Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Mechanical and Aeronautical Engineering
Selected Highlights from Research Findings
Rockfalls continue to be the biggest cause for accidents that result in fatalities and injuries in underground mines in South Africa. An effective face support system to minimise rockfalls in rockfall-prone mines was developed during a project sponsored by the Safety In Mines Research Advisory Committee (SIMRAC).
A technology demonstrator roof support unit was developed and evaluated. It consists of two similar support units connected to each other via two crank mechanisms. Different concepts were developed and evaluated against the system specifications and it was then developed and tested on surface. The process included detail design, building and testing of components and sub-systems, design reviews and then the building and commissioning of the technology demonstrator.
The testing of the system was done in a 500-ton hydraulic press, in a mock-up stope and underground. A risk analysis, in which technical, logistical and economical aspects were assessed, was done to determine the critical areas
Contact person: Dr NDL Burger.
Owing to the crippling nature of arthritis, surgeons have been trying for well over a century to successfully treat this debilitating disease particularly when attacking the hip joint.
Many different designs have been developed but they all revolve around a femoral stem, femoral head and acetabular component. Independent of the design, longevity of the implant remains a problem. The major cause of replacements, according to various hip registers, is due to aseptic loosening resulting from osteolysis.
This study performed a root cause failure analysis to determine the principal reason for mechanical failure on failed acetabular cups, retrieved during revision surgery, by making use of sound engineering failure analysis techniques.
The bearing couples varied between steel on UHMWPE and ceramic on UHMWPE. The information gained during this analysis brought to the fore that the principal mode of mechanical failure for acetabular cups is overheating of the UHMWPE. The overheating is mainly due to a lack of good and/or sufficient lubrication
Contact person: Dr NDL Burger.
Imperfections (undulations or bumps) in the geometry of cylindrical shells have a large influence on their buckling behaviour. In particular, it is well known that imperfect shells buckle at much lower applied loads than if they had a perfectly flat surface.
The manufacturing methods through which such shells are made always lead to some level of geometric imperfection. When designing structures that contain imperfect geometries – the impact-absorbing structural member hidden behind a motor vehicle’s bumper, for instance – it is important to take the effect of such geometrical imperfections into account during the numerical simulation of the crush performance.
One way to model geometric imperfections are through the use of random fields, realised through spectral series expansions (also referred to as Karhunen-Loève expansions). For these expansions to be generated, however, some knowledge of the covariance function describing the imperfection amplitude and wavelength is required.
Prof Ken Craig of the Department of Mechanical and Aeronautical Engineering has conducted research in which the methodology as implemented into the dynamic simulation code LS-DYNA® was applied to the optimal design of thin-walled cylindrical shells with cut-outs to save mass.
Using Monte Carlo simulations within a Design of Experiments metamodelling framework through the use of the design optimisation software LS-OPT, the coefficient of variation of the peak force during collapse was minimised while constraining both the maximum average peak force and the average energy absorbed by this structure.
The result of this process is a robust, optimal design, which, although heavier than its counterpart not incorporating imperfections, minimises the effect of geometrical imperfections on the resulting design’s performance
Contact person: Prof KJ Craig.
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