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Stress Relaxation and Creep

Stress Relaxation and Creep

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A. Rubber material under constant load or constant displacement undergoes degradation. In applications like sealing, rubber material used to make these products are under constant stress / strain. Hence it is important to identify the creep and relaxation properties of these materials before they are put into use for manufacturing. The reason being that these seals go into critical applications like water, oil and gas sealing applications and in defense applications like submarines where they keep the sea water out. The material undergo accelerated degradation when they are exposed to aggressive chemicals like salt present in the sea water.

The idea of every lab test is to be replicate in the best possible way, the same conditions which prevail in the application for which the material is used. Over the years, focused development and research by Elastocon have enabled them to design solutions which recreate the natural conditions in the lab.
Elastocon offer stress relaxation systems where they provide the complete ecosystem which include:
Ageing ovens to accelerate the ageing process. Multiple cells of the oven can be set at different temperature there by reducing the overall test time since it is better to perform the test on a single material at three different temperatures to get a good extrapolation. We have ageing oven models which can accommodate either 4 rigs or 6 rigs depending on the model at the same time.

The relaxation rigs which apply the necessary strain on the material and measure the temperature of the sample and the reduction in force because of the degradation using a load cell.
The amplifier box / data acquisition unit collects the data from the thermocouple and load cell and send the information to the software which is used to log the data and generate test reports for analysis.

Draught hoods which maintain the environment around the load cell at a constant temperature to reduce the influence of fluctuation of room temperature on the load cell. Since this is a long-term test, tests generally go on for 1,000 hours. The room temperature in the day will be very different to the room temperature in the night. The draught hood removes this influence on the test.

Containers for performing the test in liquids like salt water etc.
Grips for performing tensile tests, compression tests and bending tests in the relaxation method.

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Product Specifications

B. The Creep and Stress relaxation machine is the model which can do both the stress relaxation and creep test automatically because the rigs are equipped with a motor for lowering and raising rigs into the cell and also to control and hold the constant load on the sample. The difference between creep and relaxation is as follows: Creep – The test force is held constant and the strain reduction required to maintain the force constant due to degradation of the rubber material is measured. Relaxation – The material is strained by a certain percentage. The drop-in force at constant strain due to degradation of the rubber material is measured. With this model, you can perform both creep and relaxation tests. The rigs and the draught hood are integrated with the cell oven. At present, it comes with a three cell option with the possibility to use containers to test in liquid medium. It is also possible to perform tests in tension, compression and bending mode.