A support arm on a front-end loader failed in a brittle manner while lifting a load. The arm had a cross section of 50 x 200 mm (2 x 8 in.). Material used for the arm was hot-rolled ASTM A572, grade 42 (type 1), steel, which exhibited poor impact properties in the as-rolled condition and had a ductile-to-brittle transition temperature exceeding 93 deg C (200 deg F). This transition temperature was much too high for the application. It was recommended that a modified ASTM A572, grade 42 (0.15% C max), type 1 or 2, steel be used (type 1, which contains niobium, may be needed to meet strength requirements). The steel should be specified to be killed, fine-grained, and normalized, with Charpy V-notch impact-energy values of 20 J (15 ft·lbf) at -46 deg C (-50 deg F) in the longitudinal direction and 20 J (15 ft·lbf) at -29 deg C (-20 deg F) in the transverse direction.

The upper frame from a large cone crusher failed in severe service after an unspecified service duration. The ductile iron casting was identified as grade 80-55-06, signifying minimum properties of 552 MPa (80 ksi) tensile strength, 379 MPa (55 ksi) yield strength, and 6% elongation. Investigation (visual inspection, chemical analysis, unetched 30x images, and 2% nital etched 30x images) was difficult because the fracture surface of the frame section was obliterated by postfracture corrosion. Repeated attempts at cleaning using progressively stronger chemicals revealed that no telltale fracture morphology remained. However, the investigation supported the conclusion that the crusher frame failed via brittle overload fracture, likely due to excessive service stresses and substandard mechanical properties. Recommendations included additional quality-control measures to provide better spheroidal graphite morphology at the frame surface.

A new crane failed during the overload test following erection. A test load of 5 tons at the end of the jib (rated capacity 4 tons) was in the process of being slewed at the time of this failure. Inspection revealed that the collapse had resulted from the opening out of one eye of the rimming steel tie-bar of the main jib at the lower splice. This permitted the pin to pass through and allowed the jib to fall. Examination subsequently revealed that brittle fracture of two of the corner angles of the tower head assembly had also occurred. Had the tie-bar material been of satisfactory quality and/or, if the end that failed had been flamecut instead of sheared, then the damage resulting from the excessive overload would have been limited to yielding of the material in the region of the pin-joint. Such yielding on an overload test further indicated that the scantlings of the pin-joints were inadequate. Two other crane failures showed that failure resulted from the use of rimming steel, and embrittlement of the material was evident.

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.

An aircraft fuel-nozzle-support assembly exhibited cracks along the periphery of a fusion weld that attached a support arm to a fairing in a joint that approximated a T-shape in cross section. The base metal was type 321 stainless steel. Examination showed a good-quality weld penetrating to the support arm beneath, but revealed notch configurations at the inner mating surfaces at each edge of the fairing, the result of welding a poor fit-up of the support arm to the fairing. Fractures that originated at the cracks were examined by stereomicroscope and were found to contain fatigue marks that indicated crack propagation from multiple origins at the inner surface of the weld edge. Fatigue cracking was initiated at stress concentrations created by the notches at the inner surfaces between the support arm and the fairing, enhanced by poor fit-up in preparation for welding.

A number of machined end frame steel forgings made of Cr-Si-Mn alloy showed tiny cracks during magnetic particle inspection after heat treatment. The cracks were mostly confined to base edges and fillet radius. No significant abnormality was observed in chemical composition and microstructure. SEM, optical microscopy, and gas analysis revealed that the subsurface discontinuous cracks at the bore edges and in the fillet radius of the heat-treated end frame component had occurred due to hydrogen embrittlement, and not because of faulty heat treatment. This conclusion was supported by the presence of cracklike indications in machined bore surface of the annealed part.

Crane collapse due to bolt fatigue and fatigue failure of a crane support column, crane tower, overhead yard crane, hoist rope, and overhead crane drive shaft are described. The first four examples relate to the structural integrity of cranes. However, equipment such as drive and hoist-train components are often subject to severe fatigue loading and are perhaps even more prone to fatigue failure. In all instances, the presence of fatigue cracks at least contributed to the failure. In most instances, fatigue was the sole cause. Further, in each case, with regular inspection, fatigue cracks probably would have been detected well before final failure.