The
current work focuses on the fabrication of high-molecular-weight
stereocomplex poly(lactic acid)/nanohydroxyapatite (sPLA/n-HAP)-based
bionanocomposite for three-dimensional (3D)-printed orthopedic implants
and high-temperature engineering applications. To achieve the same,
n-HAP is grafted with poly(d-lactic acid) (PDLA) via in situ
ring-opening polymerization of d-lactide, followed by blending
with poly(l-lactic acid) (PLLA), which yields sPLA/n-HAP
biocomposite with improved storage modulus even at temperatures higher
than 140 °C. X-ray diffraction and calorimetric analysis ensure
the presence of 100% stereocomplex crystallites of biocomposite along
with significant improvement in the melting temperature (∼227
°C). Noteworthy improvements in the mechanical and gas-barrier
properties of the developed biocomposites are achieved due to the
uniform dispersion of n-HAP (∼60 nm) confirmed by morphological
studies. An unusual improvement in elongation at break (∼130%
at 1 wt % HAP loading) makes this composite a toughened material.
However, the tensile strength is improved by ∼16%, whereas
oxygen permeability and water vapor transmission rate are found to
reduce by ∼48 and ∼34%, respectively. Interestingly,
the developed material is processed as monofilament, followed to 3D
printing to yield a middle phalanx bone as a representative example
of orthopedic implants. In vitro studies reveal that cell adhesion
and proliferation on the surface of the developed biocomposite support
its biocompatible nature. This signifies the possible future aspects
of the material in commercial biomedical and high-temperature engineering
applications.
The objective of the present work is to carry out analytical and finite element analysis for commonly used coating materials for micro-milling applications on high-speed steel substrate and evaluate the effects of different parameters. Four different coating materials were selected for micro-milling applications: titanium nitride (TiN), diamond-like carbon (DLC), aluminium titanium nitride (AlTiN) and titanium silicon nitride (TiSiN). A 3D finite element model of coating and substrate assembly was developed in Abaqus to find the Hertzian normal stress when subjected to normal load of 4 N, applied with the help of a rigid ball. The radius of the rigid ball was 200 µm. For all the coating materials, the length was 3 mm, the width was 1 mm, and the thickness was 3 µm. For the high-speed steel substrate, the length was 3 mm, the width was 1 mm, and the thickness was 50 µm. Along the length and width, coating and substrate both were divided into 26 equal parts. The deformation behaviour of all the coating materials was considered as linear–elastic and that of the substrate was characterized as elastic–plastic. The maximum normal stress developed in the FEA model was 12,109 MPa. The variation of the FEA result from the analytical result (i.e., 12,435.97 MPa is 2.63%) which is acceptable. This confirms that the FEA model of coating–substrate assembly is acceptable. The results shows that the TiSiN coating shows least plastic equivalent strain in the substrate, which serves the purpose of protecting the substrate from plastic deformation and the TiSiN of 3 micron thickness is the most optimum coating thickness for micro-milling applications.
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