Materials Plus

Bayesian Uncertainty Update to a Model of Flexural Strength of α-SiC

Eric A. Walker — 2024-03-22

This article demonstrates a statistical method to update the uncertainty in the flexural strength of silicon carbide, α-SiC. The previously reported uncertainty for the flexural strength of α-SiC was a constant ±15%. However, this uncertainty should be adjusted as more data becomes available. A Bayesian approach is proposed to rapidly and precisely update the uncertainty. To validate the method, five scenarios are demonstrated. The first scenario assumes the experimental data is distributed as the model predicts. The second and third scenarios have the model underestimating and overestimating flexural strength, respectively. The fourth and fifth scenarios use data from a thermo-mechanical fracture model. The thermo-mechanical fracture model introduces a change in the temperature transition of flexural strength. The uncertainty decreased from 15% to a range between 8.3% and 13.4%. Two parameters are inferred in the fourth scenario while five are inferred in the fifth scenario. Inferring five parameters leads to more consistent uncertainty across temperature.

Investigation of Structural, Dielectric, Magnetic and Impedance Spectroscopy of MgO/CuFe2O4 Nanocomposites

Asif Ilyas — 2024-03-26

This study investigates the properties of (MgO)_x/(CuFe₂O₄)_1-x x= 10–50 wt.% nanocomposites (NCPs) prepared by physical mixing of both materials. The crystal structure, phase identification and morphology were analyzed by x-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The investigation revealed the formation of required phases which are in nanometer dimension (22–54 nm) computed by Debye-Sherrer’s formula. Both the real and imaginary parts of dielectric constant (ε^/& ε^//), a.c. conductivity (σ_ac), and impedance were measured in the frequency range of 1kHz to 2MHz by LCR meter. The ε^/ and ε^//revealed a decreasing trend with frequency, while MgO weight fractions in NCPs enhance the permittivity values. The real and imaginary parts of impedance (Z^/& Z^//) demonstrate a decreasing trend with frequency which is ascribed to increase in σ_ac. The complex impedance spectroscopy (CIS) analysis shows semicircular arcs at higher frequency, which are due to electrical transport properties of conducting grains. The effect of MgO contents on magnetic properties were analyzed by measuring M-H loops at room temperature through vibrating sample magnetometer (VSM). Both the saturation magnetization (M_s) and coercivity (H_c) values show a decreasing profile with MgO fractions, which are due to increase in nonmagnetic contents and decrease in surface anisotropy respectively.

Characterization of Ti-6Al-4V Bar for Aerospace Fastener Pin Axial Forging

Richard Turner — 2024-03-20

Ti-6Al-4V warm forged fasteners are a critical part of the aerospace industry, as they are used in vast quantities for mechanical joining of components for the fuselage, wing-skin and aero-engine. These components are produced in vast quantities at rapid production rates through multi-blow axial forging However the rate that they are manufactured means that manufacturers rely upon periodic part conformance testing to understand if the part is within tolerance or if any undesirable manufacturing defects such as cracks or underfilling are present. Thus, a right-first-time manufacturing approach is essential to minimize non-conformant scrap. An analysis of the Ti-6Al-4V supplied raw material for axial forging, in a variety of different bar diameter sizes and from different industrial suppliers, was conducted. This was to attempt to understand whether material property variation or operator variation was the root cause for some material behaving differently during the manufacture route. Experimental testing was performed through microstructure characterization and mechanical testing methods. The volume fraction of the β-phase was noted to be marginally higher in material with good forgeability. The hardness of the inner core of the bar appears to be a critical material property for the Ti-6Al4V bar, with an overly hard bar-core hindering forgeability of the bar. This is believed to be due to the hotter central region malleability being key for forgeability. Micro-void porosity was also noted which could lead to stress concentration locations, or crack initiation, and as such is a deleterious property for forgeability. The experienced forgeability of the Ti-6Al-4V bars have been demonstrated to be sensitive to rather small variation in measured microstructure and mechanical property. It is believed that cumulative impacts of small differences, 1% variation in α-phase volume fraction, small variations in elongation to failure, 1% variation in elastic modulus and microhardness profile variation at the center of the bar of less than 10 HV0.3, can combine to significantly impact the forgeability of Ti-6Al-4V bar.