# Force given by blades on cloth

• Rodan
In summary, the conversation discusses the difficulty of calculating force in drop testing on armor and the use of different amounts of cloth to determine the effectiveness against certain weapons. It also mentions the challenges of associating force with the tests and the impact of different materials on knife penetration. A document describing current testing methodologies and reporting for knife protection is recommended as a helpful resource.
Rodan
Hi,
I have been wracking my brains about how to work out how much force I am calculating when doing some drop testing on armour.
I was wondering if someone woudl be able to walk me through a good way to show this as simply as possible. My physics knowledge is limited but I learn fast so say what you think and I'll ask if I don't get it.

Right my problem is I am dropping various blades onto fabrics from two different heights (1.2 and 0.7m) the drop test machine has minimal friction and just drops straight downwards.

I am using different amounts of cloth to see where it starts to become effective against certain weapons strikes. However the points of blades are obviously microscopic and there is my dilema. I am having difficulty saying how many kilos per m squared force I am giving or how many joules I am releasing within a time frame.

I have some more data if someone is willing to help.

Thanks in advance

A

Try having a read through this. It's not the most thrilling document in the world, but it is a standard describing current testing methodologies and reporting for knife protection. The approach is to drop a blade of specific dimensions attached to a carriage of known mass. Specific threat levels are described by the kinetic energy of the striker upon impact. The depth of penetration into the backing material is measured, and if it's over a certain distance then the sample is not safe. A material that prevents the

The problem lies with associating force with the tests. For instance, try to appreciate the difference between a knife impact on steel, and a knife impact on butter. The steel will arrest the knife's motion over a very short distance (very small degree of penetration into the steel) but at a very high force. The butter will arrest the motion over a very long distance but at a very low force. Now ask yourself which protects you better from knife penetration.

It gets even more complicated when you consider that a knife or spike going through Kevlar weave often doesn't interact a huge amount with the material itself, instead finding space between fibres and forcing them apart and through. That's why fibre armour manufacturers often supply a stab resistant layer that roughens the blade, making it less able to slip between fibres.

That article is perfect can't believce I hadn't found that yet. The machine and blades I have used are the ones int he pictures, it is actually the MET police drop test equipment!

Thanks

A

No worries, it's probably one of the better standards I've had to work to.

## 1. What is the force given by blades on cloth?

The force given by blades on cloth is the amount of pressure or push exerted by the blades on the surface of the cloth. It is measured in units of newtons (N).

## 2. How does the force given by blades on cloth affect the cloth's movement?

The force given by blades on cloth can affect the cloth's movement in different ways depending on the direction and magnitude of the force. It can cause the cloth to move in the same direction as the force, or it can cause the cloth to stretch or tear if the force is too strong.

## 3. What factors can affect the force given by blades on cloth?

The force given by blades on cloth can be affected by factors such as the sharpness and angle of the blades, the type and thickness of the cloth, and the speed at which the blades are moving.

## 4. How is the force given by blades on cloth calculated or measured?

The force given by blades on cloth can be calculated by multiplying the pressure applied by the blades (in units of Pascals) by the surface area of the cloth that is in contact with the blades. It can also be measured using specialized equipment such as force gauges or load cells.

## 5. Can the force given by blades on cloth be harmful?

Yes, the force given by blades on cloth can be harmful if it is too strong or if the blades are not handled properly. It can cause injuries such as cuts or punctures, and it can also damage the cloth or other objects in its path. It is important to use caution and proper safety measures when working with blades and cloth.

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