Charpy and Izod Impact Testing

The ability of a material to absorb energy during rapid fracture — its impact toughness — is a property that tensile testing alone cannot measure. A steel alloy may exhibit high tensile strength yet fracture in a brittle, catastrophic manner under sudden impact loading. The Charpy and Izod impact tests are the engineering world’s primary methods for quantifying this critical distinction between strong and tough, making them essential tools in the materials & manufacturing industry for material selection, quality control, and structural safety assurance.

What Is Impact Toughness and Why Does It Matter?

Impact toughness is the energy absorbed per unit cross-sectional area by a notched specimen subjected to a single, high-rate impact blow. It reflects a material’s resistance to crack propagation under dynamic loading conditions — conditions that occur in machine components, structural members, pressure vessels, and transportation equipment during service events such as collisions, drops, and pressure surges.

Materials that appear adequately strong under slow tensile loading may behave in a completely brittle manner under rapid impact — particularly at low temperatures, in the presence of notches or stress concentrations, and when they contain hydrogen or other embrittling species. Impact testing provides the experimental evidence needed to characterise this behaviour quantitatively.

Charpy Impact Testing

Test Principle and Setup (ASTM E23 / ISO 148-1)

In the Charpy test, a square-cross-section specimen with a machined notch (V-notch, U-notch, or keyhole notch) is supported horizontally between two anvils. A heavy pendulum hammer is released from a defined height and strikes the specimen at the midpoint opposite the notch. The energy absorbed during fracture is calculated from the difference between the initial and final pendulum heights.

ASTM E23 — Standard Test Methods for Notched Bar Impact Testing of Metallic Materials — and ISO 148-1 govern Charpy testing for metals. Standard V-notch specimens are 55mm × 10mm × 10mm with a 2mm deep, 45° V-notch.

Ductile-to-Brittle Transition Temperature (DBTT)

One of the most important applications of Charpy testing is characterization of the ductile-to-brittle transition behaviour of BCC metals (particularly carbon and low-alloy steels). As the temperature decreases, absorbed energy drops sharply over a transition temperature range. Above the DBTT, fracture is ductile (high energy absorption, fibrous fracture surface, shear lips). Below the DBTT, the fracture is brittle (low energy absorption, cleavage fracture surface).

Structural integrity codes — including ASME Boiler and Pressure Vessel Code Section VIII and EN 13445 — specify minimum Charpy impact energy requirements at defined test temperatures to ensure structural components remain tough under operating and upset conditions.

Izod Impact Testing

Test Principle and Setup (ASTM D256 / ASTM E23)

The Izod test differs from the Charpy in specimen orientation and clamping. The notched specimen is clamped vertically as a cantilever beam, with the notch facing the pendulum. The hammer strikes the free end above the notch. Like Charpy, the absorbed energy is measured from the pendulum height loss.

ASTM D256 governs Izod testing for plastics — the dominant application of this test method. For plastics, impact resistance is reported in ft·lb/in or J/m of notch width rather than total absorbed energy, normalising for specimen dimensions.

Izod testing is less common for metals than Charpy, but retains application in specific materials specifications and comparative evaluations.

Instrumented Impact Testing

Modern instrumented Charpy machines measure force-versus-time during impact, enabling calculation of initiation energy (energy to initiate crack propagation) and propagation energy (energy to propagate the crack to full fracture) separately. This provides richer information about fracture mechanics than total absorbed energy alone — particularly valuable for material development and failure investigation in the materials & manufacturing industry.

Temperature Conditioning for Impact Testing

Since impact toughness is strongly temperature-dependent, ASTM E23 specifies conditioning and transfer procedures for low-temperature and elevated-temperature testing. Specimens are conditioned in liquid nitrogen (−196°C), dry ice/solvent baths (−78°C), or temperature-controlled chambers, and transferred to the impact machine within 5 seconds to minimise temperature change before impact.

Conclusion

Charpy and Izod impact testing are fundamental methods for evaluating a material’s resistance to sudden, high-rate loading conditions. Unlike tensile testing, these tests reveal how materials behave under dynamic stress, distinguishing between ductile and brittle fracture behaviour. This is particularly critical for applications where unexpected impacts, low temperatures, or stress concentrations can lead to catastrophic failure.

By providing quantitative measures of impact toughness and enabling the determination of ductile-to-brittle transition temperature, these tests play a vital role in material selection, quality assurance, and safety compliance. In the materials and manufacturing industry, Charpy and Izod testing remain indispensable tools for ensuring structural integrity and reliable performance under real-world service conditions.

Partnering with Infinita Lab for Optimal Results

Infinita Lab addresses the most frustrating pain points in the Charpy and Izod Impact Testing process: complexity, coordination, and confidentiality. Our platform is built for secure, simplified support, allowing engineering and R&D teams to focus on what matters most: innovation. From kickoff to final report, we orchestrate every detail—fast, seamlessly, and behind the scenes.

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 (FAQs)