Evaluating polymer impact toughness relies on releasing a calibrated pendulum hammer from an initial angle of 150° to strike a notched plastic specimen under controlled, high-strain loading conditions. The Qualitest QPI-Series, offering both the analog QPI-C and digital QPI-D models, measures the precise energy absorbed during specimen fracture across two primary configuration methods:
- Izod Configuration (ASTM D256 & ISO 180): The specimen is secured vertically in a positioning vise as a cantilever beam and struck on its upper free edge above the notch at striking velocities of 3.46 m/s (ASTM D256) or 3.5 m/s (ISO 180).
- Charpy Configuration (ISO 179 & ASTM D6110): The specimen rests horizontally as a simply supported beam against dual support anvils and is struck at mid-span directly behind the notch at velocities between 2.9 m/s and 3.8 m/s.
To guarantee controlled stress concentration at the notch root, test samples are prepared using the QuickNotch-Auto or QuickNotch™ II, machining uniform V-notch profiles that force crack initiation along a designated plane.
Testing & Operational Workflow
- Sample Preparation via QuickNotch-Auto: Motorized cutters machine standard 45° or 90° V-notches into plastic test bars to force consistent crack formation.
- Specimen Alignment & Vise Centering: Select the required Charpy or Izod fixture. The specimen vise includes an integrated positioning mechanism to ensure precise placement, guaranteeing that the impact point aligns centered against the pendulum path.
- Initiating the Test: Apply dynamic impact to the specimen using the pendulum hammer. The automated release feature drops the hammer from its 150° initial angle, streamlining procedure steps while maintaining consistent swing velocity behind protective safety enclosure doors.
- Real-Time Data Acquisition & Loss Compensation: Impact data displays in real time on the 7-inch PLC touchscreen. Absorbed energy measurements are automatically corrected using the machine's built-in compensation system for air resistance and friction losses.
- Data Storage & Export: The internal system memory stores up to 50 data sets on-board, allowing test results to export directly to a computer via USB for reporting and record-keeping.
Physics of Energy Measurement & Calculations
Pendulum testing operates on the conservation of mechanical potential energy (E = m · g · h). Releasing the hammer from its 150° initial position (h1) converts potential energy into kinetic velocity at the moment of impact. The energy absorbed by the specimen (Ea) equals the initial potential energy minus residual potential energy at post-impact height (h2), minus mechanical losses:
Ea = m · g · (h1 - h2) - Losses
The QPI-D Series calculates impact strength automatically by normalizing absorbed energy over the specimen's cross-sectional area behind the notch:
Impact Strength = Ea / (b · dm)
(Where b represents specimen width and dm represents remaining thickness behind the notch root).
Measurement Accuracy & Capacity Selection
To maintain measurement precision, standard testing guidelines recommend selecting a hammer capacity where absorbed energy falls between 20% and 80% of the pendulum rating:
- QPI-C System: Analog pointer display model for direct manual energy readings.
- QPI-D System: Digital 7-inch PLC touchscreen model storing up to 50 datasets with USB data export, supporting Izod capacities up to 50J and Charpy capacities up to 25J.
Standards Compliance & Methodological Factors
- Standard Parameters: The QPI-Series complies with ASTM D256, ISO 180, ISO 179, ASTM D6110, ISO 13802, and DIN 53453.
- Anvil & Striker Geometry: Differences in support anvil spacing, striker tip radii, and anvil clearance radii between ASTM and ISO standards alter bending mechanics, preventing direct numerical comparison between standard means.
- Notch Precision: Machining accuracy directly impacts stress concentration factors. Deeper or sharper notches decrease apparent toughness, while wider notch angles distribute impact forces across a larger volume. Motorized sample preparation via the QuickNotch-Auto eliminates dimensional variations across test batches.
