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<p> This thesis is a study of numerically controlled machine tools (NCMT), and is divided into four sections. </p> <p> Section A is a literature survey of current concepts, criteria and techniques in design of MCMT structures and drives. Several of the authors own ideas are also included. </p> <p> Section B deals with NCMT manual and computer aided programming techniques. The structure and function of post processors is also covered. </p> <p> Section C is a practical combination of computer design optimization and numerical control manufacture. In an example the geometrical dimensions of a hydrostatic thrust bearing are optimized and used as an input to a generalized APT programme, written to produce a numerical control tape for manufacture of this bearing type. </p> <p> Section D is the discussion and conclusion. </p> / Thesis / Master of Engineering (MEngr)

The flexural behavior of a light-weight wood-based composite system was studied through destructive experiments. The composite panel system consisted of profiled dimensional lumber, which makes up the surface layers, and 1"-thick boards running across the surface layers. Considering the changes in cross-sections along the panel due to the presence of the embedded boards, classical theories such as the Euler-Bernoulli beam and Kirchhoff-Love plate could not be implemented. Instead, the deflections and maximum failure loads of the composite system under full- and short-span bending tests were measured during their destructive bending testing, and were compared against the mechanical properties of the conventional three-ply CLT panel with the same thickness as the panel with embedded cross-laminations. According to maximum failure loads and deflections, it was concluded that full-span panels with embedded cross-laminations exhibited higher strength and stiffness, whereas short-span panels exhibited higher strength and lower stiffness properties compared to conventional CLT panels.

The use of timber in building structures is steadily increasing. cross laminated timber (CLT) is an engineered wood product made of an uneven number of layers of lamellas glued at an angle of 90 degrees to each other. This gives CLT high stiffness and strength to bending in all directions, and capability of taking load both in-plane and out-of-plane. Due to the large size of CLT elements, they allow for quick assembly of strong structures. Due to both economic and environmental reasons it is important for producers of CLT to optimize the use of the wood material by using the timber with higher stiffness and strength where it is most needed. This thesis is about evaluating the bending and shear stiffness of CLT elements, when used as plates, depending on the quality of wood used in the different layers. Four-point bending tests are carried out on elements of different compositions and a parametrized finite element model is created. Thus, the model is validated on the basis of experimental tests to evaluate the influence of different quality of different layers. The measured dynamic MoE proved to have good potential to be used as the longitudinal bending stiffness in an FE-model, with a deviation from the experimental tests of less than 1%. There is a strong correlation between the bending stiffness and bending strength of the plates. The effective rolling shear modulus in pine was calculated to be around 170 MPa for pine of dimension 40 x 195 mm2 . Grading the boards into two different classes used for different layers proved to increase the MoE of the plates by 11-17% for 3- and 5-layer CLT.

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Motivation A close association exists between hypertension and arterial stiffness. Whether the increased arterial stiffness seen in hypertensives are due to structural or functional adaptations in the vasculature is uncertain. Hypertension is more common in blacks and they have an increased arterial stiffness and higer stroke prevalence than white populations. Arterial stiffening, or a loss of arterial distensibility, increases the risk for cardiovascular events, including stroke and heart failure, as it increases the afterload on the heart, as well as creating a higher pulsatile load on the microcirculation. The stiffness of the carotid artery is associated with cardiovascular events, like stroke, and all-cause mortality. Furthermore, carotid stiffness is independently associated with stroke, probably because stiffening of the carotid artery may lead to a higher pressure load on the brain. Inflammation, endothelial activation, dyslipidemia, hyperglycemia and health behaviours may also influence hypertension and arterial stiffness. Limited information is availiable on these associations in black South Africans. The high prevalence of hypertension and cardiovascular disease in blacks creates the need for effective prevention and intervention programs in South Africa. Aim We aimed to compare the characteristics of the carotid artery between 5-year sustained hypertensive and normotensive black participants. Furthermore, we aimed to determine whether blood pressure, conventional cardio-metabolic risk factors, markers of inflammation, endothelial activation and measures of health behaviours are related to these carotid characteristics. Methodology This sub-study forms part of the South African leg of the multi-national Prospective Urban and Rural Epidemiology (PURE) study. The participants of the PURE-SA study were from the North West Province of South Africa, and baseline data collection took place in 2005 (N=2010), while follow-up data was collected five years later, in 2010 (N=1288). HIV-free participants who were either hypertensive or normotensive (N=592) for the 5-year period, and who had complete datasets, were included in this sub-study. The study population thus consists of a group of 5-year sustained normotensive (n=241) and hypertensive (n=351) black participants. Anthropometric measurements included height, weight, waist circumference and the calculation of body mass index (BMI). We included several cardiovascular measurements, namely brachial systolic- and diastolic blood pressure, heart rate, central systolic blood pressure, central pulse pressure and the carotid dorsalis-pedis pulse wave velocity. Carotid characteristics included distensibility, intima media thickness, cross sectional wall area, maximum and minimum lumen diameter. Biochemical variables that were determined included HIV status, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, triglycerides, fasting glucose, glycated haemoglobin (HbA1c), creatinine clearance, interleukin-6, C-reactive protein, intracellular adhesion-molecule-1 and vascular adhesion molecule-1. Health behaviours were quantified by measuring γ-glutamyltransferase and by self-reported alcohol, tobacco and anti-hypertensive, anti-inflammatory and lipid-lowering medication use. We compared the normotensive and hypertensive groups by using independent t-tests and chi-square tests. The carotid characteristics were plotted according to quartiles of central systolic blood pressure by making use of standard analyses of variance (ANOVA) and the analyses of co-variance (ANCOVA). Pearson correlations done in the normotensive and hypertensive Africans helped to determine covariates for the multiple regression models. We used forward stepwise multiple regression analyses with the carotid characteristics as dependent variables to determine independent associations between variables. Results and Conclusion The cardiovascular measures, including pulse wave velocity, were significantly higher in the hypertensive group (all p≤0.024). The lipid profile, markers of inflammation, endothelial activation and glycaemia, as well as health behaviours, did not differ between the hypertensives and normotensives after adjustments for age, sex, waist circumference, γ-glutamyltransferase, tobacco use and anti-hypertensive medication use. After similar adjustments, all carotid characteristics, except IMT, were significantly different between the groups (all p≤0.008). However, upon additional adjustment for cSBP, significance was lost. The stiffness and functional adaptation seen in this study are not explained by the classic cardio-metabolic risk factors, markers of endothelial activation or health behaviours of the participants. The differences that exist in terms of arterial stiffness between the normotensive and hypertensive groups may be explained by the increased distending pressure in the hypertensive group. Despite their hypertensive status, it seems that there are no structural adaptations in these hypertensive Africans. / MSc (Physiology), North-West University, Potchefstroom Campus, 2015

Motivation A close association exists between hypertension and arterial stiffness. Whether the increased arterial stiffness seen in hypertensives are due to structural or functional adaptations in the vasculature is uncertain. Hypertension is more common in blacks and they have an increased arterial stiffness and higer stroke prevalence than white populations. Arterial stiffening, or a loss of arterial distensibility, increases the risk for cardiovascular events, including stroke and heart failure, as it increases the afterload on the heart, as well as creating a higher pulsatile load on the microcirculation. The stiffness of the carotid artery is associated with cardiovascular events, like stroke, and all-cause mortality. Furthermore, carotid stiffness is independently associated with stroke, probably because stiffening of the carotid artery may lead to a higher pressure load on the brain. Inflammation, endothelial activation, dyslipidemia, hyperglycemia and health behaviours may also influence hypertension and arterial stiffness. Limited information is availiable on these associations in black South Africans. The high prevalence of hypertension and cardiovascular disease in blacks creates the need for effective prevention and intervention programs in South Africa. Aim We aimed to compare the characteristics of the carotid artery between 5-year sustained hypertensive and normotensive black participants. Furthermore, we aimed to determine whether blood pressure, conventional cardio-metabolic risk factors, markers of inflammation, endothelial activation and measures of health behaviours are related to these carotid characteristics. Methodology This sub-study forms part of the South African leg of the multi-national Prospective Urban and Rural Epidemiology (PURE) study. The participants of the PURE-SA study were from the North West Province of South Africa, and baseline data collection took place in 2005 (N=2010), while follow-up data was collected five years later, in 2010 (N=1288). HIV-free participants who were either hypertensive or normotensive (N=592) for the 5-year period, and who had complete datasets, were included in this sub-study. The study population thus consists of a group of 5-year sustained normotensive (n=241) and hypertensive (n=351) black participants. Anthropometric measurements included height, weight, waist circumference and the calculation of body mass index (BMI). We included several cardiovascular measurements, namely brachial systolic- and diastolic blood pressure, heart rate, central systolic blood pressure, central pulse pressure and the carotid dorsalis-pedis pulse wave velocity. Carotid characteristics included distensibility, intima media thickness, cross sectional wall area, maximum and minimum lumen diameter. Biochemical variables that were determined included HIV status, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, triglycerides, fasting glucose, glycated haemoglobin (HbA1c), creatinine clearance, interleukin-6, C-reactive protein, intracellular adhesion-molecule-1 and vascular adhesion molecule-1. Health behaviours were quantified by measuring γ-glutamyltransferase and by self-reported alcohol, tobacco and anti-hypertensive, anti-inflammatory and lipid-lowering medication use. We compared the normotensive and hypertensive groups by using independent t-tests and chi-square tests. The carotid characteristics were plotted according to quartiles of central systolic blood pressure by making use of standard analyses of variance (ANOVA) and the analyses of co-variance (ANCOVA). Pearson correlations done in the normotensive and hypertensive Africans helped to determine covariates for the multiple regression models. We used forward stepwise multiple regression analyses with the carotid characteristics as dependent variables to determine independent associations between variables. Results and Conclusion The cardiovascular measures, including pulse wave velocity, were significantly higher in the hypertensive group (all p≤0.024). The lipid profile, markers of inflammation, endothelial activation and glycaemia, as well as health behaviours, did not differ between the hypertensives and normotensives after adjustments for age, sex, waist circumference, γ-glutamyltransferase, tobacco use and anti-hypertensive medication use. After similar adjustments, all carotid characteristics, except IMT, were significantly different between the groups (all p≤0.008). However, upon additional adjustment for cSBP, significance was lost. The stiffness and functional adaptation seen in this study are not explained by the classic cardio-metabolic risk factors, markers of endothelial activation or health behaviours of the participants. The differences that exist in terms of arterial stiffness between the normotensive and hypertensive groups may be explained by the increased distending pressure in the hypertensive group. Despite their hypertensive status, it seems that there are no structural adaptations in these hypertensive Africans. / MSc (Physiology), North-West University, Potchefstroom Campus, 2015

Cross frames are critical for the stability of straight and curved steel bridges. Conventional cross frames are often fabricated from steel angles which are welded to gusset plates through one leg only. Due to this eccentric connection, these angles have substantial bending at the connection that can reduce the member stiffness and can potentially decrease fatigue performance. Because of the low buckling strength, cross frames with angle diagonals are often designed as tension-only systems, therefore increasing the necessary steel to be an effective brace. Improved behavior may result if concentric members are utilized. The increased buckling strength of tubes and double angles results in effective members in both compression and tension, and a single diagonal cross frame can provide effective bracing; however, a suitable connection must be developed. Tubes are often connected by slotting the tube in the center and welding to a gusset plate, which requires precise fabrication. Two proposed solutions that would connect easily to the ends of the member and seal the end of the tube include a steel casting and a T-stem connection. The dissertation studies the development of a steel casting for use in cross frame design and evaluates the performance of the various details described herein in regards to stiffness, strength, and fatigue. Additionally, the dissertation covers the behavior of single angle X and K frame configurations. To date, the determination of the single angle fatigue detail has been largely based on component tests only. The project incorporated full-scale cross frame fatigue tests to fully examine the interaction of the cross frame members with the overall structure. Results from currently used details and proposed connections provide insight to the live load behavior of these braces and multiple recommendations are made to improve the fatigue life. The project examined the stiffness behavior of current and proposed cross frame layouts with large-scale laboratory tests and computational modeling. From these results, a case study compares the fatigue analysis of a commercial structural software package to the stress ranges obtained in a three-dimensional finite element model. Suggestions on how to properly model the cross frames are given. / text

This study determined whether variation in clone, weed control treatment, or stem dimensions, could have an impact upon outerwood stiffness in 17 year old Pinus radiata stems. An experiment located south west of the Dunsandel township in Canterbury, New Zealand, was used to collect measures of acoustic velocity (windward and downward sides) from each of the 278 trees. Diameter at breast height, tree height, and height to live crown were also recorded for each tree. Findings from this research were compared with previous research carried out when the trees were ages eight and eleven. Assuming a green density of 1,000 kg/m3, Young’s Modulus equation was used to convert acoustic velocity to wood stiffness, or, Modulus of Elasticity (MOE). The effect of wind direction upon mean wood stiffness was not significant (α = 0.05). Consequently, one measure of wood stiffness was calculated per tree. Mean stem slenderness and mean wood stiffness values were calculated by block, weed control treatment, and clone. Weed control treatments had a significant impact upon mean wood stiffness in comparison to the control treatment (0.03 m2 area of weed control). Significant differences did not exist between different levels of weed control, ie., 0.75 m2, 3.14 m2 and 9 m2 chemical spot spray area. Clonal variation and stem slenderness significantly affected mean wood stiffness measures. Stem slenderness appeared to be correlated with clonal variation (interaction between clone and slenderness was not significant), however, according to Dr. Euan Mason, this finding is not corroborated by findings from other research on the wood quality of clones in Canterbury (personal communication, September 16, 2013). An analysis of covariance (ANCOVA) determined that mean height to the live crown was not a significant predictor of wood stiffness. Comparison with earlier research showed no change in the ranking of wood stiffness values by clone or treatment.

Glaucoma is a common cause of blindness worldwide, yet the etiology of the disease is unclear. A leading hypothesis is that elevated intraocular pressure (IOP) affects the biomechanical environment within the tissues of the optic nerve head (ONH), and that the altered biomechanical environment contributes to optic nerve damage and consequent loss of vision. The biomechanical environment of the ONH is strongly dependent on the biomechanical properties of sclera, particularly scleral stiffness. However there is significant variability in reported stiffness data for human sclera. Therefore, our research goal was to measure the stiffness of human sclera and incorporate this information into finite element models of the human eye to characterize and quantify the biomechanical environment within and around the optic nerve head region at different IOP levels. Human sclera adjacent to the optic nerve head showed highly nonlinear, nearly isotropic and heterogeneous stiffness which was found to be substantially lower than that previously assumed, particularly at lower levels of IOP. The products c*c1 and c*c2, measures of stiffness in the latitudinal and longitudinal directions from the Fung constitutive model, were 2.9 ± 2.0 MPa and 2.8 ± 1.9 MPa, respectively, and were not significantly different (two-sided t-test; p = 0.795). Scleral stiffness was not statistically different between left and right eyes of an individual (p = 0.952) and amongst the quadrants of an eye (p = 0.412 and p = 0.456 in latitudinal and longitudinal directions, respectively). Three stress-strain relationships consistent with the 5th, 50th and 95th percentiles of the measured scleral stiffness distribution were selected as representatives of compliant, median and stiff scleral properties and were implemented in a generic finite element model of the eye using a hyperelastic five-parameter Mooney-Rivlin material model. Models were solved for IOPs of 15, 25 and 50 mmHg. The magnitudes of strains at the optic nerve head region were substantial at even the lowest applied IOP (15 mmHg) and increased at elevated IOPs (e.g. the third principal strain in the compliant model reached as much as 5.25% in the lamina cribrosa at 15mmHg and 8.84% in the lamina cribrosa at 50 mmHg). Scleras that are “weak”, but still within the physiologic range, are predicted to lead to appreciably increased optic nerve head strains and could represent a risk factor for glaucomatous optic neuropathy. As IOP increased from 15 to 50 mmHg, principal strains in the model with a compliant sclera increased at a lower rate than in the model with a stiff sclera. We quantified the biomechanical environment within and around the optic nerve head region using a range of experimentally measured mechanical properties of sclera and at different IOPs. We showed that IOP-related strains within optic nerve head tissues can reach potentially biologically significant levels (capable of inducing a range of effects in glial cells) even at average levels of IOP and for typical human scleral biomechanical properties.