![]() The shear stresses in a beam during 3-point bending are the same regardless of specimen length. The answers to these questions are determined by the shear strength of the fibre matrix interface. Whilst we all refer to the relevant standards to tell us what spans and radii to use for these tests, what actually determines whether the test will produce a delamination or a fibre breaking failure? Additionally, at what point will the span become so narrow that we observe an invalid failure due to crushing of the specimen under the rollers? By answering these questions and understanding the parameters that determine these transitions, we can react to the failure modes being exhibited during testing ensuring that we adjust the test to get valid results. However, because of this imperfect shear state, ASTM has removed the word shear from the title of ASTM D2344, simply referring to it as short beam strength. This popularity is due to the test providing useful information on the interlaminar shear behaviour of the laminate, while also being a cheap and easy test to undertake. Depending on the span used, and with some alterations to the diameter of the loading rollers, the same test set-up can be utilised to determine both the interlaminar shear and the flexural properties of a composite material.Īlthough interlaminar shear testing doesn’t provide a pure shear state (where there are no additional compressive or tensile forces), it remains very popular in the industry. ![]() Three or four-point bend testing has long been a go-to method for the composites engineer to gather relevant design data for their material or component.
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