Deterioration Of Mechanical Properties Research Articles

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.

Study on the deterioration of mechanical properties of stainless steel S35657 exposed to overall stage of fire

Fires often have destructive effects on steel structures, putting the safety of building structures at serious risk. As a new austenite stainless steel, grade S35657, its in-fire and post-fire mechanical behavior has not been reported, which limits its application. In this paper, a total 68 stainless steel S35657 coupons were designed and tested, with 34 coupons used for in-fire tests and 34 for post-fire tests. The effects of heating temperatures, loading rates, and heating soaking times on the mechanical properties were investigated. The failure modes, as well as the stress-strain curves and mechanical properties, were acquired. Electron microscopy scanning analysis were also conducted on the coupons to study the fracture mechanisms at elevated temperatures. The test results showed a rapid decline in in-fire mechanical properties when the temperature exceeded 600 °C. The yield strength of the coupon at 1000 °C is only 9.1 % of that at room temperature. As the tensile rate increased, the strength of the coupon increased gradually. For post-fire coupons, there is no significant change in the mechanical properties of coupons at temperatures ranging from 20 °C to 900 °C. However, after reaching a temperature of 1000 °C, the coupon experienced a reduction in yield strength (up to 27.8 %) and an expansion in elongation (up to18.0 %), compared to the coupon at ambient temperature. This related to the change in grain size of the coupons after exposure to high temperatures. The heating soaking time has an insignificant effect on the post-fire mechanical properties of stainless steel S35657. Existing constitutive models in the literature cannot be well applied to stainless steel S35657, new constitutive models to predict the in-fire and post-fire mechanical properties have been established. Moreover, reduction factors for the key mechanical properties were compared with existing values, and new unified equations for stainless steel S35657 were proposed. Finally, a reliability analysis was performed to evaluate the proposed design rules, and it was deemed that the proposed design rules were reliable. The findings of this study will provide a reference for engineers in evaluating the in-fire and post-fire residual strength of stainless steel S35657, and offer guidance for fire resistance design and high-temperature repair reinforcement.

Waterborne Polyurethane Micelles Reinforce PEO-Based Electrolytes for Lithium Metal Batteries.

Although solid polymer electrolytes have been developed for several decades, poly(ethylene oxide) (PEO) or polymers with ethoxy (EO) segments are still one of the most promising candidates for advanced batteries. The low ionic conductivity and lithium-iontransference number as well as the deterioration of mechanical properties after coupling with lithium salts restrict its further adoption. Herein, a serial of PEO-based composite electrolytes optimized by waterborne polyurethane are prepared via blend method. With the assistance of H2O, ionic type waterborne polyurethane assembles into flexible micelles, in which hydrophobic segments as the core and hydrophilic groups as the shell. Utilizing this feature of waterborne polyurethane, PEO and Li salt (LiTFSI) aqueous solution is slowly added to the organic solution of waterborne polyurethane to compoundin situ, and polymer composite electrolytes are fabricated. The multilevel (hydrogen bonds with different binding energy) and multiscale (deformation of flexible micelles) dynamic interaction endows the composite electrolyte with attractive mechanical properties. The assembled Li|Li symmetric battery with the molar ratio of EO to Li salts of 8:1 exhibits excellent cycling stability up to 800 h at 0.1 mA cm-2, and the assembled Li|LiFePO4battery can be stably cycled at 1C for >400 cycles.

Disintegration and marine biodegradability of biocomposite using Pennisetum setaceum fiber and PLA as matrix

The accumulation of plastics in the environment is a well-recognized issue. To address this, biodegradable materials such polylactic acid (PLA) have been developed. In natural environments such as soil or water, PLA degradation progresses slowly but steadily. To accelerate the degradation of the material, this study investigates the degradation of a biocomposite material using PLA as a matrix and Pennisetum setaceum fiber as reinforcement. Disintegration and marine biodegradability tests, both at the seawater/sediment interface and in marine sediment, were conducted. Different measurement tests were employed to quantify the degradation of PLA and composite samples, focusing on the mass loss and the variation of the mechanical and thermal properties. The results consistently demonstrated greater mass loss and mechanical property deterioration during the disintegration test compared to the marine biodegradability tests. Notably, the composite material exhibits more significant degradation than the pure polymer without fiber. For composite, the addition of fiber increased the degree of biodegradability compared to the plastic matrix.

Time-varying moisture characteristics and C-S-H gel properties of concrete in dry and hot environments

The construction of deeply buried tunnels has intensified concerns regarding shrinkage cracking and the long-term performance deterioration of lining concrete in dry-hot environments. These issues are related to the dynamic interconversion of internal moisture states, the changing moisture behavior over time, and the evolution of calcium silicate hydrate (C-S-H) properties. However, the mechanisms underlying these phenomena are not fully understood. This study investigates the dynamics of moisture content across different states, the source and composition of evaporated water, as well as the mechanism of change in the microscopic properties of C-S-H in concrete subjected to dry-hot conditions (40℃ and 60℃) and standard curing environments through tests on water loss rates, chemically bound water, and low-field nuclear magnetic resonance. The findings reveal that at 40℃ and 60℃, hydration products were generated rapidly before mold removal, leading to significant increases in chemically bound water, interlayer water, and gel water, while capillary water was notably consumed. After mold removal, the rate of chemically bound water increase slowed, while interlayer water, gel water, and capillary water evaporated significantly, with gel water comprising 87.27 % and 83.51 % of the evaporated water at 40℃ and 60℃, respectively. From day 1 to day 28, interlayer water, gel water, and capillary water contents decreased significantly, with reductions of up to 85.98 % at 60℃. In dry-hot environments, moisture primarily exists as chemically bound water and gel water, contrasting with standard curing conditions where capillary water is also present. The study concludes that drying of C-S-H gels leads to both positive effects, such as interlayer space compression and increased indentation modulus, and negative effects, including increased microporosity and reduced matric densification, ultimately contributing to the deterioration of long-term mechanical properties.

The effects of UV aging process on the structure and properties of high-tenacity poly(ethylene terephthalate) industrial fiber

The high-tenacity poly(ethylene terephthalate) (HT PET) industrial fibers (1100 dtex/ 192f) were fixed in position with a constant fiber length and subjected to accelerated artificial ultraviolet exposure with temperature of 50 °C to assess their degradation mechanism. The structural evolutions were evaluated using a combination of ex-situ wide-angle X-ray diffraction (WAXD), ex-situ small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), and intrinsic viscosity tests based on the relaxed aged samples after different aging process. The results indicate that the structures and properties evolutions of HT PET industrial fiber under UV aging process can be categorized into three stages. In the pre-aging stage (t ≤ 0.5d), the fiber experiences a slight decline in tenacity and thermal shrinkage properties due to the combined impact of UV radiation and heat treatment. Subsequently, in the mid-aging stage (0.5d < t ≤ 28d), a notable decrease in the fiber's elongation at break is observed, accompanied by visible macroscopic defects arising from photo-oxidative aging on the fiber surface after 16 days of exposure. While the fiber's unit cell and atomic positions remains stable on atomic scale, the lamellar thickness and long period witness a significant reduction owing to high-orientation molecular breakages in the mesophase region. Moreover, rearrangement of molecular chains leads to a reduction in the tilting angle. In the late-aging stage (t > 28d), the degradation rate of mechanical and thermal shrinkage properties of the fiber decelerates, alongside a decline in intrinsic viscosity. These results suggest that the fiber's crystallinity remains unchanged post UV aging, with the deterioration in mechanical properties of HT PET industrial fiber primarily attributed to molecular degradation during UV exposure.

Investigation on the pore size characteristics and mechanical properties of grouting materials scoured by flow water

Investigating the pore size characteristics and mechanical properties of the stone bodies formed by residual grout is crucial for understanding the authentic permeability and load-bearing capacity of grouting materials after being scoured by water flow. In this study, the pore size distribution, porosity, uniaxial compressive strength (UCS), and elastic modulus (E) of stone bodies formed by residual grout from polyacrylate latex-modified cement grouting material (PLMC) were systematically investigated, and pure cement grout (PC) as a control group. First, scouring tests were conducted on grouting materials with various water-to-cement ratios (w/c, 0.6–0.8) and polymer-cement ratios (p/c, 0–0.2) under different flow velocities (0–1 m/s). Subsequently, the pore size characteristics of stone bodies formed by residual grout under various conditions were studied via nuclear magnetic resonance test. Finally, the uniaxial compression tests were conducted to investigate the impact of water scouring on the mechanical properties of grouting materials, and the relationship between pore size characteristics and macro mechanical responses was analyzed. Results show that the stone bodies formed by residual grout compared to the non-scoured state develop mesopores and macropores, and the number of micropores also increased significantly. This porosity escalation results in a reduction in UCS and E. When the flow velocity reaches 1 m/s, the porosity of PLMC with w/c = 0.8 increases by 2.95 %, while UCS decreases by 14.6 % and E decreases by 37.4 %. PC demonstrates more pronounced changes, with a porosity increase of 7.01 %, UCS decreases by 32.9 %, and E decreases by 41.5 %. With the rise in w/c, the deterioration of pore structure and mechanical properties of the stone bodies formed by residual grout is more significant compared to the non-scoured state. Increasing p/c can mitigate the deterioration of the pore structure and mechanical properties. The findings provide meaningful guidance for the grouting reinforcement under dynamic water conditions.

Longitudinal Analysis of Bone Metabolic Markers and Bone Mechanical Properties in STZ-Induced Diabetic Rats.

Background: This longitudinal study examined the early effects of type 1 diabetes on bone mechanical properties and metabolic markers in mature rats, focusing on the natural progression of diabetes-induced changes without external treatments. Methods: Forty-eight 8-month-old male Wistar rats were divided into two groups, with one group receiving a single dose of streptozotocin (STZ, 60 mg/kg). Assessments were performed 2, 4, and 8 weeks post-administration, including serum biochemical analyses, bone marker assessments, and mechanical bone tests. The data were analyzed using two-way ANOVA to evaluate the impact of time and treatment. Results: At 2 weeks, diabetic rats showed increased fasting blood glucose (p < 0.001), decreased insulin levels (p = 0.03), and changes in HOMA markers (p < 0.001), liver enzymes (p < 0.001), inflammatory markers (p < 0.001), and bone metabolism markers (osteocalcin (p < 0.001), OPG (p = 0.006), RANKL (p < 0.001), and OPG/RANKL ratio (p < 0.001)), with initial alterations in bone geometry. By week 4, decreased body weight in the diabetic group (p < 0.001) led to further changes in bone geometry and initial differences in mechanical properties. At 8 weeks, significant declines in body (p < 0.001) and bone (p < 0.001) weights were observed, along with further deterioration in bone geometry and mechanical properties. Conclusions: The study highlights the significant impact of STZ-induced diabetes on bone health as early as two weeks post-STZ administration, with marked temporal changes in biochemical markers and mechanical properties.

Comparison with the effect of the cyclic liquid nitrogen jet and liquid nitrogen immersion cooling on the deterioration of mechanical properties of high temperature rocks

In order to study the effect of liquid nitrogen jet cooling on the deterioration of mechanical properties of high temperature rocks, the cyclic liquid nitrogen jet (LNJ) cooling and liquid nitrogen immersion (LNI) cooling were carried out on 200 °C and 400 °C granite. The variations of ultrasonic velocity, tensile strength, acoustic emission and energy evolution were analyzed. The results showed that with the increase of rock temperature and cooling cycles, the deterioration of mechanical properties of high temperature rock was enhanced by cyclic LNJ and LNI cooling. Differently, the deterioration effect of LNI cooling on mechanical properties was weakened with the increase of cycles. On the contrary, the deterioration effect caused by LNJ cooling was significantly enhanced with the increase of cycles. For example, when the LNI cooling cycles exceeded 5 times for 200 °C sample and 3 times for 400 °C sample, the tensile strength and absorbed energy at failure decreased limitedly with the growth of cooling cycles. However, the deterioration degree of rock mechanical properties at 400 °C showed a linear decline trend with the increase of LNJ cooling cycles. The temperature and the number of cycles had significant effects on mechanical properties, with temperature having the greatest influence. The difference between LNJ and LNI cooling became more pronounced with increasing cycles. LNJ cooling, by creating localized high thermal stresses and non-uniform heat transfer, led to continuous deterioration of mechanical properties with each cycle. In contrast, LNI cooling's effect saturated after initial cycles. The multi-cycle LNJ cooling method could improve the fracture degree of high temperature rock under low load level, so as to improve the efficiency of high temperature hard rock formation drilling.

Experimental study on energy and damage evolution of dry and water-saturated dolomite from a deep mine

The deformation and failure of a rock is closely related to the strain energy consumption during the load process of rock. To investigate the effect of water on energy evolution and damage characteristics of dolomite samples from a deep mine, the uniaxial compression tests were carried out on dry and water-saturated dolomite samples at different burial depths (900 m–1200 m). The effects of water on the evolution characteristics of elastic and dissipative energy ratios ( Ue/ U and Ud/ U) during rock deformation and failure was analyzed. Based on the variation rate of damage factor ( Df), a new brittleness index is proposed, which can effectively characterize the brittleness characteristics of water-bearing dolomite. The results show that the uniaxial compressive strength and elastic modulus of the water-saturated dolomite are significantly reduced compared to dry sample. The energy and damage evolution process of dolomite can be divided into four stages: initial damage stage, stable damage stage, pre-peak accelerated damage stage and post-damage stage. The variation rate of damage factor of the rock samples in the stable damage stage and the pre-peak accelerated damage stage appeared to increase significantly after water saturation treatment. Compared with water-saturated samples, more pronounced energy hardening characteristics and brittleness characteristics were observed in dry samples. In addition, the possible impact on the stability of deep rock engineering after the deterioration of rock mechanical properties and energy storage properties caused by water was analyzed. Groundwater can somewhat reduce rock burst proneness. However, it also has the potential to lead to greater rock engineering destabilization and failure hazards.

Dynamics of Degradation of Polylactide-Natural Rubber Compositions under the Influence of UV Irradiation

The effect of ultraviolet radiation of various wavelengths (254 nm and 365 nm) on compositions based on polylactide with the addition of natural rubber was studied. It was found that the effect of the wavelength of 254 nm on the studied samples is much more active than 365 nm, which is characterized by a decrease in the melting temperature and the degree of crystallinity of polylactide in the compositions, as well as a deterioration in physical and mechanical properties. The IR spectroscopy method confirms the photodegradation process by changing the intensities of structurally sensitive polylactide and natural rubber bands.

Residual mechanical properties of corroded ultra-high-strength steels and weld metals

This paper presents an in-depth investigation into the residual mechanical properties of ultra-high-strength steels and weld metals after exposure to corrosive environment. The tensile specimens of weld metals were fabricated using ER100S-G, ER110S-G, ER120S-G feedstock wires by robotic gas metal arc welding, whilst ultra-high-strength steel tensile coupon specimens were machined from the Q890 and Q960 steel plates. The high-strength steel and weld metal tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. Six exposure durations were designed to achieve different corrosion degrees of specimens. A total of 23 corroded ultra-high-strength steel tensile coupon specimens and 19 corroded high-strength weld metal specimens were included. The geometric profiles of corroded steel specimens were determined via non-contact 3D laser scanning. Monotonic tensile tests were conducted to determine the stress-strain responses and key mechanical properties of corroded steel and weld specimens. Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are reported and discussed. Prediction equations on the residual mechanical properties regarding the tensile loading capacity, yield stress and ultimate tensile stress of ultra-high-strength steels and weld metals after exposure to corrosive environment were established.

Ferritic–Martensitic Steels in Power Industry: Microstructure, Degradation Mechanism, and Strengthening Methods

Ferritic–martensitic (F–M) steels are widely used for high‐temperature pressure vessels and reactor cladding structures in power plants. The high operating temperatures and pressures, as well as the radiation environment, significantly challenge the mechanical stability of these steels. Here, the degradation mechanisms in F–M steels during creep and thermal aging under these harsh environments are reviewed. The exceptional mechanical properties of F–M steels are mainly attributed to their well‐constructed microstructures and chemical compositions. Microstructural barriers such as dislocations, solid solution atoms, and precipitates play key roles in resisting degradation. During the long‐term service, the microstructures undergo gradual evolution, resulting in a deterioration of mechanical properties at the macrolevel. In addition to the degradation mechanisms, some recent advancements in strengthening methods, including microalloying strengthening, thermomechanical treatment (TMT), and oxide dispersion strengthening, are summarized, aimed at the development of next‐generation F–M steels. The strengthening of the F–M steels is mainly achieved by enhancing the thermal stability of their microstructures. Insight into both the deterioration mechanisms and strengthening methods of F–M steels may pave the way for new approaches in developing high‐performance steels for applications in next‐generation power plants operating at ultrahigh operating temperatures and pressures.

Evolution of high temperature oxidation properties of SiCf/SiCN composites with BN interphase

In this study, SiC/SiCN composites with BN interphase were prepared using chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) methods. The evolution and related mechanisms of mechanical and microwave absorption properties of the composites after oxidation at 800 °C, 1000 °C, 1200 °C, and 1400 °C were investigated. The results showed that with the elevating of oxidation temperature, the flexural strength of SiC/SiCN composites gradually decreased, with a retention rate of 56.7 % after oxidation at 1400 °C. The main reasons for the deterioration of mechanical properties were the changes in the crystal structure of SiC fibers under high-temperature conditions and the formation of brittle SiO2 phases on the surface and interior of the SiCN matrix. With the increase in oxidation temperature, the microwave absorption performance of the composites showed an enhancing trend. The main reasons were that after oxidation treatment, the reduction of free carbon content and the formation of SiO2 film layers from the oxidation of SiC and SiCN led to a decrease in the complex permittivity of the composites, resulting in better impedance matching and dielectric loss capabilities. The contributions of BN interphase to stress dispersion, interface polarization, and oxidation protection significantly enhance the mechanical and electromagnetic absorption properties of the composites. Therefore, SiC/SiCN composites are high-temperature structural microwave absorbing materials with great application prospects.

Macro–micro correlation analysis on the loess from Ili River Valley subjected to freeze–thaw cycles

The Ili River Valley in Xinjiang, China, is a typical seasonal frozen area where loess landslide disasters have become increasingly common during the freeze–thaw periods in recent years. This study analyzed the macroscopic mechanical strength and microstructure changes of the Ili loess under different freeze–thaw cycles (FTCs) through the post-freeze–thaw triaxial compression test on the unsaturated soil in laboratory. Apart from the scanning electron microscopy (SEM), and the nuclear magnetic resonance (NMR), the macro–micro correlation analysis and the cluster-principal component analysis were applied for the theoretical discussion. The results indicated that the cohesive force of the loess exhibits an initial decreases, followed by the increases, and eventually keep stable after various FTCs, while the internal friction angle showed the opposite developing trend before the final constant. Similar to the strong correlation between the cohesive force and the particle abundance, the internal friction angle is also closely related to the abundance and orientation fractal dimension of the loess particles. However, the principal component analysis results showed that cohesive force strongly correlates with the average maximum pore size and the pore size fractal dimension, for which the internal friction angle most strongly affected by the average maximum particle size. The possible reason is that the extracted principal components represent a class of microscopic parameters with the same or similar change trend, although there may be a certain offset between them. The mechanical deterioration of loess is attributed to the repeated frost heaving force and the migration potential caused by FTCs. The alterations of the microstructure accelerated the deterioration of the macroscopic mechanical properties of the loess, which further widens the understanding of the mechanism behind the deterioration of loess mechanical strength in the Ili River Valley under FTCs, and contributes to the prevention and management of the local landslide disasters.

Antibacterial properties of mesoporous silica coated with cerium oxide nanoparticles in dental resin composite

Cerium oxide nanoparticles are known for their antibacterial effects resulting from Ce3+ to Ce4+ conversion. Application of such cerium oxide nanoparticles in dentistry has been previously considered but limited due to deterioration of mechanical properties. Hence, this study aimed to examine mesoporous silica (MCM-41) coated with cerium oxide nanoparticles and evaluate the antibacterial effects and mechanical properties when applied to dental composite resin. Cerium oxide nanoparticles were coated on the MCM-41 surface using the sol–gel method by adding cerium oxide nanoparticle precursor to the MCM-41 dispersion. The samples were tested for antibacterial activity against Streptococcus mutans via CFU and MTT assays. The mechanical properties were assessed by flexural strength and depth of cure according to ISO 4049. Data were analyzed using a t-test, one-way ANOVA, and Tukey’s post-hoc test (p = 0.05). The experimental group showed significantly increased antibacterial properties compared to the control groups (p < 0.005). The flexural strength exhibited a decreasing trend as the amount of cerium oxide nanoparticle-coated MCM-41 increased. However, the flexural strength and depth of cure values of the silane group met the ISO 4049 standard. Antibacterial properties increased with increasing amounts of cerium oxide nanoparticles. Although the mechanical properties decreased, silane treatment overcame this drawback. Hence, the cerium oxide nanoparticles coated on MCM-41 may be used for dental resin composite.

Study of the dual role mechanism triggered by in-situ cross-linking in hollow fiber membrane matrix

In this paper, a novel polyvinylidene fluoride (PVDF) hollow fiber membrane with uniform pore size and hydrophilic cross-linked network in membrane matrix was developed by non‐solvent induced phase separation method. The dual role mechanism of in-situ cross-linking in regulating molecular chain arrangement during phase separation and preventing deterioration of membrane mechanical properties were analyzed. The results demonstrated that the cross-linked network formed by in-situ crosslinking entangled with PVDF molecular chains which improved the regularity of PVDF molecular chains, increasing the uniformity of the pore size distribution, the percentage of the most probable pore size of the modified membrane increased to 93.25 %. The cross-linked network was immobilized in the membrane which formed semi-interpenetrating structure, maintaining the mechanical properties of the membrane. The permeation flux of the modified membrane increased by 24.1 times to 477.7 L m−2 h−1 compared to the original PVDF membrane. The rejection of BSA was maintained at 98.5 %, with the tensile strength increased to 2.52 MPa. The modified membrane exhibited persistent hydrophilicity in 21 days washing experiment with improved antifouling performance.

Effect of welding current on the mechanical properties of Al 5083 alloy processed using high-current gas metal arc welding

This study investigated the effect of welding current during gas metal arc welding (GMAW) on the microstructure and composition of an Al 5083 alloy. As the welding current increased from 650 to 950 A, several changes were observed in the heat-affected zone (HAZ): grain coarsening and the formation of liquation cracks, and in the weld zone (WZ): increasing average secondary arm spacing and Mg loss. Therefore, the welding currents above 800 A are likely to cause liquation cracks in the HAZ and deterioration of the alloy's mechanical properties. Thus, welding condition with low heat input must be applied to improve the mechanical properties of the welds. This study provides a correlation between the weldability of Al 5083 alloy and welding current, offering a competitive advantage of liquid hydrogen storage containers.

Effect of powder composition on WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion (L-PBF) of WE43 magnesium alloy has a promising application prospect in the fields of lightweight parts and biodegradable implants. Grain refinement in these components is expected for high strength and controlled biodegradation, however, grain structure of WE43 is sensitive to composition and processing. L-PBF WE43 exhibited significant diversity on the microstructure and properties with the fluctuation of powder composition, and the influencing mechanism remained unclear. In this study, L-PBF samples were fabricated with high formation quality using four different WE43 powders, in which the content of Nd and Zr were purposely adjusted. Their microstructure, tensile properties and corrosion resistance were characterized. L-PBF specimens composed of fine equiaxed grains were obtained from Mg-3.56Y-2.45Nd-1.14Gd-0.40Zr powder, achieving ultimate strength of 316 MPa and elongation of 15%. With the minor decrease of Nd and Zr content, which was still in the range of present standards of WE43, L-PBF specimens respectively exhibited abnormal grain growth and coarse columnar grains, leading to tremendous deterioration of mechanical properties and corrosion resistance. During the multiple layers of fusion and solidification, Zr promoted the columnar-to-equiaxed transition and generated finer grains, while Nd exerted pinning effect in the heat affected zone to keep the fine grains from abnormal grain growth. The results firstly demonstrate the significant influence of the minor change of alloying elements on the performance, and indicate that a stricter compositional standard of WE43 powder is necessary to achieve reliable properties for the L-PBF process.

Alumina fiber/reduced graphene oxide composite films for high-temperature heating and sensing

Reduced graphene oxide (rGO) and its composite films have aroused intense interest in electrical heating and temperature sensing fields, but the working temperature is usually limited because the internal layer-stacked structure is breakable at high temperature. In order to promote structure stability, a series of Al2O3 fiber/rGO composite films were developed. It is found that gaseous products mainly including CO2 and CO during thermal reduction contribute to pores, bulges and intervals in rGO films, while appropriate Al2O3 fiber has an adhesion effect on rGO sheets and tightens them together, in which case defects can hardly form and the layered structure is significantly compacted. Therefore, the degree of stacking order and tensile strength tend to increase, resulting in the improvement of structure stability and decrease of electrical resistivity. However, excess Al2O3 fiber makes the formation of debris and cracks, causing the deterioration of conductivity and mechanical properties. With 20 wt% Al2O3 fiber, the composite films can bear higher heating voltage than pure rGO films and stabilize at 634.65 °C under 36 V, which also keep a good linearity between resistance and temperature from 25 to 600 °C, exhibiting a considerable temperature coefficient of resistance (TCR) with −1.70×10−3 /°C at room temperature.