Reinforcing and stiffening
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:
- Being squashed. - a pushing force
- A bending force is applied at an angle causing a material to be in compression and tension at the same time. - forces at an angle to the material
- A twisting force. - a twisting force
- A force across a material, eg scissors cut by applying a shear force. - forces acting across the material
To increase the Tensile strength is the ability of a material to resist pulling forces without snapping, eg a guitar string has high tensile strength. of paper or card, a A large molecule formed from many identical smaller molecules known as monomers. can be added to the material. If a sheet of paper or card were to be At least two layers of material bonded together. with a polymer that would also increase the tensile strength of the material.
To increase the compressive strength of card, the inner layer can be Compressing a material into small folds.. This creates a wave-like structure of triangles that is commonly referred to as A series of parallel folds added to a material to give strength. 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.
Laminating and The process of enclosing a material in a thin film of a different material. are often used to:
- add strength to paper and board materials
- prevent cross-contamination, eg provide a hygienic packaging for food
- enhance How something looks., eg metallic finishes for a high-quality effect
- protect the product
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 An indented scratch to allow paper or card to fold with ease. before bending, the damage to the paper or card can be minimised. This scored piece of paper or card is now more flexible.
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.
