SHORT BEAM SHEAR TEST FIXTURE (ASTM D 2344)
Model No. CU-SB (low carbon
An assembled short beam shear test fixture is shown in the above photograph, but without a test specimen mounted in it. This fixture is commonly used to test composite materials in interlaminar (through-the-thickness) shear, in general accordance with ASTM Standard D 2344 (see Reference 1).
ASTM Standard D 2344, in existence since 1965, now recommends a specimen span length-to-thickness ratio of four. A typical specimen on the order of 0.1" thick would thus be tested at a span length of 0.4".
However, to accommodate various types of materials, and various laminate thicknesses, the span length of the fixture is infinitely adjustable over the full range of span lengths up to approximately 4.5". Scale markings are engraved on the base to aid in setting the desired span length, by sliding the specimen supports to the required positions. These specimen supports are then clamped in place using the Allen head screws shown.
Two hardened steel alignment posts, each 0.5" in diameter, are fixed in the base. The top plate, containing linear bearings, moves freely up and down on these alignment posts, thus maintaining alignment between the two lower supports and the upper loading cylinder.
The two supports and the loading head are hardened steel cylinders, each 2.5" wide, held in vee-grooves by small springs on each end. This permits them to be rotated, and also to be easily replaced if desired. Loading heads and support blocks incorporating cylinders of any diameter can be supplied. Unless specified otherwise, 1/8" diameter supports and a 1/4" diameter loading head will be supplied, as specified in ASTM Standard D 2344. However, supports and loading heads of any other diameters can be provided, if desired. Adjustable mechanical stops for centering the specimen in the fixture can also be added as an option.
This fixture can also be supplied in a four-point loading configuration, or combined three- and four-point loading, although only the three-point loading configuration is included in the ASTM standard.
This fixture is also frequently used as a flexure fixture for testing small specimens per ASTM D 790, and to test ceramics.
The fixture is designed to rest unconstrained directly on the base of the testing machine. A compressive loading is typically applied by the loading head of the testing machine directly onto the top plate of the short beam shear test fixture. Alternatively, a 0.50"-13 UNC threaded hole is provided in the top plate, to mount an optional adapter which in turn can be attached to the crosshead of the testing machine.
Sources of Additional Information:
1) ASTM Standard D2344-84/D2344M-00, "Short Beam Strength of Polymer Matrix Composite Materials and Their Laminates by Short-Beam Method," American Society for Testing and Materials, West Conshohocken, Pennsylvania (first issued in 1965).
2) D.F. Adams and E.Q. Lewis, “Experimental Study of Three- and Four-Point Shear Test Specimens,” Journal of Composites Technology and Research, Vol. 17, No. 4, October 1995, pp. 341-349.
3) E.Q. Lewis and D.F. Adams, "An Evaluation of Composite Material Shear Test Methods," Report UW-CMRG-R-91-103, Composite Materials Research Group, University of Wyoming, Laramie, Wyoming, May 1991.
Copyright 2001 - Wyoming Test Fixtures, Inc.
Wyoming Test Fixtures Inc. 421 S. 19th Street. Laramie, WY 82070
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