An automotive front-wheel outer angular-contact ball bearing generated considerable noise shortly after delivery of the vehicle. The inner and outer rings were made of seamless cold-drawn 52100 steel tubing, the balls were forged from 52100 steel, and the retainer was stamped from 1008 steel strip. The inner ring, outer ring, and balls were austenitized at 845 deg C (about 1550 deg F), oil quenched, and tempered to a hardness of 60 to 64 HRC. Investigation (visual inspection) supported the conclusion that failure was caused by fretting due to vibration of the stationary vehicle position without bearing rotation. Recommendations included improving methods of securing the vehicle during transportation to eliminate vibrations.

After the mixing machines were introduced into service, excessive assembly stresses and inappropriate detail design caused the premature failures of ice cream drink mixer blades shortly. The mixer blade is slightly deformed by the contact between the wavy washer at the bottom of the assembly and the bends at the bottom shoulders of the two mixer arms. Multiple fatigue crack origins on the inside radii of the bends at the bottom shoulders was revealed by analysis of the failed mixer blades. It was revealed by metallographic examination that the shoulders on the arms were cold bent, introducing tensile residual stresses on the inside radii of the shoulders and creating a localized area of fatigue susceptibility due to the inherent notch sensitivity of cold-formed 300 series stainless steel. It was established that the physical root cause was the design of the mixer blade. The addition of a stand-off washer between the wavy washer and the bottom shoulders of the blade or modification of the shape of the wavy washer to prevent contact with the blade shoulders was recommended.

A welded elbow assembly (AISI type 321 stainless steel, with components joined with ER347 stainless steel filler metal by gas tungsten arc welding) was part of a hydraulic-pump pressure line for a jet aircraft. The other end of the tube was attached to a flexible metal hose, which provided no support and offered no resistance to vibration. The line was leaking hydraulic fluid at the nut end of the elbow. Investigation supported the conclusion that failure was by fatigue cracking initiated from a notch at the root of the weld and was propagated by cyclic loading of the tubing as the result of vibration and inadequate support of the hose assembly. Recommendations included changing the joint design from a cylindrical lap joint to a square-groove butt joint. Also, an additional support was recommended for the hose assembly to minimize vibration at the elbow.

In an electric power station, seven turbine blades out of 112 broke or cracked within 8 to 14 months after commencement of operation. The blades in question were all located on the last running wheel in the low pressure section of a 35,000 kW high pressure condensing turbine. They were milled blades without binding wires and cover band. They did not fracture at the fastening, i.e. the location of highest bending stress, but in a central region which was 165 to 225 mm away from the gripped end. The blades were fabricated from a stainless heat-treatable chromium steel containing 0.2C and 13.9Cr. Microstructural examination showed the blades were destroyed by flexural vibrations which evidently reached their maximum amplitude at the location of fracture. Erosion of the inlet edge, possibly in connection with vibration-induced corrosion cracking, contributed to fracture.

Stainless steel liners (AISI type 321) used in bellows-type expansion joints in a duct assembly installed in a low-pressure nitrogen gas system failed in service. The duct assembly consisted of two expansion joints connected by a 32 cm (12 in.) OD pipe of ASTM A106 grade B steel. Elbows made of ASTM A234 grade B steel were attached to each end of the assembly, 180 deg apart. A 1.3 mm (0.050 in.) thick liner with an OD of 29 cm (11 in.) was welded inside each joint. The upstream ends were stable, but the downstream ends of the liners remained free, allowing the components to move with the expansion and contraction of the bellows. Investigation (visual inspection, hardness testing, and 30x fractographs) supported the conclusion that the liners failed in fatigue initiated at the intersection of the longitudinal weld forming the liner and the circumferential weld by which it attached to the bellows assembly. Recommendations included increasing the thickness of the liners from 1.3 to 1.9 mm (0.050 to 0.075 in.) in order to damp some of the stress-producing vibrations.

During the operation of tractors with cantilevered body, the lateral wall of the hypoeutectic cast iron cylinder blocks cracked repeatedly. Three of the blocks were examined. The grain structure of the thick-walled part consisted of uniformly distributed graphite of medium flake size in a basic mass of pearlite with little ferrite. But the thin-walled part showed a structure of dendrites of precipitated primary solid solution grains with pearlitic-ferritic structure and a residual liquid phase with granular graphite in the ferritic matrix. The structure was formed by undercooling of the residual melt. In this case, it was promoted by fast cooling of the thin wall and had comparatively low strength. The fracture formation in the cylinder blocks was ascribed primarily to casting stresses. They could be alleviated by better filleting of the transition cross sections. The fracture was promoted by the formation of undercooled microstructure of low strength in the thin-walled part. Similar damage appeared in a cylinder head, in which case, the cracks were promoted by a supercooled structure.

The shaft-and-bearing assembly in a freon compressor was subjected to severe pounding and vibration after six years of service. After about one year of service, the compressor had been shut down to replace a bearing seal. One month before the shaft failed, a second seal failure occurred, requiring the collar, spacer sleeve, seal, roller bearing, and lock washer to be replaced. The shaft was made of 4140 steel, heat treated to a hardness of 20 to 26 HRC. The seal, bearing, and lock washer were commercial components. Investigation (visual inspection, 4.5x images, x-ray diffraction, hardness testing, and microscopic exam) supported the conclusion that shaft failure was initiated by fretting between the bearing race and the bearing surface on the shaft because of improper bearing installation. Once clearance was established between the bearing and the shaft, the shaft began pounding on the inner bearing race, causing final failure of the shaft surface. Recommendations included proper fitting of the shaft and bearing race to preventing movement of the bearing on the shaft. Also, the lock washer and locknut must be installed properly.

An AMS 4126 (7075-T6) aluminum alloy impeller from a radial inflow turbine fractured during commissioning. Initial examination showed that two adjacent vanes had fractured through airfoils in the vicinity of the vane leading edges, and one vane fractured through an airfoil near the hub in the vicinity of the vane trailing edge. Some remaining vanes exhibited radial and transverse cracks in similar locations. Binocular and scanning electron microscope examinations showed that the cracks had been caused by high-cycle fatigue and had progressed from multiple origins on the vane surface. Structural analysis indicated that the fatigue loading probably had been caused by forced excitation, resulting in the impeller vibrating at its resonant frequency. It was recommended that the impeller design, control systems, and material of construction be changed.

Erosion of solid surfaces can be brought about solely by liquids in two ways: from damage induced by formation and subsequent collapse of voids or cavities within the liquid, and from high-velocity impacts between a solid surface and liquid droplets. The former process is called cavitation erosion and the latter is liquid-droplet erosion. This article emphasizes on manifestations of damage and ways to minimize or repair these types of liquid impact damage, with illustrations.

A hi-rail device is a vehicle designed to travel both on roads and on rails. In this case, a truck was modified to accept the wheels for rail locomotion. The rear wheel/axle set was attached to the truck frame. Both the front and rear wheel/axle sets were raised by means of a hydraulic cylinder driven off the PTO of the truck. The wheel/axle set was rigidly fixed into an up or down position by the use of locking pins. It was assumed by the manufacturer that there would be no load on the cylinder once the wheel/axle set was in its locked position. However, as the cylinder pivoted about its mounting trunnion and extended during its motion, it interfered with a frame member. This caused both a bending load and a rotational movement. These effects caused a combination of fretting, galling, and fatigue to the internal thread structure of the clevis. As a result of these deleterious effects, failure of the thread structure of the clevis occurred. The failure occurred where the cylinder rod screws into the clevis. The rod was manufactured from 1045 steel.

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

A heat transport pump in a heavy water reactor failed (exhibiting excessive vibration) during a restart following a brief interruption in coolant flow due to a faulty valve. The pump had developed a large crack across the entire length of a bearing journal. An investigation to establish the root cause of the failure included chemical and metallurgical analysis, scanning electron fractography, mechanical property testing, finite element analysis of the shrink fitted journal, and a design review of the assembly fits. The journal failure was attributed to corrosion fatigue. Corrective actions to make the journals less susceptible to future failures were implemented and the process by which they were developed is described.

Several large-diameter type 304L stainless steel impeller/propeller blades in a circulating water pump failed after approximately 8 months of operation. The impeller was a single casting that had been modified with a fillet weld buildup at the blade root. Visual examination indicated that the fracture originated near the blade-to-hub attachment in the area of the weld buildup. Specimens from four failed castings and from an impeller that had developed cracks prior to design modification were subjected to a complete analysis. A number of finite-element-method computer models were also constructed. It was determined that the blades failed by fatigue that had been accelerated by stress-corrosion cracking. The mechanism of failure was flow-induced vibration, in which the vortex-shedding frequencies of the blades were attuned to the natural frequency of the blade/hub configuration. A number of solutions involving material selection and impeller redesign were recommended.

This report covers case histories of failures in fixed-wing light airplane and helicopter components. In a 2025-T6 or 2219 aluminum alloy propeller blade that failed near the tip, cracks started on the leading edge at surface damage in the critical area-the zone between 4 and 10 in. from the tip of the blade. Incorrect dressing and inadequate pre-flight inspection were the two main causes. Two other types of propeller blade fatigue failures resulted mainly from propeller straightening operations, usually performed after previous blade bending damage. To eliminate blade tip failures, all surface-damaged material should be removed and polished smooth before further flight. The blade should be correctly dressed. Also, the tachometer should be calibrated to ensure the engine/propeller combination is not operated in the critical speed range at normal cruising speeds.

A 2–3 mm thick electroformed nickel mold showed early cracking under thermal load cycles. To determine the root cause, investigators obtained monotonic and cyclic properties of electroformed nickel at various temperatures and identified possible fatigue mechanisms. With the help of finite element modeling, they analyzed the material as well as the design and in-service application of the mold. They discovered that overconstraining the mold, while it was in service, caused excessive thermal stresses which accelerated crack initiation and propagation. Investigators also proposed remedies to prevent additional failures.

This paper reviews several fatigue failures from the waterwall, superheater, and economizer portions of the boiler, their causes and how they were mitigated and monitored. Some cases required simple field modifications by cutting or welding, repair of existing controls, and/or changes in maintenance. Nondestructive inspections by visual, magnetic particle, ultrasonic, and radiographic methods for detecting and monitoring damage are discussed. These failures are presented to provide hindsight that will help others in increasing the success rate for anticipating and analyzing the remaining life of other units.

Shaft misalignment and rotor unbalance contribute to the premature failure of many machine components. To understand how these failures occur and quantify the effects, investigators developed a model of a rotating assembly, including a motor, flexible coupling, driveshaft, and bearings. Equations of motion accounting for misalignment and unbalance were then derived using finite elements. A spectral method for resolving these equations was also developed, making it possible to obtain and analyze dynamic system response and identify misalignment and unbalance conditions.

A forged pressure vessel made from high temperature austenitic steel X8Cr-Ni-MoVNb 16 13 K (DIN 1.4988) failed. The widest part of the burst had fine cracks on the internal wall running longitudinally. When the internal wall was cleaned, numerous even finer cracks were exposed. On the fracture surfaces in this region an irregularly formed zone was visible in the direction of the internal wall and a fibrous oriented fracture zone towards the external wall. The fracture was typical of stress-corrosion cracking in austenitic steels. Vanadium trichloride was present and tensile stresses were of necessity set up by the internal pressure. Stress-corrosion cracking does not occur if one of the basic requirements is lacking. Because the chloride agent and tensile stresses were inevitably present, the only possible way to prevent future reoccurrence is to forge the entire pressure vessel from a material immune to stress-corrosion cracking or to use interchangeable linings of such a material. A nickel alloy could be considered.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

This article explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.