Reza Hashemi

Flinders University · Biomaterials Research Group, College of Science and Engineering, Medical Device Research Institute

With the rising demand for medical implants and the dominance of implant-associated failures including infections, extensive research has been prompted into the development of novel biomaterials that can offer desirable characteristics. This study develops and evaluates new titanium-based alloys containing gallium additions with the aim of offering...

Prediction models are being increasingly used in the medical field to identify risk factors and possible outcomes. Some of these are presently being used to develop guidelines for improving clinical practice. The application of machine learning (ML), comprising a powerful set of computational tools for analysing data, has been clearly expanding in...

Tribocorrosion in passive metals involves a complex and interactive mechanism between mechanical and electrochemical actions at a rubbing contact in a corrosive environment. The mechanical wear mechanism disrupts the passive film on the metal surface; and instantly, the metal repassivates and dissolves in the corrosive environment. This surface dam...

Background The Australian Orthopedic Association National Joint Replacement Registry has developed a standardized multi-stage approach to identify prostheses with a higher-than-anticipated rate of revision when comparing a prosthesis of interest to all other prostheses within the same broad class. However, the approach does not adequately different...

This study aims to investigate the effect of ridged (micro-grooved) surface finish over the trunnion surface on the mechanics (stress, strain, and deformation) of the head–neck taper interface in hip implants. Using finite element modelling, the study focused on the geometric parameters of such micro-grooves to study how they would mechanically aff...

With the rising demand for implantable orthopaedic medical devices and the dominance of device-associated infections, extensive research into the development of novel materials has been prompted. Among these, new-generation titanium alloys with biocompatible elements and improved stiffness levels have received much attention. Furthermore, the devel...

The impact of total hip replacement (THR) and total knee replacement (TKR) on patients can be monitored by joint registries through the surveillance of prostheses and identification of devices with a higher rate of revision—outliers. The development of new statistical methods can help determine whether a device is at a higher risk of failure by con...

Fretting corrosion is a known failure mechanism of total hip replacement (THR) that can lead to revision surgery. Implant retrieval studies have thoroughly documented the occurrence of fretting corrosion in THR implants and its correlation with implant- and patient-related factors. Although implant retrieval studies benefit both clinicians and impl...

Optimization of all the process parameters for laser powder bed fusion (L-PBF), considering the effects of individual parameters on Ti6Al4V fabricated parts, can be complex and challenging. Therefore, for the first time, the effects of three main variable process parameters (laser power, scan speed, and hatch spacing) on three outcomes parameters (...

Fretting corrosion at the head–neck interface of modular hip implants, scientifically termed trunnionosis/taperosis, may cause regional inflammation, metallosis, and adverse local tissue reactions. The severity of such a deleterious process depends on various design parameters. In this review, the influence of surface topography (in some cases, cal...

The cyclic loading, in the corrosive medium of the human body, results in tribocorrosion at the interface of the head-neck taper junction of hip implants. The resulting metal ions and wear debris adversely affect the local tissues. The force applied by surgeons to assemble the junction has proven to play a major role in the mechanics of the taper j...

The tribocorrosion behaviour of Ti-6Al-4 V exposed to phosphate buffered saline was investigated under a range of normal forces in both cathodic and anodic regions to provide a basis for properly deriving the tribological constants of this alloy. To achieve this, a new customised tribotester was designed and manufactured to rub the Ti-6Al-4 V disks...

The cyclic loading, in the corrosive medium of the human body, results in tribocorrosion, at the interface of the head neck taper junction of hip implants. The resulting metal ions and wear debris can have adverse effects on the local tissues. The force applied by surgeons to assemble the head-neck junction is proven to play a major role in the mec...

This study uses an experimental approach to investigate the relationship between metal-on-metal and ceramic/metal tribocorrosive behaviours. A set of tribocorrosion experiments were conducted on Ti6Al4V/ceramic, ceramic/CoCrMo, and Ti6Al4V/CoCrMo couples. The anodic current profiles for all the studied material combinations were provided to facilit...

This paper studies the tribocorrosion behaviour of Ti-6Al-4V in phosphate buffered saline under reciprocating frequencies of 1, 5, 10, 15, 20, and 25 Hz at different normal forces of 3.5, 6, 10.8, and 17.5 N using a customised ball-on-disk test set-up. The tribocorroded scars were then post-assessed by scanning electron microscopy and energy disper...

Anisotropy in the mechanical properties of Laser Powder Bed Fusion (L-PBF)-fabricated titanium parts, which could be problematic in service, is dependent on the build directions and may be mitigated by post-fabrication treatments such as surface machining or heat treatment. However, investigation of the anisotropy in truly as-printed conditions, i....

This study proposes a new finite element (FE) model for tribocorrosion at the head-neck junction of hip implants (known as taperosis). The model addresses the synergy in tribocorrosion to separate the role played by both the mechanical and chemical mechanisms. This algorithm was conceptualised for a ball-on-disk configuration; and it was then imple...

Anisotropy in the mechanical properties with respect to the build direction of Selective Laser Melting (SLM) fabricated titanium parts is a known, challenging problem, which can be mitigated using a post processing method such as heat treatment. This paper investigates the potential sources of anisotropy associated with SLM fabricated Ti64 parts an...

Studying the mechanical properties of Selective Laser Melting (SLM) fabricated titanium parts built in a horizontal direction, parallel to the substrate, in a truly as-built condition, has always been a challenge. The problem is mainly related to the stress relaxation of horizontal parts after removal from the substrate, which causes a noticeable l...

Modular hip implants are widely used in hip arthroplasty because of the advantages they can offer such as flexibility in material combinations and geometrical adjustments. The mechanical environment of the modular junction in the body is quite challenging due to the complex and varying off-axial mechanical loads of physical activities applied to a...

Taperosis/trunnionosis is a scientific term for describing tribocorrosion (fretting corrosion) at the head-neck taper junction of hip implants where two contacting surfaces are undergone oscillatory micromotions while being exposed to the body fluid. Detached ions and emitted debris, as a result of taperosis, migrate to the surrounding tissues and...

Metallic biomaterials (biometals) are widely used for the manufacture of medical implants, ranging from load-bearing orthopaedic prostheses to dental and cardiovascular implants, because of their favourable combination of properties including high strength, fracture toughness, biocompatibility, and wear and corrosion resistance [...]

The corrosion behaviour of new generation titanium alloys (β-type with low modulus) for medical implant applications is of paramount importance due to their possible detrimental effects in the human body such as release of toxic metal ions and corrosion products. In spite of remarkable advances in improving the mechanical properties and reducing th...

The need for metallic biomaterials will always remain high with their growing demand in joint replacement in the aging population. This creates need for the market and researchers to focus on the development and advancement of the biometals. Desirable characteristics such as excellent biocompatibility, high strength, comparable elastic modulus with...

New generation titanium alloys with low elastic moduli are promising materials for medical implants, particularly load-bearing orthopaedic implants. In this paper, the effect of niobium content on the microstructure and mechanical properties of new Ti alloys including Ti-23Nb-7Zr, Ti-28Nb-7Zr and Ti-33Nb-7Zr (wt%) is studied. Ti-23Nb-7Zr was found...

The impaction force required to assemble the head and stem components of hip implants is proven to play a major role in the mechanics of the taper junction. However, it is not clear if the assembly force could have an effect on fretting wear, which normally occurs at the junction. In this study, an adaptive finite element model was developed for a...

Metallic taper junctions of modular total hip replacement implants are analysed for corrosion damage using visual scoring based on different granularity levels that span from analysing the taper holistically to dividing the taper into several distinct zones. This study aims to objectively explore the spatial distribution and the severity of corrosi...

Visual scoring of damage at taper junctions is the sole method to quantify corrosion in large-scale retrieval studies of failed hip replacement implants. This study introduces an intelligent image analysis-based method that objectively rates corrosion at stem taper of retrieved hip implants according to the well-known Goldberg scoring method. A Sup...

A new adaptive finite element model was successfully developed to simulate fretting corrosion at metallic interfaces. To do this, the Archard wear equation and a previously established electrochemical equation were simultaneously employed. The algorithm of this finite element approach is able to determine the volume of passive oxide layers removed...

An adaptive finite element simulation was developed to predict fretting wear in a head-neck taper junction of hip joint implant through a two dimensional (2D) model and based on the Archard wear equation. This model represents the most critical section of the head-neck junction which was identified from a 3D model of the junction subjected to one c...

A detailed investigation was performed to characterize the fretting wear and corrosion damage to the neck component of a CoCrMo stem from a metal-on-polyethylene implant retrieved after 99 months. The stem was a low-carbon (0.07 wt%) wrought Co-28Cr-6Mo alloy with no secondary carbide phases in the matrix (γ-phase). The original design of the neck...

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...

Modularity at the head-neck junction of hip implants may result in fretting wear and implant failure. Most previous studies have applied major simplifications to simulate this phenomenon at the taper junction (e.g. negligence of mismatch angle, simulation in dry condition). In this study, a 3D model of a Co-28Cr-6Mo head-neck junction with a proxi...

This article aims to investigate ratcheting and mean stress relaxation in a steel holed plate with interference fit by using kinematic and isotropic hardening models. To predict the fatigue life of the plates, it was necessary to estimate the residual stresses, pre-stresses and ratcheting at the pin entrance and exit faces of the hole which were co...

This paper aims to characterize the surface damage as a consequence of fretting fatigue in aluminum alloy 7075-T6 plates in double-lap bolted joints through XRD, surface profilometry, and SEM analyses. The main focus was on the surface roughness and chemical phase composition of the damaged zone along with the identification of fretting fatigue cra...

In this study, surface properties of Ti-6Al-4V alloy coated with hydroxyapatite coatings were investigated. Wear resistance and fatigue behaviour of samples with coating thicknesses of 10 and 50 µm as well as uncoated samples were examined. Wear experiments demonstrated that the friction factor of the uncoated titanium decreased from 0.31 to 0.06,...

In this study, the fatigue behaviour of spot friction welded joints of Al 5083-O was investigated using experimental and numerical approaches. In the experimental part, a single cover butt joint of aluminium sheets with a thickness of 2 mm was fatigue tested under constant amplitude cyclic loadings. The sheets were connected using a spot friction w...

This paper aims to study the mechanical behaviour and failure mode of Al 2024-T3 in double-lap bolted joints. To accomplish this, the effect of geometric parameters was investigated in both configurations of single and double fasteners. Using ABAQUS/Standard, a three-dimensional finite element model was developed and verified against the experiment...

The performance of single layer TiAlN and multilayered TiAlN/CrN physical vapour deposition coatings deposited on AISI P20 steel substrate in affecting overall fatigue resistance of notched specimens was assessed and compared with the performance of the uncoated counterparts. V-shaped circumferential notches on cylindrical specimens were adopted fo...

The purpose of this study is to examine the fretting fatigue performance of Ni–P coated (EN coated) Al 7075-T6 plates. In addition, the effect of two stress-based fretting mechanical parameters (clamping pressure and friction force) on the fretting fatigue performance is evaluated using a finite element stress analysis of the contact region. It was...

Modularity at the head-neck junction of the femoral component in THA became popular as a design feature with advantages of decreasing implant inventory and allowing adjustment of leg length, offset, and soft tissue balancing through different head options. The introduction of a new modular interface to femoral stems that were previously monoblock,...

A three dimensional analytical approach was developed to determine the frictional moment vector generated by the relative sliding of the head-cup bearing couple of a total hip replacement. The frictional moment projection onto the femoral neck was also determined over the loading cycle. Predicted frictional moments for nine combinations of bearing...

In many sense, the role of a corrosion film and a surface coating in fatigue crack initiation is similar. The performance of the TiAlN and TiAlN/CrN PVD coatings in resisting fretting fatigue failure of the AISI P20 steel was investigated. A significant increase in fretting fatigue life was observed; up to 210% and 193% when clamped at 5.6 kN and 1...

This study investigates fatigue behaviour of riveted joints in a coach peel configuration under various load ranges and load ratios. Three well-known multi-axial fatigue criteria of Smith–Watson–Topper, Glinka and Fatemi–Socie are used to predict the fatigue life of the joint based on the stress and strain components obtained from a finite element...

In this study, an investigation was conducted on the fatigue performance of Al 7075-T6 plates in the presence of stress raisers (notch, fretting, and a combination of notch and fretting). Fretting situation was induced on the surface of the aluminium plate through steel contacting pads under two different clamping forces of 2 kN and 5.6 kN. The fat...

Smart actuators are the key components in a variety of nanopositioning applications, such as scanning probe microscopes and atomic force microscopes. Piezoelectric actuators are the most common smart actuators due to their high resolution, low power consumption, and wide operating frequency but they suffer hysteresis which affects linearity. In thi...

In this paper, the fatigue behaviour of Al 7075-T6 fastener holes with symmetrical through slits was studied. The holes were coated with electroless nickel (EN) plating with a high phosphorous content of 10–13 wt% and a thickness of 40 μm. Uncoated open-hole, EN coated open-hole, uncoated bolted hole and EN coated bolted hole specimens were fatigue...

In this paper, delamination of a titanium nitride (TiN) thin film from an aluminium alloy 7075-T6 substrate has been studied under fatigue loading conditions. TiN coatings of 3 μm in thickness were deposited onto the aluminium substrate using a physical vapour deposition process. Fatigue fracture surfaces of the coated specimens, failed under a ran...

In this paper, the effect of electroless nickel–phosphorous coatings on the fatigue and fretting fatigue behaviour of Al 7075-T6 bolted plates has been investigated. A double-lap bolted joint specimen was designed and manufactured from the aluminium plates and subsequently coated with Ni–P coatings of 40 μm in thickness with a high phosphorous cont...

This paper investigates the fatigue behaviour of aluminium alloy 7075-T6 coated with 3-μm-thick titanium nitride (TiN) coatings using a physical vapour deposition (PVD) process. Preliminary work demonstrated that the high operating temperature of the deposition process markedly reduced the tensile properties of the coating-substrate system by compa...

In this paper, an experimental and numerical investigation was conducted to study the effect of geometric parameters on the stress and strain distributions in aluminium alloy 2024-T3 single-lap bolted plates. Three-dimensional (3-D) finite element (FE) models were developed using ANSYS FE code for different width and edge distance to hole diameter...

In this paper, a finite element stress analysis has been carried out to study the effect of flight temperatures on the clamping compressive stresses around aluminium bolted holes subjected to cyclic loads. A holed plate of aluminium alloy 7075-T6 was clamped with two different tightening torques of 2 and 7 Nm and then simultaneously subjected to bo...

In this paper, fatigue properties of coated aluminium alloy 7075-T6 with a TiN deposit of 3μm using physical vapour deposition (PVD) have been studied. It was determined that the application of a PVD hot process significantly decreased the tensile and fatigue strength of the substrate-coating system due to the effect of a high operating temperature...

In this work, a post heat treatment cycle is proposed with the aim to recover the lost tensile properties of aluminium alloy 7075-T6 coated with a 3μm thick titanium nitride (TiN) film by using a physical vapour deposition (PVD) process. First, it was found that the application of the PVD hot process with a high operating temperature of 450°C signi...

In this research work, fatigue behaviour of aircraft structural bolted plates at typical working temperatures has been studied. A holed plate of aluminium alloy 7075-T6 was clamped with the purpose of subjecting to both flight representative temperatures and longitudinal cyclic loadings simultaneously. In order to investigate the effect of the serv...

Numerical simulations based on finite element modelling are increasingly being developed to accurately evaluate the tensile properties of GLARE (GLAss fibre REinforced aluminium laminates). In this study, nonlinear tensile behaviour of GLARE Fibre Metal Laminates (FML) under in-plane loading conditions has been investigated. An appropriate finite e...

Accurate 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 use...

In this study, a finite element (FE) stress analysis of aircraft structural double-lap bolted joints was performed using the commercially available computational package ANSYS in order to obtain the clamping pressure distribution and estimate the stiffness of the joined plates (members) within the clamped region. The joint consists of three alumini...

The main purpose of the present work is to experimentally and numerically study why and how the magnitude of the bolt clamping force reduces in the aerospace structural bolted plates when they are subjected to a longitudinal tensile load. In the experimental method, a holed plate of aluminium alloy 7075-T6 was clamped using a single bolt fastener,...

In this research, both experimental and numerical methods were used to investigate the fatigue behaviour of bolted plates. In the experimental part of the research, a holed plate was clamped using a bolt and a nut, and then tested under axial cyclic load in a fatigue testing machine. In order to obtain S–N curves and investigate the direct effect o...

In this paper, the details of an experimental method to measure the clamping force value at bolted connections due to application of wrenching torque to tighten the nut have been presented. A simplified bolted joint including a holed plate with a single bolt was considered to carry out the experiments. This method was designed based on Hooke's law...