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Testing Materials

Marking-out

What are metals?

Hardness Testing

Toughness Testing

Ductility and Malleability

Conductivity, Permittivity & Resistivity

Compressive Strength Testing

Tensile Strength Testing

Shear Strength Testing

Fatigue Testing (Durability)

Bend Testing

Non Destructive Testing (NRT)

How can we describe mechanical forces acting on structures?

When choosing the right material for a given application it is important to understand the kinds of loads (forces) which act upon a mechanical structure or component. The most seven common types of loading are shown in the diagram below.

The video below describes in basic terms the meaning of the major physical properties of metals (and similar materials).

These forces can either be static (continuous and predictable), dynamic (changing, predictable or unpredictable), or a combination of both.

Extensive testing is carried out on materials so that engineers have a good understanding of how metals will behave and when they will fail (break) under a given loading condition.

How can we describe the mechanical properties of materials?

When we describe materials, we usually describe them in the way that they behave mechanically, that is when we try to test their physical properties. Here are some of the most notable mechanical properties of materials.

Whilst the table mainly describes metals, some of the terms in the table above are not just applicable to metals and can be used to describe the mechanical properties of other materials such as plastics.

What kinds of forces do materials often have to withstand? Let's have a look at an example.

Consider the image below of the 'rolling gear' (moving parts) and 'chassis' (load bearing structure) of a vintage light truck. Can you identify each of the different components? Consider the materials they are manufactured from? What types of loads (forces) do you think each component has been designed to withstand?

The vintage truck shown used a 'leaf suspension'. It was not a very comfortable system of transport, however served its purpose for a long while as vehicles were generally heavy, slow and cumbersome. As vehicles became faster, a new system of absorbing the shocks from the potholes and gaps in the road was necessary. The leaf suspension was subsequently replaced by the wishbone and double wishbone suspension in combination with pneumatic (compressed) gas or hydraulic shock absorbers.

Hardness Testing

Hardness is the ability of a material to withstand scratching or indentation without damage. It is a property that can be measured. Diamond was for a long while the hardest known material on earth, however this has now been superseded by an even rarer material called wurtzite boron nitride.

Toughness Testing

Toughness is the ability of a material to resist impact damage. Some of the toughest materials known to man are derived from carbon such as:

Carbon Composite
Mineral Lonsdaliete
Graphene
Carbyne

Ductility and Malleability

Ductility is often confused with malleability. Malleability is the ability of a material to be deformed without cracking. If you beat a metal with a hammer and it doesn't crack (e.g. lead) then it is malleable. Ductility, however specifically refers to how permanently stretchable a material is. Copper can be considered ductile as it is frequently drawn into long wires for example in electrical applications.