Papers by Author: Luigi Garibaldi

Abstract: In this paper a time-varying identification method is presented, in order to detect the presence of an open crack in a beam with a moving mass travelling on it. The ratio between the considered moving mass and the total mass of the beam is high, thus the identified modal frequencies of the whole structure are time-varying. This situation often occurs when considering the dynamic interaction beetween a train and a bridge and specific identification tools must be used. It is shown that the identification method, referred to here as Short-Time Stochastic Subspace Identification, can give information about the presence of damage in case of time-varying systems.

Abstract: Diagnosis of rolling elements bearing plays an important role on the running and maintenance of mechanical equipments. To enhance the feature of fault and to further diagnose the status of bearings with a small fault size so as to realize the early recognition, the method of inverse filter based on Autoregressive model is presented in this paper, and the corresponding criterion of order selection is also discussed. Analysis of simulation signals and real data show that this method could enhance feature of impulse signal. Meanwhile, it is also found that for small size fault, the root mean square feature is more effective than kurtosis value, which is considered very useful for early diagnosis of rolling elements bearings.

Abstract: The acoustic emission (AE) technique, whose modern roots are found in the early 50’s, analyses the elastic waves generated into solid materials in a frequency range usually well above the human ears limit. AE are sound waves emitted when abrupt variations occur in the local distribution of strain in a medium. These variations are generally associated with, for example, the growth of fractures, phase transformations and corrosion under various loading conditions. This is why the AE technique can be applied as a non destructive and passive tool in condition monitoring of structures, a typical application being the pressure vessels and piping field. In this paper, after a short summary on wave propagation, the AE is simulated by a pulse generator, acting on a bar and a plate. The aim is to highlight the effects of the sensors positioning on some of the parameters frequently adopted to describe the AE activity, e.g. its amplitude and strength.

Abstract: This paper describes the design of a rig devoted to testing rolling bearings. In order to control the signal-to-noise ratio of the measures, a potentially very silent test rig has been designed and assembled, with the possibility of simply changing the bearing under investigation as well as its load level and rotating speed. Acceleration data have then been examined by means of envelope, wavelet transform and cyclostationarity analyses, showing that the testing machine fulfils its task.