A forging die in a 250-ton press producing brass valves began to show signs of fatigue after a few thousand hits. By the time it reached 30,000 hits, the die was badly damaged and was submitted for analysis along with one of the last forgings produced. The investigation included visual and macroscopic inspection, metallographic and chemical analysis, SEM imaging, optical profilometry, mechanical property testing, and EDX analysis. The die was made of chromium hot-work tool steel and the forgings were made of CuZn39Pb3 heated to an initial working temperature 700 deg C. The entire surface of the die was covered with fatigue cracks and many fillets had been plastically deformed. Several other types of damage were also observed, including areas of oxidation, corrosion pits, voids, abrasive wear, die adhesion, and thermal fatigue. Fatigue cracking was the primary cause of failure with significant contributions from the other damage mechanisms.

The torque-arm assembly (aluminum alloy 7075-T73) for an aircraft nose landing gear failed after 22,779 simulated flights. The part, made from an aluminum alloy 7075-T73 forging, had an expected life of 100,000 simulated flights. Initial study of the fracture surfaces indicated that the primary fracture initiated from multiple origins on both sides of a lubrication hole that extended from the outer surface to the bore of a lug in two cadmium-plated flanged bushings made of copper alloy C63000 (aluminum bronze) that were press-fitted into each bored hole in the lug. Sectioning and 2x metallographic analysis showed small fatigue-type cracks in the hole adjacent to the origin of primary fracture. Hardness and electrical conductivity were typical for aluminum alloy 7075. This evidence supported the conclusion that the arm failed in fatigue cracking that initiated on each side of the lubrication hole since no material defects were found at the failure origin. Recommendations included redesign of the lubrication hole, shot peeing of the faces of the lug for added resistance to fatigue failure, and changing of the forging material to aluminum alloy 7175-T736 for its higher mechanical properties.

The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

An octagonal steel ingot weighing 13 tons made of manganese-molybdenum steel developed gaping cross-cracks on all eight sides in the forging press during initial pressure application. It was reported that the steel had been melted in a basic 12-ton arc furnace, oxygenated, furnished with 42 kg of 75% ferrosilicon and 12 kg aluminum additions, alloyed with 160 kg of 80% ferromanganese, and finally deoxidized in the ladle with 42 kg calcium silicon. For metallographic examination a plate approximately 100 mm thick was cut parallel to one of the eight planes. Platelet-like particles could be discerned on the conchoidal fracture planes with the SEM. The precipitates proved to be thin and partially transparent platelets of a hexagonal crystal lattice whose parameters resemble those of AIN. The precipitates were at least in part still undissolved in spite of the long holding period at high initial forging temperature. Another block melted under the same conditions and immediately after the defective one, was forged into a gear ring without any trouble. This ring was free of grain boundary precipitates, but it contained only 0.012 % AI and 0.0102 % N.

Forged austenitic steel rings used on rotor shafts in two 100,000 kW generators burst from overstressing in a region of ventilation holes. A variety of causes contributed to the brittle fractures in the ductile austenitic alloy, including stress concentration by holes, work hardened metal in the bores, and a variable pattern of residual stress.

This article discusses failures in shafts such as connecting rods, which translate rotary motion to linear motion, and in piston rods, which translate the action of fluid power to linear motion. It describes the process of examining a failed shaft to guide the direction of failure investigation and corrective action. Fatigue failures in shafts, such as bending fatigue, torsional fatigue, contact fatigue, and axial fatigue, are reviewed. The article provides information on the brittle fracture, ductile fracture, distortion, and corrosion of shafts. Abrasive wear and adhesive wear of metal parts are also discussed. The article concludes with a discussion on the influence of metallurgical factors and fabrication practices on the fatigue properties of materials, as well as the effects of surface coatings.

In addition to failures in shafts, this article discusses failures in connecting rods, which translate rotary motion to linear motion (and conversely), and in piston rods, which translate the action of fluid power to linear motion. It begins by discussing the origins of fracture. Next, the article describes the background information about the shaft used for examination. Then, it focuses on various failures in shafts, namely bending fatigue, torsional fatigue, axial fatigue, contact fatigue, wear, brittle fracture, and ductile fracture. Further, the article discusses the effects of distortion and corrosion on shafts. Finally, it discusses the types of stress raisers and the influence of changes in shaft diameter.

The large steel ring produced for a nuclear application from a billet of 8822 steel was inspected. The large billet was first forged into a doughnut preform in a large press, and then formed into the ring by ring rolling. A straight-beam ultrasonic inspection was instituted and calibrated using the back-surface-reflection method to determine whether adequate ultrasonic penetration was available. Areas of indications were noted at approximately midheight and adjacent to the bore area. An axial angle-beam inspection from the outside was performed, mainly in the area of indications to reveal detectable indications. The indications were not considered serious enough to reject the forgings. A few small indications in the areas tested were revealed by magnetic particle inspection. The area was conditioned by grinding and polishing to obtain an additional inspection at a greater depth from the inside surface. A much more severe condition was revealed after the test. The indications were classified as areas of chemical segregation and nonmetallic inclusions. The ring was considered unsatisfactory for the application and replacement of the defective ring from an acceptable billet was the most economical solution.

This article briefly introduces the concepts of failure analysis and root cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It reviews four fundamental categories of physical root causes, namely, design deficiencies, material defects, manufacturing/installation defects, and service life anomalies, with examples. The article describes several common charting methods that may be useful in performing an RCA. It also discusses other failure analysis tools, including review of all sources of input and information, people interviews, laboratory investigations, stress analysis, and fracture mechanics analysis. The article concludes with information on the categories of failure and failure prevention.

Because of the tough engineering environment of the railroad industry, fatigue is a primary mode of failure. The increased competitiveness in the industry has led to increased loads, reducing the safety factor with respect to fatigue life. Therefore, the existence of corrosion pitting and manufacturing defects has become more important. This article presents case histories that are intended as an overview of the unique types of failures encountered in the freight railroad industry. The discussion covers failures of axle journals, bearings, wheels, couplers, rails and rail welds, and track equipment.

Mechanical testing is an evaluative tool used by the failure analyst to collect data regarding the macro- and micromechanical properties of the materials being examined. This article provides information on a few important considerations regarding mechanical testing that the failure analyst must keep in mind. These considerations include the test location and orientation, the use of raw material certifications, the certifications potentially not representing the hardware, and the determination of valid test results. The article introduces the concepts of various mechanical testing techniques and discusses the advantages and limitations of each technique when used in failure analysis. The focus is on various types of static load testing, hardness testing, and impact testing. The testing types covered include uniaxial tension testing, uniaxial compression testing, bend testing, hardness testing, macroindentation hardness, microindentation hardness, and the impact toughness test.

This article provides an overview of the effects of various material- and process-related parameters on residual stress, distortion control, cracking, and microstructure/property relationships as they relate to various types of failure. It discusses phase transformations that occur during heat treating and describes the metallurgical sources of stress and distortion during heating and cooling. The article summarizes the effect of materials and the quench-process design on distortion and cracking and details the effect of cooling characteristics on residual stress and distortion. It also provides information on the methods of minimizing distortion and tempering. The article concludes with a discussion on the effect of heat treatment processes on microstructure/property-related failures.

Copper electrical feedthrough pins used in a bolting application in a refrigeration compressor had functioned without failure for years of production and thousands of units. When some of the pins began to fail, an investigation was conducted to determine the cause. Visual examination revealed that the observed fractures were mixed brittle intergranular with ductile microvoid dimples. An extensive analysis of failed samples combined with a process of elimination indicated that the fractures were due to stress-corrosion cracking caused by an unidentified chemical species within the sealed compressor chamber. A unique combination of applied stress, residual stress, stress riser, and grain size helped isolate the failure mechanism to a single production lot of material.

This article briefly introduces the concepts of failure analysis, including root-cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It initially provides definitions of failure on several different levels, followed by a discussion on the role of failure analysis and the appreciation of quality assurance and user expectations. Systematic analysis of equipment failures reveals physical root causes that fall into one of four fundamental categories: design, manufacturing/installation, service, and material, which are discussed in the following sections along with examples. The tools available for failure analysis are then covered. Further, the article describes the categories of mode of failure: distortion or undesired deformation, fracture, corrosion, and wear. It provides information on the processes involved in RCA and the charting methods that may be useful in RCA and ends with a description of various factors associated with failure prevention.

During the lifting of a piece of machinery by means of an overhead travelling crane the hook fractured suddenly. The load was attached to the hook by means of fiber rope slings and rupture occurred in a plane which appeared to coincide with the sling loop nearest to the back of the hook. The rated capacity of the crane was 15 tons. At the time of the mishap it was being used to lift one end of a hydraulic cylinder with a total weight of about 27 tons. Fracture was of the cleavage type throughout. There was no evidence of any prior deformation of the material in the vicinity, nor was there any indication of a pre-existing crack or major discontinuity at the point of origin. A sulfur print suggested the hook had been forged from a billet cogged down from an ingot of semi-killed steel. Failure of this hook was attributed to strain-age embrittlement of the material at the surface of the intrados.

Despite extensive aircraft landing gear design analyses and tests performed by designers and manufacturers, and the large number of trouble-free landings, aircraft users have experienced problems with and failures of landing gear components. Different data banks and over 200 failure analysis reports were surveyed to provide an overview of structural landing gear component failures as experienced by the Canadian Forces over the last 20 years on more than 20 aircraft types, and to assess trends in failure mechanisms and causes. Case histories were selected to illustrate typical problems, troublesome failure mechanisms, the role of high strength aluminum alloys and steels, and situations where fracture mechanics analyses provided insight into the failures. The two main failure mechanisms were: fatigue occurring mainly in steel components, and corrosion related problems with aluminum alloys. Very few overload failures were noted. A number of causes were identified: design deficiencies and manufacturing defects leading mainly to fatigue failures, and poor materials selection and improper maintenance as the principal causes of corrosion-related failures. The survey showed that a proper understanding of the failure mechanisms and causes, by thorough failure analysis, provides valuable feedback information to designers, operators and maintenance personnel for appropriate corrective actions to be taken.

This case study involves two continuously cast steel crankshaft failures. Three parties performed their own failure analyses: (1) the engine manufacturer responsible for component design, specification, and application; (2) the steel supplier and forging supplier responsible for making the steel, forging the shape, and preliminary heat treatment; and (3) a supplier that provided induction hardening, finish machining, and inspection. An independent engineering firm was subsequently involved, but because each party had its own agenda, there was no agreement on the metallurgical source of the failure and thus no continued analysis to pin down and eliminate the root cause.

This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.

This article focuses on the mechanisms and common causes of failure of metal components in lifting equipment in the following three categories: cranes and bridges, particularly those for outdoor and other low-temperature service; attachments used for direct lifting, such as hooks, chains, wire rope, slings, beams, bales, and trunnions; and built-in members such as shafts, gears, and drums.