The engine of an automobile lost power and compression and emitted an uneven exhaust sound after several thousand miles of operation. When the engine was dismantled, it was found that the outer spring on one of the exhaust valves was too short to function properly. The short steel spring and an outer spring (both of patented and drawn high-carbon steel wire) taken from another cylinder in the same engine were examined in the laboratory to determine why one had distorted and the other had not. Investigation (visual inspection, microstructure examination, and hardness testing) supported the conclusion that the engine malfunctioned because one of the exhaust-valve springs had taken a 25% set in service. Relaxation in the spring material occurred because of the combined effect of improper microstructure (proeutectoid ferrite) plus a relatively high operating temperature. Recommendations included using quenched-and-tempered steel instead of patented and cold-drawn steel or using a more expensive chromium-vanadium alloy steel instead of plain carbon steel; the chromium-vanadium steel would also need to be quenched and tempered.

A 2.3 mm diam steel wire broke during cable twisting. The fracture occurred obliquely to the longitudinal axis of the wire and showed a constriction at the end. Therefore it was a ductile fracture. File mark type work defects were noticeable on the wire surface at both sides of the fracture, but they had no effect on the breakage of the wire. Away from the fracture area, the wire had a normal structure of hyperfine lamellar pearlite (sorbite) of a “patented” and cold drawn steel wire. In the vicinity of the fracture, the cementite of the pearlite was partially spheroidized, while at the fracture itself it was completely spheroidized. Therefore the wire was locally annealed at this point. It was likely that the wire cracked at this point during the last drawing and then broke during twisting due to its lower strength in the weakened cross section after prior deformation.

The wires used in a wet precipitator for cleaning the gases coming off a basic oxygen furnace failed. The system consisted of six precipitators, three separate dual units, each composed of four zones. Each zone contained rows of wires (cold drawn AISI 1008 carbon steel) suspended between parallel collector plates. It was determined that the 1008 wires failed because of corrosion fatigue. It was decided to replace all of the wires in the two zones with the highest rates of failure with cold-drawn type 304 austenitic stainless steel wire. These expensive wires, however, failed after a week by transgranular SCC. Annealed type 430 ferritic stainless steel was subsequently suggested to prevent further failures.

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.

A farm-silo hoist used as the power source for a homemade barn elevator failed catastrophically from destructive wear of the worm. The hoist mechanism consisted of a pulley attached by a shaft to a worm that, in turn, engaged and drove a worm gear mounted directly on the hoist drum shaft. The worm and the worm gear were made of leaded cold-drawn 1113 steel and class 35-40 gray iron (nitrided in an aerated salt bath) respectively. The gearbox was found to contain fragments of the worm teeth and shavings that resembled steel wool. More than half of the worm teeth were revealed to be sheared off to almost half the depth. It was revealed on investigation that the drive pulley had been replaced with a larger pulley that generated more power than the gearbox could handle, causing failure by adhesive wear of the steel worm.

The 16 mm diam 6 x 37 fiber-core improved plow steel wire rope on a scrapyard crane failed after two weeks of service under normal loading conditions. This type of rope was made of 0.71 to 0.75% carbon steel wires and a tensile strength of 1696 to 1917 MPa. The rope broke when it was attached to a chain for pulling jammed scrap from the baler. The rope was heavily abraded and several of the individual wires were broken. a uniform cold-drawn microstructure, with patches of untempered martensite in regions of severe abrasion and crown wear was revealed by metallographic examination. As a result of abrasion, a hard layer of martensite was formed on the wire. The wire was made susceptible to fatigue cracking, while bending around the sheave, by this brittle surface layer. The carbon content and tensile strength of the wire was found lower than specifications. As a corrective measure, this wire rope was substituted by the more abrasion resistant 6 x 19 rope.

The springs formed from 3.8 mm diam cold-drawn carbon steel wire failed to comply with load-test requirements. A split wire in the spring was revealed by investigation. A smooth heat-tinted longitudinal zone was observed in the fracture. It was concluded that the spring failed in the load test due to the split wire. The reason for the condition was interpreted to be overdrawing which resulted in intense internal strains, high circumferential surface tension, and decreased ductility.

Two large tension springs fractured during installation. The springs were manufactured from a grade 9254 chromium-silicon steel spring wire. The associated material specification allows wire in the cold-drawn or oil-tempered (quenched-and-tempered) condition. The specified wire tensile strength range was 1689 to 1793 MPa (245 to 260 ksi). The finished springs were to be shot peened for greater fatigue resistance. Investigation (visual inspection, 3x images, 2% nital etched 148x SEM images, chemical analysis, hardness testing, and EDS analysis) supported the conclusion that the springs failed during installation due to the presence of preexisting defects. Crack surfaces were found to be corroded and phosphate coated, indicating that the cracks occurred during manufacture. Installation, which presumably entailed some axial extension, resulted in ductile overload failure at the crack sites. Recommendations included evaluating the manufacturing steps to identify the process(es) wherein the cracking was likely occurring. It was further recommended that a suitable nondestructive method such as magnetic particle inspection be implemented.

Cold-drawn type 303 stainless steel wire sections, 6.4 mm (0.25 in.) in diameter, failed during a forming operation. All of the wires failed at a gradual 90 deg bend. Investigation (visual inspection and 5.3x/71x/1187x SEM views) supported the conclusion that the wires cracked due to ductile overload. The forming stresses were sufficient to initiate surface ruptures, suggestive of having exceeded the forming limit. Recommendations included examining the forming process, including lubrication and workpiece fixturing.

A hoist lift hose on a loader failed catastrophically. The hoses were a 100R13 type (as classified in AS3791-1991) with 50.8 mm nominal internal diameter. They consisted of six alternating spirals of heavy wire around a synthetic rubber inner tube with a synthetic rubber outer sheath. Failure of the lift hose was approximately 50 to 100 mm away from the "upper" end of the hose, with the straight coupling that attaches to the hydraulic system. The return hose was in much better condition, with no apparent deformation and only small areas of mechanical damage to the outer sheath. There were two modes of failure of the wire: tensile and corrosion related. The predominant corrosion mechanism appeared to be crevice corrosion related, with the corrosion being driven by the retention of water by the cover material around the wire strands. In this case study (and in most wire-reinforced hydraulic hoses), the wire reinforcing strands were a medium-carbon steel in the cold drawn condition. Radiographic nondestructive testing (NDT) was recommended to determine when a hydraulic hose should be replaced.

The fan drive support shaft, specified to be made of cold-drawn 1040 to 1045 steel, fractured after 2240 miles of service. It was revealed by visual examination of the shaft that the fracture had initiated near the fillet at an abrupt change in shaft diameter. The cracks originated at two locations approximately 180 deg apart on the outer surface of the shaft and propagated toward the center. Features typical of reversed-bending fatigue were exhibited by the fracture. A tensile specimen was machined from the center of the shaft and it indicated much lower yield strength (369 MPa) than specified. It was disclosed by metallographic examination that the microstructure was predominantly equiaxed ferrite and pearlite which indicated that the material was in either the hot-worked or normalized condition. An improvement of fatigue strength of the shaft by the development of a quenched-and-tempered microstructure was recommended.

Two sections of a galvanized cable 10.5 A 160 GR +NORM M 9533 (round stranded cable of normal type, h + 6, Langslay, right-handed) were examined. One had a 100 mm long blackish-brown tarnished zone obviously caused by localized heating at one end, inside which the hemp core was missing, and the other corresponded to the original condition of the cable. The cause of the damage was unknown. About a third of the wires had fractured and the rest had been cut. All were tensile fractures with a relatively high degree of necking. The cause of the localized heating was unknown. It can only be concluded from the investigation that the temperature did not exceed the Ac3 point of the wire material, which should be about 750 deg C, and that the heating lasted a fairly long time.

A heavily worked 304 stainless steel wire basket recrystallized and distorted while in service at 650 deg C (1200 deg F). This case study demonstrates that heavily cold worked austenitic stainless steel components can experience large losses in creep strength, and potentially structural collapse, under elevated temperature service, even at temperatures more than 300 deg C (540 deg F) below the normal solution annealing temperature. The creep strength of the recrystallized 304/304L steel was more than 1000 times less than that achievable with solution annealed 304H. These observations are consistent with limitations (2000 Addendum to ASME Boiler and Pressure Vessel Code) on the use of cold worked austenitic stainless steels for elevated temperature service.

Several type 316L stainless steel wires in an electrostatic precipitator at a paper plant fractured in an unexpectedly short time. Failed wires were examined using optical and scanning electron microscope, and hardness tests were conducted. Fractography clearly established that fracture was caused by fatigue originating at corrosion pits on the surface of the wire. It was recommended that higher-molybdenum steel in the annealed condition be used to combat pitting corrosion.

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.

Locked coil wire ropes, by virtue of their unique design and construction, have specialized applications in aerial ropeways, mine hoist installations, suspension bridge cables, and so forth. In such specialty ropes, the outer layer is constructed of Z-profile wires that provide not only effective interlocking but also a continuous working surface for withstanding in-service wear. The compact construction and fill-factor of locked coil wire ropes make them relatively impervious to the ingress of moisture and render them less vulnerable to corrosion. However, such ropes are comparatively more rigid than conventional wire ropes with fiber cores and therefore are more susceptible to the adverse effects of bending stresses. The reasons for premature in-service wire rope failures are rather complex but frequently may be attributed to inappropriate wire quality and/or abusive operating environment. In either case, a systematic investigation to diagnose precisely the genesis of failure is desirable. This article provides a microstructural insight into the causes of wire breakages on the outer layer of a 40 mm diam locked coil wire rope during service. The study reveals that the breakages of Z-profile wires on the outer rope layer were abrasion induced and accentuated by arrays of fine transverse cracks that developed on a surface martensite layer.

A locked coil track rope (LCTR) is essentially composed of wires (round and rail-shaped) laid helically in different layers. These wire ropes are sometimes used in conveyors carrying empty and loaded buckets in mining areas. During service, such wire ropes may fail prematurely due to disintegration/failure of individual groups of wires. To understand the genesis of LCTR wire failures, a detailed metallurgical investigation of failed rope wires was made and included visual examination, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Two types of failed wires were investigated; one is from a 40 mm diameter locked coil track rope and the other from a 53 mm locked coil track rope. Optical microscopy of failed round wires in the 53 mm diameter rope clearly revealed fully decarburized layers at the surface and a few grain-boundary cracks. From the location of the failure, it was clear that apart from static tensile loads, the wire ropes had been subjected to bending and unbending loads near the saddle, as fully loaded or empty buckets traveled access the conveyor. The SEM studies confirmed that the fracture had been caused by initiation of fatigue cracks in the decarburized zone under conditions of repeated bending and unbending stresses superimposed on the static tensile load.

An electric transport vehicle, similar to an electric trolley or subway rail car, experienced frequent breakdowns due to in-service fractures of torsion springs that support the weight of an overhead electric pickup assembly. Scanning electron microscopy and metallographic examinations determined that the fractures stemmed from electric arc damage. Intergranular quench cracks in the transformed untempered martensite on the surface of the spring provided crack initiations that propagated during operation causing fatigue fracture.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

Distortion failure occurs when a structure or component is deformed so that it can no longer support the load it was intended to carry. Every structure has a load limit beyond which it is considered unsafe or unreliable. Estimation of load limits is an important aspect of design and is commonly computed by classical design or limit analysis. This article discusses the common aspects of failure by distortion with suitable examples. Analysis of a distortion failure often must be thorough and rigorous to determine the root cause of failure and to specify proper corrective action. The article summarizes the general process of distortion failure analysis. It also discusses three types of distortion failures that provide useful insights into the problems of analyzing unusual mechanisms of distortion. These include elastic distortion, ratcheting, and inelastic cyclic buckling.