Thermal insulating materials, Thermal insulation, Construction materials, Shear testing, Shear strength, Shear stress, Specimen preparation, Formulae (mathematics), Test specimens, Test equipment, Testing conditions, Adhesives, Mechanical testing, Reports. Shear strength is the ratio of the maximum force applied to the product, which will cause rupture along a plane parallel to the direction of the applied force, to the area of the plane on which the force acts. Shear modulus is shear stress divided by the corresponding relative deformation below the proportional limit, when the relationship is linear.