How do you find the tensile strength of rubber?

Tensile strength is one of the key factors that should be considered when selecting the right material for any application, in particular where a rubber component plays a part in sealing, supporting or anti-vibration. Tensile strength is often one of the main priorities in terms of material properties because it influences the performance of a product, especially where that product is likely to be under tension. We take a look below at how you can find the tensile strength of rubber, which factors influence tensile strength, and how it relates to FEA simulation.  

Why is the tensile strength of rubber important?  

Tensile strength is the property of a material that quantifies the maximum load it can withstand before fracturing. It applies to stiff materials such as metals, composites and natural materials like timber and stone just as much as it does to rubber. When a load that is less than the tensile strength of a material is applied, that material may deform or stretch, but should return fully or mostly to its original size and shape. As the tensile strength approaches its maximum load, the material may begin to ‘neck’, which means that it shows a permanent deformation. As the load increases further, the neck will ultimately snap. 

The tensile strength of rubber is unique to its chemical composition and structure. This particular property is important precisely because the elastic element of rubber is often the reason why it is the chosen material for an application – if you want a seal surface to remain in contact with a shaft, or a strap to retain its grip, or an AV mount to deliver long term reliable support without snapping, then rubber provides the ideal solution. 

How does the tensile strength of rubber impact product performance? 

If your application requires support, grip, flexibility or sealing, rubber is often the ideal way of delivering that outcome. It is therefore important to consider how the rubber might fail under your specific operating conditions and therefore what is required of the material to be able to operate reliably. Applications and environments can vary widely, and factors such as whether the rubber will be in compression or tension could be critical; a static pad that simply takes a long-term load may not need much tensile strength but will need good compression set properties, whereas an AV mount that could see both tension and compression cycles, as well as vibration, will need a much higher tensile strength threshold. 

How do you find the tensile strength of rubber?

There is a standardised industry-wide test used to obtain the tensile strength of a rubber material. A standard thickness sheet of rubber has a piece of rubber in the shape of a dumbbell cut out of it using set dimensions. This dumbbell sample is then gradually stretched apart until it breaks. The force applied and resultant elongation are plotted and this stress/strain curve derives the Young’s Modulus of the material. This test also provides the ultimate measure of elongation at the point at which the material breaks; this informs us how much a given rubber will stretch before failure, and although this ‘elongation at break’ figure doesn’t relate directly to the tensile strength of the material it is still a key value when calculating likely performance.

How does the tensile strength of rubber vary between different types of rubber? 

The tensile strength of rubbers can vary widely depending on the compound in question; the differences in the structures of the polymer chains and their crosslinks give a broad range of tensile strength values and elongation at break values. As ever with rubber, there is an almost infinite mix of variable properties that need to be considered for the best performance in any given application, of which tensile strength is only one – and which, in fact, may not be the most important material property for some applications.

Can you alter the tensile strength of rubber to suit the application?

It is possible to influence the tensile strength of rubber through the selection of the optimum polymer type, cure system and fillers. However, the tensile strength of a rubber may need to be compromised in order to ensure that a requirement relating to another property such as hardness, temperature or chemical resistance is met.

How do you test the tensile strength of rubber for an existing product?

To understand the tensile strength of an existing rubber component, a test piece in the actual material used to manufacture that product would have to be created. This can be done by moulding a sample sheet under the correct cure conditions from the correct compound, and then a set of dumbbell test pieces made and put through the test process described above. It is not possible to establish the information about this property from a non-standard shape, although empirical comparative testing could potentially be used to indicate better or worse performance. 

How does tensile strength relate to FEA?

FEA is used to simulate the performance of a component in situ, analysing likely failure points and providing the ability to improve a design prior to manufacture. One of the key pieces of data required for FEA is tensile strength; without knowing the tensile strength value of the rubber material intended for manufacture, it is impossible to calculate the failure point of a model being analysed under FEA. This is true of FEA for both linear and non-linear materials, but non-linear analysis needs additional information such as a fully representative stress strain curve and the type of failure mode – of which tensile stress failure is only one. 

If you would like to know more about the tensile strength of rubber materials that you are considering working with, or are considering likely failure points of a rubber component, get in touch with our team on 023 8022 6330 or email [email protected]. Whether it’s material development you need or expertise in non-linear FEA, we will be able to support you in finding the right material for your application.