Indiana University-Purdue University Indianapolis (IUPUI) / This study evaluated the feasibility of bonding brackets to porcelain for orthodontic purposes by measuring and comparing tensile strengths of five silane-based adhesive systems. Each adhesive system bonded mesh pad brackets to 10 glazed and 10 deglazed metal-ceramic crowns and the specimens were then thermocycled between 16 degrees and 56 degrees for 2500 cycles. Clinically relevant bond strengths, comparable to those of adhesives bonding brackets to enamel, were recorded for four of the systems compared. System l+ and Porcelain Primer had the highest mean values followed by Lee's Enamelite 500, then Vivadent's Silanit, Contact-Resin and Isopast, then 3M's Concise and Scotchprime. Most, if not all, failure sites for the four were at the bracket-resin interface. Two-way factorial analysis of variance demonstrated significant differences at P<.001 among the four adhesives but no contribution of surface effect, whether glazed or deglazed, was suggested statistically. Neuman-Keul sequential range tests showed significant differences between System l+ and the three other systems but no significant differences among the three were detected. Den-Mat's Ultrabond recorded extremely low tensile strength values and was of dubious clinical value. A t-test suggested that deglazing porcelain contributed no significant difference in strength compared with intact, glazed porcelain. All failure sites were at the porcelain-resin interface for this product. Since resin may remain bonded to porcelain following debonding, George Taub's diamond polishing paste and Shofu porcelain polishing wheels were compared as to their ability in restoring the porcelain to its original state. Because of the great adhesive bond of the resin to porcelain, craters, pits or tears may be created when resin is cleaned from porcelain with conventional scalers and pliers. The diamond paste gave a better restorative finish than the stones but the end result depended on the extent of original damage following cleaning. Orthodontists should take this point into account when considering bonding to porcelain crowns or veneers for esthetics sake where final risks may outweigh initial benefits. In a limited survey of 100 orthodontists responding to a questionnaire, 89% indicated that they have bonded or contemplated bonding to composite restored teeth, and 83% indicated that they have bonded or contemplated bonding to porcelain.

Resisting external forces can be a source of beauty. This work represents an effort to understand how architecture can be derived from the struggle against natural forces to create a built-form. Starting with an idea, that of a tensile roof, the design of a soccer stadium developed into what is presented here. / Master of Architecture

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The early age cracking of concrete, which includes plastic shrinkage cracking (PShC) and plastic settlement cracking (PSeC), commonly occurs in flat concrete elements such as bridge decks and slabs or at the change of a concrete section depth. These cracks typically occur once the concrete has been cast and consolidated up to the final setting time, and initiate when the tensile stresses developed in the concrete exceeds its ultimate tensile strength or, alternatively phrased, when the restrained shrinkage induced strain in the concrete exceeds its tensile strain capacity. These cracks have a premature detrimental effect on the durability and strength of concrete structures as they allow deleterious materials to penetrate the concrete, which could cause the corrosion of steel reinforcing. With this in mind, the objective of this study is to gain a fundamental understanding of the tensile properties of early age concrete, up to the point of final setting, as well as the variables that affect these properties. This is done to better understand, and ultimately reduce the risk of early age cracking. To achieve this, experimental assemblies found in literature were evaluated and built upon to create a multi-component uniaxial tensile testing setup that is able to capture the complete stress-strain behaviour of early age concrete, while still in a plastic state. The following significant findings were attained from this study: • Reducing the coarse aggregate size in a concrete mix increases both the tensile strength and Young’s modulus of early age concrete, while reducing both its fracture energy and fracture process zone (FPZ) characteristic length. • The low volume addition of microfibres to a conventional concrete mix increases both the fracture energy and the FPZ characteristic length of early age concrete. • The low volume addition of microfibres to a conventional concrete mix increases the strain capacity of early age concrete shortly before and after the initial setting time. This increased strain capacity is believed to be of great significance for the prevention of PShC. • The addition of an accelerator to a conventional concrete mix accelerates the development of the tensile properties of early age concrete, while a retarder reduces it. • The addition of a retarder to a conventional concrete mix increases the strain capacity of early age concrete shortly before and after the initial setting time. This provides a reason for the reduced PShC severity observed in retarded mixes in certain instances. From this study it is concluded that the results from the tensile tests provide a greater understanding of the tensile properties of early age concrete as well as the variables that affect them. When interpreting these results in combination with those obtained from PShC experiments, it is suggested that it is possible to determine when and if PShC will occur. / AFRIKAANSE OPSOMMING: Die vroëe-ouderdom kraking van beton, wat plastiese krimp krake (PKK) en plastiese versakkings krake (PVK) insluit, kom algemeen voor in plat betonelemente soos brug-dekke en blaaie, of by die die verandering in die deursnit diepte van betonelemente. Die krake kom tiepies voor vandat beton gegiet en gekompakteer is totdat dit die finale settyd bereik, en vind plaas sodra die trekspanning wat in die beton ontstaan sy treksterkte oorskry of, anders bewoord, wanneer die verhinderde krimp geinduseerde vervorming van die beton, die vervormings-kapasiteit van die beton oorskry. Hierdie krake het ʼn voortydige nagelige uitwerking op die duursaamheid en sterkte van betonstrukture aangesien hulle toelaat dat skadelike stowwe die beton binnedring, wat die korrosie van staalbewapening veroorsaak. Met dit ingedagte is die doel van die studie om fundamentele kennis rakende die vroëe-ouderdom trekeienskappe van beton, tot by die punt van finale set, asook die veranderlikes wat die eienskappe beinvloed, te verwerf. Om vroëe-ouederdom krake beter te verstaan en uiteindelik, te voorkom, is hierdie kennis nodig. Eksperimentele opstellings in literatuur is ge-evalueer en op voortgebou vir die bou van ʼn multi-komponet eenassige terktoetsopstelling om die volledige spanning-vervorming gedrag van vroëe-ouderdom beton vas te vang. Die volgende bevindings het uit die studie aan die lig gekom: • ʼn Kleiner aggregaat grootte in n betonmeng verhoog beide die trekstrekte en Young se modulus van vroëe-ouderdom beton, terwyl dit beide die fraktuur-energie en die fraktuur proses sone (FPS) se karakteristieke lengte verminder. • Die lae volume byvoeging van mikrovesels tot ʼn betonmeng verhoog beide die fraktuur-energie en die FPS se karakteristieke lengte van vroëe-ouderdom beton. • Die lae volume byvoeging van mikrovesels tot ʼn betonmeng verhoog die vervormings kapasiteit van vroëe-ouderdom beton kort voor en na die aanvanklike settyd. Daar word geglo dat hierdie verhoogde vervormings-kapasiteit van groot belang is vir die voorkoming van PKK. • Die byvoeging van ʼn versneller tot ʼn betonmeng versnel die ontwikkelingstempo van die trekeienskappe van vroëe-ouderdom beton, terwyl ʼn vertrager dit verlaag. • Die byvoeging van ʼn vertrager tot ʼn betonmeng verhoog die vervormings-kapasiteit van vroëe-ouderdom beton kort voor en na die aanvanklike settyd. Dit verskaf die rede vir die bevinding dat die byvoeging van ʼn vertrager PKK in sekere gevalle verminder. Hierdie studie het bevind dat die die trektoetse ʼn groter begrip rakende die trek-eienskappe van vroëe-ouderdom beton, en die veranderlikes wat die eienskappe beinvloed, gelewer het. Wanneer die resultate van die studie tesame met PShC toetse geinterpreteer word, will dit voorkom dat dit moontlik is om te bepaal wanneer, en of PKK sal plaasvind.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Katherine A. Liapi. Vita. Includes bibliographical references.

Hundreds of thousands of vascular bypass grafts are implanted in the United States every year, but there has yet to be an ideal graft material to substitute for one’s own autologous vessel. Many synthetic materials have been shown to be successful vessel replacements; however, none have been proven to exhibit the same mechanical properties as native vessels, one of the most important criteria in selecting a vascular graft material. Part of this issue is due to the fact that, currently, there is no “gold standard” for testing the longitudinal and transverse tensile properties of small diameter tubular materials. While there are ASTM and ISO standards that suggest ways to test tubes in their original form, many researchers have published tensile strength data based on cutting the tube and testing it as a flat sample. Thus, it was the aim of this thesis to understand, establish, and implement accurate tensile testing methods of small diameter polymers in their original, tubular state on Cal Poly’s campus. Two test fixtures were created based on specified design criteria in order to test materials in their tubular form in both the longitudinal and transverse directions. Both fixtures were successful in testing PLGA and ePTFE samples, and statistical data was gathered for the transverse test fixture. The new transverse test fixture was tested against the current method of testing, and a significant (α = 0.05) difference between methods was established for ultimate tensile strength. This analysis, however, cannot determine which test method is more accurate, thus more extensive testing is required to verify the design of both fixtures. By developing a method for testing small diameter polymers in tubular form on Cal Poly’s campus, it allows for more testing of various small diameter tubes and more comparative data to validate each design. It also demonstrates a need for a more detailed and widespread standardization of testing for small diameter tubes, especially in vascular substitute applications where the ideal vessel replacement has yet to be found.

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Polyurethane network binders were synthesized using polyethylene glycol (PEG) prepolymers, cellulose acetate butyrate (CAB), curative [Desmodur N100 (N100) or Desmodur N3200 (N3200)], and catalyst [dibutyltin dilaurate (DBTDL)]. Triacetin (TA) was added as plasticizer before the reaction. Polyurethanes were prepared by varying the molar ratio of ¡VNCO/-OH, weight ratio of TA/PEG, molecular weight of PEG, the amount of catalyst, the order of adding catalyst and curative, and the stirred time. Synthesized polyurethanes were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile tests, and swelling tests to study their reaction, degradation, thermal, and mechanical properties. When the ratio of ¡VNCO/-OH was between 1.2 and 1.4, polyurethane gave the best mechanical properties. Additionally, the quenched polyurethane had a lower degree of crystallinity When the weight ratio of TA and PEG was bigger than 2, crystallization of polyurethane could be minimized during the tensile testing or after quenching. In this study, it was found that PEG with molecular weight of 4000 yielded the best mechanical properties. These results indicate that better and uniform mechanical properties can be obtained by using enough stirring time via varying the amount of catalyst and adding catalyst before curing agent.