PSI - Issue 13

F.J. Gómez et al. / Procedia Structural Integrity 13 (2018) 267–272 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 1. Stress-strain curve in real and fictitious materials.

Nisitani and Hyakutake (1985) examined the fracture of symmetrical polycarbonate notched geometries with several radii, notch depths and thickness. The fictitious strength has been determined using expression (6). Fracture toughness does not appear in the previous article and has been taken from Kinloch and Young (1983). The non dimensional notch stress intensity factors, shown in Figure 2, have been calculated with expression (7), where  max is the stress at the root of the notch. The maximum value of L r is collected in Table 1. = 2 √ (7) Lee at al, (2002) analysed the behaviour of notched geometries of A508 steel at -196ºC. Prismatic specimens of 10x10x55 mm were tested with a radius varying between 0.06 and 0.28 mm. The plastic stress-strain curve of the material does not appear in the original work and has been estimated from the elastic limit,  y , and the maximum stress,  u , following the work of Kamaya (2016). The corresponding notch stress intensity factors have been obtained from expression (7). The mechanical properties of the steel and the maximum values of L r are shown in Table 1. Fuentes et al (2018) studied the influence of the notch radius on the fracture toughness of an Al7075-T651 aluminum alloy at directions TL and LT. The experimental program consisted of compact specimens of W = 40 mm, with notch radii of 0.15, 0.2, 0.5, 1.0, 2.0 mm. The stress-strain curve of the material and the values of the plastic collapse loads can be found in the original work and the fictitious fracture strength has been calculated using expression (6). The notch stress intensity factors of the geometries have been calculated using the expression (7) and appear in Figure 2. The same authors, Madrazo et al (2014), have analyzed the failure of notched geometries of S355 steel at -196 ° C. As in the previous case, compact specimens have been tested with W = 50 mm and notch radii: 0, 0.15, 0.25, 0.5, 1.0, 2.0 mm. The plastic stress-strain curve did not appear in the original work and it has been estimated from the approximation suggested by Kamaya (2016) in steels. The generalized stress intensity factors have been calculated with the expression (6). The fracture toughness, the fictitious fracture strength and the maximum value of L r appear in Table 1. Figure 2 shows the non-dimensional notch stress intensity factor for the five materials analyzed. In all cases, the new values coincide with the non-dimensional curve obtained in linear elastic materials, with the fitting proposed in the expression (5) and with the predictions of the cohesive crack model. Table 1 shows the fracture and mechanical properties used and the maximum values of L r . This physical magnitude establishes the degree of plasticity achieved at failure; in all cases it is less than 0.97.