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D1822-21 – Standard Test Method Technical Guide
📐 Test Method and Specimen Setup
This test method, designated D1822-21, covers the determination of the energy required to rupture standard tension-impact specimens of plastic materials. The energy is delivered by a single swing of a calibrated pendulum in a standardized tension-impact machine. One end of the specimen is mounted in the pendulum, while the other is gripped by a crosshead that travels with the pendulum until the instant of impact, when the crosshead is arrested.
The method is suitable for rigid materials as well as those that are too flexible or thin for other impact test methods, such as the Izod pendulum test (D256). Values are stated in SI units, with imperial units in parentheses for information only.
💡 Ensure specimens are conditioned according to Practice D618 for reliable and reproducible results.
| 🔍 Parameter | 📏 SI Unit | 📐 Imperial Unit |
|---|---|---|
| Impact Energy | kJ/m² | ft·lbf/in² |
| Cross-sectional Area | mm² | in² |
⚙️ Testing Procedure and Impact Energy Calculation
The test involves a single swing of a calibrated pendulum. The energy to fracture the specimen is determined by the kinetic energy extracted from the pendulum during the breaking process. The crosshead arrests at the instant of maximum pendulum kinetic energy, allowing accurate measurement of the absorbed energy.
The impact energy is normalized to account for minor differences in cross-sectional area. The standard approach yields energy per unit area in kJ/m². An alternative method, described in Section 10, retains the energy value in joules while still compensating for area variations.
| 🎯 Normalization Method | ⚡ Unit | 📏 Calculation |
|---|---|---|
| Standard | kJ/m² | Energy / Minimum Cross-sectional Area |
| Alternative | J | Energy with area correction factor |
⚠️ Note: This test method and ISO 8256 address the same subject but differ in technical content. Refer to the specific standard for your application.
📊 Key Measured Properties and Significance
The primary measured property is tensile-impact energy, which indicates the material’s resistance to break under high-speed tensile conditions. This property is valuable for comparing materials, quality control, and design purposes. The method is particularly useful for materials that are too flexible or thin for standard impact tests.
The significance of the test is underscored by its ability to provide data for materials that cannot be tested with pendulum impact methods like Izod or Charpy. Results are influenced by specimen preparation, conditioning, and test conditions, so adherence to the standard is critical for repeatability.
| 📚 Related Standard | 🔍 Description |
|---|---|
| D256 | Izod Pendulum Impact Resistance of Plastics |
| D618 | Conditioning Plastics for Testing |
| ISO 8256 | Plastics—Determination of Tensile-Impact Strength |
❓ Frequently Asked Questions
🔍 What is the purpose of the tensile-impact test?
The test measures the energy required to break a plastic specimen under high-speed tensile loading, providing insight into the material’s impact resistance.
💡 How is the impact energy normalized?
The energy is normalized by dividing by the minimum cross-sectional area, resulting in units of kJ/m². An alternative method retains energy in joules but adjusts for area differences.
⚡ What materials can be tested with this method?
This method is suitable for rigid plastics, as well as those that are too flexible or thin for other impact tests like Izod or Charpy.
📌 How does this test compare to ISO 8256?
Both standards address tensile-impact strength, but they differ in technical content. Users should refer to the appropriate standard based on their requirements.