Homework Help: Unsure about angle inside Mohr's circle?

1. Apr 5, 2015

influx

Can someone explain why the angle inside the triangle inside Mohr's circle is θP2 rather than θP1 ? I understand everything else but just this small point is frustrating me.

Thanks

2. Apr 6, 2015

paisiello2

I don't see θP1 defined anywhere but I assume that the subscript 2 is used with θP2 to correspond with σ2.

3. Apr 6, 2015

influx

θP2 is the angle that corresponds to σ2 and θP1 is the angle that corresponds to σ1 but what I am confused about is why the angle inside the triangle is θP2 rather than θP1? How did they know which one it is?

4. Apr 6, 2015

paisiello2

Point D corresponds with σ2 and point B corresponds with σ1. If σ2 is the minimum principle stress then by definition 2θP2 would be the angle that point A makes with the x-axis. And 2θP1 would make the angle with point E which would be 180° from point A in Figure 22.9.

Last edited: Apr 6, 2015
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