Complex Geometries Research Articles

Numerical prediction on the fatigue debonding behaviour in a complex bi-material interface: A case study on wrapped composite joints

Debonding is one of the most critical failure modes for bonded joints under fatigue loads. Numerical prediction on the fatigue debonding behaviour of bonded interfaces with complex geometry still remains a problem. This paper proposes a numerical methodology based on fracture mechanics to predict crack growth in a complex bi-material interface and illustrates the prediction procedure by a case study on wrapped composite joints. Interface coupon tests provide the fatigue crack growth properties at the composite-to-steel interface used as inputs for finite element (FE) modelling. The FE model is calibrated against fatigue tests of small scale wrapped composite joints with different steel surface roughness subject to different load levels. A sensitivity analysis is conducted to investigate the influence of key modelling parameters. The calibrated model is validated against fatigue tests on upscaled joints. Good agreements are shown between the test and modelling results in terms of crack growth and stiffness degradation, demonstrating the potential of the proposed numerical methodology for predicting fatigue debonding behaviour of complex bi-material interfaces.

Antisolvent controls the shape and size of anisotropic lead halide perovskite nanocrystals

Colloidal lead halide perovskite nanocrystals have potential for lighting applications due to their optical properties. Precise control of the nanocrystal dimensions and composition is a prerequisite for establishing practical applications. However, the rapid nature of their synthesis precludes a detailed understanding of the synthetic pathways, thereby limiting the optimisation. Here, we deduce the formation mechanisms of anisotropic lead halide perovskite nanocrystals, 1D nanorods and 2D nanoplatelets, by combining in situ X-ray scattering and photoluminescence spectroscopy. In both cases, emissive prolate nanoclusters form when the two precursor solutions are mixed. The ensuing antisolvent addition induces the divergent anisotropy: The intermediate nanoclusters are driven into a dense hexagonal mesophase, fusing to form nanorods. Contrastingly, nanoplatelets grow freely dispersed from dissolving nanoclusters, stacking subsequently in lamellar superstructures. Shape and size control of the nanocrystals are determined primarily by the antisolvent’s dipole moment and Hansen hydrogen bonding parameter. Exploiting the interplay of antisolvent and organic ligands could enable more complex nanocrystal geometries in the future.

Design, Synthesis and Bioactivity Evaluation of Ag(I)-, Au(I)- and Au(III)-Quinoxaline-Wingtip N-Heterocyclic Carbene Complexes Against Antibiotic Resistant Bacterial Pathogens.

Intending to homogenize the biological activities of both quinoxaline and imidazole moieties, the proligand, 1-methyl-3-quinoxaline-imidazolium hexaflurophosphate (1.HPF6), and [Ag(1)2][PF6], (2); [Au(1)2][PF6], (3); and [Au(1)Cl3], (4) NHC complexes were synthesized. All the synthesized compounds were characterized by elemental analysis, NMR, and UV-Vis spectroscopy. Finally, single crystal X-ray structures revealed a linear geometry for complex 2 whereas a square planar geometry for complex 4. The formation of complex 3 was confirmed and supported by its MS spectra. The antibacterial activities of all the synthesized complexes were investigated against gram-positive bacteria and gram-negative bacteria. The Au(III)-NHC complex, 4 showed the highest antibacterial activity with extremely low MIC values against both the bacterial strains (0.24 μg mL-1). Monitoring of zeta potential supports the higher activity of complex 4 compared to 2 and 3. ROS production by complex 4 has also been measured in vitro in the CT26 cancer cell lines, which is directly responsible for targetting and killing the bacterial pathogens. Cell cytotoxicity assay using 293T cell lines has been performed to investigate the biocompatibility nature of complex 4. Also, an excellent hemocompatibility was assigned to it from its hemolytic studies, which provide valuable insights into the design of novel antibacterial agents.

Elucidating Polyphosphate Anion Binding to Lanthanide Complexes Using EXAFS and Pulsed EPR Spectroscopy.

Reversible anion binding to lanthanide complexes in aqueous solution has emerged as an effective method for anion sensing. Through careful design of the organic ligand, luminescent lanthanide complexes capable of binding biologically relevant anions in a bidentate or monodentate manner can be realized. While single-crystal X-ray diffraction analyses and NMR spectroscopy have revealed the structural geometry of several host-guest complexes, the challenge remains in designing preorganized lanthanide receptors with enhanced anion selectivity for broader applications in diagnostics and bioimaging. To address this challenge, innovative and complementary methods to investigate host-anion binding geometry are becoming increasingly important. Herein, we demonstrate the combined use of Eu L3-edge extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) spectroscopy to elucidate the binding of nucleoside phosphates (ATP, ADP, and AMP) to a cationic lanthanide complex. We establish that ATP unequivocally binds the lanthanide center in a bidentate manner in water, while ADP adopts both bidentate and monodentate modes, and AMP binds in a monodentate manner. This interdisciplinary approach provides deeper insight into lanthanide host-guest chemistry in solution, laying the groundwork for designing emissive probes that undergo specific anion-induced structural changes and elicit desired optical responses upon binding.

Air Leakages at Microvalves: Pressure Decay Measurements and Extended Continuum Modelling of Knudsen Flows

To improve the performance of valves in relation to the leakage rate, a comprehensive evaluation of the valve characteristics and behavior during pressure exposure is important. Often, these low gas flow rates below 0.1 cm3/min cannot be accurately measured with conventional flow sensors. This paper presents a small and low-cost test rig for measuring gas leakage rates accurately, even far below 0.1 cm3/min, with the pressure decay method. These leakage flows are substantiated with a flow model, where we demonstrate the feasibility of modeling those gas flows with an extended Navier–Stokes framework to obtain more accurate theoretical predictions. As expected, the comparison to the experimental results proves that the classical Navier–Stokes system is unsuitable for modeling Knudsen flows. Hence, self-diffusion of gas, a wall-slip boundary condition, and an effective mean free path model were introduced in a physically evident manner. In terms of the calculated mass flow, while self-diffusion and slip boundary conditions explain deviations from the classical Navier–Stokes equation for Knudsen numbers already smaller than 1, the effective mean free path model has an effect, especially when Kn > 1. For simplified conditions, an analytical solution was presented and compared to the results of an OpenFOAM CFD-solver for flow rates through more complex gap-flow geometries of the flap valve. Hereby, acceptable deviations between 10% and 20% were observed. A comparison with measurement results was carried out. The reproducibility of the measurement method was verified by comparing multiple measurements of one silicon microvalve sample to a state-of-the-art flow sensor. Three geometrically similar passive silicon microvalves were measured with air overpressure decreasing from 15 kPa relative to atmospheric pressure. Maximum gas volume flowing in a blocking direction of 1–26 µL/min with high reproducibility and marginal noise were observed.

Complexity geometry in Hermitian and non-Hermitian quantum dynamics

Complexity geometry in Hermitian and non-Hermitian quantum dynamics

Free convective flow of Ostwald-de Waele fluid in a Π-shaped cavity with heated strip and lateral wall cooling

This paper studies the free convection of Ostwald-de Waele fluid in a Π-shaped chamber with a Π-shaped heated strip at the lower mid-section. The upper wall and the remaining sections of the lower wall are thermally insulated, while the lateral walls are maintained at a low temperature. The primary objective is to identify the optimal power-law index (n) and the geometric configurations of the strip that yield enhanced heat transfer. Furthermore, the impact of Rayleigh number (Ra) on the thermal performance of the cavity in that optimum condition is to be investigated. The Galerkin finite element approach has been employed to resolve the governing equations and auxiliary conditions. Within the study, the power-law index of the Ostwald-de Waele fluid has been systematically varied (0.6 ≤ n ≤ 1.4). At the same time, the variations in the non-dimensional height (0.1 ≤ ζ ≤ 0.5) and width (0.1 ≤ ε ≤ 0.3) of the heated strip have been explored. The results show improved thermal performance with a growth in Rayleigh number, particularly when n < 1. The average Nussetl number for n = 0.6 at Ra = 106 is approximately 14 % higher than for n = 1.4. The findings further indicate an increment of 35 % in the heat transfer rate when the height of the strip decreases from 0.5 to 0.1. This investigation provides valuable insights into the natural convection phenomena of Ostwald-de Waele fluid in complex geometries, paving the way for advanced thermal management techniques in various engineering applications.

Evaluation of particle tracking codes for dispersing particles in porous media

Particle tracking (PT) is a popular technique in microscopy, microfluidics and colloidal transport studies, where image analysis is used to reconstruct trajectories from bright spots in a video. The performance of many PT algorithms has been rigorously tested for directed and Brownian motion in open media. However, PT is frequently used to track particles in porous media where complex geometries and viscous flows generate particles with high velocity variability over time. Here, we present an evaluation of four PT algorithms for a simulated dispersion of particles in porous media across a range of particle speeds and densities. Of special note, we introduce a new velocity-based PT linking algorithm (V-TrackMat) that achieves high accuracy relative to the other PT algorithms. Our findings underscore that traditional statistics, which revolve around detection and linking proficiency, fall short in providing a holistic comparison of PT codes because they tend to underpenalize aggressive linking techniques. We further elucidate that all codes analyzed show a decrease in performance due to high speeds, particle densities, and trajectory noise. However, linking algorithms designed to harness velocity data show superior performance, especially in the case of high-speed advective motion. Lastly, we emphasize how PT error can influence transport analysis.

Feasibility study of data-driven wall interference correction framework for subsonic wind tunnel

Although the classical method is widely used for wall interference correction in wind tunnel testing, its reliability and accuracy for complex and unconventional geometries are rather limited. Studies on the evaluation of wall interference and the improvement of correction methods are desirable to enhance the reliability and generality for various geometric configurations. This study proposes a wall interference correction framework based on a deep neural network (DNN) ensemble using data obtained from the numerical panel method. The panel method is validated by comparing the results with those of Reynolds-averaged Navier-Stokes simulations. An automated process was established to generate a large amount of training data, and 600,000 datasets were generated based on the geometric parameters of the wind tunnel, test model, and angles of attack. The input variables of the DNN were determined through sensitivity analysis of the data. To alleviate the randomness of the initial weights and data distribution in the generation process of the DNN model, 20 DNNs with the same multi-layer perceptron structure were trained, and a DNN ensemble model was constructed using five ensemble members with high predictability. The accuracy of the DNN-ensemble based correction models were evaluated by comparing the correction results for the testing data.

Topology optimization of extreme mechanical metamaterials considering the anisotropy of additive manufactured parts

Abstract Additive manufacturing (AM) has the advantage of fabricating complex geometries designed by topology optimization. However, the layer-by-layer stacking of AM causes the anisotropic property of the manufactured parts, which is rarely considered in the topology optimization of metamaterials. Hence, this paper presents a new method for the topology optimization of metamaterials with anisotropic properties. First, the elastic moduli in different directions of anisotropic materials are introduced into the solid isotropic material with penalization interpolation function. Then, the effective elastic properties of anisotropic metamaterials are evaluated using the energy-based homogenization method, and the formulation of the topology optimization of anisotropic metamaterials is constructed, and it is iteratively solved by the method of moving asymptotes algorithm. Finally, several two-dimensional and three-dimensional numerical examples and a set of mechanical experiment are conducted to demonstrate the effectiveness of the proposed method.

Paste extrusion‐based 3D printing of fiber‐reinforced ultra high‐temperature ceramics

AbstractUltra–high‐temperature ceramics (UHTCs) are valued for their extremely high melting temperatures and resistance to active oxidation. However, their low fracture strengths and the difficulties in shaping them into complex geometries hamper their widespread application. This study aims to fabricate zirconium diboride–silicon carbide (ZrB2‐SiC) composites reinforced with aligned SiC fibers by formulating suspensions containing a preceramic polymer, ZrB2, and SiC fibers. This study assessed the influence of fiber alignment on electrical and thermal conductivities, as well as on mechanical strength. The results revealed a significant enhancement in thermal conductivity, particularly when the fibers were aligned, effectively doubling it compared with the non‐aligned parts. Additionally, increasing the fiber content significantly improved the fracture strength, with composites containing 22.5 vol% fibers reaching fracture strengths over 57 MPa. However, the final values did not meet the theoretical expectations because the porosity in pyrolyzed parts exceeded 10%. Furthermore, the study demonstrated a 10‐fold increase in electrical conductivity with fiber alignment compared to that for non‐aligned composites. These results highlight the capability of paste extrusion‐based additive manufacturing in tailoring ultra–high‐temperature ceramic matrix composites (UHTCMCs) with aligned fibers, realizing their suitability for aerospace applications.

Experimental and numerical investigation of the damage propagation in regularly arrayed short fiber reinforced composite laminates under low‐velocity impact

AbstractThe outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands (UACSs) give them an advantage in the manufacture of engineering structures with complex geometry. For the application of practical structures, the impact responses and damage evolution of material under low‐velocity impact must be investigated in advance. In this study, UACS laminates and continuous carbon fiber laminates with a stacking sequence of [0/90]4s and a thickness of 2 mm were fabricated for low‐velocity impact tests at 7, 11, 15, and 20 J. The impact responses and postimpact intralaminar damage area were analyzed according to the experimental results, including impact load responses and ultrasound C‐scan inspections. Moreover, to predict the damage evolution of the internal structure, the 3D finite element models were constructed in ABAQUS using a progressive damage model (PDM) through a user‐material subroutine VUMAT. Compared with continuous carbon fiber laminates, the dissipated energy of UACS laminates increases by approximately 10.64% and 57.37% for the 15 and 20 J, respectively. However, the intralaminar damage area of UACS laminates decreased by 29.96% and 28.16% at 15 and 20 J, respectively, since the discontinuous slits in UACS laminates can guide damage paths and suppress damage propagation.Highlights The regularly arrayed short fiber reinforced composite was studied. Revealed the low‐velocity impact responses and predicted the damage evolution. UACS and CFRP laminates have comparable impact performance. Illustrated the slits design can suppress the damage to a relatively small area.

Surface finishing of 3D-printed Ti–6Al–4 V alloy by electrolyte plasma polishing: Process optimization and microstructure

The electrolyte plasma polishing (EPP) technology is proposed to remove the unmelted powder particles and oxide film for high-quality surface finishing of 3D-printed Ti–6Al–4 V alloy. An orthogonal experiment is conducted to investigate multiple factors that contribute to the surface quality of the alloy during the polishing process. The optimal parameters determined for the EPP process are a voltage of 300 V, a polishing time of 12 min, a polishing depth of 12 cm, and a temperature of 75 °C. Based on the extent of the effect, the factors influencing surface roughness were ranked: voltage > time > depth > temperature. The surface crest and trough area of the alloy is substantially reduced after polishing, while the average roughness experienced a reduction of 76 %. The improvement in surface quality is attributed to the corrosion of the oxide layer by F ions in the electrolytic solution, and the melting of surface protrusions due to the impact of high-energy electrons under high-temperature and high-pressure conditions during plasma discharge. Additionally, the surface hardness of the material decreases slightly, but its corrosion resistance and hydrophobicity are enhanced, and the calibration rate of the EBSD sample can reach 92.51 %, demonstrating that it is an excellent surface finishing technique. Hence, EPP is a promising approach for smoothening 3D-printed metals, especially for alloy parts with complex geometry and porous structure.

Research and Application of Euler Cutting Path Based Optimisation Algorithm with Greedy-RRT Algorithm

With the development of social economy, mould processing enterprises have an increasingly strong demand for reducing costs and improving economic efficiency. The optimisation of steel plate cutting path is one of the key links to improve production efficiency. In this paper, the optimal cutting path problem of steel plate under different cutting tasks is investigated, and the optimal cutting path under complex geometries is found through various optimisation algorithms. For cutting task N3, the cutting path is divided into outer contour cutting, inner hole cutting and inner hole part cutting. According to the problem, all rectangular parts inside the ellipse need to be cut before the ellipse. Through the Eulerian cutting path optimisation algorithm, we solve the air-travel problem between the inner holes and the outer contour as well as the air-travel problem between the inner holes of the ellipse and the parts inside the ellipse. The total length of the finally determined optimal air-travel path is 97 units. By combining the greedy algorithm and the RRT algorithm, we determine the number and location of the bridges and design the optimal cutting path starting from the lower right corner of the steel plate. The final clearance of the bridges is 4 units, the total length of the combined optimal path clearance is 35.56 units, and the number of bridges is 8, which are located between adjacent rectangles.

Osteochondral Regeneration With Anatomical Scaffold 3D-Printing-Design Considerations for Interface Integration.

There is a clinical need for osteochondral scaffolds with complex geometries for restoring articulating joint surfaces. To address that need, 3D-printing has enabled scaffolds to be created with anatomically shaped geometries and interconnected internal architectures, going beyond simple plug-shaped scaffolds that are limited to small, cylindrical, focal defects. A key challenge for restoring articulating joint surfaces with 3D-printed constructs is the mechanical loading environment, particularly to withstand delamination or mechanical failure. Although the mechanical performance of interfacial scaffolds is essential, interface strength testing has rarely been emphasized in prior studies with stratified scaffolds. In the pioneering studies where interface strength was assessed, varying methods were employed, which has made direct comparisons difficult. Therefore, the current review focused on 3D-printed scaffolds for osteochondral applications with an emphasis on interface integration and biomechanical evaluation. This 3D-printing focus included both multiphasic cylindrical scaffolds and anatomically shaped scaffolds. Combinations of different 3D-printing methods (e.g., fused deposition modeling, stereolithography, bioprinting with pneumatic extrusion of cell-laden hydrogels) have been employed in a handful of studies to integrate osteoinductive and chondroinductive regions into a single scaffold. Most 3D-printed multiphasic structures utilized either an interdigitating or a mechanical interlocking design to strengthen the construct interface and to prevent delamination during function. The most effective approach to combine phases may be to infill a robust 3D-printed osteal polymer with an interlocking chondral phase hydrogel. Mechanical interlocking is therefore recommended for scaling up multiphasic scaffold applications to larger anatomically shaped joint surface regeneration. For the evaluation of layer integration, the interface shear test is recommended to avoid artifacts or variability that may be associated with alternative approaches that require adhesives or mechanical grips. The 3D-printing literature with interfacial scaffolds provides a compelling foundation for continued work toward successful regeneration of injured or diseased osteochondral tissues in load-bearing joints such as the knee, hip, or temporomandibular joint.

An improved phase-field model for fatigue crack growth considering constraint effects

The phase field model is a promising method for simulating fatigue crack growth (FCG) behavior. However, the conventional phase field (PF) model may not adequately account for constraint effects, where fracture toughness is affected by geometries. Therefore, stress triaxiality is incorporated into the PF model by modifying the fracture energy release rates to consider constraint effects. The model successfully simulates the FCG behavior of different geometries, such as CT, SENB, and MT specimens, as well as the mixed-mode FCG behavior of CTS specimens and other complex geometries. All simulations agree well with experiments, proving that our model is capable to capture the constraint effects in FCG behavior. These findings indicate that stress triaxiality is important to capture the constraint effects.

Competitive Fracture Mechanism and Microstructure‐Related Life Assessment of GH4169 Superalloy in High and Very High Cycle Fatigue Regimes

ABSTRACTHigh and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes.

Finite element analysis on the compression and crush responses of laminates with unidirectionally arrayed chopped strand in 0° plies

AbstractThe outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands laminates (UACS) give them an advantage in the manufacture of engineering structures with complex geometries. In this research, the mechanical response of UACS laminates with bi‐angled slits and staggered slits under quasi‐static compression and progressive crushing loads is numerically analyzed for the first time. The aim is to clarify the damage mechanism of UACS laminates under compressive and crushing load. Simulation results reveal that the compressive strength of [90/0]4s UACS laminates with bi‐angled slits is 635.9 MPa, with an error of 4.2% compared to experimental data. For the stacking sequence of [0/90]4s, the strength is measured as 581.96 MPa with a 5% error. Proposed finite element model could accurately describe the mechanical properties of UACS laminates. Additionally, the progressive crushing response is in good agreement with the experimental data, the error in energy absorption for [90/0]4s UACS laminates with bi‐angled slits is noted at 7% compared to experimental values. It has been demonstrated that bi‐angled slits significantly contribute in restraining the propagation of delamination and improving the amount of energy absorption of UACS laminates.Highlights The mechanical response of UACS laminates under compressive and progressive crushing load was numerically analyzed. The compressive damage propagation of UACS laminates with different slit patterns in 0° layer was demonstrated. The effect of different slit patterns on inhibiting delamination propagation and increasing energy absorption of UACS laminates under progressive crushing load was numerically analyzed.

Experimental and theoretical studies of carbacylamidophosphate-La (III) complexes: Synthesis, crystal structure, antibacterial activity, electronic and morphology properties

The present study tries to contribute to the body of knowledge concerning the effects of O-donor ligands based on carbacylamidophosphate on the topology, geometry, and dimensions of relevant metal complexes. Accordingly, the octa-coordinated lanthanum (III) complex with formula, [La(L1)4Cl2]Cl (C1) (L1 = 4-NC5H4C(O)NHP(O)(NC6H12)2), has been synthesized and its crystal structure has been determined. In the crystal structure, C1 is C2-symmetrical, and there are separate [La(L1)4Cl2]+ cations and Cl- anions. In the complex molecule, the four L1 ligands adopt two anti- and two syn-chelating conformations. Moreover, two other carbacylamidophosphate-based lanthanide complexes La(L2)2(NO3)3 (C2) (L2 = PhC(O)NHP(O)(NH(tert‑C4H9))2)2(NO3) and La(L3)2(NO3)3(H2O)[(CH3)2CO] (C3) (L3 = (4-NO2C6H4CONHPO(NC4H8O)2) were considered and density functional theory computations, at the B3PW91 level, were performed to gain a deeper understanding of the structural and electronic properties in complexes (C1 - C3). Nano and micro-structures of (C’1 - C’3) were prepared by means of a sonochemical process to study how the reaction condition and non-covalent forces function in terms of the form as well as the size of the particles in these complexes. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were performed on compounds C’1- C’3. The Hirshfeld surface analysis and NCI method were used to show the effects of non-covalent interactions on the compounds’ morphologies. The antimicrobial activity of all selected compounds has been screened against two Gram-positive (Bacillus subtilis, Staphylococcus aureus) and one Gram-negative (Escherichia coli) bacteria by well diffusion method. The results indicated that all selected compounds did not show any antibacterial activity against bacteria as compared to standard drugs.

Deep learning as Ricci flow.

Deep neural networks (DNNs) are powerful tools for approximating the distribution of complex data. It is known that data passing through a trained DNN classifier undergoes a series of geometric and topological simplifications. While some progress has been made toward understanding these transformations in neural networks with smooth activation functions, an understanding in the more general setting of non-smooth activation functions, such as the rectified linear unit (ReLU), which tend to perform better, is required. Here we propose that the geometric transformations performed by DNNs during classification tasks have parallels to those expected under Hamilton's Ricci flow-a tool from differential geometry that evolves a manifold by smoothing its curvature, in order to identify its topology. To illustrate this idea, we present a computational framework to quantify the geometric changes that occur as data passes through successive layers of a DNN, and use this framework to motivate a notion of 'global Ricci network flow' that can be used to assess a DNN's ability to disentangle complex data geometries to solve classification problems. By training more than 1500 DNN classifiers of different widths and depths on synthetic and real-world data, we show that the strength of global Ricci network flow-like behaviour correlates with accuracy for well-trained DNNs, independently of depth, width and data set. Our findings motivate the use of tools from differential and discrete geometry to the problem of explainability in deep learning.