Papers by Keyword: Structural Damage Detection

Abstract: In order to verify the feasibility and validity of frequency ratio as diagnostic parameter in structural damage detection proposed in the Musical Tone Law Method (MTLM), steel pipes and three-story steel frame structure model tests are carried out. According to the experiment results, it is clear that the diagnostic parameter is effective for symmetrical structure in structural damage detection, such as cable structure, framed structure, and so on. Model tests prove that the frequency ratio is effective in detecting the 3mm width crack damage of steel pipe. In the damage detection test of three-story steel frame structure, the parameter also successfully diagnosed the damage caused by bolts loosening at the node of model.

Abstract: Independent Component Analysis (ICA) is a recent method of blind source separation, it has been employed in medical image processing and structural damge detection. It can extract source signals and the unmixing matrix of the system using mixture signals only. This novel method relies on the assumption that source signals are statistically independent. This paper looks at various measures of statistical independence (SI) employed in ICA, the measures proposed by Bakirov and his associates, and the effects of levels of SI of source signals on the output of ICA. Firstly, two statistical independent signals in the form of uniform random signals and a mixing matrix were used to simulate mixture signals to be anlysed by fastICA package, secondly noise was added onto the signals to investigate effects of levels of SI on the output of ICA in the form of soure signals, the mixing and unmixing matrix. It was found that for p-value given by Bakirov’s SI statistical testing of the null hypothesis H₀ is a good indication of the SI between two variables and that for p-value larger than 0.05, fastICA performs satisfactorily.

Abstract: The development of a methodology for the accurate and reliable assessment of structural damages, as one crucial step in the structural health monitoring (SHM) field, is very important to ensure the safety, integrity and stability of structures. An improved adaptive differential evolution (IADE) algorithm is proposed for structural damage detection (SDD) based on DE algorithm and FE model-updating techniques. An objective function is defined as minimizing the discrepancies between the experimental and analytical modal parameters (namely, natural frequencies and mode shapes). It is set as a nonlinear least-squares problem with bound constraints. Unlike the commonly used line-search methods, the IADE approach, a heuristic method for the direct search of the optimal point of the given objective function, is employed to make the optimization process more robust and reliable. Some numerical simulations for single and multiple damage cases of a 25-bar space truss frame structure have been conducted for evaluation on the reliability and robustness of the proposed method. The illustrated results show that the IADE algorithm is very effective for SDD. It can not only locate the structural damages but also quantify the severity of damages. Regardless of slight damage or multiple damages, the identification accuracy is very high and noise immunity is better, which shows that the IADE algorithm is feasible and effective for SDD.

Abstract: In order to solve the inverse problem on structural damage detection (SDD) in the field of structural health monitoring (SHM), a FGAPSO algorithm is proposed by a fusion of the genetic algorithm (GA) and the particle swarm optimization (PSO) in this study. For improving the simple GA with drawbacks of easy precocious and of lower computation efficiency, the real-coded GA is implemented, the chaotic logistic mapping is chosen for initializing population, the self-adaptive crossover-mutation operators and elitist strategy are employed. The GA is then mixed with the PSO algorithm for the population diversity and convergence by exchanging genes between two new populations internally and the goal of improving GA is attained at last. Further, some numerical simulations on a 13-bar planar truss structure with several damage cases have been carried out for assessing the performance of the FGAPAO. The illustrated results show that the proposed FGAPSO algorithm is better than any of conventional GA and PSO. Even for the slight damage case, it is still more feasible and effective for SDD.

Abstract: Nonlinear acoustics deals with various nonlinear effects that occur in ultrasonic wave propagation. The method is suitable for material characterisation, as it uses different nonlinear phenomena associated with material imperfections. The method has been used for detecting nonlinearities in cracked solids by: measuring distortions of acoustic signals, estimating resonance frequency shifts or assessing nonlinear vibro-acosutic modulations. The latter is the most widely used non-classical approach to probe material nonlinearities. The method involves vibro-acoustic interactions of ultrasonic wave and modal vibration in damaged specimens. Modulation intensity that strongly relates to damage severity - is usually assessed in the frequency domain and often leads to confusing results when large modulations are involved. The paper investigates the time domain analysis of vibro-acoustic modulated signals. Several methods for instantaneous frequency calculation used to assess the intensity of modulation - are compared. Simulated and experimental data are used in these investigations.

Abstract: Lamb waves are the most widely used guided ultrasonic waves for structural damage detection. One of the major problems associate with Lamb wave propagation is the effect of temperature on wave propagation parameters. It is important that these parameters are more sensitive to damage than to varying temperature. The paper demonstrates how amplitude and arrival time of Lamb waves are affected by temperature. The analysis is performed for the experimental data gathered from Lamb wave propagation in a damaged aluminium plate. A simple clustering algorithm is used to distinguish between "undamaged" and "damaged" conditions in the presence of changing temperature.

Abstract: A growing interest in non-destructive testing methods based on nonlinear acoustics have been observed for the last ten fifteen years. The majority of methods in this area take their origin from the observation that fatigue damaged materials often behave like mesoscopic nonlinear materials (e.g. rocks) in which nonlinear phenomena have been observed for years. The most important phenomena include: higher harmonics generation, vibro-acoustic wave modulations, amplitude dependent resonance frequency shift and slow dynamic effects. All these phenomena result mainly from elastic wave interactions with contact-type defects. There is enough experimental evidence in the literature showing that these nonlinear effects are much more distinct in damaged materials than in intact ones. Despite the fact that many experimental techniques - based on nonlinear acoustic phenomena - have been developed for the last ten years, the physical mechanism of elastic wave interaction with damage materials still not clear. The main reason is the variety of possible nonlinear mechanisms involved. This includes: nonlinear elasticity and dissipation, contact acoustic nonlinearity based on herztian and rough surfaces contact theories and other effects such us adhesion, friction and thermoelasticity. This paper provides a short summary of various theoretical developments and examples of applications to damage detection in different materials.

Abstract: A new MRACO identification algorithm is proposed for structural multi-damage detection through combining MapReduce procedure and ACO method in this paper. Four classical benchmark functions are first employed to evaluate convergent performance of the MRACO algorithm, which pursues a global solution to combination optimal problem with constrained conditions. Then, a series of numerical simulations on constrained optimal problem about structural multi-damage detection of a two-story rigid frame have been conducted for assessing the applicability of the new MRACO algorithm applied to the structural damage detection field. Finally, some illustrated numerical results show that the MRACO algorithm can not only locate the structural multiple damages but also effectively quantify the severity of damages with higher accuracy and good noise immunity.

Abstract: Glass fibre reinforced composites (GFRC), used in the manufacture of wind turbine blades, can suffer unpredictable, post-manufacturing, in-situ structural failure. The economic cost of remediation of such blade failures is extremely high, both on land and offshore. We suggest using zero-time-to-echo (ZTE) magnetic resonance imaging (MRI) as a method for characterising glass fibre reinforced composites. Initially, we demonstrate that carbon-13 Nuclear Magnetic Resonance (NMR) spectra acquired at 800MHz provide finger-print like information and that there is sufficient hydrogen-1 NMR signal available to conduct MRI. This work explores the efficacy of using zero timetoecho (ZTE) magnetic resonance imaging (MRI) to detect the rapidly decaying Hydrogen-1 (¹H) NMR signal from a representative sample. A 400MHz surface resonator was developed made of a 20mm diameter loop formed with 1.5mm thick silver wire and designed with variable tuning and matching in order to investigate the ¹H-MRI signal at 9.4T static magnetic field strength. The thickness of the GFRC was determined from the MRI data to be 3.51±0.28mm while the physical measurement using a caliper device resulted in a measurement of 3.45mm. Hence, a high spatial resolution accuracy is provided by ZTE MRI. Very short T₂* (<20μs) of the material led to stronger blurring artefacts for the blade material compared to heat shrink used for insulating the silver wire of the detector. ¹H images of the blade material were acquired demonstrating that ZTE is a suitable technique for acquiring image data from glass fibre materials. Work is on-going in studying the relaxation time parameters and chemical frequency shifts for materials with and without structural weaknesses in order to improve the predictive power of the technique. In conclusion, ZTE-MRI can provide useful information about the mechanical properties of glass fibre reinforced composites.

Abstract: Based on the vibration information, a mixed sensitivity method is presented to identify structural damage by combining the eigenvalue sensitivity with the generalized flexibility sensitivity. The sensitivity of structural generalized flexibility matrix is firstly derived by using the first frequency and the corresponding mode shape only and then the eigenvalue sensitivity together with the generalized flexibility sensitivity are combined to calculate the elemental damage parameters. The presented mixed perturbation approach is demonstrated by a numerical example concerning a simple supported beam structure. It has been shown that the proposed procedure is simple to implement and may be useful for structural damage identification.