Fracture single-edge notched beam

There are two main techniques used to measure the fracture toughness of ceramics fracture stress and hardness indentation. The former measures the load to fracture of a pre-cracked specimen using a single edge notched beam (SENB) or a chevron notched beam (CNB) sample. The main drawback of this technique is ensuring that the crack tip is atomically sharp. The second method uses the crack formed at the corners of the indentation produced during a Vickers indentation hardness test. This technique is rapid and relatively inexpensive. However, the toughness values measured are those of the surface, unlike the values obtained by fracture of the pre-cracked beams which are a measure of the bulk material properties. 

The equations for monolithic ceramics together with the experimental results of the notched specimen are used to determine the fracture toughness (represented as KIC) of the 3-D C/SiC composites created with the single edge notched beam (SENB) method. Its value is calculated as 20.3 MPa-m1/2, which is much higher than that of monolithic ceramic materials (3 to 5 MPa-m1/2). It should be noted that... 

In additional results [97] for the fracture toughness, Kic, determined from a single edge-notched beam test, values of 3.6 MPa m (for a 100 pm SiC particulate preform) up to 6.2MPam (13 pm SiC) were reported. This trend is the opposite of that reported by Pickard et al. [91]. Values of the elastic modulus reported in this later work ranged from 261 to 328 GPa. 

Fig. 2.19. Fracture toughness specimens, (a) Single-edge notched beam specimen, (b) compact tension specimen.

In order to overcome many of the difficulties associated with the indentation fracture toughness measurement as noted above, the single-edged notched beam (SENB) test - which often is used for metallic and polymeric materials - has been adapted to suit ceramics [24]. For this, a bar of ceramic, usually in the order of 3 x 4 mm cross-section and 25-45 mm length, has a notch introduced on one side. The bar is then loaded in four-point bending and the fiacture toughness determined from the failure load, Pm> as per ... 

The first of the two common methods for testing fracture toughness is called the single-edge notched beam (SEND) test. The set-up for this test is shown in Figure 15.25. The load is applied through the top two rollers until the specimen fractures. This fracture load is noted as Ffr ct. and substituted in Equation 15.58. In this equation, is a calibration factor. The drawback of this test is that we may not always obtain an atomically sharp crack. 

Fracture tougnness was determined with the single-edge-precracked-beam (SERB) and chevron-notch° methods in three-point bending. 

Fig. 5.55 Schematic representation of different fracture mechanics specimens used with brittle polymers and load-displacement curves for each specimen for a constant displacement rate. SEN, single-edge notched DT, double torsion DCB, double-cantilever beam.

R. Moon, K. Bowman, K. Trumble, J. Roedel, Comparison of R curves from single edge V notch beam (SEAfB) and surface crack in flexure(SCF) fracture toughness test methods on multilayered alumina zirconia composites, J. Am. Ceram. Soc. 83 [2] 445 47 (2000)... 

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