Microstructure Of Specimens Research Articles

Sulfate attack resistance of hybrid fiber reinforced rubber concrete

To increase the strength and applicability of rubber concrete, an eco-friendly concrete called hybrid fiber-reinforced rubber concrete (HFRRC) was produced by utilization of recycled tire rubber particles, basalt fibers, and polyvinyl alcohol fibers. This study investigates the sulfate attack resistance of HFRRC and normal concrete (NC). The mass variation, ultrasonic pulse velocity, compressive strength, failure mode, and microstructure of concrete specimens were investigated. The results showed that the corrosion resistance coefficient of HFRRC was higher than that of NC throughout the age of erosion. Further, HFRRC exhibited better integrity than NC when specimens were subjected to compression test failure. The findings can provide a useful reference for the application of hybrid-fiber reinforced rubber concrete suffered from sulfate attack.

Dynamic tensile characteristics of an artificial porous granite under various water saturation levels

Underground rocks are generally subjected to water erosion and dynamic disturbances. To exclude the effect of clay minerals on the water–rock interaction mechanism, clay-free artificial porous rock (APR) was used to investigate the coupling effect of water saturation and loading rate on tensile behavior. Dynamic Brazilian disc experiments were performed on APR with six water saturation levels (100, 80, 60, 40, 20, and 0%) using a split Hopkinson pressure bar (SHPB) combined with a high-speed camera. The results indicated that the number of cracks in the APR specimens increased with the water saturation level during the dynamic damage process, with more radial cracks at the water saturation of 80–100%. The dynamic tensile strength (DTS) and dissipated energy density exhibited different change trends with water saturation levels under different loading rates and the rate dependence was most significant in the fully saturated state (100%). At lower loading rates, DTS initially decreased rapidly and then more slowly with increasing water saturation. At higher loading rates, DTS exhibited a ‘decrease then increase’ trend. Moreover, the water-affecting factor exhibited an overall decreasing trend with the loading rate and gradually converged to 1.0. These phenomena can be attributed to the interplay between the weakening and strengthening water-effect mechanisms based on the microstructure and water distribution in the APR specimens.

Comparison of the Young’s modulus of the lead free solder alloy Sn-Ag3.8-Cu0.7 determined by hot tensile tests, ultrasonic measurements and [formula omitted]-Sn single crystal calculations

Sn-based solders are known for their tendency to form coarse grained microstructures. In combination with the high elastic anisotropy of β-Sn, the overall elastic properties and their interpretation require a careful discussion of the structure–property-relationship as elastic constants are often important input parameters for creep or fatigue models. This study therefore investigates the influence of microstructure and testing method on the Young’s modulus E for the widespread lead free solder alloy Sn-Ag3.8-Cu0.7 (SAC387) using bulk specimens. Due to its already high homologous temperature at room temperature (Thom≈ 0.6 = T/Tm for Tm being the melting temperature), hot tensile tests generally bear the risk of superimposed creep deformation. Mechanical testing becomes even more challenging, since yield strengths are usually low for these alloys. Consequently, in addition to the hot tensile tests executed for the engineering strain rate ϵ̇e=1⋅10−3 s−1, two supplemental methods are used to determine the Young’s modulus comprising of the dynamic resonance frequency measurement and the calculation of the Young’s modulus based on single crystal compliance data of the majority phase β-Sn.Young’s moduli yielded from dynamic resonance frequency measurement and calculations based on single crystal compliance data showed comparable results of (E35 °C≈ 55 GPa, E80 °C≈ 51 GPa and E125 °C≈ 48 GPa). Hot tensile tests showed similar data with the largest deviation at 80 °C, where E80 °C≈ 53 GPa was determined. These absolute values and their temperature dependence can be attributed to the microstructure of the cast specimens which show a general preferred orientation of β-Sn grains close to <110> after analysis via electron backscattered diffraction (EBSD). A comparison with literature data revealed significant differences in the Young’s moduli which are likely to be attributed to differences in the preferred orientation of β-Sn grains.

Recycling single use surgical face mask waste for reinforcing cement-treated/untreated dredged marine sediments: Strength, deformation and micro-mechanisms analysis

To prevent the transmission of airborne infectious diseases (SARS, H1N1, COVID-19, and influenza), the use of disposable surgical face masks has increased dramatically in the past few years. To mitigate the environmental consequences associated with mask waste, implementing circular economy strategies with the reuse of mask waste is a sustainable method. This study explores an innovative way to reuse mask fiber (MF) with dredged sediment waste together as road construction materials. First, the MF was introduced into cement-treated/untreated dredged marine sediment mixtures with different content and lengths. Then, a variety of laboratory tests were carried out to explore the basic physical and chemical characterization of raw materials and the development of mechanical properties of mixtures. In addition, the intrinsic mechanism of MF inclusion on cement-treated sediments was analyzed by scanning electron microscope (SEM) test. The results show that the inclusion of MF significantly improves the unconfined compression strength (UCS) and splitting tensile strength (STS) of both treated and untreated specimens. The highest UCS and STS values are at the condition with an MF content of 0.25%, a length of MF of 2 cm, and a curing time of 28 days. The combined strength increase caused by cement-MF together inclusion is much greater than the strength increase caused by either of them separately. It was also found that the elastic modulus (E50) decreased with the inclusion of MF. Furthermore, the addition of MF changes the brittle behavior of the specimens, which also improves the ductility and residual strength of the specimens. The SEM analysis demonstrates the microstructure of MF and MF-reinforced specimens. The creation of a stable and interconnected microstructure is largely attributed to the bridging impact of MF and the binding effect of hydration products, which significantly improves the mechanical behavior of specimens. The MF-reinforced cement-treated sediment could be an innovative, environmentally friendly, and economical material for road construction.

MICRO-MESO CHARACTERIZATION OF PREFABRICATED CONCRETE-CLT ADHESIVE JOINTS

This study evaluates the use of five commercially available epoxy adhesives (EAs), from low to high cost, as a connection alternative of timber-concrete composites (TCCs) using cross-laminated timber (CLT) and medium-strength precast concrete (25MPa). Five alternative EAs were initially evaluated via pull-off tests to determine the adhesive strength of the interface CLT/concrete, with average results varying from 0.6MPa to 3.6MPa. Subsequently, optical and scanning electron microscopy analyses were implemented to assess the microstructure of post-tested TCC specimens, finding that usually the CLT/concrete interface was not fully glued by the EAs and that there was a positive correlation between the penetration of each EA with the corresponding tension strength of the TCCs. Then, the three EAs with the largest adhesive strengths were further tested by small double-shear (SDS) tests evaluating their shear strength and deformation, as well as damage evolution and failure modes, which were obtained using digital image correlation. The SDS test average results ranged from 2.4MPa to 8.8MPa, and the EA with the best behavior was not the one with the highest tensile strength, but rather with the highest EA penetration into concrete, demonstrating that this property highly positively impacted the shear strength of TCCs. Finally, cost/benefit analyses were obtained, and interestingly, the EA with the best adhesive/shear performance was not the most expensive alternative, opening the discussion that, even though mostly expensive EAs have been used in TCCs, the option of technically valid and low-cost EA is feasible.

Parametrically Upscaled Constitutive and Crack Nucleation Models for Investigating the Effects of Specimen Geometry and Microstructure on Fatigue Crack Nucleation in Ti Alloys Containing Micro-texture Regions

Parametrically Upscaled Constitutive and Crack Nucleation Models for Investigating the Effects of Specimen Geometry and Microstructure on Fatigue Crack Nucleation in Ti Alloys Containing Micro-texture Regions

Experimental characterization of acoustic damping materials

AbstractDue to their ease of use and low cost, passive damping methods are a preferred mean for the reduction of noise in many engineering applications. This applies in particular to foam materials, which exhibit good acoustic and mechanical damping properties. The selection of suitable materials is usually carried out experimentally and can be very labor‐intensive and time‐consuming. For this reason, it is helpful to develop qualified numerical methodsthat can be used for material design and selection. Hence, foam materials must be characterized experimentally in order to enable a later comparison with vibroacoustic simulations. This contribution, therefore, aims at providing suitable parameters for the use in numerical analyses and their validation. Firstly, the microstructure of a foam specimen is captured by means of a CT scan. In addition to providing the geometry for the multi‐physics simulations, this measurement is also used to determine characteristic foam features, for example, strut thickness and pore size distribution. In the second step, the frequency‐dependent stiffness and damping properties of the material are determined by a special experimental setup utilizing an electrodynamic shaker. Here, the dynamic system is approximated as a single‐mass oscillator, which is sufficiently accurate for low frequencies. These properties will later be used in the numerical model to evaluate different parameter identification approaches. In the third and last step of the experimental campaign, measurements with an impedance tube are conducted to obtain the coefficient of absorption. This material parameter is particularly suitable for comparing experiments and simulations. Finally, the correlation between the experimental results is examined to provide a deeper understanding of the foam materials.

Влияние технологических параметров на микроструктуру и свойства сплава AlSiMg, полученного методом селективного лазерного плавления

Introduction. The development of additive technologies is aimed at the synthesis of new powder compositions for selective laser melting plants, the study of the effect of mode parameters on the stable quality of products. The purpose of this work is to study the effect of the scanning strategy on the microstructure, elemental composition, porosity and density of specimens obtained by selective laser melting from non-spherical powders (Al — 91 wt. %, Si — 8 wt. %, Mg — 1 wt. %), subjected to special preparation to determine the optimal conditions for selective laser melting. The research methods are methods of X-ray diffraction and X-ray phase analysis, transmission electron microscopy. The paper examines specimens formed using four different scanning strategies. Results and discussions. A promising aluminum alloy AlSi8Mg is developed for selective laser melting. The material has good manufacturability and low powder cost. The technological parameters of melting make it possible to form a thin structure with a low level of porosity. The mechanism of influence of the scanning strategy on porosity, surface morphology, relative density and microstructure is investigated. A specimen from the AlSi8Mg powder composition with a high relative density of 99.97 % is produced by selective laser melting with an energy density of 200 J/mm3, a specimen scanning circuit when the direction of laser movement changes by an angle of 90° each odd layer. It is proved that the density of the AlSiMg alloy depends on the scanning strategy used. The calculated density of the specimen was 2.5 g/cm3, which corresponds to the density of silumin. Analysis of SEM images and maps of the distribution of elements (Al, Mg, Si) of the specimens showed that different specimen formation strategies do not affect the nature of silicon distribution. A unique grain structure is observed in the resulting AlSi8Mg alloy. The melt pool consists of small grains along the border and large grains in the center. The formation of fine grains is explained by the addition of Si and the high cooling rate during selective laser melting.

Formation of YOF on Y2O3 through surface modification with NH4F and its plasma-resistance behavior

Yttrium oxyfluoride (YOF) is known for exhibiting superior plasma-resistance properties compared to Y2O3, particularly in a fluorocarbon plasma environment. The formation of the YOF layer directly on the surface of Y2O3 via surface modification may be considered as a viable and cost-effective method. In this study, we employed ammonium fluoride (NH4F) salt for the surface modification of Y2O3. By using a 40 wt% NH4F aqueous salt solution, the YOF layer with a thickness of about 8.6 μm was efficaciously formed in-situ on the surface of Y2O3 based on the fluorination mechanism. The composition and microstructure of the modified Y2O3 surface was thoroughly characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis revealed the formation of distinct intermediate ammonium yttrium fluoride phases depending upon the heat treatment temperature (150 − 500 °C) through the fluorination of Y2O3 with NH4F. A stable YOF phase was formed ultimately at 300 °C. Plasma etching tests were performed using a mixture of CF4/Ar/O2 gases for 1 h. The microstructures of specimens are observed by SEM before and after plasma treatments. Plasma exposure tests demonstrated that specimens heat-treated at 500 °C for 2 h exhibit excellent plasma-resistance behavior with minimal surface damage, which is attributed to the presence of stable and dense YOF phase.

Dual Grain Refinement Effect for Pure Aluminum with the Addition of Micrometer-Sized TiB2 Particles.

The inefficiency of grain refinement processes has traditionally been attributed to the limited utilization of heterogeneous nucleation particles within master alloy systems, resulting in the formation of abundant inactive particles. This study aims to investigate the alternative influences of particles by incorporating external micrometer-sized TiB2 particles into the grain refinement process. Through a series of experiments, the refinement efficiency, grain refinement mechanism, and resultant microstructure of TiB2 particle-induced grain refinement specimens are comprehensively examined using various microscopy and analytical techniques, including polarization microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Our findings demonstrate a direct correlation between increased levels of TiB2 particles and enhanced grain refinement efficiency. Moreover, the microstructure analysis reveals the distribution of TiB2 particles along grain boundaries, forming a coating due to self-assembly phenomena, while regions with a lower particle content may exhibit irregular grain structures. DSC analysis further confirms reduced undercooling, indicating the occurrence of heterogeneous nucleation events. However, TEM observations suggest that heterogeneous nucleation is not significantly influenced by the growth restriction factor attributed to TiAl3 2DC compounds. The grain refinement mechanism involving TiB2 particles is elucidated to entail both heterogeneous nucleation and physical growth restriction effects. Specifically, a reduction in average grain size is attributed not only to heterogeneous nucleation but also to the physical growth restriction effect facilitated by the TiB2 particle coating. This study offers insights into leveraging particles that do not participate in heterogeneous nucleation within master alloy-based grain refinement systems.

Investigation of Corrosion Protection Through CNTs/ CNFs Modified Cement Mortars

background: the performance of nano modified cement based materials is substantial in terms of their mechanical durability and other similar properties that are of great importance in the functional life of cement structures. The motivation of this study is to formulate conclusions concerning the anti-corrosive impact of Carbon nanotubes (CNTs) and Carbon nanofibers (CNFs) on the properties of mortar specimens and respectively on their service life. methods: The nano additives performance, was investigated through Scanning methods, such as X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM) which analyze the microstructure of mortar specimens with 0.1 % wt addition of CNTs and 0.1 % wt addition of CNFs in their synthesis. In addition, other techniques such as total chloride content and gravimetric mass loss measurements, provide a consolidated assessment of the impact of the nano modified cement materials. In particular, (SEM) and (XRD) microstructure analysis results showed that nanoadditives are found as agglomerates in the cement paste, whereas their hydrophobic nature blocks the diffusion of corrosive factors into the cement paste. Additionally, the total chloride content in mortar specimens with CNFs is approximately 50% less than the relevant percentage of the specimens without additives, which is in compliance with the relevant percentages of porosity values. Furthermore, from the elemental analysis of all specimens, it is found that the samples that are corroded are the specimens without nano additives. results: The addition of nanomodified materials affects the porosity and the microstructure of the mortar specimens. conclusion: The addition of 0,1 % of CNTs or CNFs positively affects against corrosion impact while exposure in extremely corrosive conditions.

Influence of secondary peak temperature on simulated ICCGHAZ microstructure and toughness of high-strength low-alloy steels

Abstract The ICCGHAZ specimens of laser-arc hybrid welding under various secondary peak temperatures were prepared using welding thermal simulation technology. Investigations were conducted into how the toughness and microstructure of the simulated ICCGHAZ specimens were correlated with the secondary peak temperature. Results showed that the size, distribution, and morphology of the M-A constituents in the ICCGHAZ specimens were primarily influenced by the secondary peak temperature. With this temperature at 760 °C, the blocky M-A constituents mostly aggregated into chains along the grain boundaries. As the secondary peak temperature reached 800 °C, while the blocky M-A constituents typically stayed close to the grain boundaries, the necklace M-A constituents began dispersing. The former austenite grain boundaries vanished as the M-A constituents migrated outward when the temperature further rose to 840 °C. At secondary peak temperatures of 760 °C and 800 °C, the volume proportion of the M-A constituents was 2.9% and 3.2%, respectively. In comparison, the volume fraction rapidly decreased to 0.9% at 840 °C. The size of the M-A constituents shrank as the secondary peak temperature rose, whereas the crack initiation energy Ei, crack propagation energy Ep, and impact energy Et increased. The toughness of the ICCGHAZ specimen was diminished because of the grain boundary necklace distribution characterization and the large size of the M-A constituents.

Enhancing of Surface Quality of FDM Moulded Materials through Hybrid Techniques.

With the rapid advancement of 3D-printing technology, additive manufacturing using FDM extrusion has emerged as a prominent method in manufacturing. However, it encounters certain limitations, notably in surface quality and dimensional accuracy. Addressing issues related to stability and surface roughness necessitates the integration of 3D-printing technology with traditional machining, a strategy known as the hybrid technique. This paper presents a study of the surface geometric parameters and microstructure of plastic parts produced by FDM. Sleeve-shaped samples were 3D-printed from polyethylene terephthalate glycol material using variable layer heights of 0.1 mm and 0.2 mm and then subjected to the turning process with PVD-coated DCMT11T304 turning inserts using variable cutting parameters. The cutting depth was constant at 0.82 mm. Surface roughness values were correlated with the cutting tool feed rate and the printing layer height applied. The selected specimen's microstructure was studied with a Zeiss EVO MA 15 scanning electron microscope. The roundness was measured with a Keyence VR-6200 3D optical profilometer. The research results confirmed that the additional application of turning, combined with a reduction in the feed rate (0.0506 mm/rev) and the height of the printed layer (0.1 mm), reduced the surface roughness of the sleeve (Ra = 1.94 μm) and increased its geometric accuracy.

Dependence of the mechanical properties of nylon-carbon fiber composite on the FDM printing parameters

Nylon-based polymer reinforced with short carbon fibers (PA-CFs), fabricated using the Fused Deposition Modeling (FDM) 3D printing process, has been proposed for various applications. However, the mechanical performance of these materials as a function of printing parameters, including wall thickness at infill contents < 100 %, has yet to be reported in the literature. This paper focuses on the effects of infill percentage, nozzle temperature, and wall thickness on the porosity content, microstructure, and mechanical properties of PA-CF specimens. Employing a Taguchi (L9 − 3^3) design of experiments, tensile and flexural testing were conducted to assess their mechanical response. The printing temperature induces microstructural changes, promoting interlayer debonding due to voids and pores at wall- and skin-core interfaces. Wall thickness significantly impacts tensile strength and can be maintained between 0.8 and 1.35 mm for maximum flexural strength, while maximal tensile strength can only be achieved with a wall thickness between 1.15 and 1.5 mm.

Effect of heat treatment on the shear fracture and acoustic emission properties of granite with thermal storage potential: A laboratory-scale test

The exploitation of geothermal resources enhances the energy structure but poses challenges related to thermal–mechanical issues. This study utilizes short core in compression (SCC) specimens of granite to investigate thermo-mechanical properties. We examined the effects of heat treatment temperature on physical properties, shear fracture toughness, as well as acoustic emission (AE) characteristics. Fracture surface morphology and microstructure of the heat-treated SCC specimens were also analyzed using 3D laser scanning and scanning electron microscopy. Results indicate that both mass loss and P-wave velocity decrease with increasing heating-treated temperature, and similar trends are observed in mechanical properties. Specifically, fracture energy and shear fracture toughness decline by 51.48 % and 61.27 %, respectively, as temperature rises from 25 °C to 750 °C. The b-value and proportion of shear cracks initially increase before falling, with an inflection point at 300 °C, linked to thermal-induced microstructural deterioration. Fractal dimension (D) and joint roughness coefficient (JRC) show significant increases with higher heat treatment temperatures. Microstructural degradation, including dehydration and thermal-induced microcracking, drives the reduction in shear properties of heat-treated granites. Overall, our findings offer valuable insights into determining various methods of heat storage reconstruction with great application potential.

Effects of rare earth on nitriding microstructure and properties of a La-Ce micro-alloyed Q235RE steel

Accelerating nitriding is an interesting topic in chemical heat treatment of ferrous parts. In order to have a deeper understanding of the catalysis principles of rare earth in nitriding, a Q235 carbon steel and a Q235RE steel micro-alloyed with rare earth elements La and Ce were nitrided respectively by plasma nitriding and gas nitriding. The microstructure, phase constitution, and composition of the nitrided specimens were analyzed. The hardness profile of nitriding layer and the brittleness of surface compound layer were measured. The results demonstrate that the Q235RE specimens obtained a higher hardness and deeper effective hardening layer than the Q235 specimens without rare earth microalloying. The rare earth catalysis effects were presented as the acceleration of nitrogen diffusion and the inhibition of nitride precipitation in the diffusion layer of the Q235RE specimens. In addition, the surface compound layer of the Q235RE specimens showed higher toughness and better adhesion to the matrix than that of the Q235 specimens, which is considered to be strongly related to the rare earth elements diffused into the compound and the enhanced residual compressive stress in the layer.

Multi-scale investigation on curing time effect of lime stabilized red mudstone as fill material for high-speed railway subgrade

The utilisation of red mudstone waste as subgrade fill material after lime stabilization can meet the requirements of green development. This study aims at investigating the lime stabilization effect on the changes in mechanical properties and microstructure of compacted red mudstone fill material, with particular emphasis on the curing time effect. Red mudstone fill material were stabilized by 4 % lime, and the unconfined compressive strength, direct shear strength and microstructure of the lime-stabilized fill material specimens were determined at various curing times. Results show that the lime stabilization can significantly improve the unconfined compressive strength, modulus and direct shear strength and effectively mitigate the water sensitivity of the red mudstone fill material. The density function curve of the saturated red mudstone fill material shows monomodal characteristic, but the saturated lime stabilized fill material still maintains bimodal characteristic even with only one day of curing. The microstructure modification induced by lime stabilization mainly results from the rapid flocculation of soil particles and the formation of hydration product. During curing, the percentage of the nano-pores increases, mainly attributes to the formation of C-A-S-H which fills the micro-pores gradually.

Effects of Heat Treatment on the Chemical Composition and Microstructure of Cupressus funebris Endl. Wood

The effects of heat treatment on Cupressus funebris Endl. wood were examined under different combinations of temperature, time, and pressure. The chemical composition, crystallinity, and microstructure of heat-treated wood flour and specimens were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Vacuum heat treatment led to changes in the functional groups and microstructure of C. funebris wood, and the relative lignin content decreased with increasing treatment temperature, which was significant at lower negative pressures. Cellulose crystallinity showed a change rule of first increasing and then decreasing throughout the heat treatment range, and the relative crystallinity ranged from 102.46% to 116.39%. The cellulose treated at 120 °C for 5 h at 0.02 MPa had the highest crystallinity of 44.65%. These results indicate that although heat treatment can improve cellulose crystallinity, very high temperatures can lead to decreased crystallinity. The morphology and structure of the cell wall remained stable throughout the heat treatment range; however, at elevated temperatures, slight deformation occurred, along with rupture of the intercellular layer.

Effects of Carbon Nanotubes on Mechanical Strength, Damage Process, and Microstructure of Lithium Tailing Backfilling.

In this study, common multiwalled and carboxylated carbon nanotubes (CNTs) were added to the cemented lithium tailings backfill (CLTB). The effects of CNTs on the mechanical properties, hydration products, damage process, and microstructure of CLTB specimens were studied by uniaxial compression (UCS), infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The experimental results show that the addition of CNTs effectively increased the compressive strength compared with the blank control group. When the concentration was 0.05-0.20%, the compressive strength was proportional to the content, the optimal addition amount was 0.2%, and the enhancement effect was 75% and 95.31%, respectively. The FT-IR results indicate that the addition of CNTs increased the total amount of the hydration product but did not affect its type. The hydration of the three-dimensional reciprocal penetration network formed by moderate amounts of CNTs has a positive effect on the mechanical strength of CLTB specimens.

Healing of discontinuities in metal by the strong electromagnetic field treatment

Abstract The results of a study microstructure of polycrystalline zinc specimens under by short pulses of the high-energy electromagnetic field treatment on them are presented. The aim is to study the possibility of healing micropores and microcracks inside the material during such treatment. The equipment used and the experimental technique are described, the analysis of the experimental data obtained is carried out. Metallographic studies of the zinc microstructure before and after HEEMF treatment confirm the assumption that in the process of such treatment, the decrease in its porosity may occur in the metal and, as a consequence, a significant increase in the ultimate plastic strain before fracture. Investigations of the polycrystalline structure of the metal have shown that the decrease in porosity is not the result of recrystallization.