Personnel responsible for laboratory protection at some plants are required to participate in exercises simulating a breach of security at the site. This document reports a metallurgical investigation of blank firing adapters (BFA), one of which exploded during such a training exercise. Determination of the cause of the explosion was the primary objective of the examination. Metallographic studies included the examination of BFAs fabricated from two different types of alloys that were tested for shock reaction. Optical microscopy supported by electron microscopy and analytical methods were used. Our investigation supports the supposition that a live round of ammunition was inadvertently fired.

To forged AISI 4140 steel trailer kingpins fractured after 4 to 6 months of service. Fractographic and metallographic examination revealed that cracks were present in the spool-flange shoulder region of the defective kingpins prior to installation on the trailers. The cracks grew and coalesced during service. Consideration of the manufacturing process suggested that the cracks were the result of overheating of the kingpin blanks prior to forging, which was exacerbated during forging by deformation heating in the highly-strained region. This view was supported by results of two types of tensile tests conducted near the incipient melting temperature at the grain boundaries. All kingpins made by the supplier of the fractured ones were ultrasonically inspected and six more anticipated to fail were found. It was recommended that the heating of forging blanks be more carefully controlled, especially with respect to the accuracy of the optical pyrometer temperature readout. Also, procedures must be developed such that forging blanks that trigger the over-temperature alarm are reliably and permanently removed from the production line.

A 6150 flat spring was found to be failed. The face of the spring was revealed to be under tensile stress. The failure was concluded to have begun at the dark spot on the edge where roughness resulted from shearing during the blanking operation.

The pawl spring which was part of a selector switch used in telephone equipment failed. The springs were blanked from 0.4 mm (0.014 in.) thick tempered 1095 steel and then nickel plated. Numerous pits around the rivet holes were revealed by microscopic examination of longitudinal specimens. Delaminations that were formed at inclusion sites during punching of the rivet holes and that were filled with nickel during the plating operation were revealed by microscopic examination of the rivet hole. These delaminations were interpreted to have acted as stress raisers and initiated the fracture. Long, narrow sulfide stringers which were the probably the cause of delamination in this spring material were revealed in the raw material used to make the springs. It was concluded that fracture of the springs was caused by fatigue that had originated at delaminations around the rivet holes.

Pressure testing of a batch of AISI type 316L stainless steel thermowells intended for use in a nuclear power-plant resulted in the identification of leakage at the tips in 20% of the parts. Radiography at the tip region of representative thermowells showed linear indications along the axes. SEM examination revealed the presence of longitudinally oriented nonmetallic inclusions that were partly retained and partly dislodged. Electron-dispersive x-ray analysis indicated that the inclusions were composed of CaO. Based on the overall chemistry of the inclusion sites, the source of the CaO was determined to be slag entrapment during the steel making process. It was recommended that the thermowell blanks be ultrasonically tested prior to machining and that the design be modified to make internal pressurization possible.

Electrical contact-finger retainers blanked and formed from annealed copper alloy C65500 (high-silicon bronze A) failed prematurely by cracking while in service in switchgear aboard seagoing vessels. In this service they were sheltered from the weather but subject to indirect exposure to the sea air. About 50% of the contact-finger retainers failed after five to eight months of service aboard ship. Investigation (visual inspection, 250x images etched with equal parts NH4OH and H2O2, emission spectrographic analysis, and stereoscopic views) supported the conclusion that the cracking was produced by stress corrosion as the combined result of: residual forming and service stresses; the concentration of tensile stress at outer square corners of the pierced slots; and preferential corrosive attack along the grain boundaries as a result of high humidity and occasional condensation of moisture containing a fairly high concentration of chlorides (seawater typically contains about 19,000 ppm of dissolved chlorides) and traces of ammonia. Recommendations included redesign of the slots, shot-blasting the formed retainers, and changing the material to a different type of silicon bronze-copper alloy C64700.

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.

Macrofractographs of the fracture surface from a multibladed fan showed that cracks started at the corner where bending stress was concentrated and propagated through the blade by fatigue. Peak stress at the monitoring position was less than 10 MPa. To simulate crack growth, the rotor was repeatedly deformed by a hydraulic fatigue tester. Comparison of striations of the failed blade with that of the tested one revealed the failed blade was loaded with more than 30 MPa of stress. These tests confirmed that the rotor and blades had sufficient strength to withstand up to 3x the stress of normal operation. The casing of the fan was vibrated at 10 to 60 Hz. Peak stress easily overcame 30 MPa, which was enough to initiate cracking. The fracture surfaces and starting position were the same as those on the failed fan. It was concluded that the exciting force from an air compressor caused blade failure.

Two outboard main-wheel halves (aluminum alloy 2014-T6 forged) from a commercial aircraft were removed from service because of failure. One wheel half was in service for 54 days and had made 130 landings (about 1046 roll km, or 650 roll mi) when crack indications were discovered during eddy-current testing. The flange on the second wheel half failed after only 31 landings, when about 46 cm (18 in.) of the flange broke off as the aircraft was taxiing. Stains on the fracture surfaces were used to determine when cracking was initiated. The analysis (visual inspection, liquid penetrant inspection, and micrographs with deep etching in aqueous 20% sodium hydroxide) supported the conclusion that failure on both wheel halves was by fatigue caused by a forging defect resulting from abnormal transverse grain flow. The crack in the first wheel half occurred during service, and the surfaces became oxidized. Because the fracture surface of the second wheel half had chromic acid stains, it was obvious that the forging defect was open to the surface during anodizing. No recommendations were made except to notify the manufacturer.

This article describes the six fundamental factors that decide a tool's performance. These are mechanical design, grade of tool steel, machining procedure, heat treatment, grinding, and handling. A deficiency in any one of the factors can lead to a tool and die failure. The article presents a seven-step procedure to be followed when looking for the reason for a failure. A review of the results of the seven-point investigation may lead directly to the source of failure or narrow the field of investigation to permit the use of special tests.