A portable load cell for in-situ ore impact breakage testing

This paper discusses the design and characterisation of a short, and hence portable impact load cell for in-situ quantification of ore breakage properties under impact loading conditions. Much literature has been published in the past two decades about impact load cells for ore breakage testing. It has been conclusively shown that such machines yield significant quantitative energy-fragmentation information about industrial ores. However, documented load cells are all laboratory systems that are not adapted for in-situ testing due to their dimensions and operating requirements. The authors report on a new portable impact load cell designed specifically for in-situ testing. The load cell is 1.5 m in height and weighs 30 kg. Its physical and operating characteristics are detailed in the paper. This includes physical dimensions, calibration and signal deconvolution. Emphasis is placed on the deconvolution issue, which is significant for such a short load cell. Finally, it is conclusively shown that the short load cell is quantitatively as accurate as its larger laboratory analogues

Creep monitoring using permanently installed potential drop sensors

Creep is the primary life limiting mechanism of static high temperature, high pressure power station components. Creep state evaluation is currently achieved by surface inspection of microstructure during infrequent outages; a methodology which is laborious, time consuming and considered inadequate. The objective of this work is to develop a monitoring technique that is capable of on-load creep damage monitoring. A continuous update of component integrity will enable better informed, targeted inspections and outage maintenance providing increased power generation availability. A low-frequency, permanently installed potential drop system has been previously developed and will be the focus of this thesis. The use of a quasi-DC inspection frequency suppresses the influence of the electromagnetic skin effect that would otherwise undermine the stability of the measurement in the ferromagnetic materials of interest; the use of even low frequency measurements allows phase sensitive detection and greatly enhanced noise performance. By permanently installing the electrodes to the surface of the component the resistance measurement is sensitive to strain. A resistance - strain inversion is derived and validated experimentally; the use of the potential drop sensor as a robust, high temperature strain gauge is therefore demonstrated. The strain rate of a component is known to be an expression of the creep state of the component. This concept was adopted to develop an interpretive framework for inferring the creep state of a component. It is possible to monitor the accumulation of creep damage through the symptomatic relative increase in strain rate. By taking the ratio of two orthogonal strain measurements, instability and drift common to both measurements can be effectively eliminated; an important attribute considering the necessity to monitor very low strain rates over decades in time in a harsh environment. A preliminary study of using the potential drop technique for monitoring creep damage at a weld has been conducted. Welds provide a site for preferential creep damage accumulation and therefore will frequently be the life limiting feature of power station components. The potential drop technique will be sensitive to both the localised strain that is understood to act as precursor to creep damage at a weld and also the initiation and growth of a crack. Through the course of this project, two site trials have been conducted in power stations. A measurement system and high temperature hardware that is suitable for the power station environment has been developed. The focus of this thesis is the effective transfer of the technique to industry; the realisation of this is detailed in the final chapter.Open Acces

Passive Aeroelastic Tailoring

The Passive Aeroelastic Tailoring (PAT) project was tasked with investigating novel methods to achieve passive aeroelastic tailoring on high aspect ratio wings. The goal of the project was to identify structural designs or topologies that can improve performance and/or reduce structural weight for high-aspect ratio wings. This project considered two unique approaches, which were pursued in parallel: through-thickness topology optimization and composite tow-steering

Mechanical performance of transparent laminated materials for aircraft

To fully understand mechanical and structural performance of laminated glass, seven laminated cases were designed to assess the influence of glass types, polymer interlayer thickness, polymer interlayer types and multi-layered interlayer. An innovative apparatus combining 3D-Digital-Image-Correlation and ring on ring tests have been tested successfully, major strain and out of plane displacement at the supporting side were monitored. Novel sabot design helped the rubber projectile to eject without deformation in gas gun tests. The third innovative design was the gas gun system which allowed a stereo system of two high speed cameras for 3D-Digital-Image-Correlation and one camera monitoring impact performance, strain gauge system, and detecting velocity to be synchronised at the same time. Regarding major research findings, for monolithic glasses, an approximate 0.8% major failure strain was identified regardless of its thickness which was used as a failure criterion for laminated glass. For laminated glasses, an increase of thermoplastic-polyurethane thickness will allow laminate to absorb more energy at quasi static and low velocity ranges, but lower the supporting face strain at high velocity. Chemically strengthened glass used as frontal glass layer has better performance in terms of energy consumption in quasi static and low velocity ranges comparing to thermally strengthened glass. Different types of interlayer have different functionalities. Sentry-glass-plus is more rigid comparing thermoplastic-polyurethane and polyvinyl-butyral which can transfer more shear between layers and lower the strain at the back. However, it has poor adhesion on glass proven by large peeling off of the glass fragments after gas gun experiments. Comparing with polyvinyl-butyral, thermoplastic-polyurethane has good adhesive properties with Sentry-glass-plus and glass. A multi-layered interlayer system using structural Sentry-glass-plus and adhesive thermoplastic-polyurethane as interlayers can significantly reduce the strain during impact and prevent glass fragments from flying off at high velocity which is favourable in real scenarios (e.g. bird-strike).Open Acces

Characterization of the austenite recrystallization by comparing double deformation and stress relaxation tests

A high amount of deformation below the non-recrystallization temperature (T-nr) is a common industrial practice to achieve a good combination of toughness and strength in microalloyed steels. To combine the industrially relevant optimum combination of high productivity and product quality, an accurate knowledge of T-nr and the recrystallization kinetics is required. Although a lot of literature data is available on the recrystallization behaviour of microalloyed steels, correlations are often difficult to be made due to the effect of different experimental setups, types of analysis and test schedules that are used to obtain this data. Although this would significantly improve the knowledge about these steels, so far, no systematic comparison has been presented in literature to correlate the different techniques and methods. In this study, different hot rolling simulation techniques, testing schedules and types of analysis were used to determine the recrystallization kinetics of a microalloyed steel. On the one hand, good agreement was found between the results from different test equipment for the double deformations tests. On the other hand, stress relaxation tests showed accelerated kinetics and appeared to be less effective

Development of an intermediate strain rate compression testing machine

Includes bibliographical references.The further development of the wedge bar Intermediate Strain rate Tester (IST) presented by Cloete and Oxtoby [1] is presented in this dissertation. The concept uses a wedge mechanism to deform 5 mm diameter, 5 mm long specimens at strain rates in the region of 10 s, up to strains of 30. As impact principles are used to start and stop the experiment, it takes less than 1 of the testing duration to reach testing speed and to stop the experiment. The kinetic energy stored in the wedge bar helps ensure a near constant loading rate over the duration of the experiment. The yield stress is captured at above 80 of the average strain rate for the experiment for most of the materials investigated. The design work focuses primarily around the design of the new load-frame, load-cell, loading platforms and wedge bar displacement sensor. Finite Element Analysis (FEA) was used to investigate the dynamic response of the IST and modify the design of components where necessary. The modifications made the load-frame and load-cell result in a significant improvement in the quality of the measured signals. The wedge bar displacement sensor performed well. The back pressure driven loading concept shows potential but needs more development before it is suitable for routine testing. A range of common engineering materials was tested at quasi static, intermediate and high strain rates and compared to the results found in the literature. The results match well, however, friction effects dominate the large strain response of the metal specimens. In its current configuration the IST is used effective for testing polymers up to large strains as well as yield stress and small strain measurement of metals. For materials for which specimen friction effects are a problem, interrupted tests can be used to extend the maximum strain achievable

Optimised design of nested oblong tube energy absorbers under lateral impact loading

Dynamic lateral crushing of mild steel (DIN 2393) nested tube systems was conducted using a ZWICK ROELL impact tester. The tests were performed with impact velocities ranging between 3 and 5 m/s, achieved using a fixed mass impinging onto the specimens under the influence of gravity. The various nested tube systems consisted of one standard and one optimised design. Their crushing behaviour and energy absorption capabilities were obtained and analysed. In addition to the experimental work, numerical simulations using the explicit code LS-DYNA were conducted; boundary conditions matching those observed in experiments were applied to the models. Results from the numerical method were compared against those obtained from experiments. An over-prediction in force-deflection responses was obtained from the numerical code. An attempt was made to explain this inconsistency on the basis of the formation of plastic hinges and the validity of strain rate parameters used in the Cowper Symonds relation. It was found that the optimised energy absorbers exhibited a more desirable force-deflection response than their standard counterparts due to a simple design modification which was incorporated in the optimised design

Experimental determination of thickness influence on compressive residual strength of impacted carbon/epoxy laminate

Abstract: An experimental campaign was performed on 5.5 mm thick carbon/epoxy specimens and results were compared with data obtained in a previous work to understand thickness influence on material mechanical characteristics. In particular, this campaign consists of two different steps: impacts tests, performed by means of a modified Charpy pendulum, and Compression After Impact (CAI), using Wyoming Combined Loading Compression (CLC) test method. Impacts were performed on twenty cross-ply specimens with different energies and impact location. Other 5 specimens were tested only in compression. Non Destructive Inspections (NDI) by Ultrasonic Test (UT) were performed on impacted and pristine specimens, in order to understand damage size and correlate it with residual strength results. During CLC tests, compression strength and Young modulus values were acquired