Stress trajectories in the presence of friction

We study the stress field around an oblique closed defect in polymethylmethacrylate (PMMA) plates under uniaxial compression in the presence of friction. Every specimen (PMMA plate) with a slot may be compared to an infinite plate with an elliptical cavity where the long axis is equal to the slot length. We have calculated the stress tensor for an elliptical oblique closed slot using the system of curvilinear co-ordinates defined by two families of ellipses and homofocal hyperbolas and we have plotted the isovalues and the stress trajectories in terms of the friction intensity.