Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1790-21 – Standard Test Method Technical Guide
📐 Specimen Requirements and Conditioning
Specimens for this test must be taken from plastic sheeting with a thickness not exceeding 1.00 mm (0.040 in.). The sampling direction and folding method are critical due to their direct impact on brittleness temperature results, as emphasized in section 4.2 of the standard. Conditioning is performed in accordance with ASTM D618 to ensure controlled temperature and humidity, typically at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for a minimum of 40 hours. The user must verify the applicability of this method to non‑plasticized vinyl sheetings.
⚙️ Test Procedure and Impact Conditions
The test procedure involves impacting conditioned specimens at a series of low temperatures to identify the point of brittle failure. A minimum number of specimens are tested at each temperature, and the number of passes or failures is recorded. The brittleness temperature (Tb) is then derived statistically as the temperature where 80 % of specimens would probably pass with 95 % confidence, using probability graph paper as described in section 9.1. The apparatus must deliver a defined impact energy, and the direction of specimen folding must be strictly controlled to ensure repeatable results.
📊 Key Measured Properties
The primary result is the brittleness temperature (Tb), which indicates the material’s resistance to brittle failure under the specified impact conditions. This value is determined by plotting the cumulative percentage of specimens that pass on probability graph paper and interpolating the 80 %‑passing temperature. The test is useful for specification testing and comparative purposes, but it does not represent the lowest service temperature for the plastic sheeting.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Maximum Thickness | 1.00 mm (0.040 in.) |
| Failure Criterion | Brittle failure under impact |
| Passing Rate for Tb | 80 % |
| Statistical Confidence | 95 % |
| Data Analysis Method | Probability graph paper (Section 9.1) |
⚠️ Important: The folding direction of specimens significantly affects the brittleness temperature. Follow the standard’s detailed folding instructions explicitly to ensure consistency between test results.
💡 Note: This test method was developed jointly with the Society of the Plastics Industry primarily for plasticized vinyl sheetings. Users should verify its applicability to other types of plastic sheeting.
❓ Frequently Asked Questions
🔍 What is the brittleness temperature (Tb)?
It is the temperature, derived statistically, at which 80 % of specimens are expected to pass the impact test with 95 % confidence, obtained by plotting failure data on probability graph paper.
💡 How should specimens be prepared?
Specimens must be cut from sheeting 1.00 mm or less in thickness, paying careful attention to the direction of sampling and folding as prescribed in the standard. Conditioning per ASTM D618 is mandatory before testing.
⚡ Why is conditioning so important?
Uniform temperature and moisture content across the specimen are essential for reproducible impact performance. Conditioning per Practice D618 standardizes these parameters and minimizes variability.
📌 Does this test predict the lowest use temperature of a material?
No. The test indicates behavior only under the specific laboratory impact conditions defined. It is useful for specification and comparison but does not determine the real‑world minimum service temperature.