Damage identification based on curvature mode shape using cubic polynomial regression and chebyshev filters

Structure Health Monitoring (SHM) has been applied in various application such as aerospace, machinery and civil structures to maintain structure's safety and integrity. Gapped smoothing method (GSM) is most popular non-destructive identification (NDI) method due to its simplicity and did not require baseline data for comparisons. However, GSM is less accurate to detect wide size of damage in structure and cause false detection. Objective of this study is to propose a method to detect damage in structure using curvature mode shape data estimated from damaged structure and did not require data from undamaged structure. Finite element analysis (FEA) on a free-free boundary condition steel beam was carried out to demonstrate the feasibility of the proposed method that estimate undamaged curvature mode shape data using cubic polynomial regression (CPR) and Chebyshev filters (CF) methods. The results shows proposed method that used Chebyshev filters has better accuracy damage detection on wide notch compared to GSM. Although application of an interpolation and Chebyshev filters showed results with a high potential for overcoming the issue of false detection due to different notch size, however the proposed method still need refinement to better detection of different damage cases

Effects of parameters of Helmholtz resonator on transmission loss of hybrid muffler

Expansion chamber and Helmholtz resonators are widely used in noise control. In this paper, they are combined to use as a hybrid muffler. The analysis is done to investigate the influence of the parameters of Helmholtz resonator on transmission loss. The transfer matrix method is used in the analysis. The result of transmission loss from the transfer matrix method is validated with the result from experimental two-load method using four microphones impedance tube. After had the transmission loss of the hybrid muffler been validated, the study was proceeded to investigate the effects of parameters of Helmholtz resonator on the transmission loss. The root mean square value of transmission loss were also calculated to compare the transmission losses clearly. In this paper, we investigated the effect of length of the neck of Helmholtz resonator, the effect of diameter of the neck of Helmholtz resonator, the effect of the length of the Helmholtz resonator cavity and the effect of the diameter of the Helmholtz resonator cavity for stationary medium. It is found that the transmission loss is increased when the diameter of the neck of Helmholtz resonator is increased. When the length of the neck is reduced, the transmission loss is increased. The transmission loss can also be increased by reducing the diameter of resonator cavity. It is better to increase the transmission loss at low frequencies by increasing the length of the resonator cavity

Simple and fast damage identification on 6061 aluminium based on mode shape curvature

This paper presents a simple and fast approach for the identification of damage to isotropic steel structures. The main contribution of this work is a simplified approach using cubic polynomial regression, unlike previously developed damage identification models that use two specimens. This was achieved by differentiating the mode shape displacement from the mode shape curvature using a central finite difference equation to determine the damaged curve, and subsequently, computing the undamaged curve using a Cubic Polynomial Regression (CPR) model. To validate the accuracy of the model, five specimens with different types of damage (single and double notch) at various depths were simulated. The performance of the model was evaluated against the experimental modal test results. It was found that the presented model was capable of detecting the type of damage (whether single or double notch) in a 6061 Aluminium beam structure. However, when compared to the experimental results, the average difference could reach up to 17% due to external factors. In particular, the performance of the presented model in detecting the location of the damage was inaccurate and imprecise for both the FEA simulation and experimental cases. The CPR model is useful for operators and engineers who require a simple and fast approach to detect damage, but, in terms of accuracy, different techniques must be considered, especially those that are capable of removing and clearing out noise signals

A load-displacement prediction for a bended slotted disc using the energy method

A slotted disc spring consists of two segments: a coned disc segment and a number of lever arm segments. In this study, a load-displacement formula for the slotted disc spring is newly developed in the form of energy method by considering both rigid and bending deflections of the two segments. This formula is developed with the aim to further improve the SAE formula which is limited to a straight slotted disc spring. The coned and the lever arm angles of the straight slotted disc spring are the same. They are different for a bended slotted disc spring. Because of this limitation, it is geometrically impractical to employ the SAE formula for a bended slotted disc spring. To achieve the goal of this study, new calculations based on geometric and material properties inputs are developed for a bended slotted disc spring. A firm background study based on the theory of Almen is presented in developing new load-displacement calculations for a bended slotted disc spring

An improved load-displacement prediction for a coned disc spring using the energy method

An improved computation of the load-displacement prediction for a coned disc spring is proposed. This work is an extension work of the previous proposed energy-based computation for coned disc springs. To show the validity of the improved method, the load-displacement results using the improved computation, the previous proposed method, and the finite element analyses are compared. In this work, the improved computation and the finite element analyses have accounted for the radial deflection of the disc spring in the form of energy method. This is different in the previous work where the radial deflection of the disc spring was ignored and the comparison to the finite element analyses without accounting the radial deflection is not practical. The present work makes the comparison to the finite element analyses to be more reasonable and more practical

An improved energy based load-displacement prediction for slotted disc spring

An improved calculation of the load-displacement prediction for a slotted disc spring is proposed. There are two types of slotted disc spring; a straight slotted disc spring and a bended slotted disc spring. By considering these two types of slotted disc spring, this work attempts to extend the previous work on load-displacement prediction for the slotted disc spring using the energy method. To show the validity of the improved method, the load-displacement results using the improved computation, the previous proposed method, and the finite element analyses are compared. In this work, the improved computation and the finite element analyses have accounted for the radial deflection of the disc spring which is different in the previous work. The radial deflection of the disc spring was ignored in the previous work and the comparison to the finite element analyses without accounting the radial deflection is not practical. The present work is compared to the finite element analyses which make the comparison to be more reasonable and more practical