High-Speed Tensile Impact Testing of Plastics: Principles, Standards, and Applications

High-speed tensile impact testing measures the energy required to fracture plastic materials under an extremely rapid tensile load, making it an essential method for evaluating materials that are too ductile or too thin for conventional notched impact tests. Governed by standards such as ISO 8256, ASTM D1822, and GB/T 13525, this test provides critical data for material selection, quality control, and product safety across the automotive, packaging, and electronics industries. This article explains the test principle, specimen requirements, procedures, correction calculations, and typical applications in detail.

Technical Overview

High-speed tensile impact testing, also known as the tensile-impact test, determines the energy absorbed by a plastic specimen when it is broken by a single, extremely rapid tensile blow. The method complements the more familiar Charpy (ISO 179, ASTM D6110) and Izod (ISO 180, ASTM D256) impact tests. It is particularly valuable for ductile thermoplastics, thin sections, and flexible materials that either bend without breaking in flexural impact configurations or fail to meet the complete-break criteria required by those methods.

The test is performed on a pendulum impact machine equipped with a dedicated tensile-impact fixture. One end of the specimen is attached to the swinging pendulum, while the other end is connected to a free crosshead. As the pendulum reaches the bottom of its swing, the crosshead strikes a stationary anvil and is abruptly stopped, while the hammer continues to move, subjecting the specimen to a uniaxial tensile shock until fracture occurs. The impact velocity is typically in the range of 2.8 m/s to 3.8 m/s, depending on machine geometry, which corresponds to strain rates far higher than those of conventional tensile testing and closer to real-world events such as drops, crashes, and collisions.

The principal international and national standards for this method include ISO 8256 (Plastics — Determination of tensile-impact strength), ASTM D1822 (Standard Test Method for Tensile-Impact Energy to Break Plastics and Electrical Insulating Materials), and the Chinese national standard GB/T 13525. Results are reported as tensile-impact energy in joules (J) or tensile-impact strength in kilojoules per square meter (kJ/m²), with optional corrections for machine friction, crosshead kinetic energy, and specimen bounce.

Testing Samples

Rigid and Semi-Rigid Thermoplastics

Materials such as polyethylene (PE), polypropylene (PP), ABS, polycarbonate (PC), polyamide (PA), polyoxymethylene (POM), PBT, and various polymer blends are routinely evaluated. These ductile materials frequently show "no break" results in Izod or Charpy tests, so the tensile-impact configuration provides a more discriminating measure of their energy absorption capacity.

Thermosetting Plastics

Phenolic, epoxy, and unsaturated polyester molding compounds can also be tested, provided that specimens can be securely clamped and that a valid fracture is achieved. For very brittle thermosets, flexural impact methods are often preferred, but tensile impact remains applicable when unnotched data are required.

Plastic Films and Thin Sheets

Thin films and sheets that are too flexible for pendulum flexural impact tests can be assessed using tensile-impact fixtures adapted for soft or thin materials, making the method useful for packaging films, laminates, and membranes.

Reinforced and Filled Plastics

Glass-fiber-reinforced, mineral-filled, and other modified compounds can be tested to compare formulation effects on high-rate toughness, provided the failure occurs within the gauge region rather than at the clamping points.

Specimen Preparation and Geometry

Specimens are typically prepared by injection molding or machining in accordance with ISO 2818 or the relevant material standard. ISO 8256 specifies several specimen types, generally 80 mm in length with a preferred thickness of 4 mm, while ASTM D1822 defines long (Type L) and short (Type S) rectangular specimens approximately 64 mm and 32 mm in overall length, featuring end holes for pin mounting. The narrowest cross-section of each specimen must be measured accurately, since this area is used in calculating strength values.

Testing Items

The following quantities are typically determined and reported:

• Tensile-impact energy at break, expressed in joules (J)
• Tensile-impact strength, calculated as the absorbed energy divided by the original cross-sectional area of the narrowest section, expressed in kJ/m²
• Corrected tensile-impact strength, after subtracting energy losses from friction, windage, crosshead momentum, and bounce
• Failure mode description, such as brittle, ductile, or mixed fracture
• Optional temperature-dependent results, when testing is performed inside heated or cooled chambers

Testing Methods

Apparatus and Calibration

The test uses a pendulum impact tester with interchangeable hammers, typically ranging from 2 J to 50 J in capacity, fitted with a tensile-impact fixture consisting of a hammer attachment, a free-flying crosshead, and an anvil or stop block. Machines must be verified and calibrated in accordance with the requirements of ISO 13802 or ASTM D1822 to ensure that energy scales, velocity, and friction losses remain within tolerance. Modern instruments may use optical encoders or force sensors to record energy and load-displacement behavior during fracture.

Specimen Conditioning

Specimens are conditioned in a standard laboratory atmosphere of 23 °C ± 2 °C and 50 % ± 10 % relative humidity in accordance with ISO 291 or ASTM D618 before testing. Because impact behavior is strongly temperature dependent, the test temperature must always be reported along with the results.

Test Procedure

• Measure and record the width and thickness of the narrowest section of each specimen to calculate the cross-sectional area.
• Mount the specimen between the pendulum fixture and the crosshead, ensuring correct alignment and firm clamping without pre-stressing.
• Set the pendulum to the specified release angle, verify the zero-energy reading, and confirm that the friction and windage correction has been determined.
• Release the pendulum; the crosshead strikes the anvil and the specimen is loaded in tension at high velocity until it fractures.
• Record the absorbed energy indicated by the machine, or captured by the instrumented data system.
• Repeat the test on at least five specimens; test additional specimens if the scatter of results is high, and discard any values from specimens that failed at the clamps.
• Calculate the mean tensile-impact energy and strength, apply corrections where required, and report all relevant test conditions.

Corrections and Calculations

Because the crosshead carries away part of the pendulum energy and friction absorbs additional energy, ISO 8256 and ASTM D1822 define correction terms. The corrected strength is obtained by subtracting the friction and windage loss, the residual kinetic energy of the crosshead, and, where applicable, the bounce energy of broken specimen halves, before dividing by the original cross-sectional area. Corrected values provide better comparability between laboratories and between machines of different capacities.

Influencing Factors

• Impact velocity and pendulum capacity, which affect the strain rate applied to the specimen
• Test temperature and conditioning history, which strongly influence ductile-to-brittle behavior
• Specimen thickness, surface defects, and machining quality
• Clamping alignment and grip pressure, which can cause premature failure at the grips
• Material anisotropy and orientation, especially in injection-molded or extruded parts

Applications

High-speed tensile impact data support a wide range of engineering and commercial activities:

• Packaging development, where films and thin containers must resist drops, bursts, and handling shocks
• Automotive engineering, including interior trim, airbag covers, instrument panel components, and under-hood parts exposed to crash-level loading rates
• Consumer electronics and electrical housings, where components must withstand drops and impacts during use and transport
• Material datasheets and material ranking, offering a toughness index for ductile plastics that do not break in Izod or Charpy tests
• Quality control in compounding and injection molding, for monitoring batch-to-batch consistency and the effect of additives, fillers, and recycled content
• Research and failure analysis, where comparisons of corrected tensile-impact strength reveal embrittlement caused by aging, weathering, or processing defects

Accredited third-party laboratories commonly offer this test as part of comprehensive mechanical characterization programs for plastics, supporting manufacturers with compliance documentation, supplier qualification, and product certification submissions.

FAQ

What is the difference between tensile impact testing and Izod or Charpy testing?

Izod and Charpy tests load a specimen in bending, usually with a notch, while tensile impact testing loads the specimen in uniaxial tension at high speed. Ductile or thin materials that bend, hinge, or fail to break completely in flexural impact tests can often be evaluated effectively with the tensile-impact method.

Which standards govern high-speed tensile impact testing of plastics?

The primary standards are ISO 8256 and ASTM D1822, together with the Chinese national standard GB/T 13525. Specimen conditioning is governed by ISO 291 or ASTM D618, and machine verification is covered by ISO 13802.

How fast is the load applied?

The hammer typically strikes the fixture at a velocity between approximately 2.8 m/s and 3.8 m/s, depending on the pendulum machine. This produces strain rates orders of magnitude higher than standard tensile testing machines and representative of many real-world impact events.

Why are correction factors applied to the results?

A portion of the pendulum energy is consumed by machine friction and air resistance, carried away by the flying crosshead, or lost through the bounce of broken specimen fragments. Corrections remove these contributions so that the reported energy reflects the energy actually absorbed by fracturing the specimen, improving accuracy and inter-laboratory comparability.

Can films and very thin sheets be tested?

Yes. With appropriate fixture adaptations and lower-energy pendulums, films and thin sheets can be tested, which is one of the key advantages of the tensile-impact configuration over flexural impact methods.

How many specimens should be tested?

A minimum of five valid specimens is generally tested, with additional specimens examined when scatter is significant. Specimens that fail at the clamping points rather than in the gauge section are rejected and retested.