Single-Edge Notched Beam

To convert Pa to psi, multiply by 1.45 x lO ". For a single-edged notched beam (SENB) test. Corresponding to a 4 pt. bend. 

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... 

Hardness was estimated by Vickers indentation on sintered gradient samples, thermal expansion coefficient measurements and elastic behaviour was tested on the different dispersions. Preliminary mechanical testing (single edge notched beam, 3PB-SENB) and oxidation tests were performed on sintered FGM s. 

Figure 11.6 (a) Schematic of single-edge notched beam specimen (b) Chevron notch specimen. 

Single-edge notched beam (SENB) test... 

Figure 8.19 Single edge-notched beam geometry. Loading is usually either three- (shown here) or four-point bending.

Figure 8.28 Stress concentration factor as a function of notch radius for a single edge-notched beam. (Adapted from Rooke et al., 1981, reproduced courtesy of Elsevier Science Ltd, Kidlington, UK.)...

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. 

Notched-beam specimens with dimensions of 90 mm x 10 mm x 20 mm were fabricated as per the ASTM D 5045 standard. The notch was machined by bandsaw. A schematic of the notched beam specimen is shown in Figure 7.33. We used single-edge notched-beam (SENB)... 

Fig. 3. Load-deflection curve of ZrC/TijAlCr composite, showing a nonlinear feature, single-edge notch beam...

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

Figure 14.14 Crack growth resistance behavior as a function of grain size (4, 9, and 16nm) for alumina using a single-edge notched beam (SENB) sample. From Ref [12].

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 ... 

Single crystals of zirconia and alumina were tested by SEVNB and by the single-edge notched beam (henceforth SENB) method, and the results are shown... 

ASTM D5045 has been accepted for the determination of the critical stress intensity factor, KIC. Although KIC is temperature- and rate-dependent and the dependence is specific for any material, it is relatively independent of specimen geometry. Single-edge-notched beams are typically used for the test, but other... 

FIG. 19—Comparison of single-edge-notched bend cantilever beam and wedge-opening load test results for hydrogen embrittlement threshold of ironHiickel-cobalt steels [28],... 

The effect of test duration is demonstrated fqr a method used fy the Navy to compare materials for aircraft parts. A single-edge notched (and precracked) cantilever beam specimen is deadweight loaded and exposed to 3 1/2 % NaCl. The time-to-fad at various stress intensities is plotted in Fig. 8. The stress intensity after 1000 h exposure has been used as a measure of resistance, although lower values have been obtained if the specimens are allowed to continue for 10 000 h. 

---