Journal of Aerospace Engineering

The deformation, failure, and low-cycle fatigue life of SCS-6/Ti-15-3 composites are predicted using a coupled deformation and damage approach in the context of the analytical generalized method of cells (GMC) micromechanics model. The local effects of inelastic deformation, fiber breakage, fiber-matrix interfacial debonding, and fatigue damage are included as submodels that operate on the microscale for the individual composite phases. For the laminate analysis, lamination theory is employed as the global or structural scale model, while GMC is embedded to operate on the mesoscale to simulate the behavior of the composite material within each laminate layer. While the analysis approach is quite complex and multifaceted, it is shown through comparison with experimental data to be quite accurate and realistic, while remaining extremely efficient.

The development of an overall strategy to estimate the material parameters for a class of recent viscoplastic and damage-material models is presented. The procedure is automated through an integrated parameter estimation scheme to enable the determination of an “optimum” set of material parameters by minimizing the errors between the experimental test data and the predicted response. The core ingredients are (1) the numerical experiment simulation analysis, which utilizes a finite-element-based solution scheme; (2) sensitivity analysis utilizing a direct-differentiation approach for the material response sensitivities; and (3) a gradient-based optimization technique of an error/cost function. This scheme is then applied to a variety of materials: (1) an anisotropic polymer matrix composite (PMC); (2) a 9Cr-1Mo material at 550°C; (3) a nickel-based Waspaloy at 700°C; and (4) a Cu-4 Cr-2 copper-based material at 200°C and 400°C. These first two materials were characterized for their deformation behavior, and the last two materials are characterized for both deformation and damage behavior. A rather comprehensive set of test conditions (e.g., uniaxial, multiaxial, and cyclic/ratcheting) is considered to demonstrate the scope and effectiveness of the approach.

This paper discusses active vibration control of an E-glass/epoxy-laminated composite beam using smart sensors and actuators. The smart sensors and actuators used in this study are piezoelectric ceramic patches. The composite beam is in a cantilevered configuration. Both theoretical and numerical (finite-element analysis) studies of the laminated composite beam are conducted to reveal the beam’s fundamental modal frequencies and modal shapes. The results based on the theoretical predication and numerical simulation are then compared with those from experimental modal testing, and a good correlation is obtained. Utilizing results from the model analysis and experimental modal testing, two control algorithms, namely, positive position feedback control and strain rate feedback control, are designed. Both single-mode vibration suppression and multimode vibration suppression are studied. An experimental apparatus has been developed to implement the control algorithms. The apparatus consists of a voltage amplifier and a data acquisition and real-time control system, in addition to the composite beam with bonded piezoelectric ceramic sensors and actuators. Experiments show that the proposed controllers can achieve active vibration damping of the composite beam.

The fan case in a jet engine is a heavy structure because of its size and because of the requirement that it contain a blade released during engine operation. Composite materials offer the potential for reducing the weight of the case. Efficient design, test, and analysis methods are needed to efficiently evaluate the large number of potential composite materials and design concepts. The type of damage expected in a composite case under blade-out conditions was evaluated using a subscale test in which a glass/epoxy composite half-ring target was impacted with a wedge-shaped titanium projectile. Fiber shearing occurred near points of contact between the projectile and target. Delamination and tearing occurred on a larger scale. These damage modes were reproduced in a simpler test in which flat glass/epoxy composites were impacted with a blunt cylindrical projectile. A surface layer of ceramic eliminated fiber shear fracture but did not reduce delamination. Tests on 3D woven carbon/epoxy composites indicated that transverse reinforcement is effective in reducing delamination. A 91-cm (36 in.) diameter full-ring subcomponent was proposed for larger scale testing of these and other composite concepts. Explicit, transient, finite-element analyses indicated that a full-ring test is needed to simulate complete impact dynamics, but simpler tests using smaller ring sections are adequate when the evaluation of initial impact damage is the primary concern.

This paper outlines several issues related to the design of sandwich structures with a truss-reinforced polymeric or hollow core. The first part of the paper employs a simple analytical model that illustrates the contribution of such a core to the structure’s facing stability. While the enhancement of the facing stability due to truss reinforcement is shown to be considerable, the problems of local strength and truss-element (pin) stability have to be analyzed prior to the acceptance of the design concept discussed in the paper. Accordingly, the second part of the paper presents the results of finite-element analysis used to pinpoint potentially weak elements in the considered design. The paper results in a number of practical conclusions and recommendations that may be useful for the development and implementation of sandwich structures with truss-reinforced cores.

This paper presents a simple model of the thermal transport caused by a source moving at high speeds along an infinite half-space. The steady-state solution is obtained and examined to determine the effects of source velocity on the effective thermal penetration depth. The temperature field produced for a particular set of boundary conditions is then expanded to indicate how an abrupt temperature application can create a stress wave response incorporating the relationships included in a well-known hydrocode.