Hardness and toughness are often used to analyze the abrasive machinin
g behavior of ceramic materials, However, toughness values of silicon
nitride ceramics with microstructures containing elongated grains incr
ease with crack extension, The present study investigates the effect o
f toughness on the process of abrasive machining to determine which va
lue of toughness should be used in the analysis. The toughness curves
(i.e., toughness as a function of crack length) of ten different silic
on nitride materials are characterized by an indentation-strength tech
nique and an indentation technique, The forces in surface grinding are
measured as a function of the depth of cut, Examination of ground sur
faces by scanning electron microscopy indicates that the material-remo
val processes in grinding follows the formation of short cracks (i.e.,
microcracks) and grain-scale material dislodgement. An indentation fr
acture model for material removal in abrasive machining is used to cor
relate the grinding forces with toughness and hardness of the material
s. An agreement is obtained between the experimental results and the i
ndentation model only when the toughness associated with short cracks
is used. This study shows the importance of using appropriate toughnes
s values corresponding to the microfracture processes in analyzing abr
asive machining results for materials possessing rising toughness curv
es.