O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

18.2 Wear assessment
The following wear characteristics are distinguished:
Limit wear corresponds to the limit state of the wear product or its component. This is wear and tear at which the product is inoperable.
Allowable wear is the amount of wear at which the product retains its performance. It is less than the limit.
Local wear - wear on a separate section of the friction surface.
Wear diagram is a graphic representation of the distribution of local wear values over the friction surface or over a certain section of it.
Wear rate is the ratio of the wear value to the time interval during which it occurred.
Depending on the dimension of wear values, linear, mass and volumetric wear rates are distinguished:
(18.1)
where h, M, V are the thickness of the worn layer, the change in the volume and mass of the abraded element, t is the wear time.
Distinguish between instantaneous (at a certain point in time) and average (over a certain time interval) wear rates.
Wear resistance is the property of a material to resist wear. Wear resistance refers to certain friction conditions and is evaluated by the reciprocal of the wear rate or wear intensity.
The main trend in the development of mechanical engineering has always been the desire to increase the productivity of machines. Therefore, increasing the wear resistance of materials, machine parts and assemblies is the main and always topical task of tribological engineering.
Methods for solving it include:
1) search for the best designs of friction pairs,
2) selection of the most efficient technological processes for processing friction surfaces,
3) competent operation and an expedient system of repairs of friction pairs,
4) development and rational use of tribological materials.
18.3 Reliability of friction pairs
Reliability is a complex property of a technical object (machine, device, friction pair), consisting in its ability to perform specified functions, while maintaining its main characteristics (under certain operating conditions) within the established limits. Reliability indicators - probability of failure-free operation, time between failures, technical resource, etc.
Failure is a malfunction of a friction pair due to an unacceptable change in parameters (wear, friction coefficient, temperature, etc.) under the influence of physical and chemical processes occurring in a pair (friction, corrosion, etc.) and external mechanical, climatic or other influences.
Operating time - the duration of the operation of a friction pair for a certain period of time.
MTBF is the average value of the running time of a friction pair between failures.
Technical resource is the operating time of a friction pair until it reaches the limit state specified in the technical documentation.
The probability of failure-free operation of a device consisting of one element is determined from the expression:
(18.2)
where t is the operating time of the device from the moment it was turned on, =1/t ₀ is the probability of failures, t ₀ is the time between failures. This dependence is shown graphically in Figure 18.1. At t=0, the probability of failure is zero, therefore, the probability of failure-free operation p=1. The longer the operation time, the greater the probability of failure and the lower the probability of failure-free operation.