Materials examination scales At which observation scale is the macro-structure of a material generally examined during routine inspections or fracture analysis?

Introduction / Context:
Materials are examined at multiple size scales, from macroscopic features visible without aids to atomic-scale structures. Macro-examination is the first, simplest step and often reveals manufacturing defects, heat-treatment issues, and fracture features before more advanced methods are used.

Given Data / Assumptions:

• Macro-structure refers to features visible without high magnification.
• Typical targets: surface discontinuities, large inclusions, flow lines, weld beads, gross segregation, and fracture patterns.
• No special etching or polishing is necessarily required at this stage.

Concept / Approach:
Macro-structure is evaluated by the unaided eye (or at most with a low-power lens). This contrasts with microstructure, which requires optical or electron microscopy after careful sample preparation. X-ray methods probe internal defects and crystallography, not macro-structure per se.

Step-by-Step Solution:
Define macro-structure: features observable at low magnification or no magnification.Relate to inspection practice: visual inspection, dye penetrant background assessment, fracture surface macroscopic morphology.Therefore, “naked eye” is the appropriate tool for macro-structure.Higher-magnification devices move into microstructure or sub-surface analysis.

Verification / Alternative check:
Quality-control workflows begin with visual examination before advancing to metallography or NDT (ultrasonic, radiography).

Why Other Options Are Wrong:
Optical/metallurgical microscopes target microstructure; X-ray methods are NDT tools for internal characterization; SEM is far beyond macro-scale.

Common Pitfalls:
Assuming any microscope examination is still “macro” because of large field of view; by convention, macro-structure is unaided or very low power only.

Final Answer:
naked eye