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Sound and vibration transmission in OGO SPACECRAFT shroud system
Random numbers were generated with the aid of a digital computer and transformed such that the probability density function of a discrete random load history composed of these random numbers had one of the following non-Gaussian distributions: Poisson, binomial, log-normal, Weibull, and exponential. The resulting random load histories were analyzed to determine their peak statistics and were compared with cumulative peak maneuver-load distributions for fighter and transport aircraft in flight.
The prediction of fatigue crack growth is an important element of effective fracture control for metallic structures and mechanical components, especially in the aerospace industry. The prediction techniques available and applied today are mostly based on fatigue crack growth measurements determined in constant amplitude testing. However, while many service loadings are constant amplitude, many more loadings are random amplitude. An investigation to determine which statistics of random loadings are relevant to fatigue crack closure was conducted. The fundamentals of random processes and crack closure are briefly reviewed, then the relevance of certain random process parameters to the crack closure calculation are discussed qualitatively. A course for further research is outlined.
Papers are presented in the volume summarizing the baseline data, methodology, procedures, and results of a round-robin analysis which was conducted to predict the fatigue crack growth in 2219-T851 aluminum center-cracked specimens subjected to flight loading in random cycle-by-cycle format. The objective of the analysis was to assess whether data from constant-amplitude fatigue crack growth tests on center-cracked specimens can be used to predict fatigue crack growth lives under random loading. The following approaches are discussed in detail: a root-mean-square approach, a crack-closure model, a multi-parameter yield zone model, and a load-interaction model.
A method is developed for predicting the probability of stress-corrosion fracture of structures under random loadings. The formulation is based on the cumulative damage hypothesis and the experimentally determined stress-corrosion characteristics. Under both stationary and nonstationary random loadings, the mean value and the variance of the cumulative damage are obtained. The probability of stress-corrosion fracture is then evaluated using the principle of maximum entropy. It is shown that, under stationary random loadings, the standard deviation of the cumulative damage increases in proportion to the square root of time, while the coefficient of variation (dispersion) decreases in inversed proportion to the square root of time. Numerical examples are worked out to illustrate the general results.
Results of random-loading fatigue tests on 125 notched cantilever-beam specimens and constant-amplitude fatigue tests on 46 similar specimens are presented in terms of the root-mean-square value of peak stresses. The results from the two sets of tests are compared on the basis of time to failure, where the results from the constant-amplitude tests are expressed in terms of an equivalent time to failure based on the natural period of vibration. Compared on this basis, failure at the lower stress levels occurred in a shorter time for the random loading than for the constant-amplitude loading, whereas at the higher stress levels failure occurred in the reverse order. A theoretical result for random loading is also presented and compared with the experimental results. The theoretical result shows good agreement with experiment for low values of stress but underestimates the time to failure at the higher stresses.
Fatigue of reinforced concrete due to sinusoidal and random loadings
Fatigue life characteristics of aluminum alloy specimens under random load to failure
Fatigue life of aluminum alloy specimens for aircraft and launch vehicles under various random loading spectra
Effect of spacewise variations in random load field on response of linear system - statistical mechanics
Probability density of extreme values of deflections and stresses of elastic shell nonlinear vibrations under random loads
Statistical aspects of height of rise and fall in continuous random loading relevant to fatigue failure
Modeling laws for space vehicles under random dynamic loading
A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.
Statistical properties of dynamic response of structure to random load field, examining simple deterministic loadings
Equations for computing noise transmitted to space vehicle inside from random loading on outside
Quasi-steady aerodynamics were assumed, as well as a torsion mode where the amplitude is proportional to the distance from the rotor center. Aerodynamic torsional moment inputs are limited to the region of reverse flow where the aerodynamic center and the section center of gravity are separated by half the blade chord. Thus negligible effects of blade torsional flexibility are obtained for rotor conditions with negligible reverse flow effects. Numerical examples refer to conditions with 1.6 rotor advance ratio. It was found that the random flapping response is only moderately affected by torsional flexibility. However large random torsional loads and deflections occur even if flapping is completely suppressed. The coupling of the actual flapping motion into the blade torsional motion produces a substantial increase in the random torsional loads or deflections.
Reliability was determined for two degrading dynamic systems subject to random load processes. Damage is caused by loss of components for Daniels systems and crack extension for plates with cracks. The analysis accounted for the coupling between response and current damage state of the system. It is based on mean crossing rates of conditional processes and properties of diffusion models. Simple systems are used to illustrate proposed methods for estimating reliability.