IFMASS8

351

By joining the points at the levels of service fatigue strength

′′

and

′′′

a dissipa-

tion range is formed around the lower part of the service fatigue strength line. For the

points on the level

′

parallel with the line for time strength forms the dissipation range

around the upper part of the service fatigue strength. The third region overlaps with the

dissipation region of the failure probability for infinite life strength. Based on the

obtained border curves it is possible to determine the functions of the distribution of the

failure probabilities for any level of service fatigue strength

and for any cycle number

up to failure

. It is also possible to determine the coordinates of the breaking points of

the service fatigue strength curve for the respective failure probability as well as the

respective exponent of the service fatigue strength curve q.

CONCLUSIONS

The fatigue process of machine parts has not been studied sufficiently, particularly in

the part until cracks occur. Besides this, the process is stochastic, i.e. hard to predict

either by applying theoretical or empirical methods. Those are the reasons why experi-

mental results and mathematical statistics in the form of probability indicators – reliabi-

lity are used in practical applications.

The indicator of the possibility for the occurrence of fracture on a certain place at a

certain time in machine systems is elementary reliability. It represents the controlled risk

of the designer to allow such a place for the possibility of failure with the aim of

rationalizing the dimensions in comparison with the complete safety which is expressed

by the safety factor.

The procedure for the determination of the elementary reliability is simple and has

been presented in the initial part of the work. The gathering of the information required

for the calculation of this reliability is a big problem. Extensive research is required for

the purpose of statistic generalization. Procedures which enable rationalization in the

scope of the testing process have been presented in this work.

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Leitch, R.,

Reliability Analysis for Engineers – An Introduction

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Savić, Z., Janković, M.,

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