Bespoke Test Rig Research Articles

Quantifying efficient shape-shifting: Energy barrier measurement in multi-stable lattice metamaterials

Shape-shifting between multiple stable deformation states offers attractive pathways to design adaptive structures. Ideas have been conceptualised in diverse fields, including soft robotics and aerospace engineering. The success of shape-shifting relies on overcoming the energy barrier separating adjacent stable configurations, which necessitates efficient actuation strategies. Recently, multistable mechanical metamaterials have been designed with shape-shifting controlled by an actuator at the local scale, i.e with embedded actuation. This local, embedded actuation creates challenges for quantifying the energy barriers required for shape-shifting. Specifically, the local actuation requires a pair of forces with opposite directions and the direction of the forces must remain constant throughout the entire loading process. Moreover, the loading points must move freely in a direction perpendicular to the loading direction. We present a novel bi-axial test rig for a typical multi-stable lattice metamaterial that accurately determines the energy barrier between stable states by using an embedded actuator and inducing shape-shifting. Our experimental design features two independent actuation systems operating at different length scales: a primary one for a globally applied axial compression of the metamaterial, and a secondary local system for triggering shape-shifting between different stable configurations. Experimental data obtained using this bespoke test rig unveil the metamaterial’s response to local, embedded actuation. Excellent agreement with finite element simulations is observed, demonstrating the effectiveness of the test setup in providing measurements of the energy barrier. This work provides a valuable benchmark for measuring energy barriers in multi-stable metamaterials and paves the way for rigorous validation and verification of novel functional metamaterial and structures that leverage shape-shifting mechanisms.

Theoretical and experimental investigation of the glass tube solar collector with inclined N-S axis and relative E-W single-axis tracking flat absorber

This paper presents a new solar collector design that combines flat absorber plates and glass tubes with a compacted automatic time-controlled (E–W) single-axis tracking mechanism. The mentioned design incorporates the advantages of the single-axis tracking system with a relatively small increase in the solar collector dimensions. According to it, a mathematical model was formed, and the test sample was fabricated. Using a bespoke test rig, the experimental investigation was carried out by simultaneously measuring the thermal performances of the solar collector in question and the flat plate solar collector with the same inclined position and absorber material. The experimental results (from July 15 to October 15, 2021) showed that compared to a reference collector, the new solar collector’s average daily specific useful heat was higher in the range of 14–23%, and the overall thermal efficiency was higher in the range of 9.7–17.9%. Using the obtained experimental and simulation data, the mathematical model was verified within an average deviation of 5.67%. Despite the partial reduction of the useful heat due to the mutual shading of absorbers, the mentioned solar collector shows promising results along with a compact design. We propose that this device will present promising opportunities in future applications.

On the Added Modal Coefficients of a Rotating Submerged Cylinder Induced by a Whirling Motion—Part 1: Experimental Investigation

The operation of submerged rotating machines, such as marine current or tidal turbines, can present deleterious fluid phenomena that may provoke extreme structural vibrations. To predict their dynamic responses, it is necessary to know the added modal coefficients of their runners under a whirling motion. For that purpose, a bespoke test rig was designed to investigate the added modal coefficients of a submerged cylinder, which could rotate at different speeds both in air and completely submerged in water inside a cylindrical tank. First, the modes of vibration were experimentally measured by exciting the cylinder with a push-release method during steady tests or with ramps in rotating speed during transient tests. The calculated natural frequencies and damping ratios were then used in a mathematical model of the dynamic system to calculate the added modal coefficients. During steady tests, the natural frequencies and damping ratios of the whirling modes changed significantly as a function of the rotating speed. Additionally, a whirling mode was observed to change its direction at a given rotating speed. During transient tests, rotating speed ramps with high accelerations were found to present lower lock-in amplitude and frequencies. Moreover, fast downward ramps presented lock-in amplitudes four times higher than fast upward ramps. Consequently, the added modal coefficients changed accordingly as a function of the rotating speed, ramp acceleration, and ramp direction. For these reasons, it was confirmed that the modal responses of submerged rotating bodies must be calculated for each operational rotating speed, even at low velocities, and for each transient event in order to precisely predict their vibration behaviors.

A Miniaturized Ultrasonic Micro-Hole Perforator for Minimally Invasive Craniotomy.

Micro-hole perforation on skull is urgently desired for minimally invasive insertion of micro-tools in brain for diagnostic or treatment purpose. However, a micro drill bit would easily fracture, making it difficult to safely generate a micro-hole on the hard skull. In this study, we present a method for ultrasonic vibration assisted micro-hole perforation on skull in a manner similar to subcutaneous injection on soft tissue. For this purpose, a high amplitude miniaturized ultrasonic tool with a 500 μm tip diameter micro-hole perforator was developed with simulation and experimental characterization. In-depth investigation of micro-hole generation mechanism was performed with systematic experiments on animal skull with a bespoke test rig; effects of vibration amplitude and feed rate on hole forming characteristics were systematically studied. It was observed that by exploiting skull bone's unique structural and material properties, the ultrasonic micro-perforator could locally damage bone tissue with micro-porosities, induce sufficient plastic deformation to bone tissue around the micro-hole and refrain elastic recovery after tool withdraw, generating a micro-hole on skull without material. Under optimized conditions, high quality micro-holes could be formed on the hard skull with a force (<1 N) even smaller than that for subcutaneous injection on soft skin. This study would provide a safe and effective method and a miniaturized device for micro-hole perforation on skull for minimally invasive neural interventions.

Strength Assessment of PET Composite Prosthetic Sockets.

A prosthesis is loaded by forces and torques exerted by its wearer, the amputee, and should withstand instances of peak loads without failure. Traditionally, strong prosthetic sockets were made using a composite with a variety of reinforcing fibres, such as glass, carbon, and Kevlar. Amputees in less-resourced nations can lack access to composite prosthetic sockets due to their unavailability or prohibitive cost. Therefore, this study investigates the feasibility of polyethylene terephthalate (PET) fibre-reinforced composites as a low-cost sustainable composite for producing functional lower-limb prosthetic sockets. Two types of these composites were manufactured using woven and knitted fabric with a vacuum-assisted resin transfer moulding (VARTM) process. For direct comparison purposes, traditional prosthetic-socket materials were also manufactured from laminated composite (glass-fibre-reinforced (GFRP)), monolithic thermoplastic (polypropylene (PP) and high-density polyethylene (HDPE)) were also manufactured. Dog-bone-shaped specimens were cut from flat laminates and monolithic thermoplastic to evaluate their mechanical properties following ASTM standards. The mechanical properties of PET-woven and PET-knitted composites were found to have demonstrated to be considerably superior to those of traditional socket materials, such as PP and HDPE. All the materials were also tested in the socket form using a bespoke test rig reproducing forefoot loading according to the ISO standard 10328. The static structural test of sockets revealed that all met the target load-bearing capacity of 125 kg. Like GFRP, the PETW and PETK sockets demonstrated higher deformation and stiffness resistance than their monolithic counterparts made from PP and HDPE. As a result, it was concluded that the PET-based composite could replace monolithic socket materials in producing durable and affordable prostheses.

Advanced landing gear fibre Bragg grating sensing and monitoring system

In this paper an advanced optical-based landing gear load sensing and monitoring system is presented. The system measures strains using fibre Bragg grating sensor that are converted into loads and torque at the landing gear wheels and provides this data for use by the aircraft systems for integration with aircraft health monitoring, hard landing detection, flight management, flight controls and ground controls. A complete sensing system was developed in the European Union Clean Sky 2 Joint Technology Initiative Advanced Landing Gear Sensing and Monitoring (ALGeSMo), described herein. This involved: the integration of optical fibres into a composite structure, the development of an optical harness (cabling and connectors) meeting aircraft installation requirements, the readout of the optical fibre sensors with state-of-the-art miniature optoelectronics and the processing and communication of the data. Apart from specific tests on the various components, a bespoke test rig was developed to rigorously test the whole sensing and monitoring system on an A320 main landing gear slider tube to validate the performance of the system. The system-level tests performed on the test rig showed a very good correlation with applied actuator loads and additional conventional strain and temperature sensors. It demonstrates that loads along all three axis of the landing gear and the torque about the wheel axle can be accurately measured. Tests performed at cold and elevated temperatures, however, revealed that the generally applied one-dimensional temperature compensation equation is not accurate enough for this application, due to the non-uniform non-stationary temperature field. The ALGeSMo research activities have advanced the state of the art in several key areas for the deployment of optical sensing systems for safety-critical applications, such as integration of optical fibres into composite material, robust optical connections, avionic-compliant optical interrogator and landing gear load measurement up to technology readiness level technology readiness level 5.

Turbulence modelling for RANS CFD analyses of multi-nozzle annular jet pump swirling flows

This study focusses on the fluid mechanic analysis and performance assessment of a one-phase swirling flow multi-nozzle annular jet pump using Reynolds-averaged Navier–Stokes simulations and experimental measurements carried out with a bespoke test rig. The numerical investigation of the flow physics of the device, key to understanding its fluid dynamics and optimising its performance, is made particularly challenging by the existence of flow swirl. Thus, the predictive capabilities of two alternative approaches for the turbulence closure of the Reynolds-averaged Navier–Stokes equations, namely the k-ω shear stress transport and the Reynolds stress models, are assessed against measured static pressure fields for three regimes characterised by different swirl strength, and a thorough cross-comparative analysis of the flow physics using the two closures is performed to complement the information provided by the experimental measurements. At the lowest swirl level, the two simulation types are in very good agreement, and they both agree very well with the measured static pressure fields. As the flow swirl increases, the two numerical results differ more and the Reynolds stress model is in better agreement with the measured static pressure. At the highest swirl level the shear stress transport analysis predicts weaker dissipation of the jet energy and stronger mixing of injected and pumped streams, resulting in higher performance predictions than obtained with the Reynolds stress model. A CFD-based sensitivity analysis also highlights the impact of nozzle diameter and flow swirl on the pump performance, proving new guidelines for the design optimisation of this pump.

Application of the Thin Slice Model for Determination of Face Load Distribution along the Line of Contact and the Relative Load Distribution Measured along Gear Root

This article concerns the investigation of the relationship between stress distribution caused by contact during tooth flank engagement and tensile stress distribution due to bending at the tooth root. Four different approaches are discussed. The first refers to ISO 6336 guidelines describing the relationship with a simple empirical formula. The second is the proposed thin slice model developed in MATLAB computer software. The third approach is based on finite element analysis (FEA). The last experimental method uses a bespoke test rig designed and manufactured for this work. The thin slice model has been verified against ISO 6336 guidelines, FEA simulation, and the test rig measurements. Two phenomena have been observed: coupling and edge effect, both of which impact the relationship between load intensity distribution for contact and bending.

Investigating the impact of copper leaching on combustion characteristics and particulate emissions in HPCR diesel engines

Copper leaching in diesel fuel and its impact on combustion and emission characteristics of a Direct Injection High Pressure Common Rail (DI HPCR) diesel engine was investigated. This work was performed using a single cylinder Ricardo Hydra research engine fitted with a cylinder head, piston assembly, and crankshaft from a production 2.2 L DI diesel engine. A fuel conditioning device consisting of a helicoidally shaped copper duct and electromagnetic coils powered from the battery was installed along the fuel line just before the high pressure pump. A diesel fuel with a copper content of less than 0.2 ppm was used. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed an increase of copper content to 1 ppm when fuel flowed through the conditioning device prior to the injection and returned from the engine back to the fuel tank. Copper leaching from the conditioning device was confirmed using a bespoke test rig. Combustion characteristics were analysed via post-processing pressure measurements, while an AVL Smoke Meter was used to monitor particulate emissions. A pilot plus main strategy was used to achieve a target Brake Mean Effect Pressure (BMEP) typical of medium load. Soot reduction in the range of 7–14% was measured when the device was connected to the fuel line, compared to the baseline. The initiation and early development of combustion was also investigated using an unstirred, quiescent combustion chamber with optical access. High-speed photography showed that ignition probability was enhanced in presence of the fuel conditioning device.

Optimisation of grease application to railway tracks

Trackside lubricators are designed to deliver grease to passing wheel flanges to reduce wheel and rail wear on curves. Ensuring that they are set up to deliver sufficient grease for the range of vehicles passing a site can be a challenge. For example, vehicle dynamics modelling and site investigations have shown that the wheels of passenger vehicles do not run as close to the rail face as those of freight vehicles, meaning that they are less likely to contact the grease and lubricate subsequent curves. To investigate the effects of different trackside devices, and the influence of parameters governing grease pickup, including lateral wheel displacement and pump durations, a bespoke test rig was built at the University of Sheffield. The rig used a scaled wheel, a short section of rail and a modern trackside lubricator set-up. Experiments involving different lateral wheel displacements and pumping durations were carried out, in addition to the visualisation of the size of the grease bulb. This showed how a grease bulb grows. It also indicated that a worn profile is likely to require greater wheel displacement to make contact with grease bulbs when compared to a new wheel profile. The experimental results showed that increasing pickup of grease can be expected when an additional component called a GreaseGuide™ was fitted to a regular grease delivery unit (GDU) on the rail. The efficiency of grease pickup was investigated, and test results exploring increasing pump durations have indicated a relationship between pickup and bulb size. To validate the use of the scaled rig, similar tests were carried out using a full-scale test rig. The full-scale results were compared to the experimental results of the scaled wheel rig. This showed that whilst there were differences between the two test rigs in absolute values and anomalous results, overall trends were the same on both test scales. The effect of temperature on bulb size and pumpability of grease was also investigated. This work can be extended further by using the same method to investigate other parameters that affect the lubrication of curves. This can lead to optimised lubricator set-up to ensure that the track is fully lubricated all the time.

Vibration reduction in a hollow-shaft rotor using flexibly-mounted internal-stator magnetic bearings

A topology composed of a hollow-shaft rotor on rolling element bearings coupled with internal-stator magnetic bearings mounted on independently supported flexible shafts is considered for the purposes of vibration reduction. Details of a bespoke test rig constructed to assess this topology are presented. The rig makes use of customdesigned internal-stator magnetic bearings fabricated from Soft Magnetic Composite material. Results from standard numerical analysis of the rig are given to demonstrate the expected behaviour of the system, with a particular focus on its potential to reduce synchronous vibration seen in the rotor while passing critical speeds. These behaviours are then confirmed via a series of experimental tests. These results show that the proposed topology can be used effectively to alter the system vibration behaviour.

Equi-biaxial tension tests on magneto-rheological elastomers

A bespoke test rig has been designed to facilitate testing of magneto-rheological (MR) elastomers (MREs) under equi-biaxial tension using a standard universal test machine. Tests were performed up to 10% strain on both isotropic and anisotropic MREs with and without the application of an external magnetic field. Assumptions regarding the material’s response were used to analyse stress–strain results in the two stretching directions. The assumptions have been verified previously by uniaxial tension tests and by simulations of the magnetic flux distribution performed using a commercial multi-physics finite element software. The MR effect, which is defined as the increase in tangent modulus at a given strain, has been studied versus engineering strain. The latter was measured optically in the experiments using a digital image correlation system. Relative MR effects up to 74% were found when the particle alignment of anisotropic MREs was oriented parallel to an applied magnetic induction of just 67.5 mT.

In situ observation and analysis of ultrasonic capillary effect in molten aluminium

An in situ synchrotron radiographic study of a molten Al–10wt% Cu alloy under the influence of an external ultrasonic field was carried out using the Diamond-Manchester Branchline pink X-ray imaging at the Diamond Light Source in UK. A bespoke test rig was used, consisting of an acoustic transducer with a titanium sonotrode coupled with a PID-controlled resistance furnace. An ultrasonic frequency of 30kHz, with a peak to peak amplitude at 140microns, was used, producing a pressure output of 16.9MPa at the radiation surface of the 1-mm diameter sonotrode.This allowed quantification of not only the cavitation bubble formation and collapse, but there was also evidence of the previously hypothesised ultrasonic capillary effect (UCE), providing the first direct observations of this phenomenon in a molten metallic alloy. This was achieved by quantifying the re-filling of a pre-existing groove in the shape of a tube (which acted as a micro-capillary channel) formed by the oxide envelope of the liquid sample. Analytical solutions of the flow suggest that the filling process, which took place in very small timescales, was related to micro-jetting from the collapsing cavitation bubbles. In addition, a secondary mechanism of liquid penetration through the groove, which is related with the density distribution of the oxides inside the groove, and practically to the filtration of aluminium melt from oxides, was revealed. The observation of the almost instantaneous re-filling of a micro-capillary channel with the metallic melt supports the hypothesised sono-capillary effect in technologically important liquids other than water, like metallic alloys with substantially higher surface tension and density.

Wavespeed Measurement in Buried Water Distribution Pipes and its Significance in Leak Location

To determine the location of leaks in buried water pipes, acoustic methods are often used. These have proven to be very effective in metallic pipes but have been problematic in modern plastic pipes. In this paper the reason why this is so is discussed together with some measurements that were made on a bespoke test rig built by South Staffs Water plc. It is shown that there are significant issues in obtaining an accurate estimate of the wavespeed when a leak is present in the system. A method is proposed that overcomes some of these problems, which is discussed and is demonstrated using some data from the bespoke test-rig.

The Dynamic Behaviour of a Buried Water Pipe and its Effect on Leak Location Using Acoustic Methods

Leakage in buried pipes is one of the main concerns for water companies due to the scarcity of potable water sources. Older metallic pipelines have been replaced by plastic pipes in such systems, which makes it more difficult to locate leaks using acoustics and vibration. This is mainly because of the high attenuation of leak signals caused by the damping in the pipe-wall. To investigate acoustic methods in leak location in controlled conditions, a bespoke test rig was constructed in the UK. In this paper, data from this test-rig is used to discuss some issues that arise when using two contemporary correlators. Of particular interest, is the way in which a resonance in the system can have a profound effect on the estimate of the position of the leak depending on the way in which the leak noise signals are processed.