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Polymers are increasingly used in structures that have to withstand impact conditions. This thesis describes an investigation of strain rate properties at room temperature of four engineering polymers; polyethylene (high density, HDPE and ultra high molecular weight, UHMWPE), nylatron and polyetheretherketone (PEEK 150g). A split Hopkinson pressure bar (SHPB) system was used to study the response of these polymers in compression tests at high strain rates up to 10' S-1. Stress equilibrium in SHPB samples was studied theoretically by examining multiple reflection effects during the initial elastic loading of the polymers; this study proved very useful in the analysis of SHPB tests. To cover a wide range of strain rate, compression studies were also made at low strain rates (10-3 _10-2 S-1) using a Hounsfield screw machine. Viscoelastic models have been applied to these results. These models fit quite well with the experimental results of HDPE, UHMWPE, and nylatron, but not to the PEEK due to the yield drop in the stress - strain curves, especially at high strain rates. An exploding wire technique was used as an axial impulsive loading system for hollow cylindrical samples. An image converter camera at framing intervals of 21ls or 10 Ils recorded the radial expansion of the cylinder. The expanding cylinder was used as a driving system for a new technique called the freely expanding ring method, which was used to obtain the stress - strain behaviour of polymeric thin rings placed as a sliding fit on the cylinder. This method produced very high tensile strain rates up to fracture (> 10' S-1). Comparisons have been made between results obtained from the quasi-static, SHPB, and expanding ring tests. The freely expanding ring and SHPB results were in good agreement indicating similar tensile and compressive high strain rate behaviour. The mechanical properties of the above polymers are strongly dependent on strain rate. The Young's modulus and the flow stress increase with increasing strain rate. Nylatron showed high strain rate strain softening at high strain, this was due to the high temperature rise during loading, when the transition temperature (Tg) of the material (50 QC) was exceeded. However, the other materials showed continuous hardening behaviour. Plots of the flow stress at 5% and 10% strain vs log strain rate showed a linear increase up to a strain rate of about 103 S-1. Above 103 s-1, the stress rose more rapidly, but then showed significant drops for nylatron and PEEK. These drops in stress are probably due to both micro crack initiation in the sample and also high temperatures around the crack tips.

The compressive behavior of an annular rubber seal constrained in a pipe and the interaction between the pipe and the seal was studied experimentally using a specially designed test fixture that allowed the concentric alignment of the seal within the pipe and its axial compression using an electro-hydraulic Instron load frame. The hoop strain introduced in the pipe wall, due to the constraint of lateral expansion of the seal, displayed a parabolic distribution with a maximum value at the mid-height of the seal similar to the parabolic shape of the lateral expansion of the seal. The magnitude of the pipe strain increased with the friction coefficient of the interface between the seal and the compression rings, strain rate, and shape factor for a constant gap between the seal and the pipe wall. The relationship between the apparent compressive modulus and the shape factor (beyond experimental range) was studied using FEA. / October 2016

The shape of a liquid's surface is determined by both the body force and surface force of the liquid. In this report, the body force is solely from the gravitational force. The surface force is generated from the movement of an elastic interface between the solid and liquid. To obtain the shape of the surface, both asymptotic analysis and numerical approaches are used in this report. The asymptotic analysis is applied on the potential flow. The initial conditions are chosen to be the function of the shape of the interface between the solid and liquid and the free stream velocity far away from the interface. The time dependent contributions from the fluid system are also considered. The initial condition changes according to the function of the calculated velocity potential. The numerical approach includes two parts: calculation the velocity potential and a formalism of the change of the system as time evolves. For the first part, two idealized vertical boundaries are utilized to give a unique solution of the Laplace equation. The boundary conditions are determined as the flow under linear viscosity. For the second part, the flow is first assumed to be a potential flow, and a boundary layer is considered to make the no-slip condition valid and to give a more precise approximation for the shear stress.

Les phénomènes observés dans le comportement élastique non linéaire des roches et des bétons sont reconnus pour être étroitement reliés à leur microstructure. La signature non linéaire de ces matériaux est complexe avec notamment une perte temporaire des propriétés élastiques en sollicitation dynamique ainsi que des phénomènes d’hystérésis et de relaxation lente. Depuis les années 90, de nombreuses études académiques et industrielles ont démontré l’intérêt de l’acoustique non linéaire pour la caractérisation non-destructive avec des indicateurs dont la sensibilité à l’endommagement est décuplée par rapport à ceux utilisés jusqu’alors. Cependant, les effets tridimensionnels associés aux couplages éventuels des phénomènes non linéaires sont généralement négligés dans ces études, ce qui limite l’obtention de paramètres quantitatifs, pouvant même mener à des conclusions erronées. Dans ce contexte, ces travaux de thèse s’attachent à développer une approche théorique tridimensionnelle unifiée, adaptée de l’acousto-élasticité. Le premier chapitre, introduit le support bibliographique de ces travaux. Le deuxième chapitre expose un modèle de relaxation tridimensionnel, couplé aux coefficients élastiques d’ordre trois. Il est validé expérimentalement sur du mortier et du grès. Il est démontré que la perte temporaire des propriétés élastiques en sollicitation dynamique est un phénomène anisotrope induit. Le troisième chapitre, applique le modèle à la résonance non linéaire. Le quatrième chapitre introduit le modèle à la prospection non linéaire in situ. Les perspectives de ces travaux sont vastes, couvrant des domaines fondamentaux ou plus pratiques (contrôle non destructif). / The phenomena observed in the nonlinear elastic behavior of rocks and concretes are known to be closely related to their microstructure. The nonlinear signature of those materials is complex with temporary loss of elastic properties under dynamic loading as well as hysteresis and slow relaxation phenomena. Since the 1990s, numerous academic and industrial studies have demonstrated the value of nonlinear acoustics for non-destructive characterization with indicators whose sensitivities to damage is tenfold compared to those used up to now. However, the three-dimensional effects associated with the possible coupling of nonlinear phenomena are generally neglected in these studies, which limits the obtaining of quantitative parameters, which may even lead to erroneous conclusions. In this context, these theses work aims to develop a unified three-dimensional theoretical approach, adapted from the acousto-elasticity. The first chapter introduces the bibliographic support of this work. The second chapter presents a three-dimensional relaxation model coupled to the three-order elastic coefficients. It is validated experimentally on mortar and sandstone. It is shown that the temporary loss of elastic properties under dynamic loading is an induced anisotropic phenomenon.The third chapter applies the model to nonlinear resonance experiment. The forth chapter introduces the model to in situ nonlinear prospecting. The perspectives of this work are broad, covering fundamental domains (non-linear elasticity) or more practical (non-destructive testing and passive monitoring of buildings).

Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

Ng, Kin Sang = 球狀液滴的彈性光散射,包括高階彩虹、炫光點及形態相關共振的數值計算與實驗研究 / 吳健生. / Thesis submitted in: October 2007. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 101-104). / Text in English; abstracts in English and Chinese. / Ng, Kin Sang = Qiu zhuang ye di de tan xing guang san she, bao kuo gao jie cai hong, xuan guang dian ji xing tai xiang guan gong zhen de shu zhi ji suan yu shi yan yan jiu / Wu Jiansheng. / Acknowledgements --- p.i / Abstract --- p.ii / Table of Contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Brief history --- p.1 / Chapter 1.2 --- The theory of rainbow --- p.4 / Chapter 1.2.1 --- Rainbow position --- p.4 / Chapter 1.2.2 --- Airy theory --- p.6 / Chapter 1.3 --- Glare points --- p.9 / Chapter 1.4 --- Mie scattering theory and Debye series --- p.11 / Chapter Chapter 2 --- Interference of the nth- and higher-order rainbows --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Interference of overlapping rainbows --- p.18 / Chapter 2.3 --- Results and discussion --- p.20 / Chapter 2.3.1 --- Glare point intensity of group G(ll) --- p.20 / Chapter 2.3.2 --- "Glare point intensities of groups G(8), G(9), and G(10)" --- p.24 / Chapter 2.3.3 --- Effects of varying acceptance angle --- p.27 / Chapter 2.3.4 --- Comparison with results of Lock and Woodruff --- p.29 / Chapter Chapter 3 --- Glare points of high-order rainbows --- p.30 / Chapter 3.1 --- Introduction --- p.30 / Chapter 3.2 --- Results and discussion --- p.32 / Chapter 3.2.1 --- Glare points formed by rainbows of a particular order --- p.32 / Chapter 3.2.2 --- Glare points obtained by plane wave calculation --- p.42 / Chapter Chapter 4 --- Elastic light scattering from droplets embedded in gelatin --- p.45 / Chapter 4.1 --- Introduction --- p.45 / Chapter 4.2 --- Motivation --- p.48 / Chapter 4.3 --- Experimental Preparations --- p.51 / Chapter 4.3.1 --- Sample preparation --- p.51 / Chapter 4.3.2 --- Measurement of refractive index of gelatin --- p.53 / Chapter 4.4 --- Observation of morphology-dependent resonances by varying wavelength of incident laser light --- p.56 / Chapter 4.4.1 --- Experimental setup --- p.56 / Chapter 4.4.2 --- Results and discussion --- p.58 / Chapter 4.5 --- Observation of morphology-dependent resonances by varying temperature of droplet --- p.70 / Chapter 4.5.1 --- Experiment --- p.70 / Chapter 4.5.2 --- Results and discussion --- p.73 / Chapter 4.6 --- Scattered light intensity as a function of scattering angle --- p.77 / Chapter 4.6.1 --- Experiment --- p.77 / Chapter 4.6.2 --- Results and discussion --- p.79 / Chapter Chapter 5 --- Conclusion and future outlook --- p.89 / Appendix Program dave.for Listing --- p.92 / References --- p.101

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