Abs Impact Strength Notched Izod Charpy And What Test Temperature Changes
Evaluation of acrylonitrile butadiene styrene (ABS) impact strength: notched Izod, Charpy and what test temperature changes produce in reported values requires separating the material response from the test geometry. Acrylonitrile butadiene styrene is a two-phase system in which polybutadiene rubber domains are dispersed in a styrene-acrylonitrile matrix. The notched Izod and notched Charpy values are therefore determined partly by rubber-phase cavitation, matrix shear yielding, and crazing, and partly by notch radius, specimen thickness, pendulum energy, and thermal conditioning. General-purpose injection grades tested under ASTM D256-23 Method A at 23°C commonly exhibit notched Izod values from 160 J/m to 320 J/m, while notched Charpy values under ISO 179-1:2020 method 1eA typically range from 12 kJ/m² to 25 kJ/m². When test temperature is reduced to -30°C, the notched Izod value may fall by 50% to 70% depending on acrylonitrile content, rubber particle size distribution, and impact-modifier loading.
What Test Geometry and Pendulum Conditions Shape Notched Izod Results for ABS?
Notched Izod testing under ASTM D256-23 Method A clamps a rectangular specimen vertically as a cantilever and strikes the notched face with a pendulum. The standard specimen dimensions are 63.5 mm length, 12.7 mm width, and 3.2 mm thickness, with a machined notch having a 45° included angle and a 0.25 mm root radius. The pendulum mass and drop height are selected so that the available energy is sufficient to break the specimen within the usable range of the instrument without excessive machine damping. The reported value is the energy absorbed per unit notch length, expressed in J/m. In the ISO method, ISO 180:2019 method 1A, the specimen is 80 mm × 10 mm × 4 mm, the notch is Type A with a 0.25 mm root radius, and the reported unit is kJ/m². Because the two methods use different specimen cross-sections and clamping configurations, a direct numerical conversion between J/m and kJ/m² is not valid without correlation data on the same ABS formulation.
The notch radius is a critical variable. A larger root radius, such as 1.0 mm, reduces stress concentration and can increase the measured impact value by 50% or more relative to the standard 0.25 mm notch. In production laboratories, notches must be machined with a properly dressed cutter, and the root radius verified against an optical comparator or shadowgraph because tool wear can create an irregular radius that biases results. The clamping force must also be controlled; insufficient clamping allows bending energy to be absorbed outside the notch and inflates the reported impact value. The temperature of the specimen at the moment of impact is governed by the soak time, the thermal mass of the specimen, and the transfer time from the conditioning bath or chamber to the pendulum. A transfer delay of more than a few seconds can allow thin specimens to warm toward ambient conditions and change the failure mode from brittle to ductile.
| Standard | Test mode | Specimen dimensions | Notch root radius | Reported unit |
|---|---|---|---|---|
| ASTM D256-23 Method A | Izod cantilever | 63.5 mm × 12.7 mm × 3.2 mm | 0.25 mm | J/m |
| ISO 180:2019 method 1A | Izod cantilever | 80 mm × 10 mm × 4 mm | 0.25 mm | kJ/m² |
| ISO 179-1:2020 method 1eA | Charpy three-point | 80 mm × 10 mm × 4 mm | 0.25 mm | kJ/m² |
Production-scale injection molding of ABS at melt temperatures of 230°C to 260°C and mold temperatures from 40°C to 80°C generates orientation and skin-core gradients that alter notched impact response. A high-velocity injection with rapid cooling freezes orientation at the surface, reducing crack-propagation resistance and creating apparent notch sensitivity. Impact specimens cut from the edge of an injection molded plaque can differ from specimens cut from the center by 10% to 30% in notched Izod value because of flow-induced anisotropy of the styrene-acrylonitrile matrix and deformation of the rubber phase. Knit lines formed downstream of core pins in multi-gated molds show local impact strength reductions of 40% or more; testing standardized specimens from a knit-line region therefore underestimates bulk material toughness. Published data for this specific configuration is limited because most datasheet values are generated on end-gated or compression-molded specimens.
Low-Temperature Notched Impact Response Falls Faster in General-Purpose ABS Than in Rubber-Modified Grades
Test temperature changes alter the yield stress of the styrene-acrylonitrile matrix and the stiffness of the polybutadiene rubber phase. The polybutadiene glass transition temperature is commonly reported between -85°C and -75°C, but the surrounding glassy matrix and the rubber particle structure generate a ductile-to-brittle transition at higher temperatures in notched impact tests. At 23°C, shear yielding and crazing absorb energy over a relatively large volume ahead of the notch. As the test temperature decreases toward -20°C and -30°C, the matrix yield stress increases, the rubber phase stiffens, and the damage zone contracts. The part transitions from a stress-whitened, hinged break to a comparatively flat, brittle fracture surface with limited energy absorption. General-purpose ABS grades typically show a sharper loss in notched Izod value than high-impact extrusion grades containing higher rubber volume or a bimodal polybutadiene particle size distribution. A temperature shift of 5°C near the ductile-to-brittle transition can change the failure mode from ductile to brittle, so low-temperature specimens require conditioning chambers with a tolerance no wider than ±2°C.
| ABS grade type | Notched Izod at 23°C (J/m) | Notched Izod at -20°C (J/m) | Notched Charpy at 23°C (kJ/m²) | Notched Charpy at -30°C (kJ/m²) |
|---|---|---|---|---|
| General-purpose injection | 160–320 | 80–150 | 12–25 | 4–9 |
| High-impact extrusion | 350–500 | 190–300 | 28–40 | 12–20 |
| Flame-retardant injection | 90–180 | 40–85 | 7–14 | 2–6 |
These ranges are representative of commercial datasheet values and not a substitute for grade-specific mechanical testing. The low-temperature notched Charpy values are more sensitive to transfer time because the thinner cross-section loses thermal energy faster than a thicker Izod specimen when moved from a cold bath to the pendulum. In practice, a refrigerated circulating-air chamber adjacent to the impact tester reduces this variation. For conditioning below -40°C, a liquid bath with an appropriate heat-transfer fluid is often used, provided the fluid does not plasticize or stress-crack the ABS surface.
When Notched Charpy Values Are Required in ISO-Governed Purchase Specifications
The notched Charpy test imposes a three-point bending stress field rather than the cantilever stress field of the Izod test. Under ISO 179-1:2020 method 1eA, the specimen is supported at both ends and struck at mid-span on the notched face. The standard specimen is 80 mm × 10 mm × 4 mm, with a Type A notch having a 0.25 mm root radius and a remaining ligament width below the notch of 8 mm. The reported value is the absorbed energy divided by the fracture area at the notch, expressed in kJ/m². Because the Charpy test uses a different support span and impact position, it samples both crack initiation and crack propagation under a different constraint state. Notched Charpy values for the same ABS grade are therefore not interchangeable with notched Izod values, and procurement specifications in Europe commonly list notched Charpy data under ISO 10350-1 as the single-point mechanical property.
The temperature dependence of notched Charpy values follows the same ductile-to-brittle mechanism as Izod but can appear shifted because the stress triaxiality at the notch root differs. A high-impact ABS grade may show notched Charpy values of 30 kJ/m² at 23°C and 14 kJ/m² at -30°C, while a general-purpose grade may decline from 18 kJ/m² to 6 kJ/m² over the same temperature interval. The Charpy geometry is also more sensitive to specimen flatness and support span alignment; misaligned supports can introduce wedge effects and scatter. When Charpy data are used for incoming inspection, the test protocol should specify the notch type, the pendulum energy, the support span, and the conditioning time at temperature.
Specimen Conditioning, Notch Radius, and Residual Stress Interactions
Conditioning of ABS impact specimens is specified by ASTM D618 or ISO 291, typically at 23°C and 50% relative humidity for not less than 40 h. ABS absorbs moisture slowly because the acrylonitrile groups can associate with water, but the equilibrium moisture content is generally below 1.0%. Moisture effects on notched impact are smaller than those observed in polyamides or polycarbonates, but humidity-conditioned specimens should not be assumed to give identical values to dry-as-molded samples. For low-temperature testing, specimens are soaked at the test temperature with a minimum time of 1 h per 1 mm thickness or until thermal equilibrium is confirmed. Circulating air is preferred for temperatures above -60°C because it avoids localized surface cooling from direct liquid contact.
Notch machining introduces local heating and plastic deformation at the root. A dull broach or milling cutter may smear the notch surface and produce an effective radius different from the specified 0.25 mm. This single variable can cause interlaboratory differences larger than the temperature effect in some ABS formulations. In addition, residual stress from injection molding can superimpose with the notch stress field. Specimens cut from molded plaques often show higher scatter than compression-molded specimens because of frozen-in orientation and differential shrinkage. Annealing can reduce residual stress, but annealing also relaxes rubber-phase morphology and may shift the apparent impact response. Therefore, any comparison of notched Izod or Charpy values across suppliers must control molding parameters, specimen location, notch cutter condition, and thermal history.
Actual part performance rarely correlates with single-point notched Izod or Charpy data because the part contains variable thickness transitions, constrained ribs, weld lines, and service loading rates different from pendulum impact. The notched impact value remains a quality-control and material-selection screen, but it is not a design property for ABS components subjected to high-rate loading at low temperature. A high notched value at 23°C does not ensure ductile behavior at -20°C, and a moderate notched value at room temperature does not automatically indicate poor low-temperature toughness if the grade contains a bimodal rubber modifier. The selection of an ABS grade for cold service therefore requires testing over the full expected temperature window with the same notch geometry and specimen orientation that will be used on the production part.
