Study of stress intensity factors near cracks in plates made of linearly viscoelastic fiber composites

For the first time a method is proposed for determining the stress intensity factors (SIF) near cracks in linear viscoelastic fiber composites using the data from polarization-optical measurements. The character of the change in the SIF in time near cracks in plates made of optically sensitive viscoelastic fiber composites exposed to constant tensile stresses (creep) was investigated. In describing the mechanical and optical properties of the materials, the composite was considered a homogeneous linearly viscoelastic orthotropic body. Equations were derived which correlate the fringe ordersm(t) with SIFK _j (j=1,2) and the longrange field stress _Ox in the vicinity of the apex of a crack whose direction coincides with the main direction of the axis of orthotropy. The SIF near linear cracks whose direction forms angles =90° and =45° with the direction of the tensile stresses were determined. It was found that the character of the change in SIF in time near cracks in creep, is a function of the angle between the direction of the crack and the direction of the tensile stress.Scientific-Research Institute of Mechanics, M. V. Lomonosov Moscow State University, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 3, pp. 321–328, May–June, 1997.