The ASTM D6484, ASTM D6742, Boeing BSS 7260 (Type I) or AITM 1.0008 describe the open hole compression (OHC) and filled hole compression (FHC) tests on composite materials.
The open hole compression (OHC) test is used to determine the influence of a hole on the compressive strength of a laminate. The ratio of the OHC strength to compressive strength of the same unnotched laminate provides the OHC notch factor or the OHC knockdown factor.
If a rivet or bolt is placed in the hole of the specimen, it is called filled hole compression (FHC) test. Similarly, comparing the FHC strength with the compressive strength of the same unnotched laminate provides the FHC notch factor or FHC knockdown factor.
Open hole compression tests and filled hole compression tests are always performed with multidirectional laminates. A strain measurement is not required, since strength is the deciding characteristic value to be determined.
For the open hole compression test to ASTM D6484 and the filled hole compression test to ASTM D6742—depending on the system of units used—either a 300 mm long and 36 mm wide or 12 inch long and 1.5 inch wide composite specimen with a center hole is used. The Type I OHC specimen described in the Boeing industry standard BSS 7260 is also 12 inches long and 1.5 inches wide. For the test, the specimen is gripped in the support device described in the ASTM D6484 standard. A differentiation is made between a device for the SI and the imperial system of units.
The support device is placed in a double-actuator hydraulic grip, where force is applied to the center section of the specimen via shear force in the clamped area. Or the support device can be inserted between two compression platens. In this case the force is applied via the end faces of the device and the specimen. The only valid failure mode is compressive failure at the hole.
In addition to instructions for compression tests on unnotched laminates (specimen type A), the Airbus compression test standard AITM 1.0008 also includes a description for the open hole compression test (specimen type B) and filled hole compression test (specimen type C).
Due to the analogous specimen dimensions, compared to unnotched specimens, OHC specimen dimensions B1 and B2 as well as FHC specimen dimensions C1 and C2 can be tested in the ZwickRoell HCCF compression fixture.