Physics · Mechanical Properties Of Solids · NEET
Look at the gap between the ultimate strength point (D, the highest stress) and the fracture point (E, where it breaks). If E is far to the right of D, the material had a long plastic region and large strain before breaking, so it is ductile. If E is very close to D, the material snapped almost immediately after the peak, so it is brittle. In exam figures the ductile curve looks long and flat near the top, the brittle curve looks short and cut off soon after the peak.
Almost none. A brittle material fractures at or very near the elastic limit, so there is little to no plastic deformation. That is why the fracture point comes right after the yield or ultimate point. A ductile material, on the other hand, has a long plastic region between the yield point and fracture, which is why it can be drawn into wires.
Glass is brittle. So are cast iron and ceramics. They break suddenly with almost no warning stretch. Copper, gold, aluminium and mild steel are ductile because they show a large plastic strain before fracture, which lets them be hammered into sheets or drawn into wires.
Point D is the ultimate tensile strength, the maximum stress the material can handle. Point E is the fracture point, where the material actually breaks. Between D and E the wire keeps stretching even though the stress is falling (necking). The size of the D-to-E gap is exactly what separates ductile (big gap) from brittle (tiny gap).
The curve whose fracture point is farther from the ultimate point (longer along the strain axis) is ductile. In the standard NCERT-style question where X breaks soon after its peak and Y stretches far before breaking, X is brittle and Y is ductile.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A ductile material can be stretched a lot and deformed permanently before it breaks. It has a large plastic region on the stress-strain curve. Examples: copper, gold, aluminium, mild steel.
A brittle material breaks suddenly with almost no plastic stretch. Its fracture point is very close to its ultimate strength point. Examples: glass, cast iron, ceramics.
Because they have a large plastic region, they keep deforming permanently under stress without breaking. This property, called ductility, lets them be pulled into long thin wires.
Ordinary (mild) steel is ductile, showing a clear yield point and a long plastic region. However, very high-carbon or hardened steel can behave in a more brittle way.
NEET usually gives two stress-strain curves labelled X and Y and asks you to identify which material is ductile and which is brittle, based on the gap between the ultimate point and fracture point.
