Copper-based alloys are characterized by high thermal and electrical conductivity and are therefore well suited for demanding industrial applications. However, their processing by laser powder bed fusion (LPBF) poses significant challenges due to their high reflectance at 1064nm and high thermal conductivity. This work focuses on the newly implemented laser powder bed fusion alloy CuAg7Zr, compared with the well-established CuCr1Zr. Suitable process parameters for CuAg7Zr and CuCr1Zr are first identified and their effect on the resulting porosity is analysed. As part of a comprehensive parameter study, laser power, scan speed, and hatch spacing are varied to determine stable process windows for producing dense components. Influences of optical reflectance on the energy uptake for melting of these alloys is investigated. The findings aim to show processing of CuAg7Zr with LPBF and differences in reflectance behaviour, powder condition and process parameters in comparison to CuCr1Zr, providing valuable insights for optimizing the LPBF process for copper-based alloys.
This study aimed to culture the cyanobacterium Lyngbya confervoides (Lc) biomass for the preparation of crude aqueous and methanol extracts, and for a preliminary phycochemical investigation and molecular docking study. Biosynthesis of Lc-silver nanoparticles (Lc-AgNPs) was carried out, and nanoparticles were characterised using spectroscopic and microscopic techniques, followed by assessment of in vitro antibacterial efficacy against four multidrug-resistant (MDR) pathogens. FESEM confirmed the moderate nanoscale morphology (∼100 nm) of the Lc-AgNPs; XRD confirmed their crystalline nature; FTIR showed functional groups; and DLS observed a polydisperse size distribution. The antibacterial activity of Lc-AgNPs was evaluated against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Acinetobacter baumannii with inhibition zones of 12–16 mm and MIC concentrations of 25–50 μg/mL. MTT assay with THP-1 showed higher toxicity, with 50% reduction in cell number and an IC50 of about 20 μg/mL, compared to crude Lc (75 μg/mL) after 48 hours. Overall, the findings demonstrated the potential of Lc-AgNPs as an antibacterial agent and revealed the need for further pharmacological studies to optimise therapeutic doses.
In this work, we evaluate a comprehensive physics-based mean-field creep model with respect to its capability to describe creep behavior under varying stress conditions. Accurately accounting for stress changes is essential for extending models calibrated using standardized constant-stress creep tests to industrially relevant loading scenarios involving variable stresses. Since the microstructure and its temporal evolution are intrinsic components of the model, external parameters such as stress can be modified at every calculation timestep.Until recently, the lack of suitable experimental data has hindered a thorough validation of the model under variable-stress conditions. A high-quality experimental dataset has now been provided by Kobayashi et al., who investigated the creep behavior of the widely used martensitic 9–10% Cr steel P91 at 650 °C under both constant and variable stress conditions, while continuously recording the creep strain in situ.Comparison of the experimental and simulation results shows that creep deformation during stress variations can be reproduced accurately, provided that the maximum applied stress remains significantly below the yield stress at the respective temperature (<60%). Exceeding this threshold appears to induce a change in the governing creep mechanisms, which is not yet fully captured by the current model.
This work aims to enable the practical use of low-fidelity modelling of composite components under extreme load cases, by quantifying the uncertainty and error, contributing towards a framework enabling such models to be utilised in the design process. A key step towards useful and computationally cheap simulations is to accurately represent the behaviour of Carbon Fibre Reinforced Polymer (CFRP) structures which is challenging due to their heterogeneous and stochastic properties.In this study, full-field strain measurements obtained through Digital Image Correlation (DIC) are compared against a corresponding Finite Element Analysis (FEA) model of D5766 open hole tensile CFRP specimens. The experimental strain fields are overlaid, and statistical analysis is performed, before being mapped onto the finite element model allowing pointwise comparison of strain. Differences between the strain fields are spatially mapped, and the discrepancies quantified, identifying regions where the model and experiment diverged, evaluating model accuracy. A classical lamination theory (CLT) finite element model can capture 67% to 75% of the strain field within one standard deviation in the loading direction, with the error localised around the hole due to the overlaying of multiple optical measurement fields and laminate heterogeneity.
Vacancies show strong tendencies to segregate towards grain boundaries (GB), where they interact with them. In general, this process changes the GB structure and reduces the vacancy concentration in the bulk which is relevant for non-equilibrium vacancies found e.g. in highly deformed materials or after radiation damage. Due to structure relaxations the vacancy can, at least partially, be filled after segregation. To assess such structural modifications, density functional theory simulation of the segregation of vacancies towards GBs in tungsten are performed. The simulations are carried out for two different coverages of the GB cell. In addition to the segregation energies also changes of the dimensions of the simulation cells and the stress are evaluated. This allows not only to simulate concentrations, but also to calculate shape changes due to the annealing of vacancies. The results show overall strong segregation tendencies and a correlation between the segregation energies and structural changes are observed. The obtained results are used to interpret dilatometric experiments where length-changes between severely deformed and well-annealed samples are compared. We find that the segregation of vacancies cannot fully explain the observed length changes and are likely to originate from other relaxations mechanisms.
