Three-Dimensional Elasticity Solution for Sandwich Plates With Orthotropic Phases: The Positive Discriminant Case

2008 ◽  
Vol 76 (1) ◽  
Author(s):  
George A. Kardomateas
Keyword(s):  
Characteristic Equation ◽  
Orthotropic Material ◽  
Three Dimensional ◽  
Sandwich Plates ◽  
Elasticity Solution ◽  
Material Constants ◽  
Real Roots ◽  
Three Dimensional Elasticity ◽  
Rectangular Sandwich Plates ◽  
Positive Discriminant

A three-dimensional elasticity solution for rectangular sandwich plates exists only under restrictive assumptions on the orthotropic material constants of the constitutive phases (i.e., face sheets and core). In particular, only for negative or zero discriminant of the cubic characteristic equation, which is formed from these constants (case of three real roots). The purpose of the present paper is to present the corresponding solution for the more challenging case of positive discriminant, in which two of the roots are complex conjugates.

Three-dimensional elasticity solution for sandwich beams/wide plates with orthotropic phases: The negative discriminant case

2011 ◽  
Vol 13 (6) ◽  
pp. 641-661 ◽  
Author(s):  
George A. Kardomateas ◽  
Catherine N. Phan
Keyword(s):  
Composite Laminates ◽  
Three Dimensional ◽  
Sandwich Beam ◽  
Isotropic Case ◽  
Isotropic Phase ◽  
Sandwich Beams ◽  
Elasticity Solution ◽  
Positive Real ◽  
Three Dimensional Elasticity ◽  
Positive Discriminant

In an earlier paper, Pagano (1969) [Pagano NJ. Exact solutions for composite laminates in cylindrical bending. J Compos. Mater. 1969; 3: 398–411] presented the three-dimensional elasticity solution for orthotropic beams (applicable also to sandwich beams) for the cases of: (1) a phase with positive discriminant of the qudratic characteristic equation, which is formed from the orthotropic material constants and further restricted to positive real roots and (2) an isotropic phase, which results in a zero discriminant. The roots in this case are all real, unequal, and positive (positive discriminant) or all real and equal (isotropic case). This purpose of this article is to present the corresponding solution for the cases of (1) negative discrimnant, in which case the two roots are complex conjugates and (2) positive discriminant but real negative roots. The case of negative discriminant is frequently encountered in sandwich construction, where the orthotropic core is stiffer in the transverse than the in-plane directions. Example problems with realistic materials are solved and compared with the classical and the first-order shear sandwich beam theories.

Bifurcation of Equilibrium in Thick Orthotropic Cylindrical Shells Under Axial Compression

1995 ◽  
Vol 62 (1) ◽  
pp. 43-52 ◽  
Author(s):  
G. A. Kardomateas
Keyword(s):  
Axial Compression ◽  
Orthotropic Material ◽  
Shell Theory ◽  
Three Dimensional ◽  
Theory Of Elasticity ◽  
Elasticity Solution ◽  
Timoshenko Theory ◽  
Cylinder Axis ◽  
Dimensional Theory ◽  
Nonshallow Shell

The bifurcation of equilibrium of an orthotropic thick cylindrical shell under axial compression is studied by an appropriate formulation based on the three-dimensional theory of elasticity. The results from this elasticity solution are compared with the critical loads predicted by the orthotropic Donnell and Timoshenko nonshallow shell formulations. As an example, the cases of an orthotropic material with stiffness constants typical of glass/epoxy and the reinforcing direction along the periphery or along the cylinder axis are considered. The bifurcation points from the Timoshenko formulation are always found to be closer to the elasticity predictions than the ones from the Donnell formulation. For both the orthotropic material cases and the isotropic one, the Timoshenko bifurcation point is lower than the elasticity one, which means that the Timoshenko formulation is conservative. The opposite is true for the Donnell shell theory, i.e., it predicts a critical load higher than the elasticity solution and therefore it is nonconservative. The degree of conservatism of the Timoshenko theory generally increases for thicker shells. Likewise, the Donnell theory becomes in general more nonconservative with thicker construction.

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