Longitudinal polishing is a critical step in preparing tensile and fatigue specimens because it directly influences the accuracy, repeatability, and reliability of mechanical testing results. During machining operations such as turning or milling, surface irregularities and residual stresses can develop along the specimen’s gauge length. These imperfections often lead to premature crack initiation, localized strain concentration, or inconsistent stress distribution during testing.

By polishing along the longitudinal axis—the same direction as the applied test load—the NG-AutoPol system removes machining marks and surface defects without introducing cross-directional scratches or new stress points. This produces a smooth, low-stress surface that allows the specimen to deform naturally under load, providing true material behavior rather than surface-induced artifacts.

For fatigue testing, longitudinal polishing is especially vital: it prevents early crack initiation at micro-scratches and ensures that fatigue failure occurs due to intrinsic material properties.

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