Forces and stresses

Forces act on materials all the time - even if a material appears stationary it still has a force acting on it. There are five terms used to describe what type of force can act on a material:

Five different forces: Compression; bending; tension; torsion and shear illustrated around a main label saying ‘forces’.

To increase the tensile strength of paper or card, a polymer can be added to the material. If a sheet of paper or card were to be laminated with a polymer, that too would increase the tensile strength of the material.

To increase the compressive strength of card, the inner layer can be ‘crimped’. This creates a wave-like structure of triangles that is commonly referred to as corrugated cardboard. This gives the cardboard great compressive strength as it spreads any force applied across the waves of triangles. Corrugated cardboard is commonly used for packaging products for transportation.

A close-up view of rolled up corrugated card in green and brown.
Corrugated card

When paper or card is folded, the forces are applied at an angle. This is a bending force on the card. The inner particles of the material are under compression, and the outer particles are under tension. This force causes the card to crease. If the card is scored before bending, the damage to the paper or card can be minimised. This scored piece of paper or card is now more flexible.

A blank opened greeting card that has been scored next to a closed blank greeting card.
Scored card can be folded more easily

When paper or card is cut with scissors, the material is being damaged by a shear force. If the paper or card is either thicker, made up of multiple thicknesses or laminated with a polymer, then the shear force resistance of the material will be greater.

A pair of hands shown holding a piece of white card and a pair of scissors cutting it.
Shear force from cutting paper with scissors