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D1709-24 – Standard Test Method Technical Guide
The ASTM D1709-24 standard specifies two test methods for determining the impact resistance of plastic film by the free-falling dart method. The energy required to cause failure is expressed as the weight (mass) of the dart dropped from a specific height that results in 50% failure of the tested specimens.
📐 Test Methods and Apparatus
The standard defines two distinct test methods based on dart geometry and drop height:
| 🟦 Feature | 📏 Method A | 📏 Method B |
|---|---|---|
| Dart Head Diameter | 38.10 ± 0.13 mm (1.500 ± 0.005 in.) | 50.80 ± 0.13 mm (2.000 ± 0.005 in.) |
| Head Shape | Hemispherical | Hemispherical |
| Drop Height | 0.66 ± 0.01 m (26.0 ± 0.4 in.) | 1.52 ± 0.03 m (60.0 + 0.25, −1.70 in.) |
| Applicable Mass Range | 50 g to approx. 6 kg | 0.3 kg to approx. 6 kg |
⚙️ Test Procedures and Techniques
Two testing techniques are described in the standard, both of which determine the weight required to achieve 50% failure:
Standard Technique (Staircase Method): The missile weight is adjusted by uniform increments after the testing of each specimen. If a specimen fails, the weight is decreased for the next test. If it does not fail, the weight is increased. This method is highly efficient in converging on the critical failure mass using a minimal number of specimens.
Alternative Technique: Specimens are tested in successive groups of ten. A single missile weight is employed for each group, and the missile weight is varied in uniform increments from group to group. The standard explicitly verifies that both techniques give equivalent results for the impact failure weight and its precision.
⚠️ Critical Requirement: Test results are only valid if the film specimen actually breaks (ruptures). Films that stretch excessively without fracturing, or “bottom out” on the test instrument base, do not constitute a valid failure under D1709-24. The standard’s Note 1 specifically addresses that materials which do not break are not considered valid tests.
All specimens must be properly conditioned prior to testing, typically in accordance with ASTM D618, Practice for Conditioning Plastics for Testing.
📊 Key Measured Properties and Significance
The primary result derived from D1709-24 is the Impact Failure Weight. This is the mass of the falling dart (reported in grams or kilograms) that causes 50% of the test specimens to fail. The test is applicable to films, which are defined as sheeting having a nominal thickness not greater than 0.25 mm (0.010 in.).
Test Method A covers a broad range of films, from lightweight packaging materials requiring around 50 g to tough, heavy-duty films requiring up to approximately 6 kg to fracture. Test Method B, in contrast, is specifically intended for films with higher impact resistance, starting at approximately 0.3 kg, making it ideal for evaluating stronger films under a more severe impact event. The results are routinely used for material specification, incoming quality control, and comparing the relative impact resistance of different plastic films.
✅ Pro Tip: Selecting the correct test method is crucial. Method A should be used for films expected to have lower impact strengths. Applying Method B (heavy dart, high drop height) to a thin film will almost certainly cause 100% failure, providing no meaningful differentiation. Conversely, using Method A for a very tough, puncture-resistant film might require the maximum permissible mass, potentially exceeding the instrument’s calibrated range or requiring an impractical number of weight increments.
❓ Frequently Asked Questions
🔍 What does the “50% failure” in the results mean?
The 50% failure level (Impact Failure Weight) is the mass of the dart at which half of a large number of test specimens would be expected to fail. It is a statistically robust way to characterize the impact strength of a film, accounting for the natural variability inherent in polymer film properties.
💡 When should I use the alternative technique (group method) instead of the staircase method?
While both techniques yield equivalent results, the staircase method is generally more efficient in terms of the number of specimens required. The alternative technique, which tests groups of ten at fixed weights, can be simpler to administer in a production quality control environment where specific weight levels are of immediate interest for process monitoring.
⚡ What officially defines a “film” for the purposes of this standard?
According to Note 2 of the standard, film is arbitrarily defined as sheeting having a nominal thickness not greater than 0.25 mm (0.010 in.). Materials thicker than this may not be suitable for testing by this specific standard.
📌 How does this standard differ from the international standard ISO 7765-1?
D1709-24 is technically equivalent to ISO 7765-1:1988, but with specific differences. These include a larger tolerance on the drop height in Test Method B, smaller tolerances on the dart diameters for both Methods A and B, a requirement for a vented dart well in the instrument, and the fact that the ISO method does not allow the alternative staircase testing technique described in Section 11 of D1709.