Overview
ISO 18872:2007 - Plastics - Determination of tensile properties at high strain rates describes a standardized approach to obtain reliable tensile properties of moulding and extrusion plastics across a wide range of strain rates, including the high rates relevant to impact-loading situations. Instead of attempting direct high-speed tests (which can introduce large experimental errors), the standard combines low/moderate-rate tensile measurements with mathematical modelling and extrapolation to calculate tensile response at high strain rates.
Key topics and requirements
- Scope and principle
- Uses measured stress–strain data at low and moderate speeds, models the stress vs true plastic strain curves, and extrapolates model parameters to high strain rates.
- Test speeds
- Mandatory speeds: 0.1, 1, 10 and 100 mm/s. Optional intermediate speeds: 0.3, 3 and 30 mm/s if needed for confidence in extrapolation.
- Specimen geometry
- Use standard ISO 527-2 specimen types for low-strain (yield-region) measurements.
- For post-yield/high-strain work, a reduced-width specimen with a circular waist and a small gauge length (~4 mm) is required to localize strain and improve accuracy.
- Apparatus and instrumentation
- Servo-hydraulic testing machines are recommended for speeds above ~10 mm/s.
- Use high-stiffness, low-mass force transducers (e.g., piezoelectric) and lightweight or non-contact extensometers to reduce resonance and measurement error.
- Data-acquisition rates must be sufficient to capture force and extensometer signals at the chosen test speeds.
- Measured and calculated quantities
- Engineering stress/strain, Poisson’s ratio, true stress, true strain, true plastic strain, plastic strain rate, and tensile modulus.
- Separation of elastic and plastic components and modeling of hardening curves to enable extrapolation.
- Referenced documents
Applications and who uses it
ISO 18872:2007 is used by:
- Materials and polymer engineers characterizing rate-dependent mechanical properties.
- Test laboratories performing plastics qualification for impact-prone applications.
- Product designers and finite element analysts who need rate-dependent hardening curves for simulation of dynamic events (impact, crash, drop tests).
- Failure analysts and regulatory bodies assessing performance under high strain-rate loading.
Practical benefits:
- Avoids unreliable direct high-speed testing by providing a reproducible extrapolation methodology.
- Produces inputs suitable for dynamic finite element modelling and design validation.
Related standards
- ISO 527-1: General principles for tensile testing of plastics
- ISO 527-2: Test conditions for moulding and extrusion plastics
- ISO 2818: Preparation of test specimens by machining
Keywords: ISO 18872:2007, tensile properties, high strain rates, plastics testing, true stress, true plastic strain, impact loading, tensile modulus, ISO 527.
