Several newly developed liquid propane gas (LPG) cylinders made from Fe-0.13C-0.42Mn steel failed, each fracturing in the longitudinal direction. One of the cylinders was thoroughly analyzed to determine the cause. Deep-drawing flaws were observed on the inner wall of the cylinder, oriented in the direction of the fracture and roughly equal in length. Flaws about 1.3 mm deep, steps, and a chevron pattern were observed on the fractured surface as were cleavage facets, revealed by SEM. Hardness was relatively high and the microstructure near the fracture surface appeared elongated. In addition, the stress intensity factor KI calculated from the value of the internal pressure was lower than that estimated by the fracture toughness test. All of this suggests that the tanks were not sufficiently annealed and prone to brittle fracture. The analysis thus proves that cracks initiated by deep-drawing flaws were the primary cause of failure.

A helicopter tail rotor blade spar failed in fatigue, allowing the outer section of the blade to separate in flight. The 7075-T7351 aluminum alloy blade had fiberglass pockets. The blade spar was a hollow “D” shape, and corrosion pits were present on the inner surface of the hollow spar A single corrosion pit, 0.38 mm (0.015 in.) deep, led to a fatigue failure of the spar The failure initiated on the pylon side of the blade. Dimensional analysis of the spar near the failure revealed measurements within engineering drawing tolerances. Though corrosion pitting was present, there was an absence of significant amounts of corrosion product and all of the pits were filled with corrosion-preventative primer. This indicated that the pitting occurred during spar manufacture, prior to the application of the primer The pitting resulted from multiple nickel plating and defective plating removal by acid etching. Post-plating baking operations subsequently reduced the fatigue strength of the spar.

An AISI 4340 Ni-Cr-Mo alloy steel draw-in bolt and the collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after relatively long service life. Based on fracture surface features, it was suspected that the draw-in bolt was the first to fracture, followed by failure of the collet, which shattered one of its arms when it struck the work table. Scanning electron microscopy showed the presence of hairline crack indications along grain facets on the fracture surface of the bolt. This, coupled with stepwise cracking in the material, generally raised suspicion of hydrogen embrittlement. It appeared that fracture in service progressed transgranularly to produce delayed failure under dynamic loading. The pickling process used to remove heat scale was suspected to be the source of hydrogen on the surface of the bolt. The manufacturer was requested to change its cleaning practice from pickling to grit blasting.

The draw-in bolt and collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after a relatively long service life. The collet ejected at a high rotational speed due to loss of its vertical support and shattered one of its arms upon impact with the work table. SEM fractography and metallographic examinations conducted on the bolt revealed hairline indications along grain facets on the fracture surface and stepwise cracking in the material, both indicating failure by hydrogen embrittlement. Similar draw-in bolts were discarded and replaced with bolts manufactured using controlled processes.

Friction and wear are important when considering the operation and efficiency of components and mechanical systems. Among the different types and mechanisms of wear, adhesive wear is very serious. Adhesion results in a high coefficient of friction as well as in serious damage to the contacting surfaces. In extreme cases, it may lead to complete prevention of sliding; as such, adhesive wear represents one of the fundamental causes of failure for most metal sliding contacts, accounting for approximately 70% of typical component failures. This article discusses the mechanism and failure modes of adhesive wear including scoring, scuffing, seizure, and galling, and describes the processes involved in classic laboratory-type and standardized tests for the evaluation of adhesive wear. It includes information on standardized galling tests, twist compression, slider-on-flat-surface, load-scanning, and scratch tests. After a discussion on gear scuffing, information on the material-dependent adhesive wear and factors preventing adhesive wear is provided.

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.

One of the two AISI 4340 steel pitch horn bolts from the main rotor hub assembly failed while in service. Optical microscope revealed evidence of corrosion pitting in regions adjacent to the fracture. Fractographic examination utilizing a scanning electron microscope revealed multiple crack origins which assumed a “thumbnail” shape and displayed surface morphologies which resulted from intergranular decohesion. Many of the crack sites initiated from corrosion pits. Energy dispersive spectroscope performed on areas within the crack initiation site showed the presence of chlorides. The failure was attributed to stress-corrosion cracking. Short- and long-term recommendations to prevent future failures are given.

Steel pipes, used for years in a food factory soft water preheater, were found to leak as a result of corrosion. The pipes, made of 18/8 steel, were immersed in steam maintained at 0.5 atm and 150 deg C. They carried desalinated process water, heating it to approximately 100 deg C. Inspection revealed a reddish-brown coating on the outside of the pipe with a few flat pitting holes and incipient cracks. Corrosion was also observed on the inner walls of the pipe, consisting of rust patches with pitting scars, branching out to predominantly transcrystalline cracks. In this case, leaking appears to be the result of a combination of pitting and stress corrosion, most likely due to chlorides. The factory was recommended to use molybdenum-alloyed steels (type 18/10 or 18/12) which are more resistant to local disruption of passivating films and pitting than molybdenum-free types such as 18/8.

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

Alloy steel forgings used as structural members of a ski chair lift grip mechanism were identified to have contained forging laps (i.e., sharp-notched discontinuities) during an annual magnetic particle inspection of all chair lift grip structural members at a mountain resort. The material was confirmed to be 34Cr-Ni-Mo6. A heavy oxide on the dark area of one of the broken-open laps was revealed by scanning electron microscopy in conjunction with EDS. A bright area that contained ductile dimple rupture was observed adjacent to the dark area. The oxidized portion of the fracture was established to be the preexisting forging lap while the bright area was created during the breaking-open process. As a corrective action all forgings showing laps were recommended to be removed from service. Critical review and revision of the forging process and revisions to the nondestructive evaluation procedures at the forging supplier was recommended.

Visual examination, optical and scanning electron microscopy were used to determine the cause of failure in the connector groove of a marine riser coupling. The specified steel was AISI 4142 (0.40 to 0.45% C; 0.75 to 1.00% Mn; 0.20 to 0.35% Si; 0.80 to 1.10% Cr; 0.15 to 0.25% Mo) normalized from 9000C. Microscopic examination revealed the crack's initiation point and subsequent propagation. SEM examination of chemically stripped corrosion showed that corrosion fatigue and stress corrosion might have contributed to the initial slow crack growth. Impact tests revealed a fracture transition temperature in excess of 1000C. The sequence of events leading to failure was detailed. The main recommendation was to quench and temper existing couplings and to use a lower carbon quenched and tempered steel for new couplings.

The truck beam of the left main landing gear (MGL) of a Boeing 707 airplane collapsed on the ground just after the aircraft was unloaded and refueled. The investigation revealed that failure was caused by the propagation of an intergranular crack originating from the bottom of the pit. The crack reached the critical size and caused failure by stress-corrosion cracking (SCC) under static loading conditions in service. The failed beam was protected by a well adhering paint system. However, the presence of adequate amounts of corrosion preventive compound films (CPC) on the surfaces of the failed beam could not be conclusively established because of the long term service exposure and presence of lubricants.

Sheet forming failures divert resources from normal business activities and have significant bottom-line impact. This article focuses on the formation, causes, and limitations of four primary categories of sheet forming failures, namely necks, fractures/splits/cracks, wrinkles/loose metal, and springback/dimensional. It discusses the processes involved in analytical tools that aid in characterizing the state of a formed part. In addition, information on draw panel analysis and troubleshooting of sheet forming failures is also provided.

Postflight inspection of a gas-turbine aircraft engine that had experienced compressor stall revealed that the engine air-intake bullet assembly had dislodged and was seated against the engine-inlet guide vanes at the 3 o'clock position. The bullet assembly consisted of an outer aerodynamic shell and an inner stiffener shell, both of 1.3 mm (0.050 in.) thick aluminum alloy 6061-T6, and four attachment clips of 1 mm (0.040 in.) thick alclad aluminum alloy 2024-T42. Each clip was joined to the outer shell by 12 spot welds and was also joined to the stiffener. Analysis (visual inspection, dye-penetrant inspection, and 10x/150x micrographs of sections etched with Keller's reagent) supports the conclusion that the outer shell of the bullet assembly separated from the stiffener because the four attachment clips fractured through the shell-to-clip spot welds. Fracture occurred by fatigue that initiated at the notch created by the intersection of the faying surfaces of the clip and shell with the spot weld nuggets. The 6061 aluminum alloy shell and stiffener were in the annealed (O) temper rather than T6, as specified. Recommendations included heat treating the shell and stiffener to the T6 temper after forming.

Microstructure, corrosion, and fracture morphologies of prestressed steel wires that failed in service on concrete siphons at the Central Arizona Project (CAP) are discussed. The CAP conveys water for municipal, industrial, and agricultural use through a system of canals, tunnels, and siphons from Lake Havasu to just south of Tucson, AZ. Six siphons were made from prestressed concrete pipe units 6.4 m (21 ft) in diam and 7.7 m long, making them the largest circular precast structures ever built. The pipe was manufactured on site and consisted of a 495-mm thick concrete core, wrapped with ASTM A648 steel prestressing wire. All of the CAP failures evaluated were attributed to corrosion. Longitudinal splits reduced the service life of the pipe significantly by facilitating corrosion and introducing sharp cracks into the microstructure of the wire. A few failures were attributed to general corrosion, where the cross section of the wire is reduced until the strength of the wire is exceeded. Most of the failures evaluated were attributed to stress-corrosion cracking.

After a quick-release fitting of an ejection seat broke, an investigation was performed to determine the manner and cause of crack propagation. Most fractography-based investigations aim to characterize only qualitative characteristics, such as the fracture orientation and origin position, topology, and details of interactions with microstructural features. The aim of this investigation was to use quantitative fractography as a tool to extract information, including striation spacing and size of the stretched zone, in order to make a direct correlation with fracture mechanic concepts. As the crack propagated, striations were created on the fracture surface as a result of service-induced load changes. The size of the striations were measured to estimate crack propagation rate. Remaining lifetime estimates were also made. The dimensions of plastically stretched zones found at the tips of the cracks were evaluated using electron micrograph stereo image pairs to characterize local fracture toughness. To complete the failure analysis, nondestructive evaluation, metallographic examination, and chemical investigations were carried out. No secondary cracks could be found. Most of the broken parts showed that the microstructure, the hardness, and the chemical composition of the Al-alloy were within the specification, but some of the cracked parts were manufactured using a different material than that specified.