Abstract
The work reported in this thesis aims to investigate single particle impacts using different measurement techniques typically when the period of impact is close to the resonance period of the impacting bodies including transducers. In addition, two simple analytical models were developed to predict the measurements outputs. The experimental section, which is the main part of the work reported in this thesis, can be grouped into three main groups: first, measurements of contact time using resistive circuit technique. The second group is measurements of impact force profile using electric conductance changing during the impact time. The third group is a measurement of target mass acceleration using piezoelectric accelerometers to investigate impact force profile. Stainless steel balls were used as incident masses whereas steel objects were used as target masses such as structural steel rods and pipe elbows. The main reason for using steel is electrical properties. It has good electrical conductance which allows the use of resistive circuits to measure contact time or changing the conductance between impacting bodies during elastic collision. All the experiments are done for elastic collisions only.The results of using a resistive circuit to measure contact time show good agreement with Hertz theory. The investigations of impact force between two stainless steel balls using changing of electric conductance technique during impact do not show expected results as a result of poor repeatability for conductance measurements. It was found that the properties of the surfaces of the balls greatly affected the measurements. Also, the analytical model shows different results from practical measurements.
The measurements of impact force and contact time using piezoelectric accelerometers include two parts. The first part is using a film piezoelectric accelerometer to measure acceleration of two different sizes of steel bars not at the position of impact but at the other end. The second part is using a Kistler piezoelectric accelerometer and film piezoelectric accelerometer to measure acceleration of outer surface of pipe elbow during impact between a particle and inner surface. Even though this technique has an advantage of not changing the impact scenario because the sensor was adhered on the outer surface, the results of the measurements show high complexity and difficulties for investigations of impact force profile using this technique. The complexity of investigation of the contact time and impact force from the accelerometers output can be as a result of a number of reasons but the main reason is the interference between the impact signal and resonance signals of the target masses and transducers.
As stated previously; two simple analytical models were developed to predict the measurements outputs. The first model is aimed to predict how the electric conductance changes during impact between two stainless steel balls depending on Hertz theory. Itwas found that there is a very significant difference between theoretical results and practical results. The second model is aimed to simulate the behaviour of the steel bar that used as a target mass for impacting between it and the stainless steel ball. The model depends on using a number of mass/spring systems connected in series. The impact force was simulated as one period of off-set cosine wave. The results of the second model show good agreement with Newton’s laws and speed of waves inside materials. However, the acceleration measurements of the simulated bar during impact show poor similarity with the model results.
The most important contributions of this research can be concluded in three points; the first contribution to knowledge is the experimental work undertaken here, even if it is not directly of value due to poor repeatability for the conductance measurement and due to the resonant nature of the target mass and piezoelectric transducers. The reporting of these results will inform other researchers in this area and assist them in designing a measurement system that is appropriate to their needs.
Secondly, although using electrical technique to measure contact time between a particle and internal surface of pipe elbow is limited and has not been used before but it is useful to be used as starting point for measurement of impact force profile.
Thirdly, although the single particle impacting with a surface is not a new area of research, and simulate the incident mass and target mass as mass/ spring systems have been done previously but using multi mass/spring systems in series in one direction is useful to understand the behaviour of target mass after impact.
The most significant and challenging area of future work is the analysis of both the experimental output response signal and that from the corresponding model to determine the correlation between these, and the potential for using these together to predict contact time and impact force profile from an incident mass and target mass collision.
| Date of Award | 2017 |
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| Original language | English |
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| Supervisor | John Pugh (Supervisor), Don McGlinchey (Supervisor) & Andrew Cowell (Supervisor) |