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Layne, Christina Mann. "The Relationship of Occupational Stress, Psychological Strain, and Coping Resources to the Turnover Intentions of Rehabilitation Counselors." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/29374.
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The Occupational Stress Inventory Revised Edition (OSI-R) and an Individual Data Form were used to determine the turnover intentions of rehabilitation counselors based on an interactive model of stress, strain, and coping. Occupational stress, strain, coping resources, and turnover intentions were examined in relationship with various demographic variables collected from a national sample of 982 members of the American Rehabilitation Counselors Association (ARCA). Demographic variables included age, gender, ethnicity, certification status as a Certified Rehabilitation Counselor (CRC), years of experience, practice setting, the number of clients on a counselor's caseload, and the amount of hours worked per week.
Data were collected through a mail survey, with a response rate of 67% (N = 657). However, of those respondents only 22% (N=145) had complete data and met the inclusion criteria. Inclusion criterion consisted of considering oneself to be employed full-time as a practicing rehabilitation counselor. Based on the usable data (N=145), respondents were on average 44 years old and Caucasian, with 63% being female. Over half of the respondents were certified as rehabilitation counselors, with an average number of nine years of certification. The average number of years of experience as a rehabilitation counselor was approximately ten and respondents worked an average of 45 hours per week with an average caseload size of 88 clients.
Path analysis was used to analyze causal relationships among turnover related variables. The hypothesized model included age, experience, number of clients on a caseload, occupational stress, strain, coping resources, and turnover intention. The tested model explained 37.5% of the variance in turnover intentions. The results suggest that the turnover intentions of rehabilitation counselors is meaningfully accounted for by variables contained in the model. Occupational stress produced the largest significant effect (B=.404) and had the most influence on turnover intentions. This indicates that it is occupational stress inherent in the job functions of rehabilitation counselors, and not individual coping resources or demographic variables that account for turnover in the field of rehabilitation. Therefore rehabilitation agencies should examine the roles that they place rehabilitation counselors in versus the individual characteristics of rehabilitation counselors in order to reduce turnover in the field.Ph. D.
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Elitharp, Toni. "The Relationship of Occupational Stress, Psychological Strain, Satisfaction with Job, Commitment to the Profession, Age, and Resilience to the Turnover Intentions of Special Education Teachers." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29578.
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This paper presents findings from a study of factors that lead to special education teacher attrition and retention involving 212 special educators in the Commonwealth of Virginia. Structural equation modeling was used to test a hypothesized model of the relationship between Teacher/Administrative Support, Role Dissonance, Psychological Strain, Satisfaction with Job, Commitment to the Profession, Age, and Psychological Resilience to determine which variables directly and indirectly affect the turnover intentions of special education teachers. Structural equation modeling identified a path model wherein nine variables had a statistically significant influence on special education teacher turnover intentions. This paper reports on significant findings that emphasize for the first time the role of psychological resilience in the study of special education teacher retention. In addition, the confirmed path model suggests that one's perception of the effects of adversity due to physical or sexual abuse and adversity due to family loss play some role related to resilience. As the perception of Psychological Resilience increases, Commitment to the Profession increases, and the Intent to Leave the field of special education decreases.Ph. D.
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Chivante, Maurício Roberto de Pinho. "Avaliação experimental das relações tensão-deformação de um tecido de fibra de vidro recoberto com PTFE." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-18122009-134136/.
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Com o crescente uso de estruturas de membrana tensionada, as relações tensãodeformação do tecido utilizado em sua fabricação devem ser bem entendidas. Deste modo, esta dissertação apresenta um estudo sobre o comportamento mecânico de um tecido arquitetônico PTFE-vidro, ressaltando seu complexo mecanismo de deformação que engloba efeitos de anisotropia, não-linearidade física, troca de ondulações, histerese, remoção do espaçamento entre os fios e variação de temperatura. Diferentes métodos para modelagem do material foram estudados, com ênfase no modelo de material ortótropo representado por um funcional energia de deformação hiperelástico. Além disso, vários protocolos para ensaios de tração em tecidos recobertos foram analisados e uma série de ensaios biaxiais com amostras cruciformes foram realizados no Centro de Pesquisa e Desenvolvimento da Birdair, Inc. Um determinado funcional energia de deformação foi então ajustado aos dados de campo obtidos nestes testes, cujos resultados foram então comparados diretamente aos dados obtidos em campo e a um ajuste direto de uma superfície suave tensão-deformação. A performance do modelo ajustado não se encontra ainda em um patamar de aplicação industrial, entretanto este estudo permite um entendimento global dos mecanismos de deformação do tecido PTFEvidro, fornecendo também uma massa de dados consistentes que podem ser utilizados em situações práticas.Considering the growing use of tensioned membrane structures, the stress-strain relation of the fabric used on its construction must be well understood. This dissertation presents a study of the mechanical behavior of a PTFE coated fiberglass fabric, emphasizing its complex strain mechanism which is influenced by the material anisotropy, physical non-linearity, crimp interchange, hysteresis, removal of yarn spacing and changes in temperature. Different material models were studied, focusing on an orthotropic material model represented by a hyperelastic strain energy function. Also, different test protocols were reviewed and a series of biaxial tests on cruciform samples were performed at the Birdair, Inc.s Research and Development Center. A strain energy function was adjusted to the collected data and than its results compared to the data itself and to another stress-strain function directly adjusted to the data. The performance of the strain-energy function chosen is not on a level of industrial application; however this study gives a global understanding of the PTFE coated fiberglass strain mechanism and also provides a consistent database that may be used on real situations.
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Jesse, Dirk, and Frank Jesse. "Tragverhalten von Textilbeton unter zweiaxialer Zugbeanspruchung." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244044565376-12043.
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Das Tragverhalten von Textilbeton ist stark nicht-linear und der Verlauf der Spannungs-Dehnungs-Beziehung hängt von zahlreichen Parametern ab. Unter einaxialer Zugbelastung existieren bereits umfangreiche experimentelle Untersuchungen und theoretische Modelle zur Beschreibung des Tragverhaltens. In vielen Anwendungen, z. B. bei Querkraft- und Torsionsbeanspruchung, sind die Beanspruchungen jedoch nicht einaxial und/oder nicht axial zur Bewehrungsrichtung, und es kommt zu Interaktionen der beiden Bewehrungshauptrichtungen, primär infolge des Einflusses zweier Risssysteme in den beiden Hauptrichtungen. Das Tragverhalten textiler AR-Glas- und Carbonbewehrungen unter zweiaxialen Zugbeanspruchungen wurde experimentell untersucht, um diese Einflüsse qualitativ und quantitativ beschreiben zu können. In diesem Beitrag werden erste Ergebnisse vorgestellt.
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Tyler, Carmen M. "How the Illness Experience Predicts Key Psychosocial Outcomes in Veterans with Brain Injury." Cleveland State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=csu1494576111782556.
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Cox, Brennan Daniel. "Individual differences in the stressor-strain relationship the role of ability-based emotional intelligence /." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Theses/COX_BRENNAN_30.pdf.
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Lubonovich, Phoebe. "The Relationship Between Exercise Stage of Change and Job Strain Variables." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1087837290.
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Weyers, Megan. "Optimised mix composition and structural behaviour of Ultra-High-Performance Fibre Reinforced Concrete." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/73097.
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The overall objective of this study was to develop an optimised Ultra-High-Performance Concrete (UHPC) matrix based on the modified Andreasen and Andersen optimum particle packing model by using available South African materials. The focus of this study was to determine the optimum combined fibre and superplasticiser content for UHPC by using a response surface design.
The UHPC was appropriately designed, produced and tested. Various changes in mechanical properties resulting from different combinations of steel fibre and superplasticiser contents was investigated. The flowability, density and mechanical properties of the designed UHPC were measured and analysed. Both the fibre and superplasticiser content play a significant role in the flowability of the fresh concrete. The addition of fibres significantly improved the strength of the concrete. The results show that the superplasticiser content can be increased if a more workable mix is required without decreasing the strength significantly. The statistical analysis of the response surface methodology confirms that the designed models can be used to navigate the design space defined by the Central Composite Design. The optimum combined fibre and superplasticiser content depend on the required mechanical properties and cost. Using the modified Andreasen and Andersen particle packing model and surface response design methodology, it is possible to efficiently produce a dense Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) with a relatively low binder amount, low fibre content and good workability.
The effect of heat curing on the mechanical properties was investigated. It was concluded that heat curing is not recommended when considering the long-term strength development. The estimated strength development of concrete obtained by using the fib Model Code 2010 (2013) does not incorporate the detrimental effect of high curing temperatures on long-term strength and therefore overestimate the long-term strengths. The strength estimates for both early and long-term ages can be improved by considering this effect in the strength development functions obtained from fib Model Code 2010 (2013).
The effect of specimen size on the compressive and flexural tensile strength of UHPFRC members were established. It was found that the specimen size has a significant effect on the measured cube compressive strength. Smaller beam specimens showed higher ductility compared to those of the larger beam specimens. The crack width decreased as the beam’s depth decreased. A lower variability was experienced in the beams with limited depth (< 45 mm). Further testing is required to determine whether a span-to-depth ratio of 10 would yield optimum results.
The utilisation of by-products, such as undensified silica fume and fly ash, as cement replacement materials makes UHPFRC sustainable, leading to a reduced life-cycle cost. The calculated Embodied Energy per unit strength (EE/unit strength) and Embodied Carbon per unit strength (EC/unit strength) values for the UHPFRC mixture yield lower values compared to that of the 30 MPa concrete mixture, indicating that UHPFRC can be used to reduce the environmental footprint of the concrete industry.
The inverse analysis method used was successful in providing an improved simplified stress-strain response for the UHPFRC. The analysis provided valuable information into the stress-strain, load-deflection and moment-curvature responses of the UHPFRC. Standard material test results were used to theoretically calculate moment-curvature responses and were then compared to the experimental results obtained.
The study demonstrated that it is possible to efficiently produce a dense and workable UHPFRC with relatively low binder amount and low fibre content. This can result in more cost-effective UHPFRC, thus improving the practical application thereof.Dissertation (MEng)--University of Pretoria, 2020.
Civil Engineering
MEng (Structural engineering)
Unrestricted
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Harper, Christopher Scott. "Family-Supportive Supervisory Behaviors as a Moderator of the Relationship between Job Strain and Workers' Blood Pressure." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/198.
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Cardiovascular disease is one of the leading causes of death in industrialized nations. Research indicates that job strain may be significantly related to cardiovascular disease in employees with little to no social support. Using the JDC-S model developed by Karasek (1979) and elaborated upon by Johnson and Hall (1988), the family-supportive supervisory behaviors (FSSB) measure created by Hammer et al., (2009), and the blood pressure wrist monitor device Omron317T, this study examined FSSB as a moderator of the relationship between job strain, job demands, job control and workers' blood pressure on work and non-work days. Sixty-nine grocery store workers from a Midwest grocery store chain participated in this study, fifty-six of which were included in the analyses. Though none of the interactions were significant at the .05 level, results indicate that FSSB is significantly related to a number of blood pressure readings at the grand centered mean of job strain, job control, and job demands.
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Yakubu, Yakubu A. "The relationship between environmental health status, the attributes of female caregivers and the health status of care recipients in low-income areas in Cape Town, South Africa." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2885.
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Thesis (DPhil (Environmental Health))--Cape Peninsula University of Technology, 2016.Informal caregivers play an important role in the well-being of dependent members in a household. The burdens of these caregivers are multiple and pervasive and may contribute to mental health epidemiology as a result of worry, grief, anxiety and stress. The literature review revealed that studies in caregiving and its various facets began from a pragmatically applied interest rather than from theoretical and intellectual curiosity. The majority of the research on caregiver burden involves meta-analysis of qualitative studies with little quantitative research. Also, many of these studies are concentrated on caregivers of chronically ill patients, such as those suffering from dementia, Alzheimer’s disease, and heart disease, without much attention to care burden resulting from caring for those who are not necessarily ill. Similar studies by other researchers did not consider the impact of the physical health of the care recipients or the environmental factors that are critical in the study of female caregiver burden in low-income settings. In addition, existing studies did not adequately evaluate the many potential factors that may vary and influence the lives of the caregivers, especially in a single, comprehensive model. This study attempted to provide a more complete picture of these relationships in low-income and culturally diverse settings. The study population consisted of black/African and coloured populations living in subsidised or low-cost housing settlements. In each of the two different cultural communities, 100 black/African and 100 coloured female caregivers were selected through a systematic random sampling procedure. In addition, data were also collected from caregivers in Tamale, Ghana to assess differences between the socio-demographic profiles of the caregivers in Cape Town, South Africa and Tamale, Ghana. The theoretical paradigm used in this study is the Stress Process Model by Pearlin et al., (1990). The study instrument assessed caregiver burden with both objective and subjective measures through the use of a fully structured questionnaire. The information that was collected according to the constructs of the Stress Process Model included personal and role strains and incorporated the physical health of the care recipients and environmental factors such as kitchen and toilet hygiene. Inclusion criteria for the respondents in both Cape Town and Tamale were the principal female caregivers who were present, willing, and able to give informed consent. The Statistical Package for Social Sciences (SPSS Version 22) was used for the analyses. The Chi-square test was used to assess the relationships between environmental health, the socio-demographics of the female caregivers and the health status of the care recipients. The hierarchical regression analysis in the form of a General Linear Model was used to model caregiving burden. iv The results showed that the majority of the female caregivers were in the age group 40 – 49 years and in both Cape Town and Tamale, a large proportion was in the low-income group. Also, the majority of the informal caregivers in the two samples were in care tasks as a full-time job, providing more than 40 hours of care per week. Regarding the length of time in caregiving, a large proportion of the caregivers in both Cape Town and Tamale had been in the care role for more than three years preceding the survey, and almost all the caregivers in the Cape Town sample (98.4%) did not use any form of caregiving programme to ameliorate the negative effects of caregiving. Further, the results showed statistically significant relationships between the socio-demographic characteristics of female caregivers (age, education, population group and income status) and the diarrhoea status of the care recipients. Also, a significant relationship was shown between environmental health variables of the home (kitchen hygiene and toilet hygiene) and the physical health of the care recipients. The major predictors of female caregiver burden in the samples were the physical health of the care recipients and access to social grants. On the basis of the analyses, it was recommended that the government should recognise the importance of the physical health of the care recipients and increase the amounts of social grants to the caregivers since this could improve the circumstances of both the caregivers and the care recipients. In addition, this could aid in improving the standard of living of caregivers in these households. Future research in similar settings should disaggregate the data to compare the burden of caring for caregivers of physically strong care recipients with physically ill care recipients.
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Yao, Lan. "Experimental and numerical study of dynamic crack propagation in ice under impact loading." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI043/document.
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Les phénomènes liés au comportement à la rupture de la glace sous impact sont fréquents dans le génie civil, pour les structures offshore, et les processus de dégivrage. Pour réduire les dommages causés par l'impact de la glace et optimiser la conception des structures ou des machines, l'étude sur le comportement à la rupture dynamique de la glace sous impact est nécessaire. Ces travaux de thèse portent donc sur la propagation dynamique des fissures dans la glace sous impact. Une série d'expériences d'impact est réalisée avec un dispositif de barres de Hopkinson. La température est contrôlée par une chambre de refroidissement. Le processus dynamique de la rupture de la glace est enregistré avec une caméra à grande vitesse et ensuite analysé par des méthodes d'analyse d'images. La méthode des éléments finis étendus complète cette analyse pour évaluer la ténacité dynamique. Au premier abord, le comportement dynamique de la glace sous impact est étudié avec des échantillons cylindriques afin d'établir la relation contrainte-déformation dynamique qui sera utilisée dans les simulations numériques plus tard. Nous avons observé de multi-fissuration dans les expériences sur les échantillons cylindriques mais son étude est trop difficile à mener. Pour mieux comprendre la propagation des fissures dans la glace, des échantillons rectangulaires avec une pré-fissure sont employés. En ajustant la vitesse d'impact on aboutit à la rupture des spécimens avec une fissure principale à partir de la pré-fissure. L'histoire de la propagation de fissure et de sa vitesse sont évaluées par analyse d'images basée sur les niveaux de gris et par corrélation d'images. La vitesse de propagation de la fissure principale est identifiée dans la plage de 450 à 610 m/s ce qui confirme les résultats précédents. Elle varie légèrement au cours de la propagation, dans un premier temps elle augmente et se maintient constante ensuite et diminue à la fin. Les paramètres obtenus expérimentalement, tels que la vitesse d'impact et la vitesse de propagation de fissure, sont utilisés pour la simulation avec la méthode des éléments finis étendus. La ténacité d'initiation dynamique et la ténacité dynamique en propagation de fissure sont déterminées lorsque la simulation correspond aux expériences. Les résultats indiquent que la ténacité dynamique en propagation de fissure est linéaire vis à vis de la vitesse de propagation et semble indépendante de la température dans l'intervalle -15 à -1 degrésThe phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees
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DEY, SONAL. "ELASTICITY OF MAIN CHAIN LIQUID CRYSTAL ELASTOMERS AND ITS RELATIONSHIP TO LIQUID CRYSTAL MICROSTRUCTURE." Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1385403238.
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Liu, Shi-Bin, and 劉仕斌. "The Stress-Strain Relationship of silty sand under irregular." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/26491725687949508577.
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Hung, Hsiang-Yuan, and 洪祥瑗. "Stress-Strain Relationship of Confined Concrete in Reinforced Concrete Hollow Piers." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/15407833936815937956.
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Kuo, Tsung-Hui, and 郭聰慧. "Stress-Strain relationship of cement-matrix composites by an inclusion method." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/27738004327050187439.
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碩士國立高雄應用科技大學
土木工程與防災科技研究所
91
This research is to give a mechanical model to generate the stress-strain relationship of cement paste. An inclusion theory with the aid of the secant moduli in the analogized particle-reinforced elastoplasticity is used to simulate the stress-strain relationship of cement-based composite materials. Assuming that the mortar is a two-phase composite, that is, it consists of cement paste of the matrix and the Ottawa illinos C109 sand as the inclusion. C109 sand is considered as linearly elastic but the cement paste is nonlinear, when the applied load increasing, the elastic (stiffness) moduli decreasing. Cylindrical specimens were tested in order to obtain material properties (such as Young’s modulus. Poisson’s ratio, stress-strain curve etc.) and test loading conditions was displacement control. From experimental data and by computer’s trial and error, we can get the mathematical solution to represent the complete stress-strain relationship of cement paste. Then, comparing the mathematical equation and mechanical model, we can find four parameter’s mechanical model to represent the overall stress-strain relationship of cement paste. The four parameters have spring coefficients , , and dashpots coefficients , , Furthermore, by using the secant moduli of the matrix, we can obtain the elastic modulus of any point on the stress-strain curve of the paste. Next, from the inclusion theory and the mean-field approach, we can get the secant moduli of the composite (mortar). Besides, the overall strain of the composite material is also calculated from the micromechanical theory. So, finally the overall stress-strain curve of mortar is obtained. As compared with the experimental data of cement paste and mortar, the derived theory (a mean-field method combining with the secant moduli) is in an accuracy acceptable range below 70% of inclusion’s volume fraction in predicting the stress-strain relationship and an acceptable range below 80% of inclusion’s volume fraction in predicting the effective elastic buck and shear moduli.
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Tsai, Chong-Liang, and 蔡宗良. "On Stress-Strain-Strain Rate Relationship of Clay Based on Multi-Step Loading Creep and Shear Strength Tests." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/18752448435210000383.
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碩士國立台灣工業技術學院
營建工程技術研究所
85
ABSTRACT The stress-strain-strain rate relations between different test types are studied using a serious of multi-step loading creep and constant strain rate tests of Taipei Silty Clay.Soil creep behavior of multi-step loading creep is compared with single- step loading creep. The influence of loading rate on undrained shear strength, Young''s modulus and pore pressure response are also studied. Results from this study show that：(1) stress- strain-strain rate functionis unique regardless of test types including multi-step loading creep and constant strain rate test ; (2) Soil creep behavior of multi-step loading creep test is similar to single-step loading creep test after same creep stress is applied; (3) Undrained shear strength increases with increasing strainrate, but the effect of strain rate on the unloading-reloading modulus is insignificant.
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Kwan, Pao-Shuan, and 鄺柏軒. "Shear stress-strain relationship of sandy soil deposit using dynamic centrifuge modeling test." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/24082528917557851586.
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碩士國立中央大學
土木工程研究所
98
The relationship of shear stress and shear strain of sandy soil is an important parameter and need to determination when soil stiffness and strength degraded as a result of sand liquefaction. Centrifuge modeling tests can provide an alternative source of information and reliable test results for assessing soil mechanism under shaking situation. The centrifuge model was conducted to simulate the seismic response for a 24m thick sandy soil deposit under an artificial gravity field of 80g. The testing models are subjected to different magnitude base-input acceleration of 1Hz and 16 seconds duration. A series of accelerometer and pore water pressure transducer arrays were installed to record the soil seismic response. Utilizing the acceleration history and the pore pressure history, the shear stress and shear strain at different depths can be obtained. And then the shear modulus can be acquired through calculation. From this research, the phenomenon of shear wave propagating upward is obviously being seen in dry sand, so is the site effect. The soil dilatation and surge can be found in saturated sand.
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張恆晟. "Micro-structural model of multi-axial stress-strain relationship for concrete under confinement." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/49951133943235438606.
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Tsai, Wei-Lung, and 蔡偉隆. "Long-Term Stress-Strain Relationship of the Cement-Matrix Composite by Inclusion Method." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/844n6y.
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碩士國立高雄應用科技大學
土木工程與防災科技研究所
93
Based on the concept of composites, the materials with cement or with fly ash cement used as the matrix containing 29%, 38%, and 49% (by volume) standard sands as inclusion were formed cement-matrix composites and fly ash cement-matrix composites. Nine different material ages for 7 days, 14 days, 28 days, 2 months, 3 months, 6 months, 9 months, and 18 months were chosen in this investigation. The material parameters of four-parameter model can be determined by means of the stress-strain curves of the matrix obtained from the experimental. Long-term stress-strain curves with different mix proportions and ages were obtaining by the inclusion method and the concept of secant module. Furthermore, the stress-strain curves obtained from the simulation were compared with those obtained from the experiments to confirm the reliability of long-term stress-strain theory we propose. Results show that , , , and are four parameters of the four- parameter model in terms of material age , and can simulate the stress-strain curves of the cement paste and fly ash paste. After some the regression analysis, the relation between the four parameters and the age can be obtained with the sample correlation coefficient is approach to 1. The relation of four parameters and the age will be changed if the matrix is different. For this reason, it is possible to simulate the stress-strain curve of cement paste and the fly ash paste in different age. Comparisons of the stress-strain curves between the simulation calculations and the experiment date show that the results are in an acceptable range. Thus, it is anticipate to the long-term stress-strain relationships of cement-matrix composites and fly ash cement-matrix composites by the inclusion method.
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SINGH, VIVEK KR. "EFFECT OF TEMPERATURE ON STRENGTH & STRESS-STRAIN RELATIONSHIP FOR THE HIGHER GRADE OF CONCRETE." Thesis, 2011. http://dspace.dtu.ac.in:8080/jspui/handle/repository/13859.
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M.TECHThe structural elements subjected to high temperatures lead to significant losses due to the reduction in the strength of the concrete. In this study it is observed that strength reduction occurs in concrete on rising the temperature. For use in fire resistance calculations, the relevant thermal properties of high strength concrete were determined as a function of temperature. A number of compressive & tensile strength tests were conducted to examine the strength variation & stress-strain relationship due to rise in temperature on concrete. Tests were conducted at various temperatures (27 C, 100 C & 200°C) for 1hour. Three types of concrete mix were taken (M30, M40, M50) respectively. The results of a study on the influence of temperature on the compressive & tensile strength of concrete are evaluated. Stress-strain relationships were also studied at different temperature. The variation of temperature on concrete samples shows changes in various properties of concrete. The behaviour of concrete in fire is not well defined at present, and further research is required. The response of concrete material to heating is fundamentally complex.
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Ya-LingLin and 林雅玲. "The Relationship between Occupational Stress and Strain of Photonics Industry Employees－Work Motivation as the Moderator." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/kczukf.
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碩士國立成功大學
企業管理學系專班
101
The aim of this research is to explore relationships between the occupational stress and strain, the work motivation and strain, and the moderating effects of work motivation in the occupational stress process. The occupational stress includes work demands, work guarantees, coworker supports and interpersonal relationships. The strain is divided into the burnout（including physical and mental burnout , and over-commitment）and the turnover intention. The work motivation is divided into the intrinsic motivation and the extrinsic motivation. This study focuses on nine photonics industry employees in the Southern Taiwan Science Park and the Tainan Technology Industrial Park. The effective samples are 245 and the return-ratio is 91%. The results are as follows: First, the occupational stress has a partially positive relationship with strain. Second, the work motivation doesn’t have a relationship with the burnout. Third, the work motivation has a partially positive relationship with the turnover intention . Finally, the effect of work motivation is significant to moderate the partially negative relationship between the occupational stress and strain. In the conclusion, the study provides a summary of the research findings, managerial contributions, limitations and recommendations for future researchers.
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Kung, Ying-Nien, and 龔盈年. "Theoretical Simulation for Stress-Strain Relationship of ReactivePowder Concrete at Elevated Temperature and High Speed Loading." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/48614995348908394212.
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碩士國立高雄應用科技大學
土木工程與防災科技研究所
97
This research is to investigate the strain rate effect on the stress-strain curve of RPC composites after elevated temperature by experiments and theoretical predictions. The composite material is examined at the age of 7 days with RPC mortar as the matrix, and three volume concentrations, 1％, 2％ and 3％, of the steel fiber as the inclusion respectively. It is heated under the temperature from 200℃ to 800℃ by furance, and then applied the strain rate 6 5 10 / sec − × by MTS and se2 10 / c 2 × ~ 1 10 / sec 3 × by SHPB. By modifying formulas and four-parameter mechanics model in term of the strain rate and elevated temperature is proposed to simulate the stress-strain curves of the RPC matrix and composites. From the simulated results of the RPC matrix, the mean-field approach and the secant modulus method are used to predict the stress-strain relationship of the RPC composites. Results show that the mechanical properties decrease when the material under high temperature. On the other hand, the mechanical properties increase when the strain rate goes up. Besides, Dynamic four-parameter mechanics model can be derived from its static model, and it shows that the simulated stress-strain curves and the experimental ones are pretty close. Through matrix stress-strain curve and composites curve, it shows that predicitable curve calculated from inclusion theory and the test curve are much closed to each other in the condition of the R2 range (450/s~650/s) of dynamic strain rate and the temperature 400℃~600℃. However, a part of the result is not ideal because of the ignorance of the factors of thermal stress and expansion. The research needs to include the considedration of thermal stress and expansion, and it can help the result of the inclusion theory reach to the accuracy.
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Yang, Cong-Ming, and 楊聰明. "The Packaging Process of Metal Microcap under Room Temperature Status and Its Shear Stress-Strain Relationship Analysis." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/48849041015611660274.
Full textAbstract:
碩士國立中山大學
機械與機電工程學系研究所
92
A novel room temperature bonding method is used to package the micro-component. The bonding method utilizes metal microcap to package the micro-component under room temperature status, which not only can provide micro-component mechanical support also can prevent micro-component from contamination. The bonding condition under room temperature is the most conventional method can not achieve, which characteristic is the most significant effect factor to drive the wafer-level packaging process to improve in today. Utilizing ASTM standard, which was used as a macroscopic standard to evaluate and analyze the bonding shear strength relationship between the ASTM standard specimen and the metal microcap. The carrier wafer has been oxidized before photolithography process; the diameter of cavity and the contact area between the metal microcap and glass substrate were controlled by the photomask design and the accuracy of the photoresist exposure. The passivation treatment was developed to separate the microcap from the carrier wafer more easily. In this thesis, the metal microcap was fabricated by using electroforming process, which can control the thickness of metal microcap. The advantages of microcap are superior to the thin film poly-silicon made by the surface micromachining technique on the quality and mechanical properties. A glass is used as substrate of the metal microcap, and its transparent characteristic is a feature how we perform UV curing process. The adhesive can be cured under room temperature and the results exhibit the adhesive has excellent bonding strength. SEM is used to analyze the passivation result, the increasing rate of electroforming thickness. The shear stress-strain relationship between the metal microcap and the ASTM standard specimen is also discussed and analyzed in this thesis.
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Graça, Hugo João Mendes Prata. "Stress-Strain Relationship Characterization of Armoured Graded Aluminium and Steel Alloys Using a Digital Image Correlation Technique." Master's thesis, 2018. http://hdl.handle.net/10400.6/8322.
Full textAbstract:
The need for better and lighter armoured concepts is ever increasing. Weather due to the
challenges of the modern theatre of war, which require the vehicles to easily move in dense
urban areas and in vast soft grounded deserts, or by the nature of the increasingly ingenious
threats, traditional armour solutions fail to provide adequate protection.
The current work is part of a project intended to develop an armour solution that incorporates
cork in its composition. This work focuses on the study of metal alloys and their mechanical
characterization at low strain rates. For this purpose, a look is taken into the history and
evolution of armoured vehicles and the characteristics of the different materials adopted in
the course of armour development. The basic concepts associated with metal alloys loading
and deformation behaviour are described as well as the methodology usually employed when
preforming mechanical characterization of metals.
In order to determine the material constants required to create the strain hardening parameter
of the Johnson-Cook constitutive material model, quasi-static tests are conducted in 45
specimens composed of three rolling directions (0º, 45º and 90º) of 5 mm and 10 mm thick AW-
5083-H111 aluminium alloy and 2.2 mm thick Ramor 500 steel alloy. The strain data is processed
through strain gauges applied in the specimens’ surface and an in-house integrated digital
image correlation technique.
The experimental results show that the digital image correlation technique employed in this
study offers good results compared to both the strain gauge data and the similar examples from
the literature. It is also possible to note the difference in behaviour in the three cutting
directions in both alloys. Dynamic strain aging and instabilities of high frequency oscillation
phenomena are recorded on the aluminium alloy, just as expected from high magnesium
content alloys. The strain hardening constants and the Cockcroft-Latham failure criterion are
successfully extrapolated and compared to similar materials. As a general conclusion, this work
creates a good foundation for the full material characterisation on the larger spectrum of strain
rates and will allow for the future research necessary for the main project.A necessidade para melhores e mais leves conceitos de blindagens é sempre crescente. Quer devido às dificuldades do campo de batalha moderno, que requerem que os veículos se movam facilmente nas densas áreas urbanas e em vastos desertos de terreno macio, quer pela natureza crescentemente engenhosa das ameaças, as blindagens tradicionais falham em fornecer proteção adequada. O presente trabalho, faz parte de um projeto com o propósito de desenvolver uma solução de blindagem que incorpore cortiça na sua composição. Este estudo irá focar-se em ligas metálicas e a sua caracterização mecânica a baixas taxas de deformação. Para este fim, é feita uma breve revisão da história e evolução de veículos blindados e as características dos diferentes materiais empregados no desenvolvimento de blindagens. Os conceitos básicos associados com o comportamento de carregamento e deformação de ligas metálicas são descritos assim como a metodologia normalmente utilizada aquando da execução da caracterização mecânica de metais. A fim de determinar as constantes do material necessárias para a criação do parâmetro de endurecimento de deformação do modelo constitutivo de material de Johnson-Cook, são realizados testes quase estáticos em 45 provetes compostos pelas três direções de rolamento (0º,45º e 90º) de alumínio AW-5083-H111 de 5 mm e 10 mm de espessura e aço Ramor 500 de 2,2 mm de espessura. Os dados da deformação são processados a partir de extensómetros aplicados na superfície dos provetes e por uma técnica de correlação digital de imagem caseira. Os resultados experimentais mostram que a técnica de correlação digital de imagem empregada neste estudo oferece bons resultados quando comparado com os dados dos extensómetros e com exemplos de materiais semelhantes da literatura. Também é possível denotar o comportamento diferenciado nas três direções de corte em ambas as ligas. Os fenómenos de envelhecimento dinâmico da deformação e instabilidades de oscilação de elevada frequência são registados na liga de alumínio, tal como esperado de ligas de elevado teor de magnésio. As constantes do endurecimento da deformação e do critério de falha de Cockcroft-Latham são extrapoladas com sucesso e comparadas com materiais semelhantes. Como conclusão geral, este trabalho cria uma boa fundação para a completa caracterização dos materiais num maior espetro de velocidades de deformação e vai permitir realizar a investigação necessária para o projeto principal.
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"The role of the social support offered by trade unions as a moderator of the stress-strain relationship." Thesis, 2015. http://hdl.handle.net/10539/16900.
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Murugesan, Reddiar Madhu Karthik. "Stress-Strain Model of Unconfined and Confined Concrete and Stress-block Parameters." Thesis, 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7545.
Full textAbstract:
Stress-strain relations for unconfined and confined concrete are proposed to overcome some shortcomings of existing commonly used models. Specifically, existing models are neither easy to invert nor integrate to obtain equivalent rectangular stress-block parameters for hand analysis and design purposes. The stress?strain relations proposed are validated for a whole range of concrete strengths and confining stresses. Then, closed form expressions are derived for the equivalent rectangular stress-block parameters. The efficacy of the results is demonstrated for hand analysis applied for deriving the moment-curvature performance of a confined concrete column. Results are compared with those obtained from a computational fiber-element using the proposed stress-strain model and another widely used model; good agreement between the two is observed. The model is then utilized in the development of a new structural system that utilizes the positive attributes of timber and concrete to form a parallel. Timber has the advantage of being a light weight construction material, easy to handle, is environmentally friendly. However, large creep deflections and significant issues with sound transmission (the footfall problem) generally limit timber use to small spans and low rise buildings. Concrete topping on timber sub-floors mitigate some of these issues, but even with well engineered wood systems, the spans are relatively short. In this study, a new structural system called structural boxed-concrete, which utilizes the positive attributes of both timber and reinforced concrete to form a parallel system (different from timber-concrete composite system) is explored. A stress-block approach is developed to calculate strength and deformation. An analytical stress-block based moment-curvature analysis is performed on the timber-boxed concrete structural elements. Results show that the structural timber-boxed concrete members may have better strength and ductility capacities when compared to an equivalent ordinary reinforced concrete member.
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Martyn, Michael T., R. Joseph, W. J. McGregor, K. E. Tanner, and Philip D. Coates. "Effect of polymer matrix on the rheology of hydroxapatite filled polyethylene composites." 2002. http://hdl.handle.net/10454/2944.
Full textAbstract:
NoThe effect of matrix polymer and filler content on the rheological behavior of hydroxyapatite-filled injection molding grade high-density polyethylene (HDPE) has been studied. Studies of the flow curves revealed that the matrix and the composite exhibit three distinct regions in the flow curve, namely, a pseudoplastic region at low to moderate shear rates, a plateau and a second pseudoplastic region at high shear rates. The shear stress corresponding to the plateau (Tc) is dependent on both the filler concentration and the melt temperature. Addition of HA in the HDPE matrix increases the value of Tc and decreases compressibility of the melt. An increase in temperature also raises the value of Tc. From the nature of flow curves it is concluded that the matrix polymer largely decides the rheology of the composite.