Overview
ISO 10275:2020 specifies a standardized method for determining the tensile strain hardening exponent (n) for metallic flat products - sheets and strips. The standard defines the principle, test equipment, specimen requirements, test procedure and reporting for extracting n from the plastic portion of a uniaxial tensile stress–strain curve. The relationship used is the familiar power law: sigma = C · (epsilon_p)^n (or in log form ln sigma = ln C + n · ln epsilon_p). The method applies only where the stress–strain curve is continuous and monotonic; for serrated curves (Portevin‑Le Chatelier effect) the automatic linear‑regression procedure is recommended to ensure reproducible results.
Key topics and technical requirements
- Scope and principle: Determination of n from the uniform plastic strain region using either a manual least‑squares evaluation or an automatic linear regression on ln(true stress) vs ln(true plastic strain).
- Test environment: Ambient testing (10 °C to 35 °C), with controlled tests typically at (23 ± 5) °C when required.
- Equipment and calibration:
- Tensile testing machine verified per ISO 7500‑1 (class 1 or better).
- Extensometer per ISO 9513 (class 2; class 1 if also measuring plastic strain ratio r).
- Dimensional measurement capable to ISO 6892‑1 tolerances.
- Specimens: Sampling, machining tolerances and dimensions in line with product standards or ISO 6892‑1. Thickness is the full sheet thickness unless otherwise agreed.
- Test procedure:
- Strain rate in the plastic range should not exceed 0.008 s⁻¹ and must be constant over the interval used to determine n.
- For materials with yield‑point phenomena, lower and upper limits for the data range are specified (start of uniform hardening up to just before maximum force).
- Manual method: evaluate at a minimum of five points (geometric progression) using least squares on ln coordinates.
- Automatic method: linear regression on ln(true stress) vs ln(true plastic strain) over a plastic strain interval (minimum range 2%); useful for serrated curves.
- Calculation and reporting:
- Round n to 0.01.
- Test report must reference ISO 10275 and include material ID, specimen type, strain range(s) used, method (manual/automatic), results and any deviations.
Applications and users
ISO 10275 is essential for:
- Materials testing laboratories and quality control in sheet/strip production.
- Automotive, aerospace and appliance manufacturers requiring accurate forming data.
- Engineers performing forming simulation or finite element modeling who need validated strain‑hardening exponents.
- R&D teams evaluating alloy processing, tempering and formability.
- Procurement and certification bodies for supplier acceptance criteria.
Keywords: ISO 10275, tensile strain hardening exponent, strain hardening exponent n, sheet and strip, metallic materials, tensile testing, true stress, true plastic strain, Portevin‑Le Chatelier.
Related standards
- ISO 6892‑1 - Tensile testing at room temperature
- ISO 7500‑1 - Calibration/verification of tensile machines
- ISO 9513 - Extensometer calibration
- ISO 10113 - Determination of plastic strain ratio (r)
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