Impact Testing of Polymers

Impact testing measures how a polymer material absorbs energy and resists fracture when struck suddenly, rather than loaded gradually — a distinction that matters because many real-world failures happen fast, not slowly. A polymer that performs well under a slow bend test can still shatter under impact, because the two properties measure genuinely different things — how a material behaves at speed, not just under steady load. 

METS Laboratories carries out impact testing on polymers to confirm whether a material can withstand the kind of sudden shock it's likely to face in service, whether that's a dropped product, a vehicle collision, or a tool striking a component during installation.

What is Impact Testing?

Impact testing strikes a polymer sample with a controlled, sudden force and measures how much energy it absorbs before fracturing, or whether it fractures at all. Depending on the method and standard applied, testing may cover:

• Impact energy or impact strength, typically reported in Joules or Joules per metre
• Fracture behaviour: whether the sample breaks completely, partially, or not at all
• Ductile versus brittle failure mode
• Notch sensitivity, where a small defect or cut significantly affects the result

Polymer Products that are Commonly Tested

Impact testing applies wherever a polymer part or material needs to survive sudden shock in service:

• Automotive components (bumpers, interior trim, housings)
• Packaging materials, particularly for fragile or shipped products
• Electronic device housings and enclosures
• Pipes and fittings subject to installation or transport impact
• Protective equipment and safety-rated plastic parts
• Raw polymer resin and compounded material prior to moulding

Importance of Polymer Impact Testing 

Confirming impact performance matters for reasons specific to how these materials actually fail:

• Confirms a material won't shatter or crack under sudden, real-world shock
• Identifies brittle behaviour that slow-load tests like flexural testing can miss
• Detects batch-to-batch variation in polymer formulation, additives, or processing
• Supports material selection for safety-critical or impact-prone applications
• Required for compliance in automotive, packaging and consumer product standards
• Flags temperature sensitivity, since many polymers become more brittle in the cold

How Is Impact Testing Performed?

Impact testing follows one of several standard configurations, chosen based on the material, the application and the applicable standard:

• Izod impact test: a notched specimen is clamped vertically at one end, and a pendulum swings to strike it near the notch, with the energy absorbed calculated from how far the pendulum continues to swing after impact
• Charpy impact test: a notched or unnotched specimen is supported horizontally at both ends, and a pendulum strikes it at the centre, measuring absorbed energy the same way
• Falling dart / falling weight impact test: a weight is dropped from a set height onto a flat sample (often film or sheet), and the energy or height at which failure occurs is recorded
• Instrumented impact testing: a load cell captures the full force-time curve during impact, giving more detail on how the material fails, not just the final energy value

Standards that Govern Impact Testing

Impact testing follows internationally recognised methods, selected based on the material type, product category and destination market:

• ASTM D256: the standard Izod impact test method for plastics, widely used in North America
• ISO 180: the equivalent international Izod method
• ASTM D6110 / ISO 179: Charpy impact test methods for plastics
• ASTM D1709 / ISO 7765: falling dart impact test methods for plastic film
• ASTM D3763: instrumented impact testing for rigid plastics

The method and standard applied should always match what the product's specification or destination market requires, since Izod, Charpy and falling dart results aren't directly comparable to one another.

Evaluating Impact Test Results 

Results are reported as impact energy or impact strength (commonly J/m or kJ/m²), along with the observed failure mode, and compared against:

• The material's approved specification or datasheet values
• The relevant standard's reporting requirements
• Performance at different test temperatures, where cold-weather use is a factor
• Batch-to-batch consistency data, to flag a shift in raw material or processing

A material's impact result should always be read alongside its intended application and expected service temperature, since a value that's adequate at room temperature can fall sharply in cold conditions.

Factors Affecting Impact Test Results

Impact performance isn't a fixed property of a polymer type — it shifts with formulation, processing and test conditions:

• Polymer grade and any fillers, reinforcements, plasticisers or impact modifiers present
• Specimen thickness and the presence or sharpness of a notch
• Test temperature, since many polymers become more brittle as temperature drops
• Strain rate or impact speed, which differs between pendulum and falling dart methods
• Processing history, including moulding conditions and any residual stress

Advantages of Regular Impact Testing

Running impact tests as a routine part of quality control, rather than only during initial material qualification, gives manufacturers:

• Confirmation that each production batch meets its impact resistance specification
• Earlier detection of a raw material or processing change affecting toughness
• Data to support material selection for safety-critical applications
• Documentation to back up compliance and customer specification claims

Impact Testing at METS Laboratories

• Testing carried out on the client's own material or finished part sample
• Izod, Charpy and falling dart methods available, matched to the applicable standard
• Testing available across a range of temperatures to assess cold-weather performance
• Reports structured to support material qualification and compliance documentation
• Part of a wider Middle East, UK, China and India laboratory network for manufacturers working across multiple markets

METS Lab's ISO/IEC 17025-accredited Ajman facility carries out mechanical testing on polymers and composite materials, supporting compliance with UAE's construction and industrial standards alongside international methods such as ASTM and ISO.

Conclusion

A polymer that bends without breaking under a slow load can still fail instantly under sudden impact, which is exactly why this is tested separately from flexural or tensile properties. METS Laboratories carries out Izod, Charpy and falling dart impact testing to confirm how a material actually behaves under real-world shock, against ASTM, ISO and other applicable standards. If a polymer material or finished part needs its impact resistance confirmed, get it tested first.

Frequently Asked Questions

1.What's the difference between Izod and Charpy impact tests?

Ans: Both use a swinging pendulum to strike a sample, but the specimen is mounted differently — Izod clamps the sample vertically with the pendulum striking above the clamp, while Charpy supports the sample horizontally at both ends with the pendulum striking the centre. The two aren't directly comparable.

2.Does cold weather make plastic more likely to crack on impact?

Ans: Yes, for many polymers. Materials that absorb impact well at room temperature can become noticeably more brittle in the cold, which is why impact testing is sometimes repeated at lower temperatures for products used outdoors.

3.How do you know if a plastic part is impact-resistant?

Ans: By testing it — a weight or pendulum is used to strike a sample, and the amount of force it can absorb before cracking or breaking is measured and compared against a standard. 

4.Why does plastic sometimes shatter even though it seems strong?

Ans: Because strength under a slow push and strength under a sudden hit aren't the same thing. A plastic part can handle steady pressure just fine but still crack or shatter if it's dropped or struck quickly.