It seems as if you need to apply classic beam bending equations. For a leaf spring in three-point loading the induced surface stress is given by 3*P*L/(2*w*t*t) where P is applied load, L is the distance between the supports, w is the width and t is the thickness. Deflection in three-point loading is given by P*L*l*L/(4*E*w*t*t*t) where E is the elastic modulus.
