Engleza Intrebari unit 2

When materials are exposed to forces, such as .................... and ..................... , they ...............................- that is, they change shape.

When a material is subjected to tension, its length will increase by a certain amount. This is called ......................... or ................................. .

It is especially important to understand the performance of materials .......................... , as their ............................ (ability to resist tension) is usually lower than their ..................................... (ability to resist compression).

A material's ability to do this (extend significantly, but still return to their original shape) is called .......................... .

Rubber is an example of a very ....................... material- it can be .............................. To a considerable extent.

If a material has very low elasticity, and is strong, engineers say it is ............... .

If a material has low elasticity and is weak, it is described as .....................- that is, it .................... (breaks, due to tension) very easily.

Some materials can change shape significantly, but do not return to their original shape. We say these materials are .......................... . Often, ....................... Is described in specific terms.

A material that can be ................................................ By hammering or rolling- for example, lead (Pb)- is ............................... . A material that can be drawn out (stretched) into a long length- for example, copper (Cu)- is ........................... .

The graph below shows the typical extension behaviour of ductile materials in ..................................... -where a sample bar is subjected to a progressively increasing tensile force.

The extension of the bar is ....................................... The increase in tension.

The bar reaches the .............................................. . Beyond this point, length begins to increase at a slightly greater rate than tension.

The ........................ Is reached. Beyond this point, the bar will no longer return to its original length.

The bar reaches its ................... . Once it .................... , it continues to increase in length, even without a further increase in tension.

This is the ............................................................ Of the material. Beyond this point, a ............................ (a narrower section) appears at a point along the length of the bar, signalling that it is about to fracture. This is the ............................................ , where the bar breaks in two.

The ........................... Of a material affects its .......................... - that is, how long it will last.

Generally, ................ Materials are more ................ than ............ materials, because they are better at resisting .............. -progressively worsening damage- to their surfaces.

................................. Describes a material's ability to resist being ...................... .

Materials with a high degree of scratch hardness are said to have good .............................. - they are good at resisting damage due to ........................... (the action of two surfaces being rubbed together).

........................................... Describes a material's abil ity to resist ........................ - that is, compressions in the surface of a material caused by impacts.

Two materials problems. One is .................. , often called .................................... In metals. This problem is caused by ......................................... - forces that continually vary. In aircraft, the wings are affected by cyclic loading as they frequently ............... , continually bending up and down due to air turbulence. The consequence of fatigue is ................................................ - the formation of cracks too small to see with the eye, and which worsen over time.

The speed at which ............................................. Progresses depends on the material's .................................................... . This is a measure of how easily cracks that have already formed continue to open up and increase in length.

Another problem is ................... - where components become permanently deformed (stretched, for example), due to loads. Creep increases over time.

Some materials ....................... (carry or transmit) heat better than others. Therefore, ................................................. varies, depending on the material.

Copper, for example, is an excellent ................................... . Polystyrene, on the other hand, is an excellent .................................................... (and so a very poor thermal conductor).

As temperature increases, most materials .............. (increase in size due to heating), and as temperature falls, they ........................... (decrease in size due to cooling).

The extent to which expansion and contraction occur is measured by a material's .................................................. - that is, its change in size for a given change in temperature.