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

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

Fig. 1:  Assembled Compression After Impact Compression Test Fixture

(No Specimen Installed)

  This test method was adopted by ASTM as Standard D 7137 (Reference 1) in May 2005.  A companion standard, ASTM D 7136 (Reference 2), 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 fixture, described in Reference 6, specifies a larger specimen and thus is not as commonly used as the Boeing standard fixture.  The NASA fixture, our Models CU-CN and WTF-CN, is described in Products Section C-4 of the present web site.

The Boeing 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 in Fig. 1.  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.

Fig. 2:  Compression After Impact Compression Test Fixture

                                                  with the Loading Plate Removed

  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.

  An Airbus Industries version of the Compression After Impact Compression Test Fixture is shown in Fig. 3.  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.  However, the effective specimen boundary conditions are still “simply supported”, the same as for the Boeing fixture.  The specimen is the same size as that used with the Boeing fixture.  Although the fixture uprights are not adjustable in the width direction as they are in the Boeing fixture, this is not a problem as the standard specimen is specified to be of a specific size anyway.

      Fig. 3:  Airbus Industries Compression After Impact Compression Test Fixture

  Special Compression After Impact Compression test fixtures can also be fabricated.  Figure 4 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.

Fig. 4:  Special Large-Scale Compression After Impact Compression

                           Test Fixture Shown in the Background, with a Standard

                           Size Boeing Fixture in the Foreground

Fig. 5:  Another Special Large-Scale Compression After Impact

                               Compression Test Fixture (background), shown with a

                               Standard Size Boeing Fixture (foreground)

Fig. 6:  The Special CAI Fixture of Fig. 5 is Shown Disassembled into its

                       Component Parts.  This Fixture is Capable of Testing Specimens

                       of 1.2, 1.5, 2.5, 3, and 4” Widths and 5.8, 7, 9, 11, 13, and 17” Heights

Sources of Additional Information:

1)     ASTM Standard D7137-07 (2007), "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)     ASTM Standard D7136-07 (2007), "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)  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)    NASA Reference Publication 1092, "Standard Tests for Toughened Resin Composites," NASA-Langley Research Center, Hampton, Virginia, Revised Edition, July 1983.