Currently, NCHRP Report 356 has published an equation to estimate the ultimate strength of the local zone in normal weight concrete. The local zone is the area of concrete directly ahead of the bearing plate. The equation can be broken into two distinct parts: unconfined bearing strength of concrete enhanced by the A/A_b ratio and the enhancement of strength due to the presence of confining. Research has shown that the strength enhancement of the A/Ab ratio and confining reinforcing is less in lightweight concrete than in normal weight concrete. To determine the strength of the local zone in lightweight concrete 30 reinforced prisms, 2 unreinforced prisms, and concrete cylinders were tested. The dimensions of the prisms were 8 in. x 8 in. x 16 in. and the cylinders were 4 in. x 8 in. cylinders. The simulated reinforcing in the prisms extended only through the top 8 in. of the prism and consisted of either ties or spirals with different spacing or pitch, respectively. To determine the effect of the A/A_b ratio for each spacing or pitch arrangement of the reinforcing, one of two different size bearing plates were used. From the testing performed in this research and other research, it is apparent that the NCHRP equation is unconservative when estimating the ultimate strength of the local zone in lightweight concrete. By modifying both parts of the NCHRP equation it is possible to conservatively predict the ultimate strength of the local zone in lightweight concrete. Also investigated in this thesis are equations to predict the splitting cylinder strength and modulus of elasticity of lightweight concrete. For a sand-lightweight concrete, as defined by ACI 318-05 Building code and Commentary, the splitting tensile strength can be accurately predicted by multiplying the square root of the compressive strength by 5.7. / Master of Science

Sprains are the most common injuries to ligamentous tissues. They are classified as first-degree, second-degree, or third-degree sprains depending upon their severity. First-degree sprains are the result of over-stretching of ligaments. Second-degree sprains involve partial tears of the ligaments. In third-degree sprains, the ligaments are completely torn. Although first- and second-degree sprains are not as severe as third-degree sprains, they occur more frequently. The mechanisms leading to sprains are still not well understood. Therefore, histo-mechanical experiments and theoretical studies are needed to advance our current knowledge on the etiology of sprains. In the first part of this study, a structurally-based constitutive equation is proposed to simulate the damage evolution process in ligaments. The ligament is modeled as a bundle of crimped collagen fibers that are assumed to be oriented along one direction, the physiological loading direction. The gradual straightening of collagen fibers determines the nonlinearity in the toe region of the tensile axial stress-strain curve. Straight collagen fibers behave as a linear elastic material. The gradual damage of collagen fibers determines the nonlinearity in the failure region of the tensile axial stress-strain curve. The parameters in the constitutive equation are estimated by curve fitting experimental data on rat medial collateral ligaments (MCLs) published in the biomechanics literature. In the second part of this study, mechanical experiments are performed in order to identify and quantify damage in ligamentous tissues. MCLs, which are harvested from Sprague-Dawley (SD) rats, are subjected to displacement controlled tensile tests. Specifically, the ligaments are stretched to consecutively increasing stretch values until their complete failure occurs. The elongation of the toe region and decrease in tangent modulus of the linear region of the collected stress-strain data are analyzed and two significantly different damage threshold strains are determined. The effect of age and skeletal maturation on the damage evolution process is also investigated by performing mechanical tests on MCLs isolated from two age groups of SD rats. In the third part of this study, scanning electron microscopy (SEM) is used to determine variations in the microstructure of ligaments that are associated with the elongation of the toe region and decrease in tangent modulus of the linear region of the stress-strain curve. MCLs from SD rats are subjected to different threshold strains that produce damage and, subsequently, examined using SEM. By comparing the morphology of collagen fibers and fibrils in undamaged and damaged MCLs, the microscopic variations induced by strain are determined and correlated to the observed macroscopic mechanical damage. / Ph. D.

Three theories - the time-hardening theory, the strain-hardening theory, and the life-traction theory - are investigated in an effort to predict creep strains under conditions of varying loads from data obtained at constant load in the range of interest to the structural designer. A method is presented for computing an equivalent rupture stress for the varied load case using the lite-traction theory and the rupture curve tor constant stress tests. The analytical methods are compared with data obtained from 2024-T3 aluminum-alloy sheet under tensile creep at constant and varying loads. / M.S.

A Local Load Sharing (LLS) model recently developed by Curtin and co-workers for the numerical simulation of tensile stress-strain behavior in fiber-reinforced composites is used to predict the tensile strength of metal matrix composites consisting of a Titanium matrix and unidirectionally aligned SiC fibers. This model is extended to include the effects of free boundary conditions and non-constant load gradients and then used to predict the strength of a Ti-6Al-4V matrix reinforced with Sigma SiC fibers under 4-point flexure testing. The predicted tensile and flexure strengths agree very well with the values measured by Gundel and Wawner and Ramamurty et al. The composite strength of disordered spatial fiber distributions is investigated and is shown to have a distribution similar to the corresponding ordered composite, but with a mean strength that decreases (as compared to the ordered composite) with increasing Weibull modulus. A modified Batdorf-type analytic model is developed and similarly extended to the case of non-uniform loading to predict the strength of composites under tension and flexure. The flexure model is found to be inappropriate for application to the experimental materials, but the tensile model yields predictions similar to the Local Load Sharing models for the experimental materials. The ideas and predictions of the Batdorf-type model, which is essentially an approximation to the simulation model, are then compared in more detail to a simulation-based model developed by Ibnabdeljalil and Curtin to more generally assess the accuracy of the Batdorf model in predicting tensile strength and notch strength versus composite size and fiber Weibull modulus. The study shows the Batdorf model to be accurate for tensile strength at high Weibull moduli and to capture general trends well, but it is not quantitatively accurate over the full range of material parameters encountered in various fiber composite systems. / Master of Science

Yes / Tensile properties of powder metallurgy 3% manganese-0·8% carbon (content of green compact) steels were determined following laboratory sintering in (nearly) full, semiclosed containers with no getter powders in dry, 0-100% hydrogen-nitrogen atmospheres. Manganese was mixed with the NC 100·24 sponge iron powder as low carbon ferromanganese and carbon as a graphite addition. Dogbone compacts were pressed at 660 MPa, the sintering temperatures were 1120 and 1250°C and cooling rates ∼65 K min- 1. In specimens sintered in nitrogen containing atmospheres at 1120°C, final carbon content was ∼0·7% and for those processed at 1250°C ∼0·6%. Sintering in dry hydrogen resulted in lower carbon and oxygen contents. Independent of the H2/N2 ratio in the furnace atmosphere, however, all the specimens were ductile and exhibited similar strengths. Yield strengths R 0·2 were in the range: 426-464 MPa, tensile strengths Rm were 724-780 MPa and strains to failure were 1·6-2·0% after sintering at 1250°C. The 1120°C sintering temperature resulted in 10-15% lower strength values. The microstructures, significantly devoid of oxide networks, comprised mainly mixtures of bainite and fine (divorced) pearlite, with very little martensite and retained austenite. Reproducibly successful sintering of manganese containing compacts requires that reduction conditions exist at the sintering temperature. Ellingham Richardson diagrams dictate that the dewpoints of hydrogen required are-55 and-40°C at 1120 and 1250°C, respectively. A semiclosed container, how ever, ensures a different microclimate. It is suggested that then the initial relevant reactions there are: Mn[vapour]+H2O=MnO+H2, 3Fe2O3 +H2= 2Fe3O4+H2O, Fe3O4+H2=3FeO+H2O, FeO+H2= Fe+H2O and C+O2=CO2, which provide hydrogen andwater vapour,also within the pores. The manganese vapour further acts as a ‘shield’ by generating further hydrogen from the water vapour. The following reactions involving carbon monoxide are postulated above 927°C, when CO is a more effective reducing agent than hydrogen: C+H2O=H2+CO, 3Fe2O3+ CO=2Fe3O4+CO2, Fe3O4+CO=3FeO+CO2, FeO+CO=Fe+CO2 and C+CO2=2CO. Accordingly, irrespective of whether it is hydrogen or nitrogen in the semiclosed container, if there is a supply of carbon, reducing conditions prevail at the sintering temperature,embrittling oxidenetworks arenot formed and ductile manganese steels are processed.

In this study, the aim is to investigate the stiffness, longitudinal tensile strength and circumferential tensile strength of short fiber reinforced polyester composite pipes produced by centrifugal casting production method. To achieve this aim, theoretical calculation of modulus of elasticity of pipes was done and then test program was carried out on pipe samples produced with three different resin types which were orthophthalic, isophthalic and vinyl ester resin and three different fiber types which were E glass fiber, ECR glass fiber and basalt fiber. The tests were performed according to ISO (International Organization for Standardization) standards. When resin type and fiber type effect on the fiber reinforced polyester pipe samples were evaluated, calculated elastic modulus values were in accordance with the test results. According to the experimental test data, which were used to evaluate the effect of resin type on fiber reinforced polyester pipe properties, there is not a significant difference was observed in the stiffness, longitudinal and circumferential tensile strength test results of pipes having different resin types. In other words, there was not a significant effect of resin type on the stiffness, longitudinal tensile strength and circumferential tensile strength of short fiber reinforced pipes produced by centrifugal casting method. According to the experimental test data, which were used to evaluate the effect of fiber type on the properties of fiber reinforced polyester pipe, basalt fiber reinforced pipe samples showed higher mechanical performance over E glass fiber and ECR glass fiber reinforced pipes. However, the test results of basalt reinforced polyester pipe were not as good as the individual properties of basalt fiber. Finally, by comparing the basalt fiber reinforced pipe samples having almost the same stiffness and tensile test results as E glass fiber reinforced pipe samples, the gain in fiber and resin amount were investigated. Basalt fiber reinforced pipes were slightly lighter and thinner than E glass fiber reinforced pipes. However, the decrease in the amount of the fiber and resin in basalt reinforced pipe did not result in an overall cost reduction.

Für die Ermittlung der Ermüdungsfunktion sowie der E-Modul-Funktion sind in den europäischen Normen verschiedene Versuchsarten vorgesehen. In Deutschland werden bisher der Einaxiale Zugschwellversuch und der Spaltzugschwellversuch angewandt. Diese vergleichsweise einfachen Versuche können das Ermüdungsverhalten eines Asphaltgemisches in situ nur mit Einschränkungen (z.B. hinsichtlich des vorherrschenden Spannungszustandes) wiedergeben. Der Triaxialversuch mit Zug-/Druckschwellbelastung kann zur realitätsnahen Untersuchung des Ermüdungsverhaltens (Ermüdungsfunktion in Verbindung mit der E-Modul-Funktion) angewandt werden, da neben der frei wählbaren Zugbeanspruchung zusätzlich beliebige Druckbeanspruchungen normal zur Zugspannung auf den Probekörper aufgegeben werden können. Aufgrund der aufwändigen Versuchsdurchführung findet der Versuch bisher nur in der Forschung Anwendung. Die für die Dissertation ausgewerteten Daten umfassen die Ergebnisse von Einaxialen Zugschwellversuchen, Spaltzugschwellversuchen und Triaxialversuchen mit Zug-/Druckschwellbelastung an insgesamt sechs verschiedenen Asphaltgemischen. Die Einflüsse aus dem Hohlraumgehalt, der Belastungsfrequenz sowie der Mischgutart und -sorte auf das Ermüdungsverhalten konnten herausgearbeitet werden. Weiterhin gelang aus den Ergebnissen aller Versuchsarten die Aufstellung von Ermüdungsflächenfunktionen in Abhängigkeit von Dehnungsanteilen infolge verschiedener Spannungskomponenten (mehraxialer Spannungszustand) unter Berücksichtigung der in den Probekörpern der verschiedenen Ermüdungsversuche auftretenden Spannungskombinationen Zug- zu Druckspannung. Die Gültigkeit der ermittelten Ermüdungsflächenfunktion für andere, über die in den angewendeten Versuchsarten hinausgehende Spannungskombinationen muss mit Hilfe geeigneter (noch zu entwickelnder) Versuche überprüft werden.

The aim is to investigate models that predicts the potential of pulp and evaluate the relevance of the zero-span tensile index within these. Two chemical pulps made from softwood and eucalyptus were refined in a Voith-beater with different energy input in order to study the change of fiber morphology signals and other pulp and paper properties. Chemical, THP pulp from Södra Värö is also used as an initial analysis for morphological connections to Zero-span tensile index. The L&W Fiber Tester Plus is used in order to study the pulps fiber morphology and Pulmac 2000 for zero span. Handsheets are made for mechanical tests such as tensile properties, ZD-strength and optical properties. Many of the given signals change according to clear patterns with increasing refining energy. Using least square methods, formulas describing the development with high adaptation could be formulated. Many of the measured aspects changes over already known patterns. These are then applied in the models. Three possible models is tested: linear regression, Shear-Lag and Page. Of the three, only the two first ones where able to produce reliable models, whereas the third required data that was difficult to acquire at the same time as the adaptation was very low. The only model that use exclusively morphology data is linear regression.

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Polysaccharides are now popularly used in paper technology since they are able to improve mechanical properties of the paper. Xylan and pectin are two natural polymers that have a wide range of applications nowadays. These two polysaccharides can be used in their native forms as well as derivatives. In this study, xylan and pectin were modified to obtain cationic derivatives before adding into the paper for enhancement. The work was motivated by the fact that xylan and pectin share the same negative surface properties as cellulose. This leads to a slight repulsion effect between them once they are close. Their cationic derivatives, therefore, are believed to strengthen the paper due to electrostatic interactions between two oppositely charged objects beside hydrogen bonds. To fulfil the purposes, oat spelt xylan and apple pectin were chemically modified using different modification methods, including oxidation, amidation, and a combination of these two methods. A quantitative method to determine the adsorbed amount and relative retention capacity of xylan onto paper using high performance liquid chromatography was also developed. The results show that oat spelt and apple pectin, as well as their modified derivatives, can improve the paper mechanical properties. The oat spelt xylan significantly enhances the tensile strength, however, this contribution has a saturation level in correlation with the relative retention capacity of the xylan onto cellulose. The best retention capacity is achieved when 5% of xylan is added. This finding provides a practical approach to the application of xylan as a paper additive in consideration of economic issues. Although the application of apple pectin and its amidated derivatives in paper is rather rare, some interesting points have been discovered in this work. Among the apple pectin samples used, only the ones with low degree of esterification give a slight enhancement in tensile index at 5% dosage. The results also suggest that the dosage of the pectin added into the paper should not exceed 5% due to its viscous property at high concentrations.