Multiaxial Impact Testing of Plastics: Instrumented Puncture Impact Determination

Multiaxial impact testing, also known as instrumented puncture impact testing, is the standard method for evaluating how rigid plastics, sheets, films, and molded components behave when subjected to high-speed biaxial loading. This article provides a comprehensive technical overview of the determination, covering the underlying principles, the governing standards such as ISO 6603-2 and ASTM D3763, specimen requirements, measured parameters, test procedures, and typical industrial applications.

Technical Overview

Multiaxial impact determination is an instrumented test method in which a hemispherical-headed striker (tup) is driven at high speed through a circularly clamped plastic specimen. Unlike uniaxial pendulum tests such as Charpy (ISO 179, ASTM D6110) or Izod (ISO 180, ASTM D256), which load a notched bar along a single axis, the puncture configuration imposes a biaxial (multi-axial) stress state on the specimen. This loading condition closely reproduces the deformation modes experienced by many real plastic products during service, such as stone impact, dropped-object impact, and collision events.

Because the striker is instrumented with force and displacement sensors, the method records a complete force-versus-displacement (or force-versus-time) curve throughout the impact event. This allows engineers not only to determine whether a specimen passes or fails, but also to quantify the entire energy-absorption history and to classify the failure mode as ductile, brittle, or mixed. The principal international standards for this determination are ISO 6603-2 (instrumented puncture impact of rigid plastics), ISO 6603-1 (non-instrumented version), ASTM D3763 (high-speed puncture properties of plastics using load and displacement sensors), and corresponding national standards in the GB/T series. For flexible films, ISO 7765-2 and ASTM D5748 provide related instrumented procedures.

Testing Samples

Molded Plaques and Test Panels

Compression-molded or injection-molded flat plaques are the most common specimen form. ISO 6603-2 typically specifies square panels of approximately 60 mm × 60 mm that are clamped over a 40 mm inner-diameter aperture. Wall thickness is recorded because impact response is strongly thickness-dependent.

Sheets and Thermoformed Parts

Semi-finished sheets, extruded panels, and sections cut from thermoformed products can be tested directly, provided the surface is sufficiently flat and parallel for uniform clamping. This is widely used for transparent glazing sheets, sanitary ware, and machined plastic panels.

Sections from Finished Components

Flat areas cut from end products, such as automotive trim, housings, ducts, containers, and appliance parts, may be tested to validate the actual material as processed, including the effects of molding conditions, orientation, weld lines, and regrind content.

Films and Thin Sheets

Flexible packaging films and thin membranes are evaluated with smaller strikers and adapted clamping in accordance with ISO 7765-2 or ASTM D5748, providing puncture force and energy data relevant to bag strength and package integrity.

Testing Items

The instrumented multiaxial impact determination delivers a full force-displacement curve from which the following characteristic results are extracted and reported:

• Peak force (maximum force during the impact event)
• Deflection at peak force (puncture deformation capability)
• Energy absorbed up to peak force
• Total impact energy to failure or puncture
• Force and displacement at the yield point, where identifiable
• Failure mode classification: ductile, brittle, or mixed (partial brittle fracture)
• Brittle-to-ductile transition behavior as a function of temperature and impact speed
• Pass/fail assessment against a defined energy level or ductility criterion

Testing Methods

Specimen Conditioning and Preparation

Specimens are conditioned to the standard atmosphere (typically 23 °C / 50% relative humidity) before testing unless otherwise specified. Specimen thickness is measured at multiple points, and any molded-in defects, gates, or weld lines are documented because they can significantly influence impact response.

Instrumented Impact Test Execution

The specimen is centered over the circular clamping aperture and fixed with sufficient clamping force to prevent slippage during impact. A hemispherical striker, commonly 20 mm in diameter for ISO 6603-2 and 12.7 mm (0.5 in) in many ASTM D3763 configurations, is propelled against the specimen at a controlled velocity, frequently in the range of approximately 1 m/s to 4.4 m/s or higher depending on the standard and application. Modern drop towers and servo-hydraulic high-speed machines both generate reproducible velocity conditions, and a photometric or contactless velocity sensor records the actual striker speed just before contact.

Data Acquisition and Analysis

The instrumented tup measures force continuously at high sampling rates, while displacement is derived from striker position or integrated acceleration signals. Software converts the raw signals into a force-displacement curve, from which peak force, energies, deflections, and failure mode are determined. At least five to ten valid specimens per condition are normally tested to characterize scatter, and statistical evaluation of the distribution of brittle failures is performed when ductile-brittle transition behavior is of interest.

Temperature-Dependent Studies

To determine the ductile-brittle transition temperature, specimens are tested in temperature-controlled chambers at sub-ambient conditions (for example down to -40 °C) and at elevated temperatures. The fraction of brittle failures at each temperature is plotted, and the temperature at which 50% ductile failure occurs is often reported as a key material selection criterion for cold-climate service.

Applications

Multiaxial impact determination is applied across the full plastics value chain, from resin development to end-product validation. Typical application areas include:

• Automotive engineering: instrument panels, door trims, pillars, bumpers, underbody shields, fuel tanks, and exterior cladding evaluated for low-temperature impact safety
• Packaging: rigid containers, caps and closures, transport crates, and puncture resistance of flexible films
• Electrical and electronic products: housings and enclosures subjected to drop and mechanical abuse testing
• Household appliances and consumer goods: covers, panels, and structural plastic components
• Medical and laboratory devices: casings, fluid-handling components, and sterile packaging materials
• Construction and infrastructure: glazing sheets, roofing panels, pipes and fittings, and geomembranes
• Material research: ranking of resin grades, evaluation of modifiers and fillers, and quality control of incoming materials

Many manufacturers rely on accredited third-party laboratories to perform these determinations, particularly when results support regulatory submissions, customer specifications, or material data sheets that must be traceable to ISO, ASTM, or GB standard methods.

FAQ

What is the difference between multiaxial impact testing and Charpy/Izod impact testing?

Charpy and Izod tests load a notched or unnotched bar in a single direction and report a simple energy-to-break value. Multiaxial impact testing drives a hemispherical striker through a clamped panel, creating a biaxial stress state and producing a complete force-displacement curve. This gives far richer information about stiffness, strength, energy absorption, and ductile versus brittle failure behavior, and it better represents many real-world impact scenarios.

Which standards govern plastic multiaxial impact determination?

The primary standards are ISO 6603-2 for instrumented puncture impact of rigid plastics, ISO 6603-1 for the non-instrumented variant, and ASTM D3763 for high-speed puncture properties. Film-specific methods include ISO 7765-2 and ASTM D5748. Corresponding GB/T national standards exist and are harmonized with the ISO methodology.

What are the typical specimen and fixture dimensions?

For ISO 6603-2, specimens of about 60 mm × 60 mm are clamped over a 40 mm diameter aperture and struck by a 20 mm diameter hemispherical striker. ASTM D3763 procedures commonly use a 12.7 mm striker with specimen dimensions agreed between parties. The exact geometry used should always be stated in the test report because results from different configurations are not directly comparable.

Why is the force-displacement curve more useful than a single energy value?

The curve separates the contributions of stiffness, peak load-carrying capacity, deformation at failure, and total absorbed energy. Two materials with identical total impact energy can show completely different curves, one failing in a dangerous brittle manner at low deflection and another deforming in a safe, ductile manner with high energy absorption. The curve also enables consistent failure mode classification.

Can finished parts be tested instead of molded plaques?

Yes. Flat regions cut from finished components are routinely tested to verify the impact performance of the material as actually processed. Where the geometry is complex, whole-component or sub-assembly impact testing may be performed as a custom protocol, although results then characterize the product rather than the raw material.

What temperatures can be tested?

Standard laboratory temperature is 23 °C, but environmental chambers allow testing across a wide range, commonly from -40 °C up to elevated temperatures relevant to the application. Low-temperature testing is especially important for automotive and outdoor products to establish the ductile-brittle transition and confirm safe performance in cold service environments.