Theoretical and practical issues of processing digital information in the problems related to durability assessment in conditions of loading are considered. Due to the specifics of the problem, in which the precise dedermination of the extreme values and their sequence is of primary importance, a number of generally accepted recommendations appeared invalid. For example, the Kotelnikov theorem, which was originally proposed in relation to the problems of estimating the frequency composition of the process, can lead to significant errors. It is shown that the requirements to the analysis of random loading processes with a goal of further assessment of the durability, due to their specificity, contradict with the specified requirements, namely, when choosing a frequency according to this rule, an error can be made, and not to the margin of the strength assessment. We considered the issue regarding digital filtering of hardware overshoots. Alternative approaches to the selection of extrema of the random process are analyzed: 1) direct hardware selection of extrema and 2) discretization by the method of level crossings. The latter approach has an optimal algorithm for isolating extremes and makes it possible to isolate extremes of a random process with lower costs and greater accuracy. The natural transition to integer arithmetic provides further optimization of the algorithm. The model and real examples demonstrate gains in terms of speed and memory, which ultimately promote an increase in the reliability of the information required for assessing the durability. The savings in memory and performance will allow processing of long-term implementations and result in a more accurate estimating of the remaining life and durability at the stage of production.
The paper describes one of the most promising ways of structure health monitoring based on analysis of the kinetics of local stress-strain state. Comparison with other methods of damage detection and advantages of the stress-strain state control are considered. To implement this method of monitoring, two types of sensors are considered: strain gauges and fiber Bragg gratings (FBG). The advantages of FBG, due to which their use in operation is most preferable, are presented. The possibility of using stress-strain state control is analyzed for a promising transport aircraft using the results of tensometry under cyclic loading. The relevance of the work is confirmed by various examples of using monitoring methods in on-board systems during operation. The possibility of monitoring the airframe parts is demonstrated for longitudinal fuselage joints as an example. The change in the stress-strain state of the longitudinal joints, caused by structural damage was confirmed by tensometry analysis and by analysis of the stress-strain state of bearing sheet by the finite element method (FEM), taking into account the fatigue cracks originated during cyclic loading. The results of the calculation are compared with the tensometry data. Proceeding from the results of the calculation of the stress-strain state of the damaged and undamaged structure, the zones of the greatest deformation change are determined to optimize potential locations for the sensors. The optimal placing of the sensors for monitoring the integrity of the joints is proposed. The study confirms that the method of damage monitoring of the structure, developed on the basis of changes in the kinetics of the stress-strain state, can be successfully used in tests for maintaining the integrity of joints and other places with multi-site damages, where the methods of visual and non-destructive testing are not effective.
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