Wavy Morphology Research Articles

Numerical simulation of explosive welded titanium and Al7075-T6 bimetal composite plate using ANSYS Autodyn

The aim of this paper is to use the smoothed particle hydrodynamics (SPH) technique (in Ansys Autodyn), to create a more physically realistic 2 D numerical model for the simulation of explosive welding of Titanium with Aluminum alloy Al7075-T6. The flyer plate was made of titanium, while the base plate was made of Al7075-T6. The Al7075-T6 plate served as the foundation for the majority of the jet's components. The majority of the jet's components were built on top of the Al7075-T6 plate. The jet flew at a speed of 1100 m/s, as anticipated by the model. In addition, the pressure at the explosion site was insufficient to bind the two plates. As a result, a unique tiny region of plastic strain formed at the impact zone. Despite the fact that the two plates were facing opposite directions, there were no signs of shear forces between them. Due to severe plastic deformation and localised melting of the parent plates, the interface shape changed from straight to wavelike as the detonation wave moved across it during the simulation. Both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the previous studies.

Solution blow spinning of highly deacetylated chitosan nanofiber scaffolds for dermal wound healing.

Biocompatible fibrous scaffolds based on highly deacetylated chitosan were fabricated using high-throughput solution blow spinning. Scanning electron microscopy analysis revealed that the chitosan nanofiber scaffolds had ultrafine and continuous fibers (300-1200nm) with highly interconnected porous structures (30-75% porosity), mimicking some aspects of the native extracellular matrix in skin tissue. Post-treatment of as-spun nanofibers with aqueous potassium carbonate solution resulted in a fibrous scaffold with a high chitosan content that retained its fibrous structural integrity for cell culture. Analysis of the mechanical properties of the chitosan nanofiber scaffolds in both dry and wet conditions showed that their strength and durability were sufficient for wound dressing applications. Significantly, the wet scaffold underwent remarkable elastic deformation during stretch such that the elongation at break dramatically increased to up to 44% of its original length, showing wavy fiber morphology near the break site. The culture of normal human dermal fibroblast cells onto scaffolds for 1-14days demonstrated that the scaffolds were highly compatible and a suitable platform for cell adhesion, viability, and proliferation. Secretion profiles of wound healing-related proteins to the cell culture medium demonstrated that chitosan fibers were a promising scaffold for wound healing applications. Overall, the dense fibrous network with high porosity of the chitosan nanofiber scaffold and their mechanical properties indicate that they could be used to design and fabricate new materials that mimic the epidermis layer of natural skin.

Photomorphogenesis of Diverse Autonomous Traveling Waves in a Monolithic Soft Artificial Muscle.

Biological organisms (e.g., batoid fish, etc.) possess the remarkable ability to morph their soft, sheet-like tissues into wavy morphologies and self-oscillate to make traveling waves, enabling myriad functionalities in propulsion, locomotion, and transportation. In contrast, current manmade soft robotic systems cannot adaptively make wavy morphologies and concurrently achieve wave propagation because the controllable actuation of desired 3D morphologies in entirely soft materials is a formidable challenge due to their continuously deformable bodies that own a large number of actuable degrees of freedom. Here, we report a bioinspired robotic system that not only allows photomorphogenesis of on-demand 3D wavy morphologies but also enables autonomous wave propagation in a monolithic soft artificial muscle (MSAM). This system employs a conceptually different design strategy based on a combination of two principles derived from plant morphogenesis and the undulatory motion of ray fish. The former offers a shaping principle based on differential growth that enables morphing MSAM into target wavy configurations, while the latter inspires a driving principle that induces autonomous propagation of shaped waves by rhythmic motor patterns. This waving system can be used as adaptive "soft engines/motors" that enable directional locomotion, intelligent transportation of cargo, and autonomous propulsion. It even produces programmable, complex artificial peristaltic waves. Our design allows controllable formation of 3D wavy morphologies and autonomous wave behaviors in the soft robotic system that would be useful for broad applications in adaptive, self-regulated mechanical systems for advanced robotics, soft machines, and energy harvest.

Transitions in the morphology and critical stresses of gliding dislocations in multiprincipal element alloys

Refractory multiprincipal element alloys (MPEAs) are promising material candidates for high-temperature, high-strength applications. However, their deformation mechanisms, particularly at the dislocation scale, are unusual compared to those of conventional alloys, making it challenging to understand the origin of their high strength. Here, using an atomistically informed phase-field dislocation dynamics model, we study transitions in the morphology and critical stresses of long gliding screw dislocations over extended distances in a refractory MPEA. The model MPEA crystal accounts for the atomic-scale fluctuations in chemical composition across the glide planes via spatially correlated lattice energies and for the differences in glide resistances between screw and edge dislocations of unit length. We show that the dislocation moves in a stop-start motion, alternating between wavy morphology in free flight and nearly recovered straight screw orientation in full arrest. The periods of wavy glide are due to variable kink-pair formation and migration rates along the length, where portions with higher rates glide more quickly. The critical stress to initiate motion corresponds to the stress required to form and migrate a kink pair at the weakest region along the length of the dislocation. Heterogeneity in lattice energy leads to variability in the local stress-strain response and to a strain hardening-like response, in which the critical stress to reactivate glide increases with glide distance. Statistical assessment of hundreds of realizations of dislocations indicates that the amount of hardening directly scales with the dispersion in underlying lattice energy.

Effect of flyer plate thickness on wavy interface morphology in the A1050/C1020 magnetic pulse welded joint

Effect of flyer plate thickness on wavy interface morphology in the A1050/C1020 magnetic pulse welded joint

A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

Abstract We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

Linear analysis of Atwood number effects on shear instability in the elastic\u2013plastic solids

The evolution of shear instability between elastic–plastic solid and ideal fluid which is concerned in oblique impact is studied by developing an approximate linear theoretical model. With the velocities expressed by the velocity potentials from the incompressible and irrotational continuity equations and the pressures obtained by integrating momentum equations with arbitrary densities, the motion equations of the interface amplitude are deduced by considering the continuity of normal velocities and the force equilibrium with the perfectly elastic–plastic properties of solid at interface. The completely analytical formulas of the growth rate and the amplitude evolution are achieved by solving the motion equations. Consistent results are performed by the model and 2D Lagrange simulations. The characteristics of the amplitude development and Atwood number effects on the growth are discussed. The growth of the amplitude is suppressed by elastic–plastic properties of solids in purely elastic stage or after elastic–plastic transition, and the amplitude oscillates if the interface is stable. The system varies from stable to unstable state as Atwood number decreasing. For large Atwood number, elastic–plastic properties play a dominant role on the interface evolution which may influence the formation of the wavy morphology of the interface while metallic plates are suffering obliquely impact.

A Wavy-Structured Highly Stretchable Thermoelectric Generator with Stable Energy Output and Self-Rescuing Capability

A Wavy-Structured Highly Stretchable Thermoelectric Generator with Stable Energy Output and Self-Rescuing Capability

On the complete interface development of Al/Cu magnetic pulse welding via experimental characterizations and multiphysics numerical simulations

A complex Al/Cu magnetic pulse welding interface is systematically investigated using experimental characterizations and numerical simulations. A Coupled electromagnetic-mechanical simulation is proposed to compute the impact velocity and impact angle along the entire interface. This model allows to further understand the formation mechanism of various interface characteristics during MPW. The results revealed that the impact velocity gradually decreases in conjunction with the gradual increase of the impact angle. These simulations elucidate the experimentally observed successive interface morphologies, i.e., the unwelded zone, vortex zone, intermediate (IM) layers and wavy interface. Microstructural characterizations show that the IM layers are formed by mechanical mixing combined with melting and are characterized by highly heterogeneous porous zone with random sizes and distributions of void. Subsequently, an Eulerian simulation is proposed to investigate the thermomechanical effects during the wave formation which vastly influence the joint quality. The predicted wavy morphologies, temperature distribution and average equivalent plastic strain along the interface provided a better understanding on the formation steps of the experimentally observed wave morphologies. The actual kinematics during wave generation revealed that the wave was formed with repeated deformation of the interface material. The wave amplitude increases with increasing jetting angle; while the wavelength increases with increasing collision point velocity. The ratio between collision point velocity and impact velocity is found to be the most suitable parameter for explaining the influence of the collision parameters on the wavelength. These results indicate that the combination of the Coupled electromagnetic-mechanical simulation and Eulerian simulation can help us investigate the governing mechanisms of complex interface morphologies and further used to optimize the processing parameters during high speed impact welding.

Lithographically Formed Fine Wavy Surface Morphology for Universal Alignment Control of Mesochannels in Mesostructured Silica Films

In-plane orientation of mesochannels in mesostructured silica films is fully controlled by a lithographically formed anisotropic surface morphology of a substrate. The orientation is determined simply by elastic properties of a liquid crystal phase, which appears in the course of the formation of mesostructured silica films through the sol-gel process. When an array of linear microscopic grooves with a round cross section is closely formed on the substrate surface, the cylindrical mesochannels in the films are entirely aligned strictly perpendicular to the grooves, as a consequence of minimization of the total elastic energy. When the surface morphology geometrically fits to the hexagonal arrangement of the mesochannels, the orientation abruptly changes into the direction parallel to the long axis of the grooves. The alignment control based on the elastic property of the liquid crystal phase described in this report does not require any specific chemical interactions between the surfactant molecules and the substrate surface. Therefore, aligned mesostructured silica films with a large structural periodicity can successfully be formed using block copolymer surfactants, which hardly form an aligned mesostructure without the support of external fields. The vapor-phase synthesis, which enables considerable retardation of the solidification process of siliceous species, is the most favorable way, and totally aligned mesostructured silica films with significantly large thickness, more than 1 μm, can be obtained. Appropriate combination of the bottom-up and the top-down nanoprocesses reported in this paper, that is, self-assembly and photolithography, will enable the formation of highly anisotropic nanostructured materials, which will find various practical applications.

Study on surface state and thermophysical properties of TA15 alloy by laser ablation

The active titanium alloy is prone to form an oxide layer with poor thermal strength and fluffy during hot working. Native morphological defects also affect subsequent processing. In this study, the laser ablation was used to remove the thermally processing oxide layer and modified the surface morphology. The effect of the newly formed oxide layer on the surface thermal diffusivity was studied. As the average power increased, the native morphological defects were modified to the crater morphology. Finally, the wavy fringe morphology was formed. The thermal oxide layer of the untreated sample was composed of TiO2 (anatase), TiO2 (rutile), and Al2O3. After laser ablation, the content of TiO2 (rutile) increased. Cross-sectional morphology observation shows, above 12 W, the oxide layer appeared agitating morphology. It is proved that 12 W is the boundary between the thermal effect and the thermo-mechanical composite effect. The effectiveness of laser ablation in modulating the thermo-physical properties of the surface was verified by thermal diffusivity measurements.

Biocasting of an elastin-like recombinamer and collagen bi-layered model of the tunica adventitia and external elastic lamina of the vascular wall.

The development of techniques for fabricating vascular wall models will foster the development of preventive and therapeutic therapies for treating cardiovascular diseases. However, the physical and biological complexity of vascular tissue represents a major challenge, especially for the design and the production of off-the-shelf biomimetic vascular replicas. Herein, we report the development of a biocasting technique that can be used to replicate the tunica adventitia and the external elastic lamina of the vascular wall. Type I collagen embedded with neonatal human dermal fibroblast (HDFn) and an elastic click cross-linkable, cell-adhesive and protease-sensitive elastin-like recombinamer (ELR) hydrogel were investigated as readily accessible and tunable layers to the envisaged model. Mechanical characterization confirmed that the viscous and elastic attributes predominated in the collagen and ELR layers, respectively. In vitro maturation confirmed that the collagen and ELR provided a favorable environment for the HDFn viability, while histology revealed the wavy and homogenous morphology of the ELR and collagen layer respectively, the cell polarization towards the cell-attachment sites encoded on the ELR, and the enhanced expression of glycosaminoglycan-rich extracellular matrix and differentiation of the embedded HDFn into myofibroblasts. As a complementary assay, 30% by weight of the collagen layer was substituted with the ELR. This model proved the possibility to tune the composition and confirm the versatile character of the technology developed, while revealing no significant differences with respect to the original construct. On-demand modification of the model dimensions, number and composition of the layers, as well as the type and density of the seeded cells, can be further envisioned, thus suggesting that this bi-layered model may be a promising platform for the fabrication of biomimetic vascular wall models.

Effect of Process Parameters on Wavy Interfacial Morphology During Magnetic Pulse Welding

Abstract Magnetic pulse welding (MPW) is a solid-state welding process that bonds similar and dissimilar metals using a high velocity collision. In this paper, effects of impact velocity, target tube thickness, and mandrel inclusion on the interfacial morphology were investigated through the welding of tubular parts, Al6060T4 (flyer) to Cu-ETP (target), by electromagnetic compression. The hypothesis tested in this research is that a “well-supported target,” i.e., either a thick target or the support of a mandrel, allows for vortices to be created at the interface during MPW provided that the impact velocity is sufficient. The mandrel used in the experiments was polyurethane with a Shore hardness of 92A, which was pre-stressed via a washer and nut. The impact velocity was measured via photon Doppler velocimetry (PDV) and used for the setup of numerical simulations. A 2D axisymmetric numerical model was implemented in LS-DYNA to predict the interfacial morphology. Thermal analyses in the numerical model were used to predict the local melting locations and compared with experimental observations. Both experimental and numerical results showed that the interfacial wavelength increased with an increase in the impact velocity and target thickness. Similarly, a thin target with mandrel support also caused an increase in the wavelength. Vortices were only generated with appropriate impact velocities and well-supported targets, i.e., again either a thick target or the support of a mandrel.

Microstructure and Crystallographic Texture Changes under Torsion Loading of Pearlitic Steel Strips

Cold-drawn pearlitic steel strips exhibit a great combination of strength and ductility and are widely used in many engineering applications. Some of these applications require further mechanical conformation for the final use. An analysis of the microstructure and the change in crystallographic texture when strips are subjected to torsion processes necessary for some applications was made in the current study. It was shown that the formation of the wavy pearlite morphology associated with the fiber texture parallel to the drawing axis could improve fatigue damage. Extreme dislocation densities and crystallographic defects induced by torsion enhanced the formation of ultrafine ferritic grains accompanied by partial cementite decomposition. The relationship between ferrite and cementite interfaces successfully simulated using the Shackleton model.

Defect reconfiguration in a Ti-Al alloy via electroplasticity.

It has been known for decades that the application of pulsed direct current can significantly enhance the formability of metals. However, the detailed mechanisms of this effect have been difficult to separate from simple Joule heating. Here, we study the electroplastic deformation of Ti-Al (7 at.% Al), an alloy that is uniquely suited for uncoupling this behaviour because, contrary to most metals, it has inherently lower ductility at higher temperature. We find that during mechanical deformation, electropulsing enhances cross-slip, producing a wavy dislocation morphology, and enhances twinning, which is similar to what occurs during cryogenic deformation. As a consequence, dislocations are prevented from localizing into planar slip bands that would lead to the early failure of the alloy under tension. Our results demonstrate that this macroscopic electroplastic behaviour originates from defect-level microstructural reconfiguration that cannot be rationalized by simple Joule heating.

Comparison between Explosive Welding and Roll-Bonding Processes of AA1050/Mg AZ31B Bilayer Composite Sheets Considering Microstructure and Mechanical Properties

In this article, the effect of the manufacturing process on the microstructure and mechanical properties of AA1050/Mg-AZ31B bilayer composite sheets has been studied experimentally. In multilayer composite sheets, the interface bond strength plays a significant role in the mechanical properties of the composite. The most important factor affecting the bond strength is the manufacturing process of these sheets. So, two processes of explosive welding and roll bonding have been used to manufacture the bilayer composite sheets. The results show that the atomic diffusion in the interface is 6.5 microns in the explosive welding and 6.7 microns in the roll bonding. No intermetallic compounds have been observed in the interface of the studied bonding methods. The wavy and straight interface morphologies have been observed for explosive welding and roll bonding, respectively. Also, recrystallization has been observed in the microstructure of both methods. In the magnesium microstructure of rolled sample, twinning and deformation bands have been seen, while adiabatic shear bands have been formed in the explosive-welded sample. The ultimate tensile strength, elongation, and work of fracture (WOF) of explosive-welded sheets have been increased by 145%, 31%, and 407% relative to the rolled sheets, respectively. Besides, considering the separation of layers in the tensile test of rolled sheets compared to explosive welded ones, it can be stated that the structural failure in explosive welding occurs simultaneously for all layers. However, for roll bonding, the layer failure is independent of the entire structure failure. In this case, first, necking and fracture of the magnesium layer occur, and then, after the separation of the interface, the fracture of the aluminum layer happens.

Three-layered SS321/AA1050/AA5083 explosive welds: Effect of PWHT on the interface evolution and its mechanical strength

In this study, the effect of post-weld heat-treatment (PWHT) on the interface microstructure and its mechanical properties in the three-layered explosive welded (EXWed) SS321/AA1050/AA5083 joints fabricated with different stand-off distances were investigated. The welded specimens were heat-treated at 250 and 350 °C for 1000–10000 s. The microscopy studies exhibited that the AA5083/AA1050 interface was smooth and continuous in all conditions and was free of cracks since the SS321/AA1050 interface contained a reaction layer with variable thickness, having discontinuous and wavy morphology including some transverse and longitudinal cracks. As the stand-off distance increased, the SS321/AA1050 interface appearance altered from smooth to be wavier, and the average thickness of the developed reaction layer was enhanced from 4.95 to 6.7 μm. By PWHT, the thickness of the interfacial layer increased in proportion to the diffusion kinetics and reached a maximum of 18.56, and 15.02 μm for samples joined with a stand-off distance of 6.75 and 6 mm, respectively. For specimens with a stand-off of 6.75 and 6 mm, the diffusion driving energy values were 46.6 and 42.4 kJ mol−1, respectively, while the constant diffusion values were calculated to be 142.2 and 45.3 m2 s−1, respectively. For the samples with an applied distance of 6.75 mm, by increasing the treatment temperature and retention time, the average concentration of aluminum in the reaction layer increased since the concentration of iron decreased. Moreover, the compressive-shear strength was declined from 94.6 to 56.7 MPa. For the sample with a longer stand-off distance, lower shear strength reduction was examined after thermal treatment due to higher collision energy, the formation of wavy interface with larger amplitude, and greater plastic deformation, as well as, stronger mechanical interlocking.

Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

Explosive welding technique is widely used in many industries. This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods. Interlayer plays an important role to improve the welding quality and control energy loss during the collision process. In this paper, the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer. Microstructure details of welded composite plate were observed through optical and scanning electron microscope. Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices. Moreover, the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of Cu–Ti, i.e. CuTi, Cu2Ti, CuTi2, Cu4Ti, etc. To study the mechanical properties of composite plates, mechanical tests were conducted, including the tensile test, bending test, shear test and Vickers hardness test. Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method, Euler and Arbitrary Lagrangian-Eulerian method. The multi-physics process of explosive welding, including detonation, jetting and interface morphology, was observed with simulation. Moreover, simulated plastic strain, temperature and pressure profiles were analysed to understand the welding conditions. Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates. At the collision point, both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the experimental results.

Self-assembly in rod/coil block copolymers: Degenerate behavior under nonconfinement

The self-assembly of block copolymers containing rigid blocks have received abiding attention due to its rich phase behavior and potential for use in a variety of applications. In this work, under asymmetric interactions between rod/coil components, the self-assembly of coil/coil/rod ABC triblock copolymers is studied using self-consistent field of lattice model. In addition to micelles, centrosymmetric lamellae (CSLM), lamellae, perforated lamellae, strips and gyroids, non-centrosymmetric (NCSLM) lamellae and wavy morphologies are observed as stable phases. The phase diagram of interaction between rod and coil components versus the rod fraction is constructed given a fixed interaction between coil components. For intermediate rod fraction, degenerate behavior is observed. NCSLM and CSLM are degenerate structures. It is found that the entropy of chain conformation plays an important role for this rich behavior. A mechanism of the degenerate behavior is proposed in coil/rod block copolymers under noncofinement. This study provides some new insights into the degenerate behavior of block compolymers, which can offer a theoretical reference for related experiments.

Structure and morphology of CrSi<sub>2</sub> layers formed by rapid thermal treatment

The formation of chromium disilicide layers on n-type single crystal silicon substrates (111) during rapid thermal annealing in heat balance mode by the methods of Rutherford backscattering, X-ray diffraction and transmission electron microscopy of cross sections was investigated. Chromium films of about 30 nm thickness were deposited by magnetron sputtering of a chromium target with argon ions onto silicon substrates at room temperature. The rapid thermal treatment was carried out in a temperature range of 200 to 550 °C in a heat balance mode by irradiating the substrates backside with a non-coherent light flux of quartz halogen lamps in a nitrogen ambient for 7 s. It was established that hexagonal phase of chromium disilicide formation with grain size of 150–300 nm occurs in a threshold manner when the temperature of rapid thermal treatment exceeds 400 °C. At the same time, there are strong changes in the films surface morphology and surface roughness, and a silicide-silicon interface occur. In this case the wavy film surface morphology practically repeats silicide-silicon interface morphology (the surface exactly replicates the interface). The mechanism of CrSi2/Si interface structure roughness formation based on consideration of Kirkendall effect and deformation-stimulated diffusion of vacancies is proposed and discussed. The research results of the structure and morphology of CrSi2 layers on silicon are well-correlated with the results of the Schottky barrier electrophysical measurements. The results obtained can be used in microelectronics for forming rectifying contacts and interconnects metallization for integrated circuits, as well as for thermoelectric and optoelectronic applications.