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After 11,300 h of operation, one of the axles of the reduction gearbox of the hoist mechanism of a dockside crane failed due to the propagation of a fatigue crack. The axle contained two gears, the largest of which was mounted swith a key, while the smallest gear was an integral part of the axle. On both ends of the axle a bearing was mounted: one cylindrical bearing and one spherical roller bearing (locating bearing). The axle was made from 17CrNiMo6 steel, and the machined gear teeth were case carburised. The failure of the axle occurred in the middle between both bearings of the axle, on a non-contacting part of the gear machined on the axle. During visual inspection striations were observed on the fracture surface and three separate crack initiation zones could be observed on three neighbouring gear teeth. The ratio of final fracture versus fatigue fracture was low, indicating a low nominal stress on the axle. The three initiation sites were investigated with optical microscopy and SEM, and clear indications of a ductile overload fracture were found. In an etched longitudinal section of one of the gear teeth where initiation took place several cracks could be observed in the hardened case of the tooth. The hardness at the initiation site was found to be 777 HV, while the hardness at the final fracture (diametric position relative to the initiation of the crack) was found to be lower, namely 722 HV. It was concluded that at the initiation site during the case carburisation quenching cracks were formed, which then propagated through the whole section of the axle under relatively low operation load.

Polymers are frequently used in tribological applications because of their self-lubricating ability and loadability. However, most research on their friction and wear mechanisms is performed on small-scale test samples under relatively low normal loads. The present paper presents test results that are obtained on large-scale test samples under extremely high loads (190–3380 kN, corresponding to 8–150 MPa), providing more accurate design information for construction of e.g. sea-lock or crane guides. Performance and failure modes in overload conditions are investigated. Pure polyethyleneterephtalate (PET) shows high friction and unstable wear due to stick-slip. Filled with polytetrafluouroethylene (PTFE), friction is reduced and becomes stable even when loaded above the yield strength. The plastic deformation of the sliding surface under overload conditions allows for the formation of a transfer film on the counterface, resulting in a decrease of specific wear rate at higher loads. A model is presented for correction of wear measurements that contains both real material loss and deformation due to creep and thermal expansion. For the latter, temperatures as measured from frictional heating are corrected and evaluated according to known temperature models. Compared to small-scale cylinder-on-plate and bloc-on-ring tests, friction coefficients measured on large-scale tests are much lower due to large polymer transfer, while wear rates are much higher. The availability of PTFE and favourable plastication of the sliding surface on large-scale tests result in the build up of a coherent lubrication transfer film.

The Ghent Knee Rig was built in 2006 for studying the biomechanical behavior of postmortem human knees. To validate this test rig the patellofemoral contact pressures and areas were investigated in 3 post-mortem knees tested under the same circumstances and compared to results in literature. To load the quadriceps, the vastus intermedius and rectus femoris were separated and clamped together. The pulling cable was aligned according to the shaft of the femur to keep the Qangle at physiological values. A pressure film was inserted in the patellofemoral joint to measure the patellofemoral contact area and pressure. The results follow the general accepted trends of patellofemoral contact during knee flexion and extension; when the patella enters the trochlear groove at approximately 20 degrees of knee flexion, the intra articular contact pressure and area start to build up and the contact area on the patella shifts from distal to proximal. Though working with cadaveric specimens remains a simulation of in vivo situations with well known limitations, the test rig shows a good repeatability and reliability. The next stage of this research project is a comparison of normal with pathological knees

A test rig for studying the biomechanical behaviour of post-mortem human knees is built. For loading the quadriceps tendon a special clamping device is constructed, so the forces up to 3000 N could easily be transferred to the tendon. Several post-mortem human knees used in this study are tested to collect data about the general biomechanics of knee joint during squatting. The forces in the quadriceps tendon and in the tibia are measured continuously; the flexion angle is also measured. On this modular test rig, the contact pressures of the patellofemoral joint are measured as well. Therefore a thin pressure film is used. Not only are measured the contact pressures, but the changing contact area is also visualized and measured. The forces and rotations measured in the joint and in the contact area allowed us to obtain perfectly reproducible values as well as a positive relation between contact area, contact position and working direction of the quadriceps tendon.