Fracture property studies of paracetamol single crystals using microindentation techniques

Purpose. To study the fracture behavior of the major habit faces of paracet amol single crystals using microindentation techniques and to correlate thi s with crystal structure and molecular packing. Methods. Vicker's microindentation techniques were used to measure the hard ness and crack lengths. The development of all the major radial cracks was analyzed using the Laugier relationship and fracture toughness values evalu ated. Results. Paracetamol single crystals showed severe cracking and fracture ar ound all Vicker's indentations with a limited zone of plastic deformation c lose to the indent. This is consistent with the material being a highly bri ttle solid that deforms principally by elastic deformation to fracture rath er than by plastic flow. Fracture was associated predominantly with the (01 0) cleavage plane, but was also observed parallel to other lattice planes i ncluding (110), (210) and (100). The cleavage plane (010) had the lowest fr acture toughness value, K-c = 0.041MPa m(1/2), while the greatest value, K- c = 0.105MPa m(1/2) was obtained for the (210) plane. Conclusions. Paracetamol crystals showed severe cracking and fracture becau se of the highly brittle nature of the material. The fracture behavior coul d be explained on the basis of the molecular packing arrangement and the ca lculated attachment energies across the fracture planes.