SHORT BEAM SHEAR TEST FIXTURE  (ASTM D 2344)

Model No. CU-SB  (low carbon steel)
Model No. WTF-SB  (17-4PH stainless)

Assembled Fixture

Fixture with Loading Head Removed

An assembled short beam shear test fixture is shown in the top 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 (Reference 1).

ASTM Standard D 2344, in existence since 1965, now recommends a specimen span length-to-thickness ratio of four for all types of materials. 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.

Because of the relatively large support span possible, this fixture is also frequently used for three-point flexure testing (ASTM D 790).  And with the four-point loading head shown below, this fixture can also be used for four-point flexure testing (ASTM D 6272).

 Combined Three- and Four-Point Loading Short Beam Shear Test Fixture, shown with both Three- and Four-Point Loading Heads Installed (for illustration only)

   This fixture, in either the three-point or four-point loading configuration, is also used for the flexural testing of brittle materials such as ceramics and ceramic-matrix composites when articulation of the loading and support points is not necessary.  Articulation is often not required when these brittle specimens have been surface ground, or otherwise made flat.  If specimen twist is present in brittle materials, a Ceramic Flexural Strength test fixture, such as Model CU-CF or Model WTF-CF, may be required.

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. 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, as shown below.

                                    Adjustable Specimen-Centering stops for

                                        Short Beam Shear Test Fixture

 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.

Screw-adjustable supports (that move in or out together) are available, as shown below.

. Front and Rear Views of Short Beam Shear and/or Flexure Test
Fixture with Screw-Adjustable Supports

(an optional Fixed-Span Four-Point Loading Head and various alternate

             Support/Loading Cylinder Diameters are shown in the foreground)

Special size fixtures, either larger or smaller than the standard size, can also be fabricated, as indicated in the photograph below.

Standard Short Beam Shear (ASTM D 2344) Test Fixture (left) and Special
Compact Reduced-Span Three-/Four-Point Shear Test Fixture (right).

Sources of Additional Information:

1)    1)   ASTM Standard D2344-00 (2000), "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 published in 1965).

2)     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)     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.

4)     4)  D.F. Adams and J.M. Busse, “Suggested Modifications of the Short Beam Shear Test Method,” Proceedings of the 49^th International SAMPE Symposium, Long Beach, CA, May 2004.

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