ASTM D256, ISO 180 Determination of Izod Pendulum Impact Resistance of Plastics

    ASTM D256 Introduction

    ASTM D256 (Determination of Izod Pendulum Impact Resistance of Plastics) measures the Izod pendulum impact resistance of polymers. The force it takes to initiate a fracture and continue the process until the specimen fractures is called the “Izod impact.” The test method can evaluate the energy required for fracture initiation and fracture propagation in plastic. It usually applies to polymers and can compare the toughness of the materials and verify their unparalleled impact characteristics.

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    Get Certified ASTM D256 for Plastic Impact Strength

    ASTM D256 certification is a standardized measurement of Izod pendulum impact resistance of plastics. Compliance checks the plastic materials to absorb abrupt impact forces without breaking. It is a test procedure by ASTM International that is more commonly applied to assess the toughness and durability of plastic substances.

    The image shows the Izod pendulum impact apparatus used in determining the resistance of a plastic sample by  ASTM D256.
    An Izod Pendulum Impact Apparatus

    Scope of ASTM D256

    • Includes the findings of the Izod pendulum impact resistance of plastic substances.
    • Tests the hardness and impact of plastics.
    • Can be applied to thermosetting and rigid thermoplastics.
    • Assists in material comparison and quality control tests.
    • Offers standardized procedures of impact testing.

    ASTM D256 Equipment and Sample Preparation 

    Specimen DetailsSolid, uniform rectangular specimens are preferred. 
    Specimen dimensionsThe overall sample size is 3.0-12.7 mm (0.118-0.500 in.), on average. The specimen is 6.3mm thick, and the notch depth is 10.2mm.
    Specimen preparationThe analyst prepares specimens by injection-molding or by cutting them from extruded or molded sheets or plates.

    Applications of ASTM D256

    • Plastic products and components quality control.
    • Testing of plastic material used in automotive parts.
    • Plastic housing and consumer products testing.
    • Impact-resistant polymers research and development.
    • Comparison of various plastic make-ups.

    Common Challenges and Troubleshooting 

    Poor specimen preparation, environmental conditions, machine calibration, sample handling and storage, and test setup inconsistencies are some of the challenges experienced during testing. Troubleshooting these problems would require proper specimen preparation, a consistent testing environment, proper calibration of the impact testing machines, and proper specimen handling.

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    Aggregate Testing Technique, Process, and Data Collection

    Normal notched plastic samples are installed in an Izod impact tester. The puncture of the specimen is performed with a pendulum hammer, which fractures the specimen. The instrument measures the energy taken during breakage and records it to determine the impact resistance of the material.

    Testing Procedure and Requirements


    The analyst prepares and mounts a notched specimen vertically in the Izod impact tester with the notch facing the pendulum, and then releases the pendulum to strike the specimen at a fixed height, and finally measures the energy absorbed during sample breakage. The analyst calculates and reports the impact strength, typically in J/m or ft·lbf/in, along with specimen type and test conditions.

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    Test procedures A, C, and DThe notch creates a stress concentration, making brittle fracture more likely than ductile fracture. The pendulum swing breaks the specimen, which is an expanded vertical cantilever beam. The analyst determines the energy expended in discarding the portion of the specimen.
    Test procedure EThe testing procedure measures resistance to impact by rotating the notched specimen 180 degrees into the clamping vise. It expresses the findings as the amount of energy absorbed per unit width of the specimen.

    Analysis Results and Interpretation

    An increase in the absorbed energy values indicates high toughness and resistance to impulsive impact. The low values indicate brittle behavior and diminished durability. Findings can assist manufacturers in choosing materials for activities requiring mechanical strength.

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    Direct Link to PDF 

    Updated on June 24, 2026

    Laraib Hashmi
    About Author
    Laraib Hashmi
    Laraib Hashmi is an aspiring research enthusiast and science content professional with a strong interdisciplinary skill set, holding a postgraduate degree in Applied Microbiology from KIIT Bhubaneshwar, Odisha.
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