Friction and wear mechanisms of high performance polyetheretherketone and silicone

This work examines two high performance polymer tribology systems. Polyetheretherketone (PEEK) is a high temperature, low wear thermoplastic that has potential for several modern industries, but the understanding of its wear mechanisms in relation to transfer film is not well understood. An investigation into these mechanisms would benefit the utility of PEEK in several applications. The second polymer system investigated is high performance silicone used in implantable cardiac devices (ICDs). Understanding the wear mechanisms of silicone in-vivo is challenging, and examining the fundamental causes of wear would benefit device design in surgical implantation methods. First, the viability of using finite element analysis as a way to understand fundamental contact behavior is investigated. It was found that for high-level contact models, average roughness is a weak sole descriptor of contact behavior. Next, two PEEK studies in dry sliding were conducted. The first study examined multi-linear and reciprocating sliding in relation to roughness orientation, while proposing hypotheses to explain transfer film behavior. The second PEEK study, examined the development of transfer film and wear with respect to roughness orientation for a variety of sliding distances. From these studies, it was found that frictional heating affects the volume of transfer film, multi-directional sliding and reciprocation play a role in wear and transfer film development, and roughness orientation can greatly impact both wear and transfer film of PEEK. Lastly, a silicone lead in implantable cardiac devices was studied by using three key parameters thought to affect its wear: load, albumin protein, and silica abrasive. It was found that none of these parameters greatly impacted the wear scar metrics, but silica and albumin can lead to wear mechanisms that might impact long-term wear or other wear modes

Laser Induced Hierarchical Coatings on Titanium Alloy

Biomaterials research is an exciting and challenging area. It is exciting because of its potential applications and need for improving the quality of life. It is challenging because of the complexity with which natural biomaterials function in their environments. The gap that exists in terms of maturity and sophistication of the currently used synthetic materials from natural biomaterials is huge. It is only in the last few decades with the evolution of advanced material analytical techniques that researchers are starting to understand the complexity of nature. One such particular feature that has attracted our interest is the hierarchical nature of the bioimplant surfaces. The present work is one small step in that direction where we tried to engineer a surface that is multi-scale in nature and biocompatible at these length scales. During a discovery phase a multi-scale textured zirconia coating was done on titanium alloy using a pulsed laser. Following proof of concept a bioactive calcium phosphate based coating was deposited on titanium alloy surface using a continuous wave laser. Based on detailed morphological and chemical analysis it was evident that the multi-phase coating had a multi-scale arrangement. Owing to the complexity of the coating a fractal based approach was used to interpret the morphology of the coatings. It appeared that at higher laser processing speeds star shaped calcium titanate features exist inside calcium phosphate and titania ring like structures. By tailoring a thermal model with current material system temperature calculations were made for various laser processing speeds. Using temperature predictions and knowledge of the phase constituents the series of self assembling steps that led to the formation of star and ring shaped arrangement are discussed. The biocompatibility of the coatings was evaluated by immersing in simulated body fluids. The morphological and chemical evolution of hydroxyapatite precipitation along the calcium phosphate rich ring like structures coupled with the porous structure supports the possibility of enhanced osteointegration. The presence of calcium titanate ensured an interaction between the substrate and the precursor coating material. Wear measurements indicated that the laser processed samples possessed better mechanical properties than unprocessed surfaces

Scientific Advances in STEM

Following a previous topic (Scientific advances in STEM: from professors to students; https://www.mdpi.com/topics/advances_stem), this new topic aims to highlight the importance of establishing collaborations among research groups from different disciplines, combining the scientific knowledge from basic to applied research as well as taking advantage of different research facilities. Fundamental science helps us to understand phenomenological basics, while applied science focuses on products and technology developments, highlighting the need to perform a transference of knowledge to society and the industrial sector

Biomedical Engineering

Biomedical engineering is currently relatively wide scientific area which has been constantly bringing innovations with an objective to support and improve all areas of medicine such as therapy, diagnostics and rehabilitation. It holds a strong position also in natural and biological sciences. In the terms of application, biomedical engineering is present at almost all technical universities where some of them are targeted for the research and development in this area. The presented book brings chosen outputs and results of research and development tasks, often supported by important world or European framework programs or grant agencies. The knowledge and findings from the area of biomaterials, bioelectronics, bioinformatics, biomedical devices and tools or computer support in the processes of diagnostics and therapy are defined in a way that they bring both basic information to a reader and also specific outputs with a possible further use in research and development

Prediction Of The Coefficient Of Friction In The Single Point Incremental Forming Of Truncated Cones From A Grade 2 Titanium Sheet

The aim of this paper is to analyze the effect of the process parameters on the coefficient of friction (COF) in the single-point incremental forming process. This investigation may be useful for further FEM analyses where the tool-workpiece contact must be set appropriately to obtain adequate results. The friction was analyzed between a solid tungsten carbide ⌀8 hemispherical ended tool with a radius of 4 mm and a grade 2 pure titanium sheet. As a lubricant, 10W40 engine oil was used. The experiment was of a central composite design and 20 runs in random order were carried out. The influence of input factors, namely spindle speed, tool feed and incremental step depth, was analyzed for the COF response. Two type of equations founded in the literature have been acquired to calculate COF values. An investigation of COF analysis was done for initial tool contact, the first tool full depth contact and stabilized forming region. Additionally, single components of the horizontal force (X-axis and Y-axis) were taken into account. Analysis of variance shows that there is no correlation between the input factors and the COF responses. However, the mean model fitted to the results obtained allows for the prediction of the COF by using the vertical force component and only one horizontal force component. The resulting mean value of the COF between the tool and the workpiece equals 0.4 for Eq. (1) initial contact, stabilized forming: Eq. (1) 0.656 and Eq. (2) 0.469

Direct metal laser sintering of titanium alloys for biomedical applications

Published ThesisOngoing scientific progress shifts conventional methods to the much celebrated Additive Manufacturing (AM) due to its freedom of design, flexibility in feedstock and material optimization. It has shown that Direct Metal Laser sintering (DMLS), one of the AM technologies, is an attractive manufacturing route for the biomedical applications. Ti6Al4V is the most widely used titanium alloy for the implants. However, there still remain issues of relative low ductility of DMLS Ti6Al4V and infections after implantation which have triggered the current research into producing implants of high ductility with antibacterial properties by DMLS, while establishing a body of knowledge about the relationship between the laser-matter interaction, microstructure, and mechanical properties. The type of material used in biomedical applications depends on specific implant applications and different types of implant need different mechanical properties. The current study is designed to investigate DMLS lattice structures from traditional Ti alloy such as T6Al4V ELI and the possibility of producing novel alloys by in-situ alloying for DMLS process. Learning from nature, it can be understood that cellular structures would be more preferable for biomedical implants than dense solid structures’ since the architecture of bone tissues in the human body are not completely dense and solid. Cellular structures of different nodes and strut sizes were produced and mechanically investigated to mimic the anisotropic porous nature of bones. A finite element analysis (FEA) was conducted to determine the applicability of graded/gradient implant based on each patient requirement. From the FEA it was hypothesized that implant design with cellular structures with relative low Elastic modulus would bridge the Elastic modulus gradient between dense solid metallic implants and the porous bones. An advanced lightweight mandible model was proposed whereby a damaged mandible could be replaced with a graded material based on the functional requirements of the damaged part. Mixing different elemental powders for in-situ alloying by DMLS would definitely increase the material pallet for AM. Understanding the effects of the parameters on DMLS process is paramount to gaining full control over density, microstructure and the mechanical properties of the DMLS parts. Only a careful combination of the process parameters would result in optimum process parameters for each type of powder. A wide range of process parameters were investigated to gain in-depth knowledge into the interaction between the laser beam and the powder bed by in-situ alloying powders with vastly different melting points and similar particle size distribution (45 μm). Due to difference in thermo-physical properties between the powders (Ti6Al4V, Cu, Mo, Ti), sintered materials were inhomogenous. Rescanning was employed but there was no significant change in the volume fraction of the unmelted Mo particles in the Ti15Mo alloy matrix. Due to the inherent high rate of heating and cooling simultaneously of the DMLS process, martensitic phase was found in the as-built Ti15Mo and Ti6Al4V–1at.%Cu samples. The martensitic properties reduce the ductility of the as-built samples significantly. Optimum process parameters were determined for both molybdenum-bearing titanium alloy (85% Ti and 15% Mo) and copper-bearing titanium alloy (Ti6Al4V and 1at.%Cu). Successful manufacturing of non-porous samples was done. In-situ alloying Ti6Al4V+1%Cu was successful and therefore there are promising ways to manufacture materials with embedded antibacterial properties. Incorporating copper into the bulk material by in-situ alloying would prevent the fall-off of antibacterial deposition coatings used in the past, since the material matrix (implant) would be antibacterial agent. The mechanical properties investigations with mini-samples presented ductility values below what was recommended for biomedical materials. It was concluded that finer Mo particles have to be chosen for in-situ alloying Ti15Mo for producing biomedical objects. Future work have to be done with elaboration of heat treatment procedures for higher ductility for structural bearing implants in a single step by the DMLS process. The results obtained developed new knowledge that is important for understanding the in situ alloying process during DMLS and new material production. The illustrated effects of process parameters on the properties of the synthesized material would be paramount for advanced implants with unique properties

Alkali activation of waste materials: sustainability and innovation in processing traditional ceramics

Environmental issues linked both to OPC production and waste management brought researchers to find new solutionsfor the production of more eco-efficient binders. In this frame, alkali-activated materials are receiving increasing attention. They are obtained by reaction of an alkali metal source, generally sodium or potassium, with amorphous calcium-aluminosilicate precursors. More recently, also the reuse of mining wastes was investigated due to the impressive production of sludges and muds which do not have practical applications and shall be landfilled. The aim of our researches was to investigate the use of semi-crystalline/high-crystalline by-products in the production of alkali-activated materials. Thus, two different powders were used: an alumino silicate mud, composed by quartz, feldspars, biotite and dolomite; and a carbonatic one, composed of calcite and small amounts of dolomite. Both powders were alkali-activated using a solution of NaOH and Na2SiO3. Pastes were produced mixing the activating solution and the powder in different liquid/solid ratiosandinvestigatingthe use of waste glass powder as further source of amorphous silica. Samples were oven-cured for 24h at 60-80 °C and then cured in different environments (dry, humid and immersed in water) for other 27 days before testing physical and mechanical properties. Very promising results were obtained in terms of compressive strength (about 30 MPa for the aluminosilicate sludge and up to 45 MPa for the carbonatic one), showing their potential as innovative building products

Tensile strength of pine and ash woods – experimental and numerical study

The mechanical properties define the behaviour of the timber under external loads, resulting directly from the timber anisotropic and heterogeneity characteristics. Depending upon the type of applied load the failure can be tensile, shear or torsion. When load enter the plastic regime, the stress-strain relationship passes through a maximum called the tensile strength. The tensile strength of wood being constant above the fibre saturation point, it increases with decreasing moisture content below the fibre saturation. This can be related to where the water is absorbed in the microstructure. Their study is of great interest allowing the rational use of different wood species for structural and building purposes