Damage Assessment of Structures VII

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Authors: Teresa Berruti, Christian M. Firrone, M. Pizzolante, Muzio M. Gola
Abstract: Forced vibrations can lead to an irreparable damage of a blade array. Devices called “underplatform damper” that dissipate the vibration energy are employed in order to reduce blade vibration amplitude. The present paper deals with the design of the underplatform damper. A numerical code to calculate the forced response of a blade array with dampers has been previously purposely developed. A method is here proposed for the estimation of the unknown contact parameters demanded by the code. The computation results are here validated by means of comparison with experimental results on a static test rig. Three dampers with different shape are tested.
Authors: Chun Sheng Wang, Yue Xu, Ai Rong Chen, Wei Zhen Chen
Abstract: According to the fatigue damage failure mechanism of riveted members, a riveted member probabilistic fatigue failure model (RMPFFM) was proposed, and a fracture finite element program is developed to calculate the geometry function of RMPFFM. Furthermore, a system fatigue damage reliability model of riveted bridges was proposed, and based on Monte-Carlo method, a large system fatigue damage reliability analysis program was developed to calculate the system fatigue failure probability. Then the system evaluation model was used to predicate the system fatigue damage reliability of Ganjiang Railway Bridge. According to assessment results, the probabilistic remaining fatigue life, safe inspection intervals and maintenance strategy are determined, which can control and avoid fatigue failure accident and reduce the contingent disaster in bridge service life.
Authors: Soo Yeon Seo, Hyun Do Yoon, Cheol Woo Park
Abstract: Three RC slab specimens were designed and manufactured to investigate the fatigue behavior of RC slab retrofitted with carbon fiber mesh (CFM) and mortar. Among three slab specimens, two slabs were pre-loaded to introduce damage prior to the fatigue loading tests. Fatigue loading was applied to the top of slab maintaining 40% of the ultimate strength of specimen at 2Hz loading speed. The fatigue test was terminated when the loading cycle exceeded 1,000,000 cycles. From the test results, the effectiveness of the retrofitting using CFM was evaluated. Test result showed that the specimens retrofitted after either severe or light damages had very similar strength and stiffness to those of the specimens retrofitted without damage. It was found that the strength was even slightly improved in the specimen retrofitted with CFM.
Authors: Janice M. Dulieu-Barton, M. Sahin, F.J. Lennard, D.D. Eastop, A.R. Chambers
Abstract: The findings of a year-long programme carried out by a multidisciplinary engineering/conservation team are described. A mass-produced textile material that can be used to represent tapestries is identified and mechanical tests are detailed which demonstrate it behaves in a similar way to tapestry. The feasibility of using optical fibre sensors, full-field optical strain measurement techniques and thermography for monitoring tapestry degradation is assessed. The results of preliminary findings are presented and a rationale is developed for in-situ quantitative strain monitoring of tapestries.
Authors: Simon P. Shone, Brian R. Mace, Tim P. Waters
Abstract: The wave reflection coefficients of damage such as cracks, notches and slots in otherwise uniform beams depend on frequency and on the size of the damage. Experimental results are presented for the wave power reflection coefficients of transverse slots of various depths sawn into a number of beam specimens. These results are compared with a conventional spring model to estimate the depth of the slot. The method appears to work well for larger slot depths (greater than about 30% of the thickness of the beam) and at higher frequencies, allowing their existence to be inferred and their size to be estimated. This is due to the fact that the reflection coefficients are larger in these regimes. For smaller slots or at low frequencies, noise and experimental errors, such as miscalibration errors and ill-conditioning, become more significant.
Authors: Nicola Maria Pugno
Abstract: In this paper the damage assessment of nanostructures is discussed. As an example we assess the damage of nanobeams with non destructive dynamical resonance or destructive tensile tests: a small number of nanocracks, i.e., ~10, with length of ~1nm, is accordingly estimated.
Authors: Daley Chetwynd, T.L. Lew, Keith Worden, Jem A. Rongong
Abstract: This work was conducted as part of the European Union project ARTIMA and it investigates the potential for a dual use active constrained layer damping treatment for both vibration control and structural health monitoring. It examines a curved aluminium plate with an ACLD treatment formed by mounting a large piezoceramic patch with Araldite 2027. The plate was investigated by ultrasonic Lamb waves generated by the patch, and several smaller piezoceramic transducers were used as sensors. Damage was simulated by adding incrementally increasing saw cuts to the plate, and the technique of outlier analysis was used to classify when this damage had occurred.
Authors: Irina Trendafilova, Emil Manoach, Matthew P. Cartmell, Wiesław M. Ostachowicz, Arkadiusz Zak
Abstract: This study investigates a possibility for representing, interpreting and visualising the vibration response of aircraft panels using time domain measurements. The aircraft panels are modelled as thin orthotropic plates and their vibration response is simulated using FE modelling. The vibration response of a thin aluminium panel is simulated using FE modelling. The first ten resonant frequencies are estimated for the FE model and for the dynamically tested panel. They were found to show somewhat low sensitivity to damage. Then the simulated vibration response of the panel is transformed and expanded in a new phase space. This presents an alternative way to study and analyse the dynamics of a structure. A two dimensional phase space is used in this investigation. Thus instead of studying the single dimension measured vibration characteristics one is faced with expanded two dimensional variables which can be visualised and this facilitates the comparison between the damaged and the non-damage states.
Authors: Piotr Kurowski
Abstract: Modal models are commonly encountered forms of dynamic characterization of mechanical structures. They are applied in machine-condition diagnosing as well as in monitoring processes. In research practice the most frequently applied method is Experimental Modal Analysis, and in exploitation - Operational Modal Analysis. Difficulties associated with the EMA and OMA have contributed to the increase of OMAX model applications, especially in case of energetic machines. Theoretical assumptions related with modal analysis are very strong. In reality when big and heavy structures are considered often those assumptions are not fulfilled. In the paper such situations are considered and practical solutions are showed.

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