ASTM D7028-07 Glass Transition Temperature of Polymer Matrix Composites

The glass transition temperature (Tg) is determined using the standard testing method ASTM D7028-07. Dynamic Mechanical Analysis (DMA) technique is used for testing. The values are reported in the SI unit.

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ASTM D7028-07 Glass Transition Temperature of Polymer Matrix Composites

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM D7028-07 describes a test method for determining the glass transition temperature (Tg) of polymer matrix composites using dynamic mechanical analysis (DMA). The glass transition is the temperature range over which the polymer matrix transitions from a rigid, glassy state to a rubbery, viscoelastic state, thereby significantly reducing the composite’s stiffness and load-bearing capacity.

This test is critical for aerospace, automotive, and structural composite applications where maximum service temperature must remain well below Tg to preserve structural performance.

Scope, Applications, and Benefits

Scope

ASTM D7028-07 applies to continuous fiber-reinforced polymer matrix composites and measures Tg via:

Storage modulus (E’) onset temperature
Loss modulus (E”) peak temperature
Tan delta (loss factor), peak temperature. The method covers the single-cantilever, dual-cantilever, and three-point-bending DMA modes.

Applications

Aerospace composite structural qualification
Automotive composite part temperature rating
Cure verification and post-cure optimization
Thermal degradation and hot-wet conditioning assessment
Material comparison for high-temperature composite selection

Benefits

Non-destructive, small specimen requirement
Measures multiple Tg indicators simultaneously
Detects incomplete cure or moisture-induced plasticization
Provides data for maximum service temperature determination
Essential for aerospace composite airworthiness documentation

Test Process

Specimen Preparation

Rectangular composite specimens are cut to defined dimensions and conditioned per test requirements (dry or wet).

DMA Setup

Specimens are clamped in the appropriate fixture (single-cantilever, dual-cantilever, or 3-point bend) and loaded into the DMA furnace.

Temperature Ramp

A dynamic oscillatory force is applied while temperature is increased at a controlled rate (typically 3–5°C/min); E', E'', and tan δ are continuously recorded.

Tg Determination

Tg is identified from the onset of E' reduction, E'' peak, and tan δ peak; all three values are reported.

Technical Specifications

Parameter	Details
Test Principle	Dynamic mechanical analysis (DMA)
Applicable Materials	Continuous fiber-reinforced polymer matrix composites
Heating Rate	1–5°C/min
Frequency	1 Hz (default)
Measured Outputs	E' onset Tg, E'' peak Tg, tan δ peak Tg

Instrumentation Used for Testing

Dynamic mechanical analyzer (DMA) with environmental furnace
Single-cantilever, dual-cantilever, or 3-point bending fixture
Liquid nitrogen cooling option for subambient testing
Calipers for specimen dimension measurement
Data analysis software with modulus and phase angle calculation

Results and Deliverables

Storage modulus (E’) vs. temperature curve
Loss modulus (E”) vs. temperature curve
Tan delta (loss factor) vs. temperature curve
Tg values from all three methods
Full DMA test report with specimen and test conditions

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Frequently Asked Questions

Aerospace specifications typically use the E' onset or E'' peak, which are more conservative than tan δ peak; the appropriate value depends on the governing specification or OEM requirement.

Absorbed moisture plasticizes the polymer matrix, reducing Tg — this is why aerospace composites are often tested in both dry and conditioned (hot-wet) states.

The method applies to thermoset (epoxy, bismaleimide, PEEK) and thermoplastic matrix composites with continuous fiber reinforcement.

Typical specimens are 50–60 mm long, 10–15 mm wide, and 2–4 mm thick; exact dimensions depend on the DMA fixture selected.

Yes — the measured Tg can be compared to the theoretical fully cured Tg to estimate degree of cure; under-cured laminates show a lower Tg than fully cured material.