Charpy V-Notch vs. Izod Impact Testing — Specimen Orientation, Striking Geometry & Which Industries Prefer Each
A technical guide explaining the difference between Charpy and Izod impact testing methods — specimen mounting orientation, notch and striking geometry, and why Charpy dominates metals testing (including nearly all forging specifications) while Izod remains more common in plastics testing. Shivam Forge, Rajkot, India. Call +91-9265772827.
Charpy and Izod impact testing both measure a material's impact toughness — the energy absorbed when a notched specimen is fractured by a swinging pendulum striker — using broadly similar pendulum test equipment, but the two methods differ in a specific, consequential way: specimen mounting orientation and where the pendulum strikes relative to the notch. In Charpy testing, the specimen is mounted horizontally, simply supported at both ends like a beam, with the pendulum striking the specimen's center directly opposite the notch. In Izod testing, the specimen is mounted vertically, cantilevered (fixed at one end like a diving board), with the pendulum striking the free end above the notch. This geometric difference means the two tests aren't simply interchangeable measurements of the same thing expressed in different units — they represent genuinely different loading configurations, which is part of why metals industry standards (including essentially all forging material specifications referencing impact toughness, such as low-temperature piping steel and pressure vessel grades) specify Charpy testing almost universally, while Izod testing remains more commonly associated with plastics and polymer material testing instead.
The Charpy specimen is mounted horizontally, simply supported at both ends across a fixed span, with the pendulum striker impacting the specimen's center directly opposite (behind) the notch — a three-point bending-like loading configuration at the moment of impact.
The Izod specimen is mounted vertically in a cantilever fixture, clamped rigidly at one end, with the pendulum striking the free (unsupported) end of the specimen above the notch — a cantilever bending loading configuration distinct from Charpy's simply-supported beam arrangement.
Both methods use standardized notched specimens (commonly V-notch geometry for Charpy, though other notch types exist for both methods), with specimen dimensions and notch geometry precisely standardized to ensure comparable, repeatable results between laboratories.
Because the loading configuration genuinely differs (simply-supported vs. cantilevered), Charpy and Izod results for the same material are not simply convertible to each other through a fixed conversion factor — they represent genuinely different test conditions, even though both report results in similar energy-absorbed units.
Essentially all metals and forging industry impact toughness specifications — low-temperature piping steel (like ASTM A350 LF2/LF3), pressure vessel grades, and general structural steel toughness requirements — specify Charpy V-notch testing, per ASTM E23 or equivalent standards.
Izod testing remains the more commonly specified method in plastics and polymer material testing (per ASTM D256 or equivalent), reflecting that industry's own historical standards convention distinct from metals testing practice.
Charpy V-notch impact testing is available for the metals and forging applications this site's material grade pages typically reference, following the standard convention those industries and applicable standards specify.
When reviewing an impact test report, confirming which method (Charpy or Izod) was used — and the specific specimen/notch configuration — is essential before comparing results against a specification's minimum requirement or against results from another source.
Impact toughness testing exists to answer a question standard tensile testing genuinely cannot address: how does a material behave under sudden, high-strain-rate loading, rather than the slow, controlled loading a tensile test applies? This distinction matters because some materials that perform adequately under slow loading can fail in a brittle, low-energy-absorbing manner under sudden impact, particularly at low temperature — precisely the failure mode low-temperature piping and pressure vessel steel specifications are designed to screen against through mandatory impact testing requirements.
Both Charpy and Izod testing measure this impact behavior using conceptually similar equipment — a pendulum of known mass and height swings down to strike a notched specimen, and the energy the pendulum loses (calculated from how high it swings past the specimen after fracture, compared to its initial height) represents the energy the specimen absorbed during fracture. This shared basic principle is where the similarity between the two methods largely ends, however, since the specimen mounting and strike geometry genuinely differ: Charpy's simply-supported horizontal specimen, struck at its center opposite the notch, creates a loading condition closer to three-point bending, while Izod's vertically cantilevered specimen, struck at its free end above the notch, creates a cantilever bending condition instead.
This geometric difference is precisely why Charpy and Izod results cannot be reliably converted between each other using a simple fixed factor, despite both being reported in similar energy units (joules or foot-pounds) — the specimens are experiencing genuinely different stress distributions and loading conditions at the moment of impact, meaning a material's Charpy result and its Izod result, while both reflecting the same underlying material toughness in some general sense, aren't measuring precisely the same thing and shouldn't be treated as interchangeable data points when reviewing specification compliance.
For customers requiring Charpy V-notch impact testing on forged components per applicable metals industry standards, Shivam Forge provides testing and documentation supporting your specification's low-temperature or general toughness requirements. Contact our quality engineering team at +91-9265772827 or sales@shivamforge.com with your component and test temperature requirement to discuss scope and quotation.
Charpy V-notch testing (per ASTM E23 or equivalent) is essentially universal across metals and forging industry impact toughness specifications, including low-temperature piping steel, pressure vessel grades, and general structural steel requirements. Izod testing is rarely, if ever, specified for metals applications.
Not reliably through a fixed conversion factor — the two tests use genuinely different loading configurations (simply-supported vs. cantilevered specimen), meaning results aren't directly interchangeable even though both are reported in similar energy-absorbed units. If a specification requires Charpy results, an Izod test result generally cannot substitute.
This largely reflects each industry's own historical standards development rather than one method being inherently superior — metals industry standards converged on Charpy V-notch testing, while plastics industry standards (like ASTM D256) converged on Izod testing, and each industry has continued that convention for consistency with decades of existing specification and historical data.
Yes. Charpy V-notch impact testing is available for material grades and applications requiring documented impact toughness verification, following standard metals industry convention and applicable specification requirements.
Confirm which method (Charpy or Izod) was used, the specific specimen and notch configuration, and the test temperature, since impact toughness is temperature-dependent — all of these details must match your specification's requirements before comparing the reported result against a minimum acceptance value.
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