Download or read book The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide written by Lee M. Nicholson and published by . This book was released on 2000 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of ~2500 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.
Download or read book The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-11 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of M (bar) (sub w) 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.Nicholson, Lee M. and Whitley, Karen S. and Gates, Thomas S.Langley Research CenterAGING (MATERIALS); GLASS; MOLECULAR WEIGHT; TEMPERATURE EFFECTS; THERMOPLASTICITY; VISCOELASTICITY; POLYIMIDES; CREEP TESTS; ERROR ANALYSIS; TIME TEMPERATURE PARAMETER; GLASS TRANSITION TEMPERATURE; DURABILITY
Download or read book The Combined Influence of Molecular Weight and Temperaturee on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide written by Lee M. Nicholson and published by . This book was released on 2000 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide written by Lee M. Nicholson and published by . This book was released on 1999 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mechanical Testing of an advanced thermoplastic polyimide (LaRC-TM-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength were all determined as a function of molecular weight and test temperature. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. A critical molecular weight (Mc) was observed to occur at a weight-average molecular weight (Mw) of approx. 22000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Furthermore, inelastic analysis showed that low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. The microstructural images supported these findings.Nicholson, Lee M. and Whitley, Karen S. and Gates, Thomas S. and Hinkley, Jeffrey A.Langley Research CenterMOLECULAR WEIGHT; MECHANICAL PROPERTIES; POLYIMIDES; ELASTIC PROPERTIES; THERMOPLASTICITY; TENSILE STRENGTH; DUCTILE-BRITTLE TRANSITION; TEMPERATURE DEPENDENCE; FRACTOGRAPHY; GLASS TRANSITION TEMPERATURE; STRESS-STRAIN DIAGRAMS; MODULUS OF ELASTICITY; MICROSTRUCTURE; POLYMER MATRIX COMPOSITES; NOTCHES; TENSILE TESTS
Download or read book The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide written by Lee M. Nicholson and published by . This book was released on 2001 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mechanical testing of the elastic and viscoelastic response of an advanced thermoplastic polyimide (LaRC-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The notched tensile strenght was shown to be a strong function of both molecular weight and temperature, whereas stiffness was only a strong function of temperature. A critical molecular weight was observed to occur at a weight-average molecular weight of ~22,000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure.
Download or read book The Role of Molecular Weight and Temperaturee on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide written by Lee M. Nicholson and published by . This book was released on 2001 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comprehensive Structural Integrity written by Ian Milne and published by Elsevier. This book was released on 2003-07-25 with total page 4647 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this major reference work is to provide a first point of entry to the literature for the researchers in any field relating to structural integrity in the form of a definitive research/reference tool which links the various sub-disciplines that comprise the whole of structural integrity. Special emphasis will be given to the interaction between mechanics and materials and structural integrity applications. Because of the interdisciplinary and applied nature of the work, it will be of interest to mechanical engineers and materials scientists from both academic and industrial backgrounds including bioengineering, interface engineering and nanotechnology. The scope of this work encompasses, but is not restricted to: fracture mechanics, fatigue, creep, materials, dynamics, environmental degradation, numerical methods, failure mechanisms and damage mechanics, interfacial fracture and nano-technology, structural analysis, surface behaviour and heart valves. The structures under consideration include: pressure vessels and piping, off-shore structures, gas installations and pipelines, chemical plants, aircraft, railways, bridges, plates and shells, electronic circuits, interfaces, nanotechnology, artificial organs, biomaterial prostheses, cast structures, mining... and more. Case studies will form an integral part of the work.
Download or read book Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide written by Lee M. Nicholson and published by . This book was released on 1999 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Langley Scientific and Technical Information Output 2000 written by and published by . This book was released on 2001 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Springer Handbook of Experimental Solid Mechanics written by William N. Sharpe, Jr. and published by Springer Science & Business Media. This book was released on 2008-12-04 with total page 1100 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Springer Handbook of Experimental Solid Mechanics documents both the traditional techniques as well as the new methods for experimental studies of materials, components, and structures. The emergence of new materials and new disciplines, together with the escalating use of on- and off-line computers for rapid data processing and the combined use of experimental and numerical techniques have greatly expanded the capabilities of experimental mechanics. New exciting topics are included on biological materials, MEMS and NEMS, nanoindentation, digital photomechanics, photoacoustic characterization, and atomic force microscopy in experimental solid mechanics. Presenting complete instructions to various areas of experimental solid mechanics, guidance to detailed expositions in important references, and a description of state-of-the-art applications in important technical areas, this thoroughly revised and updated edition is an excellent reference to a widespread academic, industrial, and professional engineering audience.
Download or read book NASA Langley Scientific and Technical Information Output 2001 written by and published by . This book was released on 2002 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polymide written by Jerry M. Allen and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polymide written by Lee M. Nicholson and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Characterization and Modeling of Isothermal and Nonisothermal Physical Aging in Glassy Polymer Films written by Yunlong Guo and published by . This book was released on 2009 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fiber-reinforced polymer matrix composites (PMCs) using high-temperature thermoplastics as the matrix material represent a lightweight design solution for applications above 250°F. This is often required for aircraft structures subjected to supersonic airflows. While thermoplastic matrix PMCs may be successfully designed for such temperatures, they generally exhibit a time-dependent material response which must be well understood for successful design. One important aspect of this response is physical aging, which causes the viscoelastic behavior of amorphous polymers below their glass transition temperature to change with time. While isothermal physical aging has been extensively studied, physical aging during a varying temperature history has received less scrutiny. This dissertation focuses on nonisothermal physical aging of polymers from both experimental and theoretical aspects. The study concentrates on pure polymers rather than fiber-reinforced composites; this step removes several complicating factors to simplify the study. It is anticipated that the findings of this work can then be applied to composite materials applications. The physical aging tests in this work are performed using a dynamic mechanical analyzer (DMA). The viscoelastic response of glassy polymers under various loading and thermal histories are observed as stress-strain data at a series of time points. The first stage of the experimental work involves the characterization of the isothermal physical aging behavior of two advanced thermoplastics. The second stage conducts tests on the same materials with varying thermal histories and with long-term test duration. This forms the basis to assess and modify a nonisothermal physical aging model (KAHR- a te model). Based on the experimental findings, the KAHR- a te model has been revised by new correlations between aging shift factors and volume response; this revised model performed well in predicting the nonisothermal physical aging behavior of glassy polymers. In the work on isothermal physical aging, short-term creep and stress relaxation tests were performed at several temperatures within 15-35°C below the glass transition temperature ( T g ) at various aging times, using the short-term test method established by Struik. Stress and strain levels were such that the materials remained in the linear viscoelastic regime. These curves were then shifted together to determine momentary master curves and shift rates. In order to validate the obtained isothermal physical aging behavior, the results of creep and stress relaxation testing were compared and shown to be consistent with one another using appropriate interconversion of the viscoelastic material functions. Time-temperature superposition of the master curves was also performed. The temperature shift factors and aging shift rates for both PEEK and PPS were consistent for both creep and stress relaxation test results. Nonisothermal physical aging was monitored by sequential short-term creep tests after a series of temperature jumps; the resulting strain histories were analyzed to determine aging shift factors ( a te ) for each of the creep tests. The nonisothermal aging response was predicted using the KAHR- a te model, which combines the KAHR model of volume recovery with a suitable linear relationship between aging shift factors and specific volume. The KAHR- a te model can be utilized to both predict aging response and to determine necessary model parameters from a set of aging shift factor data. For the PEEK and PPS materials considered in the current study, predictions of mechanical response were demonstrated to be in good agreement with the experimental results for several complicated thermal histories. In addition to short-term nonisothermal aging, long-term creep tests under identical thermal conditions were also analyzed. Effective time theory was unitized to predict long-term response under both isothermal and nonisothermal temperature histories. The long-term compliance after a series of temperature changes was predicted by the KAHR- a te model, and the theoretical predictions and experimental data showed good agreement for various thermal histories. Lastly, physical aging behavior of PPS near the glass transition temperature was investigated, in order to observe the mechanical response in the process of the evolution of the material into equilibrium. At several temperatures near T g , the time need to reach equilibrium were determined by the creep test results at various aging times. In addition to isothermal physical aging, mechanical shift factors in the period of approaching equilibrium at a common temperature after temperature up-jumps and down-jumps are monitored from creep tests; prior to these temperature jumps, the materials were aged to reach equilibrium states. From these tests, asymmetry of approaching equilibrium phenomenon in ate was observed, which is first-time reported in the literature. This finding shows the similarity between the thermodynamic and mechanical properties during structural relaxation. This work will lead to improved understanding of the viscoelastic behavior of glassy polymers, which is important for better understanding and design of PMCs in elevated temperature applications. With the above findings, this dissertation deals with nonisothermal physical aging of glassy polymers, including both experimental characterization and constructing a framework for predictions of mechanical behavior of polymeric materials under complicated thermal conditions.
Download or read book Papers Presented at the Meeting written by American Chemical Society. Division of Polymer Chemistry and published by . This book was released on 2001 with total page 788 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Physical Aging on the Thermal and Mechanical Behaviors of Glassy Polycarbonate microform written by Chinh Ho-Huu and published by Library and Archives Canada = Bibliothèque et Archives Canada. This book was released on 2003 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt:
