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.

A steering knuckle used on an earthmover failed in service. The component fractured into a flange portion and a shaft portion. The flange was 27.9 cm (11 in.) in diam around which there were 12 evenly spaced 16 mm diam bolt holes. The shaft was hollow with a 10.5 cm (4 in.) OD and a wall thickness of 17 mm. The steering knuckle was made of 4340 steel and heat treated to a hardness of about 415 HRB (yield strength of about 1069 MPa, or 155 ksi). The vehicle had been involved in a field accident six months before the steering knuckle failed. Several components, including portions of the frame, had been damaged and replaced, but there was no observed damage to the steering. Analysis supported the conclusion that the fracture was the result of the prior accident, the most likely explanation being that the shaft was bent and that continued use caused a crack to initiate and propagate to fracture. No evidence of a defective design, improper microstructure, high inclusion count, or other stress-raising condition was observed. No recommendations were made.

A cast dragline bucket tooth failed by fracturing after a short time in service. The tooth was made of medium-carbon low-alloy steel heat treated to a hardness of 555 HRB. The fracture surface was covered with chevron marks. These converged at several sites on the surface of the tooth. A hardfacing deposit was located at each of these sites. Visual inspection of the hardfacing deposits revealed numerous transverse cracks, characteristic of many types of hardfacing. This failure was caused by cracks present in hardfacing deposits that had been applied to the ultrahigh-strength steel tooth. Given the small critical crack sizes characteristic of ultrahigh-strength materials, it is generally unwise to weld them. It is particularly inadvisable to hardface ultrahigh-strength steel parts with hard, brittle, crack-prone materials when high service stresses will be encountered. The operators of the dragline bucket were warned against further hardfacing of these teeth.

The boom lift equalizer hose on an excavator failed and the resultant release of high-pressure hydraulic fluid damaged the operator cabin. The hose was a heavy duty, high-impulse, multiple-spiral wire-reinforced, rubber covered hydraulic hose equivalent to 100R13 specifications as set in AS3791-1991. It had a maximum operating pressure of 34.5 MPa (5000 psi). The failure occurred adjacent to one of the couplings, although some of the wire strands had not broken. The two outer layers of reinforcement wire on the failed end had experienced extensive corrosion, corroding away completely in most areas. This corrosion was fairly uniform around the circumference of the hose. The loss of two spirals/layers of wire reinforcement effectively reduced the pressure carrying capacity of the hose to below that of the maximum operational pressure experienced. Either the hose (or assembly) was already corroded prior to being fitted, or, the hose experienced aggressive conditions causing rapid corrosion of the exposed wire strands.

An anchorage plate which fractured was one of a pair used as intermediate members through which the boom suspension ropes were attached to the jury-mast of an excavator. Failure of the plate released the ropes on one side of the boom, resulting in extensive damage to the latter and also bending of the other anchorage plate. The anchorage plates were 23 x 9 in. and had been flame-cut from mild steel plate. Collars were fillet-welded on each side at both ends to provide extra bearing area for the pins. Holes had then been flame-cut slightly under size and bored to final dimensions. The plates were given a slight set after flame-cutting to provide a more direct line of pull for the ropes. The fracture surface was bounded by narrow lips, indicative of shear failure. Failure of the anchorage plate was attributed to cracks present at the junctions of the fillet welds, and deficient notch-ductility of the material from which the plates were made.

Tie bars of a dragline excavator each consisted of a rectangular section steel bar to which eye-pieces, to facilitate anchorage, were attached by butt-welds. Failure of one weld in each bar after seven years of service allowed the boom to fall and become extensively damaged. The appearance of the fracture faces of the two welds showed partial-penetration joints. Failure in each bar had taken place through the weld metal. The presence of built-in cracks introduced zones of stress concentration and the fluctuating loads to which the ties were subjected in service served to initiate fatigue cracks. While the partial-penetration type of weld may be tolerated in a component subjected to bending stresses it is undesirable in one that is required to withstand fluctuating tensile stresses.