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Left ventricular mechanical dyssynchrony after chemotherapy in breast cancer patients with normal rest gated SPECT-MPI.

Early diagnosis of chemotherapy-induced cardiotoxicity plays an important role in preventing heart failure. The main aim of our study was to assess left ventricular (LV) dyssynchrony measured by phase analysis of gated single-photon emission computed tomography (SPECT) as an early sign of cardiotoxicity after breast cancer chemotherapy. This cross-sectional study was conducted on patients with stage ≤ 3 breast cancer and no history of cardiovascular disease or diabetes. After mastectomy, the patients underwent rest gated SPECT myocardial perfusion imaging (MPI). Sixty patients with normal gated SPECT-MPI were selected and the imaging was performed after chemotherapy with doxorubicin, cyclophosphamide and paclitaxel. LV function and contractility parameters were extracted by QGS software and the results were compared with the t test method. The abnormality of at least one of the three phase analysis indices was considered as left ventricular dyssynchrony (LVD). The average LV end-systolic volume and ejection fraction (LVEF) before and after chemotherapy were (16.2 ± 8.0ml and 21.6 ± 11.6ml) and (73.4 ± 7.9% and 67.5 ± 9.2%) respectively, which showed a significant decrease (P < 0.05). In 2 patients (3.3%), the LVEF decreased to less than 50% after chemotherapy. The average parameters of left ventricular contractility before and after chemotherapy were, respectively, as follows: PHB (24.1 ± 7.5 and 33.8 ± 16.4), PSD (9.4 ± 6.1 and 5.7 ± 1.9) and entropy (28.9 ± 7.1 and 35.6 ± 9.7), which showed a significant increase (P < 0.05). LVD was observed in 14 patients (23.4%) after chemotherapy and prevalence of LVD was significantly higher in patients who had received a cumulative dose of doxorubicin of more than 400mg/m2 (P = 0.005). There was no relationship between age and body mass index with the incidence of LVD after chemotherapy (P > 0.05). Using phase analysis of gated SPECT-MPI, chemotherapy-induced LVD was seen in a significant number of patients with breast cancer, especially with a high cumulative dose of doxorubicin. LVD might indicate chemotherapy-induced cardiotoxicity before LVEF becomes abnormal.

Influence of distribution and size of graphite particle on the machinability of nodular cast iron

Nodular cast iron (NCI), also known as particulate metal matrix composites (PMMCs), is extensively utilized in the manufacturing of pistons for high-power engines. However, poor machinability is a significant problem due to the inherent microstructural inhomogeneity of the NCI. Therefore, this study aims to investigate influence of graphite particle distribution and size on the machinability of NCI. Microstructure of NCI is experimentally examined and quantitatively analyzed, and NCI is treated as a three-phase composite (i.e., matrix-interface-graphite particles). Graphite particles are considered as a plastic material, and debonding of interfaces is taken into account. Based on average particle size and volume fraction of graphite nodules, four microstructural models with different particle sizes and distributions are discussed, and turning experiments are conducted to validate simulation results. The findings reveal that graphite particles of different sizes and distributions affect stress–strain distribution in the cutting region of the material. As the distance between the graphite particles and the cutting tool increases, their influence on the stress–strain distribution becomes less significant. Furthermore, random distribution of graphite particles is more likely to result in complex crack initiation and expansion, leading to more pronounced serrated chips. The distribution of graphite particles has a more significant impact on the stability of cutting forces compared to the particle size. Both experiments and simulation results show that cavities and burrs are appeared along the cutting path because of graphite nodules, which reduces the surface quality and affects the subsequent use of the parts. On the one hand, the present work provides guidance for the finite element modelling of NCI, which is helpful to improve the precision of cutting simulation. On the other hand, by integrating advanced manufacturing technology to regulate the microstructure and cutting parameter of NCI, the present study can provide data basis and numerical analysis support for improving the machinability of NCI.

Quantifying the influence of microstructure on the corrosion of Mg-Li alloys by using X-ray CT

The microstructure of multi-component Mg-Li alloys played a decisive role in their corrosion properties due to the potential differences between the matrix and the secondary phases. In this study, the effects of secondary phases (AlLi, AlX(Gd, Y, Mn), and Mg2Sn) on the corrosion behavior of Mg-Li alloys have been quantified by using in situ X-ray CT. The microstructure-property correlation was established between the type, morphology, distribution, and dimensions of the secondary phases and the microscopic corrosion behavior. The corrosion parameters, such as average equivalent diameter, distance, number density, and volume fraction of the secondary phases and corrosion pits, were quantified as a function of corrosion time. The dominating secondary phase was identified by combining SKPFM analysis and electrochemical testing, giving quantitative information on corrosion control by designing secondary phases.

Numerical Modeling of Two-Phase Flow inside a Wet Flue Gas Absorber Sump

A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air.

Experimental study on fracture propagation in anisotropy rock under cyclic hydraulic fracturing

Hydraulic fracturing is commonly used to enhance the hydraulic conductivity of geothermal, oil, and gas reservoirs, particularly those situated in enclosed and unconventional formations. Shale oil and gas reservoirs exhibit distinct characteristics in rock mechanics parameters, morphology, natural fracture geometry, and geological features. Structural anisotropy in materials generally arises from changes in grain type and size, weak layering, and variations in layering angles. This study aims to investigate the impact of two key factors, namely cyclic injection and structural anisotropy, on the hydraulic fracturing process. To achieve this goal, the phenomenon of hydraulic fatigue in rock was examined through various cyclic injection methods, and true-triaxial hydraulic fracturing tests were conducted on cubic samples composed of different materials and layers. To evaluate and analyze the fracture morphology of these samples, CT scan X-ray imaging technology was employed. The results revealed that samples subjected to cyclic injection exhibited an average breakdown pressure approximately 30% lower than those subjected to monotonic injection. Fracture geometry in the cyclic injection samples displayed a network pattern with multiple crack branches, while monotonic injection primarily resulted in a single-surface pattern. In samples with differences in horizontal stress, the anisotropy of the sample did not affect the fracture, and the single fracture surface extended in the direction of maximum stress. The energy generated by cyclic injection using the damage-controlled method (cycle duration: 16 s) was concentrated around the borehole, creating a complex fracture network with shorter crack lengths. Conversely, cyclic injection using the ramp signals method (cycle duration: eight seconds) produced more straightforward cracks with greater expansion and penetration. Examination of CT scan images of the fractured samples revealed average tortuosity and fracture volume fraction parameters of 1.117 and 0.027 for cyclic injection, respectively, in contrast to 1.026 and 0.008 for monotonic injection. Furthermore, the S-N damage model based on the results of true-triaxial hydraulic fracturing was introduced to describe rock damage behavior and the concept of fatigue under cyclic loads.

Determining the Role of Acicular Ferrite Carbides in Cleavage Fracture Crack Initiation for Two Medium Carbon Microalloyed Steels.

Two medium-carbon microalloyed steels with a predominant acicular ferrite microstructure were investigated in this study in order to determine the initial micro-crack formation mechanism and the role of acicular ferrite structure in cleavage fracture. In order to ensure cleavage fracture, samples were investigated at -196 °C for uniaxial tension and four point bending fracture. Previous investigations have shown that cleavage fracture for steels with a predominant acicular ferrite microstructure has not been initiated by the fracture of coarse TiN particles as in ferrite-pearlite, bainite, or martensitic microalloyed steels. The average maximal thickness of cementite plates measured in this work is 0.798 µm and 0.966 µm, for V and TiV steel, respectively. The corresponding stress values required for their fracture according to Griffith's equation are 1970 MPa and 1791 MPa, respectively. Estimated values of the effective surface energy for the V steel with an average cementite volume fraction of 3.8% range from 40 Jm-2 to 86 Jm-2, and for the TiV steel with an average cementite volume fraction of 18.3% range from 55 Jm-2 to 82 Jm-2. The fracture of coarse cementite plates was found to not to be responsible for the cleavage fracture initiation in case of both steels.

Short-Term Evaluation of Bone-ACL-Bone Complex Allograft in ACL Reconstruction in a Rabbit Model.

The study is to evaluate incorporation of a bone-anterior cruciate ligament-bone (B-ACL-B) allograft in anterior cruciate ligament (ACL) reconstruction in a rabbit model. A total of 61 New Zealand white rabbits were used, with 23 donor rabbits for harvesting B-ACL-B allografts and 38 recipient rabbits undergoing unilateral ACL reconstruction with B-ACL-B allograft. Animals were euthanized for biomechanical testing, micro-computed tomography examination, histological analysis, multi-photon microscopy and transmission electron microscopy testing at 2, 4 and 8 weeks after surgery. Gross inspection and radiographs confirmed the intact ACL allograft in the proper anatomic position. Progressive healing occurred between the bone block and the bone tunnel as demonstrated by a gradual increase in average bone volume fraction and total mineral density at 4 and 8 weeks. Histological analysis showed new bone formation at the bone block-tunnel interface, with maintenance of the native ACL enthesis. Ultrastructural analysis demonstrated the maintenance of overall collagen matrix alignment, while there was repopulation with smaller diameter collagen fibrils. There was no significant difference between 4 and 8 weeks in mean failure force (p = 0.39) or stiffness (p = 0.15) for the B-ACL-B allografts. This study demonstrates the restoration of the normal anatomy of the ACL and progressive graft incorporation and remodeling using a B-ACL-B allograft for ACL reconstruction in the rabbit knee.

A comprehensive numerical study based on topology optimization for cooling plates thermal design of battery packs

This article focuses on the problem of fluctuating cooling system flow caused by different working states such as acceleration and braking during the actual operation of electric vehicles, which prevents the system from effectively dissipating heat from the battery for a long time. In the past, liquid cooling heat dissipation schemes designed based on structural parameters often relied on the experience of CFD engineers. There is no in-depth study of the heat propagation characteristics. At present, research on the application of topology optimization method in cooling plate design mainly focuses on the relative positions of single inlet and outlet, objective functions, and constraint conditions. There are very few studies evaluating the adaptability of different cooling plate structures at different flow rates. In this perspective, this work proposes a two-dimensional topology optimization method for obtaining the cooling plates with different topological structures such as the series of cooling plate structures with dual entrances and exits. The method comprises of a comprehensive study on variations of the inlet flow rate under different average fluid volume fraction, outlet width, and temperature weight conditions. The results indicate that setting an excessive inlet flow rate can actually lead to an increase in the average temperature of the optimized cooling plate. Subsequently, the cooling plate structure obtained through topology optimization at inlet flow rates of 0.015 m/s, 0.02 m/s, and 0.025 m/s was selected, and a three-dimensional electrothermal fluid coupling model was established based on its two-dimensional channel structure. Its cooling performance, flow characteristics, and heat transfer characteristics were analyzed, and compared with two straight channel reference models. The results indicate that the optimized cooling plate structure under low flow conditions has better heat dissipation performance. At a flow rate of 0.56 × At 10-6m3/s, compared to traditional cooling plates(CASE D, CASE E), the highest temperature of the battery using topology optimized cooling plates (CASE A) decreased by 3.5 K and 1.79 K, respectively, and the standard deviation of temperature decreased by 48% and 14%, respectively. Under the same inlet flow velocity, the area of the fluid region increases with the increase of the mean fluid volume fraction, and the width of the flow channel increases gradually and the branches increase significantly, from the concentrated solid region to the dispersed isolated region. At a low flow rate, the normalized temperature of the cooling plate increases with the increase of the flow rate of the coolant inlet, and when the flow rate reaches a certain value, in order to reduce the power loss of the cooling plate, the flow path is gradually concentrated on both sides of the cooling plate. This leads to the decline of the normalized temperature of the cooling plate.

Characteristics, Sources, and Contributions to Ozone Formation of Ambient Volatile Organic Compounds in Huanggang, China

Based on the offline sampling data of volatile organic compounds (VOCs) and the simultaneous online measurements of conventional gaseous air pollutants and meteorological parameters in urban Huanggang, the volume fractions and component characteristics of VOCs were analyzed. The sources and ozone (O3) formation sensitivity of VOCs during severe ozone pollution episodes were analyzed using the positive matrix factorization (PMF) model and the photochemical box model coupled with master chemical mechanism (PBM-MCM), respectively. The results revealed that the average volume fractions of total volatile organic compounds were (21.57±3.13)×10-9, with higher volume fractions in winter and spring compared to those in summer and autumn. Among these, alkanes (49.9%) and alkenes (16.4%) accounted for the highest proportion. The PMF analysis results showed that fuel combustion (27.8%), vehicle emission (19.9%), solvent use (15.7%), industrial halogenated hydrocarbon emission (12.1%), chemical enterprise emission (10.5%), natural sources (7.8%), and diesel vehicle emission (6.2%) were the main sources of VOC emissions. Anthropogenic VOCs emitted by solvent use, fuel combustion, and chemical enterprises contributed significantly (60.9% in total) to generating O3, which indicates that these three types of anthropogenic sources should be controlled first when it comes to preventing and controlling ozone pollution. Further, the relative incremental reactivity (RIR) and empirical kinetic method approach (EKMA) revealed that O3 formation was in a VOCs-limited regime during the observation period in Huanggang, China. Furthermore, O3 formation was more sensitive to m-xylene, p-xylene, ethylene, 1-butene, and toluene; therefore, reducing these VOCs should be prioritized.

Effects of transverse concentration gradients on the vented explosion of methane-air mixtures

Experiments were performed in a 90-L vessel with a side vent to investigate the effects of transverse concentration gradients on the vented explosion of non-uniform methane-air mixture. Controlled by a mass flow meter, methane was injected uniformly into the vessel through 18 nozzles that are evenly distributed at the top to configure a methane-air mixture with an average methane volume fraction of 10.9%. Various transverse concentration gradients were obtained by altering the free diffusion time of the methane in the vessel. The deflagration flame was recorded through a high-speed camera at a frequency of 1000 Hz, and the internal overpressure at different locations was captured through three piezoelectric sensors. Experimental results reveal that larger concentration gradient resulted in lower flame propagation rate, longer time for the burst of the vent cover, and stronger pressure oscillations. Concentration gradient affects the typical flame structure, especially the formation and development of the tulip flame. Under the present experimental conditions, Helmholtz oscillations occurred in all tests. Concentration gradient has a negative correlation with the frequency of Helmholtz oscillations but a positive correlation with the duration of oscillations. In conclusion, the variation of concentration gradient obviously affects flame propagation and pressure evolution during vented explosions, which deserves more attention in the design of explosion protection.

Preferential distribution behavior of B and its enhancement on creep strength of alumina-forming austenitic heat-resistant steel

The addition of a trace amount of 20 ppm B significantly enhanced the creep performance of the 2.5Al-AFA alloy at 650 °C, demonstrating sustained improvement even after prolonged thermal aging. Boron (B) preferentially distributed in the Laves phase within the matrix, rather than in the NiAl or Cr - rich phases. APT analysis revealed M23C6 may serve as a reservoir of B, gradually allowing B diffusing into the surrounding Laves phase at grain boundaries (GBs). Creep cracks propagated mainly along GBs, with the σ phase serving as initiation sites. The average volume fraction of σ phase exhibited a linear correlation with the reciprocal of creep rupture time. B accelerated the precipitation of Laves with a larger size and higher volume fraction, which played a dual role of improved GB strengthening and more effective suppression of σ phase growth.

Local microstructure and strengthening mechanisms of double-sided friction stir welded Al-Mg-Mn-Er alloy joint

Local microstructure and strengthening mechanisms of double-sided friction stir welded Al-Mg-Mn-Er alloy joint were investigated to reveal its softening mechanism. The results showed that a fine equiaxed grain structure (5.61 μm) was formed in the nugget zone (NZ), while the thermo-mechanically affected zone (TMAZ, 45.32 μm) and heat-affected zone (HAZ, 100.73 μm) maintained a fibrous grain structure. The fraction of low angle grain boundaries decreased from 75.6% of the base metal (BM) to 15.6% of the NZ. The annealing effect resulted in obvious reduction in dislocation density from 1.8×1014 m−2 of the BM to 4.5×1012 m−2 of the NZ. The average diameter size and volume fraction of Al3(Er, Zr) precipitates of the NZ, TMAZ and HAZ were close to those of the BM (13.7 nm and 0.13%). The NZ and TMAZ exhibited the lowest yield strength of about 201 MPa while the BM had the highest yield strength of about 295 MPa. The loss of the dislocation strengthening and substructure strengthening was the main reason for the decrease of yield strength from the BM to the NZ.

Numerical Simulation of the Cold-Start Process of Polymer Electrolyte Fuel Cell

In this study, the cold-start process of a polymer electrolyte fuel cell has been numerically investigated under various ambient temperatures and operating currents, ranging from subzero to 283 K. The water desorbed from the electrolyte, when the cell temperature is below the freezing point, is assumed to exist in a state of either supercooled water or ice. The evolution of cell voltage, temperature, membrane water content, and the averaged volume fraction of supercooled water or ice in the catalyst layer and gas diffusion layer are presented. The results indicate that the cold-start process may fail due to ice blocking of the cathode catalyst layer when the desorbed water is in the form of ice and the ambient temperature is sufficiently low. However, when the desorbed water is in a supercooled state, it can diffuse from the cathode catalyst layer to the cathode gas diffusion layer, avoiding water clogging and enabling a successful cold-start process. During the cold-start process, as the ice undergoes a melting process, the membrane water content inside the membrane would increase rapidly, and a larger operation current with anode gas humidification is helpful to the cold-start process.

Explosive characteristics of non-uniform methane-air mixtures in half-open vertical channels with ignition at the open end

In this study, the explosive characteristics of non-uniform methane-air mixtures in a 1.5 m half-opened vertical channel with ignition at the open end were experimentally studied. The results revealed significant oscillation characteristics in the flame image, velocity, and pressure variations. Notably, a strong similarity was observed between the flame velocity and pressure profiles. Furthermore, it was experimentally demonstrated that the explosion characteristics of methane-air mixtures in vertical channels with the same average volume fraction differed. These variations in characteristics were attributed to the degree of non-uniformity, where both the direction and steepness of the methane concentration gradient influenced the explosion flame behavior. When the diffusion time was very short, resulting in a small concentration above the channel and a large gradient, an obvious cusp appeared at the flame front, which was absent in the case of longer diffusion times. In addition, as the methane diffusion time increased, the methane in the vertical channel gradually accumulated upward. Consequently, the time required to reach maximum velocity and pressure after ignition decreased, leading to a larger maximum amplitude. In summary, our study highlights the importance of considering non-uniformity and diffusion time in understanding the explosion characteristics of methane-air mixtures in vertical channels.

Numerical study on spray characteristics of liquid jets in supersonic crossflow

The spray characteristics of liquid jets in supersonic crossflow at different injection jet-gas momentum ratios are investigated numerically. The compressible two-phase flow large eddy simulation (LES) method is based on the Eulerian-Lagrangian scheme. The average droplet volume fraction is defined to quantify spray concentration distribution, which can also reflect the oscillation boundary of the spray. The LES predicted the spray boundaries at different injection jet-gas momentum ratios in the central and cross-sectional planes, which agree reasonably well with the experiment. Two sets of counter-rotating vortex pair (CVP) are in the gas-liquid mixing region. As injection momentum ratio q increases, the upper CVP increases. Still, the absolute size of the wall CVP remains almost unchanged, which means that the relative size of the wall CVP to the upper CVP becomes smaller. As q increases, the spray's overall distribution position is generally upward, and the number of droplets entering the near-wall region becomes small. Thus, droplet-wall interactions are weakened. The spray body increases with the increase of q, while the spray foot decreases gradually. In the central plane, the coherent structures near the wall are mainly composed of splashed droplets, and this phenomenon gradually weakens as q increases. Although the increase of q can increase the total droplet mass flow rate, the proportion of the droplet mass flow rate in the near-wall region to the total mass flow rate decreases, and the droplet mass flow rate in the near-wall region decreases.

A theoretical investigation on the relative stability of the columnar hexagonal and columnar square phases of discotic molecules

We have employed a mean field theory, which is a modified Ginzburg-Landau expansion in terms of the scalar order parameter Φ(r), to stabilize the ordered phases such as square and hexagonal phases of the discotic molecules. The Φ(r) represents the local volume fraction differential between the stiff core and the outside alkyl chain regions of the discotic molecules. The current theoretical analysis stabilizes the ordered phases, particularly the square (S) and 2D hexagonal (H) phases. The present study also identifies the direct hexagonal (HI) and reverse hexagonal (HII) phases, with the phases occurring in the following order: disorder(D) - HI - S - HII - disorder(D) with increase in the average volume fraction difference, Φo. Contrarily, the stability area of the S phase accounts for around 10% of the total area of the ordered phase, whereas the HI and HII phases each occupy about 45% of the total area of the ordered phase.

Improvement of the bubble separation through eccentric planar cyclones: Experiments and CFD simulations

Planar cyclones have great advantages as electrolyzers, photocatalytic reactors, and gas–liquid separators. For planar cyclones, the separation efficiency of bubbles is a key parameter. The effect of eccentricity on bubble separation efficiency in planar cyclones was studied through a combination of experiments and simulations. When eccentricity dc = 0 mm, the separation efficiency of the bubbles decreased with an increase in the liquid injection velocity. This indicates that a greater centrifugal acceleration in planar cyclones does not contribute to bubble separation. Eccentricity dc = −5 mm resulted in a higher bubble separation efficiency. Each planar cyclone was divided into 12 sub-regions with equal areas. When eccentricity dc = −5 mm, subregions 11 and 12 exhibited larger bubble sizes, and a higher bubble separation efficiency was achieved. The area weighted average sauter mean diameter ds reached 0.47 mm and 0.475 mm and area weighted average gas volume fraction εs reached 2.75 % in subregion 11 when liquid Reynolds numberRel = 20075.4 and gas Reynolds number Reg = 23.8. The maximum separation efficiency can be increased from 43 % to 60 % when Rel = 20075.4 and Reg = 6.8 when the eccentricity varies from 0 to − 5 mm. Bubble size changes due to coalescence and breakup have an important influence on bubble separation. The trajectory of bubbles exhibits helix. The gradually decreasing curvature radius of the bubble trajectory dominates the bubble separation. Eccentric swirling field provides a sudden decrease in the swirl radius which promotes the reduction of the curvature radius of the bubble trajectory. This study provides an optimization method for the structural design of cyclones.

Study on heterogeneous gas-solid structure and interparticle collision behavior in a vibrated fluidized bed of Geldart D particles using CFD-DEM simulations

The spatiotemporal characteristics of the heterogeneous gas-solid structure and interparticle collisions in fluidized beds of Geldart D particles with and without vibration were comparatively studied by the coupled CFD-DEM simulations. The effects of vibration on the spatiotemporal distributions of particle configuration and particle dynamics were revealed utilizing data visualization and frequency domain analysis. The results show that the input vibration facilitates the formation of square-nosed slugs and improves the uniformity of gas-solid contacts. Moreover, vibration causes fluctuations in static air pressure on the entire bed simultaneously. It is revealed that the introduction of vibration can significantly increase the intensity and uniformity of interparticle collisions, the number of particles involved in collisions, and the total kinetic energy of the bed. The results also show that there exists a positive correlation between average collision number and solid volume fraction while an inverse correlation between granular temperature and solid volume fraction.

Laser powder bed fusion fabricated Cu-1.8Cr-1.0Nb-2.0Fe alloy with in-situ precipitation strengthening

Copper alloys fabricated by laser powder bed fusion (LPBF) have been widely utilized in a diverse range of industrial sectors, including electrical, electronics, aerospace, etc. This study centers on an LPBF-fabricated in-situ precipitation-hardening Cu-1.8Cr-1.0Nb-2.0Fe copper alloy and comprehensively investigates its densification, microstructure, mechanical properties, strengthening mechanisms, and coarsening resistance. The results demonstrate that optimal process parameters enable the fabrication of nearly full specimens with a relative density (RD) of 99.98%. The microstructure of the as-built (AB) and direct aging (DA) treatment specimens consists of columnar grains. During the LPBF process, an Nb(FeCr) core-shell nanostructure in-situ precipitates, inducing a strong precipitation effect that results in an exceptional ultimate tensile strength (UTS) of 444 MPa. After aging treatment, the average radius and volume fraction of the Nb(FeCr) core-shell nanostructure remains unchanged. Another reinforced phase of FeCr σ-phase forms to further enhance the tensile strength, resulting in a higher UTS of 498 MPa for DA specimens. Precipitation strengthening is the dominant mechanism among the four strengthening mechanisms for both AB and DA specimens. The excellent coarsening resistance of Nb(FeCr) core-shell nanostructure is confirmed by (i) the almost unchanged size and volume fraction after aging treatment and (ii) the close contribution value of precipitation strengthening induced by Nb(FeCr) core-shell nanostructure to YS for AB and DA specimens. This study provides valuable insights into the in-situ precipitation behavior for LPBF-fabricated copper alloys.

Thermoplastic Pultrusion Process of Polypropylene/Glass Tapes.

The present work focuses on the pultrusion of pre-impregnated glass-reinforced polypropylene tapes. An appositely designed laboratory-scale pultrusion line, consisting of a heating/forming die and a cooling die, was used. The temperature of the advancing materials and the pulling force resistance were measured by using thermocouples embedded in the pre-preg tapes and a load cell. From the analysis of the experimental outcomes, we gained insight into the nature of the material-machinery interaction and the transitions of the polypropylene matrix. The cross-section of the pultruded part was analyzed by microscope observation to evaluate the distribution of the reinforcement inside the profile and the presence of internal defects. Three-point bending and tensile testing were conducted to assess the mechanical properties of the thermoplastic composite. The pultruded product showed good quality, with an average fiber volume fraction of 23% and a limited presence of internal defects. A non-homogenous distribution of fibers in the cross-section of the profile was observed, probably due to the low number of tapes used in the present experimentation and their limited compaction. A tensile modulus and a flexural modulus of 21.5 GPa and 15.0 GPa, respectively, were measured.