A structure had been undergoing fatigue testing for several months when a post-like member heat treated to a tensile strength of 1517 to 1655 MPa (220 to 240 ksi) ruptured. The fracture occurred in the fillet of the post that contacted the edge of a carry-through box bolted to the member. At failure, the part was receiving a second set of loads up to 103.6% of design load. Visual investigations showed rubbing and galling of the fillet. Microscopic and metallographic examination revealed beach marks on the fracture surface and evidence of cold work and secondary cracking in the rubbed and galled area. Electron fractography confirmed that cracking had initiated at a region of tearing and that the cracks had propagated by fatigue. Mechanical properties of all specimens exceeded the minimum values specified for the post. This evidence supports the conclusion that fatigue was the primary cause of failure. Rubbing of the faying surfaces worked the interference area on the post until small tears developed. These small tears became stress-concentration points that nucleated fatigue cracks. Recommendations included rounding the edge of the box in the area of contact with the post to ensure a tangency fit.

The T-section cross member of the lifting sling failed in service while lifting a 966 kg (2130 lb) load. The L-section sling body and the cross member were made of aluminum alloy 5083 or 5086 and were joined by welding using aluminum alloy 4043 filler metal. The fracture was found by visual examination to have occurred at the weld joining the sling body and the cross member. Inadequate joint penetration and porosity was revealed by macrographic examination of the weld. Lower silicon content and a higher magnesium and manganese content than the normal for alloy 4043 filler metal were found during chemical analysis. It was revealed by examination of the ends of the failed cross member that a rotational force that had been applied on the cross member caused it to fracture near the sling body. It was concluded that brittle fracture at the weld was caused by overloading which was attributed to the misalignment of the sling during loading. Aluminum alloy 5183 or 5356 filler metal was recommended to be used to avoid brittle welds.

Four truck cross members intended for use in heavy-duty transport trucks were investigated. Two of the members had cracked on a prototype vehicle and two had been fatigue tested in the laboratory. The cross members were fabricated from SAE 950X plate and consisted of a formed channel section and an internal fillet-welded diaphragm. Sections from each of the cross members were subjected to a complete analysis, including chemical analysis, magnetic particle testing, mechanical testing, scanning electron microscope/fractography, and metallography. The primary mode of failure was found to be fatigue cracking that initiated at the toes of the fillet welds. Secondary fatigue cracking occurred at the torque rod mounting holes. Failure was attributed to cyclic stresses at the weld toes that exceeded the lowered fatigue strength at this location. A design change that eliminated the fillet welds alleviated the problem.

A series of resistance spot welds joining Z-shape and C-shape members of an aircraft drop-tank structure failed during ejection testing. The members were fabricated of alclad aluminum alloy 2024-T62. The back surface of the C-shape members showed severe electrode-indentation marks off to one side of the spot weld, suggesting improper electrode contact. Visual examination of the weld fractures showed that the weld nuggets varied considerably in size, some being very small and three exhibiting an HAZ but no weld. Of 28 welds, only nine had acceptable nugget diameters and fusion-zone widths. The weld deficiencies were traced to problems in forming and fit-up of the C-shape members and to difficulties in alignment and positioning of the weld tooling. The failure of the resistance spot welds was attributed to poor weld quality caused by unfavorable fit-up and lack of proper weld-tool positioning. The problem could be solved by better forming procedures to provide an accurate fit-up that would not interfere with electrode alignment.

Bending fatigue caused crack propagation and catastrophic failures at several locations near the welds on the low-carbon steel tubular cargo box frame of police three-wheel motorcycles. ANSYS finite element analysis revealed that bending stresses in some of the frame members were aggravated by poor detail design between vertical and horizontal tubes. Stresses observed in the ANSYS analysis were not sufficient to cause the onset of fatigue. However when compounded by stress concentration factors and in-service dynamic loading, the frame could have been regularly subjected to stresses over the fatigue limit of the material. A strain gage static loading test verified FEM results, and finite element techniques were applied in the design of reinforcing members to renovate the frames. Material properties were determined and welding procedures specified for the reinforcing members. Inspection intervals were devised to avoid future problems.

A flat spring for the main landing gear of a light aircraft failed after safe execution of a hard landing. The spring material was identified by chemical analysis to be 6150 steel. The fracture was found to have occurred near the end of the spring that was inserted through a support member about 25 mm thick and attached to the fuselage by a single bolt. Brinelling (plastic flow and indentation due to excessive localized contact pressure) was observed on the upper surface of the spring where the forward and rear edges of the spring contacted the support member. It was indicated by chevron marks that brittle fracture had started beneath the brinelled area at the forward edge of the upper surface of the spring. The origin of the brittle fracture was found to be a small fatigue crack that had been present for a considerable period of time before final fracture occurred. Fracture of the landing-gear spring was concluded to have been caused by a fatigue crack that resulted from excessive brinelling at the support point. Regular visual examinations to detect evidence of brinelling and wear at the support in aircraft with this configuration of landing-gear spring were recommended.

The structural collapse of an iron-ore bucket-wheel stacker reclaimer at the beginning of operation was investigated by means of mechanical tests, microstructural characterization, and computational structural analysis. The mechanical failure was a consequence of a brittle fracture by cleavage. The crack followed the heat-affected zone of a welded joint connecting a rectangular hollow section member and a plate flange. The main factors contributing to failure were related with a combination of design-in and manufacturing-in factors like high load-strength ratio at the point of failure, local stress concentration as a result of geometry restrictions, and weld defects. This particular section was responsible for the load transfer between the front tie member and the boom extremity, and its failure was the main cause of the catastrophic failure of the equipment.

Alloy steel forgings used as structural members of a ski chair lift grip mechanism were identified to have contained forging laps (i.e., sharp-notched discontinuities) during an annual magnetic particle inspection of all chair lift grip structural members at a mountain resort. The material was confirmed to be 34Cr-Ni-Mo6. A heavy oxide on the dark area of one of the broken-open laps was revealed by scanning electron microscopy in conjunction with EDS. A bright area that contained ductile dimple rupture was observed adjacent to the dark area. The oxidized portion of the fracture was established to be the preexisting forging lap while the bright area was created during the breaking-open process. As a corrective action all forgings showing laps were recommended to be removed from service. Critical review and revision of the forging process and revisions to the nondestructive evaluation procedures at the forging supplier was recommended.

The types of metal components used in lifting equipment include gears, shafts, drums and sheaves, brakes, brake wheels, couplings, bearings, wheels, electrical switchgear, chains, wire rope, and hooks. This article primarily deals with many of these metal components of lifting equipment in three categories: cranes and bridges, attachments used for direct lifting, and built-in members of lifting equipment. It first reviews the mechanisms, origins, and investigation of failures. Then the article describes the materials used for lifting equipment, followed by a section explaining the failure analysis of wire ropes and the failure of wire ropes due to corrosion, a common cause of wire-rope failure. Further, it reviews the characteristics of shock loading, abrasive wear, and stress-corrosion cracking of a wire rope. Then, the article provides information on the failure analysis of chains, hooks, shafts, and cranes and related members.

A valve-seat retainer spring (made of 0.23 mm thick 17-7 PH stainless steel) from a fuel control on an aircraft engine was found to be broken after 3980 h of service. The two inner tabs were found to be broken off. The part was revealed to be in relative rotation against its contacting member by the radial wear marks on the convex surface. Beach marks indicating that fatigue fracture had been initiated at the convex surface of the washer and had propagated across to the concave surface were revealed by examination of the fractured surfaces of the washer. The cracks were revealed to have originated in the 0.38-mm radius fillet between the tab and the body of the washer. It was interpreted from the analysis of the compound fracture that it was composed of fatigue fractures caused by the formed tab being loaded so as to compress the spring along the axis of its centerline and produce torsional vibrations. It was concluded that the two inner tabs had broken in fatigue as the result of cyclic loading that compressed and torsionally vibrated the spring. The fillets were replaced with slots to minimize stress concentration at the corners as a corrective measure.

Cold cracking of structural steel weldments is a well-documented failure mechanism, and extensive work has been done to recognize welding and materials selection parameters associated with it. These efforts, however, have not fully eliminated the occurrence of such failures. This article examines a case of cold cracking failure in the construction industry. Fortunately, the failure was identified prior to final erection of the structural members and the weld was successfully reworked. The article explains how various welding parameters, such as electrode/wire selection, joint design, and pre/postheating, played a role in the failure. Human factors and fabrication practices that contributed to the problem are covered as well.

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.

A railway tank car developed a fracture in the region of the sill and shell attachment during operation at -34 deg C (-30 deg F). On either side of the sill-support member, cracking initiated at the weld between a 6.4 mm thick frontal cover plate and a 1.6 mm thick side support plate. The crack then propagated in a brittle manner upward through the side plate, through the welds attaching the side plate to a 25 mm (1 in.) thick shell plate (ASTM A212, grade B steel), and continued for several millimeters in the shell plate before terminating. Other plates involved were not positively identified but were generally classified as semi-killed carbon steels. Investigation (visual inspection, hardness testing, chemical analysis, Charpy V-notch testing, and drop-weight testing) supported the conclusions that the fracture was initiated by weld imperfections and propagated in a brittle manner as a result of service stresses acting on the plate having low toughness at the low service temperatures encountered. Recommendations included that the specifications for the steel plates be modified to include a toughness requirement and that improved welding and inspection practices be performed to reduce the incidence of weld imperfections.

After 14 months of service, cracks were discovered in castings and bolts used to fasten together braces, posts, and other structural members of a cooling tower, where they were subjected to externally applied stresses. The castings were made of copper alloys C86200 and C86300 (manganese bronze). The bolts and nuts were made of copper alloy C46400 (naval brass, uninhibited). The water that was circulated through the tower had high concentrations of oxygen, carbon dioxide, and chloramines. Analysis (visual inspection, bend tests, fractographs, 50x unetched micrographs, 100x micrographs etched with H4OH, and 500x micrographs) supported the conclusions that the castings and bolts failed by SCC caused by the combined effects of dezincification damage and applied stresses. Recommendations included replacing the castings with copper alloy C87200 (cast silicon bronze) castings. Replacement bolts and nuts should be made from copper alloy C65100 or C65500 (wrought silicon bronze).

A hypoid pinion made from 4820 Ni-Mo alloy steel was the driving member of a power unit operating a rapid transit car. The pinion had been removed from service at the end of the initial test period because it showed undue wear. The mode of failure was severe abrasive wear. The cause of failure was insufficient surface hardness, resulting from improper heat treatment. A service recall for the remaining pinions was immediately initiated.