In the current mechanistic-empirical (M-E) design procedures for flexible pavements, the primary transfer functions are those that relate (a) maximum tensile strain in the hot-mix asphalt (HMA) surface layer to fatigue cracking and (b) compressive strain at the top of the subgrade layer to rutting at the surface. These functions, called fatigue and rutting equations, are usually derived from statistically based correlations of pavement condition with observed laboratory specimen performance, full-scale road test experiments or by both methods. Hot-mix asphalt fatigue behavior is an important component of a M-E design procedure; unfortunately, most of the existing models do not reflect field fatigue behavior. This is manifested in the fact that HMA fatigue failure is achieved much faster under a laboratory setting than in a field environment. This difference has been typically accounted for by the use of a single shift factor based mainly on engineering experience. The flexible pavement portion of the Virginia Smart Road includes 12 different flexible pavement designs. Each section is approximately 100m long. The sections are instrumented with pressure cells, strain gages, time-domain reflectometry probes, thermocouples, and frost probes. The instruments were embedded as layers were built. Laboratory fatigue tests of field cores and field-mixed laboratory-compacted specimens along with measured response from the instrumented pavement sections at the Virginia Smart Road were used to quantify the differences between laboratory and field environments. Four shift factors were identified to correlate field and lab fatigue behavior: stress-state, material difference, traffic wander, and healing. Field-measured critical strains and strain energy exerted during truck loading were both used to determine the stress state shift factor. Strain measurements of truck loading distribution (wander) were used to determine the wander shift factor. Finally, results from laboratory fatigue tests on cores and laboratory compacted specimens were used to evaluated a shift factor to account for the difference in compaction procedures. While the derived shift factors utilize the measured stresses and strains at the Virginia Smart Road, calculated strains and stresses, based on appropriate pavement and loading modeling, may also be used. / Ph. D.

We use molecular mechanics (MM) simulations with the tight-binding (TB) potential to study local and global instabilities in initially defect-free finite specimens of gold crystals deformed in shear, simple shear, tension/compression, simple tension/compression, and triaxial tension/compression. The criteria used to delineate local instabilities in a system include the following: (i) a second order spatial derivative of the displacement field having large values relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the potential energy of an atom becoming nonpositive, (iii) and structural changes represented by a high value of the common neighborhood parameter. A specimen becomes globally unstable when its potential energy decreases significantly with a small increase in its deformations. It is found that the three criteria for local instability are satisfied essentially simultaneously at the same atomic position. Deformations of a specimen are quite different when it is deformed with some bounding surfaces free from external forces as opposed to essential boundary conditions prescribed on all bounding surfaces. It is found that the initial unloaded configuration (or the reference configuration) of the minimum potential energy has significant in-plane stresses on the bounding surfaces and nonzero normal stresses at interior points. In tensile/compressive deformations of a rectangular prismatic nanobar the yield stress defined as the average axial stress when the average axial stress vs. the average axial strain curve exhibits a sharp discontinuity depends upon the specimen size; a similar result holds for simulations of shear deformations. Specimens deformed with essential boundary conditions on all bounding surfaces experience instabilities at a higher value of the average strain than identical specimens deformed similarly but with one or more pairs of opposite bounding surfaces traction free. For the former set of deformations, the response of a specimen prior to the onset of instability is the same as that of a hyperelastic body with the strain energy derived from the TB potential and deformations obeying the Cauchy-Born rule. Specimens with some traction free bounding surfaces experience local instabilities prior to the onset of a global instability but the two instabilities occur simultaneously in specimens with essential boundary conditions prescribed on all bounding surfaces. It is believed that because of residual stresses in the reference configuration, the average axial stress at yield in compression is nearly one-half of that in tension. / Ph. D.

Monolitinio pastato įrąžoms skaičiuoti, projektuotojas kurdamas pastato skaičiuotinį modelį, jį traktuoja kaip ,,akimirksniu“ pastatytą. Pastato statybos metu nuolatinė apkrova nuo perdangų savojo svorio, auga palaipsniui, betonuojant aukštą po aukšto, kol galiausiai, užbetonuojamas paskutinis aukštas. Darbe pasiūlytas ir skaitiškai realizuotas modelis, įvertinantis betono ir armatūros įtempių bei deformacijų kitimo istoriją dėl laike palaipsniui augančios apkrovos nuo perdangų savojo svorio. Darbe taikomas superpozicijos principas betono valkšnumo deformacijoms, atsižvelgiant į Volterra lygtį. Pasiūlyta matematinė formuluotė pagrįsta matriciniu skaičiavimu ir apibendrintąja funkcijos vidurkio teorema taikant betono valkšnumui. Skaitiniu būdu gauti rezultatai patikrinti analitiškai. Modelis pritaikytas daugiaaukščio pastato papildomų šlyties jėgų perdangose, atsirandančių dėl gretimų kolonų skirtingų poslinkių vystymosi per laiką radimui. Gauti rezultatai patikrinti su apytikslio skaičiavimo rezultatais, taikant normų EC-2 reikalavimus betono valkšnumo deformacijoms. Perdangų praspaudimą kolona, kai pastarosios yra greta pastato standumo branduolių, kurių deformatyvumas yra ženkliai mažesnis, reiktų tikrinti atsižvelgiant į papildomas šlyties jėgas, atsirandančias dėl betono susitraukimo ir valkšnumo įtakos. Darbo apimtis – 99 p. teksto, 54 iliustr., 12 lent. ir 9 literatūros šaltiniai. Atskirai pridedami priedai. / The designer calculates a building as an instantly built. However, during construction the permanent load is increasing gradually because the floors are built step by step. This paper introduces a numerically implemented mathematical model for the column analysis accounting for the stress and strain change in reinforcement and concrete with time due to the increasing in time permanent loads induced by the self-weight of each slab during construction. The mathematical formulation is based on the superposition principle for the creep strain described by Volterra's integro-differential equation and involves a matrix solution of linear equations derived via application of the generalized mean theorem for integration. The results obtained are also verified analytically. Finally, the proposed model is applied to calculate extra shear forces caused by the deflections appearing to the adjacent columns of different cross-sections. The results obtained are also compared with the approximate calculation treating the building as an instantly built. The results indicate that additional shear forces due to different displacements of the adjacent columns are quite mild. However, the additional shear forces can be sufficiently high, if the column is located near the high stiffness walls in a non-sway building. In this case, the extra shear forces should be determined via time-dependent analysis accounting on the creep and shrinkage strains relying on the gradually increasing load during... [to full text]

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This thesis apply High Resolution Electron Back Scatter Diffraction (HR-EBSD) technique to a variety of microstructure features and their interactions in pure h.c.p polycrystals. By correlating high quality Kikuchi patterns with a reference pattern, the relative state and distribution of strain, stress, and geometrically necessary dislocation (GND) density can be obtained with high strain sensitivity (10^-4) and angular resolution (10<sup-4</sup> radian). This technique is companied by a further investigation of subsurface features using Differential Aperture X-ray Micro-diffraction (DAXM) technique. The two technique have shown excellent agreement in capturing the magnitude and distribution of stress and GND. Stress field and GND distribution induced by slip band and grain boundary interactions, including blocked slip band with no observable slip transfer in SEM and slip transfer, were characterised. It was found that some blocked slip bands lead to high and localised stress concentration in the neighbouring grain while others did not, and no stress concentration were correlated with transferred slip bands. These three categories of interactions were rationalised using a slip transfer criteria (called LRB criteria) by investigating the geometric alignments between the impinging slip system and all possible slip systems in the neighbouring grain. The level of stress concentration were quantified into a stress intensity factor K, following the Frank, Eshelby, and Nabarro (FEN) model. It was found that the level of stress intensity correlates well with the number of dislocations within the pile up plane. The slip band and grain boundary interaction case that led to the highest magnitude of stress intensity factor was further investigated using DAXM experiments. The 3D data set informed us additional information hidden below the sample surface. The distribution of stress concentration in 3D is a ribbon conforming to the line of intersection between slip plane and grain boundary. Stress intensity factor calculation along this ribbon have shown large variations which led to a concern that sometimes 2D results might not be conclusive. For example, if damage is observed in sample surface, there is a possibility that large populations of damage already exist below sample surface as a result of the stress fluctuations. The level of stress concentration and distribution measured by both HR-EBSD and DAXM agree with each other and 3D lattice rotation gradient used in DAXM GND calculation was found to affect the range of GND distribution and how fast it decays away from grain boundary. Twinning is a deformation mechanism in HCP metal that is equally important as dislocation slip. The stress concentrations associated with twin propagation, approaching grain boundary, and thickening were characterised using HR-EBSD, from which the calculated stress tensor were used to generate a local Schmid factor (LSF) map. It was found that during twin propagation, local positive shear provides a favourable LSF condition that promote twin tip extension while supress it from thicken. When twin tip is approaching the grain boundary, the positive shear stress field no longer favour twin propagation, a narrow positive LSF field still exist at the tip of twin, promoting it to grow thick. During propagation and thickening process, the LSF seem to only affect the tip of twins and therefore these processes are possibly tip controlled.

In recent years, the interest in mental strain has increased, mainly due to the increasing demands of the individual professions. The consequences of mental strain can also influence private life, so it is important to solve such situation. The diploma thesis deals with the psychological burden of the employees in a private company that produces CNC machine parts. The aim was to find out what the level of mental strain on all employees of the company is, using the method of quantitative and qualitative research. Three research questions have been identified. I have examined whether the demographic factors of the worker, the physical factors in the working environment and the way of rest after work affect the psychological burden. The investigation was carried out using three hypotheses. I assumed that a significant level of psychological burden would be present in relation to the age and that it would also vary by gender. I also expected that the differences in the level of psychological burden would be present depending on the length of the years worked in the company. A qualitative survey was conducted using sixteen open questions in a semi-structured interview. The results were divided into eleven categories and there was a mind map created for each of them. For better understanding of the mind maps, the data was extended by quantitative questionnaire research, which was implemented using standardized CBI questionnaires (Copenhagen Burnout Inventory) and the Meister questionnaire. Questionnaire survey was carried out at each workplace of the surveyed company. The data were processed statistically and graphically. Mixed research has not shown a significant level of mental strain on company employees. When compared the ratio of mental strain in relation to gender, it has shown that the strain on both men and women is the same. The length of employment in the company has not reflected into increased rates of mental strain.

<p>In the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry, bonding and joining play an important role in the manufacturing and assembly process, which is critical to the cost, safety, reliability, and design freedom of systems. The goal of this thesis is to understand and evaluate the usage of adhesive bonds in the manufacture of HVAC&R systems, specifically in regards to leakage/reliability characterization and stress analysis under loading.</p> <p>The bonding performance under static loading is first studied using a commercial epoxy adhesive product. In addition to the traditional surface preparation methods of mechanical and chemical etching, a novel laser-interference surface structuring preparation technique was utilized to improve bonding performance. Laser interference structuring uses a ND:YAG laser beam that is split into two beams that are re-directed to overlap on the same area of a copper alloy. A structuring pattern near the interference structuring limits is achieved due to the phase shift between the beams that is imparted as they are re-directed. Two different laser structuring methods were tested: spot-by-spot and laser raster. Different structuring parameters were varied including the laser spot size and pulses per spot (2, 4, 6, 8, 10, 12 pulses/spot) for the spot-by-spot method, and raster speed (2, 4, 6, 8, 10, 12 mm/s) for laser raster method. The microstructure morphology and surface profile after processing were characterized using the scanning electron microscopy (SEM) and profilometry for all surfaces. It was found that the laser-interference structuring removed the surface contaminants efficiently and formed dot- or net-shaped structures on the surface. This indicates that melting, vaporization, and solidification of the metal happened differently. Due to the much higher speed of the laser raster method, considering practical industrial applications, it is selected for additional investigation for shear strength improvement. The shear strength is measured by a single lap shear test which pulls apart adhesively bonded single lap joint specimen under shear loading using a mechanical tester.</p> <p>Based on the surface profiles, three different laser raster speeds of 2 mm/s, 6 mm/s and 12 mm/s were selected for the manufacture of single lap joint specimens for comparison with the traditional surface preparation methods. The shear lap strength and displacement at maximum load were obtained for the specimens. The laser raster at 6 mm/s increased these values by approximately 11.0% and 25.1%, respectively, while the 12 mm/s condition had an increase of 16.8% and 43.8%, compared with the baseline traditional surface preparation method. It is concluded that laser structuring can enhance the single lap shear joint bonding performance. Within the tested laser processing parameters, a higher laser raster speed results in a larger enhancement. </p> <p>In addition to the static loading test with epoxy adhesive, different adhesive formulations are investigated and developed by the collaborating adhesive manufacturer to determine their suitability for use under the temperature and pressure conditions in HVAC&R systems. Reliability, especially fatigue failure, is another major concern because the strength of the adhesive joints is sufficient for HVAC&R applications. Two primary types of fatigue may happen in practical applications: thermal fatigue and vibration fatigue. Two test facilities were designed and built to test the adhesive performance and understand the failure mechanisms. For the thermal fatigue testing, a novel pressure and temperature cyclic (PTC) test stand was designed to simulate the pressure and temperature changes that may occur in HVAC&R systems. The test stand was designed to switch between hot high-pressure gas and cold low-pressure gas by using a compressor with hot gas bypass setup. For the vibration testing, a standard industrial shaker was used to provide the required vibration at a given displacement and frequency with a specially designed fixture for the tested joints. In both tests, adhesive joints were tested in parallel with brazed joints, undergoing extreme thermal and vibration loading conditions. All the samples were leak-checked before and after the testing, which were found to be leak-free after the testing, indicating that they pass the required qualification test according to available standards. It is confirmed that adhesive joints can be a potential alternative when dealing with thermal and vibration fatigue in the common working conditions of HVAC&R systems.</p> <p>The qualification testing is specific to the required loading conditions, such as pressure and temperature variations, and limited to certain tube sizes. An analytical model is developed to allow for design and evaluation across various operating conditions. The model aims to predict the adhesive stress and strain fields of in tube-to-tube joints based on the geometric parameters, material properties, and the loading conditions. In particular, the model uniquely considers the influence of thermal expansion and contraction in the joint, which is necessary for the periodically changing temperatures in HVAC&R systems. It is numerically solved using Mathematica and validated against the published data in the literature. The exact same solutions are achieved using the reported data in the literature, under simplified conditions without any temperature change involved. The validated model is then used in parametric studies to investigate the influence of geometric sizes and temperature change. Several conclusions are made about the trend of stress changes as well as the maximum stress, which provide insight from a perspective of general design guidance. Adhesive bonding length should be selected such that the maximum stress is smaller than the allowed material strength for both normal and shear stress. Adhesive thickness has less impact in the parametric range considered and is nevertheless usually dictated by the manufacture recommendation in view of other practical considerations. In regard to the thermal stresses, it is found that in practical HVAC&R working environment, the temperature-induced thermal stress dominates the stress fields and leads to significant change in the stress distribution across the adhesive layer. If a temperature change is present, the combination of all possible loading and temperature change should be analyzed to find the most extreme loading condition. This work demonstrates the first stress and strain analysis of tube-to-tube adhesive joints considering the working conditions of HVAC&R applications involving temperature cycling. All of these results provide a detailed guidance for use of adhesive joints across different application or locations in HVAC&R systems. The model can be also used as a framework to evaluate and compare the performance of different adhesives, as long as the adhesive properties are available.</p> <p>Lastly, it is also essential to demonstrate the application of these joints in real HVAC&R systems. A proof-of-concept test was done to demonstrate that the use of adhesive joints in a real system would cause no change in operation or leakage. A commercial heat pump dryer system was used to perform the testing at the Ray W. Herrick Laboratories. Two adhesive joints were installed to replace the brazing joints at the compressor inlet and outlet, where the most extreme temperature and pressure conditions are present. Results show that the system operates without any change in performance and experience no obvious leakage after more than 50 hours of testing over 6 months. </p> <p>This work explores the feasibility and reliability of adhesive bonding of copper for HVAC&R applications. The bonding strength of adhesive was studied and tested with both traditional surface preparation and advanced laser-interference structuring technique. The results show that for the tested structural epoxy adhesive, the bonding strength is large enough considering the internal pressure in the tube and the laser structure technique can increase the shear strength. </p> <p>The long-term reliability with respect to thermal, stress and vibration fatigue are then experimentally investigated and the adhesive joints pass the qualifications tests required by the standard. Further modeling work for predicting the stress distribution in adhesively bonded joints is developed to understand the influence on geometric parameters and temperature change. The adhesive length can influence the stress distribution significantly and temperature-induced stress dominates the stress distribution under the HVAC&R loading conditions. Further material characterization is needed for crack propagation or detailed fatigue analysis, which is highly dependent on the adhesive formula, working environment and loading conditions, which can be performed with a more specific targeted application. The experimental and modeling work in this thesis provides a foundation for adhesives to be applied in HVAC&R applications and a framework to further develop, optimize, and utilize adhesive joining in HVAC&R applications. </p>

This master thesis analyses stress and strain of iliac artery with atheroma. Model of artery is created as 2D and symmetric about the y-axis. The first part of the thesis deals with a research, which includes obtaining information from medicine, which is necessary fort the right solution of the task. Next part dedicates to nonlinear mechanics, constitutive modeling from the view of biomechanice and computational modeling of arteries. In the next part is made analysis for load on artery by physiological and also by high blood pressure. In the end were specified uncertainties of the used model and evaluated chance of atherosclerotic plaque rupture.

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