Biomechanical Performance Analysis of the Monolateral External Fixation Devices with Steel and Composite Material Frames under the Impact of Axial Load  
[PERSON]  
1 Department of Mechanical Design, Faculty of Mechanical Engineering, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; [PERSON]L_ADDRESS] (E.M.); [EMAIL_ADDRESS] (A.J.M.); [EMAIL_ADDRESS] (M.D.); [EMAIL_ADDRESS] (E.M.).  
2 Department of Vehicle Engineering, Faculty of Mechanical Engineering, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; [EMAIL_ADDRESS] (E.M.).  
3 Department of Physics and Mathematics, Faculty of Mechanical Engineering, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; [EMAIL_ADDRESS] (E.M.).  
4 Correspondence: [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Mechanical Design, Faculty of Mechanical Engineering, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; [EMAIL_ADDRESS] (E.M.); [EMAIL_ADDRESS] (A.J.M.); [EMAIL_ADDRESS] (M.D.); [EMAIL_ADDRESS] (E.M.).  
[PERSON]  
1 Department of Mechanical Design, Faculty of Mechanical Engineering, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; [PERSON]L_ADDRESS] (E.M.); [EMAIL_ADDRESS] (A.J.M.); [EMAIL_ADDRESS] (M.D.); [EMAIL_ADDRESS] (E.M.).  
[PERSON]  
In order to improve necessary tests and make improvements, researchers seek to develop theoretical background of the fixation thematic based on the principles of structural mechanics [2; 3]. Stiffness of the fixation device is defined according to specific type of load: axial load due to pressure force, bending and torsion [4; 5]. Additionally, for the purposes of defining properties of these devices, researchers rely on force transducers [6; 7].  
In the context of biomechanical research, great focus is put on analyzing the influential construction parameters on the fixation device stability. These parameters include stiffness, maximum von Mises stress for zones of interest and bearing capacity of the pin-bone connection, as shown in many experimental studies [8; 9; 10; 11].  
We note that, today, ring external fixators are more often used than monolateral external fixators. One of the most commonly used ring external fixators is the Ilizarov external fixator. Investigations of five different frame models (one standard and four hybrid Ilizarov) were performed in order to determine the stiffness characteristics of standard and hybrid Ilizarov fixators [12]. In the second study, research was conducted with the aim of determining the stiffness of the Ilizarov fixator depending on the type of derotation mechanism [13].  
In recent periods, conducted research is not only based on experimental investigations but also on benefits of 3D modeling and numerical analysis. This way, a more complete image and understanding of fixation device behavior is obtained [14; 15; 16; 17; 18].  
During the 1970s and 1980s and with development of new biomechanical materials such as polymers and composites, new research directions are established [19; 20; 21; 22; 23; 24].  
All of the commercial fixation device, which are in use today, have undergone the biomechanical tests before usage. Biomechanical investigation of the Sarafix fixation device, due to war conditions in which it was created, was not conducted by the means of the exact estimation of its stability under the loads. Baseline quantity for the stability assessment is system stiffness, which is gained on the basis of the interfragment displacement in the fracture, i.e., load zone. This paper describes the biomechanical research of the Sarafix external fixation device with frames built from two different materials (stainless steel and composite material) for two device configurations (B50 and C50). The main goal of this research was to quantify the mechanical behavior of the standard Sarafix device under the impact of the axial load for the different frame materials and configurations.