Advanced High-Strength Steels are ever increasingly used in industry, and unlike mild steels the crack propagates through the weld nugget. At the present time, any method to measure the strength of the fusion zone is unavailable. Therefore a new test setup enforcing crack propagation through the weld nugget was developed. In the wedge test proposed, this device provides stable crack growth as the wedge is displaced. Thus, along with in situ observations, this device, without any prior assumptions is able to measure energy dissipation rate as well as crack opening angle. This is very significant because from these two data, a mechanical modeled was established to predict the cohesive energy and strength in the weld nuggets of AHSS. This method: the experimental setup and mechanical model were then applied to commercial alloys and synthetic grades successfully. This indicates that this methodology can be applied to any type of alloy.