Open-Hole Compression Testing of CFPR

Carbon fiber reinforced plastic (CFRP) has become popular owing to its low weight and strength, and has been rapidly adopted for use in astronautics and aeronautics. In terms of specific strength and high rigidity, CFRP has exceptional strength characteristics but it also loses much of its strength when a cut-out is made. As a result, composite materials employed in aeroplanes must be evaluated by tests that use specimens with a hole cut out of their center. Open-hole compression testing of a CFRP according to ASTM D6484 was subsequently performed.

Measurement System

T800S/3900 was used as the CFRP specimen. As shown in Figure 1, a hole was created in the center of the specimen. Test methods in both SI and Imperial units, where the dimensions of the jigs and specimens differ in each, are described in ASTM D6484. Table 1 shows the specimen information.

Two loading methods are included in the ASTM D6484 which are described as Method A and Method B. In Method A, the test fixture and the specimen are first clamped in a gripping device, and the fixture and gripping device apply a shear force to compress the specimen. In Method B, compression plate is present at the ends of the fixture and specimen, and is used to compress the specimen. Method B was used, as depicted in Figure 2. Table 3 shows the test conditions used and Table 2 shows a list of the equipment used.

Table 1. Specimen information

Figure 1. Test setup

Figure 2. Specimen

Table 2. Experimental Equipment

Table 3. Test conditions

Results

Measurements were carried out twice. Test results are depicted in Table 4, and stress-displacement curves are shown in Figure 3. As illustrated in Table 4, the mean open hole compressive strength was 275.6 MPa.

Table 4. Test results

Figure 3. Stress-Displacement Curves

Results (DIC Analysis)

The TRViewX non-contact extensometer was used to image and capture the specimen to be collected and synchronized with test result collection. In addition, applying an arbitrary pattern of paint to the observed specimen surface enables the video or images to be used to find out the strain distribution on the observed specimen surface during the test by DIC analysis. Using the specimen described in Table 5, open-hole compression testing and DIC analysis were carried out. An image of the open-hole compression test system with a noncontact extensometer is shown in Figure 4. Figure 5 displays strain distributions around the open hole in the specimen that were acquired by DIC analysis. Figure 5 also shows that strain builds up at the vertical sides of the open hole (regions (1) and (3)), strain appears along the axis of compression from those points, and the final break takes place at the vertical sides of the hole. In the interim, almost no strain appears in the central part of the hole (region (2)) throughout the test. Probably, this strain distribution occurred due to a 0˚ fiber orientation on the specimen surface.

Table 5. Specimen Information (DIC)

Figure 4. Experimental Setup (DIC)

Figure 5. DIC Analysis results

Conclusion

With the help of this test system, open-hole compression testing of a CFRP was successfully carried out according to ASTM D6484 standard. A non-contact extensometer made it easy to capture video (images), synchronized with the test force and crosshead displacement data acquired from the testing machine. Performing DIC analysis based on this video made it possible to evaluate the strain distribution on the observed specimen surface. This testing system will be very useful for developing CFRPs and products that use CFRPs

1) DIC analysis is an analysis method that measures strain and shows the strain distribution in a specimen based on movement of a random pattern of paint applied to the observed specimen surface before and during testing.

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

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