Search Results (85)

Polymer co-extrusion experiments are described simulating the dynamics of two different magmas (e.g., silicic and mafic having different viscosities) flowing simultaneously in a vertical volcanic pipe or conduit which results in the effusion of composite lava domes on the surface. These experiments, involving geologically realistic conduit length-to-diameter aspect ratios of 130:1 or 380:1, demonstrate that co-extrusion of magmas having different viscosities can explain not only the observed normal zoning observed in planar dikes and the pipelike conduits that evolve from dikes but also the compositional layering of effused lava domes. The new results support earlier predictions, based on observations of induced core-annular flow (CAF), that dike and conduit zoning along with dome layering are found to depend on the viscosity contrast of the non-Newtonian (shear-thinning) magmas. Any magma properties creating viscosity differences, such as crystal content, bubble content, water content and temperature may also give rise to the CAF regime. Additionally, codependent flow behavior involving the silicic and mafic magmas may play a significant role in modifying the nature of volcanic eruptions. For example, lubrication of the flow by an annulus of a more mafic, lower-viscosity component allows a more viscous but more volatile-charged magma to be injected rapidly to greater vertical distances along a dike into a lower pressure regime that initiates exsolving of a gas phase, further assisting ascent to the surface. The rapid ascent of magmas exsolving volatiles in a dike or conduit is associated with explosive silicic eruptions. Full article

Nanoindentation can be leveraged to aid in the high fidelity modeling of dislocation mediated plasticity in pentaerythritol tetranitrate (PETN), an anisotropic energetic molecular crystal. Moreover, nanoindentation tip parameters such as tip geometry, size, and degree of acuity can be utilized to target anisotropic behavior. In this work, nanoindentation was conducted across a range of orientations on the (110) face of PETN to characterize resultant yield behavior, mechanical property measurements, and resultant slip behavior and fracture initiation. Three different indentation tips were utilized: a 3-sided pyramidal Berkovich tip, a 4-sided high aspect ratio Knoop tip, and a 90° conical tip. Ultimately, indenter tip radius was documented to impact yield behavior, whereas tip geometry affected larger scale processes such as slip, and tip acuity was the dominating factor that led to fracture. The axisymmetric conical tip, serving as a baseline, showed the least amount of variation in mechanical property measurements but also the largest distribution of maximum shear stress at which initial yielding occurred. Its high degree of acuity, however, was more prone to induce fracture at higher loads. The Knoop tip was shown to be suitable for average measurements, but also for elucidation of certain anisotropic features. A distinctly higher perceived hardness at 45° was measured with the Knoop tip, indicating less dislocation motion in that direction also observed in this work via scanning probe microscopy. Lastly, the commonly used Berkovich tip was a good compromise whereby it provided a representative volume element describing the average behavior of the material. These results can be utilized to target desired anisotropic behavior in a wider range of molecular crystals, as well as to inform theoretical considerations for dislocation mediated plasticity in PETN. Full article

The present work investigates the rheological behavior of ceramic slurries made of hydroxyapatite powders doped with magnesium and strontium ions and selected as particularly relevant for biomedical applications. The incorporation of doping ions into the apatite crystal structure is a well-known way to enhance the bioactivity of hydroxyapatite through compositional and structural changes, however, this also affects the rheological properties relevant to the fabrication of ceramic devices by forming techniques based on the manipulation of aqueous slurries. We analyzed the effect of different apatitic chemical compositions, powder content, and dispersant amount on the shear behavior and flowability of slurries, thus finding that the structural changes in hydroxyapatite induced by ion doping significantly affected the colloidal stability of the apatite powders and the viscoelasticity of the slurries. This leads to improved rheological behavior in the hydroxyapatite suspensions, which is suitable for the future development of ceramic slurries, particularly for achieving novel ceramic devices by extrusion-based techniques. Full article

A study of the azimuthal variation in the surface wave fundamental-mode phase velocity is performed for the Philippine Sea Plate (PSP). This azimuthal variation has been anisotropically inverted for the PSP to determine the isotropic and anisotropic structure of this plate from 0 to 260 km. This azimuthal variation is due to anisotropy in the upper mantle. The crust is found in an isotropic structure, but the lithosphere and asthenosphere exhibit anisotropic structures. For the lithosphere, the main cause of anisotropy is the alignment of anisotropic crystals approximately parallel to the direction of seafloor spreading, and the fast axis of the seismic velocity is in the direction of ~163° of azimuth. For the asthenosphere, the seismic anisotropy can be derived from the lattice-preferred orientation (LPO) in response to the shear strains induced by mantle flow, and the fast axis of the seismic velocity is also the direction of ~163° of azimuth. This result suggests that a mantle flow pattern may occur in the asthenosphere and seems to be approximately parallel to the direction of seafloor spreading observed for the lithosphere. Finally, the changes in the parameter ξ with depth are studied to estimate the depth of the lithosphere–asthenosphere boundary (LAB), observing a clear change in this parameter at 80 km depth. Full article

Soil erosion is a serious environmental problem that leads to land degradation and ecological imbalance, thereby eliciting extensive and profound worldwide concern. Biological soil crusts (biocrusts) play a crucial role in soil stabilization; however, the underlying microbial enzymatic mechanisms remain poorly understood. The present study aimed to characterize carbonatogenic bacteria and investigate the role of their carbonic anhydrase-induced carbonate crystals in promoting soil shear strength within biocrusts. The results demonstrated a significant increase in the activity of carbonic anhydrase during biocrust formation and development (p < 0.05). A total of 35 strains exhibiting carbonic anhydrase activity were isolated from biocrusts, belonging to Actinomycetota, Bacillota, Pseudomonadota and Cyanobacteriota. The subsequent investigation revealed a positive correlation between the carbonic anhydrase activities of the strains and the shear strength during sand consolidation. Specifically, strain SCSIO19859, a type of cyanophyta, exhibited the highest carbonic anhydrase activity, of 1.50 U/mL. It produced 0.70 g/day of calcium carbonate and demonstrated a shear strength that was 6.09 times greater than that of the control group after sand consolidation for seven days of incubation under optimal conditions. X-ray diffraction and scanning electron microscope analysis revealed that SCSIO19859 produced calcite and vaterite carbonates, which significantly increased the shear strength of the sand grains (p < 0.05). This study provides evidence for the ecological function of biocrusts in promoting soil erosion resistance from the perspective of carbonatogenic bacteria-derived carbonic anhydrase. The functional strains with carbonic anhydrase obtained from this study have significant potential applications in enhancing soil erosion resistance. Full article

An experimental study is conducted on the surface shear stress vector distribution on a plate in a supersonic jet flow, with a focus on the separation region. The shear-sensitive liquid crystal coating (SSLCC) technique is employed for the flow visualization and measurement, which is based on the shear stress distribution, and the flow pattern on the plate is captured. The results demonstrate that the nozzle pressure ratio (NPR) is the main inducement to flow evolution, and a high NPR causes a separation region on the plate, where the adverse flow is challenging to the SSLCC technique. Therefore, an improved measurement method for the SSLCC is proposed to successfully obtain the wall shear stress distribution inside the separation and reattachment area. The flow structures on the plate, including the separation and reattachment positions and vortex and adverse flows, are accurately captured in detail, which indicates that this method is practical for measuring the wall shear stress in separated flow. Full article

In recent years, wind energy has emerged as one of the fastest-growing green technologies globally, with projections indicating that decommissioned wind turbine blades (WTBs) will accumulate to millions of tons by the 2030s. Due to their thermosetting nature and high glass/carbon fiber content, the efficient recycling of WTBs remains a challenge. In this study, we utilized solid-state shear milling (S3M) to produce a fine WTB powder, which then underwent surface modification with a silane coupling agent (KH550), and we subsequently fabricated WTB-reinforced polypropylene (PP) composites with enhanced mechanical performance through solid-state stretching. The stretching-process-induced orientation of the PP molecular chains and glass fibers led to orientation-induced crystallization of PP and significant improvements in the mechanical properties of the PP/WTB@550 composites. With 30 wt. % WTB content, the PP/WTB@550 composite achieved a tensile strength of 142.61 MPa and a Young’s modulus of 3991.19 MPa at a solid-state stretching temperature of 110 °C and a stretching ratio of 3, representing increases of 268% and 471%, respectively, compared to the unstretched sample. This work offers both theoretical insights and experimental evidence supporting the high-value recycling and reuse of WTBs through a cost-effective, environmentally friendly, and scalable approach. Due to the enhanced mechanical properties of the PP/WTB composite and the intrinsic waterproofing and corrosion resistance of PP, it is hoped that such a composite would be used in road engineering and building materials, such as geogrids, wall panels, floor boards, and floor tiles. Full article

Molybdenum disulfide is a 2D material with excellent lubricant properties, resulting from weak van der Waals forces between lattice layers and shear-induced crystal orientation. The low forces needed to shear the MoS₂ crystal layers grant the tribological system low coefficients of friction (COF). However, film oxidation harms its efficacy in humid atmospheres, leading to an increased COF and poor surface adhesion, making its use preferable in dry or vacuum conditions. To overcome these challenges, doping MoS₂ with elements such as Nb, Ti, C, and N emerges as a promising solution. Nevertheless, the adhesion of these coatings to a steel substrate presents challenges and strategies involving the reduction in residual stresses and increased chemical affinity to the substrate by using niobium-based materials as interlayers. In this study, Nb-doped MoS₂ films were deposited on H13 steel and silicon wafers using the pulsed direct current balanced magnetron sputtering technique. Different niobium-based interlayers (pure Nb and NbN) were deposited to evaluate the adhesion properties of Nb-doped MoS₂ coatings. Unlubricated scratch tests, conducted at room temperature and relative humidity under a progressive load, were performed to analyze the COF and adhesion of the coating. Instrumented indentation tests were conducted to assess the hardness and elastic modulus of the coatings. The microstructure of the coatings was obtained by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Transmission Electron Microscopy (TEM), with Energy-Dispersive X-Ray Spectroscopy (EDS). Results indicated that niobium doping on MoS₂ coatings changes the structure from crystalline to amorphous. Additionally, the Nb concentration of the Nb:MoS₂ coating changed the mechanical properties, leading to different cohesive failures by different loads during the scratch tests. Results have also indicated that an NbN interlayer optimally promoted the adhesion of the film. This result is justified by the increase in hardness led by higher Nb concentrations, enhancing the load-bearing capacity of the coating. It is concluded that niobium-based materials can be used to enhance the adhesion properties of Nb-doped MoS₂ films and improve their tribological performance. Full article

We studied the rheological properties under both shear and elongational flow and crystallization behaviors after shear history for binary blends of poly(lactic acid) (PLA) and ethylene–vinyl acetate copolymer (EVA) with a slightly lower shear viscosity. EVA was immiscible with PLA and dispersed in droplets in the blend. The addition of EVA significantly reduced the shear viscosity, which is attributed to the interfacial slippage between PLA and EVA. In contrast, under elongational flow, the addition of EVA provided strain hardening in the transient elongational viscosity. Consequently, the degree of neck-in behavior in T-die extrusion, i.e., a decrease in the film width, was reduced with the high orientation of the PLA chains. Furthermore, it was found that the addition of EVA accelerated the shear-induced crystallization of PLA, although EVA showed no nucleating ability without a flow field. Because the EVA addition can improve the mechanical toughness, this modification technique is attractive for various industrial applications of PLA. Full article

In this work, a coating method was used to prepare a liquid crystal physical gel with a high orientation of liquid crystal molecules, excellent electrical conductivity, and mechanical stability. The liquid crystal matrix used was nematic phase liquid crystal (5CB), the gel factor was polyvinyl alcohol (PVA), and the conductive filler was carbon nanotubes/polyaniline (CNT/PANI). Chemical in situ polymerization was used to create CNT/PANI composites, wherein polyaniline encapsulates the carbon nanotubes to enhance their dispersion. At 4 mm/s, 7.2 N of coating pressure, and 72 s of interval duration, the shear flow-induced orientation was achieved. The consistent and large-area orientation of the liquid crystal molecules was realized and the orientation direction of the liquid crystal molecules was parallel to the coating direction. Additionally, a type of stress sensor assembly based on multiple coating demonstrated a good sensor performance in the 90° bending test and high sensitivity in the 20% tensile test, with a sensor sensitivity of 23.25. Regarding the use of liquid crystal materials in flexible electronic devices, it is quite important. Full article

The decades-long paradigm of continuous and perpetual lamellar twisting constituting banded spherulites has been found to be inconsistent with several recent studies showing discontinuity regions between consecutive bands, for which, however, no explanation has been found. The present research demonstrates, in three different semicrystalline polymers (HDPE, PEG10000 and Pluronic F-127), that sequential transcrystallinity is the predominant mechanism of banded spherulite formation, heterogeneously nucleated on intermittent self-shear-oriented amorphous layers excluded during the crystals’ growth. It is hereby demonstrated that a transcrystalline layer can be nucleated on amorphous self-shear-oriented polymer chains in the melt, by a local melt flow in the bulk or in contact with any interface—even in contact with the interface with air, e.g., in contact with an entrapped air bubble or at the edges of the sample—or nucleated following the multiple directions and orientations induced by a turbulent flow. The bilateral excessive local exclusion of amorphous non-crystallizable material, following a short period of initial non-banded growth, is found to be the source of dislocations leading to spirally banded spherulites, through the transcrystalline layers’ nucleation thereon. The present research reveals and demonstrates the sequential transcrystalline morphology of banded spherulites and the mechanism of its formation, which may lead to new insights in the understanding and design of polymer processing for specific applications. Full article

Resistant starch (RS) has the advantage of reshaping gut microbiota for human metabolism and health, like glycemic control, weight loss, etc. Among them, RS3 prepared from pure starch is green and safe, but it is hard to achieve structural control. Here, we regulate the crystal structure of starch with different chain-length distributions (CLDs) via extrusion at low/high shearing levels. The change in CLDs in extruded starch was obtained, and their effects on the fine structure (Dm, d_Bragg, d_Lorentz, degree of order and double helix, degree of crystal) of RS and its physicochemical properties were investigated by SAXS, FTIR, XRD and ¹³C NMR analyses. The results showed that the RS content under a 250 r/min extrusion condition was the highest at 61.52%. Furthermore, the crystalline system induced by high amylopectin (amylose ≤ 4.78%) and a small amount of amylose (amylose ≥ 27.97%) was favorable for obtaining a high content of RS3-modified products under the extruding environment. The control of the moderate proportion of the A chains (DP 6–12) in the starch matrix was beneficial to the formation of RS. Full article

Polylactic acid (PLA) is a biobased, biodegradable, non-toxic polymer widely considered for replacing traditional petroleum-based polymer materials. Being a semi-crystalline material, PLA has great potential in many fields, such as medical implants, drug delivery systems, etc. However, the slow crystallization rate of PLA limited the application and efficient fabrication of highly crystallized PLA products. This review paper investigated and summarized the influence of formulation, compounding, and processing on PLA’s crystallization behaviors and mechanical performances. The paper reviewed the literature from different studies regarding the impact of these factors on critical crystallization parameters, such as the degree of crystallinity, crystallization rate, crystalline morphology, and mechanical properties, such as tensile strength, modulus, elongation, and impact resistance. Understanding the impact of the factors on crystallization and mechanical properties is critical for PLA processing technology innovations to meet the requirements of various applications of PLA. Full article

It is generally known that the incorporation of crystals in the glass matrix can enhance the ductility of metallic glasses (MGs), at the expense of reduced strength, and that the deformation of MGs, particularly during shear banding, can induce crystal formation/growth. Here, we show that these known trends for the interplay between crystals and deformation of MGs may hold true or become inverted depending on the size of the crystals relative to the shear bands. We performed molecular dynamics simulations of tensile tests on nanocrystal-bearing MGs. When the crystals are relatively small, they bolster the strength rather than the ductility of MGs, and the crystals within a shear band undergo redissolution as the shear band propagates. In contrast, larger crystals tend to enhance ductility at the cost of strength, and the crystal volume fraction increases during deformation. These insights offer a more comprehensive understanding of the intricate relationship between deformation and crystals/crystallization in MGs, useful for fine-tuning the structure and mechanical properties of both MGs and MG–crystal composites. Full article

Mineral transformations often induce microstructural deteriorations during temperature variations. Hence, it is crucial to understand why and how this microstructure weakens due to mineral alteration with temperature and the correlated physical and mechanical responses. Therefore, in this study, physical, chemical, thermal, petrographic, and mechanical analyses were carried out to comprehend better the thermal behaviors of Egyptian granodiorite exposed to temperatures as high as 800 °C. The experimental results indicate that the examined attributes change in three distinct temperature phases. Strength zone (up to 200 °C): During this phase, the temperature only slightly impacts the granodiorite mass loss and porosity, and the P-wave velocity and E slightly decrease. However, the rock structure was densified, which resulted in a minor increase in strength. After that, the transition zone (200–400 °C) was distinguished by the stability of most studied parameters. For instance, mass and porosity did not significantly alter, and the uniaxial compressive strength steadily increased with an axial failure mode. When the temperature rises, transgranular cracks cause the P-wave velocity and elastic modulus to decrease moderately. The decay zone started after 400 °C and continued to 800 °C. This zone is characterized by complicated factors that worsen the granodiorite properties, lead to color shift, and produce a shear failure mode. The properties of granodiorite became worse because of chemical reactions, structural and crystal water evaporation, rising thermal expansion coefficient variation, and quartz inversion at 575 °C (α to β, according to the differential thermal analysis). Thermal damage greatly affected granodiorite’s physical and mechanical properties and microstructure at 800 °C. As a result, UCS measurements were extremely small with a complex failure pattern, making Vp and E unattainable. Full article