MecMovies 4.0 : M2.5: Shear Strain in a Plate

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The figure shows a triangular plate P Q R S before and after deformation. The base of the triangle is Q R S and it is fixed to the ceiling. The length of the segment Q R is 900 millimeters and the length of the segment R S is 300 millimeters. The apex of the triangular plate is P. The angle at Q is 30 degrees, the angle at S is 60 degrees and the angle at P is 90 degrees. After deformation, the apex P, extends downwards by 1 millimeter and the angle at P is pi over 2 minus gamma.

After $P$ has been displaced downward by $1 mm$ , the angle at $P$ is $π / 2 - γ$ . To compute the shear strain $γ$ , the angle at $P$ must be determined after the $1 mm$ deformation.