Abstract
The report describes a theoretical and experimental investigation of the stress distributions in vibrating cantilever blades of rectangular cross-section, pretwisted about their centroid axes. The reflecting layer photo-elastic technique was chosen for the investigation and a method is described by which stress free photo-elastic models of pretwisted cantilever blades may be constructed with inserted reflecting layers at their centroid axes. The flexural and edgeways bending stresses are calculated from observations of isochromatic fringe order at the edges of the blade. The stress distributions obtained photo-elastically are confirmed by electrical resistance strain gauge readings. Theoretical stress distributions are calculated from displaced shapes obtained by the Rayliegh Ritz method using a finite series of the characteristic functions of straight beams. There is close agreement between the theoretical and experimental stress distributions for the flexural modes, but there are some discrepancies in the distributions for the edgeways mode which was investigated, possibly due to end constraint effects.