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D1004-21 解读
📐 Specimen Geometry and Test Applicability
ASTM D1004-21 is specifically designed to determine the tear resistance of flexible plastic film and sheeting. This test method measures the force required to initiate tearing by utilizing a specimen geometry that produces a stress concentration in a small area. The maximum stress, typically observed near the onset of tearing, is recorded as the tear resistance value in newtons (or pounds-force).
The standard stipulates a very low rate of loading of 51 mm/min (2 in./min). It is explicitly not applicable for materials where brittle failures occur during testing, or where the maximum extension is greater than 101.6 mm (4 in.). Within the context of this standard, “film” is arbitrarily defined as sheeting having a nominal thickness not greater than 0.25 mm (0.010 in.).
| 🟦 Parameter | 📏 Specification / Value |
|---|---|
| Standard Designation | D1004 – 21 |
| Test Type | Tear Resistance (Graves Tear) |
| Rate of Grip Separation | 51 mm/min (2 in./min) |
| Measurement Objective | Force to initiate tearing |
| Exclusion Criteria | Brittle failures; Max extension > 101.6 mm (4 in.) |
| Material Scope | Flexible plastic film and sheeting |
| Film Definition | Nominal thickness ≤ 0.25 mm (0.010 in.) |
⚙️ Test Procedure and Rate of Loading
This test method employs a constant-rate-of-grip separation machine. The force necessary to initiate the tear is calculated from the load-time or load-displacement data generated during the test. Specimen extension is measured directly by the grip separation, ensuring a direct correlation between machine crosshead movement and the elongation of the strained material.
💡 Understanding Normalization Limitations: While tear resistance can be expressed in newtons per micron (or pounds-force per mil) of specimen thickness, this is only advisable where a correlation has been established for that specific material. The standard explicitly states: “In most cases, comparison between films of dissimilar thickness is not valid.”
The method is governed by ASTM Committee D20 on Plastics and has been approved for use by agencies of the U.S. Department of Defense. Careful specimen conditioning, as guided by Practice D618, is critical to achieving reproducible results.
📊 Referenced Standards and Unit Guidelines
ASTM D1004-21 harmonizes with several related standards to ensure a complete testing framework. Verification of the testing machine’s force output is governed by Practices E4, while physical dimension measurements of specimens are guided by Test Methods D5947. Precision data for the method is established in accordance with Practice E691.
| 🎯 Referenced Standard | 📐 Purpose / Application |
|---|---|
| D618 | Practice for Conditioning Plastics for Testing |
| D5947 | Test Methods for Physical Dimensions of Solid Plastics Specimens |
| E4 | Practices for Force Verification of Testing Machines |
| E691 | Practice for Conducting an Interlaboratory Study (Precision) |
The values stated in SI units are regarded as the standard for this test method. Values provided in parentheses (e.g., inches, pounds-force) are provided for information only. There is no known ISO equivalent to this standard.
⚠️ Safety and Applicability Notice: This standard does not purport to address all safety concerns, if any, associated with its use. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use. The method is not suitable for materials exhibiting brittle failure or excessive extension.
❓ Frequently Asked Questions
🔍 What specific property does the Graves Tear test measure?
ASTM D1004-21 is designed to measure the force required to initiate tearing in a plastic film or sheeting specimen. It specifically records the maximum stress, usually found near the onset of tearing, as the tear resistance.
💡 What is the specific test speed for this method?
The test must be conducted at a very low rate of grip separation: 51 mm/min (2 in./min). This constant rate of loading is a critical parameter of the standard.
📌 When is this test method explicitly not applicable?
The method is not applicable for materials that exhibit brittle failures during testing. It is also invalid for materials where the maximum extension during the test is greater than 101.6 mm (4 in.).
⚡ Can I directly compare the tear resistance of films with different thicknesses?
Generally, no. Although tear resistance can be divided by thickness to express it in N/µm, the standard states this is only advisable when a correlation has been established for the specific material. In most cases, comparison between films of dissimilar thickness is not valid.