Testing the Elongation Rate of Liquid Silicone Rubber (LSR)
1. Introduction
Liquid Silicone Rubber (LSR) is a versatile elastomer widely used in medical, automotive, and consumer electronics industries due to its excellent flexibility, thermal stability, and biocompatibility. Elongation at break (or elongation rate) is a critical mechanical property that measures how much the material can stretch before breaking, indicating its toughness and durability.
This article outlines the standard testing methods for determining the elongation rate of LSR, following ASTM (American Society for Testing and Materials) and ISO (International Organization for Standardization) guidelines.
2. Materials and Equipment
To perform elongation testing, the following are required:
Liquid Silicone Rubber (LSR) samples (cured into standardized shapes, typically dumbbell-shaped specimens per ASTM D412 or ISO 37).
Tensile testing machine (universal testing machine with a load cell and extensometer).
Mold (for preparing test specimens).
Curing equipment (oven or hot press, depending on LSR curing conditions).
Calipers or micrometer (for measuring specimen dimensions).
3. Sample Preparation
Molding the Specimens
Pour uncured LSR into a dumbbell-shaped mold (Type C per ASTM D412 or Type 1/2 per ISO 37).
Cure the LSR at the recommended temperature and time (e.g., 150–200°C for 5–10 minutes).
Remove the cured specimens and allow them to cool to room temperature.
Measuring Dimensions
Use a caliper to measure the width and thickness of the narrow section of the dumbbell specimen.
Mark a gauge length (typically 25 mm for ASTM or 20 mm for ISO standards) on the specimen.
4. Testing Procedure
Mounting the Specimen
Clamp the specimen in the tensile testing machine, ensuring the marked gauge length is centered.
Attach an extensometer (if available) for precise elongation measurement.
Conducting the Test
Set the machine to a constant crosshead speed (typically 500 mm/min for LSR).
Start the test and record the force vs. elongation data until the specimen breaks.
Calculating Elongation at Break
Measure the final gauge length (��Lf) at the point of rupture.
The elongation rate (�E) is calculated as:
�(%)=��−�0�0×100E(%)=L0Lf−L0×100
Where:
�0L0 = initial gauge length
��Lf = final gauge length at break
5. Factors Affecting Elongation Rate
Curing conditions (temperature, time)
Filler content (higher filler content may reduce elongation).
Crosslinking density (higher crosslinking can decrease elongation).
Strain rate (faster stretching may lead to lower elongation values).
6. Conclusion
The elongation rate of LSR is a key indicator of its flexibility and durability. By following standardized testing methods (ASTM D412 or ISO 37), manufacturers can ensure consistent material performance. Accurate measurement requires proper sample preparation, precise clamping, and controlled testing conditions.
For further validation, multiple specimens should be tested, and statistical analysis (mean, standard deviation) should be applied to ensure reliability.