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End Notch Flexure Test:

The End Notch Flexure test is based in the flexure of a beam with an initial crack in one of its ends. The test has been applied to a composite made of carbon fibers with an epoxy polymeric matrix. Fibers are oriented in the longitudinal direction of the beam and initial crack is created introducing an insert in the laminate during its fabrication. The width of the gap generated by this insert must be smaller than 50µm. The span of the beam is 100 mm and it is loaded with a concentrated load at its mid-span. The test is made with a displacement controlled mechanism. Three different series (GRIN006, GRIN015, GRIN024), each one containing five different samples, where tested during the experimental campaign. To perform the numerical simulation, the first sample of serie GRIN006 has been considered (beam 3M101, according to the notation used in the test). The dimensions of this sample, as well as the dimensions considered for the numerical simulation, are shown in Fig.6.3.

The experimental test applies a vertical displacement to the beam, as shown in Fig.6.3, until the initial crack starts its propagation. The imposed displacement is applied until the crack propagation stops and the beam recovers its linear behavior. At this point, the sample is unloaded. Main results obtained from this test are two: The force-displacement graph, which shows the structural performance of the composite beam, and the final length of the initial crack. These two results are the ones that will be compared with the numerical model developed. The exact properties of the composite material used in the experimental simulation were unknown when the experimental tests were performed. However, the composite is known to be made of carbon fibers and an epoxy polymeric matrix from Hexcel composites. For the numerical simulation, the mechanical values considered to define the composite are the ones described in Table 6.1, obtained from Hexcel Product data description. The fiber (AS4) and matrix considered are the ones found in Hex Ply 8552 UD prepegs.

(Pedro P. Camanho, Mechanical Response of Composites, p.132)