ABS plastic impact strength testing is a critical quality control and material qualification procedure used to evaluate the toughness of acrylonitrile butadiene styrene under rapid loading conditions. This guide explains the most widely used test methods, including Izod and Charpy impact testing, specimen preparation requirements, applicable international standards such as ASTM D256 and ISO 180, and how the results are applied across automotive, electronics, and consumer product industries.
Technical Overview
Acrylonitrile butadiene styrene (ABS) is an amorphous engineering thermopolymer that combines the rigidity, gloss, and heat resistance of the styrene-acrylonitrile matrix with the exceptional toughness supplied by its finely dispersed rubbery polybutadiene phase. This two-phase morphology gives ABS its characteristic ductile behavior under shock loading, which is why it is one of the most widely specified plastics for housings, trim, and structural components that must survive drops, collisions, and mechanical vibration.
Impact strength testing quantifies the energy a material absorbs during fracture under a high strain rate load. Because commercial ABS grades span a broad performance range, typically from about 100 J/m to more than 500 J/m in notched Izod values, standardized testing is essential for grade selection, incoming resin inspection, batch-to-batch quality control, part validation, and failure analysis. Most laboratories evaluate ABS using pendulum-based Izod or Charpy configurations, supplemented by instrumented drop-weight methods when full force–deflection data or crash-relevant performance is required.
Testing Samples
Standard Injection-Molded Specimens
The reference specimen for ABS impact testing is an injection-molded bar produced under documented conditions. ASTM D256 specifies a specimen of 63.5 mm × 12.7 mm × 3.2 mm, while the ISO counterpart uses an 80 mm × 10 mm × 4 mm bar. Melt temperature, mold temperature, injection speed, and gate location must be recorded, because processing-induced molecular orientation and residual stresses can measurably shift impact results in either direction.
Notched Specimens
Notched specimens measure resistance to crack propagation from a stress-concentrating flaw. A precision notch with a 0.25 mm root radius (Type A notch per ISO, the standard notch per ASTM) is machined to a controlled depth using a sharp cutter mounted in a motorized notching machine. Fresh cutting tools and controlled feed rates are mandatory; a dull cutter smears or heats the polymer at the notch root and produces artificially high or highly scattered results.
Specimens Machined from Finished Parts
For production verification or failure investigation, samples can be cut directly from molded components. The sampling location, distance from the gate, presence of weld lines, and orientation relative to flow direction must always be documented, since these factors strongly influence measured impact energy.
Conditioned and Temperature-Controlled Samples
Unless otherwise specified, specimens are conditioned at 23 °C ± 2 °C and 50 % ± 10 % relative humidity for at least 40 hours in accordance with ISO 291 or ASTM D618. For cold-climate or automotive underhood evaluations, specimens are equilibrated in an environmental chamber, typically at temperatures from −40 °C to 0 °C, and tested within seconds of removal to prevent warming.
Testing Items
A comprehensive ABS impact characterization program typically includes the following test items:
- Notched Izod impact strength (ASTM D256, ISO 180) — the primary specification property for most ABS grades
- Unnotched Izod impact strength — indicates total energy absorption without a crack initiator; ductile ABS often does not break completely under this condition
- Notched Charpy impact strength (ISO 179-1, ASTM D6110) — the preferred method in many European automotive supply chains
- Unnotched Charpy impact strength
- Tensile impact strength (ISO 8256, ASTM D1822) — used for thin sections where bending tests are impractical
- Instrumented puncture and drop-weight impact (ISO 6603-2, ASTM D3763) — records full force–deflection curves and distinguishes ductile from brittle failure modes
- Temperature-dependent impact profiles — a series of tests from −40 °C to +23 °C used to define the ductile–brittle transition behavior
Testing Methods
Izod Impact Testing (ASTM D256 / ISO 180)
The specimen is clamped as a vertical cantilever beam and struck by a swinging pendulum on the notched face at a fixed distance above the clamp. The energy absorbed during fracture is corrected for windage and friction losses and reported in J/m of notch width (ASTM) or kJ/m² of cross-sectional area (ISO). The pendulum capacity is selected so the absorbed energy falls between 10 % and 80 % of the available range. A minimum of five, and preferably ten, specimens are tested, and the mean value is reported together with the observed failure mode.
Charpy Impact Testing (ISO 179-1 / ASTM D6110)
In the Charpy configuration the specimen rests horizontally on two anvils and is struck at midspan, directly opposite the notch, by the pendulum. Because no clamping is required, Charpy testing is well suited to low-temperature campaigns and to brittle failure analysis, and it is the reference method in ISO-based supply chains.
Instrumented Drop-Weight Impact (ISO 6603-2 / ASTM D3763)
A force-instrumented striker impacts a clamped flat plaque at velocities between approximately 1 and 4.4 m/s while a high-speed data system records the complete force–deflection history. This method reveals peak force, absorbed energy, and whether failure was ductile, brittle, or transitional, making it the preferred technique for automotive exterior applications and laptop or appliance enclosure validation.
Procedure and Data Interpretation
- Verify pendulum calibration and aerodynamic friction losses at the start of each test session
- Confirm notch geometry with optical projection before testing, checking radius, depth, and included angle
- Test in the standard laboratory atmosphere unless a temperature program is specified
- Report the mean, standard deviation, individual values, and failure classification: complete break, hinged break, partial break, or non-break
- Exercise caution when comparing ASTM values in J/m with ISO values in kJ/m², since the differing geometries and notch dimensions prevent direct unit conversion
Applications
ABS impact strength test data directly support material specification and product safety decisions in a wide range of industries:
- Automotive: interior trim, dashboard structures, pillar and door panels, wheel covers, and grille components that must retain ductility at subzero temperatures
- Consumer electronics: television and monitor housings, laptop enclosures, printer chassis, and remote-control bodies requiring drop-test survivability
- Household appliances: vacuum cleaner shells, blender bases, washing machine control panels, and refrigerator liners
- Consumer goods: luggage shells, helmets, toys, power tool housings, and sporting equipment
- Pipes and fittings: ABS drainage and pressure systems where impact resistance after installation is a certification requirement
- Quality assurance: incoming resin lot release, regrind content evaluation, and root-cause investigation of cracked or brittle field returns
FAQ
What is a typical notched Izod impact strength for ABS?
General-purpose ABS grades typically show notched Izod values of roughly 150 to 350 J/m, equivalent to approximately 15 to 30 kJ/m² in ISO terms. High-impact grades can exceed 500 J/m, while heat-resistant, flame-retardant, or glass-filled formulations generally fall lower. Always confirm the exact grade datasheet values, the test standard used, and the specimen thickness, since thicker specimens yield lower per-unit-area results.
Why does ABS lose impact strength at low temperatures?
The rubbery butadiene phase that toughens ABS has a glass transition well below room temperature, but as the ambient temperature drops toward and below that transition, the rubber phase stiffens and can no longer effectively blunt and arrest propagating cracks. The material shifts from ductile to brittle behavior, so grades intended for outdoor or automotive cold-climate service must be verified by impact testing at the lowest service temperature.
Should I specify notched or unnotched testing?
Notched testing is the industry default because it measures resistance to crack propagation from a sharp defect and provides discriminating, reproducible numbers. Unnotched testing measures overall energy absorption and frequently results in non-break outcomes for ductile ABS, which limits its comparative value. Notched data are recommended for specifications, while unnotched results are useful as a supplementary screen for gross embrittlement.
What causes unexpectedly low impact results in ABS?
Common root causes include excessive moisture or contamination in the resin, degraded or over-reground material, incorrect molding temperatures producing high residual stress, poor weld-line formation in the test area, an improperly machined notch, and testing at elevated or reduced temperatures without adjustment. A systematic review of processing records, notch quality, and failure surfaces usually isolates the cause.
Are ASTM and ISO impact results interchangeable?
No. The two systems use different specimen dimensions, notch depths, clamping conditions, and energy-reporting units, so data cannot be converted by simple arithmetic. When a specification cites one system, testing must be performed to that system, or an empirical correlation must be established for the specific ABS grade involved.