In this paper a numerical investigation of replacement implant for partial hip arthroplasty is presented. The long-term stability of hip implants depends, among other things, on the loads acting across the joint. Forces occurring in vivo can be much greater than the recommended test values, because a typical gait cycle generates forces up to 6–7 times the body weight in the hip joint. A finite element analysis (FEA) was performed using 3-dimensional models to examine the mechanical behaviour of the femoral component at forces ranging from 2.5 to 6.3 kN. This implant design was chosen for numerical analysis because stress concentration in femoral component lead to implant fracture. Results show that the force magnitudes acting on the implant are of interest, and that they can cause implant stress field changes and implant stability problems, which can lead to implant failure

In this paper numerical analysis of hip replacement implant behaviour from a fracture mechanics perspective is presented. It is necessary to understand the fatigue crack initiation and propagation characteristics in order to prevent catastrophic failure of the implant. For the simulation of crack propagation extended finite element method (XFEM) was used, as being one of the most advanced modeling techniques for this type of problem. Short theoretical background information on the XFEM is provided, as well as the representation of crack and the stress intensity factors computation. For chosen titanium alloy hip implants numerical modeling and analysis were done in ABAQUS software. It is shown that is possible to assume hip implant mechanical behaviour to the existence of defects such as cracks by application of numerical simulation crack behaviour. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in complicated biomedical structures, without the need to re-mesh during the propagation if the finite element mesh is well defined

The paper presents a study on the surface modifications of nickel based superalloy Nimonic 263 induced by laser shock peening (LSP) process. The process was performed by Nd³⁺:Yttrium Aluminium Garnet (YAG) picosecond laser using the following parameters: pulse duration 170 ps; repetition rate 10 Hz; pulse numbers of 50, 100 and 200; and wavelength of 1064 nm (with pulse energy of 2 mJ, 10 mJ and 15 mJ) and 532 nm (with pulse energy of 25 mJ, 30 mJ and 35 mJ). The following response characteristics were analyzed: modified surface areas obtained by the laser/material interaction were observed by scanning electron microscopy; elemental composition of the modified surface was evaluated by energy-dispersive spectroscopy (EDS); and Vickers microhardness tests were performed. LSP processing at both 1064 nm and 532 nm wavelengths improved the surface structure and microhardness of a material. Surface morphology changes of the irradiated samples were determined and surface roughness was calculated. These investigations are intended to contribute to the study on the level of microstructure and mechanical properties improvements due to LSP process that operate in a picosecond regime. In particular, the effects of laser wavelength on the microstructural and mechanical changes of a material are studied in detail.

Reliable and resilient constructions are basic for ensuring the safety of various structures. The superalloys are used as constructive materials due to their superb mechanical properties and endurance. However, even these materials can have certain areas where the stress concentration is higher than expected, such as drilling holes, which are common in various structures that need additional enhancement. Surface laser modifications of the areas surrounding the holes drilled in Nimonic 263 sheets are done by pulsed picosecond and nanosecond Nd:YAG laser irradiations with pulse durations of 170 ps and ≤8 ns, respectively. Following the laser surface treatment, the effectiveness of the enhancement was analyzed by the microhardness test and the deformation test. The results show that the deformation and stress values are decreased by 25−40 percent, showing the improvement in the resilience to deformation. The Vickers microhardness test results indicate an improvement in the Nimonic 263 microhardness. The dimensions of the microcracks are higher for the untreated material in comparison to the laser-treated material.

U ovom radu prikazano je eksperimentalno i numeričko istraživanje mehaničkog ponašanja umjetnog kuka od legure titana. Eksperimentalno istraživanje je bazirano na standardnim metodama ispitivanja mehaničkih svojstava i na primjeni...

This paper presents an experimental and numerical analysis of the mechanical behaviour of orthopaedic implants with crack-type defects, considering the principles and advantages of the modern X-FEM method, which was used due to limitations of traditional FEM in terms of crack growth simulation, especially for complex geometries. In X-FEM, the finite element space is enriched with discontinuity functions and asymptotic functions at the crack tip, which are integrated into the standard finite element approximation using the unity division property. Though rare, femoral component failures are well-documented complications that can occur after hip prosthetic implantation. Most stem fractures happen in the first third of the implant due to the loosening of the proximal stem and fixation of the distal stem, leading to bending and eventual fatigue failure. The main goal of this paper was to obtain accurate and representative models of such failures. Experimental analyses of the mechanical behaviour of implants subjected to physiological loads, according to relevant standards, using a new combined approach, including both experiments and numerical simulations was presented. The goal was to verify the numerical results and obtain a novel, effective methodology for assessing the remaining fatigue life of hip implants. For this purpose, the analysis of the influence of Paris coefficients on the total number of cycles was also considered. Hence, this simulation involved defining loads to closely mimic real-life scenarios, including a combination of activities such as ascending stairs, stumbling, and descending stairs. The tensile properties of the titanium alloy were experimentally determined, along with the Paris law coefficients C and m. The finite element software ANSYS 2022R2 version was used to develop and calculate the three-dimensional model with a crack, and the resulting stresses, stress intensity factors, and the number of cycles presented in the figures, tables, and diagrams. The results for the fatigue life of a partial hip implant subjected to various load cases indicated significant differences in behaviour, and this underscores the importance of analysing each case individually, as these loads are heavily influenced by each patient’s specific activities. It was concluded that the use of numerical methods enabled the preliminary analyses of the mechanical behaviour of implants under fatigue loading for several different load cases, and these findings can be effectively used to predict the possibility of Ti-6Al-4V implant failure under variable cyclic loads.