Assessment of fracture toughness and microstructure of bone cements
Arkadiusz Szarek, Dariusz Kwiatkowski, Hubert Dębski
Quarterly No. 3, 2011 pages 192-196
DOI:
keywords: bone cement, carbon fibre, fracture toughness, numerical simulation, SENB
abstract Bone cement used in orthopaedics (PMMA) is a viscoelastic material. Macroscopically, the cement structure is composed of aggregates in the form of polymer spheres with the dimensions of 10÷18 micrometers connected with polymerized monomer bridges. After mixing, it is initially a fluid, which then becomes increasingly viscous and hardens. During polymerization, the material is plastic and can be easily moulded and it penetrates deep into the fine trabecular structure of the bone. PMMA is characterized by low impact strength, which, in cements without fillers, reaches the level of KC = 1.16÷5.2 kJ/m2. This causes the material to show tendencies to crack at even a low dynamic load. A number of studies have demonstrated that PMMA tends to fragment and chip in artificial hip joints. The paper presents the investigations of the PMMA structure carried out for bone composites with implanted hip joint prostheses. The results of empirical investigations which allow for the determination of PMMA crack resistance were also presented. In order to determine crack resistance in bone cement, strength tests were carried out by means of an Inspekt Desk 20 machine manufactured by Hegewald & Peschke, equipped with a device for three-point bending. The measure of crack resistance was a critical value of the stress intensity factor KQ. In order to compare the results, numerical calculations of the stress intensity factor (WIN) were also carried out for the three-point bending of a SENB sample made of SIMPLEX P + carbon fibre.