Impact strength testing is a fundamental mechanical evaluation used to verify that plastic toys can withstand drops, knocks and rough play without shattering into sharp fragments or small parts that could injure children. This article explains the testing principle, applicable international standards (ISO, ASTM, EN, GB), specimen preparation, testing procedures and quality-control applications of impact strength determination for plastic toy materials and finished toy products.
Technical Overview
Impact strength is the ability of a plastic material to absorb energy when subjected to a rapidly applied blow, and it is typically expressed as the energy absorbed per unit area of the fracture cross-section, in kilojoules per square meter (kJ/m²). Because toys are routinely dropped, thrown, struck and crushed during play, brittle fracture of a plastic component can generate sharp edges, sharp points or small parts, all of which are prohibited by mechanical and physical safety requirements in ISO 8124-1, EN 71-1, ASTM F963 and GB 6675.
Impact strength determination for plastic toys is therefore carried out at two levels. The first is the material level, where molded specimens of the toy polymer (such as ABS, PP, PE, HIPS, PS or PVC compounds) are fractured under pendulum or falling-weight impact in accordance with material standards such as ISO 179, ISO 180, ASTM D256, GB/T 1043 and GB/T 1843. The second is the product level, where finished toys are subjected to impact and drop tests defined directly by the toy safety standards. Together, these evaluations confirm that both the resin and the finished article provide adequate toughness under realistic and severe handling conditions.
- Material-level standards: ISO 179-1, ISO 180, ASTM D256, ASTM D6110, GB/T 1043.1, GB/T 1843
- Product-level standards: ISO 8124-1, EN 71-1, ASTM F963, GB 6675.2
- Supporting standards: ISO 291 and ASTM D618 for conditioning, ISO 294 for specimen molding, ISO 6603-2 for instrumented puncture impact
Testing Samples
Standard Injection-Molded Specimens
For pendulum impact tests, the preferred sample is a rectangular bar of 80 mm × 10 mm × 4 mm molded directly from the toy resin in accordance with ISO 294-1 or an equivalent molding procedure. Specimens must be free of flash, sink marks, voids and internal stresses, because molding defects can severely distort the measured impact energy. Prior to testing, specimens are conditioned in a standard atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity for at least 16 hours in accordance with ISO 291 or ASTM D618.
Notched Specimens
Notched specimens are prepared by machining a precise notch into the tensile face of the bar to create a controlled stress concentration. ISO and GB standards define notch types A, B and C with notch radii of 0.25 mm, 1.0 mm and 0.1 mm respectively, leaving a remaining ligament thickness of 8 mm for a 10 mm wide specimen. A sharp, freshly cut notch is essential, because a blunt or damaged notch artificially raises the measured impact strength.
Specimens Cut from Toy Components
When the toy is made from a material grade that cannot be re-molded, or when the actual component condition must be evaluated, test pieces are cut from toy housings, shells, wheels and structural parts. These samples are machined to the standard dimensions where possible, and any deviation in thickness or orientation is recorded in the test report.
Films, Sheets and Complete Articles
Flexible components such as film bags, inflatable parts and thin sheet sections are evaluated by falling-dart or puncture methods using circular disc specimens. Complete finished toys are also retained as samples for product-level impact testing under the toy safety standards.
Testing Items
The impact evaluation program for plastic toys typically covers the following measured parameters, each reported with the test standard, notch type, specimen dimensions and failure mode classification:
- Charpy impact strength, notched and unnotched, in kJ/m² (ISO 179-1, GB/T 1043.1)
- Izod impact strength, notched and unnotched, in kJ/m² (ISO 180, ASTM D256, GB/T 1843)
- Falling-dart and falling-weight impact resistance of films and molded parts (ISO 7765-1, ISO 6603-2, ASTM D5628, GB/T 9639)
- Low-temperature impact strength, commonly determined at −20 °C or −30 °C after cold conditioning
- Failure behavior classification: complete break, hinged break, partial break or non-break
- Product-level impact and drop performance of finished toys against sharp-edge, sharp-point and small-part criteria
Testing Methods
Charpy Impact Test
In the Charpy configuration of ISO 179-1, GB/T 1043.1 and ASTM D6110, the specimen is mounted horizontally on two support anvils set 62 mm apart for a 4 mm thick bar, with the notch facing away from the striker. A pendulum hammer of a suitable energy capacity is released, and the fracture energy is read after correction for friction and windage losses. The impact velocity is approximately 2.9 to 3.8 m/s, and the pendulum capacity must be selected so that the absorbed energy falls between 10 % and 80 % of the nominal capacity to ensure valid readings.
Izod Impact Test
In the Izod configuration of ISO 180, ASTM D256 and GB/T 1843, the notched specimen is clamped as a vertical cantilever beam, and the pendulum strikes the notched face at a fixed height above the clamp. ASTM D256 uses bars of 63.5 mm × 12.7 mm with a 2.54 mm deep notch, while the ISO/GB system uses the 80 mm × 10 mm × 4 mm geometry. Consistent clamping torque is critical because specimen slippage produces falsely low energy values.
Falling-Weight and Falling-Dart Tests
For thin sections and full components, a falling mass with a hemispherical or dart-shaped striker is dropped from a controlled height. Instrumented puncture testing under ISO 6603-2 drives a 20 mm diameter striker into a clamped disc at 4.4 m/s and records the full force-deflection curve, yielding peak force and energy to puncture. Film materials are screened by the staircase or constant-height dart-drop procedures of ISO 7765-1 and GB/T 9639.
Product-Level Impact Tests under Toy Safety Standards
EN 71-1, ISO 8124-1 and ASTM F963 prescribe impact tests on finished toys in which a calibrated falling mass is dropped onto the toy or its components from a defined height, often after temperature conditioning appropriate to the intended use environment. After each impact, the toy is examined for the creation of sharp edges, sharp points, small parts and hazardous driven mechanisms, and any such failure results in non-conformity.
Low-Temperature and Conditioning Procedures
Because many plastics become significantly more brittle in cold conditions, specimens and finished toys intended for outdoor or winter use may be conditioned at sub-zero temperatures immediately before testing. The transfer from the conditioning chamber to the test position is timed so that testing is completed before the sample warms beyond the tolerance limits.
Applications
Impact strength determination supports the toy industry at every stage from resin development to market surveillance. Typical applications include:
- Incoming quality control of ABS, PP, PE, HIPS and PVC resin batches against supplier impact specifications
- Material grade selection and comparison for ride-on toys, building blocks, doll housings and outdoor play equipment
- Evaluation of the effect of fillers, colorants, lubricants and recycled content on toughness
- Cold-weather performance verification for toys marketed in temperate and cold climates
- Failure analysis of returned or field-broken toys, distinguishing material brittleness from design or processing defects
- Generation of technical documentation and conformity dossiers for regulatory submissions, supported by accredited third-party laboratories where required
FAQ
What is the difference between Izod and Charpy impact tests?
The Charpy test supports the specimen horizontally on two anvils and strikes it at mid-span, while the Izod test clamps the specimen as a vertical cantilever and strikes it above the clamp. The two methods use different geometries and clamping conditions, so results are not directly interchangeable, and the test standard must always be cited alongside the numerical value.
Why are impact specimens notched?
The notch acts as a controlled stress concentrator that promotes brittle, crack-initiation-controlled fracture. Notched impact strength measures the material sensitivity to sharp features such as gate marks, weld lines and scratches that inevitably exist on real molded toy parts, making it a more conservative and safety-relevant indicator than unnotched data.
At what temperature should the tests be performed?
The standard reference condition is 23 ± 2 °C with 50 ± 5 % relative humidity after adequate conditioning. For toys intended for outdoor use, low-temperature testing at −20 °C or −30 °C is strongly recommended, since polypropylene and polystyrene-based materials show a marked ductile-to-brittle transition as temperature decreases.
How many specimens are required for a valid result?
ISO 179 and ISO 180 require a minimum of five specimens per condition, increased to ten when the material is known to be heterogeneous or when results show high scatter. All individual values, the arithmetic mean and the observed failure mode should be reported.
What results indicate a safety risk for a plastic toy?
A low notched impact strength combined with a complete-break failure mode, particularly at low temperature, signals a risk that the component may shatter and release sharp fragments or small parts. Such findings trigger design review, material reformulation or direct product-level impact verification under EN 71-1, ISO 8124-1, ASTM F963 or GB 6675 before the toy is released to market.