging. Undesirable conditions occur when a component occasionally cracks during the quenching process, and when tensile specimens fail prematurely during mechanical testing. These two failures prompted an investigative analysis and a series of studies to determine the causes of the cracking and erratic behavior observed in this alloy. Quench-related failures whereby components that cracked either during or immediately after the heat treatment/quenching operation were sectioned for metallographic examination of the microstructure to examine the degree of phase transformation. Examination of premature tensile specimen failures by scanning electron microscopy and X-ray imaging of fracture surfaces revealed pockets of inclusions at the crack origins. In addition, tests were conducted to evaluate the detrimental effects of internal hydrogen on ductility and crack initiation in this alloy.

Some 99.90 pure tin tubes (0.15 mm thick) used for packaging a chemical compound cracked on bending and underwent brittle fracture prior to filling, while others remained ductile and showed no sign of failure. Examination showed that specimens prepared by mechanical methods such as electrolytic and hand polishing and the vibration method resulted in poor edge and crack edge definition due to material thickness. Etching experiments involved a grain surface attack and hence produced a rather strong surface relief from which the grain boundary cracks could again not clearly be differentiated. The sections were therefore examined unetched in polarized light. The microstructure of the cracked tubes was shown to have much smaller grains than the ductile and showed cracks from the surface down along the grain boundaries. Material hardness also differed between the unusable tubes and the ductile, and chemical analysis showed a higher level of aluminum in the brittle specimens. Failure obviously occurred due to the high material aluminum content that increased hardness which then caused embrittlement at the surface which led to cracks or fracture on bending. Since no explanation of how the aluminum entered the tin was available, no recommendations could be made.

A 75 cm OD x 33 mm thick pipe in a horizontal section of a hot steam reheat line ruptured after 15 years in service. The failed section was manufactured from rolled plate of material specification SA387, grade C. The longitudinal seam weld was a double butt-weld that was V-welded from both sides and failure was found to propagate along the longitudinal seam and its HAZ. The fracture surface near the inner wall of the pipe was found to have a bluish gray appearance, while the fracture surface near the outer wall was rust colored (oxides). The transverse-to-the-weld specimen from the longitudinal seam weld was revealed to have lower elongation and a shear type failure rather than the cup-cone failures. It was concluded that the welded longitudinal seam exhibited embrittlement. A low-ductility intergranular fracture that progressed through the weld metal was revealed by scanning electron microscopy. The cracks were revealed to be in existence for some time before the final failure which was indicated by the extent and amount of corrosion products. It was concluded that low ductility was responsible for the original initiation of cracks in the pipe.

Six wrist pins in a high-performance six-cylinder automotive engine failed after 4800 km (3000 mi) of normal operation. The pins were made of low-carbon steel that had been carburized both inside and outside. Two failed pins were examined. One had fractured into three pieces. The other had not fractured, but exhibited circumferential cracks on the surface of the central zone. Visual surface examination and metallographic and chemical analyses were performed on the specimens. Cracking was attributed primarily to poor heat treatment, resulting in a brittle grain-boundary network of cementite, and to a design that had a raised central section of the inner diameter whose fillets were locations of high stress concentration. Rough machining of the inner diameter and an excessively deep case also contributed to failure. A double type of heat treatment after carburizing and change of the design to eliminate the raised central section were recommended.

This article focuses primarily on what an analyst should know about applying X-ray diffraction (XRD) residual stress measurement techniques to failure analysis. Discussions are extended to the description of ways in which XRD can be applied to the characterization of residual stresses in a component or assembly. The article describes the steps required to calibrate instrumentation and to validate stress measurement results. It presents a practical approach to sample selection and specimen preparation, measurement location selection, and measurement depth selection, as well as an outline on measurement validation. The article also provides information on stress-corrosion cracking and corrosion fatigue. The importance of residual stress in fatigue is described with examples. The article explains the effects of heat treatment and manufacturing processes on residual stress. It concludes with a section on the XRD stress measurements in multiphase materials and composites and in locations of stress concentration.