Showing papers by "Jack R. Vinson published in 2002"

Adhesive Layer Effects in Surface-Mounted Piezoelectric Actuators

Abstract: The role of the adhesive layers in active panels with surface-mounted (bonded) piezoelectric layers is studied. The investigation focuses on the strain transfer mechanism between the active layers and the host structure, the stress concentrations involved, and the influence of the geometrical and mechanical properties of the adhesive layers on the static response of the panel. The analysis is based on the High-Order approach and uses 2D elasticity to model the adhesive layers. The mathematical formulation is derived using variational principles, compatibility requirements, and the piezoelectric constitutive equations. Confirmation of the analytical model is achieved through an experimental study that reveals good agreement between the theoretical predictions and the behavior of the active structure. Numerical results are presented for a typical piezoelectric active panel and compared to detailed 2D finite element analysis. The results reveal the high-order effects and the stress concentrations in the tran...

Determination of moisture effects on impact properties of composite materials

Abstract: Many applications of structural materials involving composites include impact or dynamic loading in a humid environment. Composite materials are known to degrade when subjected to humid conditions, and therefore the humidity confounds the difficulty of determining the high strain rate behavior of composites. Several researchers have found that water absorption by composites causes degradation of matrix dominated quasi-static properties. However, very little is known of the effect of absorbed moisture on the high strain rate properties of polymer matrix composites, that are useful in the automotive, aerospace, and naval applications of composite structures. A Split-Hopkinson Pressure Bar facility is used herein to study the effect of absorbed moisture in high strain rate tests (200–1200/s) of a unidirectional IM7/8551-7 graphite/epoxy composite. The study includes dry, medium, and saturated moisture conditions. The tests show significant variation of high strain rate properties from static properties, and the reasons are identified. In addition, a better understanding of the effect of the matrix and fiber/matrix interface on the high strain rate properties of composites is achieved.

Analysis and Optimization of Foam-Reinforced Web Core Composite Sandwich Panels Under In-Plane Compressive Loads

Abstract: This paper presents the analysis and optimization of sandwich plates simply supported on all four edges with a foam-reinforced web core subjected to inplane compressive loads. Due to many failure modes of this kind of sandwich structure such as overall instability of the sandwich as a whole, face plate instability, face wrinkling and instability of the webs, the analysis of each mode is investigated and discussed in order to understand the physical behaviors of the whole structure and its components. Then, the sandwich plate subjected to a uniaxial compressive load is optimized for the minimum weight by taking into account the above four failure criteria. The “weakest link in the chain” concept is used, by which each of these assumed independent failure modes occurs at the same buckling stress in order to attain the minimum weight. Additionally, for any given set of materials, the optimum face thickness, web component thickness, web core component spacing, core depth, and foam core modulus for any values ...

Modeling of Tapered Sandwich Panels Using a High-Order Sandwich Theory Formulation

Abstract: A newly developed high-order sandwich theory formulation is presented, which enables the analysis of sandwich beams or plates with variable core thickness. The faces are assumed to be of constant thickness and may be inclined arbitrary angles α 1 and α 2 , respectively, relative to the sandwich panel reference plane. The core thickness may change linearly over the length of the sandwich panel. The core is modeled as a specially orthotropic solid possessing stiffness in the out-of-plane direction only, thus including the transverse core flexibility in the modeling. The faces are modeled as laminated beams or plates including bending-stretching coupling and transverse shear effects. To validate the proposed high-order theory, the numerical results are compared with results obtained from finite element analysis, and a close match is observed. Furthermore, to demonstrate the features of the developed high-order sandwich theory formulation, numerical results obtained for two different types of tapered sandwich beams in three-point bending are presented. The characteristics of the elastic responses of the two sandwich panel configurations are compared with special emphasis on the complicated interaction between the faces through the core material. The analyses show that severe localized bending effects are displayed in the vicinity of load introduction and support points and in the vicinity of points/locations of abrupt geometric changes. These localized bending effects induce severe stress concentrations and may severely endanger the structural integrity of the sandwich panels under consideration.

Conceptual design principles for non-circular pressurized sandwich fuselage sections: A design study based on a high-order sandwich theory formulation

Abstract: Results obtained as part of a design study regarding a non-circular pressurized sandwich fuselage section are presented. The originating problem is associated with preliminary studies for the “Global Range Transport” envisaged by the “New World Vistas” program of the United States Air Force. The modeling and analysis is conducted usinga high-order sandwich theory formulation in which the elastic response of each face laminate is accounted for, includingbending-stretching couplingand transverse shear deformations, and where the transverse flexibility of the core is included. The sandwich fuselage envisaged may contain flat, tapered and curved sandwich elements, and a high-order sandwich theory formulation is developed to analyze each of these configurations. The paper includes a presentation of the adopted high-order sandwich theory with special emphasis on the application for the analysis of sandwich panels with variable core thickness, and for the analysis of curved sandwich panels. Numerical results obt...

Low Temperature Effects on IM7/977-3 Cross-Ply Composite Material Properties at High Strain Rates

Abstract: Composite materials are used in a wide variety of low temperature applications because of their unique and highly tailorable properties. These low temperature applications of composites include their use in Arctic environments and most of them involve dynamic loads, for example, spacecraft applications where they use cryogenic engines, hypervelocity impact situations at very high altitudes, civil engineering applications in extreme cold regions, and offshore structures in cold regions. The U.S. Navy stated that under certain conditions naval vessels might encounter strain rates up to 1200/sec. Because the dynamic properties of composite materials may vary widely with both strain rates and temperature, it is important to use the dynamic properties at the expected temperatures when the loading conditions involve high strain rates and extreme temperatures. Very few materials have been characterized at high strain rates even at room temperature. Still less effort has been spent in trying to model the high strain rate properties to develop a predictive capability at room temperature. It has been hoped that earlier modeling for metals, such as Johnson and Cook [1], and Zerilli and Armstrong [2] might be used for composite materials. The Johnson-Cook model was modified by Weeks and Sun [3] for composite materials. Other recent modeling research has been performed by Theruppukuzki and Sun [4], Hsiao, Daniel and Cordes [5] and Tsai and Sun [6]. Woldesenbet and Vinson [7] have characterized the high strain rate and fiber orientation effects on one typical graphite/epoxy composite. Most of these characterizations model ultimate strengths only.Copyright © 2002 by ASME

Low Temperature Effects on E-glass/Urethane Composite Materials at High Strain Rates

Abstract: Composite materials are used in a wide variety of low temperature applications because of their unique and highly tailorable properties. These low temperature applications of composites include their use in Arctic environments and most of them involve dynamic loads. The U.S. Navy stated that under certain conditions naval vessels may encounter strain rate up to 1200/sec. Because the dynamic properties of composite materials may vary widely with strain rate it is important to use these dynamic properties when the loading conditions require it. All too few materials have been characterized both at high strain rates and at low temperature. Still less effort has been spent in trying to model the high strain rate properties to develop a predictive capability. It has been hoped that earlier modeling for

On the Modeling of the Mechanical Properties of Composite Materials at High Strain Rates

Abstract: High strain rate compressive and tensile ultimate strength properties for a wide variety of composite materials as function of strain rate are modeled, using the Weeks — Sun equation. These include unidirectional, quasi-isotropic and woven composites, made of glass, graphite and aramid fibers in various thermoset and thermoplastic polymeric matrices. Through modeling, using the Weeks — Sun equation, dynamic composite material properties can be easily used in the design and analysis of composite material structures rather than static material properties. By doing so, excess weight or unexpected failure may be avoided.