Unsure about angle inside Mohr's circle?

[influx]

Can someone explain why the angle inside the triangle inside Mohr's circle is θ_P2 rather than θ_P1 ? I understand everything else but just this small point is frustrating me.

Thanks

 

[paisiello2]

I don't see θ_P1 defined anywhere but I assume that the subscript 2 is used with θ_P2 to correspond with σ₂.

 

[influx]

I don't see θ_P1 defined anywhere but I assume that the subscript 2 is used with θ_P2 to correspond with σ₂.

θ_P2 is the angle that corresponds to σ₂ and θ_P1 is the angle that corresponds to σ₁ but what I am confused about is why the angle inside the triangle is θ_P2 rather than θ_P1? How did they know which one it is?

 

[paisiello2]

Point D corresponds with σ₂ and point B corresponds with σ₁. If σ₂ is the minimum principle stress then by definition 2θ_P2 would be the angle that point A makes with the x-axis. And 2θ_P1 would make the angle with point E which would be 180° from point A in Figure 22.9.