Fatigue under variable amplitude loading is currently assessed by applying the Palmgren-Miner linear rule in structural standards. However, this linear rule is inadequate in natural scenarios with coupled fatigue and corrosion effects, because the coupled corrosion-fatigue process synergistically accelerates deterioration. In view of the absence of specifications for the coupled fatigue-corrosion effect in structural standards, the objective here is to develop a simple and practical correction factor that will ensure a conservative linear summation of damage, taking the corrosion-fatigue effect into account. The theoretical consistency and the feasibility of the new adapted rule are tested in a case study.
Fatigue under variable amplitude loading is currently assessed with the Palmgren-Miner rule in structural standards, ignoring the order of loading, which would require non-linear or mixed rules, especially for the random loading sequences applied to certain structures. Therefore, the goal is to develop a practical and simple correction factor ensuring the linear summation of damage is conservative, so as to take the sequence effect into account in random loading from natural sources. The theoretical consistency of this approach is demonstrated and a case study is developed to test the feasibility of the new rule and its simplicity.
Thermoplastic polymer–filler composites are excellent materials
for bone tissue engineering (TE) scaffolds, combining the functionality
of fillers with suitable load-bearing ability, biodegradability, and
additive manufacturing (AM) compatibility of the polymer. Two key
determinants of their utility are their rheological behavior in the
molten state, determining AM processability and their mechanical load-bearing
properties. We report here the characterization of both these physical
properties for four bone TE relevant composite formulations with poly(ethylene
oxide terephthalate)/poly(butylene terephthalate (PEOT/PBT) as a base
polymer, which is often used to fabricate TE scaffolds. The fillers
used were reduced graphene oxide (rGO), hydroxyapatite (HA), gentamicin
intercalated in zirconium phosphate (ZrP-GTM) and ciprofloxacin intercalated
in MgAl layered double hydroxide (MgAl-CFX). The rheological assessment
showed that generally the viscous behavior dominated the elastic behavior
(
G
″ >
G
′) for the
studied composites, at empirically determined extrusion temperatures.
Coupled rheological–thermal characterization of ZrP-GTM and
HA composites showed that the fillers increased the solidification
temperatures of the polymer melts during cooling. Both these findings
have implications for the required extrusion temperatures and bonding
between layers. Mechanical tests showed that the fillers generally
not only made the polymer stiffer but more brittle in proportion to
the filler fractions. Furthermore, the elastic moduli of scaffolds
did not directly correlate with the corresponding bulk material properties,
implying composite-specific AM processing effects on the mechanical
properties. Finally, we show computational models to predict multimaterial
scaffold elastic moduli using measured single material scaffold and
bulk moduli. The reported characterizations are essential for assessing
the AM processability and ultimately the suitability of the manufactured
scaffolds for the envisioned bone regeneration application.
There is still a considerable gap in the definition of the weldability of Duplex Stainless Steel (DSS). A lack of clarity that is explained by the standard specification of the maximum content of equivalent carbon that defines a “weldable” steel coupled with the fact that the alloying elements of DSS exceed this defined limit of weldability. In this paper, welding quality in an inert environment and in presence of chlorides is analyzed with the aim of defining optimum welding conditions of 2001, 2304, and 2205 DSS. The same procedure is followed for a hybrid weld between DSS 2205 and a low carbon mild steel, S275JR. As main output, this study defined the optimal welding conditions with tungsten inert gas without filler for each type of DSS weld that showed excellent anti-corrosion performance, with the exception of the DSS 2205-S275JR weld where widespread corrosion was observed. Additionally, this study established a relationship between the thermal input during welding and the content of alloying elements in defect-free joints. Furthermore, it demonstrated that an increase in ferrite content did not lead to a worse corrosion resistance, as expected after passivation.
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