The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide PDF Download
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Author: Lee M. Nicholson Publisher: ISBN: Category : Molecular weights Languages : en Pages : 26
Book Description
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.
Author: Lee M. Nicholson Publisher: ISBN: Category : Molecular weights Languages : en Pages : 26
Book Description
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.
Author: Lee M. Nicholson Publisher: ISBN: Category : Molecular weights Languages : en Pages : 44
Book Description
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.
Author: Rui Miranda Guedes Publisher: Elsevier ISBN: 0857090437 Category : Technology & Engineering Languages : en Pages : 605
Book Description
Creep is the tendency of materials to deform when subjected to long-term stress, particularly when exposed to heat. Fatigue phenomena occur when a material is subjected to cyclic loading, causing damage which may progress to failure. Both are critical factors in the long-term performance and reliability of materials such as polymer matrix composites which are often exposed to these types of stress in civil engineering and other applications. This important book reviews the latest research in modelling and predicting creep and fatigue in polymer matrix composites. The first part of the book reviews the modelling of viscoelastic and viscoplastic behaviour as a way of predicting performance and service life. Part two discusses techniques for modelling creep rupture and failure. The final part of the book discusses ways of testing and predicting long-term creep and fatigue in polymer matrix composites. With its distinguished editor and international team of contributors, Creep and Fatigue in Polymer Matrix Composites is a standard reference for all those researching and using polymer matrix composites in such areas as civil engineering. - Reviews the latest research in modelling and predicting creep and fatigue in polymer matrix composites - A specific focus on viscoelestic and viscoplastic modelling features the time-temperature-age superposition principle for predicting long-term response - Creep rupture and damage interaction is examined with particular focus on time-dependent failure criteria for lifetime prediction of polymer matrix composite structures illustrated using experimental cases
Author: G. M. Odegard Publisher: ISBN: Category : Languages : en Pages : 38
Book Description
In this study, a technique is presented for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Because the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties can no longer be determined through the traditional micromechanical approaches that are formulated by using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalent-continuum modeling method. The micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube lengths, concentrations, and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/polyimide composite systems.
Author: Lee M. Nicholson
Author: Lee M. Nicholson
Author: Lee M. Nicholson
Author: Michael Hyer
Author: Rui Miranda Guedes
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Author: G. M. Odegard
Author: Lee M. Nicholson
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