This paper broadly reviews the stress-based, strain-based, and crack growth aproaches to fatigue life prediction, and it attempts to suggest some choices and variations of these that might enhance their inclusion in undergraduate education and their more routine use by practicing engineers. For the stress-based approach, emphasis should shift toward the use of data on actual components, and it should be recognized that damage below the usual fatigue limit may occur. Also, evaluation of mean stress effects by the modified Goodman diagram should be replaced by other methods. The usefulness of the strain-based approach for simple situations may be extended by adding empirical adjustments for surface finish and size. It may also be desirable to lower the long-life end of the strain-life curve to obtain agreement with limited component test data, producing a component-specific strain-life curve. Use of the crack growth approach is hampered by the lack of a widely accepted set of materials constants for describing da/dN versus ΔK curves. It is recommended that this situation be remedied by representing the intermediate growth rate region with a Paris-type exponent, an associated coefficient, and a third constant that characterizes the sensitivity to R-ratio according to the equation of Walker. Limits or asymptotic behavior for the low and high growth rate regions should then be handled separately.
A steady-state thermoelasticity problem of a multilayered anisotropic medium under the state of generalized plane deformation is considered in this paper. By utilizing the Fourier transform technique, the general solutions of thermoelasticity for layers with transversely isotropic, orthotropic, and monoclinic properties are derived. The complete solution of the entire layered medium is then obtained through introducing the thermal and mechanical boundary and layer interface conditions. This is accomplished via the flexibility/stiffness matrix method. As a numerical illustration, the distributions of temperature and thermal stresses in a laminated anisotropic slab subjected to a uniform surface temperature rise are presented for various stacking sequences of fiber-reinforced layers.
The stress analysis of multilayered anisotropic media subjected to applied surface tractions is performed within the framework of linear plane elasticity. The solutions are obtained based on the Fourier transform technique together with the aid of the stiffness matrix approach. A general solution procedure is introduced such that it can be uniformly applied to media with transversely isotropic, orthotropic, and monoclinic layers. As an illustrative example, responses of the semi-infinite media composed of unidirectional and angle-ply layers to a given surface traction are presented.
This paper is concerned with the problem of suppressing the acoustic radiation pressure generated by a structure vibrating in air. The approach is to control the vibration of the modes of the structure most responsible for the radiation pressure. This control is carried out by active means, i. e., by feedback control. As a numerical example, the problem of active control of the far-field radiation pressure generated by the vibration of a simply-supported rectangular elastic plate is considered. The influence on the control effectiveness of various design parameters, such as the number of controlled modes, the choice of controlled modes, the number of actuators and the location of the actuators, is investigated. The conclusion is that, depending on the magnitude of the excitation frequency, satisfactory control can be achieved by using a sufficient number of actuators and by controlling a relatively large number of modes.
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