Materials Testing, Characterization and Quality Assurance
Materials Testing, Characterization and Quality Assurance tests your command of the mechanical test standards, the non-destructive methods, and the documentation chain that makes a result credible. The examiner rewards candidates who know what a test does not prove.
Mechanical testing
Tensile testing to ISO 6892-1 gives Rp0.2 by the 0.2% offset, Rm, elongation on a proportional gauge length and reduction of area; strain rate must be controlled in the elastic and yield regions, and machine compliance corrected if modulus is reported. Charpy V-notch testing to ISO 148-1 gives absorbed energy, lateral expansion and shear percentage - a comparative toughness index, not a design property. Hardness (Brinell HBW, Vickers HV, Rockwell HRC) is a cheap proxy; conversion tables in ISO 18265 are approximations and must not be written into acceptance criteria. Fracture toughness (KIC, CTOD, J) and fatigue testing to ISO 1099 require a stated geometry and analysis method.
Non-destructive testing
Penetrant finds surface-breaking defects in any non-porous material; magnetic particle finds surface and near-surface defects but only in ferromagnetic steel, never in austenitic stainless or aluminium; ultrasonic detects internal planar defects using a couplant and reference blocks; radiography images volumetric defects and depends on density contrast. Welds are judged against ISO 5817 quality levels, with procedures and personnel qualified to ISO 15614 and ISO 9606/EN ISO 9712.
The quality chain
Traceability runs from mill certificate to installed item. EN 10204 distinguishes 2.1 (declaration of compliance), 2.2 (non-independent test results), 3.1 (specific results from the manufacturer's authorised inspection representative) and 3.2 (independent inspection). Laboratory competence is shown by ISO/IEC 17025 accreditation with a stated measurement uncertainty; product quality systems by ISO 9001.
Worked example
A 12.5 mm bar (area 122.7 mm2) gives yield load 45 kN, maximum load 58 kN and 25% elongation. Then Re = 45 000/122.7 = 367 MPa, Rm = 473 MPa, ratio 1.29. Against EN 10025-2 S355 for thickness up to 16 mm (Re at least 355, Rm 470-630, A at least 22%) all three criteria pass. Against a B500B rebar specification the same bar fails on yield - the numbers must be judged against the correct product standard.
Traps
Reporting yield from the upper yield point without noting Luders behaviour; treating one specimen as the population; quoting hardness conversions as compliance; using magnetic particle inspection on austenitic welds; forgetting that radiography is poor at detecting tight planar cracks; accepting a 3.1 certificate as a substitute for receiving inspection.