Life Prediction of O-Rings

Life prediction of O-Ring can use compression stress relaxation test because most polymeric part are intended to be in service for several year. O-Ring experience changes in properties under heat , high temperature, mechanical stress and fluids. Service life prediction of  an O-Ring is of practical and engineering interest to predict the behaviour of the component over the service life cycle. Main factor for O-Ring degradation can shown in picture 1

The two important properties of O-Ring are compression stress relaxation and resilience. Resilience is a measure of the ability of the seal to retract to its original shape after a constraint has been removed. The force decay of elastomer component under constant compressive strain is known as compression stress relaxation. The test measures the sealing force exerted by seal or O-Ring under compression between two plates.

Test condition for compression stress relaxation. 

• Accelerated aging : Accelerated Oven Aging at 100 , 125 and 150 degree celsius. 
• Sample were aged inside jigs with 25% compression.
• Failure Criteria : Compression stress relaxation 40%

Compression stress relaxation test data is used to Service Life prediction by Arrhenius equation and WLF equation. 

The rubber ring spring

The rubber ring spring, known as a low-frequency stud mounting, can be, as shown in Figure 1 (a), stress by three types of loading A, B, and C. The elasticity of rubber ring has different values in the separate directions. It is largest in direction B and smallest in direction A, as shown in the characteristic lines in Figure 1(b). In compressive loading (direction A), the compression may be so large that the hole is completely closed. The description ‘low-frequency mounting’, mean that this rubber ring is suitable for such cases where a low natural frequency is required. It can be loaded up to 100 N per mounting. Thus rubber ring uses lies in the field of precision instrument applications.

Figure 1 Rubber ring spring