Design And Application Of A Drill Pipe Fatigue Test Facility

This paper reports on the design and application of a fatigue testing facility for drill pipes. A reversed bending load is applied using a rotating drill pipe in a four point static bend arrangement with the possibility of applying an additional static tension load. Drill pipes were tested with and without static tension at different cyclic bending stresses. The stress amplitudes ranged from 30 MPa to 230 MPa on the outside surface of the drill pipe. The test results show a consistent failure mode with a circumferential crack propagating in the groove of the first engaged thread of the pin, i.e. the male section of the joint. The fracture surface as well as ultrasonic monitoring of the sample during the testing suggest that the circumferential crack growth rate is fast, and final fracture occurs within a relatively small number of cycles as soon as a through wall crack has been formed. The S-N curve collected from a total of 18 samples shows a linear trend in the logarithm of the fatigue life versus stress amplitude

Assessment of structural integrity through coupled vibration

A vibration-based technique is employed to evaluate the structural integrity using mode coupling property. The methodology is first demonstrated on a single hollow section beam by analytical simulation and experimental validation. A welded test rig with a fatigue crack is then investigated by applying this technique. The test rig consists of chord members cross-connected by smaller branches. The fatigue crack is generated by a reciprocating mechanism. The proposed approach discriminates the cracked member through the emergence of coupled mode that is observable on FRF plots. The test results of the structure under intact and cracked states are presented. It is suggested that this method has the potential to detect cracks in welded structures

The influence of backward wave transmission on quantitive ultrasonic evaluation using Lamb wave propagation

In view of the various novel quantitative ultrasonic evaluation techniques developed using Lamb wave propagation, the influence of an important related phenomenon, backward transmission, is investigated in this paper. Using the discrete layer theory and a multiple integral transform method, the surface displacement and velocity responses of isotropic plates and cross-ply laminated composite plates due to the Lamb waves excited by parabolic- and piston-type transmitting transducers are evaluated. Analytical expressions for the surface displacement and velocity frequency response functions are developed. Based on this a large volume of calculations is carried out. Through examining the characteristics of the surface displacement and velocity frequency response functions and, especially, the different propagation modes’ contributions to them, the influence of the backward wave transmission related to quantitative ultrasonicnondestructive evaluation applications is discussed and some important conclusions are drawn

Experimental study of multiple cracks detection utilizing a probabilistic approach

This paper studies the possibility of using measured transient vibration data in the detection of multiple cracks on beams by following the Bayesian probabilistic framework. The proposed method adopts different classes of models in modelling a beam with different numbers of cracks. The number of cracks on the beam can then be identified by calculating the probability of a model class conditional on a given set of measured transient vibration data. By following the Bayesian probabilistic framework, the posterior probability density functions (PDFs) for a set of crack parameters, such as the crack locations and the corresponding extents, can be calculated. The PDFs allow engineers to quantify the uncertainties associated with the results of crack detection. The paper reports not only the theoretical developed but also the experimental verification of the proposed method

Prediction and direct measurement of scattered plate-wave fields using S0 to A0 mode conversion at non-symmetric circular inhomogeneities

The scattering of A0 waves from blind holes and added masses when plane S0 waves are incident was investigated. Predictions from an approximate theoretical model and experimental results were found to be in good agreement at low frequency thickness products. The presented technique has the advantage of being most sensitive to the mode converted scattered A0 field while it hardly picks up any of the incident wave mode. This method has potential applications in plate wave diffraction tomography where the wave field of the scattered flexural wave has to be accurately determined in order to reconstruct an image of damage such as corrosion thinning or laminar disbonds

Optimization of neural network pattern recognition systems for guided waves damage identification in beams

Neural network pattern recognition is an advanced regression technique that can be applied to identify guided wave response signals for quantifying damages in structures. This paper describes a procedure to optimize the design of a multi-layer perceptron backpropagation neural network with signals preprocessed by the wavelet transform. The performance can be further improved using a weight-range selection technique in a series network since there is increased sensitivity of the neural network to experimental damage patterns if the training range is reduced. Damage identification in beams with longitudinal guided waves is used in this study

Crack identification in hollow section structures through coupled response measurements

This paper present a feasible method for crack identification in hollow section structures based on the coupling vibration behaviour of cracked members. From the last several decades lots of techniques have been developed by many researchers to detect, locate and quantify damage by using changes to modal parameters such as natural frequency, mode shape or damping ratio. However, these approaches suffer from the fact that the structural damage has a low sensitivity to changes in these parameters. A related option is offered through coupled response measurements. A transverse surface crack is well known to produce local flexibility due to the stress-strain singularity in the vicinity of the crack tip. The local flexibility can be represented by the way of a 6x6 matrix for a beam element that includes the crack. This matrix contains off-diagonal terms that cause coupling response along the direction corresponding to these terms. This coupling property due to the crack is evidence of the existence of the cracks. Coupled response of cracked hollow section structures was studied. Hollow section structures demonstrate a more pronounced coupling when cracks occur. In this paper, both an analytical simulation and the early results of experimental implementation are presented. This method is fairly discriminative even for small cracks

Metal-polymer functionally graded materials for removing guided wave reflections at beam end boundaries

This paper investigates the potential of a metal-polymer functionally graded material (FGM) to remove beam end boundary wave reflections that produce complicated interference patterns in the response signals used for guided wave damage identification methodologies. The metal-polymer FGM matches the material properties to a metal beam for total wave transmission on one side and is continuously graded to a viscoelastic polymer on the other side. An Aluminium-Polycarbonate (Al-PC) FGM was fabricated and characterised using microscopy, hardness testing and through-transmission ultrasonics to verify the continuous gradient. Measurements of guided waves on an aluminium beam attached to the FGM on one end show reduction in boundary wave reflections that varies with wave frequency. A damaged aluminium beam attached with the FGM produced promising improvements in a damage identification system

Analysis of myocardial motion using generalized spline models and tagged magnetic resonance images

Heart wall motion abnormalities are the very sensitive indicators of common heart diseases, such as myocardial infarction and ischemia. Regional strain analysis is especially important in diagnosing local abnormalities and mechanical changes in the myocardium. In this work, we present a complete method for the analysis of cardiac motion and the evaluation of regional strain in the left ventricular wall. The method is based on the generalized spline models and tagged magnetic resonance images (MRI) of the left ventricle. The whole method combines dynamical tracking of tag deformation, simulating cardiac movement and accurately computing the regional strain distribution. More specifically, the analysis of cardiac motion is performed in three stages. Firstly, material points within the myocardium are tracked over time using a semi-automated snake-based tag tracking algorithm developed for this purpose. This procedure is repeated in three orthogonal axes so as to generate a set of one-dimensional sample measurements of the displacement field. The 3D-displacement field is then reconstructed from this sample set by using a generalized vector spline model. The spline reconstruction of the displacement field is explicitly expressed as a linear combination of a spline kernel function associated with each sample point and a polynomial term. Finally, the strain tensor (linear or nonlinear) with three direct components and three shear components is calculated by applying a differential operator directly to the displacement function. The proposed method is computationally effective and easy to perform on tagged MR images. The preliminary study has shown potential advantages of using this method for the analysis of myocardial motion and the quantification of regional strain

Imaging flexural inhomogeneities using plate-wave diffraction tomography

This paper presents the first experimental implementation of plate-wave diffraction tomography for the quantitative evaluation of laminar damage in plates using normal incidence inspection. The technique is investigated for origin centered, cylindrical bonded-mass of various size and severity. The results show that diffraction tomography using Lamb waves and Mindlin plate theory offers excellent sensitivity and has the potential for detecting corrosion thinning, disbonds and delamination damage in structural integrity management applications