This worksheet demonstrates the use of Maple for calculate plastic zone shapes and sizes for plane stress and plane strain for cracks under static loading. The sizes of plastic zones were obtained by equaling VonMises criteria (using Irwin's elastic solutions), to monotonic yield strength of material (Sy). For this reason, the shape and size of plastic zones showed here do not take into account the strain hardening of material within plastic zone. Sizes in polar coordinates r and theta are functions of quadratic relation between elastic stress intensity factor K and Sy (K/Sy)^2. For a established angle theta, the graphic shows the estimated sizes of plastic zones (coordinate r, in meters) for different relations of (K/Sy)^2. Parameters of procedure "plastic_zones" are n, Sy, Kini, Kfin and material, where n is the number of frames, Sy is the yield strength of material (in MPa), Kini and Kfin are the initial and final stress intensity factors (in MPa*m^1/2), respectively, which define the view frame.