%% Function name
%       maximumstress

%% Revised
%       16 January 2014

%% Author
%       Autar Kaw & Trey Moore
%       Section : All
%       Semester : Fall 2012

%% Purpose
%       Given ultimate strengths of a unidirectional lamina, angle of the 
%       ply in degrees, and the global stresses acting on the lamina, output
%       the strength ratio of the lamina based on maximum strain theory

%% Usage
%       function [SR] = maximumstress(stress_glo,angle,strength)
% Input variables
%       stress_glo=vector of global stress applied to unidirectional lamina
%       [stress_glo]=[sx;sy;txy]
%       sx=longitudinal global stress
%       sy=transverse global stress
%       txy=in-plane shear stress
%       angle=angle of ply in degrees
%       strength=vector of the five ultimate strain strengths of the 
%                unidirectional lamina
%       [strength]=[s1tu s1cu s2tu s2cu s12u] 
%       s1tu=ultimite longitudinal tensile strength
%       s1cu=ultimite longitudinal compressive strength
%       s2tu=ultimite transverse tensile strength
%       s2cu=ultimite transverse compressive strength
%       s12u=ultimite in-plane shear strength
% Output variable
%       SR=Strength Ratio
% Keyword
%       maximum stress failure theory
%       strength ratio
%       angle ply

%% License Agreement
%       http://www.eng.usf.edu/~kaw/OCW/composites/license/limiteduse.pdf

%% Code
function [SR] = maximumstress(stress_glo,angle,strength)
% Sine of the angle of the lamina
s=sind(angle);
% Cosine of the angle of the lamina
c=cosd(angle);
% Inverse Transformation Matrix
T=[c^2 s^2 2*s*c; s^2 c^2 -2*s*c; -s*c s*c c^2-s^2];
% Calculating the local strains
stress_loc=T*stress_glo;
if stress_loc(1)>0 
    SRp(1)=strength(1)/stress_loc(1);
end
if stress_loc(1)<0
    SRp(1)=-strength(2)/stress_loc(1);
end
if stress_loc(2)>0
    SRp(2)=strength(3)/stress_loc(2);
end
if stress_loc(2)<0
    SRp(2)=-strength(4)/stress_loc(2);
end
if stress_loc(3)>0
    SRp(3)=strength(5)/stress_loc(3);
end
if stress_loc(3)<0
    SRp(3)=-strength(5)/stress_loc(3);
end
% Defining the Strength Ratio Vector
SR=min(SRp);
end