An analytical calculation of frictional and bending moments at the head-neck interface of hip joint implants during different physiological activities

This study predicts the frictional moments at the head-cup interface and frictional torques and bending moments acting on the head-neck interface of a modular total hip replacement across a range of activities of daily living. The predicted moment and torque profiles are based on the kinematics of four patients and the implant characteristics of a metal-on-metal implant. Depending on the body weight and type of activity, the moments and torques had significant variations in both magnitude and direction over the activity cycles. For the nine investigated activities, the maximum magnitude of the frictional moment ranged from 2.6 to 7.1 Nm. The maximum magnitude of the torque acting on the head-neck interface ranged from 2.3 to 5.7 Nm. The bending moment acting on the head-neck interface varied from 7 to 21.6 Nm. One-leg-standing had the widest range of frictional torque on the head-neck interface (11 Nm) while normal walking had the smallest range (6.1 Nm). The widest range, together with the maximum magnitude of torque, bending moment, and frictional moment, occurred during one-leg-standing of the lightest patient. Most of the simulated activities resulted in frictional torques that were near the previously reported oxide layer depassivation threshold torque. The predicted bending moments were also found at a level believed to contribute to the oxide layer depassivation. The calculated magnitudes and directions of the moments, applied directly to the head-neck taper junction, provide realistic mechanical loading data for in vitro and computational studies on the mechanical behaviour and multi-axial fretting at the head-neck interface.Hamidreza Farhoudi, Reza H. Oskouei, Ali A. Pasha Zanoosi, Claire F. Jones and Mark Taylo

A finite element stress analysis of aircraft bolted joints loaded in tension

AbstractAccurate stress and strain analysis in bolted joints is of considerable interest in order to design more efficient and safer aerospace structural elements. In this paper, a finite element modelling of aluminium alloy 7075-T6 bolted plates, which are extensively used in aircraft structures, is discussed. The ANSYS Finite Element (FE) package was used for modelling the joint and estimating the stresses and strains created in the joint due to initial clamping forces and subsequent longitudinal tensile loadings. A double-lap bolted joint with a single bolt and nut was considered in the study. A three-dimensional (3D) finite element model of the joint was generated, and then subjected to three different simulated clamping forces followed by different levels of longitudinal tensile load. 3D surface-to-surface contact elements were employed to model the contact between the various components of the bolted joint. Friction effects were considered in the numerical analysis; and moreover, the clearance between the bolt and the plates was simulated in the model. FE results revealed beneficial compressive stresses near the hole edge as a result of applying the clamping. It was found that a higher clamping force can significantly decrease the magnitude of the resultant tensile stress at the hole edge and also bearing stress in the joint when subjected to the longitudinal tensile load.</jats:p

Nano-mechanical characterization of SLM-fabricated Ti6Al4V alloy: etching and precision

In this research, we are reporting that the nanoindentation results vary between etched and unetched SLM-fabricated titanium alloy (Ti6Al4V) in spite of the same microhardness values. The dimensionless roughness parameter α, as a metric for the sensitivity of nano-hardness values on the surface roughness, is used to highlight whether etching plays any role. Although the value of α for both samples is below the recommended maximum value, the effect of etching is still significant. The hypothesis for a 19% increase in nano-hardness of etched samples is also discussed in this paper. Furthermore, the maximum proposed value of α (α < 0.05) appeared to be invalid for SLM-fabricated titanium and a lower value of α may need to be proposed as a critical value.Alireza Dareh Baghi, Reza Ghomashchi, Reza H. Oskouei, Heike Ebendorff-Heideprie