ASTM D256 & ISO 180 Test for Izod Impact

Written by Rahul Verma | Updated: October 18, 2025

Introduction

The Izod impact Test, governed by ASTM D256 and ISO 180 standards, is a popular method for determining a material’s impact strength (notch toughness) or capacity to absorb energy during a powerful strike.

Scope

Izod impact tests mainly use plastics, composites, and brittle metals. They use a notched specimen. Energy is specific; when the specimen fractures, the power may be determined by a swinging pendulum hammer. The test provides valuable information about a material’s breakability under impact loading conditions.

Test Procedure

The following table contains the test procedure based on ASTM D256 standards:

Steps	Description
Sample Size & Preparation	ASTM D256: Generally, a base sample size of 500 grams is suggested for fine totals, and a bigger size, from 10 to 50 kilograms, is indicated for coarse totals, contingent upon the total material size. ISO 180: Utilizes different sample dimensions compared to ASTM D256 but maintains the principle of selecting a sample size for the material tested. The standard specimen for ISO testing is a Type 1A multipurpose specimen with the end tabs removed. The resulting test sample measures 80 x 10 x 4 mm and is 8 mm beneath the notch.
Testing Machine	Izod Impact Tester: Use a pendulum-type impact tester, where a pendulum hammer is released from a fixed height and swings to strike the notched specimen. Pendulum Hammer: The pendulum should have a specified weight and be capable of swinging through a fixed arc. The test equipment should be appropriately calibrated.
Clamping the Specimen	The specimen is placed vertically into the testing machine and secured in a vice with the notch facing the direction of impact (usually perpendicular to the hammer swing).
Impact Test	The pendulum hammer is released and strikes the notched specimen with a known force.
Measuring Energy	The amount of energy the specimen absorbs is measured by observing the height to which the pendulum swings after impact.
Calculation	The energy absorbed by the specimen is calculated based on the height of the pendulum swing before and after impact.
Reporting Results	The final result is the energy absorbed by the specimen in ft-lb/in (foot-pounds per inch) or J/m (joules per meter), depending on the units used.

Result Analysis

The critical information obtained from the Izod Impact Test is the impact strength, represented by the energy absorbed during fracture. Higher values indicate a material’s ability to withstand impact loads without breaking. The following are a few key elements impacting the experimental outcomes:

Geometry and Depth of Notch: The notch geometry and depth affect the fracture initiation and energy absorption, which impacts the stress concentration at the notch tip.
Temperature: Temperature can impact the behavior of a material under impact. Usually, impact strength diminishes as temperatures decrease.

Considering these aspects when interpreting test results and comparing materials is essential. Also, the test guidelines (ASTM D256 and ISO 180) indicate that data correction models are needed for impact strength because of the material type and planning application.

Conclusion

Under ASTM D256 and ISO 180 standards, the Izod Impact Test is a pivotal tool for scrutinizing a material’s resilience to sudden impacts. High applicability for the material has been seen in cutting plastics, composites, and brittle metals, and some main insights into fracture resistance under different conditions. Further, it becomes essential to focus deeper on variables such as notch geometry, thermal impact, and specimen dimension to interpret results better. Besides fracture toughness, malleability, and comparisons with similar assessments, a broader approach has been applied regarding material efficiency. Thorough examination and scrutiny become the doors to engineering disciplines as engineers pave a path for discerning material choice.

FAQs

What is the purpose of the ASTM D256 Izod Impact Test?

The ASTM D256 Izod Impact Test measures the impact strength of materials, typically plastics, to determine their ability to resist sudden or forceful impacts.

What is the purpose of the ISO 180 Izod Impact Test?

The ISO 180 Izod Impact Test aims to determine a material's impact strength or toughness, typically plastics, by measuring its ability to resist a sudden, forceful impact.

What is the significance of the notch?

The notch is critical because it creates a weakened point in the specimen.

Can ASTM D256 be used for all types of plastics?

Yes, ASTM D256 can be used for thermoplastics, thermosets, and elastomers.