In-Built Customised Mechanical Failure of 316L Components Fabricated Using Selective Laser Melting

The layer-by-layer building methodology used within the powder bed process of Selective Laser Melting facilitates control over the degree of melting achieved at every layer. This control can be used to manipulate levels of porosity within each layer, effecting resultant mechanical properties. If specifically controlled, it has the potential to enable customisation of mechanical properties or design of in-built locations of mechanical fracture through strategic void placement across a component, enabling accurate location specific predictions of mechanical failure for fail-safe applications. This investigation examined the process parameter effects on porosity formation and mechanical properties of 316L samples whilst maintaining a constant laser energy density without manipulation of sample geometry. In order to understand the effects of customisation on mechanical properties, samples were manufactured with in-built porosity of up to 3% spanning across ~1.7% of a samples’ cross-section using a specially developed set of “hybrid” processing parameters. Through strategic placement of porous sections within samples, exact fracture location could be predicted. When mechanically loaded, these customised samples exhibited only ~2% reduction in yield strength compared to samples processed using single set parameters. As expected, microscopic analysis revealed that mechanical performance was closely tied to porosity variations in samples, with little or no variation in microstructure observed through parameter variation. The results indicate that there is potential to use SLM for customising mechanical performance over the cross-section of a componen

Laser melting functionally graded composition of Waspaloy® and zirconia powders.

An approach for fabricating functionally graded specimens of supernickel alloy and ceramic compositions via Selective Laser Melting (SLM) is presented. The focus aimed at using the Functionally Graded Material (FGM) concept to gradually grade powdered compositions of Zirconia within a base material of Waspaloy®. A high power Nd:YAG laser was used to process the material compositions to a high density with gradual but discrete changes between layered compositions. The graded specimens initially consisted of 100% Waspaloy® with subsequent layers containing increased volume compositions of Zirconia (0-10%). Specimens were examined for porosity and microstructure. It was found that specimens contained an average porosity of 0.34% with a gradual change between layers without any major interface defects

Comparison of Dexamethasone Plus Metoclopramide, with Dexamethasone Alone in The Prevention of Postoperative Nausea and Vomiting in Patients Undergoing Elective Craniotomy

Objective:  To compare the efficacy of combination of dexamethasone plus metoclopramide with dexamethasone alone for control of postoperative nausea and vomiting in patients undergoing elective craniotomy. Study Design:  Double blinded randomized controlled clinical trial. Material and Methods:  One hundred ASA I – II patients listed for elective craniotomy were randomized to two groups of 50 patients each. Group A received dexamethasone 8 mg (2 ml) plus metoclopramide 10 mg (2 ml) pre-pared in two different syringes, and group B received dexamethasone 8 mg (2 ml) and normal saline (2 ml), pre-pared in two separate received syringes just before induction of anaesthesia. Anaesthesia was standardized. All episodes of Postoperative Nausea and Vomiting (PONV) during the first 24 hours postoperatively were evaluated at 3 time periods : 2, 4, and 24 hours. The presence or absence of nausea and vomiting (by simply yes or no) was assessed by research nurses aware of the study but blinded to the group to which the patient belonged.  Results:  The frequency of nausea and vomiting was clinically and statistically lower in dexamethasone plus metoclopramide group as compared to dexamethasone alone p-value 0.032 and 0.028 for nausea and vomiting respectively. Conclusion:  Combination of dexamethasone plus metoclopramide is more effective in preventing postoperative nausea and vomiting than dexamethasone alone when used for prophylaxis of Post-operative Nausea and Vomiting (PONV) before the induction of anaesthesia in patients undergoing elective craniotomy

Laser diode area melting for high speed additive manufacturing of metallic components

Additive manufacturing processes have been developed to a stage where they can now be routinely used to manufacture net-shape high-value components. Selective Laser Melting (SLM) comprises of either a single or multiple deflected high energy fibre laser source(s) to raster scan, melt and fuse layers of metallic powdered feedstock. However this deflected laser raster scanning methodology is high cost, energy inefficient and encounters significant limitations on output productivity due to the rate of feedstock melting. This work details the development of a new additive manufacturing process known as Diode Area Melting (DAM). This process utilises customised architectural arrays of low power laser diode emitters for high speed parallel processing of metallic feedstock. Individually addressable diode emitters are used to selectively melt feedstock from a pre-laid powder bed. The laser diodes operate at shorter laser wavelengths (808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient energy absorption for specific materials. The melting capabilities of the DAM process were tested for low melting point eutectic BiZn2.7 elemental powders and higher temperature pre-alloyed 17-4 stainless steel powder. The process was shown to be capable of fabricating controllable geometric features with evidence of complete melting and fusion between multiple powder layers

Effect of pre-emptive in situ parameter modification on residual stress distributions within selective laser-melted Ti6Al4V components

The effect of thermally induced residual stresses is not dynamically considered during a selective laser melting (SLM) build; instead, it processes using invariable parameters across the entire component’s cross-section. This lack of pre-emptive in situ parameter adjustment to reduce residual stresses during processing is a lost opportunity for the process with the potential to improve component mechanical properties. This investigation studied the residual stresses introduced during manufacturing of SLM Ti6Al4V benchmark components and adapted process parameters within a build (layer-to-layer specific modifications) to manage and redistribute stresses within these components. It was found that temporarily switching to an increased layer thickness during the build, directly below highly stressed regions within the component, redistributed stresses and reduced the overall stresses within the structure by 8.5% (within the 80–320-MPa residual stress range) compared to standard invariable SLM processing parameters. This work demonstrates the need for current SLM systems to focus on developing a more intelligent processing architecture with parameters that adapt on the fly during a build, in order to manage residual stresses within the built structure

Energy use analysis and simulation of MUN CSF Building using BEopt

This paper presents yearly energy use data of MUN Core Science Facility (CSF) building. The data shows that 12,876,967 kWhr of electricity and 38,432,359 kBTU of heat energy was used by the CSF building in 2022. Thermal model of CSF building is developed in Building Energy Optimization Tool (BEopt) using the collected building envelope parameters. Envelope parameters include R values of walls, windows, roofs, floors, and HVAC parameters such as total heating/cooling capacity, fan power, and outside air minimum ventilation. A comparison between actual energy consumption and consumption predicted by BEOpt is also included. The Simulink thermal model of CSF building is also developed to demonstrate that the building indoor temperature can follow varying set point temperature. Results show that the heat energy calculated by our BEopt model is 35,824,572 kBTU, which is only 6.8% less than the real CSF building heat energy use

Mutational landscape of head and neck squamous cell carcinomas in a South Asian population

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer type globally and contributes significantly to burden of disease in South Asia. In Pakistan, HNSCC is anmong the most commonly diagnosed cancer in males and females. The increasing regional burden of HNSCC along with a unique set of risk factors merited a deeper investigation of the disease at the genomic level. Whole exome sequencing of HNSCC samples and matched normal genomic DNA (n=7) was performed. Significant somatic single nucleotide variants (SNVs) were identified and pathway analysis performed to determine frequently affected signaling pathways. We identified significant, novel recurrent mutations in ASNS (asparagine synthetase) that may affect substrate binding, and variants in driver genes including TP53, PIK3CA, FGFR2, ARID2, MLL3, MYC and ALK. Using the IntOGen platform, we identified MAP kinase, cell cycle, actin cytoskeleton regulation, PI3K-Akt signaling and other pathways in cancer as affected in the samples. This data is the first of its kind from the Pakistani population. The results of this study can guide a better mechanistic understanding of HNSCC in the population, ultimately contributing new, rational therapeutic targets for the treatment of the disease

Dielectric properties of (CuO,CaO₂, and BaO)y/CuTl-1223 composites

We synthesized (CuO, CaO₂, and BaO)y/Cu₀,₅Tl₀,₅Ba₂Ca₂Cu₃O₁₀–δ (y = 0, 5%, 10%, 15%) composites by solid-state reaction and characterized by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties such as real and imag-inary part of dielectric constant, dielectric loss, and ac-conductivity of these composites are studied by capacitance and conductance measurement as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). The x-ray diffraction analysis reveals that the characteristic behavior of Cu₀,₅Tl₀,₅Ba₂Ca₂Cu₃O₁₀–δ supercon-ductor phase and its structure is nearly undisturbed by doping of nanoparticles. The scanning electron microsco-py images show the improvement in the intergranular links among the superconducting grains with increasing nanoparticles concentration. Microcracks are healed up with the inclusion of these nanoparticles and superconduct-ing volume fraction is also increased. The dielectric properties of these composites strongly depend upon the fre-quency and temperature. The zero resistivity critical temperature and dielectric properties show opposite trend with the addition of nanoparticles in Cu₀,₅Tl₀,₅Ba₂Ca₂Cu₃O₁₀–δ superconductor matrix

In situ alloying of elemental Al-Cu12 feedstock using selective laser melting

This investigation developed selective laser melting (SLM) processing parameters for the in situ fabrication of an Al-Cu12 alloy from pure elemental blends of aluminium and copper powders. Use of elevated pre-heat temperatures (400°C) created a coarser dendritic cell microstructure consisting of supersaturated Al-rich with a uniform Al 2 Cu phase granular microstructure compared to non-pre-heated samples. Al-Cu12 in situ samples achieved maximum tensile strength values comparable to that of sand cast pre-alloyed Al-Cu12. Processing at elevated pre-heat temperatures created components with higher ultimate tensile strength and ductility compared to standard room temperature-built samples due to it assisting a more complete melting of Al and Cu particles. Additionally pre-heating enabled an artificial age hardening, producing an equilibrium α + θ microstructure. The creation of an alloy in situ through the use of elemental powder blends represents a low-cost and flexible methodology for exploration of new SLM material compositions and potential candidate materials for semi-solid processing using SLM