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Triangular shell element, locking check

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Problem. The tests check that the result on a triangular mesh does not depend on the diagonal pattern. The diagonal direction cannot be controlled in an imported mesh, so this is a condition for using the element.

Reference document. Timoshenko & Woinowsky-Krieger Table 35 is used for the clamped plate and the Kirchhoff value for the thin simply supported limit.

In the thin plate limit the centre deflection of a simply supported square plate takes this value.

w=0.00406 q a4Dw = 0.00406\,\dfrac{q\,a^4}{D}

Numerical model. The locking sweep uses eight by eight cells and the diagonal pattern sweep sixteen by sixteen. Alternating, fixed and random diagonal patterns are tested at a thickness ratio of one thousandth.

Simply supported square plate, locking check at the thin limit, triangular mesh

Parameters. t/a = 0.001 · mesh = 8×8×2 triangles

Published source. Kirchhoff plate theory, simply supported square plate

w=0.00406 qa4/Dw = 0.00406\,qa^4/D
QuantityReferenceComputedDeviation
Centre deflection-0.112251-0.1105721.50%

Clamped square plate, t/a = 1/1000, alternating diagonal pattern

Parameters. mesh = 16×16×2 triangles · diagonal pattern = alternating

Published source. Timoshenko & Woinowsky-Krieger, Table 35

QuantityReferenceComputedDeviation
Centre deflection as a ratio of the Timoshenko solution10.9950760.492%

Clamped square plate, t/a = 1/1000, fixed diagonal pattern

Parameters. mesh = 16×16×2 triangles · diagonal pattern = fixed

Published source. Timoshenko & Woinowsky-Krieger, Table 35

QuantityReferenceComputedDeviation
Centre deflection as a ratio of the Timoshenko solution10.9957460.425%

Clamped square plate, t/a = 1/1000, random diagonal pattern

Parameters. mesh = 16×16×2 triangles · diagonal pattern = random

Published source. Timoshenko & Woinowsky-Krieger, Table 35

QuantityReferenceComputedDeviation
Centre deflection as a ratio of the Timoshenko solution10.9953940.461%