# Grip Mechanics Problem: Designing for Rubber at 1kN Force

• ljaeggi
In summary, the grip will have two flat plates that will grip the rubber in place. The plates will be shaped to avoid stress concentration at the edges where they grip the rubber sample. The grips will be used to test rubber that has a low coefficient of friction.
ljaeggi
I have a small dilemma with a statics problem that isn't really static...

I have been asked to design a grip for a tensile testing machine specifically for rubber that will supply up 1kN of force through the rubber
I have chosen aluminium to make the main body of the grip and will be driven pneumatically.

I have gone for a grip design of two flat plates that will hold the rubber in place.
One grip would be stationary at the bottom of the test piece and the other would be moving at about 1cm/s gripping the top of the test piece.

The test piece is in a dumbbell format according to standards and the test piece will weigh no more than 10 grams.

Therefore, assuming a 0.5 coefficient between rubber and aluminium, is it a simple static problem and the force required to keep the rubber in place would be 2kN?
Or do I have to treat the two systems independent of each other?

Have you thought about how you will shape the edges of the flat plates in order to avoid (or at least reduce) stress concentration at the edges where the plates grip the rubber sample? This can have a profound effect on your results, I would think. It should relate also to the profile of the rubber sample.

OldEngr63 said:
Have you thought about how you will shape the edges of the flat plates in order to avoid (or at least reduce) stress concentration at the edges where the plates grip the rubber sample? This can have a profound effect on your results, I would think. It should relate also to the profile of the rubber sample.

I have shaped the plates to account for the phenomena known as necking where by too much pressure to the rubber makes the rubber spill over the plates. A simple round and adjustable pressure accounts for this. this has been previously documented

However, multiple test pieces will be used ranging in material and overall size. This also is why I want to calculate the force required. (μ=0.5 for the lowest coefficient of rubber on test btw)

But while the rubber is approaching its ultimate tensile strength (the point of rupture) including a factor of safety, at the 1kN max, I am assuming the dimensions of the rubber would not change however during the test its elongation is about 400% (very roughly). I want to be very close to the equilibrium point of the system to ensure the least stress to the test piece.

## 1. What is the purpose of studying grip mechanics for rubber at 1kN force?

The purpose of studying grip mechanics for rubber at 1kN force is to understand the behavior and performance of rubber materials under high forces, which is crucial for designing products that require strong grip or traction, such as tires, shoe soles, and mechanical grips.

## 2. How is the force of 1kN chosen for this study?

The force of 1kN (kilonewton) is a commonly used unit for measuring large forces, and it falls within the range of forces that rubber materials may experience in real-world applications. Therefore, it is a suitable force to study the grip mechanics of rubber materials.

## 3. What factors affect the grip mechanics of rubber at 1kN force?

The grip mechanics of rubber at 1kN force can be affected by various factors, such as the type and composition of rubber, the surface roughness of the object it is gripping, the temperature and humidity of the environment, and the duration of the applied force. These factors can influence the adhesion, friction, and deformation of the rubber material.

## 4. How is the design process impacted by the findings of this study?

The findings of this study can provide valuable insights into the behavior of rubber materials at high forces, which can be used to optimize the design process for products that require strong grip or traction. Designers can use this information to select the most suitable rubber material, surface texture, and other design parameters to achieve the desired grip performance.

## 5. What are the potential applications of the findings from this study?

The findings from this study can have various applications, such as improving the design and performance of tires, shoe soles, and mechanical grips, enhancing the safety and efficiency of industrial processes that involve rubber materials, and developing new and innovative products that require strong grip or traction.

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