All real materials in one way or another, exhibit a departure from ideal elastic behaviour, even at very small strain values. Under cyclic deformation, these departtures result in irreversible energy losses in material. The causes of such losses are many, and include the irreversible transfer of mechanical energy into heat, growth of cracks and other defects, and the microplastic deformaton of crystals to name a few. Several terms have been suggested to define these phenomena including damping, energy dissipation, imperfect elasticity and internal friction. This book is about materials damping; with damping or energy dissipation processes in vibrating solids.

All real materials in one way or another, exhibit a departure from ideal elastic behaviour, even at very small strain values. Under cyclic deformation, these departtures result in irreversible energy losses in material. The causes of such losses are many, and include the irreversible transfer of mechanical energy into heat, growth of cracks and other defects, and the microplastic deformaton of crystals to name a few. Several terms have been suggested to define these phenomena including damping, energy dissipation, imperfect elasticity and internal friction. This book is about materials damping; with damping or energy dissipation processes in vibrating solids.

Various damages, which develop in structural composites, cause a softening behavior which can cause significant load redistribution in non-critical as well as critical areas of various structural elements. The strain energy dissipation (SED) concept provides a set of consistent nonlinear constitutive relations for stress analyses and the in-plane loader (IPL) provides a way for material characterization. Damage surfaces for moderate values of dissipated energy densities (DED) were estimated to match the response of conventional (+/-theta) sub ns coupon tests, which are influenced by matrix mode damages. Softening behaviors for high values of DED which can result from fiber breakage/pull out were estimated using engineering judgement. Nonlinear finite element analyses were performed for two classes of structural elements; namely. (i) a (+/- theta) sub ns cylindrical pressure vessel, where the nonlinearities in load- deformation responses are noticeable before fiber failure. and (ii) open hole tension of two quasi-isotropic layups, where local failure and softening in the fiber direction become critical to cause catastrophic failure. The results show the usefulness of the approach for design purposes and for explaining the complex problem of the so called "hole size" effect. Extension of the SED concept to the 3-D problem is suggested and a new approach to the problem of certification is discussed. Usefulness of the data generated by the IPL could not be assessed since they were not available for use. However, it appears that such data would be useful if they can provide full information up to high DED levels required for complete softening due to fiber breakage and pull out. Additional studies are suggested for the following phases for utilizing the full potential of the approach. Use of the test devices (IPL) and/or other tests by other testing organizations are also recommended to determine their acceptability and versatility

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An approach to characterizing failure behavior and degree of load induced internal damage in composite materials and structures is formulated. This approach is based on a systematic experimental procedure to observe response of composite materials subjected to multiaxial load environment. The energy dissipated by internal failure mechanisms is employed as a measure of internal damage and is characterized by an energy dissipation function, which is identified by means of a deconvolution procedure data provided by NRL's automated in-plane loader. Use of this information as a failure analysis and prediction tool is demonstrated by simulating the structural response of some naval structural components made from several different composite materials. In addition, a general theory for the derivation of the constitutive behavior of the damaged composites is presented.

This paper presents a method for the estimation of the vibratory fatigue strength of composite materials that is based on the accumulated dissipated energy. The accumulated dissipated energy was measured with a special measuring technique, which is able to catch quasi-continuously the mechanical properties of the tested samples. The curves of the accumulated dissipated energy were approximated with an equation that includes several parameters. These parameters were identified for experiments with different types of load and for samples with different contents of micropores. For samples that reach more than 106 load cycles, the accumulated dissipated energy in one-load-stage tests is a linear function. With this, the fatigue limit of the samples can be predicted.