The objective of this research is to simulate the response of an isolated substructure such that the response of the substructure in isolation would be the same as the substructure within the structure. Generally, the behaviour of an isolated subsystem (substructure) subjected to dynamic loading is different than the behaviour of the same substructure within a system (structure). This is primarily caused by the boundary conditions that are imposed on the substructure from the surrounding subsystem in the entire structure. A new systematic approach (methodology) is developed for performing impact analysis on the isolated substructure. The developed technique is fundamentally based on enforcing the mode shapes around the boundary of the substructure in the full structure to be similar to the mode shapes of the isolated substructure. This is achieved by providing a consistent adjustment to the loading conditions (impact velocity and mass) to account for the loss of restraint at the interface with the full structure. Another important aspect of this research is experimental validation of proposed method. This method allows the experimental testing of an isolated substructure since the testing is performed by impacting the isolated substructure with an appropriate mass and velocity. In the finite element analysis, the structure is analyzed, and then the isolated substructure simulation is performed using the developed technique. The results obtained from the numerical simulations, for both the substructure in situ and the substructure in isolation, are compared and found to be in good agreement. For instance, the effective plastic strains, kinetic and internal energies for the substructure within the structure and the substructure in isolation range from 7% to 12% discrepancies between two analyses. The numerical simulations of a full structure are verified by performing a series of experimental impact tests on the full structure. Finally, the experimental applicability of the technique is studied and its results are validated with FE simulation of substructure in isolation. This problem of experimentally testing an isolated substructure had previously not been addressed. The comparisons of FE simulation and experimental testing are made based on the deformed geometries, out-of-plane deflections and accelerometer readings. For example, the out-of-plane deformations from the FE analysis and the experimental test were determined to be within 7% to 9%. The experimental validation and numerical simulations indicates the technique is reliable, repeatable and can predict dynamic response of the substructures when tested in isolation. / Thesis / Doctor of Philosophy (PhD)

In the field of physical chemistry, the relatively recently developed technique of velocity-map imaging has allowed chemical dynamics to be explored with a greater depth than could be previously achieved using other methods. Capturing the scattering image associated with the products resulting from fragmentation of a molecule allows the dissociative pathways and energy landscape to be investigated. In the study of particle physics, the neutron has become an irreplaceable spectroscopic tool due to the unique nature of the interaction with certain materials. Neutron spectroscopy is a non-destructive imaging technique that allows a number of properties to be discerned, including chemical identification, strain tensor measurements and the identification of beneath the sample surface using radiography and tomography. In both of these areas, as well as a multitude of other disciplines, a flight tube is used to separate particles, distinguishing them based upon their mass in the former case and their energy in the latter. The experiments can be vastly enhanced by the ability to record both the position and arrival time of the particle of interest. This thesis describes several new developments made in instrumentation for experiments involving time-of-flight particle imaging. The first development described is the construction of a new velocity-map imaging instrument that utilises electron ionisation to perform both steps of molecular fragmentation and ionisation. Data from CO2 is presented as an example of the ability of the instrument, and a preliminary analysis of the images is performed. The second presented project is the design of a time-resolved and position-resolved detector developed for ion imaging experiments. The hardware, software and firmware are described and presented alongside data from a variety of the experiments showcasing the breadth of investigations that are possible using the sensor. Finally, the modifications made to the detector to allow time-resolved neutron imaging are detailed, with an in-depth description of the various proof-of-concept experiments carried out as part of the development process.

Les nids d'abeille d’aluminium combinent légèreté et grande capacité d’absorption d'énergie. Ils sont alors de plus en plus utilisés dans les secteurs du transport (automobile, aéronautique …) pour contribuer conjointement à l’allègement structural et à la sécurité. Dans cette thèse, le comportement à l’écrasement des nids d'abeille est étudié en tenant compte de l'effet combiné de l'angle d'orientation dans le plan des cellules, de l’angle de chargement et de la vitesse de sollicitation, que la littérature ne relate pas. Un dispositif de chargement mixte compression/cisaillement est conçu pour mener l’étude expérimentale. L’analyse des résultats porte sur le pic initial d’effort, le plateau d’effort, ainsi que sur les modes de déformation. Les résultats montrent une augmentation de la résistance sous sollicitation dynamique dépendante de l’angle de chargement Ψ. Elle devient moins significative quand l’angle de chargement augmente jusqu’à atteindre un angle critique. Pour Ψ > Ψcritique, les réponses quasi-statiques sont même plus élevées que les réponses dynamiques. Une étude numérique est alors entreprise. Elle permet de comprendre ce phénomène qui est imputé aux mécanismes de déformation locaux des cellules. Les résultats numériques montrent également que l’effet de l’angle d’orientation □ dans le plan est plus prononcé sur la force tangentielle que sur la force normale, que cela influence également les modes d’effondrement et donc la réponse mécanique. Ces simulations numériques, couplées aux résultats expérimentaux, permettent alors de dissocier les composantes normale et tangentielle de la réponse des nids d’abeille et d’identifier les paramètres d'un critère macroscopique de résistance exprimé en fonction de la vitesse d'impact, de l'angle de chargement et de l'angle d'orientation dans le plan. Finalement, dans le but de réduire le coût des simulations numériques, un modèle élément fini (EF) réduit basé sur un critère de périodicité tenant compte de l'angle d'orientation dans le plan est proposé et son domaine de validité est évalué. / Aluminium honeycombs combine lightweight with an efficient energy absorption capability (specific energy). They are widely used as crash energy absorbing and protective structures in a wide range of transport applications (automotive, aircraft …) to reduce energy consumption and greenhouse gas emission. Reducing vehicle mass has however to be done while at least maintaining the same safety levels. In this thesis, the honeycomb behaviour is investigated under mixed shear-compression loadings taking into account the combined effect of the in-plane orientation angle and the impact velocity, which has not been deeply investigated in the literature. Experimental study based on an improvement of a mixed shear-compression loading device is realised. Experimental analysis focuses on the initial peak and average crushing forces as well as the deforming pattern modes. Comparing quasi-static and dynamic results, a dynamic enhancement depending of the loading angle Ψ is observed under mixed shear-compression loading until a critical loading angle (Ψcritical). Beyond, a negative enhancement is observed. Thus, a numerical study is carried out. The negative enhancement phenomenon is attributed to the collapse mechanisms which are affected by the loading angle Ψ. Numerical results also highlight that the in-plane orientation angle has an effect on the collapse mechanisms and consequently on the mechanical response. This effect is more pronounced on the tangential force than the normal force. The combined effect of the in-plane orientation angle and the loading angle is analysed on the three identified deforming pattern modes. Combining numerical and experimental results, the average crushing normal and shear forces are dissociated. Therefore, the parameters of a macroscopic yield criterion for the mixed shear-compression honeycomb behaviour depending of the impact velocity, the loading angle and the in-plane orientation angle are identified. Finally, in order to optimise the cost in CPU-time of the numerical simulation, a reduced FE model based on the periodicity procedure taking into account the in-plane orientation angle is proposed and its validity range is evaluated.

This dissertation focuses on the development of and applications for Nano-Composite Piezoresponsive Foam (NCPF). This self-sensing foam sensor technology was discovered through research in a sister technology, High Deflection Strain Gauges (HDSG), and was subsequently developed with some of the same base materials. Both technologies use nano and micro conductive additives to provide electrically responsive properties to materials which otherwise are insulative. NCPF sensors differ from HDSGs in that they provide a dual electrical response to dynamic and static loading, which is measured through an internally generated charge, or a change in resistance. This dissertation focuses on the development of the dynamic or piezoresponsive aspect of the NCPF sensors which tends to have more consistent electrical response over a larger number of cycles. The primary development goal was to produce a sensor that was accurate, while providing a consistent, repeatable response over multiple impacts. The hypothesized electric generation is attributed to a triboelectric interaction between the conductive additives and the polyurethane foam matrix. This hypothesis was validated by examining different conductive additives with varying loading levels and specific surface areas while accounting for other design considerations such as the electrode used to harvest the response. The results of this analysis support the triboelectric model and point to carbon or nickel-based additives for optimal performance. The NCPF response measured by digital signal acquisition devices is directly dependent upon its input impedance. Increased input capacitance has a negative effect on the signal, however, higher input resistance has a positive linear correlation to voltage. Other considerations that affect the electrical response include the temperature and humidity in which the sensor is used and result in a scaled electrical response.NCPF sensors are ideally suited for use in systems which benefit from impact energy attenuation while measuring the same. This work demonstrates how the NCPF sensors can be used to detect severity and location of impacts in systems with multiple sensors (football helmets), and those with one continuous sensor (carpets). When NCPF sensors were used in a football helmet the impact severity and location of impact was accurately identified. NCPF sensors provide the benefit of simplified design by replacing existing foam while providing a direct measure of the forces. Additional research was conducted on the changes in material properties, specifically how it affects the foam structures ability to absorb energy in quasi static loading scenarios. NCPF sensors are demonstrated as viable tool to measure many different biomechanical systems.