Do You Know More About the Perfect Impact Test?
What Is Impact Testing?
Impact testing is a fundamental mechanical testing method that evaluates a material’s ability to absorb energy and resist fracture when subjected to a sudden, high-velocity load — a condition fundamentally different from the slow, controlled loading of tensile or flexural testing. The ability to withstand impact without fracture (toughness) is one of the most critical engineering properties for components that experience shock loads, drops, collisions, or rapidly applied forces in service.
Impact testing bridges the gap between controlled laboratory stress and real-world dynamic loading — revealing brittle behavior, notch sensitivity, temperature effects on toughness, and the energy absorption capacity of metals, polymers, composites, and ceramics that static tests alone cannot capture.
Why Impact Toughness Is Distinct from Strength
A material can be very strong — able to withstand high static loads — yet be completely brittle under impact. High-carbon steel, glass, and certain engineering ceramics are examples of materials with high compressive strength but low impact toughness. Conversely, a relatively soft, ductile material such as annealed low-carbon steel or thermoplastic elastomer can absorb enormous impact energy through plastic deformation without fracturing.
Understanding this distinction is critical for design engineers — selecting materials that are not just strong enough but tough enough for their intended dynamic service environment.
Major Impact Testing Methods
Charpy Impact Test (ASTM E23, ASTM D6110)
In the Charpy test, a notched specimen is placed horizontally on two supports and struck in the center from behind the notch by a swinging pendulum hammer. The energy absorbed during fracture is measured from the reduction in pendulum swing height after breaking the specimen.
Charpy for Metals (ASTM E23): Standard specimen is 10×10×55 mm with a 2 mm deep V-notch, U-notch, or keyhole notch. Used extensively for structural steels, pressure vessel steels, weld qualifications, and alloy development. Charpy V-notch (CVN) impact testing at multiple temperatures establishes the ductile-to-brittle transition temperature (DBTT) — a key design parameter for structural steels in cold environments.
Charpy for Plastics (ASTM D6110): Adapted for polymer specimens — smaller standard dimensions and modified striker geometry appropriate for the lower toughness range of most polymers. Both notched and unnotched Charpy tests are used.
Izod Impact Test (ASTM E23 for metals, ASTM D256 for plastics)
In the Izod test, the specimen is clamped vertically in a vise, and the pendulum strikes the free, notched end. Unlike Charpy (supported beam, struck from behind), Izod is a cantilevered beam test — struck from the front above the notch.
Izod for Plastics (ASTM D256): The most widely used impact test for plastics. Notched Izod impact (Method A) is the standard for comparing polymer grades and characterizing notch sensitivity. Unnotched Izod (Method E) eliminates notch effects to measure inherent material toughness. Results are reported in J/m or ft·lbf/in of notch.
Notch Sensitivity: The ratio of notched to unnotched Izod values reveals a material’s notch sensitivity — the degree to which a stress concentration reduces impact resistance. Highly notch-sensitive materials require careful attention to part design (avoiding sharp corners and abrupt section changes).
Drop Weight Impact Test (ASTM D7136, ASTM G14)
A defined mass is dropped from a defined height onto a flat composite or plastic panel. This geometry more closely simulates actual impact events (tool drops, hail, foreign-object impacts) than pendulum tests do. ASTM D7136 is the standard for low-velocity impact damage resistance of fiber-reinforced polymer (FRP) composite panels — critical for aerospace structural composite qualification.
Falling Dart (Falling Weight) Impact Test (ASTM D5420, D5628)
For thin films, sheets, and flexible packaging, a weighted dart is dropped onto a clamped specimen. The drop height or weight at which 50% of specimens fail (F₅₀) characterizes the impact resistance of flexible materials.
Gardner Impact (ASTM D5420)
A hemispherical punch is driven into the specimen by a falling weight. Widely used for sheet metal coatings, plastic films, and packaging materials — characterizing resistance to deformation-associated coating cracking and adhesion loss.
Temperature Effects on Impact Properties
One of the most important applications of impact testing is the characterization of the ductile-to-brittle transition temperature (DBTT) of structural steels. Below the DBTT, steels fracture in a low-energy, brittle manner with little warning — a catastrophic failure mode that has historically caused numerous ship hull fractures and structural failures. By testing at multiple temperatures and plotting absorbed energy vs. temperature, the DBTT is defined — establishing the minimum safe service temperature for structural steel applications.
Industry Applications
Structural Steel: Charpy CVN testing at specified temperatures qualifies structural, pressure-vessel, and pipeline steels for cold-temperature service — a requirement on offshore platforms, cryogenic vessels, and Arctic structures.
Automotive: Polymer bumper systems, instrument panels, door panels, and safety components undergo Izod and drop weight impact testing to ensure occupant protection in crash events.
Aerospace: Composite fuselage panels, wing skins, and structural components undergo ASTM D7136 impact testing to characterize damage tolerance — the ability to sustain service loads after an impact damage event.
Packaging: Drop-weight and falling-dart tests qualify corrugated boxes, clamshell containers, and flexible film packaging for their ability to protect products during shipping and handling.
Electronics: Housings, screen protectors, and portable device enclosures are tested for impact resistance to simulate drops during consumer product qualification testing.
Conclusion
Impact testing — spanning Charpy, Izod, drop weight, falling dart, and Gardner methods per ASTM standardized protocols — provides the toughness and energy-absorption data critical for qualifying metals, polymers, composites, and packaging across structural, automotive, aerospace, and consumer-product applications. Selecting the right test method for the material, geometry, and service loading conditions determines whether a component possesses not just sufficient strength but the dynamic toughness required to survive real-world shock, drop, and impact events — making impact characterization as essential to safe material selection as any static mechanical test.
Why Choose Infinita Lab for Impact Testing?
Infinita Lab is a leading provider of impact testing services and streamlined material testing, addressing the critical challenges faced by emerging businesses and established enterprises. With access to a vast network of 2,000+ accredited partner labs across the United States, Infinita Lab provides rapid, accurate, and cost-effective Charpy, Izod, drop-weight, and falling-dart impact testing solutions in accordance with ASTM and ISO standards.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote.
Frequently Asked Questions
What is the difference between Charpy and Izod impact tests? Charpy uses a horizontally supported, simply supported notched beam struck from behind — providing absolute energy absorption in joules. Izod uses a vertical, cantilevered notched specimen struck from the front — results reported per unit notch width. Charpy is standard for metals; Izod is dominant for plastics. Both provide toughness information but are not directly comparable.
What is the ductile-to-brittle transition temperature (DBTT)? DBTT is the temperature below which a material transitions from ductile (high-energy, plastic fracture) to brittle (low-energy, cleavage fracture) failure under impact. For structural steels, this transition typically occurs between -20°C and +20°C depending on chemistry and heat treatment — and must be known for safe design of cold-temperature structures.
Why is the notch important in impact testing? The notch creates a stress concentration that simulates real surface defects, scratches, and geometric discontinuities that components encounter in service. Notched impact tests reveal notch sensitivity — how much a stress concentration reduces toughness — which is critical information for part design and material selection.
Which impact test is standard for comparing plastic grades? Notched Izod impact testing per ASTM D256 is the dominant standard test for comparing and specifying plastic material grades. It is performed at standard laboratory temperature (23°C) and often also at -30°C or -40°C to evaluate low-temperature impact performance.
What ASTM standards govern impact testing for metals vs. plastics? For metals: ASTM E23 (Charpy and Izod methods). For plastics: ASTM D256 (Izod) and ASTM D6110 (Charpy). For composites: ASTM D7136 (drop weight impact). For films and sheets: ASTM D5420 and D5628 (falling weight/dart methods).
