Not just for carbon fiber vs steel, I went to a seminar and heard that the team was researching how to make the steel sheets used for car making to be 'stronger', so that, a car can be safer using their material. Then, when I asked what does it actually mean when they say their improved steel is 'stronger' than normal steel, and their answer was higher modulus. As far as I know, strength, young's modulus, and toughness are different things. strength means it can tolerate force more before plastic deformation, Young's modulus or stiffness means it bends lesser for the same force, Toughness means more energy to deform it, Then, about how the skin material of a car should be to make it safer for collisions, Isn't it toughness that should be higher? more energy to deform = consume energy from the collision and lesser shock to a driver ? Anyhow, we can see Ferraris literally scatteringly break when an accident happens. Then, 1) Why does higher strength mean more safety to the driver if it breaks anyway ? 2) or in case when force from the collision is smaller than the capable strength?