ISO 12110-2:2013

Overview

ISO 12110-2:2013, "Metallic materials - Fatigue testing - Variable amplitude fatigue testing - Part 2: Cycle counting and related data reduction methods", specifies cycle counting techniques and optional data reduction methods used when processing variable amplitude fatigue load histories for metallic materials. Cycle counting is mandatory for each test or test series; data reduction is optional. The standard applies equally to force, stress, or strain signals and is intended to support ISO 12110-1 (general principles, test method and reporting).

Key technical topics and requirements

• Cycle counting methods described include:
  • Level-crossing counting
  • Peak counting (including mean-crossing peak counting)
  • Simple range counting (and range-mean counting)
  • Range-pair counting
  • Rainflow counting (detailed in informative Annex A)
• Sampling and digitization:
  • Analog signals must be digitized; the standard recommends filtering to remove noise and a sampling density such that each analog cycle is represented by at least 20 digital points (sampling frequency ≳ 20× the observed maximum frequency).
• Pre-processing:
  • Extract peaks and valleys prior to cycle counting; establish levels/classes if required.
  • Filtering small excursions or specifying level thresholds to avoid counting insignificant cycles.
• Counting outputs and presentation:
  • Cycle counts, range-mean matrices, and summarized cycle distributions suitable for fatigue life estimation and test reporting. Annex C gives an example of result presentation for Rainflow counting.
• Selection guidance:
  • Selection of a counting method should consider the loading spectrum bandwidth and the irregularity factor. Rainflow is widely used but other methods may be preferred by industry sector.
• Scope exclusions (not covered):
  • Constant amplitude tests with isolated overloads/underloads, large structures, environmental/time-dependent effects (corrosion, creep, temperature interactions), and multiaxial loading.

Practical applications

• Processing in-service or test load histories for fatigue life prediction, test plan design, and formulation of variable-amplitude fatigue tests.
• Converting raw force/stress/strain signals into cycle counts usable in damage accumulation models (Miner’s rule, S–N or strain-life approaches).
• Test data preparation for laboratory fatigue testing, fatigue analysis of components where time/frequency effects and multiaxiality are not dominant.
• Commonly applied in automotive, aerospace, rail, and general mechanical component fatigue testing where variable amplitude loading is relevant.

Who should use this standard

• Fatigue test laboratories, materials engineers, structural and reliability engineers, test-data analysts, and manufacturers developing fatigue test programs or interpreting variable amplitude load histories.

Related standards

• ISO 12110-1 (General principles, test method and reporting requirements) - normative reference and companion document for variable amplitude fatigue testing.

Keywords: ISO 12110-2, cycle counting, Rainflow counting, variable amplitude fatigue testing, metallic materials, data reduction, peak counting, level-crossing, sampling, fatigue life prediction.