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Mechanical properties of concrete are most commonly determined using destructive tests including: compression, flexure, and fracture notch specimen tests. However, nondestructive tests exist for evaluating the properties of concrete such as ultrasonic pulse velocity and impact echo tests. One of major issues with concrete (which has cement as its prime ingredient) is that unlike steel it is quasi-brittle material. It tends to want to crack when tensile stresses develop. Fibres have been added to concrete for many years to reduce the amount of and size of cracks cause by temperature changes or shrinkage. In more recent years, significant research has been carried out into the effect of the addition of basalt fibres to cement has on its mechanical strength. As well, developing concrete that is more durable, flexible, stronger, and less permeable than traditional concrete has been explored. It has become important to test and verify improvements that are made to the cement by basalt fibres as well as testing the general strength of concrete to stand up to constant pressure at varied strengths.

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The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The Mg65Cu25Gd10 and Mg65Cu15Ag10Gd10 bulk metallic glasses with different diameters from 3 to 6 mm were successfully fabricated by conventional copper mold casting in an inert atmosphere. The Mg65Cu25Gd10 bulk metallic glass shows the high glass forming ability and good thermal stability. However, the addition of Ag in the Mg65Cu15Ag10Gd10 alloy degrades the thermal stability. Based on the DSC results, the supercooled liquid region

The electric potential changes under uniaxial loading in some minerals and rocks have long been recognized. To daylight the electrical response of some minerals and rocks against applied stress, both theoretical studies and laboratory experiments are conducted. Some theories are also proposed by different researchers, in order to explain the electric potential variations. However, the mechanisms leading to electrical potential generation have not been fully explained yet. In the explanation of electric potential changes observed in rocks, type of the observed rock and the rock forming minerals in the rock fabric play an important role. One theory is based on the fundamentals of piezoelectricity only. However the relation between the stress state and the electric generation is not fully understood. This thesis aims to make a further contribution to the studies on understanding the electric potential change in rocks, containing quartz, which is a common piezoelectric mineral, under uniaxial loading conditions. Three types of rocks, namely quartz-sandstone, granite and granodiorite, are tested, and the stress and electric potential (EP) variations are recorded during the uniaxial loading experiments in a continuous manner. The experiments are conducted at three different loading rates, in order to investigate the effect of loading rate on the electrification mechanism. Also step loading experiments are conducted. Results indicated that, application of uniaxial stress creates a clear change in the EP responses of three quartz bearing rock types. The possible relationships between the EP generation and the level of applied stress are investigated based on the initial and final potential values (EPinitial, EPfinal), the potential just before the time of failure (EPUCS), the spike-like potential jump at the time of failure (&amp / #8710 / V), which are derived from the recorded data of the experiments.

[pt] Recentemente alguns estudos, especialmente em rochas, vêm considerando a região pós-pico da curva tensão x deformação visto o grande número de situações que ocorrem na prática, como as deformações pós-ruptura de pilares de minas e túneis. A dificuldade desses estudos está no fato das amostras se mostrarem em um estado intrinsecamente instável nesta região. Para controlar a ruptura das amostras após as mesmas atingirem suas resistências máximas é usado atualmente máquinas servo-controladas. Ocorre que mesmo nessas máquinas, alguns materiais que possuem comportamento tipo Classe II, a velocidade em que se propagam as fissuras é tão alta que o sistema de controle não consegue receber a tempo o sinal de realimentação e a amostra acaba rompendo sem o controle adequado. Assim os tradicionais métodos de controle, como carga e deformação constante,deixam espaço para o surgimento de técnicas alternativas que se mostram mais eficazes no controle do pós-pico de rochas. Dentre essas técnicas, está a da combinação linear de tensão e deformação e que será usada neste trabalho para controlar o pós-pico de rochas (leptinitos) e argamassas numa máquina de testes servo- controlada pouco rígida. Este fato é de grande valia pois com este controle alternativo é possível controlar um material Classe II, material este que, na maioria das situações práticas em que se deseja obter a porção pós- ruptura da sua curva tensão x deformação, a máquina de ensaios usada deve ter uma rigidez bem elevada. Ao longo do trabalho são discutidos também todos os problemas envolvidos num ensaio de compressão simples e aqueles intimamente ligados a região do pós-pico. / [en] Recently, some studies, especially in rocks, have been considering the post peak region of stress-strain curve due to the large number of practical instances such as post rupture strains in mine and tunnel piles. The difficulty lies in that the samples exhibit an intrinsically instable state in this region. For the samples rupture be controlled, after the maximum stress have been attained, servo controlled machines are currently being used. The matter is that, even in these machines in some materials, which have a class II behavior, the propagation velocity of the fissures is so high that the control system is not able to receive on time the feedback signal and the sample ends up disrupted with no suitable control. Accordingly, traditional control methods, such as constant load and strain, have given raise to alternatives techniques, which exhibit a more efficient post peak control in rocks. Among these techniques, there is the linear combination of stress and strain, which will be used in this work to control the post peak of rocks and mortars in a not very rigid servo controlled machine of tests. This fact is very important because with this alternative control it is possible to control a material Class II in which most of the practical situations to obtain the behavior post rupture of curve tension x deformation, the machine of tests should have a very high rigidity. Along with the work problems concerned with a uniaxial compression test and that intimately associated with post peak region are discussed. / [es] Debido al gran número de situaciones que ocurren en la práctica, algunos estudios recientes, especialmente en rocas, han considerado la región pospico de la curva tensión x deformación, como las deformaciones posruptura de pilares de minas y túneles. La dificuldad de esos estudios se debe a que las muestras se colectan en un estado intrínsecamente inestable de esta región. Actualmente, para controlar la ruptura de las muestras después que ellas alcanzan su máxima resistencia, se utilizan máquinas servo-controladas. Sucede que incluso en estas máquinas, algunos materiales que poseen comportamiento tipo Clase II, la velocidad en que se propagan las fisuras es tan alta que el sistema de control no consigue recibir a tiempo la señal de realimentación y la muestra se rompe sin el control adecuado. Es por ello que los métodos tradicionales de control, como carga y deformación constante, dan espacio para el surgimiento de técnicas alternativas, más eficazes en el control del pospico de rocas. Una de estas técnicas es la combinación lineal de tensión y deformación, que será usada en este trabajo para controlar el pospico de rocas (leptinitos) en una máquina de pruebas servo-controlada poco rígida. Este hecho tiene gran importancia ya que con este control alternativo es posible controlar un material Clase II. Enn la mayoría de las situaciones prácticas en que se desea obtener la porción posruptura de la curva tensión x deformación con este tipo de material, la máquina de ensayos utilizada debe tener una rígidez elevada. A lo largo del trabajo se discuten todos los problemas de un ensayo de compresión simple y aquellos íntimamente ligados con la región del pospico.

The application of high resolution electron backscatter diffraction (HR-EBSD) techniques has been used in order to study the evolution of geometrically necessary dislocation (GND). The tested materials were taken from AZ31 magnesium sheet which had strong basal texture. Because of low symmetry of the magnesium crystal lattice, the von Mises criteria cannot be satisfied by the three independent, easily activated, basal slips. The strain along the c-axis of the crystal must be accommodated by either twinning and/or slip systems. HR-EBSD data was taken in order to investigate these phenomena. The HR-EBSD results were post processed in order to resolve total GND density onto the observed possible slip systems. The first chapter of the investigation focused on the correlation between resolved GNDs with tensile twin nucleation, and the subsequent propagation path in the microstructure. For this purpose, 2.5 % strain was applied in a uniaxial compression test along the transverse direction (TD). Several fine scan were done at the boundaries where twin formed. The results show that in order for a twin to nucleate spontaneously at the grain boundaries, two criteria should generally be met: high angle grain boundaries (35-45°) and pile ups of basal slip system in neighboring grain at the other side of the boundary. Furthermore, once nucleation has initiated, twin propagation can occur through low angle grain boundaries (15-25°); if a twin reaches a high angle boundary, it will generally terminate at the boundary at low strain levels. A twin may pass through high angle boundaries with further deformation. In the second chapter, deformation of the AZ31 magnesium alloy was study for different strain paths. For this purpose, compression and tension in-situ tests were done and the texture and GND evolutions were investigated. The results show that the load paths, compression and tension, evolve the microstructure in different ways. Massive twin fractions were formed in compression, and higher GND contents were observed in tension tests. It was observed that at higher strain levels GND contents are roughly independent of the initial texture but the activation of slip systems at low strain strongly depends on initial structure. If the samples were loaded along RD, GND density increased sharply at low strain. In contrast, for the samples loaded along TD, GND increased moderately. A small amount of repetition is apparent in the two parts of the thesis due to them being formatted for individual publication as journal papers.

Thesis (PhD (Industrial Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Back pain is a common concern amongst a growing population of people across the world today, where in most cases the pain can become unbearable resulting in major lifestyle adjustments. Seventy to eighty percent of the population of the Western world experiences low-back pain at one time or another. Pain can be produced as a worn disc becomes thin, narrowing the space between the vertebrae. Pieces of the damaged disc may also break off and cause irritation to the nerves signalling back pain. Depending on the severity of a patient’s condition, and after conservative treatment options have been exhausted, a disc replacement surgery (arthroplasty) procedure may be prescribed to restore spacing between vertebrae and relieve the pinched nerve, while still maintaining normal biomechanical movement. Typical complications that are however still observed in some cases of disc implants include: anterior migration of the disc, subsidence (sinking of disc) and lateral subluxation (partial dislocation of a joint). Issues such as function, correct placement and orientation, as well as secure fixation of such a disc implant to the adjacent vertebrae are highly important in order to replicate natural biomechanical behaviour and minimise the occurrence of the complications mentioned. As various imaging and manufacturing technologies have developed, the option for individual, patientspecific implants is becoming more of a practical reality than it has been in the past. The combination of CT images and Rapid Manufacturing for example is already being used successfully in producing custom implants for maxilla/facial and cranial reconstructive surgeries. There exists a need to formalise a process chain for the design and manufacture of custom-made intervertebral disc implants and to address the issues involved during each step. Therefore this study has investigated the steps involved for such a process chain and the sensible flow of information as well as the use of state-of-the-art manufacturing technologies. Strong emphasis was placed on automation of some of the processes as well as the user-friendliness of software where engineers and surgeons often need to work together during this multi-disciplinary environment. One of the main benefits for customization was also investigated, namely a reduction in the risk and potential for implant subsidence. Stiffness values from pressure tests on vertebrae were compared between customized implants and implants with flat endplate designs. Results indicated a statistically significant improvement of customized, endplate matching implants as opposed to flat implant endplates. Therefore it may be concluded that the use of customized intervertebral disc implants with patient specific endplate geometry may decrease the risk and potential for the occurrence of subsidence. / AFRIKAANSE OPSOMMING: Rugpyn is ‘n algemene bekommernis vir ‘n groeiende populasie van mense in die wêreld vandag, waar in meeste gevalle die pyn ondraagbaar kan raak en groot leefstyl aanpassings vereis. Sewentig tot tagtig persent van die populasie in die Westerse wêreld ondervind lae rugpyn op een of ander stadium. Die pyn kan veroorsaak word deur ‘n intervertebrale skyf wat verweer en dunner word, en veroorsaak dat die spasie tussen die vertebrae vernou. Stukkies van die beskadigde skyf mag ook afbreek en irritasie aan die senuwees veroorsaak wat verdere pyn kan veroorsaak. Afhangende van die ernstigheid van ‘n pasiënt se geval, en nadat opsies vir konservatiewe behandeling uitgeput is, kan ‘n skyf vervangings-prosedure (artroskopie) voorgeskryf word om die spasie tussen die vertebrae te herstel en sodoende die geknypte senuwee te verlos. Die skyf vervanging herstel spasiëring tussen vertebrae terwyl die normale biomeganiese beweging ook behoue bly, in teenstelling met ‘n fusieprosedure wat die betrokke vertebrae aanmekaar vasheg en normale beweging belemmer. Tipiese komplikasies wat egter steeds na ‘n skyf vervanging in sommige gevalle waargeneem word sluit in: anterior migrasie van die inplantaat, insinking, sowel as laterale sublukasie (gedeeltelike dislokasie van ‘n gewrig). Faktore soos funksie, korrekte posisionering en orientasie, sowel as vashegting van so ‘n skyf inplantaat tot die aanliggende vertebrale bene is besonder belangrik om natuurlike biomeganiese beweging te herstel en sodoende bogenoemde komplikasies te verminder. Soos wat verskeie beeldings- en vervaardigingstegnologië verbeter het oor die laaste dekade, het die moontlikheid vir individuele, pasiënt-spesifieke inplantate al hoe meer ‘n praktiese realiteit begin word. Die kombinasie van Gerekenariseerde Tomografie (GT), tesame met Snel Vervaardiging word byvoorbeeld reeds suksesvol aangewend tydens die ontwerp en vervaardiging van pasiënt-spesifieke inplantate vir maksilla- en kraniale rekonstruktiewe chirurgie. Daar bestaan egter ‘n behoefte om ‘n formele prosesketting vir die ontwerp en vervaardiging van pasiënt-spesifieke intervertebrale skyf inplantate te ontwikkel en om belangrike faktore tydens elke stap noukeurig te beskryf. Hierdie studie het na die verskillende stappe in die prosesketting gekyk om ‘n sinvolle vloei van informasie en benutting van hoë gehalte vervaardigingstegnologië saam te snoer. Sterk klem was gelê op outomatisering van prosesse asook gebruikersvriendelikheid van sagteware waar ingenieurs en medici dikwels saam moet werk tydens hierdie kruisdissiplinêre omgewing. Een van die hoof verwagte voordele met die gebruik van pasklaar skyf inplantate, naamlik die vermindering van moontlike insinking van die inplantaat in die been, is ook ondersoek. Die ondersoek het druktoetse behels en die vergelyking van ooreenstemmende styfheid tussen inplantate wat die kontoer van die bene volg teenoor gewone plat eindplate. Die resultate was statisties beduidend in die guns van die pasklaar inplantate wat die beenkontoere gevolg het, en bewys dus dat die risiko vir insinking verminder is.

This thesis present novel non-destructive laboratory test methods to characterize asphalt concrete. The testing is based on frequency response measurements of specimens where resonance frequencies play a key role to derive material properties such as the complex modulus and complex Poisson’s ratio. These material properties are directly related to pavement quality and used in thickness design of pavements. Since conventional cyclic loading is expensive, time consuming and complicated to perform, there has been a growing interest to apply resonance and ultrasonic testing to estimate the material properties of asphalt concrete. Most of these applications have been based on analytical approximations which are limited to characterizing the complex modulus at one frequency per temperature. This is a significant limitation due to the strong frequency dependency of asphalt concrete. In this thesis, numerical methods are applied to develop a methodology based on modal testing of laboratory samples to characterize material properties over a wide frequency and temperature range (i.e. a master curve). The resonance frequency measurements are performed by exciting the specimens using an impact hammer and through a non-contact approach using a speaker. An accelerometer is used to measure the resulting vibration of the specimen. The material properties can be derived from these measurements since resonance frequencies of a solid are a function of the stiffness, mass, dimensions and boundary conditions. The methodology based on modal testing to characterize the material properties has been developed through the work presented in paper I and II, compared to conventional cyclic loading in paper III and IV and used to observe deviations from isotropic linear viscoelastic behavior in paper V. In paper VI, detailed measurements of resonance frequencies have been performed to study the possibility to detect damage and potential healing of asphalt concrete.  The resonance testing are performed at low strain levels (~10^-7) which gives a direct link to surface wave testing of pavements in the field. This enables non-destructive quality control of pavements, since the field measurements are performed at approximately the same frequency range and strain level. / <p>QC 20141117</p>