Methods to accurately determine the maximum bending moment Mb for a spot weld are provided. The methods include subjecting a test coupon including a spot weld, to a coach peel test and monitoring the test coupon using digital image correlation in order to determine the bending moment arm length at peak force. The bending moment arm length at peak force is multiplied by the peak force value to provide an accurate maximum bending moment for the spot weld. The calculated maximum bending moment Mb is used in a combined force based spot weld failure calculation to predict failure of a spot weld under a combined loading condition.