In this region (between points 2 and 3), the rate at which extension is increasing is going up, and the material has passed the elastic limit. It will no longer return to its original shape. After point 1, the amount of stress decreases due to necking at one point in the specimen. If the stress was recorded where the necking occurs we would observe an upward curve and an increase in stress due to this reduction in area(stress = Force / area, thus stress increases during necking). The material will now 'give' and extend more under less force.
"What's beautiful about drones is they do provide a new territory for making measurements which was not possible before," said Zappa. "But you still want to use the best possible instrument and platform for whatever experiment you're doing…. sometimes it would be the UAV, sometimes not…You want to identify the tool that's most useful for your science goal." Explore further: Chinese online retailer developing one-ton delivery drones