IB Design Technology Topic A3.1.6 Mechanical Properties of Materials Revision Notes (SL/HL)

IB Design Technology Topic A3.1.6 Mechanical Properties of Materials Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

Mechanical Properties: How a Material Answers a Force

A3.1.1 defined the mechanical family, so this lesson goes straight to the nine properties inside it.
The nine group naturally into four ideas: strength, stiffness and elasticity, toughness and hardness, and permanent shaping.
Keeping the nine apart is the whole skill here, because everyday speech uses their names interchangeably and the exam does not.

Note

Mechanical properties are intrinsic to the material.
They do not change unless the composition or internal structure of the material is altered.
This is why heat treatment and alloying change a metal's properties, but cutting it in half does not.

Strength: Resisting Tension and Compression

Tensile Strength

Definition

Tensile Strength

Tensile strength is the ability of a material to withstand pulling forces without breaking or deforming.

Tensile strength is the force a material withstands while being pulled apart, measured in pascals (Pa) or megapascals (MPa).
It is the property that matters for cables, ropes and structural beams, anything that carries a pulling load.

Note

A Universal Testing Machine (UTM) is used to measure tensile strength.
Two grips hold the sample, one fixed and one that moves slowly to pull it.
The machine records the force applied in newtons and how far the sample stretches.
The test runs until the material breaks, which is why it is a destructive test.

Compressive Strength

Definition

Compressive Strength

The ability of a material to withstand forces that try to squash or compress it without breaking or deforming.

Compressive strength is the force a material withstands while being squashed, also measured in pascals or megapascals.
It is the property that matters for columns, foundations and pavements, anything that carries a pushing load.
A material can be excellent at one and poor at the other, which is exactly why concrete is reinforced with steel.

Example

Concrete has high compressive strength, which makes it suitable for building foundations.
Its tensile strength is poor, so steel bars are added to carry the pulling loads it cannot.

Stiffness and Elasticity: What Happens Before Anything Is Permanent

Stiffness

Definition

Stiffness

The ability of a material to resist bending or deflection when a force is applied, helping it maintain its shape.

Stiffness is a material's resistance to bending or deflecting under a load, and it is not the same thing as strength.
A steel wire is strong yet flexible, which shows a material can take a big load and still bend a long way.
High stiffness means very little bending, as in glass and steel.
Low stiffness means it bends easily, as in rubber and many plastics.
It is critical in structural design, where a product must hold its shape under load rather than simply survive it.

Example

Carbon fibre is very stiff for its weight.
That makes it ideal for aerospace and automotive parts, where rigidity must be bought without adding mass.

Elasticity

Definition

Elasticity

The ability of a material to return to its original shape after being stretched, compressed, or deformed, once the force is removed.

Elasticity is the ability to return to the original shape once the force is removed, so the deformation is temporary.
Stretch a material past its elastic limit and it will no longer come back, which is the boundary between elasticity and plasticity.

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Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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Mechanical Properties: How a Material Answers a Force

A3.1.1 defined the mechanical family, so this lesson goes straight to the nine properties inside it.
The nine group naturally into four ideas: strength, stiffness and elasticity, toughness and hardness, and permanent shaping.
Keeping the nine apart is the whole skill here, because everyday speech uses their names interchangeably and the exam does not.

Note

Mechanical properties are intrinsic to the material.
They do not change unless the composition or internal structure of the material is altered.
This is why heat treatment and alloying change a metal's properties, but cutting it in half does not.

Strength: Resisting Tension and Compression

Tensile Strength

Definition

Tensile Strength

Tensile strength is the ability of a material to withstand pulling forces without breaking or deforming.

Tensile strength is the force a material withstands while being pulled apart, measured in pascals (Pa) or megapascals (MPa).
It is the property that matters for cables, ropes and structural beams, anything that carries a pulling load.

Note

A Universal Testing Machine (UTM) is used to measure tensile strength.
Two grips hold the sample, one fixed and one that moves slowly to pull it.
The machine records the force applied in newtons and how far the sample stretches.
The test runs until the material breaks, which is why it is a destructive test.

Compressive Strength

Definition

Compressive Strength

The ability of a material to withstand forces that try to squash or compress it without breaking or deforming.

Compressive strength is the force a material withstands while being squashed, also measured in pascals or megapascals.
It is the property that matters for columns, foundations and pavements, anything that carries a pushing load.
A material can be excellent at one and poor at the other, which is exactly why concrete is reinforced with steel.

Example

Concrete has high compressive strength, which makes it suitable for building foundations.
Its tensile strength is poor, so steel bars are added to carry the pulling loads it cannot.

Stiffness and Elasticity: What Happens Before Anything Is Permanent

Stiffness

Definition

Stiffness

The ability of a material to resist bending or deflection when a force is applied, helping it maintain its shape.

Stiffness is a material's resistance to bending or deflecting under a load, and it is not the same thing as strength.
A steel wire is strong yet flexible, which shows a material can take a big load and still bend a long way.
High stiffness means very little bending, as in glass and steel.
Low stiffness means it bends easily, as in rubber and many plastics.
It is critical in structural design, where a product must hold its shape under load rather than simply survive it.

Example

Carbon fibre is very stiff for its weight.
That makes it ideal for aerospace and automotive parts, where rigidity must be bought without adding mass.

Elasticity

Definition

Elasticity

The ability of a material to return to its original shape after being stretched, compressed, or deformed, once the force is removed.

Elasticity is the ability to return to the original shape once the force is removed, so the deformation is temporary.
Stretch a material past its elastic limit and it will no longer come back, which is the boundary between elasticity and plasticity.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

A. Design in theory8 subtopics

B. Design in practice8 subtopics

C. Design in context8 subtopics

IB Design Technology Topic A3.1.6: Mechanical Properties of Materials Notes

A. Design in theory8 subtopics

B. Design in practice8 subtopics

C. Design in context8 subtopics

Mechanical Properties: How a Material Answers a Force

Strength: Resisting Tension and Compression

Tensile Strength

Compressive Strength

Stiffness and Elasticity: What Happens Before Anything Is Permanent

Stiffness

Elasticity

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Mechanical Properties: How a Material Answers a Force

Strength: Resisting Tension and Compression

Tensile Strength

Compressive Strength

Stiffness and Elasticity: What Happens Before Anything Is Permanent

Stiffness

Elasticity

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account