Impact toughness testing is a critical evaluation method for determining how new and advanced materials resist sudden dynamic loads and fracture under high strain rates. This article provides a comprehensive technical overview of impact toughness testing for new materials, covering test specimens, testing items, internationally recognized methods such as Charpy and Izod impact, and their applications across aerospace, automotive, and new energy industries.
Technical Overview
Impact toughness is a measure of a material's capacity to absorb energy during plastic deformation and fracture under rapidly applied dynamic loading. For new and advanced materials—including next-generation alloys, fiber-reinforced composites, engineering polymers, technical ceramics, and additively manufactured components—impact toughness is one of the most important mechanical properties for assessing structural reliability and service safety.
Unlike quasi-static tensile testing, impact toughness testing subjects a notched or unnotched specimen to a high strain rate, typically in the range of 10² to 10³ s⁻¹, using a swinging pendulum, a falling weight, or an instrumented impactor. The energy absorbed during fracture reveals a material's susceptibility to brittle failure, which is especially relevant for materials operating in low-temperature environments, under vibration, or in crash-relevant structures.
Accredited third-party laboratories perform impact toughness testing in accordance with internationally recognized standards published by ISO, ASTM, EN, GB, and JIS. Typical capabilities include room-temperature and low-temperature (down to liquid nitrogen temperatures of −196 °C) impact testing, instrumented impact analysis, and full fracture surface characterization.
Testing Samples
Metallic New Materials
Advanced metallic materials form the largest category of samples for impact toughness evaluation. Common sample types include advanced high-strength steels (AHSS), low-temperature steels for LNG and cryogenic service, aluminum-lithium alloys, titanium alloys, magnesium alloys, high-entropy alloys (HEAs), amorphous alloys, metal matrix composites, and powder metallurgy products. Welded joints, heat-affected zones (HAZ), and additive manufactured (3D-printed) metal parts are also frequently tested because these regions often exhibit reduced toughness compared with the base material.
Polymer and Rubber Materials
Engineering plastics, thermoplastics, thermosetting resins, modified polymers, biodegradable plastics, and elastomeric materials are tested to evaluate their resistance to impact-induced cracking. Specimens may be notched or unnotched, depending on the applicable standard and the information required.
Composite Materials
Fiber-reinforced polymer composites, including carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) laminates, honeycomb sandwich structures, ceramic matrix composites, and hybrid laminates, are evaluated for impact damage tolerance. Impact testing helps identify delamination, fiber breakage, and energy absorption characteristics critical for structural design.
Ceramics and Inorganic Non-Metallic Materials
Structural ceramics, glass-ceramics, functional ceramics, and architectural glass products are tested using specialized impact methods such as ball drop, dart drop, and small-particle impact to characterize their brittle fracture behavior and surface damage resistance.
Coatings, Films, and Thin Products
Functional coatings, protective films, packaging materials, and metal sheets are assessed using drop weight, free-falling dart, and reverse impact methods to evaluate adhesion integrity and puncture resistance under dynamic loading.
Testing Items
Impact toughness testing programs for new materials typically cover the following measurement items:
- Charpy V-notch and U-notch impact absorbed energy (KV2, KV8, KU2), expressed in joules (J)
- Izod impact strength, expressed in kJ/m² or J/m
- Ductile-to-brittle transition temperature (DBTT) determined from transition curves
- Lateral expansion of fractured metallic specimens, expressed in millimeters
- Fracture appearance assessment, including percent shear fracture area (SFA) and fibrous fracture ratio
- Drop weight and falling dart impact failure energy for polymers, composites, and sheets
- Instrumented impact parameters, including maximum force, energy at maximum force, initiation energy, and propagation energy derived from force–displacement curves
- Multi-axial impact and puncture resistance for thin sheets and molded components
- Temperature-dependent impact behavior at elevated or sub-zero temperatures
Testing Methods
Charpy Pendulum Impact Test
The Charpy test is the most widely used method for metallic materials. A notched beam specimen (typically 10 mm × 10 mm × 55 mm) is supported horizontally at both ends and struck at mid-span by a swinging pendulum hammer. The absorbed energy is calculated from the difference in pendulum height before and after fracture. Primary standards include ISO 148-1, ASTM E23, EN 10045-1, GB/T 229, and JIS Z 2242. The test can be performed at ambient temperature or at controlled low temperatures to construct transition temperature curves.
Izod Impact Test
In the Izod configuration, a notched specimen is clamped vertically as a cantilever beam and struck near its free end by the pendulum. This method is predominantly applied to plastics and light metals. Governing standards include ISO 180, ASTM D256, ASTM D4508, and GB/T 1843. Results are reported as impact strength normalized by specimen width or notch width.
Drop Weight and Falling Dart Impact Test
Drop weight methods apply a known mass from a controlled height onto a supported specimen, allowing flexible energy selection across a wide range. These methods are suited to polymers, composites, coatings, packaging, and sheet products. Common standards include ASTM D5628, ASTM D5420, ASTM D7136, ISO 6603-2, ISO 7765-1, and GB/T 11548. Statistical procedures such as the staircase (bruceton) method are used to determine the 50 percent failure energy.
Instrumented Impact Test
Instrumented impact systems incorporate force and displacement sensors on the striker, recording complete force–displacement–energy curves throughout the impact event. This enables separation of crack initiation energy from crack propagation energy and detailed analysis of failure mechanisms. Relevant standards include ISO 14556, ISO 6603-2, and ASTM E2298.
Drop-Weight Tear Test (DWTT)
For thick-section pipeline steels and pressure vessel plates, the drop-weight tear test evaluates fracture appearance over a full plate thickness under dynamic loading. Applicable standards include ASTM E436 and API RP 5L3, and the result is expressed as the percent shear fracture area at a given temperature.
Applications
Impact toughness testing of new materials supports material qualification, design verification, and quality control across numerous advanced industries:
- Aerospace: qualification of aluminum-lithium alloys, titanium structures, composite airframe laminates, and additively manufactured flight hardware against bird strike and impact damage tolerance requirements.
- Automotive and new energy vehicles: validation of advanced high-strength steel body structures, crash components, battery pack housings, and polymer interior materials requiring impact performance at low temperatures.
- Rail transit: evaluation of structural steels, welding joints, and interior polymer materials for rolling stock operating in cold-climate service.
- New energy sector: impact assessment of wind turbine blade composites, photovoltaic module glass and backsheets, and cryogenic materials for LNG storage and hydrogen service.
- Construction and infrastructure: verification of structural steel toughness, seismic dampers, polymer pipes and fittings, and safety glazing products.
- Electronics and consumer goods: impact durability testing of enclosures, connectors, display covers, and packaging materials under drop and multi-axial impact conditions.
- Marine and offshore engineering: determination of toughness for hull steels, riser materials, and welded joints subject to low-temperature and dynamic loading environments.
- Research and development: characterization of novel alloys, nanostructured materials, and bio-based polymers to support material innovation and standards development.
FAQ
What is the difference between Charpy and Izod impact tests?
The Charpy test strikes a horizontally supported beam specimen at mid-span, and is primarily used for metals, while the Izod test strikes a vertically clamped cantilever specimen near its free end, and is primarily used for plastics. Both methods measure absorbed energy, but specimen geometry, support conditions, and reporting units differ according to the applicable standard.
What is the ductile-to-brittle transition temperature (DBTT)?
DBTT is the temperature range over which materials with body-centered cubic crystal structures, such as ferritic steels, transition from ductile, high-energy fracture to brittle, low-energy fracture. It is determined by testing replicate specimens at a series of temperatures and plotting absorbed energy, lateral expansion, or shear fracture percentage against temperature.
Can impact toughness testing be performed at low temperatures?
Yes. Accredited third-party laboratories routinely conduct impact testing at temperatures down to −196 °C using liquid nitrogen cooled baths, as well as at elevated temperatures, to evaluate temperature-dependent toughness behavior for cryogenic, arctic, and high-temperature applications.
What specimen dimensions are required?
For metallic Charpy testing, the standard full-size specimen is 10 mm × 10 mm × 55 mm with a 2 mm V-notch or specified U-notch. Sub-size specimens (for example, 7.5 mm or 5 mm thickness) may be used when material thickness is limited. Polymer and composite specimens follow the dimensions defined in the respective ISO, ASTM, or GB standards.
How many specimens are needed for a valid test program?
A single-temperature Charpy test typically requires at least three specimens. For transition temperature determination, a minimum of ten to twelve specimens spread across the transition range is recommended. Statistical methods such as the staircase approach may require twenty or more specimens for drop weight testing.
Why is impact toughness important for new materials?
Many new materials exhibit excellent static strength but may behave unpredictably under dynamic loading due to notch sensitivity, microstructural anisotropy (especially in additive manufacturing), or low-temperature embrittlement. Impact toughness testing provides essential data to ensure structural integrity, prevent catastrophic brittle fracture, and support certification of new materials for safety-critical applications.
Which standards are most commonly referenced?
Frequently used standards include ISO 148, ISO 179, ISO 180, ISO 6603-2, ISO 14556, ASTM E23, ASTM D256, ASTM D6110, ASTM D5628, ASTM E436, EN 10045, GB/T 229, GB/T 1043, GB/T 1843, and JIS Z 2242. Test plans should always specify the exact standard edition appropriate to the material and end use.