A test of a metal rod gives these readings.

Step 1. Young's modulus. Every row gives $\dfrac{2.8 \times 10^{7}\ \text{Pa}}{0.0004} = 7.0 \times 10^{10}\ \text{Pa}$, the value for aluminium.

Step 2. Prediction. $7.0 \times 10^{10}\ \text{Pa} \times 0.0080 = 5.6 \times 10^{8}\ \text{Pa}$.

Step 3. Compare. The real stress, $1.6 \times 10^{8}\ \text{Pa}$, is far lower: the rod has yielded and is flowing.