Key Engineering Materials Vols. 413-414

Abstract: Structural health monitoring is receiving much attention as a means to prevent catastrophic failure in structures in operating conditions. In most cases fracture is caused by the growth of crack, which cannot be precluded in many engineering structures. Moreover, to have an accurate quantitative estimate of crack tolerance of a structure to prevent fracture of load bearing components, an effective non-destructive evaluation procedure becomes necessary to monitor the structure under working conditions.

Abstract: During annual inspections of one of Sweden’s most important railway bridges, the Söderström Bridge in central Stockholm, cracks in the web of the main steel beams have been discovered. Extensive theoretical work has been undertaken to assess the remaining service life of the bridge. Furthermore, the bridge has recently been instrumented to enhance the theoretical predictions by monitoring the real railway traffic as well as the response of the bridge. This article describes the monitoring program and the analysis methods used. Some interesting results regarding the remaining fatigue life are presented.

Abstract: During this decade, piezoelectric elements are explored and applied successfully in SHM, which has positioned them as an enabling technology for damage assessment. When permanently bonded to the structure, they provide the bi-directional energy conversion, which is used in impedance-based SHM. In this method, the variations of the structure’s impedance are monitored by piezoelectric elements. However, before experiments are performed, it is important to position correctly the piezoelectric elements on the structure. Therefore, the capability of piezoelectric actuators is explored under the aspect of sensor position. This work presents the investigation of sensing ability of surface-bonded piezoelectric element using numerical simulation and experiment. The results of numerical and experimental investigation are shown in this paper, which illuminates the model in the aluminium plate could be used to predict the state of it. In the experimental investigation, it also shows the factors which influence strongly the capability of sensor detection. Dealing with high frequency excitation, calculation requires a very dense finite element mesh, hence, the spectral element method (SEM) is chosen as model-based method, which is much more efficient than classical FEM. The structure, self-sensing elements as well as damage are modelled, from which the spectra of E/M impedance is computed. It gives the theoretical basis for the experiment design. The numerical results are verified and validated by experimental investigation. With such a numerical tool, the efficiency of the E/M impedance method can be clearly improved with respect to the determination of suitable piezoelectric element locations.

Abstract: Statistical damage detection in a structure operating under different temperatures via vibration testing is addressed by means of a stochastic global model based approach. The approach relies upon novel global models of the Functionally Pooled (FP) form, which are capable of describing the dynamics under any temperature, and statistical decision making. In its present form the approach utilizes response (output–only) vibration data, although excitation–response data may be also used. Its effectiveness is confirmed via a large number of experiments performed on a smart composite beam under different temperatures within the [¡20; +20]oC range.

Abstract: This paper presents a novel approach for structural damage detection. The cross-entropy method is used to estimate the structural parameters of a simply supported beam from its response to a static load consisting of a heavy vehicle. Various states of beam damage are modelled through local reductions in flexural rigidity. The proposed method estimates the distribution of stiffness throughout the beam using the deflections due to a heavy load located on the beam. Parameters such as initial distribution values, structural model, number of readings and sample size are varied to assess their influence on the prediction of the damage severity and its location.

Abstract: Damage identification methods based on Vibration are summarized in the paper. Their specialities are compared. Some problems of damage identification technology based on vibration and the past, current applications of the technology to mechanical engineering are introduced. The critical issues for further research in this field are also pointed out.

Abstract: The objective of this study is to show the potential of the crack detection method based on Wavelet Packet Transform (WPT), which is depending on the response at a single point on a beam subject to moving load. In this paper, an ANSYS model of a cracked beam is established. The moving load is transient analyzed by shifting the point of the concentrated force. The response at mid-span of the beam is calculated and wavelet packet transformed. The crack on the beam can be found by the abnormal signal in WPT branches. The size is also estimated by a defined damage index (Dindex) which relates to the energy of the abnormal signal. Finally, the effects of both crack location and wavelet selection on Dindex are discussed in detail.

Abstract: An overload limiter is used to prevent its overturning accident during an operating of a movable crane. Recently the indirectly measuring method, which measures hoisting load and overturning moment of overload limiter, demands instead of the existing method, which measures only hoisting load. The indirectly measuring method is how to conduct the hoisting load and overturning moment as measuring the load of hydraulic cylinder for a luffing driving of boom. So we need to develop the many-angular pin type load cell with the measuring angle of ±10 degree instead of the existing load cell with the measuring angle of ±2 degree. In this study we conducted the finite element analysis in order to evaluate the effect of the aspect ratio of measuring cross section on the measuring limit of the load cell to develop the many-angular pin type load cell. For this investigation, the aspect ratio of measuring cross section and load applying angle were adopted as design parameters and the stresses of measuring part were evaluated for each parameter.

Abstract: Model-based gear dynamic analysis and simulation has been a promising way for developing e®ective gearbox vibration monitoring approaches. In this paper, based on the dynamic model of a one-stage gearbox with spur gears and one tooth crack, we investigate statistical indicators and the discrete wavelet transform (DWT) technique to identify e®ective and sensitive health indicators for re°ecting the crack propagation level. Our results suggest that the root mean square (RMS) indicator is a good statistical indicator to re°ect the crack propagation in the early stage; DWT can improve the sensitivity of the RMS indicator and the RMS indicator becomes more sensitive with the increase of the DWT level.

Abstract: The ultrasonic time-of-flight-diffraction (TOFD) detection method has been widely used in crack size assessment. The key issue in TOFD is to determine the arrival time of crack tip diffracted signal. In the traditional cross correlation method, the resulting maximum peak of cross correlation function between two signals indicates the time of flight between them. In practical ultrasonic measurement, the transmission wave may be distorted and phase shift may be introduced. This paper presents a method using cross correlation and phase shift correction to improve the accuracy of crack sizing in the TOFD framework. The resulting maximum peak of the cross correlation function between two signals combining with time delay introduced by phase shift determine the arrival time of diffracted signal. Experimental results are used to demonstrate the advantage of the proposed method.