A system for modifying a stiffness of a structure of a vehicle using vibrational energy of the vehicle includes a variable-stiffness layer, having a selectively controllable Young's modulus, attached to the structure, and a conversion layer, coupled to the variable-stiffness layer, the conversion layer configured to convert vibrational energy from the structure into electrical energy, and to supply the electrical energy to the variable-stiffness layer to adjust a stiffness of the variable-stiffness layer.