BOEING COMPRESSION AFTER IMPACT COMPRESSION
TEST FIXTURE  (ASTM D 7137)

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

Assembled CAI Fixture, Without Specimen

This test method was adopted by ASTM as Standard D 7137 (Reference 1) in May 2005.  A companion standard, ASTM D 7137, defines the method of impacting the test specimen prior to performing the compression test.

This Compression After Impact (CAI) Compression Test Fixture was developed by the Boeing Company, as described in References 3 and 4.  A slight fixture modification is described in SACMA Recommended Method SRM 2R-94 (Reference 5). The specimen, typically, but not necessarily, a quasi-isotropic laminate, is 6" long, 4" wide, and approximately 0.2" thick. A NASA standard, described in Reference 6, specifies a larger specimen and thus is not as commonly used as the Boeing standard.

The test specimen is first impacted as defined in Reference 2, typically using a drop-weight impact testing apparatus, and then is compression loaded to failure in the fixture shown above. The specimen is simply supported along all four edges, the fixture being fully adjustable as indicated by the large number of socket head cap screws, to accommodate small variations in specimen width and thickness. The top (loading) plate, which is not directly attached to the lower portion of the fixture, slips over the top edge of the test specimen to provide simple support for this fourth edge. The side rails are short enough to insure that a gap between the side rails and the top plate is maintained during the compression test.

The assembled fixture, with a specimen installed, is positioned unconstrained on the flat base of the testing machine, the compressive loading being applied directly to the top plate by a platen in the crosshead of the testing machine.

Compression After Impact Compression Test Fixture

Because the laminate is quasi-isotropic or something similar, and thus does not have a high inherent compressive strength, and furthermore has been typically weakened by the prior impact loading, it can be edge-loaded without crushing, even though it is untabbed.

Special Compression After Impact Compression test fixtures can also be fabricated.  The following photograph shows one such example.  In the foreground is a standard Boeing fixture.  In the background is a specially designed fixture, capable of testing specimens either 6” or 10.5” tall and 4”, 8.5”, or 10.5” wide.

Special Large-Scale Compression After Impact
Compression Test Fixture Shown in the Background, with a Standard Boeing Fixture in the Foreground

The next photograph shows a sub-scale Compression After Impact Compression test fixture, compared in size to a standard Boeing fixture.

                    Special Sub-Scale Compression After Impact                               Compression Test Fixture Shown in the Foreground,

with a Standard Boeing Fixture in the Background

 An Airbus Industries version of the Compression After Impact Compression Test Fixture is shown in the next photograph.  Screws are provided to forcibly push the top, bottom, and side plates against the test specimen, providing a positive clamping force to all four sided of the specimen.  The specimen is the same size as used with the Boeing fixture.  The fixture uprights are not adjustable. 

      Airbus Industries Compression After Impact Compression Test Fixture

Sources of Additional Information:

1)     1)   ASTM Standard D7137-05 (2005), "Standard Test Method for Compression Residual Strength Properties of Damaged Polymer Matrix Composite Plates,”  American Society for Testing and Materials, West Conshohocken, Pennsylvania (first issued in 2005).

2)     2)   ASTM Standard D7136-05 (2005), "Standard Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Dynamic Impact Event,” American Society for Testing and Materials, West Conshohocken, Pennsylvania (first issued in 2005).

3)   Boeing Specification Support Standard BSS 7260, "Advanced Composite Compression Tests," The Boeing Company, Seattle, Washington (originally issued February 1982, revised December 1988).

4)   4) Boeing Document D888-10026, "Test Methods for Advanced Composites, Revision A, Section 7.4, The Boeing Company, Seattle, Washington, January 1996.

5)  SACMA Recommended Method SRM 2R-94, "Compression After Impact Properties of Oriented Fiber-Resin Composites," Suppliers of Advanced Composite Materials Association, Arlington, Virginia, 1994.

6)     6)   NASA Reference Publication 1092, "Standard Tests for Toughened Resin Composites," NASA-Langley Research Center, Hampton, Virginia, Revised Edition, July 1983.

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Copyright 2005 - Wyoming Test Fixtures, Inc.

Wyoming Test Fixtures Inc. 2960 E. Millcreek Canyon Rd.
Salt Lake City, UT  84109
wyomingtestfixtures.com  Phone: 801-484-5055  Fax: 801-484-6008
E-mail: wtf@wyomingtestfixtures.com