MECHANICAL SYSTEMS RELIABILITY

Mechanical Systems Reliability



Mechanical Systems Reliability

Selecting a set of bearings to support the anticipated loads is a common design task teams transmission power. Another concerns the search for a cumulative component reliability that exceeds the standard 90% to a specified number of cycles or hours.

A good way to start a feasibility study defines what constitutes a failure. Then identify the most important failure modes for the team. The next step analyzes the test data for each failure mode to establish the reliability of each function of time, cycles, or some other quantifiable measure. In other words, at time t:

R1= f1(t),

R2= f2(t)

and so on. Then total system reliability becomes:

Rsystem= R1 R2R3

and so on at time t.

As a general rule, evaluate the test data in terms of Weibull distribution, because it is rare that any set of field and laboratory data clearly fit a particular standard distribution such as exponential, binomial or normal. In addition, a particular failure mode can not occur until something else has led to a certain level. In other words, a failure mode can be at least partially, a secondary failure. These usually appear as an excessively high number of Weibull slope. Usually can be corrected by applying third parameter Weibull, or offset, from the origin. This is a fairly simple calculation for most any software routine reasonably capable of Weibull.

Bearing present a unique problem because they are usually specified by the manufacturer in terms of a dynamic load. For ball bearings, this is the charge in which approximately 10% of them when turned to 1 million revolutions of the outer race. Roller bearings are specified using a similar system, but the failure of 10% corresponds to 3,000 hours at 500 rpm or 90 million revolutions. rpm of the machine can be converted to hours.

At 2,500 rpm, this corresponds to

Where L10h = bearing life, hr , and= bearing speed, rpm

This is the first 10% failure point.

This is all very well to find one with 10% of hours failure (or revolutions). However, designers should be interested in the complete system that includes probably more of a bearing. The reliability of the hardware or farm equipment is usually specified by the marketing group, something like "There is no failure more than 1% (99% confidence) through the first year and not take more than 10% (90% reliability) to the fifth year. "Many consumer products are subject to similar requirements, particularly in the first year.

To arrive at a system that is over 99% reliability during the first year and 90% through the fifth, all reliability critical components exceed these figures in a significant amount. The bearings are generally included in the category of critical components.

Reliability is an indicator of the Weibull plots. For example, several research projects tend to show a range of variability in the value of Beta, Weibull shape (slope) factor bearing. It is also reasonable to assume that the level of load bearing or perhaps even the relationship between the capacity of base load applied dynamics can affect the shape ...