Chapter 19 - Forces & Stresses on Materials and Objects

What are the five main types of forces that can act on a material?

Tension, compression, bending, torsion, and shear.

What type of force is described as a pulling force exerted by each end of an object?

Tension.

The force of _ is described as being squashed or a pushing force.

compression

What two forces are simultaneously at play when a bending force is applied to a material?

Compression and tension.

What is torsion?

A twisting force.

A force that acts across a material, such as when scissors cut paper, is known as a _ force.

shear

How can the strength of smaller and lighter electronic products be improved to stop damage from compression and bending?

By adding extra materials to reinforce thinner areas and improve its shape.

What is the term for strengthening a material that could weaken when a force is applied?

Reinforce.

What is a 'composite' material?

A material built from more than one thing, often to make it stronger.

What are two examples of composite materials used for strong housing in electronic systems?

Carbon fibre and fibreglass.

How are composites like carbon fibre and fibreglass constructed?

Fibres are layered together with a polymer resin.

What is a common method for strengthening the plastic shells of electronic products while reducing material usage and cost?

Adding ribs of thicker material around the case.

What is housing (in product design)?

An exterior case or enclosure for a system.

What is casing (in product design)?

A removable outer layer of a product.

How can the tensile strength of a metal be tested?

By fixing a piece of the metal to a point and then loading it with a pulling force.

What property describes the maximum tension a material can withstand without breaking?

Tensile strength.

The shape of a _, used in construction, is specifically designed to withstand bending and compression forces.

Rolled steel joist (RSJ)

How can a metal be tested for its ability to withstand torsion?

By securing one end in a vice and twisting the other end.

What technique can be used to prevent deformation in metal due to both torsion and shear forces?

Bracing one piece of metal to another.

What tool is used for cutting metal by providing a shear force?

Tin snips.

What are two ways to increase the tensile strength of paper or card?

Add a polymer to the material or laminate it with a polymer.

What process is used to increase the compressive strength of card by creating a wave-like inner layer?

Crimping.

Cardboard with a crimped inner layer that creates a structure of triangles is commonly called _ cardboard.

corrugated

How does corrugated cardboard achieve great compressive strength?

It spreads any applied force across the waves of triangles.

When paper or card is folded, what forces are acting on the inner and outer particles?

The inner particles are under compression, and the outer particles are under tension.

What can be done to paper or card before bending to minimize damage and make it more flexible?

It can be scored.

What is meant by the word scored (in papercraft)?

An indented scratch to allow paper or card to fold with ease.

How can the shear force resistance of paper or card be increased?

By making it thicker, using multiple thicknesses, or laminating it with a polymer.

Why is it difficult to generalize the properties of polymers?

Because there are so many different types, each with different characteristics.

What is the common use for the polymer PET (Polyethylene terephthalate)?

Plastic water bottles.

HDPE (High density polythene) is a common polymer used for what type of product?

Fabric conditioner bottles.

The polymer PVC, or Polyvinyl chloride, is commonly used for making what products?

Plastic toys, cling film, and blister packs.

What is a common use for LDPE (Low density polythene)?

Bread bags.

The polymer PP, or Polypropylene, is typically used for which items?

Yogurt pots and pen lids.

What are common uses for the polymer PS (Polystyrene)?

Packaging and coffee cups.

What is the term for the force that stretches a fabric?

Tension.

_ is an example of a fabric with high tensile strength, making it strong and hard to tear.

Acrylic

What simple sewing technique can stop a curved edge of fabric from stretching and becoming misshapen?

Stay stitching.

What does 'compressibility' refer to in the context of textiles?

How much a fabric can squash or flatten.

Why are fabrics with high compressibility, like heavy wool, usually warm and comfortable?

The weave creates air pockets that help insulate the wearer.

What is the term for twisting fabric in opposite directions to extract liquid?

Wringing.

Which fabric type becomes permanently misshapen if it is twisted?

Woollen clothing.

The shear strength of a fabric is most affected by what aspect of its construction?

The way it is woven, knitted, or bonded.

Which type of fabric construction has the lowest shear strength and tears most easily?

Plain weave.

How is the fabric denim made stronger than plain weave fabrics?

It has a twill weave.

Why are knitted fabrics more resistant to shear forces?

They are made up of interlocking fibres.

What is 'laminating' in the context of textiles?

Bonding layers of material together to improve strength.

Besides strength, what other properties can be improved by laminating fabrics?

Making them waterproof or warmer.

Quilting is made from wadding enclosed and sewn between two layers of ____.

fabric

What method of knitting creates columns of knit that add texture, thickness, and warmth?

Knitted rib.

What is rigidity (in materials)?

Resistance to bending.

What are 'boning' strips used for in garments like ball gowns?

They are flexible plastic strips used to hold fabric rigid and provide a strong shape.

How are areas like shirt collars and cuffs typically stiffened?

By bonding interfacing to the inside of the fabric.

How can a fabric's ability to regain its shape after stretching be improved?

By adding elastic fibres, such as elastane, into the blend.

What kind of fibre is elastane?

A durable fibre used in stretchy sportswear like leggings.

Why does timber have good tensile and compressive strength?

Due to its fibrous structure.

What often happens to untreated timber when it is bent?

It snaps.

What are two ways to make timber more flexible to prevent it from snapping when bent?

Soak it in water or expose it to steam.

What is kerfing?

The process of cutting slots along the inside face of timber to allow it to cope with compressive force during bending.

How is the manufactured board 'plywood' strengthened?

By having layers of timber glued with their grains at right angles to each other.

What property, a desirable feature of plywood, refers to its ability to withstand flexing?

High cross-sectional stability.