FRACTURE-TOUGHNESS OF TIB2 AND B4C USING THE SINGLE-EDGE PRECRACKED BEAM, INDENTATION STRENGTH, CHEVRON-NOTCHED BEAM, AND INDENTATION STRENGTH METHODS

The mode I fracture toughness (K-Ic) of boron carbide (B4C) and titani um diboride (TIB2) was determined using four competing techniques. The indentation strength (IS), chevron notched beam (CNB), and indentatio n fracture (IF) methods are common techniques that were compared to th e recently standardized single-edge precrack beam (SEPB) method. The S EPB method was more difficult to apply, but it represents the most rig orous method for K-Ic determination, because it uses few assumptions a nd requires a direct measurement of crack length. The IS method was an expeditious and economical alternative when low indentation loads wer e used. CNB K-Ic values were virtually rate-independent when displacem ent rates less than or equal to 0.5 mm/min were used. The IF method wa s the least satisfactory technique, because of high variability in K-c values and because of the low differentiation between the two materia ls studied.