Vibration-Based Method for Damage Detection at Welded Beams and Rods

Abstract

simple point or mostly on several points on the structural component, and having an access to the damaged section is not required. Therefore, a method able to measure global parameters of structures that could provide information on the structural integrity from a few selected measurement points is very attractive for non-destructive testing (Smart and Chandler, (1995);Sohn et al., (2001)).When a welding section fails, or starts to fail, on an elastic structural element, the damage introduces local flexibility due to strain energy concentration. This effect has been already recognized and the idea of an equivalent spring has been used to quantify, in a macroscopic way, the relation between the applied load and the strain concentration around the welded section like in Adams et al. (1978).This model has also been used for fatigue damaged structural elements, and to simulate the presence of cracks. Dimarogonas, (1996) presents a review on this problem. In the case of crack detection by VBM, different approaches have been developed. In some cases, lumped models for elastic massless elements have been used (Adams et al, (1978); Chondros and Dimarogonas, (1980); Rizos and Aspragathos, (1990); Morassi, (2000); Loya et al, (2006); Kindova-Petrova, (2014)), in others, a modified rigidity matrix has been employed in the Finite Element Method (Kisa, (2000); Saavedra et al. (1996)) and also a model of distribution of rigidity on the beam based on fracture mechanics methods has been used ) and Chondros et al. (1998 b)); Chondros and Labeas, (2007)). In the problem of crack detection, not only the determination of the presence and size of the crack is important but also its location. Abdel-Mooty (2014) used a different approach to treat the identification of cracks based on the computation of the higher derivatives of structural modes for detecting the precise location of damage. Recently, the method has been applied for more complex systems like for crack detection on fluid-conveying pipes by Eslami et al (2016) and to solve the inverse problem of crack size and location based on the natural frequencies for an Euler-Bernoulli beam by Mostafa and Tawfik (2016). However, we are only interested in determining the quality or degradation of the welded section, showing that the added mass by the welding process has to be incorporated when modelling the system in order to reproduce the welded element behavior accurately.The purpose of this paper is then to develop a robust and cost effective monitoring system for welded structural elements. The concept has also been applied to other welded systems like the work by Yunnus et al. (2011). After extreme events, such as earthquakes or blast loading, or due to aging and degradation resulting from operational environments, a welded section may reduce its structural properties and NDT based on vibration measurements can be a rapid condition screening to provide, in near real time, reliable information regarding the integrity of the structure. In this investigation, it is assumed that the ...

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