Stiffness in materials engineering

Stiffness is shape retention capacity for stable deflection, absorption of energy and failure instabilities. Stiffness is defined by second moment of area and Young's modulus. Second moment of area is design aspect and Young's modulus is material property. Designs may be design of cross sections, bonding, solid or hollow sections and radius of gyrations. Stiffness in strut and panels are facts of density in weight and offsets
from density or anisotropy. Stiffness has main effects over mega structures as crash barrier to absorb kinetic energy.