Topic 11: Deformation of solids

What is the correct unit for strain?

• Pa

• Nm^-2

• No unit

• Nm²

A brass wire has reached its elastic limit. It means that

• if any further stress is applied, the wire will break.

• if any further stress is applied, the deformation of the wire will not be reversible.

• the deformation no longer obeys Hooke's law

• the wire will continue deforming with no additional stress.

Figure below shows a stress-stain graph for a ductile metal under tension. Which part represents the plastic deformation?

• P → Q

• Q → R

• R → T

• R → U

The Young's Modulus is defined as...

• The gradient of a stress strain graph

• The energy required to stretch a material.

• Stress/Strain

• Force/Extension.

Ultimate tensile strength of a steel rod is the stress at which the rod

• fractures.

• deforms.

• returns to original shape when the stress is removed

• becomes soft and starts form necking

The variation of stress with strain for materials P and Q until their breaking points are shown in the graph below. Which is TRUE about materials P and Q

• Material Q is stiffer than material P.

• Material P is brittle but material Q is ductile.

• Material P is more difficult to break compared to material Q.

• Material P needs more work to break compared to material Q

Figure below shows a graph of stress-strain for a ductile material. Which pair of the points shows the elastic limit and fracture point?

• P and Q

• P and R

• R and S

• Q and T

If the material recovers the original dimensions, when an external load is removed, this deformation is known as ______ deformation

• plastic

• permanent

• elastic

• reversible