A drawbar connecting two tank-type trailers of a highway gasoline rig broke while the rig was on an exit ramp of an interstate highway. The drawbar was a weldment of steel plates, tubes, and castings. Light fractography showed no discernable causes for the failure, but a TEM fractograph at 20,000x revealed fatigue striations and corrosion products on the fracture surface, indicating that this area was probably the site of fracture origin and that it had cracked before the accident happened. The casting on the right side of the drawbar contained large voids and a significant amount of porosity. Electron fractography established that the cast connection on the left side failed by brittle fracture. Metallographic examination showed poor weld quality in the casting-to-tube joint. Evidence found supports the conclusions that the drawbar fractured in fatigue, which originated in the weld joining the cast connector to the right side of the drawbar assembly. The crack initiated in a region of poor weld quality. A contributing factor to fracture of both connectors was the presence of voids and porosity in the castings. Recommendations included revising the welding procedures and instituting receiving inspection of the connection castings.

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.

The interior surface of a type 316L stainless steel trailer barrel used to haul various chemicals showed evidence of severe pitting after less than 1 year of service. Two sections were cut from the barrel and microscopically examined. Metallographic sections were also prepared at the weld areas and away from the weld zones. Terraced, near-surface pits with subsurface caverns and a high level of sulfur in the pit residue, both indicative of bacteria-induced corrosion, were found. No evidence of weld defects or defective material was present. Testing of the water used at the wash station and implementation of bacteria control measures (a special drying process after washing and use of a sanitizing rinse) were recommended.

A supplementary axle, which was used as an extension to a highway-trailer tractor to increase its load-bearing capacity, failed in service. The rolled steel channel extensions that secured the axle assembly to the tractor main-frame I-beams fractured transversely, with the crack in each instance initiating at a weld that joined the edge of the lower flange to the support bracket casting. The cracks propagated through the flange on each side until the effective cross-sectional area had been reduced sufficiently to bring about sudden and complete fracture of the remaining web and upper flange. Fatigue fracture was caused by a combination of high bending stresses in the bottom flanges of the channels due to the heavy load being carried, concentration of stresses due to the rapid change in section modulus of the channel at its point of attachment to the support-bracket casting, and brittleness of the high-hardness HAZ of the weld associated with the abnormally high carbon content in the central part of the channel. Welding of channel edges contributed to harmful gradients in section moduli and should be avoided in future assemblies.

The rear outside wheel of an over-the-road 18-wheel tractor-trailer failed at its bolt holes, permitting the tire and wheel to separate from the hub. Failure analysis was conducted using photographic examination of actual fracture surfaces and SEM examination of fracture replicas. The examinations indicated that fatigue cracks had originated at the rim backside and propagated to the rim midsection. Catastrophic failure occurred at a final overland. Fatigue fracture of the wheel rim was attributed to cyclic loading created by improper wheel mounting of a spare tire.

A double-flange trailer wheel, in service on a coke-oven pusher car for about five years, broke. Specifications called for rolled steel track wheels conforming to ASTM A 186 (since reclassified as A 504). Chemical analysis showed the metal in the wheel to be medium-carbon steel within the ranges given in ASTM A 186. Visual examination of the broken wheel revealed that cracks ran parallel with the base of the lower row of numbers stamped with heavy indentation on the web section. Microscopic examination showed the metal in the web, rim, and tread to be in the normalized condition. Evidence found supports the conclusions that fatigue failure of the wheel was the result of heavy stamp marks that acted as stress raisers in the weaker web section. Because this was a double-flange wheel, considerable side thrust was applied to the wheel, causing stress concentration at the web. Recommendations included following the ASTM specification A 504 regarding location of stamped identification numbers (marks identifying the wheels must be stamped on the back face of the rim not less than 3.2 mm from the inner edge of the rim).

Each of the ten studs on one wheel of a semitrailer used to haul coal broke in half while the trailer was in operation. Both halves of each of three studs were sent to the laboratory to determine the cause of failure. Visual examination of the fracture surfaces of the studs disclosed beach marks, indicative of fatigue cracking, starting at opposite sides of each stud, with final fracture occurring across the stud. Each failure occurred in the first thread of the stud. It was concluded that the wheel studs fractured by reversed-bending fatigue. To minimize the possibility of a recurrence, the wheel nuts were tightened with an air impact wrench to a torque of 610 to 678 J (450 to 500 ft · lb) dry. All wheel studs were checked at normal maintenance periods to ensure uniform and proper loading, and no further failures occurred.

The right front spring hanger on a dual rear axle of the tractor of a tractor-trailer combination failed, causing the vehicle to roll-over. The hanger was made from malleable cast iron that had been heat treated to produce a decarburized surface layer and a pearlitic transition layer. It had been repair welded after breaking into two pieces longitudinally in a prior incident, using cast iron as weld metal. The repair weld bead on both surfaces missed the fracture over 15 to 20% of their lengths. The incomplete repair weld and brittleness of the weld metal and heat-affected zones led to the failure.

The working fluid of a hypersonic wind tunnel is freon 14 heated in molten-metal-bath heat exchangers. The coils of the heaters have failed several times from various causes. They have been replaced each time with a stainless steel deemed more appropriate, but they continue to fail. In this case study, the history of failures is traced, the causes are analyzed, and recommendations are made for future design and maintenance. Coils fabricated from AISI 316 should provide satisfactory service life if reasonable precautionary measures are observed during maintenance and testing.

This article provides assistance to a failure analyst in broadening the initial scope of the investigation of a physical engineering failure in order to identify the root cause of a problem. The engineering design process, including task clarification, conceptual design, embodiment design, and detail design, is reviewed. The article discusses the design process at the personal and project levels but takes into consideration the effects of some higher level influences and interfaces often found to contribute to engineering failures.

The intent of this article is to assist the failure analyst in understanding the underlying engineering design process embodied in a failed component or system. It begins with a description of the mode of failure. This is followed by a section providing information on the root cause of failure. Next, the article discusses the steps involved in the engineering design process and explains the importance of considering the engineering design process. Information on failure modes and effects analysis is also provided. The article ends with a discussion on the consequence of management actions on failures.

Failure analysis of a mobile harbor crane wheel hub that included SEM and EDS analyses demonstrated that the mechanism of failure was fatigue. The wheel hub was a ductile cast iron component that had been subjected to cyclic loading during a ten-year service period. The fracture surface of the fatigue failure also contained corrosion deposit, suggesting that cracking occurred over a period of time sufficient to allow corrosion of the cracked surfaces. Replacement and alignment of the failed wheel hub was recommended along with inspection of the nonfailed wheel hubs that remained on the crane.

This paper describes the remote ultrasonic (UT) examinations of a high-level radioactive waste storage tank at the Savannah River Site in South Carolina. The inspections, carried out by E.R. Holland, R.W. Vande Kamp, and J.B. Elder, were performed from the contaminated, annular space of the 46 year old, inactive, 1.03 million gallon waste storage tank. A steerable, magnetic wheel wall crawler was inserted into the annular space through small (6 in., or 150 mm, diam) holes/risers in the tank top. The crawler carried the equipment used to simultaneously collect data with up to four UT transducers and two cameras. The purpose of this inspection was to verify corrosion models and to investigate the possibility of previously unidentified corrosion sites or mechanisms. The inspections included evaluation of previously identified leak sites, thickness mapping, and crack detection scans on specified areas of the tank. No indications of reportable wall loss or pitting were detected. All thickness readings were above minimum design tank-wall thickness, although several small indications of thinning were noted. The crack detection and sizing examinations revealed five previously undetected indications, four of which were only partially through-wall. The cracks that were examined were found to be slightly longer than expected but still well within the flaw size criteria used to evaluate tank structural integrity.

During the installation of power transmission lines across a major interstate highway, a temporary anchor stabilizing one of the poles failed, resulting in the loss of the pole and the associated power lines. It also contributed to a single vehicle incident on the adjacent roadway. Post-failure analysis revealed that the fracture was precipitated by a preexisting weld-related crack. Closed form and numerical stress analyses were also conducted, with the results indicating that the anchor was installed properly within the parameters intended by the manufacturer.