Truncated Octahedron Research Articles

Two- and Three-Dimensional Ag-Au Nanoalloying: Heterogeneous Building Blocks Enhancing Near-Field Focusing.

In this study, we report a strategy for fabricating binary surface-enhanced Raman scattering (SERS) substrates composed of plasmonic Pt@Ag and Pt@Au truncated-octahedral (TOh) dual-rim nanoframes (DNFs) functioning as a "nanoalloy." Pt TOh frameworks act as a scaffold to develop nanoarchitectures with surface decoration using plasmonically active materials (i.e., Au or Ag), resulting in identical sizes and shapes for the two distinct plasmonic elements, facilitating the fabrication of a "nanoalloy" blend of two shape-complex building blocks. The structural complexity from the dual-rim on (111) facets, combined with the mirror charge effect (i.e., enhanced polarization between Ag and Au) at the interface of heterogeneous components, significantly amplifies SERS activity. We carefully investigated near-field focusing of binary SERS substrates through single-particle and bulk SERS measurements corroborated by finite element method (FEM) calculations. Crucially, we developed free-standing superpowders (SPs) in which each heterogeneous building block formed micron-sized supercrystals with adjustable component ratios. These plasmonic SPs were applied to contaminated areas for analyte detection, demonstrating their potential for practical SERS applications.

The influence of toe geometry on toe armour stability for conventional rubble mound breakwaters

Rubble mound breakwaters have toe structures that provide support to the armour layer and prevent damage to the structure from scouring. In this way, toe failure may be regarded as one of the primary failure modes of rubble mound breakwaters. Several formulae have been proposed for toe stability with conflicting results owing to the neglect of factors such as storm duration and armour layer slope. In the present study, a statically stable rubble mound with rock armoured toe was tested under irregular waves. The effects of wave height, wave period, armour layer slope, water height in front of the structure, water height above the toe, and toe width on the hydraulic stability of a toe structure are investigated. Toe width was found to be ineffective on toe stability, while the relative depth was found as an effective parameter for the toe stability. Greater toe damage was observed by increasing wave height and storm duration. The results highlighted the necessity for a new stability number involving the type of wave breaker on the armour slope with a critical Iribarren value of 4.1. Based on the data from the present study and the findings of another study, new formulae have been developed for estimating toe damage in rubble mound breakwaters. Evaluating the proposed formula using other researchers’ data and formulae highlighted its strengths.

Evaluation of the roughness of lattice structures of AISI 316 stainless steel produced by laser powder bed fusion

The present work evaluates the surface roughness of lattice structures produced in AISI 316 stainless steel, with laser powder bed fusion (LPBF). To this end, five lattice types were evaluated, namely cubic (C), truncated octahedron (TO), truncated cubic (TC), rhombicuboctahedron (RCO) and rhombitruncated cuboctahedron (RTCO) to determine the average roughness Sa by profilometry. For comparison, the surface roughness of a bulk specimen was also measured. The average roughness was Sa=7.3 mm for the bulk specimen, for the C and TC arrangements it was around 11 mm, while for configurations RCO, RTCO and TO it was in the range 18-22 mm, meaning that surface roughness increases for more complex structures. Values of Sa around 10-25 mm are reported in the literature for parts fabricated by LPBF for medical implants. If complex lattice arrangements are required, a study of the printing parameters is relevant, to achieve scaffolds with improved biomechanical performance.

The chemical ordering and local pressure dependence for truncated octahedron PdAuRh nanoalloys

The optimal chemical ordering configurations of 38-atom trimetallic Pd n Au(32−n)Rh6 nanoalloys with truncated octahedron (TO) geometry were determined through Monte Carlo Basin-Hopping algorithm employing the Gupta potential, followed by local relaxations. Variations in mixing energy were assessed to compare relative stability, revealing the lowest excess energy at Pd16Au16Rh6 composition at the Gupta level. Furthermore, a comprehensive analysis of local atomic pressure was conducted, exploring the factors influencing these pressures.

Evaluation of Lattice Structures for Medical Implants: A Study on the Mechanical Properties of Various Unit Cell Types

Lattice structures are a prime candidate for applications in the medical implant industry due to their versatile mechanical behaviour, which can be tailored to meet specific patient needs and reduce stress shielding, while enabling the natural flow of body fluids. In this work, the mechanical properties of metallic lattices made of five different unit cell types, Cubic (C), Truncated Octahedron (TO), Truncated Cubic (TC), Rhombicuboctahedron (RCO), and Rhombitruncated Cuboctahedron (RTCO), were evaluated under uniaxial compression at three different relative densities, 5%, 15%, and 45%. The evaluation was experimental, and it was compared with previous and new finite element simulations. Specimens for the experimental tests were fabricated in stainless steel 316L by laser powder bed fusion, and stress–strain curves were obtained for the different lattices. The combination of the test results with a critical interpretation of the deformation mechanisms allowed us to confirm that two unit cell types, TO and RTCO, are stable for the whole range of relative densities evaluated. The other three unit cells exhibit more unpredictable behaviour, either due to manufacturing defects or limitations, or because their unstable compression behaviour leads to bucking. For these reasons, TO and RTCO unit cell types are mechanically more adequate for applications in the medical implant industry.

Compression properties of cellular iron lattice structures used to mimic bone characteristics

Recently, cellular materials made by the repetition of unit cells, that is, iron lattices have become appealing to mimic the structure of bone. The aim of the study is to choose the most adequate lattice structures, which have the compressive mechanical properties closer to the ones of bone, in the perspective of their use as temporary implants. Five types of unit cells were selected, such as, cubic (C), truncated octahedron (TO), truncated cubic (TC), rhombicuboctahedron (RCO), and rhombitrucated cuboctahedron (RTCO). The mechanical properties were assessed by numerical simulations with a finite-element analysis. The size effect was studied with the comparison of results among samples with different numbers of unit cells. Simulations covered a wide range of relative densities. Graded dense-in and dense-out configurations were constructed with lattices of types RTCO and TO, being the unit cells, themselves graded. Lattice structures RTCO and TO were found to be stable at every relative density studied, while C, TC and RCO lattices are unstable at low densities. The evaluation of size effects was not conclusive, which could be biased by other factors. The Young's modulus of RTCO and TO lattices enable to reproduce the properties of both trabecular and cortical bone, with an appropriate choice of the relative density. To mimic trabecular bone, only RTCO and TO structures with low relative densities, can be used, while arrangements of C, TC and RCO cells can only replicate the properties of cortical bone. Graded cells may have the same properties as non-graded with lower density.

Structural Stability Study of Nanocluster PD-based Catalyst

The rapidly growing population in the world demands an increase in the support of human life by providing massive production of food and medicine. As a result, the catalyst used in the production of the material plays a key role leading to intensive research. Synthesis of nanomaterials is becoming an important way to discover new catalysts by changing sizes and combining two or more metals on the nanoscale. Pd-based catalysts are well-known catalysts such as Pd-Pt, Pd-H, and Pd-Au for many chemical reactions such as the direct synthesis of hydrogen peroxide. Therefore, the provision of nanocluster bimetallic catalysts offers more benefits such as the rearrangement of surfaces to suit characteristics and lower material costs. However, the stability of the catalyst challenges researchers beyond reactivity and selectivity. In this paper, we predict the structural stability of Pd-based catalysts using a density functional theory approach. We use the 38-atom model in the M6@Pd32 core shell, where M is Hg, Pt, Au, Cu, Ni, Cu, Zn, Ag, Pd, and Cd, Pt. We prepared and investigated a series of structures such as truncated octahedral (TO) and polyhedral (PH) by calculating the excess energy. Based on our calculations and placing the monometallic Pd38 nanocluster as a reference, the TO structure is more stable than that of PH. The Zn6@Pd32 system showed the most stable followed by Cd6@Pd32 and Hg6@Pd32 was the worst.
 Keywords: structural stability, core-shell, nanocluster, Pd-based catalyst

Life-cycle Cost assessment of Post Weld treatments: Effect of local weld geometries

The fatigue life of welded structures is dependent on the local geometry and imperfections of the welds. Therefore, optimizing the manufacturing processes to improve the local weld geometry and remove possible imperfections can considerably affect the fatigue life of the structure. Post-weld treatments such as burr grinding, and High Frequency Mechanical Impact (HFMI) treatment are commonly used techniques to extend the fatigue life of a weld by modifying the local weld toe geometry. However, employing additional manufacturing processes can have an adverse effect on the Life-cycle cost of a welded structure by increasing production costs. On the other hand, extending the fatigue life of a structure can result in lower maintenance and replacement costs. Therefore, a thorough yet predictive life-cycle cost assessment is required to assess the viability of such treatments and design economically efficient weld structures.This study assesses the life-cycle cost of welded joints. The fatigue life of the weld in this study is analyzed using the effective Notch Stress method (NS). Furthermore, the weld is post-treated with an automated HFMI treatment to prolong its fatigue life. Moreover, the effect of weld quality on the production cost is analyzed. The results show that every phase of the weld's life-cycle has a significant contribution to the life-cycle cost with the use-phase being the more dominant. The results also depict the impact of the changes in weld quality in the overall life-cycle cost.

Approach for the probabilistic fatigue assessment of welded joints based on the local geometry of the weld seam

AbstractWelded joints show large variation of the weld toe geometry along the weld seam, which is one important reason for the comparably large scatter in fatigue life. Therefore, it is crucial to take the local geometry at the weld toe into account, to reduce the conservatism in fatigue assessment of welded joints. This study is based on the IBESS procedure for the calculation of the fatigue strength, whereby the evaluation of local geometrical parameters is carried out by means of 3D surface scans. The approach is validated against 26 fatigue test series. The fatigue life is in general overpredicted, whereas good agreement is achieved for high stress ratio ( ). A sensitivity analysis conducted with IBESS shows that weld toe radii ρ < 2 mm and flank angle α < 30° have a significant influence on the calculated fatigue strength. In contrast to this, no strong correlation between and the fatigue strength was determined experimentally in this study.

Local MIL-HDBK-5D equivalent stress based fatigue assessment of the gusset welded joint improved by Portable Pneumatic Needle-Peening treatment

This study proposes a local MIL-HDBK-5D equivalent stress (LMES) based approach to investigate the fatigue lives of Portable Pneumatic Needle-Peening (PPP) treated gusset welded joints made of SM490. The LMES range is identified by the elastic–plastic local stress cycle simulated by the muti-process finite element analysis, including welding, PPP, and fatigue loading processes. Using the LMES, Fatigue test results of as-welded (AW) and PPP treated joints are consolidated into a single S-N curve. This LMES based S-N curve can be used for evaluating fatigue life comprising the influence of residual stress, cyclic stress relaxation, and local weld toe geometry for welded joints studied in this work.

Mechanical properties of additively manufactured Al2O3 ceramic plate-lattice structures: Experiments & Simulations

Ceramic lattice structures (CLSs) have been widely studied and applied because of their excellent properties of ceramics. Among them, the ceramic plate-lattice structures (CPLSs) are new lattice structures, which have better mechanical properties than other CLSs. In this study, we designed and additively manufactured Al2O3 ceramic truncated octahedron (TO) plate-lattice structures with different relative densities to explore their quasi-static and dynamic compressive behaviors in detail. At the same time, to further study the influence of plates on CPLSs, we added two other structural configurations, truncated octahedral plates with plates added only in the loading direction (TOH) and truncated octahedral plates with plates added in all directions (TOA), as a comparative study. It was demonstrated that the relative density (ρ¯) had a significant effect on the quasi-static and dynamic mechanical properties of CPLSs. However, the study of different structures with the same relative density showed that the TOH had the best performance in Young's modulus and compressive strength, followed by TOA and TO. This also confirmed that the plate had a significant effect on CPLSs. Furthermore, the mechanical properties of CPLSs were surprisingly improved under dynamic conditions compared to static conditions, which indicated that CPLSs could effectively cope with extreme environments. In addition, it was revealed by experiment and simulation that the compression destruction and failure of CPLSs, which was helpful to analyze the damage mechanism. These findings would provide valuable guidance for the optimization design and additively manufactured of CPLSs.

Multi-Layered PtAu Nanoframes and Their Light-Enhanced Electrocatalytic Activity via Plasmonic Hot Spots.

Here, the rational design of complex PtAu double nanoframes (DNFs) for plasmon-enhanced electrocatalytic activity toward the methanol oxidation reaction (MOR) is reported. The synthetic strategy for the DNFs consists of on-demand multiple synthetic chemical toolkits, including well-faceted Au growth, rim-on selective Pt deposition, and selective Au etching steps. DNFs are synthesized by utilizing Au truncated octahedrons (TOh) as a starting template. The outer octahedral (Oh) nanoframes (NFs) nest the inner TOh NFs, eventually forming DNFs with a tunable intra-nanogap distance. Residual Au adatoms on Pt skeletons act as light entrappers and produce plasmonic hot spots between inner and outer frames through localized surface plasmon resonance (LSPR) coupling, which promotes enhanced electrocatalytic activity for the MOR. Importantly, the correlation between the gap-induced hot carriers and electrocatalytic activity is evaluated. The highest catalytic activity is achieved when the gap is the narrowest. To further harness their light-trapping capability, hierarchically structured triple NFs (TNFs) are synthesized, wherein three NFs are entangled in a single entity with a high density of hot regions, exhibiting superior electrocatalytic activity toward the MOR with a sixfold larger current density under light irradiation compared to the dark conditions.

Computational evaluation of the compressive properties of different lattice geometries to be used as temporary implants

Additive manufactured iron lattice structures present unprecedented capabilities for fulfilling the role of bone temporary implants. Iron structures are biodegradable, eliminating the need for removal surgeries, and can help reduce stress shielding significantly by mimicking the properties of bone locally. Although several types of lattice structures have been proposed in the literature, there is the need to evaluate the effect of the relative density on their mechanical properties, in order to resemble bone properties.In the present work, the effects of relative density on the mechanical behavior and in particular, in elastic mechanical properties, were evaluated with finite element simulations, for several types of cells.Lattices, i.e, arrays of unit cells, were designed for 5% increments of relative density, from 5% up to the maximum allowed for each specific cell, for 5 different cell types, creating a total of 63 lattice structures. Finite element models were created for each geometry simulating a compression test, obtaining stress-strain curves and thus the Young's modulus. The material data introduced in the finite element analysis was obtained experimentally from a compression test on bulk iron.The results suggest that all lattice structures evaluated were stable for high density. Cubic (C), truncated cubic (TC), and rhombicuboctahedron (RCO) cells presented instability at low densities while truncated octahedron (TO) and rhombitruncated cuboctahedron (RTCO) cells remained stable at low densities, reaching the value of the Young's modulus of very low-density trabecular bone.Two cell types, RTCO and TO, showed the ability to reproduce the whole range of mechanical properties of bone in a stable manner. The other cell types experienced instability phenomena, like buckling, at low densities.

A two-step optimization approach for structures investigation of Pd-Ir bimetallic nanoclusters

The structures of nanoalloys are crucial for understanding their catalytic performance because the stable structures can affect the activity and selectivity of nanocatalysts. Therefore, investigating the stable structures of nanoalloys is important to understand their catalytic activities. In this article, a two-step optimization approach by combining a basin hoping genetic algorithm (BHGA) and DFT calculation is employed to investigate the structural stability of Pd-Ir alloy nanoclusters. Different compositions (Pd and Ir atoms proportion) and different initial configurations of 38-atom Pd-Ir alloys are considered. The combination of BHGA and DFT method can effectively find the stable structures of truncated octahedral (TO) configurations for 38-atom Pd-Ir alloys with high accuracy and low time complexity. Furthermore, the formation energy and bond energy of Pd-Ir clusters are calculated and analyzed, the results show the bond strength follows Pd-Pd > Pd-Ir > Ir-Ir. The most stable configuration is Pd6Ir32 with all the core sites are occupied by Pd, which shows better electrochemical performance.

The local atomic pressures in 79 atom Pd-Ag-Pt truncated octahedron structure

The best chemical ordering structures of 79-atom trimetallic PdnAg(60−n)Pt19 nanoalloys with truncated octahedron (TO) geometry were optimized and local relaxations were performed by using Monte Carlo Basin-Hopping algorithm within Gupta potential. The mixing energy variations were calculated to compare the relative stability. The lowest excess energy value was obtained at the compositions of Pd25Ag35Pt19 at Gupta level. In addition, a detailed investigation of local atomic pressure has been carried out. The factors affecting local atomic pressures were discussed.

Fatigue strength of laser-dressed non-load-carrying fillet weld joints made of ultra-high-strength steel

Laser dressing or remelting is one of the post-weld treatment methods that is based on the modification of the local weld toe geometry, and generally, it is similar to TIG or plasma dressing. However, the laser dressing is not covered by common fatigue design guidelines and recommendations of welded structures at the moment. In this research, the effect of laser dressing on the fatigue performance of non-load-carrying fillet-welded cruciform joints made of direct quenched S960 grade steel was studied by means of experimental fatigue testing and geometry and residual stress measurements together with finite element analyses and different statistical calculation processes, such as nominal, structural and effective notch stress methods. In addition, the 4R method was also employed and its applicability for fatigue assessment of laser-dressed weld joints in question was investigated. The experimental results showed the enhancement of the fatigue strength for laser-dressed fillet weld joints compared to as-welded condition and the recommended FAT class for similar TIG dressing case was exceeded. However, the fatigue strength improvement of laser dressing was less compared to the corresponding TIG-dressed joints when applied stress ratio was low. In proportion, the disparity between the improvement effect of laser and TIG dressing methods was reduced with higher applied stress ratio. This can be explained by different residual stress state in the critical weld toe treatment area of laser- and TIG-dressed joints that can be taken into account when using the 4R fatigue assessment method.

Ir nanocluster shape effects on melting, surface energy and scaling behavior of self-diffusion coefficient near melting temperature

Shape effect on Metallic Nano particles has many applications in technology, engineering and industry. Molecular dynamic simulations have been performed to investigate size and shape effects of Iridium nanocluster on its surface energy (Esur) and self-diffusion coefficient (D) as a function of temperature (T). Truncated octahedron (TO), octahedron (Oh), cubic (C), and face center cubic (FCC) of Iridium nanocluster were studied in this survey. At temperatures lower than 1000 K, Esur order is as follows: TO > C > Oh > FCC while at temperatures higher than 1000 K it has a different order as TO > Oh > C > FCC. Self-diffusion coefficient increases versus temperatures as expected, but results show that it is roughly the same for all systems at T < 1800 K and T greater than 2500. At temperature range T (1800, 2500), self-diffusion coefficient order is as follows: TO ≈ Oh ≈ C < FCC. TO≅Oh≅C<FCCInterestingly, DFCC is smaller than D for other shapes of Iridium nanocluster. Self-diffusion coefficient as a function of nanocluster size was calculated with molecular dynamics simulation. It is shown there is a peak for D at N = number of particles = 700 which corresponds to surface effect. MD results show that FCC has more solid like long-range interaction, but others have more liquid like order.

Shape Changes in AuPd Alloy Nanoparticles Controlled by Anisotropic Surface Stress Relaxation.

The shape of AuPd nanoparticles is engineered by surface stress relaxation, achieved by varying the Au content in nanoparticles of Pd-rich compositions. AuPd nanoparticles are grown in the gas phase for several compositions and growth conditions. Their structure is atomically resolved by HRTEM/STEM and EDX. In pure Pd distributions the dominant structures are FCC truncated octahedra (TO), while increasing the Au content there is a transition to icosahedral (Ih) structures in which Au atoms are preferentially placed at the nanoparticle surface. The transition is sharper for growth conditions closer to equilibrium. The physical origin of the transition is determined with the aid of computer simulations. Global optimization searches and free energy calculations confirm that Ih become the equilibrium structure for increasing the Au content. Atomic stress calculations demonstrate that the TO → Ih shape change is caused by a better relaxation of anisotropic surface stress in icosahedra.

An algorithm for statistical evaluation of weld toe geometries using laser triangulation

Commonly, to evaluate the influence of the local weld geometry in fatigue test, small-scale specimens are used, assuming those represent a longer weld adequately. In this study, a comparison between short specimens and a long weld is performed. A method is developed for the statistical evaluation of weld toe radii and angles, stress concentration factors and weld quality classes. The results show a strong sampling rate dependence and lower ISO 5817:2014 weld quality results for higher sampling rates. Comparable results between short specimens and a long weld can be achieved using modal values of the parameters assuming a lognormal distribution.

Investigation of the chemical ordering for PdnPt(32−n)Rh6 nanoalloys in TO structure

Using basin-hopping algorithm within the quantum corrected Sutton-Chen (Q-SC) many-body potential, a systematic investigation has been performed for the best chemical ordering structures of 38-atom trimetallic PdnPt[Formula: see text]Rh6 nanoalloys with truncated octahedral (TO) geometry. The atomic mixing degrees of Pd, Pt and Rh atoms were investigated by using order parameter ([Formula: see text]). The results show that demixing is energetically favorable for the investigated structures, where the number of Rh atoms fixed at 6. The only compositions with the number of hetero bonds lower than the homo bonds are Pt[Formula: see text]Rh6, Pd1Pt[Formula: see text]Rh6, Pd[Formula: see text]Pt[Formula: see text]Rh6 and Pd[Formula: see text]Rh6 which make segregation energetically favorable. The surface segregation of Pd atoms is explained by the lower cohesive energy of Pd atoms than Pt and Rh. The segregation of Pd atoms to the surface is also associated with the smaller surface energies compared with Pt and Rh atoms. Due to the comparable cohesive energies of Rh and Pt atoms, a computation occurs for filling the octahedral core between two kinds.