It was his lifelong ambition to bring to metallurgy, a ﬁeld rich in observations but still mostly phenomenological in method, the quantitative and predictive rigor of the recent developments in atomic-scale physics.
His work on dislocations was a ﬁrst success in this endeavor. The dislocation had been introduced as a theoretical concept in 1934 to explain the ease of plastic ﬂow in crystals: moving a line defect that localizes shear
deformation requires a much lower stress than uniform shearing of the crystal planes. The concept was only gradually accepted. Even though dislocations provided key insights into mechanical behavior and crystal growth, it was only in 1956 that electron microscopy produced the ﬁrst direct images of moving dislocations. In the late 1940s, Cottrell showed that dislocation theory could be used to make quantitative predictions.
A very nice piece!