Plastic Tensile Impact Testing: Principles, Standards, and Applications

Plastic tensile impact testing measures the energy required to fracture plastic specimens under high-speed tensile loading, providing essential data on material toughness at strain rates that conventional tensile or bending tests cannot reproduce. Governed by standards such as ISO 8256, ASTM D1822, and GB/T 13525, the method is widely applied to thin sheets, films, rigid plastics, and electrical insulating materials in quality control, material qualification, and research. This article explains the test principle, specimen requirements, testing procedure, calculation of tensile-impact strength, and typical industrial applications.

Technical Overview

The plastic tensile impact test, also referred to as tensile-impact strength testing, determines the energy absorbed by a plastic specimen when it is broken by a rapidly applied axial tensile load. Unlike a standard tensile test performed at low crosshead speeds, this method uses a pendulum-type impact machine to load the specimen at velocities of several meters per second, simulating the high strain-rate conditions encountered during drops, collisions, and sudden mechanical loading.

The test is particularly useful for materials that cannot be evaluated reliably with Izod or Charpy bending impact methods, such as thin sheets, films, very flexible plastics, and extremely brittle compounds. A dumbbell-shaped specimen is clamped at one end to a lightweight crosshead mounted on the pendulum and at the other end to a stationary fixture. As the pendulum swings through its arc, the specimen is subjected to an abrupt uniaxial pull and fractures. The absorbed energy is determined from the loss of pendulum height or from instrumented force sensors, corrected for system losses, and then normalized by the cross-sectional area of the specimen to yield the tensile-impact strength.

The method is primarily governed by the following standards organizations' publications:

• ISO 8256 – Plastics – Determination of tensile-impact strength
• ASTM D1822 – Standard Test Method for Tensile-Impact Energy to Break Plastics and Electrical Insulating Materials
• GB/T 13525 – Determination of tensile-impact properties of plastics (Chinese national standard)

Testing Samples

Dumbbell (Dogbone) Specimens

Standard specimens are flat dumbbell-shaped pieces produced by injection molding, compression molding, or machining from sheets, plates, or finished parts. For ISO 8256, flat specimens approximately 80 mm in overall length with thicknesses typically between 1 mm and 4 mm are used. ASTM D1822 defines two specimen geometries, the long (Type L) and short (Type S) dumbbell specimens, which allow the method to be adapted to different pendulum fixtures and material behaviors.

Thin Sheets and Films

Because the load is applied axially rather than in bending, the method is well suited to thin-gauge materials such as plastic films, membranes, and electrical insulating sheeting that are too flexible or too thin for notched bending impact tests. Specimens are usually die-cut directly from production material to reflect real-world performance.

Notched Specimens

Where notch sensitivity must be assessed, specimens can be machined with a defined notch in the narrow section to act as a stress concentrator. Comparing notched and unnotched results helps characterize a material's resistance to crack propagation under rapid loading.

Testing Items

Typical test items and reported parameters include:

• Tensile-impact strength (kJ/m²) of unnotched specimens
• Tensile-impact strength (kJ/m²) of notched specimens
• Total energy to break (J) absorbed by each specimen
• Failure classification: break, partial break, or non-break
• Fracture appearance characterization: brittle, ductile, or mixed-mode failure
• Temperature-dependent tensile-impact strength, including sub-ambient and elevated-temperature testing
• Comparative evaluations after heat aging, UV exposure, humidity conditioning, or exposure to chemical media

Testing Methods

Specimen Conditioning and Preparation

Specimens are conditioned prior to testing in accordance with ISO 291 or ASTM D618, most commonly at 23 °C and 50 % relative humidity, unless a specific application environment requires other conditions. The width and thickness of the narrow parallel section of each specimen are measured accurately, since these dimensions directly determine the calculated strength value.

Test Procedure

One end of the specimen is secured in the crosshead attached to the pendulum, and the other end is clamped in the stationary fixture of the impact tester. A pendulum of suitable capacity is selected so that the absorbed energy falls within the recommended working range of the machine, commonly between 10 % and 80 % of its nominal energy. The pendulum is released from a defined height, striking through its arc and subjecting the specimen to a rapid tensile load. The energy absorbed during fracture is recorded, and the failure mode of each specimen is documented.

Energy Correction and Calculation

The raw energy reading must be corrected for machine friction and windage losses, which are determined through free-swing calibrations, and for the kinetic energy carried away by the flying crosshead after specimen separation. The corrected absorbed energy is divided by the original cross-sectional area of the narrow section to obtain the tensile-impact strength:

Tensile-impact strength = corrected absorbed energy / (specimen width × specimen thickness), with the result reported in kJ/m².

A statistically meaningful result normally requires testing multiple specimens per condition, with the mean value, standard deviation, and failure modes all reported. Instrumented pendulum systems can additionally record force–time or force–displacement curves, enabling detailed analysis of crack initiation and propagation energies.

Applications

Tensile impact testing supports material development, product design, and quality assurance across many industries:

• Quality control of plastic films, membranes, and flexible packaging materials
• Verification of thin-wall injection-molded components for consumer electronics and appliances
• Qualification of electrical insulating materials, sheets, and tapes covered by the scope of ASTM D1822
• Automotive interior and exterior trim evaluation, including parts exposed to low-temperature service
• Comparison of candidate materials under high strain-rate loading during material selection
• Research into ductile-to-brittle transition behavior, notch sensitivity, and the effects of fillers, additives, or recycled content
• Compliance verification for specifications referencing ISO 8256, ASTM D1822, or GB/T 13525 in submissions to accredited third-party laboratories

FAQ

How does a tensile impact test differ from Izod and Charpy impact tests?

Izod and Charpy tests break a specimen in bending with a striking pendulum, whereas the tensile impact test loads the specimen axially in tension at high speed. This makes the tensile impact method more suitable for thin, flexible, or very brittle materials that cannot withstand the clamping and bending configuration of conventional notched impact tests.

What units are used to report results?

The primary result is the tensile-impact strength expressed in kJ/m², obtained by dividing the corrected absorbed energy by the original cross-sectional area of the specimen's narrow section. The raw absorbed energy in joules is also commonly reported for reference.

Why is energy correction necessary?

Without a specimen, the pendulum still loses energy to friction and air resistance, and after fracture the crosshead departs with kinetic energy that is not registered as absorbed energy. Correcting for these effects ensures the reported value reflects the true energy consumed in breaking the specimen.

How many specimens are required?

A minimum of five to ten specimens per test condition is typical, depending on the governing standard and the required statistical confidence. All values, together with the mean, standard deviation, and observed failure modes, should be included in the test report.

Can the test be performed at low temperatures?

Yes. When the impact machine is fitted with an environmental chamber, tests can be conducted at sub-ambient or elevated temperatures to map the ductile-to-brittle transition of a material, which is critical for outdoor, automotive, and cold-chain applications.