Increasing Sample Thickness Research Articles

Parameter dependence of depth and lateral resolution of transmission Kikuchi diffraction

The spatial resolution of transmission Kikuchi diffraction (TKD) depends on experimental parameters such as atomic number, accelerating voltage, sample backtilt and thickness. In this work, the dependence of spatial resolution on these parameters is explored by using bilayered coarse-grained/nanocrystalline samples to determine the depth resolution. Digital image correlation of the Kikuchi patterns across grain boundaries is used to measure the lateral resolution. The depth resolutions of TKD in aluminium, copper and platinum at 30 kV for an untilted sample were 80, 32 and 14 nm respectively. These worsened with increasing sample backtilt and slightly improved with decreasing accelerating voltage. The best physical lateral resolution obtained was 6 nm, at 30 keV in a 41 nm thick aluminium sample with no backtilt. The lateral resolution worsened with increasing sample thickness and backtilt, contrasting with some previous reports. Accelerating voltage and atomic number did not have a significant impact on the measured lateral resolution within the scatter in the data.

Comparing microstructure and mechanical properties of AlSi10 alloy produced by powder bed fusion-laser beam and high pressure die casting

PurposePowder bed fusion-laser beam (PBF-LB) is a rapidly growing manufacturing technology for producing Al-Si alloys. This technology can be used to produce high-pressure die-casting (HPDC) prototypes. The purpose of this paper is to understand the similarities and differences in the microstructures and properties of PBF-LB and HPDC alloys.Design/methodology/approachPBF-LB AlSi10Mg and HPDC AlSi10Mn plates with different thicknesses were manufactured. Iso-thermal heat treatment was conducted on PBF-LB bending plates. A detailed meso-micro-nanostructure analysis was performed. Tensile, bending and microhardness tests were conducted on both alloys.FindingsThe PBF-LB skin was highly textured and softer than its core, opposite to what is observed in the HPDC alloy. Increasing sample thickness increased the bulk strength for the PBF-LB alloy, contrasting with the decrease for the HPDC alloy. In addition, the tolerance to fracture initiation during bending deformation is greater for the HPDC material, probably due to its stronger skin region.Practical implicationsThis knowledge is crucial to understand how geometry of parts may affect the properties of PBF-LB components. In particular, understanding the role of geometry is important when using PBF-LB as a HPDC prototype.Originality/valueThis is the first comprehensive meso-micro-nanostructure comparison of both PBF-LB and HPDC alloys from the millimetre to nanometre scale reported to date that also considers variations in the skin versus core microstructure and mechanical properties.

Effect of shade and thickness on the microhardness of resin-based composite specimens at different points considering curing light beam’s inhomogeneity

BackgroundRecent studies have reported the inhomogeneity in the light emitted by dental light-curing units (LCUs). It is essential to understand how this uneven light distribution affects the physical properties of resin-based composites (RBCs) at various points across their surfaces. This study aimed to evaluate the effect of LCU beam’s inhomogeneity on the microhardness of RBCs with different shades and thicknesses.MethodsFour body (A1B, A2B, A3B, and A4B), one dentin (A3D), and one enamel shade (A3E) of RBC (Filtek Z350 XT) were examined. The specimens were fabricated in four thicknesses (1, 2, 3, and 4 mm) and subjected to a 40-second light-curing. Vickers microhardness testing was performed at the center point, and 3 mm left and right from the center at the bottom surface of each sample. The LCU beam profile was characterized using a beam profiler, while irradiance after specimen passage was measured using a spectrometer. One-way analysis of variance (ANOVA) and Tukey’s post-hoc tests were used to analyze the effects of shades and thicknesses on irradiance and microhardness, respectively. One-way repeated-measures ANOVA was used to compare the microhardness across different points. Pearson’s correlation analysis examined the relationship between irradiance and microhardness.ResultsThe beam profile of LCU revealed inhomogeneous light distribution. Light irradiance was decreased with both the increase in thickness and darker shade of the specimens (p < 0.05). Microhardness was found to decline with an increase in sample thickness (p < 0.05), and was consistently higher at the center point compared to the periphery, particularly in thicker (3 and 4 mm) and darker shades (A3B, A4B, and A3D). A positive correlation was found between the irradiance and microhardness across all evaluated points (p < 0.05).ConclusionsInhomogeneous light emission from LCU significantly influences the microhardness of RBC samples, depending on the thicknesses and shades. The findings underline the importance of considering LCU beam inhomogeneity in clinical settings to ensure optimal polymerization of RBC.

Ultra-low-cost and high-fidelity NIR-II confocal laser scanning microscope with Bessel beam excitation and SiPM detection.

Confocal laser scanning microscopy (CLSM) is one of the most important imaging tools in the biomedical field, and near-infrared-II (NIR-II, 900-1700nm) fluorescence imaging technology has also made fruitful research progress in deep imaging in recent years. The NIR-II based CLSM has problems such as an expensive detector and reduced image resolution caused by long wavelength excitation. Here, by simultaneously using a low-cost silicon photomultiplier (SiPM) as a detector and a Bessel beam as an excitation, we developed an ultra-low-cost and high-fidelity NIR-II confocal laser scanning microscope. The use of SiPM reduces the cost of the NIR-II fluorescence detection module in CLSM, while enabling the detection of ultra-broadband fluorescence signals spanning visible to NIR-II regions. The introduction of the Bessel beam compensates to some extent for the weakening of spatial resolution caused by the increase in the wavelength of light in the NIR region. Experimental results show that the use of the Bessel beam can improve the resolution by 12% when observing thin samples. With the increase of sample thickness, the imaging resolution of the Bessel beam at NIR-II wavelengths is better than that of the Gaussian beam at NIR-I wavelengths at the penetrable depth of the NIR-I light. At deeper depths, the imaging resolution and imaging depth of Bessel beam CLSM is superior to Gaussian beam CLSM at the same excitation power.

Dynamic mechanical response and failure behavior of solid propellant under shock wave impact

Solid rocket motor propellants are typically subjected to shock wave loads during ignition. To analyze the dynamic mechanical response and failure behavior of hydroxyl-terminated polybutadiene (HTPB) propellant under varying shock intensities, this study innovatively employed a shock tube apparatus in conjunction with schlieren imaging and 3D-DIC techniques. Shock loading experiments were conducted on propellant samples of three different thicknesses under pressures ranging from 0.3 to 0.7 MPa, capturing the dynamic deformation processes. Results revealed that deformation initiated at the clamped region, extending towards the center and forming a parabolic shape. The maximum deformation of the samples shows an approximately linear relationship with the launch pressure and decreases with increasing sample thickness. The 5 mm sample failed under a 0.6 MPa shock pressure, with electron microscopy images identifying matrix damage, particle debonding, and particle fracture as the principal failure mechanisms. Finite element simulations based on the generalized Maxwell linear viscoelastic constitutive model were conducted, demonstrating good agreement with experimental data. The critical stress for fracture was determined to be 4.12 MPa, and the ultimate shock wave pressures for 3, 6, 9, and 12 mm thicknesses were approximately 0.3 MPa, 0.65 MPa, 1.1 MPa, and 1.4 MPa, respectively. These findings provide valuable insights for assessing the structural integrity of solid rocket motors under ignition shock conditions.

Characterization of X-ray Beam for Half and Quarter Value Layers

Introduction: The aim of this work is to assess the penetrating ability of an X-ray beam through a specific material, in conditions of narrow-beam geometry. Materials and Methods: During the experiment, samples were switched with the X-ray tube turned off, and the primary intensity of the unshielded X-ray beam (fixed 2.5mm shielding) was measured. Parameters were kept constant throughout, and the electrometer was used to stabilize the readings. Subsequent measurements aimed to determine the Half-Value Layer (HVL) and Quarter-Value Layer (QVL) by interpolating various sample slices to achieve intensity values of I/2 and I/4, respectively. The data were used to plot and analyze HVL and QVL graphs, providing insights into the attenuation properties of the X-ray beam through different materials. Findings of the result: The primary findings indicated that the initial unshielded X-ray beam intensity, with parameters set to 37.5 kV and 40 mA, provided a stable baseline measurement. The results showed a consistent decrease in intensity with increased sample thickness, confirming the exponential attenuation of X-rays. The HVL was determined by identifying the sample thickness that reduced the initial intensity by half, and the QVL by the thickness reducing it to one-fourth. The experimental data closely followed theoretical predictions, with HVL and QVL values providing a quantitative measure of the material's attenuation properties. Conclusion: Graphical analysis of the results demonstrated clear linear relationships on a semi-logarithmic scale, validating the accuracy of the measurement process and the reliability of the electrometer readings. These findings contribute to a better understanding of X-ray attenuation in different materials, which is crucial for various applications in medical physics and radiography.

Fire retardation, compressive strength and durability analysis of concrete reinforced with novel plasters: An experimental, computational and statistical research

Concrete is an essential component of the construction industry, valued for its high compressive strength (CS) and durability. However, when exposed to extreme conditions like fire without protective structural elements, its physical integrity deteriorates rapidly, leading to significant alterations in its mechanical properties. This research aims to provide a potential solution to this issue by assessing the fire resistance of various concrete samples, including unplastered (UNP), roughly plastered (RP), and those with contemporary insulation plaster (CIP) substitutions, at different thicknesses. These samples are subjected to varying temperatures and exposure times within an oven, followed by CS testing. These temperature levels and time intervals correspond to 300 °C, 450 °C, and 600 °C, with the time range is restricted to 60, 90, and 120-min, respectively. The results indicate that an increase in sample thickness correlates with a reduction in concrete degradation at high temperatures. Moreover, the findings reveal that after 120-min of exposure at 600 °C, UNP, RP, and CIP-reinforced samples achieve CSs of 27.435 MPa, 27.74 MPa, and 30.28 MPa, respectively. Notably, the 3 cm CIP-reinforced sample exhibits a CS exceeding 30 MPa under the most extreme conditions. The research incorporates regression and computational fluid dynamics (CFD) analyses to complement the experimental investigation. The regression analysis suggests that CIP-reinforced samples can withstand temperatures up to 600 °C for approximately 173-min, while the study implies that they could endure temperatures as high as 861 °C during a 120-min exposure.

Impact of filler and gelling catalyst/agent on properties of flexible polyurethane foam

AbstractIn this study, the physiomechanical properties of carboxymethylcellulose sodium salt (Na‐CMC salt) filler‐loaded foam and its impact on the wicking capacity of the foam were investigated in juxtaposition with the increasing tin concentration. According to the study's findings, standard unfilled foam demonstrated no wicking at all, while flexible PU foam filled with Na‐CMC salt, even with low porosity and subpar mechanical traits, displayed wicking heights of 4 mm, 3.4 mm, and 2.8 mm in test specimens of thicknesses of 6 mm, 8 mm, and 10 mm. Moreover, filled foam with a higher porosity level exhibited significantly better wicking heights of 11.4 mm, 10.8 mm, and 8.2 mm. The inclusion of CMC filler in the PU foam matrix is the reason for enhanced wicking property in foam. The sample thickness and wicking height trends are consistent among all foams; as foam sample thickness increases, wicking height progressively falls. The correlation between the foam's porosity value and the number of closed cell windows is confirmed by stereomicroscopy and the porosity values. According to this study, the infused filler's characteristics have a greater influence on the foam's wicking capacity than the foam's porosity. This study contributes significant insights into ongoing initiatives to enhance user experience, well‐being, and hygiene through innovative and meticulously designed new developed mattress foam using Na‐CMC as a filler.Highlights Co‐relation between concentration of tin and infused filler on wicking property. Standard unfilled foam demonstrated no wicking at all. Na‐CMC salt filled foam displayed wicking heights. After 15% increase in tin level, mechanical properties of foam degrade. Wicking depends on nature of infused filler and the foam's porosity.

Writing temperature and thickness dependence of perpendicular magnetic-dot magnetization reversal probability

Investigation is necessary to figure out magnetization dynamics at high temperatures due to the low power requirement for heat-assisted magnetic recording technology. The Landau-Lifshitz-Gilbert equation was employed to assess the dynamic of magnetization in perpendicular magnetic-dots at elevated temperatures, considering the thermal contribution to the effective field. The simulated perpendicular magnetic-dot has a 50×50 nm2 surface area with thicknesses of 10 nm, 50 nm, and 100 nm. This study reveals that the probability of magnetization reversal and the threshold field in the thermally-assisted magnetic reversal process of a magnetic dot is influenced by the thickness and writing temperature. Below the Curie point, as sample thickness increases, demagnetization energy increases, requiring a larger external magnetic field for magnetization reversal. For the thicker sample, the magnitude of the writing field decreases as the temperature increases, which corresponds to temperature-dependent magnetization. Meanwhile, the optimum writing field is obtained below the Curie point. The magnetic-dot with 100 nm of thickness has an effective writing temperature of 739.7 K with a corresponding writing field is 250 Oe while its reversal probability at zero magnetic field is up to 0.2. Magnetic-dot thickness affects magnetization reversal probability due to domain wall propagation mechanisms during magnetic switching that result from the demagnetization factor. Moreover, as the temperature approaches the Curie temperature, the probability of zero-field magnetization reversal in the absence of an external magnetic field is observed to escalate which has a direct impact on the writing field magnitude. It was found that the effective writing temperature is below the Curie temperature, which allows several hundred Oersted of the writing field.

Sound absorption and thermal insulation performance of sustainable fruit stone panels

The sound absorption and thermal insulation behavior of panels made of different fruit stones, including peach, apricot, plum, date, and black cherry, were investigated. To this end, samples in the crushed and uncrushed forms were fabricated with thicknesses of 30 and 50 mm. The FE-SEM (Field Emission Scanning Electron Microscopy) and Atomic Force Microscopy (AFM) images showed that the studied stones have different morphological and topological surfaces, which in turn lead to different sound absorption coefficients (SACs) and effective thermal conductivities (Keff). It was found that smaller fruit stones with higher surface roughness generally have higher noise reduction coefficients, and this was more pronounced for samples of 50 mm thickness. In addition, samples in the crushed form enjoyed superior sound absorption performance compared with their uncrushed counterparts. The SAC peak in the crushed form appeared at lower frequencies and its value was higher than that of the uncrushed stones. Moreover, when the air gap was introduced, all samples showed excellent sound absorption at frequencies of 400–600 Hz. It was found that, while an increase in sample thickness led to an enhancement in SAC at low and middle frequencies, the Keff values did not significantly change. Uncrushed samples demonstrated enhanced thermal insulation properties compared to their crushed counterparts. The Keff values of the specimens were found to be in the range of 0.087–0.204 W.m−1 K−1, indicating the good thermal insulation performance of the panels. The frequency-dependent SACs of fruit stone panels were predicted using the Johnson-Champox-Allard and Attenborough models, and acceptable consistency was observed.

Structure Analysis and Its Correlation with Mechanical Properties of Microcellular Polyamide Composites Reinforced with Glass Fibers

Thin-walled and thick-walled microcellular moldings were obtained by MuCell® technology with nitrogen as a supercritical fluid. 2 mm thick polyamide 6 (PA6) with 30% wt. glass fiber (GF) samples were cut from automotive industrial elements, while 4 mm, 6 mm, and 8.4 mm thick moldings of PA6.6 with 30% wt. GF were molded into a dumbbell shape. The internal structure was investigated by scanning electron microscopy (SEM) and X-ray computed microtomography (micro-CT) and compared by numerical simulations for microcellular moldings using Moldex3D® 2022 software. Young’s modulus, and tensile and impact strength were investigated. Weak mechanical properties of 2 mm thick samples and excellent results for thick-walled moldings were explained. SEM pictures, micro-CT, and simulation graphs revealed the tendency to decrease the cell size diameter together with increasing sample thickness from 2 mm up to 8.4 mm.

Oxidation-creep interactions for an Hf-doped Ni-based superalloy with different wall thickness at 760 °C

Stress rupture tests of an Hf-containing Ni-based superalloy with different wall thicknesses were carried out at 760 °C/691 Mpa using the RD-100 electronic machine. At the fracture edge, electron backscatter diffraction (EBSD) analysis showed that recrystallization (RS) occurred, and the width of RS increased with increasing sample thickness. The RS induced the intergranular corrosion cracking and accelerated the failure of the sample. At the interior of the substrate, voids were preferentially nucleated at the site of the Hf(Ta)C carbides, and the thinner sample suffered lighter creep damage than the thicker sample. Consequently, the thinner sample had a superior creep life.

Size effects in molecular dynamic simulations of fracture in bcc iron crystals

Three-dimensional (3D) simulations via molecular dynamics (MD) show that the brittle or ductile behavior of the atomistic samples with the edge crack (001)[110] (crack plane/crack front) depend on size of the self-similar atomistic crystals. Since the basic continuum predictions concerning cracks do not consider the random thermal atomic motion, we are restricted in this study to MD simulations with initial temperature of 0 K. For all samples tested, the crack initiation is brittle. However, the subsequent crack growth can be inhibited by twin formation on oblique planes {112}, crack branching along {011} planes and new dislocation emissions on {123} slip planes and the final fracture can also be then ductile, which depends predominantly on the thickness of the atomistic sample. The representative quantity, the atomistic fracture toughness initially increases with increasing sample thickness and later saturates near Griffith level for plane strain state along the crack front. The tested loading rates are equivalent to a cross head speed of 0.833 · 10−4 m s−1 used in one our previous experiment. These new MD results comply with the stress analysis performed by the anisotropic linear fracture mechanics (LFM) and with some experimental observations.

Preparation of newly developed porcelain ceramics containing WO3 nanoparticles for radiation shielding applications

Abstract We fabricated porcelain ceramics embedded with WO3 nanoparticles (NPs) for radiation shielding applications. The linear attenuation coefficients were experimentally determined to study the efficiency of the manufactured samples against gamma rays. When the thickness increases from 0.5 to 2 cm, there is a reduction in the photon transmission through the ceramics. At 0.662 MeV, the transmission factor for Porc-1 changes from 0.91 (thickness: 0.5 cm) to 0.83 (thickness: 1 cm), and to 0.69 (thickness: 2 cm). From I/I 0 results, we found that attenuation performance is improved as the sample thickness increases. We evaluated the mass attenuation coefficient (MAC) and examined the influence of the concentration of WO3 NPs on the MAC. We found that Porc-5 which contains a greater quantity of WO3 NPs compared to the other samples has the highest MAC. At 0.06 MeV, the HVL (half value layer) for Porc-1 is 1.063 cm, while at 1.333 MeV this increases to 5.247 cm. Meanwhile, for Porc-2, at 0.06 MeV, a thin layer of thickness 0.806 cm is required to shield 50% of the photons, and at 1.333 MeV, the thickness of the layer must increase to 5.058 cm to shield the photons.

Investigation of structural parameters of acoustic panels produced from post-industrial textile wastes containing different raw materials

Although noise pollution appears to be a minor issue, it worsens as a result of urbanization and population growth. Unwanted noises have a wide range of negative effects, including anxiety, hostility, high blood pressure, tinnitus, hearing loss, and sleep difficulties. The researchers are compelled to conduct a creative search in order to uncover future environmental solutions due to the noise problem, which is becoming each day worse. Moreover, the textile sector, which is growing day by day, generates huge amounts of waste with the effect of fast fashion trend. The objective of this study is to develop ecofriendly acoustic panels utilizing recycled textile waste and thermoplastic polypropylene (PP) fibers. Within the scope of the study, waste fabrics made of viscose, lyocell, flax, cotton, and polyester are shredded into fibers, and sandwich panels including waste fibers bonded together with PP fibers are generated using the hot press technique. In addition to the use of natural and synthetic fibers, the effects of surface shape (perforated-imperforated) and layer thickness (5 mm and 10 mm) on acoustic performance are examined. The results of the sound absorption and sound transmission loss tests reveal that the acoustic properties of the samples improve as the sample thickness increases, but the perforation process does not have the desired favorable impact on samples of the same thickness. Additionally, the outcomes demonstrate that around 2000 Hz, natural and regenerated fibers with high cellulose content had the best sound absorption coefficients around 0.60. The findings indicate that these eco-friendly panels can be used to reduce unwanted noise in open offices, co-working spaces, and meeting rooms.

Relating the microstructural and glass transition temperature evolution of a carbon–carbon composite precursor during pyrolysis using thermomechanical analysis

AbstractPolybenzoxazine thermoset resins exhibit significant potential as precursors for carbon–carbon composites, owing to their high char yield upon pyrolysis. During pyrolysis, the resin is converted to an amorphous carbon‐rich material through a series of mechanisms, resulting in a linear increase of the glass transition temperature (TG) from 133 to 396°C at 0.48 pyrolytic conversion. To better understand this relationship, a non‐isothermal kinetic model was integrated, enabling the prediction of the TG onset, inflection, and endpoint based on the heat treatment protocol (process temperature (TP) vs. time) and the total volume of pyrolytic gases generated. By considering the TG behavior and anticipated gas effects, three distinct mechanisms were identified: (1) gas accumulation and matrix expansion leading to increased sample thickness (TG &lt; TP), (2) crack network formation caused by gas‐pressure‐induced brittle failure (TG &gt; TP), and (3) sample thickness reduction due to gas venting through the crack network (TG &lt; TP). To validate this theory, thermal mechanical analysis was performed during pyrolysis, and changes in thickness (±ΔL/L0) were attributed to gas pressure‐related matrix deformation. Conversely, no change in ΔL/L0 indicated the formation of an interconnected crack network through which gases could vent without building a measurable internal pressure.

Harnessing Skyrmion Hall Effect by Thickness Gradients in Wedge-Shaped Samples of Cubic Helimagnets.

The skyrmion Hall effect, which is regarded as a significant hurdle for skyrmion implementation in thin-film racetrack devices, is theoretically shown to be suppressed in wedge-shaped nanostructures of cubic helimagnets. Under an applied electric current, ordinary isolated skyrmions with the topological charge 1 were found to move along the straight trajectories parallel to the wedge boundaries. Depending on the current density, such skyrmion tracks are located at different thicknesses uphill along the wedge. Numerical simulations show that such an equilibrium is achieved due to the balance between the Magnus force, which instigates skyrmion shift towards the wedge elevation, and the force, which restores the skyrmion position near the sharp wedge boundary due to the minimum of the edge-skyrmion interaction potential. Current-driven dynamics is found to be highly non-linear and to rest on the internal properties of isolated skyrmions in wedge geometries; both the skyrmion size and the helicity are modified in a non-trivial way with an increasing sample thickness. In addition, we supplement the well-known theoretical phase diagram of states in thin layers of chiral magnets with new characteristic lines; in particular, we demonstrate the second-order phase transition between the helical and conical phases with mutually perpendicular wave vectors. Our results are useful from both the fundamental point of view, since they systematize the internal properties of isolated skyrmions, and from the point of view of applications, since they point to the parameter region, where the skyrmion dynamics could be utilized.

Optimization design of laser-EMAT and its application in high-temperature forgings detection

In high-temperature continuous forging process, according to the real-time monitoring of workpiece thickness and flaws, the processing parameters can be adjusted accordingly, so we can remove defective components in time, which has essential research value for avoiding the interruption of production line and improving their yield and quality grade. We established a finite element (FE) model of the carbon steel’s laser-electromagnetic acoustic transducer (laser-EMAT) testing process. Based on the simulation model, we analyzed the effects of laser parameters, EMAT parameters, and sample thickness on the detected ultrasonic signal amplitude, and we also achieved the optimized Laser-EMAT design parameters. Subsequently, we developed a high-temperature resistant spiral coil EMAT and measured the high-temperature forging with a thickness of 100 mm and temperatures from 300 °C to 730 °C. Based on the experiments, we researched the effect of specimen temperature on the received ultrasonic wave amplitude. The results show that the excitation efficiency of laser-induced ultrasonic waves improves by decreasing pulse duration, decreasing laser spot radius, and increasing pulse laser energy. The receiving efficiency of the shear wave (SW) detected by the EMAT enhances when reducing the diameter of the EMAT wire and increasing the permanent magnet height. When the radius of the permanent magnet is equal to the radius of the EMAT coil, the receiving efficiency of SW is the highest. As the sample thickness increases, the size of the EMAT should increase accordingly to the acoustic beam divergence for obtaining a higher ultrasonic wave intensity. The amplitude of the SW signal received by the EMAT increases by 679% after the optimization design. With rising carbon steel forging temperature, the SW signal amplitude increases first and then decreases sharply, reaching its maximum at 617 °C, which is 29% higher than at room temperature, and the signal-to-noise ratio (SNR) of the SW is 20.5 dB.

The influence of residual plural scattering after deconvolution in electron magnetic chiral dichroism

This work investigated the existence and influence of residual plural scattering in electron magnetic chiral dichroism (EMCD) spectra. A series of low-loss, conventional core-loss, and q-resolved core-loss spectra at Fe-L2,3 edges were detected from areas of different thicknesses in a plane-view sample of Fe/MgO (001) thin film. It reveals by comparison that there remains noticeable plural scattering in q-resolved spectra acquired at two particular chiral positions after deconvolution, and the residual scattering is more significant in thicker areas than thinner ones. Accordingly, the orbital-to-spin moment ratio extracted from EMCD spectra, which is the difference between the two q-resolved spectra after deconvolution, would be in principle increased with increasing sample thickness. The randomly fluctuated moment ratios displayed in our experiments are greatly attributed to a slight and irregular variation of local diffraction conditions due to the bending effect and imperfect epitaxy in detected areas. We suggest EMCD spectra should be acquired from sufficiently thin samples to minimize the plural scattering effect in originally detected spectra before any deconvolution. In addition, great care should be taken for slight misorientation and imperfect epitaxy when performing EMCD investigation on epitaxial thin films using a nano beam.

Experimental investigation on weak shock wave mitigation characteristics of flexible polyurethane foam and polyurea

In recent years, explosion shock wave has been considered as a signature injury of the current military conflicts. Although strong shock wave is lethal to the human body, weak shock wave can cause many more lasting consequences. To investigate the protection ability and characteristics of flexible materials and structures under weak shock wave loading, the blast wave produced by TNT explosive is loaded on the polyurethane foam with the density of 200.0 kg/m3 (F-200) and 400.0 kg/m3 (F-400), polyurea with the density of 1100.0 kg/m3 (P-1100) and structures composed of the two materials, which are intended for individual protection. Experimental results indicate that the shock wave is attenuated to weak pressure disturbance after interacting with the flexible materials which are not damaged. The shock wave protective capability of single-layer materials is dependent on their thickness, density and microscopic characteristics. The overpressure, maximum pressure rise rate and impulse of transmitted wave decrease exponentially with increase in sample thickness. For the same thickness, F-400 provides better protective capability than F-200 while P-1100 shows the best protective capability among the three materials. In this study, as the materials are not destroyed, F-200 with a thickness more than 10.0 mm, F-400 with a thickness more than 4.0 mm, and P-1100 with a thickness more than 1.0 mm can attenuate the overpressure amplitude more than 90.0%. Further, multi-layer flexible composites are designed. Different layer layouts of designed structures and layer thickness of the single-layer materials can affect the protective performance. Within the research range, the structure in which polyurea is placed on the impact side shows the optimal shock wave protective performance, and the thicknesses of polyurea and polyurethane foam are 1.0 mm and 4.0 mm respectively. The overpressure attenuation rate reached maximum value of 93.3% and impulse attenuation capacity of this structure are better than those of single-layer polyurea and polyurethane foam with higher areal density.