{"id":16374,"date":"2024-09-19T10:03:47","date_gmt":"2024-09-19T08:03:47","guid":{"rendered":"https:\/\/dev.shimadzu-testing.com\/?p=16374"},"modified":"2025-02-05T11:19:15","modified_gmt":"2025-02-05T10:19:15","slug":"observing-the-failure-of-open-hole-cfrp-specimens-in-tensile-tests","status":"publish","type":"post","link":"https:\/\/shimadzu-testing.com\/en\/know-how\/high-speed-video-camera\/observing-the-failure-of-open-hole-cfrp-specimens-in-tensile-tests\/","title":{"rendered":"Observing the Failure of Open-Hole CFRP specimens in Tensile Tests"},"content":{"rendered":"\t\t
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Introduction<\/strong><\/h2>\nOffering superior specific strength, even compared to other composite materials, carbon fiber reinforced plastic (CFRP) is used in aircraft and some transport vehicles for the purpose of saving fuel through weight reduction. Composite materials have excellent mechanical properties. However, a general feature of composite materials is that their strength decreases markedly when they are notched. CFRP is no exception, so tests of notched specimens are important. In this case, testing is performed using specimens notched with a circular hole at the center. In this experiment, tensile tests were performed using CFRP specimens (laminate method [45\/0\/-45\/90]2s) with a total length of 150 mm, a width of 36 mm, and a thickness of\n2.5 mm, prepared with a 6 mm circular hole at the center. The failure process of the CFRP specimens was observed during the tensile tests. In particular, it is important to confirm the failure process of weak regions, such as the periphery of circular holes, for CFRP development and to confirm the validity of CAE analysis. However, since the failure of CFRP is a brittle phenomenon, where failure occurs instantaneously, it cannot be confirmed with the naked eye. For this reason, high-speed video cameras are used to observe the failure. In this experiment, synchronized images were obtained at the front and the side of the specimens using two HPV-X2 high-speed video cameras.\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Measurement System<\/strong><\/h2>\nIn this experiment, the AG-Xplus precision universal\ntesting machine and two HPV-X2 high-speed video\ncameras were used. Table 1 shows the instruments\nused. To observe the specimen failure in a tensile test, a\ntrigger signal synchronized to the failure must be\ntransmitted to the high-speed video cameras. The\nfailure starts on the periphery of the circular hole.\nAccordingly, aluminum foil was affixed to the periphery\nof the circular hole using adhesive, as shown in Fig. 1,\nso that conduction would be lost when the specimen\nfails. The failure was observed using this timing to\ntrigger the cameras.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Table 1 Testing Equipment<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Measurement Results<\/h2>\nTable 2 shows the measurement conditions, and Fig. 2\nshows the test configuration. As shown in Fig. 2, the\nfailure of the specimen was recorded from the front by\ncamera (1) and from the side by camera (2). Fig. 3\nshows the test results from the AG-Xplus. Failure begins\nwhere the test force suddenly drops in Fig. 3. Fig. 4\nshows the specimen failure observed from the front,\nand Fig. 5 from the side. Image (2) in Fig. 4 shows that\nthe failure starts on the left side of the circular hole. In\nimage (3), a crack also appears on the right side of the\ncircular hole. Subsequently, cracks progressed in an\norientation of 45 degrees, the orientation of the fibers\nin the outer layer. Further, as the test progressed,\nmultiple cracks were confirmed, as in images (7) and\n(8). In the observations from the side, no failure was\nconfirmed at the time the failure started, and was only\ninitially confirmed in image (5). This is likely because the\ncracks started at the periphery of the circular hole\nreached the side of the specimen in image (5).\nSubsequently, failure was confirmed in multiple layers,\nexcept for the 0-degree layer, in image (6). Further, in\nimage (7), failure was confirmed in the 0-degree layer,\nafter which the failure progressed toward the\noutersurface. The final condition of the specimen is\nshown in Figs. 6 and 7.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Table 2 Measurement Conditions<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Fig. 2 Test Configuration<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fig. 3 Test Results<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fig. 4 Images from Camera (1) (5 \u03bcs between images)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fig. 5 Images from Camera (2) (5 \u03bcs between images)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Fig. 6 Specimen After Failure (front)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fig. 7 Specimen After Failure (side)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Conclusion<\/h2>\nThe cinventional HPV-X dose not have a synchronization function, and so is incapable of\nrecording from two directions. Also, the sensitivity of\nthe HPV-X is insufficient, so it cannot record at imaging\nspeeds of 500,000 fps or faster. The HPV-X2 is\nequipped with a synchronization function, and features\nimproved sensitivity, so this instrument is capable of\nsynchronized recordings at 2 Mfps, as in this case. As a\nresult, failures can be observed in tensile tests of\nmaterials like CFRP that fails at high speeds.\nGenerally, failure observations are often recorded from\nthe front of the specimen. However, adding recording\nfrom the side enables confirming the failure process\nthat cannot be observed just from the front. In\nparticular, with CFRP materials with different fiber\norientations for each lamination layer, where failure\nprogresses in different manner for each layer, as shown\nin this article, the failure process can be observed in\nmore detail by recording from two directions.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Download<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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