Symmetric laminate with MS layer at the mid plane

In the first case, a nine layer symmetric laminate beam [0/90/0/45/m/45/0/90/0] with MS layer in the middle is subjected to actuating current causing magnetostriction to develop in the MS layer leading to compression in it and equivalent balancing stresses in other layers. With increase in magnetostriction by increasing the current rating, the stress and strain level at various interfaces will increase. Variation of stress and strain at various interfaces including the MS layer and voltage induced in MS layer at the time of delamination are shown in Figures 32.1, 32.2 and 32.3.

Figure 32.1 Stress variations at various interfaces and in MS layer at the time of delamination when the laminate is subjected to only actuator current

Figure 32.2 Stress variations at various interfaces and in MS layer at the time of delamination when the laminate is subjected to only actuator current

Figure 32.3 Open circuit voltage in MS layer at the time of delamination when the laminate is subjected to only actuator current

Due to the symmetric stacking sequence and the assumption that only axial forces are acting, a number of interfaces can attain the delaminating stress simultaneously (1, 2, 7 and 8) and have theoretically equal chances of delamination. Fibers oriented in the longitudinal direction can bear the maximum stress while those oriented in the transverse direction could bear the least. Thus, fibers with 90⁰ orientations will make those layers reach the allowable stress for the layer at an early stage causing delamination. Figures 32.1, 32.2 and 32.3 show that at a stress of approximately 17.53 MPa, all the four interfaces involving 90⁰ fiber orientations will reach the delaminating stress and an open circuit voltage of around 57 mV is obtained in the sensing coil at this stress. The strain at the time of delamination is 223 micron in the laminate and a compressive stress of 58.3 MPa is developed in the MS layer.