Processing and tribology of thermoplastic polyurethane particulate composite materials

The processing, mechanical and tribological properties of wax containing thermoplastic polyurethane–filler composites were studied for different weight ratios of graphite, TiO2, MoS2, and ZrO2 microparticles and SiO2 nanoparticles. The composites were compounded by extrusion and processed by compression molding. The rheological, thermal, and mechanical properties were measured, and the wear characteristics were tested with ball-on-plate reciprocating tribometer tests under fixed friction conditions and then observed by scanning electron microscopy. Correlations between the friction, wear, and mechanical properties were observed, and their mechanisms are discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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Tribological and tribocorrosion behavior of nickel sliding against oxide ceramics

Shoufan Cao, Junxiao Du, Stefano Mischler

Nickel is widely used as a coating material in electroplating because of its good corrosion and wear resistance even at high temperature. Tribocorrosion has been identified as one of the main degradation mechanisms of nickel. This study evaluated the tribocorrosion behavior of pure nickel in citrate buffer solution (pH 4.5) under controlled mechanical, chemical and electrochemical conditions as well as wear of pure nickel in dry condition sliding against alumina or zirconia balls, respectively. The results showed that the wear of nickel was higher in passive domain due to wear accelerated corrosion compared to that in the cathodic domain. Surprisingly, both alumina and zirconia were worn by nickel in tribocorrosion condition under passive potentials as well as in dry condition. However, in the cathodic domain, negligible wear was observed on the alumina and zirconia balls. The formation of mixed nickel and aluminum/zirconium oxides was proposed as the wear mechanism of alumina and zirconia.

ELSEVIER SCIENCE SA2019

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A comparative surface analysis of explanted hip joint prostheses made of different biomedical alloys

Angela Bermudez Castañeda, Adriana Esguerra Arce, Johanna Esguerra Arce, Stefano Mischler

The introduction of modular design in total hip arthroplasty has enabled the use of different materials in one single configuration and the adjustment of the prosthesis to the patient's body, and facilitated medical revisions. However, modularity leads to the presence of new interfaces created between pieces in contact, raising the issue of degradation. Tribocorrosion phenomena have been identified as the main degradation mechanism due to the mechanical, chemical, and electrochemical conditions acting on the materials. In addition, conditions inside the human body are unclear, regarding electrochemical settings and the interaction between the electrochemical and mechanical action. This work is focused on the degradation of monopolar hip joint implants made from biomedical alloys such as stainless steel, Ti, and CoCr alloys. Three cases are presented and analyzed in terms of the degradation level along the trunnion length. Surface analysis done on a titanium trunnion showed a significant ploughing on the distal part, compared to what was found for stainless steel and cobalt-chromium alloys, which can produce a stuck in this area. Meanwhile, in the proximal part, wear debris is found, which suggests more movement in the internal part. Although few debris particles were identified in CoCr trunnion, a large amount of material inside the contact was observed. This could be related to the ploughing generated in the distal thread pattern, which allowed the material to come inside and outside the contact.

IMPRENTA UNIV ANTIOQUIA2021

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Fracture toughness of weft-knitted fabric composites

Pierre-Etienne Bourban, Jan-Anders Månson, Ignaas Herman Johannes Verpoest

The mode I inter-laminar fracture toughness of advanced knitted textile composites was investigated. Two complex weft-knitted glass fabrics were selected for the study: a triple rib knit and a Milano knit were impregnated with a tough epoxy resin and tested using a double cantilever beam geometry. For both knitted composites, the influence of the growth direction was studied by investigating crack propagation in both the wale and course directions. The fracture toughness was quantified by determining the critical strain energy release rate (GIC) using the modified beam theory. The specimens had to be stiffened with layers of glass woven composites added on top and bottom of the beams. This was necessary in order to avoid plastic deformation of the beams and crack deviation out of the inter-laminar plane. The results clearly showed that knitted fabric composites have exceptional inter-laminar fracture toughness properties, namely, more than 7000 J/m2. The origin of the high GIC values, which are superior to woven or UD laminates, lies in the very complex fabric architecture. The threedimensional loop structure induces various energy consuming mechanisms, which do not occur in other composites. Toughening mechanisms such as crack branching, friction, yarn bridging and breakage were identified using scanning electron microscopy.

2002

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