Wing Kong Chiu

Structural health monitoring in the railway industry: a review

Wayside detection monitors critical parameters relating to the condition of in-service railway vehicles. Economic decisions about the maintenance of vehicles can be made, and servicing can occur when a particular vehicle is likely to cause even small amounts of damage to the track, to itself, or when the cost of damage is significant, such as in catastrophic failure. Vehicles with poorly performing axle bearings, out-of-round (skidded or spalled) wheels, vehicles which exhibit transient lateral motion (‘hunting’), and vehicles with poorly performing brakes are all likely to fall into the category of requiring maintenance, in order to save the track and the vehicle owners money. In the present paper, the parameters that define vehicle condition and their measurable effects are stated. There are frequently a number of wayside detection methods of inspecting a vehicle for the same vehicle condition and each of these is described in detail. This investigation reveals the need for further research to enable rollingstock owners to make better decisions about the cost of operating their vehicles, based on the output from wayside detectors and the observed trends in wheel impact.

Composite repairs to rib stiffened panels

Abstract There are several methods available for obtaining a first estimate for the design of composite repairs to cracks in thin metallic skins. One approach uses analytical formulae, which build on an analogy with the problem of a bonded symmetric lap joint (Rose LRF. An application of the inclusion analogy for bonded reinforcements. Int J Solid Struct 1981;17:827–838; Fredell RS. Damage tolerant repair techniques for pressurized aircraft fuselages. PhD Thesis, Delft University of Technology, June 1994; Baker AA, Jones R. Bonded repair of aircraft structures. Dordrecht: Martinus Nijhoff, 1988). The present paper extends this methodology to include the bonded repair to rib stiffened wing skins. To this end the present paper presents the results of a series of 3-D finite element analysis of various composite repair configurations. This study reveals that, after repair, the stress intensity factors exhibits an asymptotic behaviour as the crack length increases and that this stress intensity factor is a weak function of the stiffener spacing.

Unified constitutive model for thermoset adhesive, FM73

This paper discusses the use of a unified constitutive model to predict the behaviour of a thermoset adhesive, FM73. This adhesive is widely used in the bonded repair of aircraft structures. The results presented in this paper include monotonic and cyclic tests conducted at room temperature. The time-dependent properties of this film adhesive are significant even at room temperature. Considerable stress relaxation was observed during strain hold experiments. The adhesive was also found to creep when the load was held constant. The monotonic shear stress-strain behaviour, time-dependent characteristics and cyclic behaviour of the adhesive can be adequately described using a unified constitutive model.

Distributed Optical Fibre Sensors and their Applications in Pipeline Monitoring

Health monitoring of civil infrastructure systems has recently emerged as a powerful tool for condition assessment of infrastructure performance. With the widespread use of modern telecommunication technologies, structures could be monitored periodically from a central station located several kilometres away from the field. This remote capability allows immediate damage detection, so that necessary actions are taken to reduce the risk. Optical fiber sensors offer a relatively new technology for monitoring the performance of spatially distributed structures such as pipelines. In this regards, several commercially available strain and temperature sensing equipment such as discrete FBGs (Fibre Bragg Gratings) and fully distributed sensing techniques such as Raman DTS (distributed temperature sensor) and Brillouin Optical Time Domain Reflectometry (BOTDR) typically offer sensing lengths of the order of 100 kms. Distributed fiber optic sensing offers the ability to measure temperatures and/or strains at thousands of points along a single fiber. In this paper, the authors will give a brief overview of these optical fiber technologies, outline potential applications of these technologies for geotechnical engineering applications and experience in utilising BOTDR in water pipeline monitoring application.

Anisotropy related spring-in of angled composite shells

During the manufacture of curved or angled shell composite structures, the enclosed angle of such structures tends to be reduced after cure. This phenomenon is referred to as “spring-in”. It is believed that such distortion is caused mainly by the significant difference between the in-plane coefficient of thermal expansion (CTE) and the through-thickness CTE. This might result in a larger out-of-plane contraction than the in-plane contraction during the time that a composite structure is cooling down from the curing temperature. In this paper, a 3-D Finite Element Analysis procedure was developed to predict “spring-in” resulting from anisotropy for both thin and thick angled composite shell structures. The results of the FE analysis were evaluated together with those from the analytical study and experimental investigation conducted by Jain at the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) in Australia. It was concluded, based on these results, that the FE model gives more accurate results than the analytical model, particularly for thicker composite shells. The corner radius effect, shell thickness effect, and lay-up effect on “spring-in”, together with the effect of tool/part interaction on the total distortion were also discussed. Comparison was made with the experimental results reported by Radford and Rennick.

Review of techniques for monitoring the healing fracture of bones for implementation in an internally fixated pelvis

Sacral fractures from high-impact trauma often cause instability in the pelvic ring structure. Treatment is by internal fixation which clamps the fractured edges together to promote healing. Healing could take up to 12 weeks whereby patients are bedridden to avoid hindrances to the fracture from movement or weight bearing activities. Immobility can lead to muscle degradation and longer periods of rehabilitation. The ability to determine the time at which the fracture is stable enough to allow partial weight-bearing is important to reduce hospitalisation time. This review looks into different techniques used for monitoring the fracture healing of bones which could lead to possible methods for in situ and non-invasive assessment of healing fracture in a fixated pelvis. Traditional techniques being used include radiology and CT scans but were found to be unreliable at times and very subjective in addition to being non in situ. Strain gauges have proven to be very effective for accurate assessment of fracture healing as well as stability for long bones with external fixators but may not be suitable for an internally fixated pelvis. Ultrasound provides in situ monitoring of stiffness recovery but only assesses local fracture sites close to the skin surface and has only been tested on long bones. Vibration analysis can detect non-uniform healing due to its assessment of the overall structure but may suffer from low signal-to-noise ratio due to damping. Impedance techniques have been used to assess properties of non-long bones but recent studies have only been conducted on non-biological materials and more research needs to be done before it can be applicable for monitoring healing in the fixated pelvis.

Detection of Disbond Growth in a Cyclically Loaded Bonded Composite Repair Patch Using Surface-mounted Piezoceramic Elements

This paper reports on an experimental study in which an array of surface-mounted lead zirconate titanate elements (PZT) are used for the in situ detection of disbond growth in a bonded composite repair patch. Two techniques are used to track the evolution of disbond growth: the transfer function method and the electromechanical impedance method. Both techniques were found to provide a reliable and robust basis for the detection of disbond growth. The results also demonstrate the importance of transducer placement relative to the disbond location as a factor in the sensitivity to disbond growth.

Fatigue damage monitoring of a composite step lap joint using distributed optical fibre sensors

Over the past few decades, there has been a considerable interest in the use of distributed optical fibre sensors (DOFS) for structural health monitoring of composite structures. In aerospace-related work, health monitoring of the adhesive joints of composites has become more significant, as they can suffer from cracking and delamination, which can have a significant impact on the integrity of the joint. In this paper, a swept-wavelength interferometry (SWI) based DOFS technique is used to monitor the fatigue in a flush step lap joint composite structure. The presented results will show the potential application of distributed optical fibre sensor for damage detection, as well as monitoring the fatigue crack growth along the bondline of a step lap joint composite structure. The results confirmed that a distributed optical fibre sensor is able to enhance the detection of localised damage in a structure.

Energy harvesting from heavy haul railcar vibrations

Vibration energy harvesting has shown promise as technique for powering sensor networks and wireless devices. Previously, a biaxial vibration energy harvester approach was reported that used a wire-coil transducer and a permanent magnet/ball-bearing arrangement. In response to host accelerations the ball-bearing (i.e. proof mass) oscillates with two translational degrees of freedom, hence producing a varying magnetic field across the coil and therefore inducing an electromagnetic force (EMF) that could potentially be used to power a sensor. Vertical host accelerations, somewhat stochastic in nature, were measured from the bogie of a heavy haul railcar. The measured railcar accelerations were filtered, and replicated in a laboratory environment using a vibration shaker arrangement. The shaker arrangement was used to excite a non-optimised prototype energy harvester which employed a steel ball-bearing proof-mass with 31.8 mm diameter. The harvester, when excited by stochastic vibrations similar to those found on a railcar (and having an RMS acceleration of 4.16 ms-2), produced a peak power of 1.71 mW and a longer term RMS power of 874 μW.

Modelling orthotropic viscoelastic behaviour of composite laminates using a coincident element method

In this paper a finite element procedure for modelling the viscoelastic behaviour of orthotropic composites is presented. The procedure uses the commercially available finite element package ABAQUS and requires no code development. The procedure utilises two coincident shell elements to model the orthotropic viscoelastic behaviour of a composite laminate. The first element exhibits isotropic and viscoelastic behaviour, while the second element exhibits orthotropic and elastic behaviour. The elements are superimposed in such a way that they are coincident. That is, the two shell elements share the same nodes and hence deform together. Consequently, it is expected that this combined hybrid model will exhibit combined orthotropic and viscoelastic behaviour. Numerical examples are presented to illustrate the capability and accuracy of the new procedure.