Toughness is proportional to the amount of energy stored/put in to a material (or structure) when a stress is applied. Compact bone from the tibia has a tensile failure stress of 150 MPa and a tensile strain at failure of 1.5%. The anterior collateral ligament has a tensile failure stress of 35 MPa and a strain at failure of 30%. Which is probably mechanically tougher, the bone or the ligament? We calculated Young's Modulus for each but aren't sure of how to relate Youngs Modulus to Toughness.