Destructive and Mechanical Testing
Destructive testing sacrifices the specimen to quantify material or joint properties. Know the standard tests and what each measures. Tensile test yields yield strength, ultimate strength, elongation, and reduction of area; the stress–strain curve distinguishes elastic region (Young's modulus) from plastic. Hardness (Brinell, Rockwell, Vickers) is an indentation measure; conversions between scales are approximate and must not be treated as exact. Impact (Charpy/Izod) measures toughness/energy absorbed; results depend strongly on temperature and specimen orientation - ductile-to-brittle transition is a key concept. Bend test assesses ductility/formability of welds. Fatigue tests cyclic loading; creep tests time-dependent deformation at elevated temperature.
Traps: (1) Treating hardness conversion as exact equivalence. (2) Confusing strength with toughness - high strength can mean low toughness. (3) Ignoring that Charpy energy depends on temperature, notch geometry, and orientation. (4) Assuming a bend test gives a strength value - it gives pass/fail on ductility. (5) Forgetting specimen preparation and grip alignment affect tensile results.
Rule of thumb: report the test standard, specimen geometry/orientation, temperature, and rate - a number without these is meaningless. Worked example: a Charpy specimen tested at −20 °C absorbs 18 J versus 95 J at room temperature, indicating a ductile-to-brittle transition; a specification requiring ≥ 27 J at −20 °C would fail this material at that temperature despite passing at ambient.