Effect of Conditioning on PU Foam Matrix Materials Properties

This article deals with the characterization of the thermal-induced aging of soft polyurethane (PU) foams. There are studied thermal and mechanical properties by means of thermal analysis, tensile, compression and dynamic mechanical vibration testing. It was found in this study, that the increasing relative humidity of the surrounding atmosphere leads to the initiation of the degradation processes. This is reflected in the observed decreased mechanical stiffness. It is attributed to the plasticization of the PU foams wall material. It is in agreement with the observed increase of the permanent deformation accompanied simultaneously with the decrease of Young’s modulus of elasticity. The latter phenomenon is studied by the novel non-destructive forced oscillations vibration-damping testing, which is confirmed by observed lower mechanical stiffness thus indicating the loss of the elasticity induced by samples conditioning. In parallel, observed decreasing of the matrix hardness is confirming the loss of elastic mechanical performance as well. The effect of conditioning leads to the significant loss of the PU foam’s thermal stability.

Easily Sinterable Low-Alloy Steel Powders for P/M Diamond Tools

The work presents the design and fabrication procedures used to manufacture inexpensive iron-base powders employed as a matrix in diamond-impregnated tool components. Three newly developed low alloy steel powders, containing from 94.4 to 99.4 wt.% Fe, have been formulated with the assistance of ThermoCalc software and produced by means of a proprietary process patented by AGH-UST. It has been shown that the powders are readily pressureless sintered to a closed porosity condition (>95% theoretical density) at a temperature range between 840 and 950 °C. All as-consolidated materials achieve the desired tool matrix hardness of more than 200 HV. One of the experimental powders has been designed to partly melt within the sintering window. This is particularly important in fabrication of wire saw beads by the conventional press and sinter route because sintering of a diamond-impregnated ring and its further brazing to a tubular steel holder can be combined into one operation.

A 3D Bioprinted Pseudo-Bone Drug Delivery Scaffold for Bone Tissue Engineering

A 3D bioprinted pseudo-bone drug delivery scaffold was fabricated to display matrix strength, matrix resilience, as well as porous morphology of healthy human bone. Computer-aided design (CAD) software was employed for developing the 3D bioprinted scaffold. Further optimization of the scaffold was undertaken using MATLAB® software and artificial neural networks (ANN). Polymers employed for formulating the 3D scaffold comprised of polypropylene fumarate (PPF), free radical polymerized polyethylene glycol- polycaprolactone (PEG-PCL-PEG), and pluronic (PF127). Simvastatin was incorporated into the 3D bioprinted scaffolds to further promote bone healing and repair properties. The 3D bioprinted scaffold was characterized for its chemical, morphological, mechanical, and in vitro release kinetics for evaluation of its behavior for application as an implantable scaffold at the site of bone fracture. The ANN-optimized 3D bioprinted scaffold displayed significant properties as a controlled release platform, demonstrating drug release over 20 days. The 3D bioprinted scaffold further displayed formation as a pseudo-bone matrix, using a human clavicle bone model, induced with a butterfly fracture. The strength of the pseudo-bone matrix, evaluated for its matrix hardness (MH) and matrix resilience (MR), was evaluated to be as strong as original bone, having a 99% MH and 98% MR property, to healthy human clavicle bones.

Erosion in a Melt-Infiltrated SiC/SiC Ceramic Matrix Composite

Erosion phenomenon of ceramic matrix composites (CMCs), attributed to their unique architectural configurations, is markedly different from conventional monolithic ceramic counterparts. Prior to further integration of CMCs into hot-section components of aeroengines subject to erosive environments, their erosion behavior needs to be characterized, analyzed, and formulated. The erosion behavior of a 2D woven melt-infiltrated (MI) SiC/SiC CMC was assessed in this work as a function of variables such as particle velocity and size. The erosion damage was characterized using appropriate analytical tools such as optical and scanning electron microscopy (SEM). A phenomenological erosion model was developed for SiC/SiC CMC material systems with respect to the kinetic energy of impacting particles in conjunction with nominal density, matrix hardness, and elastic modulus of the SiC/SiC CMCs. The model was in reasonable agreement with the experimental data.

Examination of Heat Treatment on the Microstructure and Wear of Tool Steels

The microstructure of the investigated X153CrMoV12 grade tool steel in delivered condition consisted of spheroidal matrix and primary carbides. The primary carbides were not dissolved under austenitisation time on either 1030°C or 1070°C. The microstructure and abrasion resistance of the steel changed due to quenching from different austenitisation temperatures. After conventional quenching from the higher austenitising temperature, there is more residual austenite in the steel than at quenching from the lower austenitisation temperature, which decreased the wear resistance. As a result of quenching from 1070°C followed by a multiple tempering process around 500 to 540°C, the retained austenite content is reduced and finely dispersed carbides are precipitated in the matrix, resulting in a higher matrix hardness and an increased wear resistance. After cryogenic treatment, the residual austenite content decreases compared to the conventional process, which leads to an increase in hardness and wear resistance.

Erosion in an MI SiC/SiC Ceramic Matrix Composite (CMC)

Erosion phenomenon of ceramic matrix composites (CMCs), attributed to their unique architectural configurations, is markedly different from conventional monolithic ceramic counterparts. Prior to further integration of CMCs into hot-section components of aeroengines subject to erosive environments, their erosion behavior needs to be characterized, analyzed, and formulated. The erosion behavior of a 2-D woven melt-infiltrated (MI) SiC/SiC CMC was assessed in this work as a function of variables such as particle velocity and size. The erosion damage was characterized using appropriate analytical tools such as optical and scanning electron microscopy (SEM). A phenomenological erosion model was developed for SiC/SiC CMC material systems with respect to kinetic energy of impacting particles in conjunction with nominal density, matrix hardness and elastic modulus of the SiC/SiC CMCs. The model was in reasonable agreement with the experimental data.