Question

i need an easy experiment ( creativity and fun) that can be done at home related to one of this topics  elastic/plastic deformation the effect of heat on various properties,, ductile vs. brittle fracture.

Answer 1

For engineering materials, there are two basic fracture modes are possible:

i) Ductile and

ii) Brittle

Ductile Fracture:

Classification is based on the ability of a material to experience plastic deformation. Ductile materials typically exhibit substantial plastic deformation with high energy absorption before fracture.

Fig (a) Highly ductile fracture in which the specimen necks down to a point

Fig (b) Moderately ductile fracture after some necking

Experiment:

If we apply a force to a copper rod that contains a small notch the rod plastically deforms and the notch does not decrease the force required to break the rod. Apply force as shown and note the bend in copper rod.

Before bending:                                                          After bending:

The fracture of a copper rod is an example of ductile fracture. In ductile fracture there is a lot of plastic deformation, and significant energy is absorbed before the fracture.

Brittle Fracture:

Brittle fracture accompany normally little or no plastic deformation with low energy absorption. Brittle fracture occurs suddenly and catastrophically without any warning; this is a consequence of the spontaneous and rapid crack propagation.

Fig c) Brittle fracture without any plastic deformation

Breaking of chalk:

Materials that do not fail in a ductile manner will fail in a brittle manner.

Brittle fractures are characterized as having little or no plastic deformation prior to failure.

Materials that usually fracture in a brittle manner are glasses, ceramics, and some polymers and metals. Under some circumstances some metals that are usually ductile will fail in a brittle manner, possibly with catastrophic results.

c)

Ductile-to-brittle transition:

At low temperatures some metals that would be ductile at room temperature become brittle. This is known as a ductile to brittle transition. The ductile-to-brittle transition is related to the temperature dependence of the measured impact energy absorption.

The ductile to brittle transition temperature is strongly dependent on the composition of the metal. Steel is the most commonly used metal that shows this behaviour. The ductile-to-brittle transition is related to the temperature dependence of the measured impact energy absorption.

Note: The reason for Titanic sank ductile to brittle transition. During the construction of ship, the engineers didn’t account the brittle nature of steel at low temperature.

d)

Fatigue is a form of failure that occurs in structures subjected to dynamic and fluctuating stresses (e.g., bridges, aircraft, and machine components). Under these circumstances it is possible for failure to occur at a stress level considerably lower than the tensile or yield strength for a static load.

The term “fatigue” is used because this type of failure normally occurs after a lengthy period of repeated stress or strain cycling.