A stuffing box (sand cast from ASTM A 536, grade 60-45-10, ductile iron) began leaking water after two weeks of service. The machine was operating at 326 rpm with a discharge water pressure of 21.4 MPa (3100 psi). Investigation (visual inspection, mechanical analysis, and nital etched 100x magnification) supported the conclusion that the crack initiated at the inner edge of a lubrication hole and had propagated toward both the threaded and flange ends of the casting. An appreciable residual-stress concentration must have been present and caused propagation of the crack. The residual stress might have been caused when a fitting was tightly screwed into the lubrication hole, and it might have been concentrated by notches at the inner end of the hole created when the drill broke through the sidewall to the stuffing box.

The A2 tool steel mandrel, part of a rolling tool used for mechanically joining two tubes was fractured after making five rolled joints. A 6.4 mm diam hole was drilled by EDM through the square end of the hardened mandrel due to difficulty was experienced in withdrawing the tool. The fracture progressed into the threaded section and formed a pyramid-shape fragment after it was initiated at approximately 45 deg through the hole in the square end. An irregular zone of untempered martensite with cracks radiating from the surface of the hole (result of melting around hole) was revealed by metallographic examination. A microstructure of fine tempered martensite containing some carbide particles was exhibited by the core material away from the hole. Brittle fracture characteristics with beach marks were exhibited by the fracture surfaces which is characteristic of a torsional fatigue fracture. As a corrective measure, the hole through the square end of the mandrel was incorporated into the design of the tool and was drilled and reamed before heat treatment and specified hardness of the threaded portion and square end of the mandrel was reduced.

A sledge hammer chipped during use. The chip struck a by stander in the eye, leading to its loss. The hammerhead surface was examined visually, nondestructively (magnetic particle method), and stereo microscopically, and a microstructural analysis of a cross section of the head was conducted using optical microscope. Chemical composition of the hammerhead was determined by emission spectrometry. The chemical compositions of the chip and hammer head were compared using energy-dispersive analysis. Microhardness versus distance from the striking face was also determined. The hammerhead material was UNS G10800 (AISI/SAE grade 1080). Excessive hardnesses were measured in the first 3 mm (0. 12 in.) below the striking surface, indicating that there was lack of control during the final tempering operation.

This paper summarizes the results of a failure analysis investigation of a fractured main support bridge made of 7075 aluminum alloy from an army helicopter. The part, manufactured by “Contractor IT,” failed component fatigue testing while those of the original equipment manufacturer (OEM) passed. Metallurgical data collected during this investigation indicated that the difference in fatigue life between the components fabricated by IT and by OEM may be attributable to a difference in dimensions at the web where fatigue crack initiation occurred. The webs of the two OEM parts examined had cross-sectional thicknesses significantly larger than the web cross-sectional thicknesses of the IT components. Recommendations included changing the web reference dimension of 0.38 in. to include a tolerance range based upon a fracture mechanics model. Also, the shot peening process should be controlled especially at the critical areas of the web, to assure complete coverage and proper compressive residual stresses.

Two AISI type 316 stainless steel components intended for use in a reducer section for sodium piping in a fast breeder test reactor were found to be severely corroded—the first soon after pickling, and the second after passivation treatments. Metallographic examination revealed that one of the components was in a highly sensitized condition and that the pickling and passivation had resulted in severe intergranular corrosion. The other component was fabricated from thick plate and, after machining, the outer surface represented the transverse section of the original plate. Pickling and passivation resulted in severe pitting because of end-grain effect. Strict control of heat treatment parameters to prevent sensitization and modification of pickling and passivating conditions for machined components were recommended.

The source of cracking in the circumferential weld seam in a JIS-SM50B carbon-manganese steel pipe used in a CO2 absorber was investigated, the absorber had been in service for 18 years. The seam had been weld-repaired twice, and the repair welds had been locally stress relieved. Longitudinal seams in the same vessel, which had been stress relieved in a furnace, showed no tendency toward cracking. The solution passing through the vessel contained CO2-CO-H20, KHCO, and Cl− ions. Nondestructive testing revealed that the cracks originated in the heat-affected zone and propagated into the base metal and weld. Severe branching of the cracks characteristic of stress-corrosion cracking was observed. Microexamination revealed that crack propagation was transgranular further supporting the possibility of stress-corrosion cracking. Simulation tests carried out in the vessel confirmed this mode of cracking. It was recommended that weld seams be furnace heat treated at a temperature of 600 to 640 deg C (1110 to 1180 deg F) for a minimum of 1 h per inch of section thickness.

Failure analysis was performed on threaded Ti-6Al-4V fasteners that had fractured in the threads during installation. Scanning electron microscopy (SEM) and optical metallography revealed that the fractures initiated in circumferential shear bands present at the thread roots. The fractures propagated by microvoid coalescence typical of that observed in notched tensile specimen fractures of the same material. For comparison, Ti-6Al-4V fasteners from various commercial sources were tested to failure in uniaxial tension and examined in the SEM. In all cases, the fracture appearances were similar to that exhibited by the fasteners that failed during installation. In addition, results of optical microscopy indicated that the geometry and extent of the shear bands appeared to depend on the fabrication process employed by the individual manufacturers. Causes of shear band formation are discussed along with potential methods to eliminate these microstructural in homogeneities.

The cause of the fatigue failure in the retaining ring of the compressor region of an aero-engine turbine was found to be the presence of a high concentration of nonmetallic inclusions. The results of chemical analysis were used to estimate the phases present. The most frequently observed inclusions were spinel solid solutions of the type MO middot; N2O3, where M = Fe, Mn, or Mg and N = Cr or Al. The detrimental inclusions were corundum, calcium aluminates, cristobalite, and silicates. The most detrimental phases were traced on the surfaces of the specimens fractured using impact loading; the comparison is being made with the polished surfaces and the tensile specimen fracture surfaces. The inclusions in the failed retaining ring were compared with the ones in a similar component obtained from a used engine. In the case of the latter, a large number of fine and elongated (Mn, Cr, Fe)S inclusions were present along with spinels. The nondeformable, rigid oxide particles are considered more undesirable than the sulfides as far as fatigue life of the component is concerned. It has been reported that the presence of sulfides may eliminate the stresses due to oxides.

The repeated failure of a welded ASTM A283 grade D pipe that was part of a 6 km (4 mi) line drawing and conducting river water to a water treatment plant was investigated. Failure analysis was conducted on sections of pipe from the third failure. Visual, macrofractographic, SEM fractographic, metallographic, chemical, and mechanical property (tension and impact toughness) analyses were conducted. On the basis of the tests and observations, it was concluded that the failure was the combined result of poor notch toughness (impact) properties of the steel, high stresses in the joint area, a possible stress raiser at the intersection of the spiral weld and girth weld, and sudden impact loading, probably due to water hammer. Use of a semi- or fully killed steel with a minimum Charpy V-notch impact value of 20 J (15 ft·lbf) at 0 deg C (32 deg F) was recommended for future water lines. Certified test results from the steel mill, procedure qualification tests of the welding, and design changes to reduce water hammer were also recommended.

This article briefly reviews the analysis methods for spalling of striking tools with emphasis on field tests conducted by A.H. Burn and on the laboratory tests of H.O. McIntire and G.K. Manning and of J.W. Lodge. It focuses on the metallography and fractography of spalling. The macrostructure and microstructure of spall cavities are described, along with some aspects of the numerous specifications for striking/struck tools. The article also describes the availability of spall-resistant metals and the safety aspects of striking/struck tools in railway applications.

Impact or percussive wear is defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another body. Impact wear, however, has many analogies to the field of erosive wear. The main difference is that, in impact wear situations, the bodies tend to be large and contact in a well-defined location in a controlled way, unlike erosion where the eroding particles are small and interact randomly with the target surface. This article describes some generic features and modes of impact wear of metals, ceramics, and polymers. It discusses the processes involved in testing and modeling of impact wear, and includes two case studies.

A catastrophic brittle fracture occurred in a welded steel (ASTM A517 grade H) trapezoidal cross-section box girder while the concrete deck of a large bridge was being poured. The failure occurred across the full width of a 57 mm (2 1 4 in.) thick, 760 mm (30 in.) wide flange and arrested 100 mm (4 in.) down the slant web. Failure analysis revealed a major deficiency in fracture toughness. The failure occurred as a brittle fracture after the formation of a welding hot crack and approximately 40 mm (1 1 2 in.) of slow crack growth. It was recommended that bridges fabricated from this grade of steel undergo frequent inspection and that stringent test requirements be imposed as a condition of use in non-redundant main load-carrying components.

This article discusses the thermal properties of engineering plastics and elastomers with respect to chemical composition, chain configuration, and base polymer conformation as determined by thermal analysis. It describes the processing of base polymers with or without additives and their response to chemical, physical, and mechanical stresses whether as an unfilled, shaped article or as a component of a composite structure. It summarizes the basic thermal properties of thermoplastics and thermosets, including thermal conductivity, temperature resistance, thermal expansion, specific heat, and glass transition temperature. It also provides information on polyimide and bismaleimide resin systems. Representative examples of different types of engineering thermoplastics are discussed primarily in terms of structure and thermal properties.

Erosion occurs as the result of a number of different mechanisms, depending on the composition, size, and shape of the eroding particles; their velocity and angle of impact; and the composition of the surface being eroded. This article describes the erosion of ductile and brittle materials with the aid of models and equations. It presents three examples of erosive wear failures, namely, abrasive erosion, erosion-corrosion, and cavitation erosion.

This article discusses the most common thermal analysis methods for thermosetting resins. These include differential scanning calorimetry, thermomechanical analysis, thermogravimetric analysis, and dynamic mechanical analysis. The article also discusses the characterization of uncured thermosetting resins as well as the curing process. Then, the techniques to characterize the physical properties of cured thermosets and composites are presented. Several examples of stress-strain curves are shown for thermosets and thermoplastic polymers.

Flow forming technology has emerged as a promising, economical metal forming technology due to its ability to provide high strength, high precision, thin walled tubes with excellent surface finish. This paper presents experimental observations of defects developed during flow forming of high strength SAE 4130 steel tubes. The major defects observed are fish scaling, premature burst, diametral growth, microcracks, and macrocracks. This paper analyzes the defects and arrives at the causative factors contributing to the various failure modes.