End notched flexure

The pure mode II interlaminar fracture testing can be performed using both the end notched flexure (ENF) specimen (Russell and Street, 1984, 1985) and the end loaded split (ELS) specimen (Corleto and Bradley, 1987 Prel et al.. 1989) (Fig 3.32). 

Gillespie Jr., J.W., Carlsson, L.A. and Pipes, R.B. (1986). Finite element analysis of the end notched flexure (ENF) speeimen measuring mode II fraeture toughness. Composites Sci. Technol. 26, 177. 

Carlsson, L.A. and Aksoy, A. (1991). Analysis of interleaved end-notched flexural specimen for measuring mode II fracture toughness. Int. J. Fracture 52, 66-77. 

Whilst test methods to measure the mode I fracture resistance of polymer fibre-composites [1] and stmctural adhesive joints [2,3] have now proceeded to full standards, the efforts to standardise a mode II method have been beset by a number of problems. Firstly, there exist a number of competing tests e.g. the end-loaded split (ELS), the end-notched flexure (ENF), the four point end-notched flexure (4-ENF) and the stabilised end-notched flexure (S-ENF) have all been proposed and have been subjected to various inter-laboratory evaluations. However, the results of these programmes have always revealed a very large scatter in the values of Gnc measured e.g, [4], and this scatter has been variously attributed to friction... 

Fig 2. Four point end notched flexure specimen (Dimensions are in mm). 

Perez CL, Davidson BD. Evaluation of precracking methods for the end-notched flexure test. AIAA J 2007 45 2603-11. http //dx.doi.org/10.2514/L24188. 

Horiguchi K, Shindo Y, Kudo H, Kumagai S. End-notched flexure testing and analysis of mode U interlaminar fiacture behaviour of glass-cloth/epoxy laminates at cryogenic temperatures. J Compos Technol Res 2002 24 239-45. http //dx.doi.org/10.1520/CTR10930J. 

Davies et al. [64] studied the influence of water absorption on the interlaminar shear strength and end notch flexure (ENF mode II shear) fracture toughness of quasi-unidirectional (88% 0°, 12% 90°) E-glass fibres in DGEBA epoxy resin cured with an amine hardener. Laminates were immersed in (a) distilled water and (b) the Atlantic Ocean ( at Boca Raton, Florida) for up to 8 months at temperatures of 20°C, 50°C and 70°C. Sea water was more slowly absorbed than distilled water. This observation has frequently been made and it provides some reassurance that laboratory tests using distilled water are useful, if slightly cautious, estimates of behaviour in the ocean. 

In order to evaluate the healing efficiency for the Mode II fracture test, end-notched flexure (ENF) specimens can be used (see a schematic in Figure 8.11). Recently, Ouyang and Li [57] derived a formulation of a Mode II energy release rate for the ENF joints bonded with dissimilar materials. When the adhesively bonded joint becomes a standard ENF specimen, that is, the two adherends have identical thickness and are made of identical material, we have [57]... 

Ouyang, Z. and Li, G. (2009) Nonlinear interface shear fracture of end notched flexure specimens. International Journal of Solids and Structures, 46, 2659-2668. 

Todo M, Jar P-Y B, Takahashi K (2000) Initiation of a mode-B interlaminar crack from an insert film in the end-notched flexure composite specimen. Compos Sci Technol 60 263-272. 

X = 0.25 mm and a is the crack length h and / - semi-thickness and semi-span, respectively, of the end-notch flexure (ENF) geometry [1316,1317]. The obtained results are depicted in Figure 3.484. 

Fracture toughness ASTME-399 NASA 1092 End notched flexure mode 11 Cracked lap shear (mixed modes I and 11) Edge delamination NASA 1092... 

The mode-II fracture parameters can be found by matching numerical and experimental results for the loads, displacements and the extent of crack propagation in three-point bending tests of adhesively bonded, end-notched flexure (ENF) specimens (see the inset of Fig. 19). These were determined to be F o = 5.4 kJ m" and f = 35 MPa [60]. Fig. 19 shows the resultant comparisons between the numerical and experimental load-displacement curves for ENF specimens fabricated from various thicknesses of aluminum adherends and a 0.25-mm-thick... 

Mode II, tapered end notched flexure (TENF) test specimen... 

Martin RH, Davidson BD (1999) Mode II fracture toughness evaluation using four point bend, end notched flexure test. Plast, Rubber Compos 28(8) 401-406... 

When the system is subjected to the combined loadings, the Gic, Guc, Gmc, and Gi, Gii, Gill the critical energy release rates and energy release rates in mode 1,11 and 111, respectively. The values of Gic, Guc, and Gmc for the interlaminar level of composite material were taken from Liao and Sun (1996), where the values were determined experimentally by implementing a new analytical series solution for AS4 (3501-6 C/E). In the case of steel—composite interface, the values were obtained from Andre and Linghoff (2009), in which the Gic, Guc, and Gmc were determined experimentally via double-cantilever beam and end-notch flexure tests. The corresponding values are listed in Table 9.3. 

The filament wound flat specimens with a pre-crack were submitted to ENF-end notched flexural tests according to the determinations defined by protocol proposed by the ESIS task group [6]. The specimen geometry is schematically represented in figure la). The... 

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