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D6456-10 – Standard Test Method Technical Guide
ASTM D6456 – 10 (Reapproved 2018) provides a definitive specification for finished parts and machined shapes fabricated from semi-crystalline polyimide (PI). Serving as the direct replacement for the legacy MIL-R-46198 and Provisional Standard PS 93, this standard establishes a reliable framework for qualifying polyimide components used in demanding industrial and aerospace environments.
🔍 Scope, Application, and Material Characteristics
This specification is intended for finished plastic parts ready for industrial or consumer use (Section 1.1). The material covered is a semi-crystalline polyimide, classified as a thermosetting resin. Per Section 1.4, the material shows no softening or melting when tested by dynamic mechanical analysis (DMA) per Practice D4065 at or below 260°C (500°F).
Applications typically require a specific combination of properties, including a low coefficient of friction and low thermal expansion. The standard ensures reliable performance for continuous operation at temperatures up to 260°C (500°F), with short-term excursions permitted upward to 482°C (900°F), as outlined in Section 1.8.
⚠️ No Recycled Content Provisions: Because PI is a thermoset resin, the standard explicitly states in Section 1.5 that no provisions are included for recycled products. All material used must adhere to the strict virgin material requirements to pass the specified tests.
📊 Property Validation and Test Methods
To ensure consistency and performance, the specification references several standardized test methods. The classification system is designed to be identical to the Department of Defense system used for over 20 years, providing a seamless transition for existing procurement specifications.
| 🟦 Thermal Performance Characteristic | 📐 Standard Value | 📌 Reference |
|---|---|---|
| Material Type & Behavior | Thermoset / Semi-crystalline PI | Scope (§1.2, §1.4) |
| Continuous Service Temperature | Up to 260°C (500°F) | Scope (§1.8) |
| Short-Term Peak Temperature | Up to 482°C (900°F) | Scope (§1.8) |
| DMA Softening/Melting Point | No softening or melting ≤ 260°C | Practice D4065 / Scope (§1.4) |
| Friction and Expansion | Low coefficient / Low thermal expansion | Scope (§1.8) |
| 🟦 Mechanical Property | 📏 Standard Test Method | 🎯 Typical Application |
|---|---|---|
| Tensile Strength & Elongation | D638 / D1708 | Determining load capacity in tension |
| Compressive Properties | D695 | Evaluating structural bearings and bushings |
| Flexural Properties / Modulus | D790 | Measuring stiffness and resistance to bending |
| Density & Specific Gravity | D792 | Verifying material consistency and void content |
✅ Standard Units: Per Section 1.7, SI units are regarded as the standard for all property and dimensional tables. Inch-pound units are provided in parentheses for reference purposes to ensure compatibility with legacy design data.
📋 Classification and Procurement Rules
The specification uses a detailed classification callout system directly aligned with the former MIL-R-46198. Procurement under D6456 requires adherence to specific quality assurance provisions, including sampling plans per ANSI Z1.4 and packaging procedures outlined in Practice D3892. Careful attention must be paid to the line callout to ensure the correct grade and class of polyimide is supplied for the intended application.
❓ Frequently Asked Questions
🔍 What specific type of polyimide is covered by ASTM D6456?
It covers finished parts and machined shapes made from a semi-crystalline polyimide (PI) resin, which is a thermosetting material that does not soften or melt below 260°C (500°F).
💡 What are the exact temperature limits specified for these parts?
The standard specifies continuous operation up to 260°C (500°F) and allows for short-term temperature excursions upward to 482°C (900°F).
⚡ Which military and provisional standards does this document replace?
This specification is intended to replace the legacy MIL-R-46198 and Provisional Standard Specification PS 93.
📌 What test methods are used to verify the tensile properties of the parts?
The tensile properties can be verified using either Test Method D638 for standard specimens or Test Method D1708 for microtensile specimens, depending on the part geometry.