I'm doing a research on anisotropic yield criteria for a FCC alloy and I have to do biaxial tensile experiments to get the yield locus in the biaxial stress space.I have two kinds of samples: 

         1. metal sheet with dimensions of 150mm x 70mm x 15mm(thickness); 

         2. rod with diameter of 20mm and length of 150mm. 

I'm new to this web,but I know this is a wonderful  forum for reserchers where you can discuss scientific problems with others.(some professors are  experts in their fields). I'm now studying anisotropic yield criteria,so I need  a graph software which can plot implicit funtions (such as  ellipse in the form of x^2-x*y+y^2=1) as well as experimental data.

I know Graph can plot implicit funtions,but the quality of  its graph is not good enough.Anyone knows other softwares please give me some advice,thanks in advance.