Transverse Propagation Research Articles

Synergistic enhancement mechanism of mechanical properties and hydrogen embrittlement resistance in medium Mn steels by coupling warm/cold rolling and delta ferrite

In the present research, Fe-0.2C–6Mn–3Al-0/0.6Si steels were labeled as 0Si (without δ-ferrite) and 6Si samples (with abundant δ-ferrite). The hot-rolled annealed 0Si samples (i.e. 0SiHRA), and 6Si samples subjected to the warm-rolling, warm-rolled annealing and cold-rolled annealing (i.e. 6SiWR, 6SiWRA and 6SiCRA) were investigated. 0SiHRA shows the lath-type, 6SiWR shows the elongated and 6SiWRA and 6SiCRA reveal the equiaxed microstructure. Compared to 0SiHRA, the mechanical properties and the hydrogen embrittlement (HE) resistance are generally enhanced in 6Si samples. H-induced cracks (HICs) in 0SiHRA mainly nucleate at γ(α′)/α interfaces and propagate along the prior austenite grain boundaries with little propagation resistance, thus showing the low HE resistance. HICs in 6SiWR and 6SiWRA nucleate at γ(α′)/α and (γ(α′)+α)/δ interfaces and propagate longitudinally. Subsequently, the elongated microstructure tearing in 6WR and the equiaxed grains intergranular fracture in 6SiWRA result in HICs transverse propagation. The fracture behaviors in 6SiWR and 6SiWRA consume the vast energy, thus enhancing HE resistance. This work provides a vital insight for the rolling technology and the microstructural design to improve the mechanical properties and HE resistance for the high-strength medium Mn steels.

Phase-locked high-brightness interband cascade laser array with multimode interferometer couplers.

We report on the design, fabrication, and characterization of an interband cascade laser (ICL) array incorporating multimode interference (MMI) couplers for phase-locking emitters. The ICL array, emitting at 3-4 µm, was developed to address the challenges of heat dissipation and in-phase operation in mid-infrared lasers. The array features a 7.5-µm-wide ridge design for fundamental transverse mode propagation and employs MMI structures to realize an in-phase operation of multiple emitters. The far-field patterns, characterized by periodic and symmetrical interference fringes, confirm the coherent operation of the array and the efficacy of MMI couplers in achieving phase-locking. The single-ridge side of the array exhibits a single-lobe far-field profile, with higher-order transverse modes effectively suppressed, showcasing a nearly diffraction-limited beam quality (M2 ≈ 1.31) at high output powers (390 mW from the 1 × 4 array). The robust performance and scalable design of the ICL array, validated by experimental results and theoretical simulations, indicate its potential for high-power mid-infrared applications and as an optical phased array.

Long ranged stress correlations in the hard sphere liquid.

The smooth emergence of shear elasticity is a hallmark of the liquid to glass transition. In a liquid, viscous stresses arise from local structural rearrangements. In the solid, Eshelby has shown that stresses around an inclusion decay as a power law r-D, where D is the dimension of the system. We study glass-forming hard sphere fluids by simulation and observe the emergence of the unscreened power-law Eshelby pattern in the stress correlations of the isotropic liquid state. By a detailed tensorial analysis, we show that the fluctuating force field, viz., the divergence of the stress field, relaxes to zero with time in all states, while the shear stress correlations develop spatial power-law structures inside regions that grow with longitudinal and transverse sound propagation. We observe the predicted exponents r-D and r-D-2. In Brownian systems, shear stresses relax diffusively within these regions, with the diffusion coefficient determined by the shear modulus and the friction coefficient.

Network- and CFD/CAA-modelling of the high frequency flame response in multi-jet combustors

Low order networks are widely used for linear stability analysis of combustors in the low frequency limit. High frequency stability analysis, however, is limited to cost-intensive numerical or experimental methods, since derivation of analytical solutions is either cumbersome or impossible. The article at hand provides a quasi-two-port network model for the effective modal acoustic pressure and axial velocity normalised with the transverse acoustic field for cylindrical combustors. This network modelling approach includes transfer matrices of acoustic area jumps, ducts for longitudinal, standing and spinning transverse and mixed mode wave propagation. The purely acoustic transfer matrices are validated with a generic non-reactive experiment. On the basis of phase-locked [Formula: see text] images of an engine-similar multi-jet combustor with a forced T1 mode, a locally distributed flame response model is derived, which is reduced to a global flame transfer matrix. A locally resolved convective flame response model is implemented in a numerical model in order to verify the provided theory by the comparison of the analytical and numerical flame transfer matrix for the high-frequency regime.

Fatigue analysis of selective laser melting Inconel 718 and the mechanism of ductile–brittle continuous alternating steps during fatigue process

In this paper, Inconel 718 powber fabricated by selective laser melting were studied to explore the mechanical characteristics and microstructures. The results of microstructure show that the material exhibits the columnar, honeycomb, and mixed crystal structures. The microhardness is very uniform, with a average value of 317 HV. Tensile test shows the ultimate tensile strength of 785Mpa, elongation of 4.93%, which is high stress brittle fracture. The fatigue strength of 180 MPa was obtained from the fatigue test. The fatigue life was sensitive to the effect of stress. In the scanning electron microscope observation, small crack propagation was found in the fracture, and a large number of step-like fracture characteristics of repeated transformation of toughness and brittleness were found. The mechanism analysis of the step-like ductile–brittle fracture is carried out, which is divided into four stages. Mathematically analyzing the tough-brittle fracture of the step type, where the crack is subjected to both the stress field around the pore and the stress field at the crack tip on the way to extension, a stress field model for crack propagation around the pore and a fracture toughness formula for transverse and longitudinal propagation of tough-brittle steps applicable to this paper are proposed.

Flexural performance and damage mechanisms of stitched composites under different stitch patterns and densities by acoustic emission

The flexural performance of standard composites has been extensively studied; however, the response of stitched composites with different stitch patterns and densities has received little attention and is not well understood. This study systematically explored the flexural performance of stitched composites with different stitch patterns and densities. The stitches weakened the flexural strength while improving the residual strength of the composites, particularly under a high stitch density. In addition, the stitch threads in the longitudinal stitch pattern preferably resisted the deformation of the bottom side of the specimen, showing superior flexural strength compared with the diagonal and transversal stitch patterns. However, the stitch threads in the diagonal and transverse stitch patterns impeded crack propagation and enhanced the residual strength of the composites. In addition, acoustic emission was used to confirm that the acoustic emission signals and the first moment of rapid increase in cumulative acoustic emission energy were detected earlier under a high stitch density, suggesting that the increase in stitch defects promotes damage initiation and severe damage. The durations with high values and a continuous increase in the cumulative acoustic emission energy after brittle failure indicated that the stitched composites experienced non-catastrophic failure.

Low‐velocity impact damage behavior of glass fiber reinforced composites with different crack propagation

AbstractGlass fiber‐reinforced resin matrix composites are widely used and studied for their good mechanical and impact resistance properties. In this paper, five glass fiber reinforced nylon 6 (PA6)‐based composites were prepared by mechanical blending combined with the molding process. The flexural strength, shear strength, pendulum impact strength, and low‐velocity impact properties of five composites were comparatively investigated. The crack extension modes of the composites were characterized and analyzed by light microscopy, scanning electron microscopy (SEM), and computerized X‐ray tomography (XCT), and the effects of different crack extension modes on the mechanical and impact resistance properties of the composites were researched. Experimental results show that: (1) Cracks in the composite material mainly exist in two expansion modes: transverse propagation parallel to the direction of fiber layup and longitudinal propagation perpendicular to the direction of fiber layup; (2) Different crack extension modes will cause different damage situations to the composites, however, the crack extension mode has minimal impact on the flexural, shear and pendulum impact strength of the composites; (3) The flexural and shear strengths of the composites co‐reinforced using fly ash and glass fibers were preferably 484.5 and 46.1 MPa; (4) The crack extension mode has a significant impact on low‐velocity impact performances of the composite material. The composite co‐reinforced with glass beads (GB) and glass fibers had the best impact resistance, with maximum impact force (Pmax), residual impact force (Pr), and absorbed energy (Ea) of 7015.2 N, 6273.6 N and 15.4 J, respectively.Highlights The propagation of cracks inside the composites was observed using SEM and XCT etc. A relationship between crack propagation mode and low‐velocity impact resistance of composites was established. The low‐velocity impact properties of composites are carefully analyzed.

Restoration of Strength in Polyamide Woven Glass Fiber Organosheets by Hot Pressing: Case Study of Impact and Compression after Impact.

Thermoplastic composite organosheets (OSs) are increasingly recognized as a viable solution for automotive and aerospace structures, offering a range of benefits including cost-effectiveness through high-rate production, lightweight design, impact resistance, formability, and recyclability. This study examines the impact response, post-impact strength evaluation, and hot-pressing repair effectiveness of woven glass fiber nylon composite OSs across varying impact energy levels. Experimental investigations involved subjecting composite specimens to impact at varying energy levels using a drop-tower test rig, followed by compression-after-impact (CAI) tests. The results underscore the exceptional damage tolerance and improved residual compressive strength of the OSs compared to traditional thermoset composites. This enhancement was primarily attributed to the matrix's ductility, which mitigated transverse crack propagation and significantly increased the amount of absorbed energy. To mitigate impact-induced damage, a localized hot-pressing repair approach was developed. This allowed to restore the post-impact strength of the OSs to pristine levels for impact energies below 40 J and by 83.6% for higher impact energies, when OS perforation was observed. The measured levels of post-repair strength demonstrate a successful restoration of OS strength over a wide range of impact energies, and despite limitations in achieving complete strength recovery above 40 J, hot-pressing repair emerges as a promising strategy for ensuring the longevity of thermoplastic composites through repairability.

Gravitational instability in magnetized viscoelastic fluid with radiation pressure effect

This study examines the gravitational instability of a finitely conducting magnetized viscoelastic fluid, under the influence of radiation pressure within the framework of a generalized hydrodynamic fluid model. The general dispersion relation, valid for strongly and weakly coupled fluids under kinetic and hydrodynamic limits respectively, is derived using normal mode analysis for a transverse wave propagation mode. The obtained Jeans instability criteria, in terms of critical Jeans wavenumbers under both limits, are modified by the presence of radiative effects, viscoelastic compressional speed, and Alfvén wave velocity. The findings highlight that viscoelastic compressional speed and radiative pressure slow the Jeans instability's growth rate, exerting a stabilizing effect on the initiation of gravitational collapse. The present investigation provides valuable insights into the role of radiative mechanisms in the gravitational collapse within the strongly coupled region of molecular cloud clumps.

Mechanical properties and failure behavior of additively manufactured Al2O3 lattice structures infiltrated with phenol-formaldehyde resin

The lightweight design and load-bearing capacity of underwater vehicles remain perennial focal points. Ceramic lattice structures (CLSs) offer significant weight reduction while maximizing structural strength; however, their inherent brittleness poses a limitation. To optimize the performance of CLSs for underwater vehicle applications, a biomimetic Al2O3/phenol-formaldehyde (PF) resin composite structure (APCS) was proposed and fabricated by infiltrating additive-manufactured Al2O3 lattice structures (ALSs) with PF. Comprehensive assessments of the quasi-static mechanical properties were conducted using both experimental and simulation methods. The specific compressive strength and specific energy absorption of the APCSs under quasi-static compressive loading exhibited remarkable improvements, with the maximum values achieved from the body-centered cubic (BCC)/PF structure increasing by ∼15.23 and ∼307.93 times, respectively. In contrast to ALSs, the failure process of APCSs was gradual, with the confining pressure introduced by the PF promoting transverse crack propagation and layer-by-layer failure, thereby strengthening the ceramic lattice. Toughing mechanisms (i.e., crack arrest, crack deflection, and branching) were also observed in the APCSs. Furthermore, the simulation results aligned well with the experimental results, providing an in-depth analysis of internal damage and crack propagation. The improvements introduced by the composite structure in this study provide a reliable approach for obtaining lightweight and strong materials, thereby accelerating the application of ceramic-based materials in underwater vehicles.

Ballistic impact wave and bulge profile propagation characteristics and blunt injury assessment of UHMWPE laminate composite

Amid escalating localized conflicts worldwide, the elucidation of the mechanisms and quantification blunt trauma the emergency services and military personnel confronted becomes imperatively. However, the understanding of bullet-induced bulge formation on the laminate's back face, impact wave propagation, and consequent trauma assessment methods remains incomplete. This study applies 3-dimension digital image correlation (3D-DIC) method to reveals these phenomena by utilizing a lead-core bullet traveling at 334.93 m/s to impact an ultra-high molecular weight polyethylene (UHMWPE) laminate. The results show that the initial transverse propagation velocity of bulge profile is 24.79% smaller than the theoretical calculation, which indicates the reduction caused by cohesive matrix. The transverse wave demonstrates a double exponential attenuation pattern, which could be decomposed into two single exponential attenuation curves. The bulge profile shows hyperbolic pattern, which reveals the stability of the bulge shape and the temporal evolution pattern. Increasing the laminate-body gap leads to a decline in Blunt Criterion (BC) and the Abbreviated Injury Scale (AIS) values reduce from 2 to 0 correspondingly. The numerical model confirms the compression wave velocity as 1447.77 ± 123.10 m/s in the thickness direction and 9542.86 ± 3087.75 m/s in the fiber direction. These findings reveals and quantified the propagation patterns of back bulge and compressive wave, and thus could provide data-driven insights to improve body armor performance and blunt trauma assessment for individual soldiers.

Analysis of the Structural, Morphological, and Elastic Properties of Nanosized CuFe2O4 Spinel Synthesized via Sol-Gel Self-Combustion Method

Nanosized CuFe2O4 ferrite was synthesized through the sol-gel self-combustion technique, using iron and copper nitrates with citric acid as fuel. The synthesized ferrite was subsequently analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). X-ray diffraction studies validated the crystalline nature of the CuFe2O4, identifying it as having a mixed spinel structure within the Fd3m space group. Particle sizes were quantified using several methods including Debye-Scherrer, Williamson-Hall, Halder-Wagner, modified Debye-Scherrer, and size-strain plot (SSP), with all methods indicating a consistent average particle size of 28 nm. The elastic properties of the nanoparticles were extensively characterized, utilizing both diffraction line broadening (via the Williamson-Hall method) and Fourier-transform infrared spectroscopy (FTIR) to evaluate the materials' structural dynamics. Additionally, microstrain within the crystal lattice and various elastic constants, such as Young's modulus, Shear modulus, Debye temperature, and the velocities of longitudinal and transverse wave propagation were calculated. An electron density distribution was also constructed from the X-ray diffraction data, providing insight into the electronic environment and bonding characteristics of the material.

Effects of mixture initial conditions on deflagration to detonation transition enhanced by transverse jets

To explore the effects of mixture initial conditions on the deflagration to detonation transition (DDT) enhanced by transverse jets, numerical studies were conducted on the flame acceleration of H2/Air mixture under different initial conditions, including initial pressure, temperature, and equivalence ratio. The results indicate significant differences in flame acceleration processes under different initial pressures (0.05, 0.1, 0.15, and 0.2 MPa). Changes in jet intensity and combustion rate induced by variations in mixture initial pressure collectively influence the flame acceleration process, but the impact of jet intensity is more significant. However, effective coupling between transverse wave propagation and flame acceleration is also crucial for the DDT process. Changes in mixture initial temperature (300, 350, 400, and 450 K) and equivalence ratio (0.8, 1.0, 1.2, and 1.4) have negligible impact on jet intensity. The variation trend of flame velocity under different initial temperatures or equivalence ratios is consistent, but the detonation initiation performance is slightly different. As the initial temperature increases, the DDT distance and DDT time are shortened. With an increasing equivalence ratio, the DDT distance and DDT time initially decrease and then increase, reaching the shortest at slightly rich fuel conditions.

Debye temperatures and nanostructuring of polyurethane auxetics

Based on experimental values of longitudinal and transverse ultrasonic wave propagation velocities and surface Rayleigh wave velocities were calculated phonon energies and Debye limiting frequencies and temperatures were determined of metal-filled polyurethane auxetics samples. Modeling the structural formations of such systems and obtaining the value of the lattice and Grüneisen acoustic parameter made it possible to find the root-mean-square displacement of the atomic groups of the macromolecule, as well as the limits of forced elasticity, shear deformation, and deformation of the interstructural bond. The relationship between Debye frequencies (temperatures) and Poisson's ratio, Grüneisen parameter, was established. A quantum-mechanical approach to the movement of electrons, atomic groups of macromolecules, thermal and sound phonons made it possible to estimate the size of nanoformations in the composition. The theoretical values of Poisson's ratio obtained based on models of polymer auxetics and processes of propagation of ultrasonic waves in such systems are analyzed.

Radiation pressure and galactic cosmic rays-driven gravitational instability in rotating and magnetized viscoelastic fluids

This paper studies the combined effects of radiation and galactic cosmic ray pressures on the gravitational instability of magnetized and rotating viscoelastic fluids. The dispersion relations are derived using the normal mode analysis and discussed in the hydrodynamic (weakly coupled fluid) and kinetic (strongly coupled fluid) limits. These dispersion relations are analyzed separately for transverse and longitudinal wave propagation modes. Jeans instability criteria are obtained for kinetic and hydrodynamic limits for both modes of wave propagation, and it is found that the critical Jeans wavenumbers in each case are modified due to the presence of viscoelastic effects, radiation and cosmic rays pressures, and Alfvên wave velocity. It is also observed that the radiation pressure, cosmic ray pressure and viscoelastic parameters suppress the growth rate and thus have stabilizing effects on the Jeans instability. However, cosmic ray diffusion has a destabilizing effect on the onset of gravitational instability. The effects of various parameters on the growth rate of instability are calculated numerically and the outcomes are depicted graphically. The results of the present analysis shall be helpful in understanding the impact of cosmic rays and radiative mechanisms on the gravitational collapse in the viscoelastic region of molecular cloud clumps.

Rotationally symmetric transverse magnetic vector wave propagation for nonlinear optics

In this paper the theory and simulation results are presented for 3D cylindrical rotationally symmetric spatial soliton propagation in a nonlinear medium using a modified finite-difference time-domain general vector auxiliary differential equation method for transverse magnetic polarization. The theory of 3D rotationally symmetric spatial solitons is discussed, and compared with two (1 + 1)D, termed “2D” for this paper, hyperbolic secant spatial solitons, with a phase difference of π (antiphase). The simulated behavior of the 3D rotationally symmetric soliton was compared with the interaction of the two antiphase 2D solitons for different source hyperbolic secant separation distances. Lastly, we offer some possible explanations for the simulated soliton behavior.

Numerical Simulation of Transverse Crack on Composite Structure Using Cohesive Element

Due to their anisotropic behavior, composite structures are weak in transverse direction loading. produces transverse cracks, which for a laminated composite, may lead to delamination and total failure. The transition from transverse crack to delamination failure is important and the subject of recent studies. In this paper, a simulation of transverse crack and its transition to delamination on cross-ply laminate was studied extensively using a cohesive element Finite Element Method (FEM). A pre-cracked [0/90] composite laminate made of bamboo was modeled using ABAQUS/CAE. The specimen was in a three-point bending configuration. Cohesive elements were inserted in the middle of the 90° layer and in the interface between the 0° and 90° layer to simulate transverse crack propagation and its transition to delamination. A load–displacement graph was extracted from the simulation and analyzed. As the loading was given to the specimen, stress occurred in the laminates, concentrating near the pre-cracked region. When the stress reached the tensile transverse strength of the bamboo, transverse crack propagation initiated, indicated by the failure of transverse cohesive elements. The crack then propagated towards the interface of the [0/90] laminates. Soon after the crack reached the interface, delamination propagated along the interface, represented by the failure of the longitudinal cohesive elements. The result of the numerical study in the form of load–displacement graph shows a consistent pattern compared with the data found in the literature. The graph showed a linear path as the load increased and the crack propagated until a point where there was a load-drop in the graph, which showed that the crack was unstable and propagated quickly before it turned into delamination between the 0o and 90° plies.

Azimuthal Scanning Excitation Surface Plasmon Resonance Holographic Microscopy

AbstractSurface plasmon resonance (SPR) holographic microscopy exploits surface plasmon wave as illumination and acquires both SPR intensity and phase images. It detects extremely tiny variations of weakly interacting objects owing to high sensitivity and has been applied in cell biology, material science, surface chemistry, etc. However, it is very challenging to solve the problem of poor spatial resolution due to the transverse propagation of surface plasmon wave. In this paper, an azimuthal scanning excitation method is proposed in SPR holographic microscopy to improve the spatial resolution by engineering the Fourier spectra of SPR images from dual‐arc to circular shape. The study modulates the light field with spatial position, wavevector, and polarization to realize azimuthal scanning excitation of SPR. Systematic experiments of dielectric spheres, nanowires, two‐dimension materials, and complex nanostructure are conducted to show the resolution improvement with one order of magnitude, the higher detection sensitivity of SPR phase than that of SPR intensity, and the necessities of both of high‐resolution SPR intensity and phase images to retrieve sample information in certain scenarios. Benefiting from the high detection sensitivity and spatial resolution, the proposed microscopy will find wide applications in nanoparticle analysis, low‐dimensional material characterization, and imaging extremely thin or transparent samples.

Optimal arrangement of AE sensors for prestressed hollow slabs based on AE propagation characteristics

Acoustic emission (AE) health monitoring is crucial for effective data collection, rational monitoring of results, and economical engineering applications in prestressed hollow slabs. To achieve an optimal sensor arrangement, experiments were performed to measure AE attenuation with different propagation paths in both the longitudinal and transverse directions of a full-scale prestressed hollow slab. Then, the AE amplitude and AE energy are chosen as evaluation indexes to investigate the hybrid arrangement of AE sensors under multiple damage conditions. The results indicate that when the AE signal propagates along the longitudinal direction of the prestressed hollow slabs with the same propagation distance, the attenuation in the steel strand is smaller. Additionally, the attenuation in the concrete directly under the bottom strand is smaller than that in the concrete between the bottom strands. The attenuation of AE propagation is smaller in the complete hinge than in the defective hinge. In terms of transverse propagation, the attenuation of AE signals is less in the bottom slab concrete than in the bottom slab steel strands. At the longitudinal 1/3 section of the prestressed hollow slab, the amplitude attenuation rate shows a turning point, and the variation in the attenuation rate of the AE signal is relatively small. For greater efficiency, it is recommended to position the sensors in the middle part of the hollow slab hinge joint and the bottom slab cross section, as well as on the concrete surface directly under the bottom slab strand.

ASYMMETRIC FLEXURAL BEHAVIOR OF GLULAM BEAMS BASED ON BAMBOO-INSPIRED FUNCTIONALLY GRADED STRUCTURE FOR HIGH BENDING LOAD APPLICATIONS

ABSTRACT Natural materials are being further processed into functionally engineered products to reduce their natural variability and enhance their performance for use in construction, given their noteworthy recyclability, availability and sustainability traits. To date, the mechanical strengths of natural and engineered wood products are limited by their inherent micromechanical characteristics which are outclassed by homogeneous materials like steel and concrete. This study proposes a less process-intensive technique to improve the strength of engineered wood products by considering glulam based on a bio-inspired functionally graded structure. The finite element method was considered to investigate the effects of the functionally graded arrangement on the asymmetric flexural deformation and on the underlying fracture mechanisms in glulam beams. The numerical results showed that the functionally graded arrangements across the cross-section led to an improvement in the bending strength and consequently enhanced the resistance to transverse crack propagation. In the functionally graded glulam beam, the stiffer layers at the bottom were found to promote the onset for longitudinal crack initiation. Moreover, transverse cracks tended to propagate sideways in an orthogonal direction in the beam layers with a high longitudinal to transverse stiffness ratio whereby the tangential normal stress was a maximum. The improvement in performance, which resulted from a shift of the neutral axis and redistribution of stress within the glulam beams, was attributed to the degree of graded arrangement across their cross-section besides the orthotropic characteristics of their individual layers. Key findings of this study could be useful to further develop high-strength engineered wood products based on bio-inspired solutions to replace conventional materials in the construction industry for improved sustainability.