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Tribological failure investigation: (the science of wear, friction, lubrication and mechanical failure)
General misbehaviour and tribological failure affects all mechanical devices. There are two main reasons for determining the reason for the failure of mechanical components. The first is the need to establish who is responsible for the failure and accountable for making good the damage. The second and probably the most important reason, is the need to ensure the problem is correctly identified to prevent its recurrence.
Abnormal noises, overheating, power loss, low oil pressure, misfiring, difficult starting, drivability and performance complaints can all be indications of problems that need to be addressed. The underlying cause may be something minor or major. There’s no way of knowing unless someone investigates.
In the event of total failure, the diagnostic techniques used to analyse and determine the failure cause often depends upon whether or not the failure is an isolated case or a high incidence occurrence.
Most failures exhibit several conditions which collectively produce the end result hence, a single cause failure is a very rare occurrence. Conditions which inevitably lead to malfunction or failure are a consequence of wear, component fatigue, misassembly, flaw in component manufacture or lack of attention to routine maintenance. The ultimate failure is usually related to [a] temperature, [b] lubrication or [c] misassembly.
The mechanical breakdown “post-mortem” starts by obtaining as much information as possible surrounding the circumstances that preceded the failure. In addition, as much information and data as possible is collected in terms of the vehicle type, specification, operating environment and maintenance history. A decision is ultimately reached from the condition of the defective components in terms of whether or not the failure would have been possible by the mode described by the vehicle operator.
Components and fractured surfaces are analysed carefully. Defective components and fracture surfaces do not have a personality – they do not tell lies and hence provide an accurate picture of the failure mechanism. Machines are not supposed to break, and mechanical components such as shafts, gears, belts, gaskets, fasteners and structures are not supposed to fail. But when they do fail, the defective components, residual debris and fractured surfaces can tell exactly why.
The causes for more than 90% of all mechanical failures can be detected with careful physical examination using low power magnification and some basic physical testing. Inspection of failures show the forces involved, whether nor not the load was applied cyclically or was single overload, the direction of the critical load, and the influence of outside forces such as residual stresses or corrosion. Then, accurately knowing the physical roots of the failure, the human errors and the latent causes of these physical roots may be established.
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