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ASTM D575 - Rubber Compression Testing

astm d575 compression platens

Standard Test Methods for Rubber Properties in Compression - PDF

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ASTM D575 is very similar to ASTM D395. For 95% of people we recommend jumping straight to the ASTM D395 page. The Method B Fixture is most popular.

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ASTM D575 is the standard test method for determining the compressive properties of unvulcanized or vulcanized rubber materials. It’s commonly used to measure a rubber compound’s ability to resist deformation under a compressive load. The test provides data such as compressive stress-strain behavior, modulus, and hysteresis (energy loss).

There are two main procedures under this standard:

  • ASTM D575 Method A: Compression with measurement of stress and strain

  • ASTM D575 Method B: Constant deflection test for evaluating stress relaxation and hysteresis

Common Applications of ASTM D575

  • Evaluating rubber seals, bushings, mounts, pads, and gaskets

  • Material selection for applications involving compressive loads

  • Quality control during rubber manufacturing

  • R&D for comparing different rubber compounds

  • Measuring compression set, fatigue resistance, and deformation behavior

What Does ASTM D575 Measure?

The primary properties measured include:

  1. Compressive Stress at Given Strain

  2. Modulus in Compression (e.g., stress at 10%, 20%, or 30% strain)

  3. Stress Relaxation Over Time (Method B)

  4. Hysteresis / Energy Loss (difference between loading and unloading curves)

  5. Permanent Set after compression

These results give insight into a material’s stiffness, energy absorption, and long-term behavior under compression.

Equipment Required

To perform ASTM D575 testing accurately, the following equipment is required:

1. Universal Testing Machine (UTM)

  • Load cell capacity: Typically 10 kN to 100 kN, depending on rubber stiffness

  • Precise crosshead speed control (especially important for Method A)

  • Capable of recording load vs. displacement data

2. Compression Platens

  • Hardened steel platens with smooth, parallel surfaces

  • Flatness tolerance: within 0.025 mm

  • Lubrication (e.g., talc or soap solution) may be used to reduce friction

  • Alignment must be precise to avoid off-axis loading

3. Deflection Measuring Device

  • Dial gauge, LVDT, or extensometer to measure the change in thickness

  • Resolution: at least 0.01 mm or better

4. Spacers (for Method B)

  • Metal spacers used to maintain constant deflection

  • Typically 6.35 mm thickness

ASTM D575 Specimen Dimensions

Standard Specimen for Both Methods:

  • Cylindrical Rubber Specimen

    • Diameter: 28.6 mm ± 0.13 mm (1.13 in)

    • Thickness: 12.5 mm ± 0.13 mm (0.5 in)

  • Ends must be parallel and flat

  • For Method B, multiple specimens are often tested simultaneously

ASTM D575 Method A: Compression Stress-Strain

Objective:

To determine the stress-strain behavior of a rubber specimen under increasing compressive load.

Procedure:

  1. Condition specimen at standard laboratory temperature (typically 23 ± 2°C).

  2. Place the specimen between the platens.

  3. Compress at a constant crosshead speed of 12.5 mm/min (0.5 in/min).

  4. Record load and deformation at regular intervals (e.g., every 5% strain).

  5. Plot stress vs. strain curve.

  6. Calculate:

    • Stress at 10%, 20%, 30% strain

    • Modulus of elasticity in compression

    • Hysteresis from the loading and unloading curves

Notes:

  • Minimize friction between platens and specimen by using lubrication or thin PTFE sheets.

  • Do not allow lateral movement or bulging to influence the measurement.

ASTM D575 Method B: Constant Deflection Test

Objective:

To evaluate stress relaxation, hysteresis, and set under constant compression.

Procedure:

  1. Place the specimen between the compression platens using a spacer (typically 6.35 mm thick) to maintain a fixed deflection.

  2. Apply a load just sufficient to compress the specimen to the spacer height.

  3. After a defined time (usually 5 to 10 minutes), remove the spacer and measure the remaining force required to maintain the same deflection.

  4. Optionally, repeat measurements over time to evaluate stress relaxation.

  5. Calculate:

    • Initial and final loads

    • Percent stress relaxation

    • Hysteresis

    • Compression set after removal and recovery period

Notes:

  • Method B is more qualitative but useful for comparing rubber compounds.

Data Reporting Requirements

An ASTM D575 test report should include:

  • Specimen dimensions

  • Rubber type and cure state

  • Environmental conditions (temperature, humidity)

  • Load and displacement data

  • Stress at specified strain levels (e.g., 10%, 20%, 30%)

  • Stress-strain curve (Method A)

  • Stress relaxation values (Method B)

  • Percent hysteresis

  • Notes on bulging, failure, or anomalies during test

Related and Similar Standards

Best Practices for Accurate ASTM D575 Testing

  • Ensure platens are parallel and well-aligned to avoid bending or eccentric loading.

  • Use lubrication to reduce friction and prevent bulging or sticking.

  • Avoid over-tightening clamps or fixturing tools which can induce pre-stress.

  • Use digital displacement measurement tools for high-precision deflection data.

  • Always condition specimens in the testing environment for at least 16 hours.

  • Perform multiple tests to validate results and assess consistency across batches.

Summary

ASTM D575 is the foundational test method for evaluating rubber under compression. It offers insights into the stiffness, deformation behavior, and energy dissipation properties of elastomeric materials. Whether you're developing new rubber compounds or performing routine QC testing, understanding the nuances of both Method A and Method B will help you ensure accurate and repeatable results.

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