Structural Health Monitoring Using Two Stage Algorithm Combines Non Model-Based and Model Based Techniques

Abstract

The aging of civil infrastructure and aerospace structures has led to an increased need to monitor the overall structural health. If growing damage not identified on time, it may has serious consequences, both safety related and economic. However, the complexity of large structures and the difficulty in accessing them makes the use of commonly existing conventional Non Destructive Evaluation (NDE) methods such as visual inspection and instrumental evaluation methods, impractical. An effective alternative in Structural Health Monitoring (SHM) is the use of methods that depend on Vibration-Based Damage Identification (VBDI) techniques. These methods use limited instrumentation to detect the changes in the measured modal characteristics of the structure, that is, its frequencies and mode shapes. These characteristics change with the physical properties of the structure (stiffness, mass and damping matrices) and can be used to help find the location and extent of damage. Optimal matrix update method is one of the VBDI algorithms that depends on finite element modelling (FEM) of the structure and is therefore referred to as model-based damage identification algorithm. The FRF differences method is also one of the VBDI techniques that depends on the directly measured frequency response functions data and is therefore referred to as non model-based or modal-based damage identification algorithm. However, VBDI algorithms still faces a number of challenges that have not been fully resolved. Some of these challenges are highlighted through modal tests designed to provide estimates of damage in a 3D eight-bay free-free frame. Details of tests on a healthy structure as well as on a structure in which predetermined damage has been introduced are presented. A proposed algorithm combining the aforementioned model-based and non-model based methods is introduced to improve the reliability of damage detection. The algorithm is first tested through numerical simulation to predicting damage on the basis of modal test data and the predictions are compared with the known damage.

Experimental Verification of Two Stage Algorithm for Health Monitoring of Aerospace Structures

“…This method depends on the directly measured frequency response functions data and is therefore referred to as non model-based or modalbased damage identification algorithm. In a previous study [6], a new damage identification algorithm is introduced to improve the reliability of damage detection. In which, the optimal matrix update method (model-based method) is combined with the FRF difference method (non-model based method).…”

“…In which, the optimal matrix update method (model-based method) is combined with the FRF difference method (non-model based method). The algorithm has proven an acceptable level of success when tested through numerical simulation to predicting damage on the basis of analytically created modal test data [6].…”

“…Details of modal tests on the frame structure in which many scenarios for predetermined damage have been introduced are presented next. The acquired FRF's for the damaged structure is paired with their counterparts of the healthy structure to calculate the DDI for the affected degrees of freedom [6]. The Damaged region is identified based on the maximum values of the DDI's from which only limited number of elements are determined as susceptible candidates for damage.…”

“…In the present study a Damage Detection Index DDI that interprets the differences between the FRF's measured for the healthy and damaged structure can be used to detect damaged region. This index introduced by Napolitano et al [4] and modified by [6]. The modification insures that all the FRF' data is included consequently the modified DDI is reduced to the form:…”

Identification of Damage in Plate-Like Structures Using Two Stage Algorithm Combines Non- Model Based and Model Based Techniques

“…included in the optimization process. In order to overcome this defect, Amin et al [1] combined an optimal matrix update technique with FRF differences technique, which is independent on a FEM of the monitored structure (i.e. non-model-based algorithm).…”