Comment on Hyperbolicity of Wave Problem for Valanis’ Global Damage Theory
In a very interesting and stimulating recent paper, Valanis (199l) proposed a new type of nonlocal damage theory, called the global damage theory. Some conclusions of this paper, however, require further analysis, which is the purpose of this technical note. Offering as motivation some questionable and unfounded critical comments on the nonlocal damage theory originally proposed by Pijaudier-Cabot and Baiant (1987) and Baiant and Pijaudier-Cabot ( 1988), Valanis formulated a different theory and cltrimed it to be superior because, as he stated, it exhibits unconditional hyperbolicity of the wave problem. On closer scrutiny, though, Valanis' claim is found to be invalid, and for further development of nonlocal damage models it is important to understand why.
Nonlocal damage theory
In the usual local finite element analysis, strain softening causes spurious mesh sensitivity and incorrect convergence when the element is refined to vanishing size. In a previous continuum formulation, these incorrect features were overcome by the imbricate nonlocal continuum, which, however, introduced some unnecessary computational complications due to the fact that all response was treated as nonlocal. The key idea of the present nonlocal damage theory is to subject to nonlocal treatment only those variables that control strain softening, and to treat the elastic part of the strain as local. The continuum damage mechanics formulation, convenient for separating the nonlocal treatment of damage from the local treatment of elastic behavior, is adopted in the present work. The only required modification is to replace the usual local damage energy release rate with its spatial average over the representative volume of the material whose size is a characteristic of the material. Avoidance of spurious mesh ...
AN ANALYSIS OF POLYMERIC THICK-FILM RESISTORS AS PRESSURE SENSORS
Abstract The strain-sensing characteristics of thick-film polymer-based resistors printed and cured on 96% alumina are presented. Two layout configurations have been analysed: planar and sandwich. Various strain-gauge characteristics have been studied, including the mechanical and temperature-dependent properties of the polymeric films. It has been shown that the planar polymer resistors exhibit low sensitivity, comparable to that of metal-foil gauges, whereas the MRM (metal-resistor-metal) configurations exhibit similar characteristics to those of cermet thick-film MRM gauges. It has also been observed that the mechanical properties of the polymeric films are significantly poorer than those of cermet-based gauges. This degradation in performance is attributed to the epoxy/pseudo-plastic structure of the polymeric thick-film resistor layer.