$)$

$(cm($:$v_2\}$

given square, $in$ the undeformed $(deformed)$ configuration. They are defined $as$ follows:

$V_1=Ai+Bj$

$V_2=Ci+Dj$

and the corresponding deformed vectors

$v_1=ai+bj$

$v_2=ci+dj$

The deformation gradient tensor $t$ ras calculated $at$ the centroid $of$ each element, using equation $1.$

$\frac{?}{xI}$ AOMI$\left[\begin{array}{cc}a& c\\ \text{B}\text{A}\text{D}& ?\end{array}\right]=F*\left[\begin{array}{cc}A& C\\ B& D\end{array}\right],=>,F=\left[\begin{array}{cc}a& c\\ b& d\end{array}\right]{\left[\begin{array}{cc}A& C\\ B& D\end{array}\right]}^{-1}.$