CAI Test: Compression After Impact

The HIT230F instrumented drop weight tester with an adjustable drop height up to 1 meter, integrated speed measurement on the point of impact, anti-rebound device, corresponding impactor for the impact test (16 mm diameter) and the easily changeable weights for setting different impact energies is specifically designed to meet the requirements for pre-damaging CAI specimens.

The HIT600F instrumented drop weight tester is also ideal for the application of pre-damaging forces in the CAI test, and can reach even higher velocities and impact energies with a higher drop distance setting and the addition of an optional acceleration unit. It is therefore also suitable for the performance of multi-axial puncture tests on plastic specimens.

The CAI fixture is positioned between two compression platens in the materials testing machine. During the CAI test, the specimen is subjected to a compressive load up to the point of failure. The compression after impact test is valid if the specimen fails in the area of the centrally applied impact damage. Failure at or near the upper or lower clamp is not permitted.

Advantages:

• Easy specimen changes through simple handling of the CAI fixture
• Use in a large temperature range of -70 °C to +300 °C
• Increased side stiffness through support bars prevents lateral bending of the fixture, especially when using unconventional laminate structures
• Interchangeable carbide inserts on the upper and lower contact surfaces with the specimen minimize wear of the heavily loaded force application surfaces

In the compression after impact test, the use of a relatively large specimen measuring 100 mm x 150 mm x 5 mm (width x length x thickness) can easily generate forces in excess of 100 kN. This also depends on the type of composite material tested (e.g. CFRP or GFRP), the type of fiber reinforcement used (e.g. UD, scrim or fabric), or use of laminate constructions and laminate thicknesses other than the nominal laminate constructions and laminate thicknesses defined in the above test standards.

CAI tests should therefore be performed on a static materials testing machine with a nominal load of 150 kN to 250 kN. For the CAI test with very thick laminates, reinforced CAI fixtures and static materials testing machines with a higher nominal load up to 600 kN can also be used.

To verify accurate alignment of the test arrangement and the dimensional accuracy of the CAI compression fixture, test specimens with strain gauges applied to both sides must be used for each test when setting up the test arrangement or at specified intervals, depending on the CAI test standard used (a total of 4 per specimen). The strain gauge signals can either be integrated into the testing machine with pre-assembled strain gauge boxes or by using a suitable universal measuring amplifier.