Impact test standards define the standardized procedures used to measure a material's resistance to fracture under rapid, dynamic loading, providing critical data for material qualification, quality control, and product safety compliance. This guide explains the principal international impact test standards published by ISO, ASTM, EN, GB, UL, and JIS, covering specimen requirements, test methods, measured parameters, and typical industrial applications.
Technical Overview
Impact testing, also referred to as shock or dynamic loading testing, evaluates how materials and components behave when subjected to rapidly applied forces at high strain rates. Unlike quasi-static tensile testing, impact testing reveals a material's toughness, its capacity to absorb energy before fracture, and its susceptibility to brittle failure under service conditions involving vibration, collision, dropping, or sudden loading. The results are essential for structural integrity assessments, welding procedure qualification, material certification, and product design validation.
Because absorbed impact energy is highly sensitive to specimen geometry, notch preparation, striking velocity, and test temperature, strict adherence to recognized standards is mandatory to ensure repeatability and comparability between laboratories. The major families of impact test standards include ISO 148 and ASTM E23 for metallic pendulum impact testing, ISO 179 and ISO 180 together with ASTM D6110 and ASTM D256 for plastics, EN ISO 148 for European harmonized metallic testing, GB/T 229, GB/T 1043, and GB/T 1843 for the Chinese national framework, the JIS Z 2242 and JIS K 7110 series for Japanese practice, and IEC 60068-2-27 for mechanical shock testing of finished equipment.
Depending on the method, results are expressed as absorbed energy in joules (J), impact strength per unit area (kJ/m² or J/cm²), impact resistance per unit width (J/m), or as a transition temperature at which a material changes from ductile to brittle behavior. Accredited third-party laboratories routinely perform these tests for certification, research, failure analysis, and incoming material inspection.
Testing Samples
Metallic Materials
The standard Charpy impact specimen for metals is a bar measuring 55 mm in length with a 10 mm × 10 mm square cross-section, machined with a V-notch 2 mm deep, having a 45° included angle and a 0.25 mm root radius. U-notch configurations with a 5 mm depth and 1.0 mm radius are also permitted under ISO 148 and ASTM E23 when specified by the product standard. When product thickness is limited, sub-size specimens of 7.5 mm or 5 mm width may be used with proportionally reduced acceptance values. Samples are typically taken from plate, pipe, forging, casting, or bar stock, and from weld joints, where base metal, weld metal, and heat-affected zone (HAZ) must frequently be evaluated separately.
Plastic Materials
Plastic impact specimens under ISO 179 and ISO 180 are commonly 80 mm × 10 mm × 4 mm bars, tested either unnotched or notched with A-type (0.25 mm radius), B-type (1.0 mm radius), or C-type (0.1 mm radius) notches. ASTM D256 Izod specimens measure 63.5 mm × 12.7 mm with thicknesses typically between 3.2 mm and 12.7 mm. Specimens are preferably injection molded under controlled conditions, since molding parameters, gate location, and internal stresses can significantly affect measured toughness.
Films, Sheets, Coatings, and Components
Flexible films are tested as circular or square specimens clamped in a falling-dart fixture per ISO 7765-1, ASTM D1709, or GB/T 9639.1. Rigid sheets and coated panels are evaluated with dart or ball drop methods such as ASTM D5420 and ASTM D2794. Finished products, sub-assemblies, and packaged goods are tested as complete items using drop and shock procedures defined by IEC 60068-2-27 or ASTM D4169 for distribution simulation.
Testing Items
Typical test items and reported parameters under recognized impact test standards include:
- Charpy V-notch absorbed energy (KV2, KV8) for metals, per ISO 148-1, ASTM E23, EN ISO 148, GB/T 229, and JIS Z 2242
- Charpy U-notch absorbed energy (KU2) for metals
- Izod impact strength of plastics, notched and unnotched, per ISO 180, ASTM D256, and GB/T 1843
- Charpy impact strength of plastics, edgewise and flatwise, per ISO 179-1, ASTM D6110, and GB/T 1043
- Tensile impact strength of plastics per ISO 8256 and ASTM D1822
- Instrumented puncture impact properties, including peak force, deflection at peak force, and total puncture energy, per ISO 6603-2
- Free-falling dart impact resistance (F50 failure mass) for films per ISO 7765-1, ASTM D1709, and GB/T 9639.1
- Ductile-to-brittle transition temperature (DBTT) determined from energy-temperature or fracture-appearance curves
- Shear fracture appearance percentage and lateral expansion for metallic fracture assessment
- Nil-ductility transition (NDT) temperature by drop-weight testing per ASTM E208
- Mechanical shock response of equipment, including peak acceleration, pulse duration, and pulse shape, per IEC 60068-2-27
Testing Methods
Pendulum Impact Testing (Charpy and Izod)
In the pendulum method, a weighted hammer arm is released from a raised position to swing through the specimen, which is supported on anvils (Charpy) or clamped as a cantilever (Izod). The machine directly indicates the energy absorbed in breaking the specimen, corrected for friction and windage losses. Metallic Charpy machines typically operate with capacities of 150 J, 300 J, or 450 J and a striker velocity of approximately 5.0 to 5.5 m/s, while plastics pendulums use lower capacities, commonly 0.5 J to 50 J, with velocities around 3.5 m/s. Machine verification follows ISO 148-2, ISO 179-2, and the calibration annexes of ASTM E23, combining direct geometric checks and indirect verification using certified reference specimens.
Instrumented Impact Testing
Instrumented machines fitted with strain-gauged strikers record the full force-time or force-deflection curve during the impact event, as standardized in ISO 14556, ASTM E2298, and GB/T 19748. This method separates the energy consumed in crack initiation from the energy consumed in crack propagation, providing far more diagnostic information than a single absorbed-energy value, and is particularly valuable for weld assessments, failure analysis, and advanced material development.
Falling Dart and Drop Weight Testing
Drop methods release a dart or weight from a controlled height onto a supported or clamped specimen. The staircase (bracketing) statistical procedure determines the impact mass at which 50% of specimens fail, while instrumented drop towers capture force and energy histories for rigid sheets, composites, and molded parts. Drop-weight tear testing and drop-weight NDT testing extend the principle to thick-section and pipeline steels, where run-arrest behavior is critical.
Tensile Impact Testing
Tensile impact testing, per ISO 8256 and ASTM D1822, strikes a dumbbell-shaped specimen held between a fixed grip and a crosshead, fracturing it in tension at high speed. It is used for materials too flexible to fail meaningfully in bending, such as very tough or elastomeric plastics, and reports tensile impact strength in kJ/m².
Temperature Conditioning and Transition Testing
Because body-centered cubic steels become brittle at low temperature, impact testing is frequently performed across a temperature range, typically from -196°C using liquid nitrogen baths to elevated temperatures, to construct transition curves. Specimens are conditioned at the target temperature with tolerances of ±1°C to ±2°C and must be broken within a short time, normally 5 seconds, after removal from the conditioning medium. Many structural steel specifications require a minimum absorbed energy of 27 J at the designated minimum service temperature.
Applications
Impact test standards underpin material qualification and safety verification across virtually every engineering sector:
- Pressure vessels, boilers, and piping: demonstrating adequate toughness at minimum design metal temperature, with weld joints and HAZ zones tested separately
- Oil and gas pipelines: verifying fracture resistance and shear area requirements for line pipe steels in low-temperature service
- Structural and bridge engineering: certifying steel grades under EN, GB, and ASTM product standards for seismic and cold-region applications
- Automotive: evaluating crash-relevant components, bumper materials, plastics, and composites under dynamic loading
- Aerospace: qualifying fasteners, castings, and alloys for damage tolerance and bird-strike or impact scenarios
- Electronics and electrical products: mechanical shock testing of devices and packaging per IEC 60068-2-27, and polymeric material evaluations under frameworks such as UL 746A
- Packaging and logistics: drop and shock simulation of transport packaging per ASTM D4169
- Plastics and consumer products: quality control of molded parts, films, and household goods against brittle failure
- Welding procedure qualification: impact testing of weld metal, fusion line, and HAZ as required by fabrication codes
FAQ
What is the difference between the Charpy and Izod test?
The Charpy test supports the specimen horizontally on two anvils and strikes the face opposite the notch, while the Izod test clamps the specimen vertically as a cantilever and strikes the notched face. Charpy testing dominates metallic materials, whereas Izod testing is most common for plastics under ASTM D256 and ISO 180.
Are ISO and ASTM impact results directly comparable?
No. Although the methods are conceptually similar, ISO and ASTM standards use different specimen dimensions, notch geometries, striker radii, support spans, and result units (kJ/m² versus J/m). Results must not be converted arithmetically between systems; the applicable standard must be agreed before testing.
What specimen size is required for a standard Charpy test?
The full-size metallic Charpy specimen is 10 mm × 10 mm × 55 mm with a machined notch. If the product thickness does not permit this, sub-size specimens of 7.5 mm or 5 mm may be used, with acceptance criteria adjusted in proportion to the specimen width according to the governing product standard.
Why are impact tests performed at low temperatures?
Many steels undergo a ductile-to-brittle transition as temperature decreases, meaning toughness can drop sharply in cold service. Testing at or below the minimum design temperature confirms that the material, weld, and HAZ retain sufficient absorbed energy to prevent catastrophic brittle fracture.
How are impact test results reported and what do the units mean?
Metallic results are reported in joules (J) as absorbed energy. Plastics results are normalized: ISO methods express impact strength in kJ/m² based on the cross-sectional area, while ASTM D256 expresses Izod resistance in J/m based on specimen width. Transition temperatures, shear area percentages, and lateral expansion may accompany the energy values.
How often must impact testing machines be verified?
Machines require direct verification after installation or major repair and periodic indirect verification, typically at intervals not exceeding one year, using certified reference specimens traceable to national metrology institutes, as specified in ISO 148-2, ISO 179-2, and ASTM E23.