Processing of Blade Monitoring System Data
The paper describes a new method for evaluating a relative damage accumulated in critical points of all blades of one rotating turbine disc out of sparsely sampled positions of their tips provided by blade monitoring system. The measured signals are reconstructed with the help of information on approximate resonant frequencies by reconstructing aliased Fourier spectra. The reconstructed signals contain as many resonant frequencies as have been applied for. The relative damage is estimated from Palmgren-Miner law of linear cumulation of elementary damages caused by closed hysteretic loops found by means of a multi-channel rain flow method applied to the reconstructed signals.
Software Support of Fatigue Tests
The paper deals with a problem of preparation of non-standart tests to be run on hydroelectric loading systems, and processing measured data. The goal of tests is to obtain new information on material properties under random loading. The current fatigue tests are carried out on the computer controlled systems. Hence, a set of special programs should be available besides of the standard ones, which are delivered with the control system. Those programs having a research character should be prepared either on the order or do it yourself bases. Program modules for preparing loading processes with a prescribed spectral properties, and for a decomposition of random signals into a sequence of full cycles (rain-flow), damage estimations based on hypotheses of Palmgren-Miner, Corten-Dolan and Haibach are described in the paper. In all of them, the influence of the mean values are taken into account.
The Influence of Power Spectral Density on Durability of the Constructions Under Random Loading
Stress - strain dependence is not linear in a plastic zone of notches and fronts of propagating fatigue cracks. Of rather great importance is here a plastic strain amplitude, and under plastic deformation also a deformation rate dependent on a volume of energy supplied in a given moment. Power spectral density yields an information on total energy distribution in selected frequency band of a wideband random process. The paper follows the effect of power spectral density shape on fatigue life of three random wideband processes with Gaussian amplitude distribution and frequency range 0 ÷ 10 Hz. Compared are three modes: constant (white noise), linearly increasing and linearly decreasing. Total strain power is constant in all cases. Fatigue life of mentioned processes is compared to compressed processes with the same frequency, intensity and sequence of amplitudes, running only under one frequency of 10 Hz.
An estimation of the residual life of blades
The paper deals with a problem of estimating the length of life of long turbine blades out of measurements of stresses during an operation. A relative damage of the blades is estimated basing on law of linear cumulation of damage due to Palmgren and Miner. Results of simulated measurements of hypotetic blades are presented.
