Specially orthotropic lamina

A so-called specially orthotropic lamina is an orthotropic lamina whose principal material axes are aligned with the natural body axes ... 

Because of the presence of Q g and Q2e in Equation (2.84) and of 3 g and 326 f Equation (2.87), the solution of problems involving so-called generally orthotropic laminae is more difficult than problems with so-called specially orthotropic laminae. That is, shear-extension coupling complicates the solution of practical problems. As a matter of fact, there... 

For a single specially orthotropic layer of thickness, t, and lamina stiffnesses, Qjj, given in Equation (2.61), the laminate stiffnesses are... 

A very common special case of symmetric laminates with multiple specially orthotropic layers occurs when the laminae are all of the same thickness and material properties, but have their major principal material... 

The second special case is an orthotropic lamina loaded at angle a to the fiber direction. Such a situation is effectively an anisotropic lamina under load. Stress concentration factors for boron-epoxy were obtained by Greszczuk [6-11] in Figure 6-7. There, the circumferential stress around the edge of the circular hole is plotted versus angular position around the hole. The circumferential stress is normalized by a , the applied stress. The results for a = 0° are, of course, identical to those in Figure 6-6. As a approaches 90°, the peak stress concentration factor decreases and shifts location around the hole. However, as shown, the combined stress state at failure, upon application of a failure criterion, always occurs near 0 = 90°. Thus, the analysis of failure due to stress concentrations around holes in a lamina is quite involved. 

Angle-ply laminates have an equal number of laminae at +0 and —0 fibre orientations with equal thickness. It is quite easy to demonstrate that gle-ply laminates verify A16 = A26 = 0, based on the fact that 0i6(- ) = - 0ie( ) and 026(- ) = - 026( ) Hence angle-ply laminates are specially orthotropic. Contrary to cross-ply laminates, D16 0 D26 0, because the and -0... 

The macromechanical behavior of a lamina was quantitatively described in Chapter 2. The basic three-dimensional stress-strain relations for elastic anisotropic and orthotropic materials were examined. Subsequently, those relations were specialized for the plane-stress state normally found in a lamina. The plane-stress relations were then transformed in the plane of the lamina to enable treatment of composite laminates with different laminae at various angles. The various fundamental strengths of a lamina were identified, discussed, and subsequently used in biaxial strength criteria to predict the off-axis strength of a lamina. 

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