Abstract This paper reports about a precision positioning XY stage utilizing flexure hinges and piezoelectric actuators. XY stage was designed with the aim of reducing the stress-concentration of flexure hinges and the low interference between two actuating axes. Utilized the expression of matrix to figure out the properties of the bellow-type flexure hinges, and proved these by mathematical software. Experiments demonstrated that the stage actuated by a stairstep driving signal with maximum displacement 1.3£gm and interference 50nm along X axis; along Y axis with maximum displacement 0.8£gm and interference 11nm. The stage actuated by a ramp signal with maximum displacement 1.2£gm and interference 45nm along X axis; along Y axis with maximum displacement 0.9£gm and interference 35nm. The finite element method (FEM) was used to analyse the stress-concentration of the stage. and the simulated results were compared with the experiments. Referred to the testing results, the target object could be moved in the aimed position accurately.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 163).

Submitted in fulfillment of the Degree of Master in Technology: Dental Technology in the Department of Dental Services Faculty of Health Sciences, Durban University of Technology, 2008. / Globally in the field of Dental Technology, polymethyl methacrylate (PMMA) resin continues to be the popular material for the fabrication of denture bases in removable prosthodontics. However, the mechanical strength of the denture base is a concern due to fractures occurring intra-orally or when accidentally dropped. The objective of this in vitro investigation was therefore to evaluate and compare the flexural strength and microstructure of stick® glass fibre and wire mesh reinforced PMMA resin after thermocycling. The selection of the materials used in this study was based primarily on their popularity and availability in South Africa. These materials were selected to ensure that the results of this study would have further implicational value in the commercial dental industry when published. This investigation was conducted by means of fabricating a total of 90 PMMA resin specimens and divided in three groups consisting of 30 specimens each. Sample groups 1 and 2 were reinforced with stick® glass fibres and wire mesh respectively. The un-reinforced sample group was the control. All 90 specimens were thermocycled in water at temperatures between 5˚C and 55˚C for 2100 cycles. The flexural strength of each specimen was tested using a universal testing machine and the microstructure of the fractured surfaces was then analysed using scanning electron microscopes (SEM). SPSS version 15.0 was used for data analysis. A p-value of <0.05 was considered as statistically significant. Data were analysed using parametric and non-parametric statistical methods. Statistically significant differences in flexural strength existed between the three sample groups (p<0.001) with the stick® glass fibre and wire mesh sample groups being significantly superior to the control. Furthermore there was a significant association between fracture modes and sample groups. Microscopic analysis revealed the presence of voids. Statistically, in terms of microstructure (% of voids present), a significant difference existed between all sample groups. With regards to surface texture of the compression and tension sides of the test specimens, significant differences existed between the three sample groups. Furthermore microscopic analysis revealed partial impregnation and distribution of the fibres to the PMMA resin matrix and un-bonding between the wire mesh and PMMA resin matrix. Statistically, the Mann-Whitney test was conducted to compare flexural strength between sample groups with and without voids. The flexural strength was higher in sample groups with voids than those without. This is an important finding from the clinical perspective because, in some structures of dentures, toughness is a desired property. Nevertheless in order to find the long-term data especially on clinical behaviour of these new fibre reinforcement systems, more studies should be conducted.

No description available.

The structural behaviour of simply supported reinforced concrete (R.C.) beams strengthened in flexure by externally bonded steel or fibre reinforced plastic (FRP) plates has been investigated. A novel theoretical model coupled with simple (hence, practical) procedure(s) for designing such beams against premature plate peeling failure has been developed. The theoretical model and the design procedures have been validated by an extensive number (169) of mainly large-scale test data (using steel or FRP plates) from other sources. The effects of variations in the magnitude of Young's modulus for FRP plates on the potential changes in the flexural ultimate load of R. C. beams with externally bonded FRP plates, in the absence and/or presence of plate peeling, have been investigated in some detail with the theoretical predictions of various failure loads and associated modes of failure supported by an extensive number of test results from other sources. Moreover, brief theoretical parametric studies for other first order composite beam design parameters have also been carried out in order to clarify the effects of variations in such parameters on the predicted modes of failure. It has been shown (both, theoretically and by using large scale experimental data) that the load bearing capacity for a plated beam could (under certain circumstances) be significantly lower than even that for the corresponding unplated beam with the mode of failure being of an undesirable brittle nature. Such brittle failures can obviously have serious implications in practice, where this method has been used extensively for upgrading both bridges and buildings in a number of countries, with the design calculations very often not having properly accounted for the possible occurrence of premature plate peeling phenomenon, especially when FRP plates have been used. Further work in this area included a quantitative theoretical insight into the effect of pre-cracking of the beams (under service conditions) on the ultimate plate peeling load. A critical quantitative examination of a number of previously available theoretical models, as proposed by others, has also been carried out, and some of these models for predicting the plate peeling failure of R. C. beams have been shown to suffer from rather serious shortcomings.

The use of fiber-reinforced polymer (FRP) composites as a repair and strengthening material for reinforced concrete (RC) members has increased over the past twenty years. The tendency for FRP sheets to debond at loads below their ultimate capacity has prompted researchers to investigate various approaches and designs to increase the efficiency of FRP strengthening systems. Various anchors, wrapping techniques and clamps have been explored to postpone and/or delay the debonding process which results in premature failure. FRP anchors are of particular interest because they can be selected to have the same material properties as the FRP sheets that are installed for strengthening or repair of the RC member and can be done so using the same adhesives and installation techniques. This research study aimed to investigate the effectiveness of using commercially manufactured FRP anchors to secure FRP sheets installed to strengthen and repair RC beams in shear and RC slabs in flexure. Twenty one shear critical RC beams were strengthened in shear with u-wrapped FRP sheets and FRP anchors. Eight RC one-way slabs were strengthened in flexure with FRP sheets and FRP anchors. The test variables include the type of FRP sheets (GFRP,CFRP), type of FRP anchors (CFRP, GFRP) and the strengthening configuration. The test results of the shear critical RC beams revealed that the installation of commercially manufactured FRP anchors to secure externally applied u-wrap FRP sheets improved the shear behaviour of the strengthened beam. The installation of FRP anchors to secure u-wrapped FRP sheets provided an average 15% increase in the shear strength over companion unanchored beams and improved the ductility of failure experienced with the typical shear failure in beams. The use of FRP anchors allowed the FRP sheets to develop their tensile capacity. Premature failure by FRP debonding was eradicated with the presence of FRP anchors and the failure modes of the strengthened beams with FRP anchors was altered when compared to the companion unanchored beam. Additionally, as the width of a u-wrapped FRP sheet was increased; larger increases in strength were obtained when FRP anchors were used. The test results of the flexure critical RC slabs revealed that the installation of commercially manufactured FRP anchors to secure externally applied u-wrapped FRP sheets improved the behaviour of strengthened slabs. Installation of FRP anchors to secure flexural FRP sheets provided an average 17% increase in strength over companion unanchored beams. The use of FRP anchors allowed the FRP sheets to develop their full tensile strength. Premature failure by CFRP debonding was not eliminated with the presence of FRP anchors; rather the critical failure zone was shifted from the bottom soffit of the slab to the concrete/steel rebar interface. The failure modes of slabs with FRP anchors were altered for all specimens when compared to the companion unanchored slab. The effective strain in the FRP sheet was predicted and compared with the experimental results. The efficiency of FRP anchors defined as the ratio of effective strain in the FRP sheet with and without anchors was related to the increase in strength in beams and slabs. A good correlation was established between the FRP anchor efficiency and the increase in strength. A step-by-step FRP anchor installation procedure was developed and a model to predict the number of FRP anchors required to secure a FRP sheet was proposed. This is the most comprehensive examination of beams and slabs strengthened with FRP sheets and FRP anchors conducted to date. This study provides an engineer with basic understanding of the mechanics, behaviour and failure modes of beams and slabs strengthened with FRP sheets and anchors.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 24, 2008) Includes bibliographical references.

Thesis (M.S.)--Ohio University, June, 2004. / Title from PDF t.p. Includes bibliographical references (leaves 95-96).

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 214-223) Also available in print.

Thesis (M.S.)--Ohio University, August, 1993. / Title from PDF t.p.