
(a)
Find the orientation and magnitude of the principal strains in the plane.
(a)

Answer to Problem 149P
The orientation of the principal strains is θp=30°and 120°_.
The in-plane maximum principal strain is εmax=560×10−6 in./in._.
The in-plane minimum principal strain is εmin=−140×10−6 in./in._.
Explanation of Solution
Given information:
The normal strain in Rosette 1 is ε1=−93.1×10−6 in./in..
The Rosette 1 makes an angle with the x-axis is θ1=−75°.
The normal strain in Rosette 2 is ε2=+385×10−6 in./in..
The Rosette 2 makes an angle with the x-axis is θ2=0°.
The normal strain in Rosette 3 is ε3=+210×10−6 in./in..
The Rosette 3 makes an angle with the x-axis is θ3=75°.
Calculation:
Write the equation for the normal strain 1 as follows;
ε1=εxcos2θ1+εysin2θ1+γxysinθ1cosθ1
Substitute −93.1×10−6 in./in. for ε1 and −75° for θ1.
−93.1×10−6=εxcos2(−75°)+εysin2(−75°)+γxysin(−75°)cos(−75°) (1)
Write the equation for the normal strain 2 as follows;
ε2=εxcos2θ2+εysin2θ2+γxysinθ2cosθ2
Substitute +385×10−6 in./in. for ε2 and 0° for θ2.
385×10−6=εxcos2(0°)+εysin2(0°)+γxysin(0°)cos(0°)=εx+0+0εx=385×10−6 in./in.
Write the equation for the normal strain 3 as follows;
ε3=εxcos2θ3+εysin2θ3+γxysinθ3cosθ3
Substitute +210×10−6 in./in. for ε3 and 75° for θ3.
+210×10−6=εxcos2(75°)+εysin2(75°)+γxysin(75°)cos(75°) (2)
Add equation (1) and (2).
−93.1×10−6+210×10−6=(εxcos2(−75°)+εysin2(−75°)+γxysin(−75°)cos(−75°)+εxcos2(75°)+εysin2(75°)+γxysin(75°)cos(75°))116.9×10−6=(εxcos2(−75°)+εysin2(−75°)−0.25γxy+εxcos2(75°)+εysin2(75°)+0.25γxy)=εxcos2(−75°)+εysin2(−75°)+εxcos2(75°)+εysin2(75°)
Substitute 385×10−6 in./in. for εx.
116.9×10−6=((385×10−6)cos2(−75°)+εysin2(−75°)+(385×10−6)cos2(75°)+εysin2(75°))=5.158×10−5+1.866εyεy=35×10−6 in./in.
Substitute 385×10−6 in./in. for εx and 35×10−6 in./in. for εy in Equation (2).
+210×10−6=(385×10−6)cos2(75°)+(35×10−6)sin2(75°)+γxysin(75°)cos(75°)=2.579×10−5+3.266×10−5+0.25γxyγxy=606.2×10−6 in./in.
Find the orientation (θp) of the principal strains using the relation.
tan2θp=γxyεx−εy
Substitute 606.2×10−6 in./in. for γxy, 385×10−6 in./in. for εx, and 35×10−6 in./in. for εy
tan2θp=606.2×10−6385×10−6−35×10−6θp=30°and 120°
Therefore, the orientation of the principal strains is θp=30°and 120°_.
Find the average normal strain (εave) using the relation.
εave=εx+εy2
Substitute 385×10−6 in./in. for εx and 35×10−6 in./in. for εy.
εave=385×10−6+35×10−62=210×10−6 in./in.
Find the radius of the Mohr’s circle (R) using the equation.
R=√(εx−εy2)2+(γxy2)2
Substitute 385×10−6 in./in. for εx, 35×10−6 in./in. for εy, and 606.2×10−6 in./in. for γxy.
R=√(385×10−6−35×10−62)2+(606.2×10−62)2=350×10−6 in./in.
Find the in-plane maximum principal strain (εmax) using the relation.
εmax=εave+R
Substitute 210×10−6 in./in. for εave and 350×10−6 in./in. for R.
εmax=210×10−6+350×10−6=560×10−6 in./in.
Find the in-plane minimum principal strain (εmin) using the relation.
εmin=εave−R
Substitute 210×10−6 in./in. for εave and 350×10−6 in./in. for R.
εmin=210×10−6−350×10−6=−140×10−6 in./in.
Therefore,
The in-plane maximum principal strain is εmax=560×10−6 in./in._.
The in-plane minimum principal strain is εmin=−140×10−6 in./in._.
(b)
Find the in-plane maximum shearing strain.
(b)

Answer to Problem 149P
The in-plane maximum shearing strain is (γmax)in-plane=700×10−6 in./in._.
Explanation of Solution
Refer to part (a);
The radius of the Mohr’s circle is R=350×10−6 in./in.
Find the in-plane maximum shearing strain (γmax)in-plane using the relation.
(γmax)in-plane=2R
Substitute 350×10−6 in./in. for R.
(γmax)in-plane=2×350×10−6=700×10−6 in./in.
Therefore, the in-plane maximum shearing strain is (γmax)in-plane=700×10−6 in./in._.
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