Tutorial. Signal processing aspects of structural impact testing (original) (raw)
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Time Effective Structural Frequency Response Testing With Oblique Impact
2018
Structural frequency response testing is accurate in identifying the dynamic characteristic of a machinery structure. In practical perspective, conventional structural frequency response testing such as experimental modal analysis with impulse technique (also known as "impulse testing") has limitation especially on its long acquisition time. The high acquisition time is mainly due to the redundancy procedure where the engineer has to repeatedly perform the test in 3 directions, namely the axial-, horizontal- and vertical-axis, in order to comprehensively define the dynamic behavior of a 3D structure. This is unfavorable to numerous industries where the downtime cost is high. This study proposes to reduce the testing time by using oblique impact. Theoretically, a single oblique impact can induce significant vibration responses and vibration modes in all the 3 directions. Hence, the acquisition time with the implementation of the oblique impulse technique can be reduced by a...
Improved impact-echo approach for non-destructive testing and evaluation
Proceedings of the 3rd …, 2010
This study examines rationale of correction factor β in the formula of thickness resonant frequency, fundamental to the impact-echo (IE) approach in non-destructive testing and evaluation for integrity appraisal and damage diagnosis of infrastructure systems. It shows the role of the factor in the resonant frequency which is typically obtained with average characteristic from traditional fast Fourier transform or FFT data analysis of IE recordings. A time-frequency data analysis termed Hilbert-Huang Transform or HHT is then introduced to overcome the shortage of FFT analysis in identifying the resonant frequency from IE recordings. With the FFT and HHT analyses of five data sets of sample IE recordings from sound and damaged concrete structures and comparison with referenced ones, this study reveals that the proposed IE approach with HHT data analysis not only eliminates the use of correction factor in the formula, it also improves greatly the accuracy in the IE approach.
This study examines rationale of correction factor β in the formula of thickness resonant frequency, fundamental to the impact-echo (IE) approach in non-destructive testing and evaluation for integrity appraisal and damage diagnosis of infrastructure systems. It shows the role of the factor in the resonant frequency which is typically obtained with average characteristic from traditional fast Fourier transform or FFT data analysis of IE recordings. A time-frequency data analysis termed Hilbert-Huang Transform or HHT is then introduced to overcome the shortage of FFT analysis in identifying the resonant frequency from IE recordings. With the FFT and HHT analyses of five data sets of sample IE recordings from sound and damaged concrete structures and comparison with referenced ones, this study reveals that the proposed IE approach with HHT data analysis not only eliminates the use of correction factor in the formula, it also improves greatly the accuracy in the IE approach.
Frequency analysis of reinforced concrete structures subjected to accidental impacts
The purpose of our study consists in the research of new ways of designing reinforced concrete structures submitted to commercial aircraft impact. We will particularly focus on the shaking resulting from such load case. The cutoff frequency for this type of loading is typically within the to range, which would be refered to as the medium frequency range [1]. The determination of the shaking induced by an aircraft impact on an industrial structure requires dynamic simulation. The response, especially during the transient stage, cannot be completely described using classical finite element method associated with explicit numerical schemes. Indeed, the medium frequency range is often ignored unless the calculation is carried out with a very refined mesh and consequently, a refined time discretization. This could lead to prohibitive computation times. The linear behaviour is not questioned outside the impact area, however, the non-linearity of the portion of the impacted structure can have a significant influence. The method consists in an initial FFT (Fast Fourier Transform) of the signal loading. The VTCR then ensures an efficient calculation of the response of the structure. The obtained signals are then processed by inverse FFT (IFFT) to reconstruct a time signal and a response spectrum. A new multiscale computational strategy, the Variational Theory of Complex Rays [2], is developed for the analysis of the vibration of structures in the medium frequency regime. Using two-scale shape functions which satisfy the dynamic equation and the constituve relation within each substructure, the VTCR can be viewed as a mean of expressing the power balance at the different interfaces between substructures in a variational form. The solution is searched as a combination of propagative and evanescent waves. Only the amplitude of these waves, which are slowly varying quantities of the solution, is discretized. This leads to a numerical model with few degrees of freedom in comparison with a Finite Element model. The aim is to develop a robust method to get mid-frequency spectra generated by an aircraft impact on a simplified structure.
A simplified method for the impact test of beams using a pseudo-dynamic (PSD) process
Mechanics Research Communications, 2006
The impact test in structural parts for dynamic applications is an essential procedure for their certification in the presence of time dependent loads. In the case of beam elements, either built with one material or as an assembly of different material members joined with recent developed bonding techniques, an impact test is of leading importance, once the dynamic resistance of the joints involved in the beam fabrication is assessed and evaluated. The pseudodynamic method is an alternative to dynamic analysis of structures, here offering to the researcher the possibility of examining with detail the specimen in test for the initiation and progress of eventual damage mechanisms arising in the beam element joints whenever included in the design.
Experimental study of the behaviour of building structural elements under soft impact
DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
Dynamic three-point bend tests are performed on small beams specimen made of a quasi-brittle material. The most classical hypotheses needed to analyse the tests with SHPB, which are based on a state of quasi-static balance of the body, cannot be used. In order to get the behaviour it is necessary to perform a transient analysis of the specimen response. In most cases, the useful duration of the test -the elapsed time between the beginning of the load and the total failure -is lower than the time needed by the waves to reach the supports. The test is thus called a "one point bending test". In the case of bending failure, an analysis of the tests is possible by using only the measures given by the input bar. The technique is based on the knowledge of the analytical solution of the transient elastic response of the specimen. The failure mechanisms involved are specific features of the dynamic response. Different failure modes can be observed according to the loading rate: bending or shear fracture, single or multiple fractures. The determination of the bending moments and the rotations of the beam section, where the failure occurs, lead to an estimation of the strength and the failure energy. a b 1 2 3 4