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D3851-17 – Standard Test Method Technical Guide
📐 Scope and Classification of Microcellular Polyurethane Shoe Soling Materials
ASTM D3851-17 (2022) establishes the standard specification for microcellular polyurethane (MPU) materials intended for shoe soling applications. This specification defines the minimum physical property requirements and identifies the specific ASTM test methods required for verifying material conformance. The standard applies to materials with a cellular structure characterized by very small cell diameters, typically ranging from 0.1 to 200 µm.
Materials covered by this specification are systematically classified into three distinct performance grades — Grade 1, Grade 2, and Grade 3. This grading system allows manufacturers and purchasers to select the appropriate material based on required physical properties, specifically emphasizing abrasion resistance and cut-growth resistance.
⚠️ Unit Selection Note: SI units are regarded as the preferred units of measurement (Section 1.2). Contractual parties may mutually agree to use inch-pound values.
⚙️ Physical Property Testing and Requirements
All physical testing of microcellular polyurethane soling materials shall be conducted in accordance with Test Methods D3489 — the primary guide for microcellular urethane materials. The material must conform to the property limits specified in Table 1 of the standard. The principal properties and their respective test methods are as follows:
| 🧪 Property Category | 📏 Referenced Standard | 🎯 Measurement Focus |
|---|---|---|
| Hardness | D2240 | Durometer hardness of the shoe soling material. |
| Density & Specific Gravity | D792 / D1622 | Determination of apparent density and relative density. |
| Tensile & Elongation | D412 | Ultimate tensile strength and elongation at break. |
| Tear Strength | D624 / D1938 | Resistance to tearing (Die C method or Trouser Tear). |
| Cut Growth (Flex Fatigue) | D1052 | Resistance to crack propagation under repeated Ross Flexing. |
✅ Testing Guidance: Ensure all specimens are properly conditioned and tested strictly according to the latest revision of D3489, which governs the standard testing procedures for microcellular urethane materials.
📊 Grading System for Performance Selection
The three-grade classification system provides a clear framework for selection. The fundamental distinction between grades is based on abrasion resistance, cut-growth resistance, and other critical physical properties required by the intended footwear application.
| 🌟 Material Grade | 🛡️ Primary Performance Characteristic | 👟 Typical Application Guidance |
|---|---|---|
| Grade 1 | Highest abrasion resistance & cut-growth resistance | Demanding high-performance work boots and athletic footwear |
| Grade 2 | Moderate abrasion resistance & cut-growth resistance | Standard casual, dress, and mid-range footwear |
| Grade 3 | Standard abrasion resistance & cut-growth resistance | Economy footwear and low-cycle consumer applications |
💡 International Standard Note: As explicitly stated in Note 1 of the standard, there is no known ISO equivalent to ASTM D3851. Engineers developing international product specifications must rely directly on this ASTM standard.
❓ Frequently Asked Questions
🔍 What is the specific scope of ASTM D3851?
This specification covers microcellular polyurethane materials designed for shoe soling applications. It provides the definitive physical property requirements and identifies the standard test methods for determining those properties (Section 1.1).
💡 How is “microcellular polyurethane” technically defined?
According to Section 3.2.1, microcellular polyurethane is an elastomeric material produced by the chemical interaction of a polyol and an organic isocyanate, resulting in a structure with very small cell diameters. For shoe sole materials, cell diameters typically fall within the range of 0.1 to 200 µm.
⚡ Which test methods are most crucial for material qualification under this standard?
All physical tests must adhere to Test Methods D3489. The critical individual test methods referenced include D1052 (Cut Growth via Ross Flexing), D624 (Tear Strength), D412 (Tensile Strength and Elongation), and D2240 (Durometer Hardness). These methods collectively evaluate the durability and performance of the soling material.
📌 How does the standard handle purchasing and inspection requirements?
Section 8 of the standard states that the inspection of the material shall be mutually agreed upon in writing between the purchaser and the supplier as part of the purchase contract. Testing for conformance must strictly follow this specification and Test Methods D3489 (Section 8.2).