Extra high strength zinc-coated 1080 steel welded wire was wound into seven-wire cable strands for use in aerial cables and guy wires. The wires and cable strands failed tensile, elongation, and wrap tests, with wires fracturing near welds at 2.5 to 3.5% elongation and through the welded joints in wrap tests. The welded wire was annealed by resistance heating. The wire ends had a chisel shape, produced by the use of sidecutters. Tests of the heat treatment temperatures showed that the wire near the weld area exceeded 775 deg C (1425 deg F). Metallographic examination revealed martensite present in the weld area after the heat treatment. The test failures of the AISI 1080 steel wire butt-welded joints were due to martensite produced in cooling from the welding operation that was not tempered adequately in postweld heat treatment, and to poor wire-end preparation for welding that produced poorly formed weld burrs. The postweld heat treatment was standardized on the 760 deg C (1400 deg F) transformation treatment. The chisel shape of the wire ends was abandoned in favor of flat filed ends. The wrap test was improved by adopting a hand-cranked device. Under these conditions, the welded joints withstood the tensile and wrap tests.

A wire hoisting rope on a drilling rig failed during a lift, after a few cycles of operation, causing extensive damage to support structures. The failure investigation that followed included mechanical property testing and chemical, metallurgical, and finite element analysis. The rope was made from multiple strands of 1095 steel wire. Its chemical composition, ferrite-pearlite structure, and high hardness indicate that the wire is a type of extra improved plow steel (EEIPS grade). The morphologies of the fracture surfaces suggest that the wires were subjected to tensile overloading. This was confirmed by finite element analysis, which also revealed compressive contact stresses between the wires and between the rope and sheave surface. Based on the results, it was concluded that a tensile overload, due to the combined effect of a sudden load and undersized sheave, is what ultimately caused the rope to fail.

Fractures and a crack occurred in a length of excavator boom rope. Failure took place at regions where local corrosion was evident. Microscopic examination of longitudinal sections disclosed that the majority of the cracks were broad, these being typical of corrosion-fatigue fissures. In addition, cracking took the form more typical of a fatigue crack and appeared to have originated at a stress-raiser introduced by a corrosion pit on the surface of the wire. The tendency for corrosion-fatigue cracking or the formation of pits from which fatigue cracks can develop can he reduced, if not prevented, in wire ropes by regular attention to lubrication.

The fatigue failure of a wire rope used on a skip hoist in an underground mine has been studied as part of the ongoing research by the Bureau of Mines into haulage and materials handling hazards in mines. Macroscopic correlation of individual wire failures with wear patterns, fractography, and microhardness testing were used to gain an understanding of the failure mechanism. Wire failures occurred predominantly at characteristic wear sites between strands. These wear sites are identifiable by a large reduction in diameter; however, reduction in area was not responsible for the location of failure. Fractography revealed multiple crack initiation sites to be located at other less noticeable wear sites or opposite the characteristic wear site. Microhardness testing revealed hardening, and some softening, at wear sites.

Music wire springs used in a printer return mechanism failed near the bend in the hook portion of the spring during qualification testing. Samples were examined in a scanning electron microscope equipped with an energy-dispersive x-ray microprobe. Fatigue fractures originated at rub marks on the inside edge of the spring. An investigation of loads encountered in service indicated that the springs had been loaded to a large fraction of the yield strength. Redesign of the spring mechanism was recommended.

A 6 x 19 fiber core steel wire rope failed as it was being used to lower a steel television tower. Fracture of the rope occurred at a point under one of two clips used to fashion a spliced loop that was directly connected to the top of the tower. Microscopic examination of the fracture surfaces and the condition of the individual wires revealed that 59% of the wires failed by shear, 39% failed in tension, and 2% had been cut. In addition, 87% of the wires showed some degree of crushing damage, ranging from mild to severe. The failure was attributed to improper installation of the clips.

Cerclage wire, which was used with two screws and washers for a tension band in a corrective internal fixation, was found broken at several points and corroded after nine months in service. The material was examined using energy-dispersive x-ray analysis and determined not to be in compliance with standards (type 304 stainless steel without molybdenum). The screws and washers were found to be made of remelted implant-quality type 316L stainless steel and were intact. Signs of sensitization, characterized by chromium carbide precipitates at the grain boundaries, were revealed by the microstructure. Intercrystalline corrosion with pitted grains was indicated by SEM fractography. Improper heat treatment of the steel was interpreted to have led to intercrystalline corrosion and implant separation.

The small cable (drop wire) providing service for individual subscribers from the aerial plant is held in place by a clamp made of a tin-coated brass body (attached to the cable) and a copper tail wire loop (attached to a galvanized steel hook or to a porcelain insulator). The tail wire is 2.6 mm (0.102 in.) diam annealed copper, and the clamp assembly must withstand a 2470 N (555 lb) load without breaking or slipping. A number of these clamps, located a few hundred feet from the ocean, have failed. The sharply broken wire indicated to weakening by abrasion. The copper tail wire failures had characteristics generally associated with corrosion fatigue. The broken wires showed multiple transgranular cracks near the failure, originating at the bases of pits. It was diagnosed that the copper tail wire failures were due to corrosion fatigue. The solution to this problem was to change the tail wire material for direct seashore exposure from annealed copper to annealed Monel.

An electron probe microanalyzer was applied to the study of service failures (due to severe heating) of aluminum wire connections in residential electrical circuits. Perturbed regions in which the composition underwent a change during the failure were revealed by optical and scanning electron microscopy of the contacts. A sequence of iron-aluminum compositions that shift from the pure aluminum of the wire to the nearly pure iron of the screw was revealed by analyses of two distinct layers formed on the aluminum/iron region. The compositions were found to correspond to specific intermetallic compounds found in the aluminum-iron phase diagram. Similar compositional variations were noted at the aluminum/brass interface. It was concluded that the failure of the electrical junction due to extreme heating was related to the formation of intermetallic compounds at the current carrying interfaces. These intermetallics were established to have a high resistance causing significant resistive heating.

A production lot of plastic wire clips was failing after limited service. The failures were characterized by excessive relaxation of the clips, such that the corresponding wires were no longer adequately secured in the parts. No catastrophic failures had been encountered. Parts representing an older lot, which exhibited satisfactory performance properties, were also available for reference purposes. The clips were specified to be injection molded from an impact-modified grade of nylon 6/6. However, the part drawing did not indicate a specific resin. Investigation included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. The spectrum representing the reference parts showed a relatively higher level of a hydrocarbon-based impact modifier, while the results obtained on the failed parts showed the presence of an acrylic-based modifier. Also, the reference clip thermogram showed a melting transition attributed to a hydrocarbon-based impact modifier. The conclusion was that the control and failed clips had been produced from two distinctly different resins. It appeared that the material used to produce the failed clips had different viscoelastic properties, which produced a greater predisposition for stress relaxation.

A cadmium-plated music-wire return spring that operated in a pneumatic cylinder designed for infinite life at a maximum stress level of 620 MPa failed after 240,000 cycles. An extremely hard and small kernel, which looked like a weld deposit, was observed at the center of the fractured surface. The kernel was assumed to have resulted from extreme localized overheating. These springs were reported to have been barrel electroplated after fabrication. The intermittent contact with the dangler (suspended cathode contact) as the barrel rotated allowed high local currents when the last contact was broken was revealed to have resulted in an arc that caused local melting of the metal being plated. The molten metal was interpreted to have been quenched instantly by the plating solution and by the mass of the cold metal of the spring. The hard spot caused by arcing during plating was concluded to be the reason of the fatigue failure. Rack plating or barrels with fixed button contacts at many points instead of dangler-type contacts were recommended to avoid hard spots.

A drawing plant which processed steel wire of designation 105 Cr 2 for ball bearings had losses due to crack formation and wire breakage during drawing. To establish the reason for the breakage, seven fractures were submitted for investigation with contiguous wire segments on both sides of the fracture of 300 mm each. Missing in the lamellar surface structure, with the exception of the remnants of a coarse network, were the pre-eutectically precipitated carbides to be expected in this steel. Surrounding the ferritic region in the surface structure, a ring of lamellar pearlite is seen, which turns into the granular annealed structure towards the core. The described structural phenomena were noted in all of the seven fracture regions. Their intensity always decreased with increasing distance from the fracture. Surface decarburization caused the formation of lamellar pearlite during annealing. This investigation further revealed that the localized decarburization and pearlite formation was present already in the rolled wire in uneven distribution over the entire coil length.

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.

Banding wires of the rotor of an 1800 hp motor were renewed following replacement of the banding rings. After about six months of service, a breakdown occurred due to bursting of the banding wires in several places. The 0.064 in. diam wire was nonmagnetic and of the 18/8 Cr-Ni type of austenitic stainless steel. The fractures were short and partially crystalline, with no evidence of slowly developing cracks of the fatigue type. Microscopical examination of sections taken through the fractures showed the cracking to be of the multiple branching type. Because the material was in the heavily cold-worked condition, it was not possible to determine with certainty if the cracks were of the inter- or trans-granular type. It was concluded that failure was due to stress-corrosion cracking in a chloride environment. Failure of the wires was likely due to the use of a chloride-containing flux during the soldering operation.

Wire ropes, pulleys, counterweights, and connecting systems are used for auto tensioning of contact wires of electric railways. A wire rope in one such auto tensioning system suffered premature failure. Failure investigation revealed fatigue cracks initiating at nonmetallic inclusions near the surface of individual wire strands in the rope. The inclusions were identified as Al-Ca-Ti silicates in a large number of stringers, and some oxide and nitride inclusions were also found. The wire used in the rope did not conform to the composition specified for AISI 316 grade steel, nor did it satisfy the minimum tensile strength requirements. Failure of the wire rope was found to be due to fatigue; however, the ultimate fracture of the rope was the result of overload that occurred after fatigue failure had reduced the number of wire strands supporting the load.

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.

During construction of a river bridge with 80 twisted cables, one or more fractures were found in each of 21 wires of 18 cables before assembly. All were located at the outside wrapping whose Z-profile wires were galvanically zinc-coated. It was suspected that hydrogen played a role during crack formation, and that it penetrated during pickling or galvanizing. This supposition was confirmed also by the fact that the wire fractures were not observed during cable winding, but only subsequently to it, and therefore seemed to have appeared only after a certain delay.

Microstructure, corrosion, and fracture morphologies of prestressed steel wires that failed in service on concrete siphons at the Central Arizona Project (CAP) are discussed. The CAP conveys water for municipal, industrial, and agricultural use through a system of canals, tunnels, and siphons from Lake Havasu to just south of Tucson, AZ. Six siphons were made from prestressed concrete pipe units 6.4 m (21 ft) in diam and 7.7 m long, making them the largest circular precast structures ever built. The pipe was manufactured on site and consisted of a 495-mm thick concrete core, wrapped with ASTM A648 steel prestressing wire. All of the CAP failures evaluated were attributed to corrosion. Longitudinal splits reduced the service life of the pipe significantly by facilitating corrosion and introducing sharp cracks into the microstructure of the wire. A few failures were attributed to general corrosion, where the cross section of the wire is reduced until the strength of the wire is exceeded. Most of the failures evaluated were attributed to stress-corrosion cracking.

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.

A 3.8-cm diam 6 x 37 rope of improved plow steel wire failed in service during dumping of a ladle of hot slag. A heavy blue oxide extending 0.6 to 0.9 m back from each side of the break was revealed on examination of the rope. Tensile fractures were shown by the broken ends of the rope. Recrystallization of the steel was revealed during microscopic examination of the wires adjacent to the break which indicated that the wires had been heated in excess of 700 deg C (1292 deg F). The tensile strength of the wires in the rope that broke was 896 MPa whereas the specification required it to be 1724 MPa. Thus, a 50% loss in tensile strength of the wires was caused by overheating which lead to failure of the rope. It was recommended that prolonged exposure of wire ropes to extreme conditions should be avoided.