Book Section records
https://feeds.library.caltech.edu/people/Tschoegl-N-W/book_section.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 14:24:46 +0000Time-Dependence in Materials
https://resolver.caltech.edu/CaltechAUTHORS:20201124-074041827
Authors: {'items': [{'id': 'Tschoegl-N-W', 'name': {'family': 'Tschoegl', 'given': 'N. W.'}}]}
Year: 1998
DOI: 10.1007/978-3-642-51062-5_1
The last ten or fifteen years have seen some highly significant changes in what needs to, and what can be, achieved in the area of the characterization of materials with time-dependent mechanical properties. On the one hand we have seen a tremendous increase in the use and variety of materials with time-dependent properties such as composites and semi-crystalline engineering materials, as well as the development and application of multiphase materials (e. g., block and graft copolymers, and polyblends), requiring new or improved methods of characterization. On the other hand, there have been notable advances in the availability and sophistication of state-of-the-art sensors, and of methods of data acquisition and manipulation. It appears that the need for better characterization has not been universally recognized, and that, consequently, the possibilities for implementing it have not been fully exploited. The lecture examines these issues and suggests some new-old approaches.
The mechanical properties (and other properties: dielectric, optical, etc.) of ALL materials are time-dependent. This is simply a necessary consequence of the Second Law of Thermodynamics according to which a part of the energy of deformation is always dissipated by viscous forces even while the rest is stored elastically. Time-dependent behavior may range from virtually purely elastic to virtually purely viscous behavior. Polymeric materials are typically viscoelastic and thus fall in-between. As a consequence their mechanical properties must be described by time- (or, equivalently, frequency-) dependent material response functions, not elastic or viscous constants.https://authors.library.caltech.edu/records/zjgz8-jca61Apparatus for Measuring the Time-Dependent Poisson's Ratio in Uniaxial Tension
https://resolver.caltech.edu/CaltechAUTHORS:20200716-130505825
Authors: {'items': [{'id': 'Samarin-M', 'name': {'family': 'Samarin', 'given': 'M.'}}, {'id': 'Emri-I', 'name': {'family': 'Emri', 'given': 'I.'}}, {'id': 'Tschoegl-N-W', 'name': {'family': 'Tschoegl', 'given': 'N. W.'}}]}
Year: 1998
DOI: 10.1007/978-3-642-51062-5_239
Polymers and composite materials are widely used in applications requiring lightweight and high damping capacity. Since these materials show viscoelastic behavior under static and dynamic loading, the stress analysis involving such materials has recently become an important subject. The time-dependent Poisson's ratio as well as the tensile relaxation modulus are the primary input properties for finite element methods (FEM), and are also required in the constitutive modeling of a material's mechanical behavior (Emri et al., 1997). Previous attempts at measuring the time-dependent Poisson's ratio have shown convincingly that it is indeed difficult to obtain experimentally. Because the total range of response is compressed effectively between 0.3333 and 0.5 the measurements require high accuracy. This is made more complicated because they are strongly influenced by number of parameters such as e. g. temperature, pressure, humidity, etc., and the reproducibility of the material properties of the specimen. We report here on the development of an apparatus designed to enable us to determine the time-dependent. Poisson's ratio, v(t), with the required accuracy while simultaneously determining the tensile relaxation modulus, E(t). Using the E-T algorithm (Emri and Tschoegl, 1992–1997) we hope to be able to obtain the fundamental moduli, the shear relaxation modulus, G(t), and the difficult-to-determine bulk relaxation modulus, K(t), by computer calculation.https://authors.library.caltech.edu/records/165dp-r0416