Failure of the chassis of roller skates for agonistic figure skating

Failure analysis of air cooled condenser gearbox

Gears are very reliable components and normally work 5–6 years without failure. This article is a case study of failure analysis of a gearbox which was failed in three months after its installation. The problem was identified by maintenance engineers through vibration monitoring of gearbox. Hardness measurement of case and core revealed that the core was harder than case and the applied load was sufficiently high for failure of gear. Recommendations were given to improve the fatigue life of gearbox.

Fig. 2. Photographs of the (a) damaged intermediate pinion; (b) damaged output gear; and (c) enlarged view of Fig. 2b, showing starting area of pitting and directions of spread.

Ratio of the maximum to average surface roughness values is in the range of 6–8.6. This ratio should be less than 5 for enhanced tribological performanceof the gears.

Fatigue fracture of cutter blade made of high-speed steelThe subject of the analysis was the broken blade of cutter Ku 500VX that was used in meat processing. The aim of the study was to determine the failure cause and to give an answer how it could be avoided. General view of broken blade with marked area of the damage is shown in Fig. 1. The performed tests included hardness measurements, fractography analysis and metallographic studies using stereoscopic, light and scanning electron microscopes.

Fig. 1. General view of the broken blade. The arrow indicates the place where sample was taken for testing and indicates the place where the inscription (number “1”) was made with engraving tool.

This inscription was probably burnt during manual process with any sort of electric engraving tool used for marking materials or

components (Fig. 4).

Additional macroscopic examination of the blade's fracture shows features of the fatigue fracture. Origin of the fracture is in place where the inscription was burnt (Fig. 5, Fig. 6). Around the origin of the fracture, in place of burnt inscription, there were found cracks and changes of the microstructure (Fig. 7, Fig. 8).

Cylinder Explosion on Cruise Ship Was Due to Corrosion

Bicycle crank failure

Using the wrong type of fasteners to secure the Bike Rack

Failure Analysis of Corrosion on Stainless Steel FastenersMetallurgical Technologies, Inc. (MTi) received five stainless steel bolts from a marine environment. The bolts exhibited corrosion predominantly on the head of the bolt around the set screw, underneath the head of the bolt, and in the threads. MTi was requested to determine the cause of the corrosion.

Results of the examination determined the bolts were manufactured from a free machining grade of stainless steel, not 316L stainless steel, which was specified. The free machining grade inherently contains a multitude of manganese sulfide inclusions. The inclusions led to localized galvanic cells between the base material and the inclusion. The parts were also partially sensitized (intergranular carbide precipitation), due to improper annealing. This resulted in corrosion attack along the grain boundaries.

The crevices created by the set screw holes and underneath the bolt heads allowed crevice corrosion to occur. Chloride stress corrosion cracks were also found at the corrosion sites. The use of 316L would be more resistant to crevice corrosion attack. The use of a duplex stainless steel with molybdenum (such as stainless alloys 2205 or 2507) would resist crevice corrosion and stress corrosion cracking.