Showing papers by "Arthur W. Lees published in 2005"

Detection of severe sliding and pitting fatigue wear regimes through the use of broadband acoustic emission

Abstract: Acoustic emission techniques have been used to monitor severe sliding and pitting fatigue processes during four-ball testing. Results are presented that arose from a collaborative programme between the Naval Research Laboratory (Washington, DC) and the University of Wales Swansea, sponsored by the US Office of Naval Research. The ultimate aim of the research is to develop a systematic fusion technology approach to condition-based maintenance of wear-related surface distress of critical components in naval air and surface combatant engine and transmission systems. The principal monitoring technique utilized in this investigation was acoustic emission (AE). A custom data acquisition system was developed using a novel approach to collect AE signals. Post-test analysis of the data, in the frequency domain, demonstrates the advantage of analysing continuous AE and not just AE pulses.

A conforming unified finite element formulation for the vibration of thick beams and frames

Abstract: Beams and frames are common features in many engineering structures and in this paper an approach is given to model their dynamic behaviour adequately. Whilst the eigen-frequencies of continuous systems comprising of slender beams can be identified, in most cases of practical interest, by means of Euler or Timoshenko beam theory, for structures comprising of thick beam models this is not necessarily true since such idealizations constrain the cross-sections to remain planar. This paper suggests an alternative approach by means of a unified fully conforming plane stress rectangular finite element which is believed to allow for more realistic representation of the shear effects and hence the strain field around the joints of such structures. The usefulness and functionality of this improved numerical approach is explored via comparison against a non-conforming two-dimensional plate as well as one-dimensional Euler–Bernoulli and Timoshenko finite element formulations corresponding to a variety of beam aspect ratios representing the structures of a rotor and a portal frame. The idealization is shown to be particularly advantageous for simulating the effects of shear distortion where beams join at right angles and the transverse forces in one member interact with the extensional forces of the adjoining structure. Copyright © 2004 John Wiley & Sons, Ltd.

Uncertainty Quantification using Maximum Likelihood: Experimental Validation

Abstract: Parameter uncertainty is extensively used to analyze the robustness and reliability of a structure. However this analysis requires the specification of the uncertainty, and for many parameters this is not an easy quantity to estimate. This paper uses a maximum likelihood approach, combined with either a perturbation or Monte Carlo method for the forward propagation of uncertainty, to estimate the parameter mean and variance. The method is demonstrated on two experimental examples, namely cantilever and free-free beams with a moving mass.