SHEAR-LAG BEHAVIOUR OF LAMINATED COMPOSITE BOX BEAMS

Abstract

According to elementary beam theory, bending stress distribution will be uniform across the width of the flange. However, in the case of wide flanged beams, longitudinal bending stress will no longer remain uniform and elementary beam theory is not applicable. The non uniform variation of longitudinal bending stress across the width of the beam gives rise to shear lag. The shear lag effect is enhanced due to the presence of orthotropy. Hence, - orthotropic materials suffers tremendous shear lag than conventional materials. Laminated composites, which are of orthotropic nature, earlier limited aerospace applications are gradually being applied in structural applications. Because of its orthotropic nature, study of shear lag effect in laminated composite box beams assumes foremost importance. Considerable amount of understanding on positive shear lag behaviour is available both on laminated composites and structures made of conventional materials. Hence, the present work intends to explore the negative shear lag behaviour in laminated composite box beams. Several gaps are identified and among all of them, effects of orthotropy on shear lag phenomenon is selected as the present problem. Orthotropy is induced through fibre orientations. The studies are planned to study the orthotropic effects by changing webs, top flange and bottom flange orthotropy. As a consequence, some important results are observed. It is observed that the top flange and web orthotropy has considerable influence, but bottom flange orthotropy found insignificant. Also, it is observed that length of negative shear lag region changes with change in orthotropy. Finally, generalisation of the behaviour is attempted through developed programme based on expressions for shear lag parameters 'K', `c.o'. Based on these studies generalized results which have practical significance are discussed