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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Evaluation of SCPT-surveys as method for accessing dynamic modulus

Granskär, Joakim January 2018 (has links)
The purpose of this master thesis is to evaluate the results from the completed SCPT (Seismic Cone Penetration Test) surveys with respect to the methods ability to estimate dynamic young´s modulus. This has been done by comparing the result from SCPT to other seismic methods and dynamic parameters converted from “static” geotechnical surveys. SCPT is a relatively new method which has not been used by Sweco or in Sweden to any greater extent and is therefore of interest to be looked in to. By adding two geophones to an ordinary CPT (Cone Penetration Test) equipment as well as including strike plates, hammer and logger system one can log dynamic parameters in addition to the regular parameters logged by a CPT system. This is done by stopping the otherwise continuous CPT survey every meter and striking the strike plates, which are placed under the tracks of the drilling rig. Seismic waves will then travel through the soil down to the geophones and be used to calculate dynamic parameters. For this master thesis a total of 47 geotechnical and geophysical surveys have been considered. The location of these 47 are approximately 7 km north of Norrköping and have been conducted between the years 2016-2017 for the East Link Project. The geotechnical surveys are composed of weight-sounding, ram-sounding and CPT while the geophysical ones are SCPT, refraction-survey and MASW (Multichannel Analysis of Surface Waves). Static elastic parameters have been calculated using the geotechnical survey results according to the Swedish transportation administrations standardized methods. These have then been converted to dynamic parameters with the help of different relationships. When these have been converted they can be compared to SCPT results and other seismic survey methods which also use wave velocity, Poisson’s ratio and density to calculate dynamic elastic parameters. Based on the results from this thesis it can be concluded that the seismic test add-on to a standard CPTu survey is a good method for accessing dynamic modules and it gives extended information of the soil stratigraphy from one single survey point. After the studies and analyses conducted for this thesis it can be concluded that the proposed conversion between static and dynamic young’s modulus using the Alpan curve gives slightly higher values than the ones derived directly from shear waves using SCPT. The other conversion using cone tip resistance to shear wave velocity gives on the other hand slightly lower values than the ones measured with the SCPT. The analysis also indicate similar trends in results between the different seismic methods. These results does however also shows that the used assumptions are somewhat general for accurate comparisons between the methods.
82

Adhesion Comparison of Low Dielectric Constant Thin Films Using Four Point Bend and Nanoscratch Testing

Vilceus, Daniel 29 May 2008 (has links)
As the semiconductor technology moves further into scaled down device structures, modern day complexities in the fabrication processes become more prevalent. This thesis focuses on the issues associated with mechaincal and adhesion failure in low dielectric constant (low-k) thin films. In this thesis the four point bend test and nanoscratch test method was used for evaluating adhesion of boro-phosphate-silicate glass (BPSG) and tetraethylorthosilicate (TEOS) low-k thin films to silicon subtrates. Nanoindation tests were also performed on the low-k films to evaluate material properties such as hardness and elastic modulus. The sample preparation and testing set up for the four point bend test and nanoscratch test were observed to be greatly disparate. Nanoscratch and nanoindentation sample preparation and sample testing were able to be carried out much quicker than in four point bending. It was observed that nanoscratch testing holds an immense potential for reducing the time needed to evaluate thin film adhesion then in FPB testing. Nanoindentation performed on the BPSG and TEOS dielectric thin films showed uniform mechinacal properties throughout the surface of the films. The adhesion energy for BPSG and TEOS using FPB testing ranged from 29.5390 J/m² - 3.0379 J/m². While the adhesion energy for BPSG and TEOS using nanoscratch testing ranged from 0.0012 J/m² - 0.0028 J/m². It was observed that the difference in adhesion energy for FPB and nanoscratch testing was due to differing failures modes.
83

Stiffness Reduction of Steel W-Shapes: Comparison Between the Modified Tangent Modulus and a New Inelastic Material Model

Unknown Date (has links)
This research focused on demonstrating the effectiveness of a new inelastic material model, τBTR, and was compared with an existing modified tangent modulus model, τTM, at matching the limit load response of detailed finite element models of steel frames. The influence of stiffness reduction was studied on seven W8x31 columns and eleven benchmark frames. The column study considered minor axis bending with L/r ratios of 40, 60, 80, 100, 120, 180, and 200. Limit load analyses were conducted on steel frames with major-axis and minor-axis bending. The extent of yielding and lateral displacements were evaluated for all benchmark frames at the collapse condition. Discussion is given regarding the two material models and their ability to match the limit load responses of the finite element models. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection
84

Comprehensive evaluation of four warm asphalt mixture regarding viscosity, tensile strength, moisture sensitivity, dynamic modulus and flow number

Sampath, Anand 01 May 2010 (has links)
Hot Mix Asphalt (HMA) has been used over the years for laying roads. It required the aggregate and the binder to be heated to temperatures above 160°C (320°F). Heating the aggregate and binder in large quantities consumed a lot of fuel. This called for alternative solutions in the technology of laying roads. This brought about a new technology called Warm Mix Asphalt (WMA). WMA is an emerging technology that can allow asphalt to be produced and compacted at a significantly lower temperature. In the past, a number of researchers evaluated various WMA mixtures using selected testing procedures in the laboratory. However, none of them evaluated all the major WMA products and compared them with WMA mixtures without an additive using a comprehensive set of testing protocols. This paper presents a comprehensive evaluation result of three major WMA additives (Sasobit®, Evotherm J1 and RedisetTM) regarding their viscosity, tensile strength, moisture sensitivity, dynamic modulus and flow number. These three additives were chosen since all of them are prepared from a base wax product. The asphalt showed a decreasing trend in viscosity with increase in the concentration of the additives. The WMA specimen with additives exhibits similar air voids as control WMA specimens which indicate these WMA additives are effective in compacting asphalt mixtures at low temperatures. The Indirect Tensile Strengths (ITS) and Tensile Strength Ratio (TSR) values of the WMA specimen with admixtures were found to be higher than the control WMA specimens. This result indicates that the admixtures play a significant role in enhancing the properties of WMA. WMA mixtures with additives exhibited higher dynamic modulus than the control WMA at all temperatures. All the specimens passed the requirement of 10,000 cycles of repeated loading. The WMA specimen with Sasobit® additive exhibited the lowest permanent deformation. Based on overall test results it can be concluded that Sasobit®, Evotherm J1 and RedisetTM WMA additives are effective in producing WMA mixtures in the laboratory which have high strengths.
85

Micro-mechanical predictive modelling as an aid to CAD based analysis of composite sporting equipment

Paul Ewart, D. January 2008 (has links)
The sport and leisure industry in New Zealand (NZ) has the potential to become a major user of composite materials. Given the size of NZ industry, design and manufacturing strategies based on virtual engineering should be developed to suit NZ requirements. Virtual methods use computer aided engineering capabilities to find faults, explore alternatives and optimise product performance before detailed design or prototyping. When doing computer aided simulation the required mechanical properties of individual reinforcement and matrix components are well documented. However, the mechanical properties of composite materials are not as simple to obtain. Micro-mechanical modelling could therefore be used to aid the design and development of composite equipment, where mechanical properties are unknown. In this study, solids modelling was used to produce an analog model of a composite, and it was found that it lead to reductions in file size and simulation time. Representing a composite with an analog model implies that the behavioural characteristics are modelled, but not the physical characteristics of the individual components. Three micro-mechanical models were developed to predict the flexural modulus of composite materials, based on perfect, partial and no adhesion. It was found that the partial adhesion model was both practical and consistently accurate. The partial adhesion model accounted for adhesion between components by considering an 'effective shear value' at the interface. Validation of the models was done by flexural testing injection moulded samples of glass, wood and carbon fibre reinforced polyethylene. It was shown that the adhesion coefficient range was 0.1 for carbon fibre, 0.5 for glass fibre and 0.9 for the wood fibre composites. It was concluded that the adhesion coefficient is crucial and it is recommended that further work is done to validate effective shear values by empirical means. The predicted flexural modulus values were used to enable finite element simulation of modelled analog beams as well as commercial kayak paddles. It was determined that accurate simulation is possible for composite equipment using the partial adhesion model.
86

The effect of the duration and amplitude of spinal manipulation therapy on the spinal stiffness of a feline model

Vaillant, Michele 11 1900 (has links)
Introduction: The purpose of this study was to determine the effect of spinal manipulation therapy (SMT) duration and amplitude on spinal stiffness. Methods: Simulated SMTs were performed at the L6 spinous process in twenty-two felines. SMTs ranging from 25 to 250 ms duration were performed. Groups 1 and 2 received maximal displacements of 1.0mm to 3.0mm. Groups 3 and 4 received maximal loads of 25% to 85% body weight. Local stiffness was quantified by applying an indentation to the vertebra. Results: Repeated SMTs caused minimal changes in stiffness. The interaction effect of duration X displacement in Groups 1 and 2, and the effect of duration in Group 3 were significant. Conclusion: Repeated SMTs cause minimal changes in stiffness thought to be due to a viscoelastic response. Some of the changes following select SMT conditions may be the result of an interaction effect between SMT duration and amplitude. No specific threshold condition was identified as causing a greater stiffness change. / Physical Therapy
87

Resilient Modulus and Strength Index Properties of Stabilized Base for Tennessee Highways

MacDonald, Wesley M 01 May 2008 (has links)
Typical material used by the Tennessee Department of Transportation for highway bases was evaluated for application to the new Mechanistic-Empirical Pavement Design Guide. Two types of granular Tennessee highway base material were mixed with different stabilizers and tested in the lab according to AASHTO T-307 99 (2003). Unconfined Compressive Strength and California Bearing Ratio tests were also done in an effort to correlate these results with resilient modulus. Three different combinations of base and stabilizer were tested and modeling coefficients were produced. Base structural layer coefficients were generated and compared to coefficients currently in use by TDOT.
88

Use of a BCD for compaction control

Li, Yanfeng 01 November 2005 (has links)
Compaction of soil is essential in the construction of highways, airports, buildings, and bridges. Typically compaction is controlled by measuring the dry density and the water content of the compacted soil and checking that target values have been achieved. There is a current trend towards measuring the soil modulus instead or in addition to density. The reasons are that the density measurements are made using nuclear density meter, an undesirable tool in today??s political environment and that pavement design uses moduli as an input parameter. Although there are many apparatus available to measure soil modulus in the field such as Falling Weight Deflectometer, Dynamic Cone Penetrometer and Seismic Pavement Analyzer, a light weight and easy to use device which can measure the soil modulus fast and accurately is in great need. Briaud Compaction Device (BCD) is a portable device which can measure a soil modulus in several seconds. The principle of the BCD is to use the bending of a plate resting on the ground surface as an indicator of the modulus of the soil below. Numerical simulations show that within a certain range, the soil modulus is simply related to the plate bending. Strain gauges are glued on the top of the plate of BCD and a double half Wheatstone bridge is used to measure the strain. BCD tests were done in parallel with plate tests of the same size. A good correlation was found between the ratio of the plate pressure over the bending strain measured with a BCD and the reload soil modulus obtained from the plate test. This correlation can be incorporated into the BCD processor to display the soil modulus directly. To transit from dry density based compaction control to modulus based compaction control, BCD tests were also performed in the laboratory on top of a soil sample compacted inside the Proctor mold followed by plate tests. That way, a soil modulus versus water content curve is developed which parallels the approach for the dry density versus water content. The soil modulus versus water content curve can be used to provide the target values for compaction control in the field.
89

Effects of manufactured fine aggregate on physical and mechanistic properties of Saskatchewan asphalt concrete mixes

Anthony, Anna Maria 23 April 2007
Saskatchewan Highways and Transportation (SDHT) rely on dense-graded hot mix asphalt concrete mixes for construction and rehabilitation of asphalt pavement surfaced highways. As a result of increased commercial truck traffic on the provincial road network, over the last two decades, some of Saskatchewans recently placed dense graded hot mix asphalt concrete (HMAC) pavements have been observed to show a susceptibility to premature permanent deformation in the asphalt mix. One of the aggregate properties thought to have significant influence on mix performance under traffic loading is the shape of the aggregate. Specifically, the physical properties of the fine aggregate (smaller than 5 mm in diameter) are of particular importance in dense graded mixes. Although empirical evidence suggests that there are performance benefits associated with using angular fine aggregate, the relationship of this parameter on mechanistic mix performance and resistance to permanent deformation has not yet been clearly defined.<p>The primary objective of this research was to conduct laboratory analysis to determine the physical, empirical, and mechanistic behaviour sensitivity to the proportion of manufactured and natural fine aggregate in SDHT Type 72 hot mix asphalt concrete. The second objective of this research was to compare the mechanistic behaviour of the Type 72 mixes considered in this research to conventional SDHT Type 70 structural hot mix asphalt concrete.<p>Physical and mechanistic properties of a SDHT Type 72 mix at levels of 20, 40, and 60 percent manufactured fines as a portion of total fines (smaller than 5 mm), and for a SDHT Type 70 mix (which contained 38 percent manufactured fines) were evaluated. Ten repeat samples were compacted for each mix using 75-blow Marshall compaction, and ten samples for each mix were compacted using the Superpave gyratory compaction protocols. Marshall stability and flow testing was conducted on the Marshall-compacted samples. Triaxial frequency sweep testing was conducted on the gyratory-compacted samples using the Rapid Triaxial Tester (RaTT) at 20°C. The testing was conducted at axial loading frequencies of 10 and 0.5 Hz, and at deviatoric stress states of 370, 425, and 500 kPa, respectively. The resulting dynamic modulus, axial and radial microstrains, Poissons ratio, and phase angle were evaluated.<p>The research hypothesis stated that the increased amount of manufactured fines improves mechanistic properties of the Type 72 mix under typical field state conditions, and Type 72 mix with increased manufactured fines can exhibit mechanistic properties equivalent to or exceeding those of a typical type 70 mix. <p>Based on the improved densification properties, increased Marshall stability, increased dynamic modulus, and reduced radial and axial strains, it was demonstrated that increasing manufactured fines content in the SDHT Type 72 mix does improve the mechanistic properties of this dense-graded asphalt mix. It should be noted that there appears to be a minimum level of manufactured fines content that is required to affect mix response to loading, and that this threshold lies somewhere between 40 and 60 percent manufactured fines content for the Type 72 mix tested as part of this research.<p>Further, the Type 72 mix exhibited comparable or improved mechanistic properties relative to the Type 70 mix, which SDHT consider a structural mix. This is illustrated by the Type 72 mix with 60 percent manufactured fines resulting in higher Marshall stability and dynamic modulus, and lower axial microstrains than the Type 70 mix evaluated in this study.<p>It is recommended that other Type 72 and Type 70 mixes are evaluated using similar testing protocols. In addition, field test sections should be used to further verify the research hypothesis investigated here. <p>Economic analysis indicates that substantial savings in life cycle costs of SHDT asphalt concrete surfaced roadways can be realized by engineering well-performing, rut-resistant mixes. The life cycle costs can be reduced annually by approximately $7.4 million, which translates into $102.5 million savings over 18 years, during which the entire pavement network would be resurfaced with well-performing asphalt concrete mixes.<p>Further, enhanced crushing of smaller aggregate top size decreases the amount of rejected material, and increases manufactured fines to coarse aggregate ratio, resulting not only in better engineering properties, but also in the optimized use of the provinces diminishing gravel resources. Pressures on aggregate sources are also reduced by improving life cycle performance of Saskatchewan asphalt concrete pavements. The total potential aggregate savings that can be realized by implementing well-performing Type 72 HMAC mixes amount to 4.3 million metric tonnes of aggregate in the next 42 years. These aggregate savings can help decrease the predicted shortage of aggregate between 2007 and 2049 by approximately 6 percent. The total potential cost savings after 18 years of paving 500 km per year with rut-resistant, well-performing HMAC mixes amount to $112.4 million in present value dollars. The 42 year savings amount to $193.7 million in present day dollars. It is recommended that a more detailed economic analysis be carried out.
90

Recovery of the Shear Modulus and Residual Stress of Hyperelastic Soft Tissues by Inverse Spectral Techniques

Gou, Kun 1981- 14 March 2013 (has links)
Inverse spectral techniques are developed in this dissertation for recovering the shear modulus and residual stress of soft tissues. Shear modulus is one of several quantities for measuring the stiffness of a material, and hence estimating it accurately is an important factor in tissue characterization. Residual stress is a stress that can exist in a body in the absence of externally applied loads, and beneficial for biological growth and remodeling. It is a challenge to recover the two quantities in soft tissues both theoretically and experimentally. The current inverse spectral techniques recover the two unknowns invasively, and are theoretically based on a novel use of the intravascular ultrasound technology (IVUS) by obtaining several natural frequencies of the vessel wall material. As the IVUS is interrogating inside the artery, it produces small amplitude, high frequency time harmonic vibrations superimposed on the quasistatic deformation of the blood pressure pre-stressed and residually stressed artery. The arterial wall is idealized as a nonlinear isotropic cylindrical hyperelastic body for computational convenience. A boundary value problem is formulated for the response of the arterial wall within a specific class of quasistatic deformations reflexive of the response due to imposed blood pressures. Subsequently, a boundary value problem is developed from intravascular ultrasound interrogation generating small amplitude, high frequency time harmonic vibrations superimposed on the quasistatic finite deformations via an asymptotic construction of the solutions. This leads to a system of second order ordinary Sturm-Liouville problems (SLP) with the natural eigenfrequencies from IVUS implementation as eigenvalues of the SLP. They are then employed to reconstruct the shear modulus and residual stress in a nonlinear approach by inverse spectral techniques. The shear modulus is recovered by a multidimensional secant method (MSM). The MSM avoids computing the Jacobian matrix of the equations and is shown to be convenient for manipulation. Residual stress is recovered via an optimization approach (OA) instead of the traditional equation-solving method. The OA increases the robustness of the algorithms by overdetermination of the problem, and comprehensive tests are performed to guarantee the accuracy of the solution. Numerical examples are displayed to show the viability of these techniques.

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