Fluorosilicone Rubber (FVMQ) Resilience Testing: Standards, Methods, and Applications

Fluorosilicone rubber (FVMQ) resilience testing measures the rebound elasticity of this fuel- and oil-resistant elastomer, a key indicator of dynamic performance for seals and damping components in aerospace and automotive fuel systems. This article explains the test principle, specimen requirements, internationally recognized methods such as ISO 4662, ASTM D2632, JIS K 6255 and GB/T 1681, and how the results are interpreted and applied.

Technical Overview

Fluorosilicone rubber, designated FVMQ under the nomenclature of ASTM D1418 and ISO 1629, is a fluorinated methylvinyl polysiloxane elastomer that combines the wide service-temperature flexibility of silicone rubber with outstanding resistance to aviation fuel, gasoline, oils, and many non-polar solvents. Typical compounds remain flexible from approximately -60 °C to +175 °C, with short excursions possible up to 200 °C.

Rebound resilience, commonly shortened to resilience, quantifies the ability of a vulcanized rubber to store and return elastic energy when subjected to impact deformation. It is expressed as the percentage of the applied mechanical energy that is recovered after a ball, indenter, or pendulum hammer strikes the test piece. For FVMQ compounds, rebound resilience typically falls between 30 % and 55 % depending on hardness, filler loading, crosslink density, and test temperature.

Because resilience correlates directly with vibration behavior, impact absorption, and seal energization, rebound testing is a routine quality-control and material-qualification item for fluorosilicone compounds used in dynamic sealing and damping applications. Accredited third-party laboratories routinely perform these tests to internationally recognized standards.

Testing Samples

Standard Molded Specimens

Preferred test pieces are molded cylindrical buttons, for example approximately 12.5 mm in thickness with a diameter of about 29 mm, cured under production-equivalent conditions. Molded specimens are free of surface buffing and density gradients that can bias rebound readings and therefore yield the most reproducible data.

Specimens Taken From Finished Products

When molded buttons cannot be produced, test pieces may be cut or stacked from finished articles such as O-rings, gaskets, diaphragms, and molded seals. Stacked and lightly bonded layers must meet minimum thickness requirements, and fabric impressions, coatings, and surface defects must be removed carefully without overheating the rubber.

Sample Conditioning

Unless otherwise specified, specimens are conditioned at 23 ± 2 °C and 50 ± 5 % relative humidity for a minimum of 16 hours in accordance with ISO 23529. For low-temperature resilience evaluation, additional conditioning at the test temperature, for example -30 °C or -50 °C, is applied to ensure thermal equilibrium before impact.

Testing Items

Common resilience-related test items for fluorosilicone rubber include:

• Vertical (ball) rebound resilience at standard laboratory temperature
• Pendulum rebound resilience using Schob-type or equivalent impact devices
• Rebound resilience at low temperatures inside a temperature-controlled chamber
• Resilience retention after immersion in reference fuels, oils, or service fluids
• Resilience retention after accelerated heat aging
• Supporting measurements such as hardness, tensile properties, and compression set to contextualize the resilience data

Testing Methods

Ball Rebound (Vertical Rebound) Method

Vertical rebound testing per ASTM D2632 and GB/T 1681 uses a free-falling ball or impactor released from a fixed height onto the flat surface of the specimen. Rebound resilience is calculated as the ratio of rebound height to drop height, expressed as a percentage. The method is fast, requires relatively simple apparatus, and is widely used for routine quality control of FVMQ compounds.

Pendulum Rebound Method

ISO 4662 and JIS K 6255 specify rebound resilience determination using pendulum-type impact devices, such as the Schob pendulum, in which a hammer strikes the specimen and the rebound angle or height of the pendulum arm is measured. The energy returned to the pendulum, relative to the energy of the initial stroke, gives the resilience value. Readings are commonly taken after a defined number of conditioning impacts on the same point.

Procedure and Calculation

In a typical sequence, the conditioned specimen is placed on a rigid anvil, the instrument is leveled and calibrated, and a specified number of impacts are performed at several points on the surface, with the initial conditioning impacts discarded. The median of the recorded readings is reported as rebound resilience R, where R = (rebound energy / impact energy) × 100 %, together with the test method, test temperature, specimen type, and hardness of the compound.

Factors Influencing Results

Rebound resilience of FVMQ is sensitive to temperature, generally decreasing as the material approaches its glass transition region, as well as to filler type and loading, crosslink density, and fluid uptake after fuel immersion. Consistent specimen preparation, strict temperature control, and regular instrument calibration are therefore essential for comparable results.

Applications

Resilience data for fluorosilicone rubber support material selection and qualification in demanding sealing environments, including:

• Aerospace fuel system seals, O-rings, and grommets exposed to jet fuel and wide temperature swings
• Automotive fuel injection, fuel line, and emission-control components requiring long-term flexibility
• Diaphragms and valves in contact with fuels, oils, and hydraulic fluids
• Vibration isolators and damping elements where energy return must be balanced against heat dissipation
• Material certification, incoming inspection, and batch release by manufacturers and accredited third-party laboratories

FAQ

What is a typical rebound resilience value for fluorosilicone rubber?

General-purpose FVMQ compounds with a hardness of about 50 to 70 Shore A typically show rebound resilience in the range of roughly 30 % to 55 % at room temperature. Exact values depend strongly on formulation and the test standard used, so comparisons should always reference the same method and temperature.

Which standards are most commonly used for FVMQ resilience testing?

ISO 4662 and JIS K 6255 cover pendulum-based rebound resilience, while ASTM D2632 and GB/T 1681 cover vertical ball rebound. The methods give related but not numerically identical results, so the specific standard must always be stated in the test report.

Does fuel exposure affect the resilience of fluorosilicone rubber?

FVMQ is highly fuel resistant, but prolonged exposure can still cause slight swelling and changes in the crosslink network, which may reduce rebound resilience. Measuring resilience before and after immersion in reference fuels is a practical way to assess service durability.

Why test resilience at low temperature?

Near its low-temperature limit, FVMQ loses elastic energy return as molecular mobility decreases. Low-temperature resilience measurements verify that seals remain sufficiently elastic for dynamic duty in cold environments, such as high-altitude aerospace service.

How is resilience different from damping?

Resilience measures the fraction of impact energy returned, whereas damping measures the fraction dissipated as heat. Together, the two properties characterize the complete dynamic response of fluorosilicone components under vibration and impact loading.