Orthotropic Laminae and Laminate:

For orthotropic, symmetric laminates with  and  laminae, the effective axial modulus and Poisson’s ratio is given as

(8.8)

where, the quantities with asterisk are for laminate as mentioned in Chapter on Laminate Theory. These properties can be measured directly from a tensile test on a specimen of thickness   under axial force per unit length  as follows:

(8.9)

The tensile strength is defined as the average stress at failure. Thus, the tensile strength can be given using the maximum applied force per unit length  and thickness   as

(8.10)

It should be noted that the failure of laminates is often influenced by inter laminar stresses along the free edge effects of the coupon. These factors will be explained in brief in one of the lecture.

The measurement of tensile strength by experiments can also provide information on the comparison of laminate theory with experiments.