Quick questions on Material testing methods for QCE Engineering Unit 3

The tensile test is the workhorse of materials testing. A machined specimen of known cross-section and gauge length is clamped in a universal testing machine and pulled apart at a steady rate while the force and extension are recorded. Converting force to stress and extension to strain produces the stress-strain curve, from which you read Young's modulus (stiffness), the yield stress, the ultimate tensile strength and the ductility. Ductility is reported as the percentage elongation:

Hardness is resistance to local plastic deformation, scratching and wear. A hardness test presses a hard indenter into the surface under a known load and measures the size or depth of the indentation:

Toughness is the energy a material absorbs before fracturing, especially under a sudden blow. The Charpy and Izod tests clamp a notched specimen and strike it with a swinging pendulum hammer. The height the pendulum rises to after impact reveals the energy absorbed in fracturing the specimen, measured in joules. A tough material absorbs a lot of energy; a brittle one shatters with little.

The tests above destroy the specimen, so they are used on samples, not finished structures. To inspect an actual bridge weld or aircraft part without damaging it, engineers use non-destructive testing (NDT):