Residual Properties Research Articles

Gradient microstructure and prominent performance of wire-arc directed energy deposited magnesium alloy via laser shock peening

Wire-arc directed energy deposition (DED) has attracted significant interest for the fabrication of large-sized, lightweight Mg-alloy components. However, these components generally exhibit poor mechanical properties and limited corrosion resistance owing to their inherent residual stress and non-equilibrium microstructures. Herein, laser shock peening (LSP) was adopted to successfully modify the stress state and microstructure of AZ31 Mg-alloy fabricated using wire-arc DED. The influence of LSP on the residual stress, mechanical properties, electrochemical behaviour, and microstructural evolution was systematically investigated. The experimental results indicate that, compared with the as-built specimen, the performance of the LSP-treated specimen was notable, with a ≈63.8% decrease in the corrosion current density and ≈30% and ≈13% decreases in the yield strength (YS) and ultimate tensile strength, respectively. The enhanced corrosion resistance can be attributed to the LSP-induced compressive residual stress, nanograins, and nanoparticles. Nanocrystallisation, particle refinement, dense mechanical twins (MTs), and planar dislocation arrays (PDAs) jointly contributed to the enhancement of the YS. The LSP-induced nanocrystallisation was rationalized by the accumulation of PDAs, the intersection of multiple nano-MTs, and the transformation of nano-MTs blocks into sub-grains and then into nanograins owing to continuous dynamic recrystallisation. The particle refinement mechanism involved dislocation proliferation and the development of dislocation slip bands, which eventually led to fragmentation and separation. Therefore, this study introduces a LSP post-treatment technology for the residual stress regulation, microstructural modification, and performance enhancement of Mg alloys fabricated using wire-arc DED. Based on the ability of LSP to tailor the microstructure and performance of Mg alloys, a novel method of wire-arc DED with online LSP treatment is proposed. This method can achieve in-situ surface strengthening and the integrated formation of large-sized components with complex geometries.

Review of Ultrasonic Pulse Methods for Evaluation of Mechanical Properties of Concrete with Different Percentages of Non-sintered Hwangto at High Temperature

In this study, the effect of non-sintered hwangto on the high-temperature residual mechanical properties of concrete is analyzed. The specimens are classified as NC and HT, which are mixed with 15% and 30% non-sintered hwangto, respectively, and the W/B is set 0.33. The unit weight, compressive strength, and ultrasonic pulse velocity of the specimens heated at room temperature and at 100 °C, 200 °C, 300 °C, 500 °C, and 700 °C are analyzed, and the correlation between ultrasonic pulse velocity and residual compressive strength is analyzed. The analysis result shows that the higher the mixing ratio of non-sintered hwangto, the lower is the mass loss rate at high temperature and the higher is the residual compressive strength of HT compared with those of NC. Meanwhile, the ultrasonic pulse velocity of HT is similar to or slightly higher than those of NC in areas with high temperatures of 300 °C or beyond. Results of correlation analysis shows a difference of approximately 10.0% between the NC and the HT specimens.

A study on static properties of high-performance steel after corrosion damage

This paper experimentally investigates the mechanical properties of high-performance steel (690 MPa) under different corrosion degrees. The tensile specimens are examined by indoor salt spray accelerated corrosion tests with varying durations. Tensile tests are performed on the corroded specimens to obtain the corrosion kinetics (corrosion rate) model and residual mechanical properties under different degrees of corrosion, and the correlations between residual mechanical properties and corrosion weight loss rate are discussed. In addition, the paper will adopt Q235 steel as the control to compare the difference in corrosion characteristics between conventional-strength steel and the new high-performance steel under the same corrosion conditions and to compare their corrosion kinetics curves. The paper will establish a new constitutive model for high-performance steel and calibrate the relevant parameters. A new constitutive model was proposed based on the modification of Ramberg-Osgood model. On this basis, the paper will obtain a prediction expression of constitutive parameters considering the degree of corrosion damage. It is found that that the proposed corrosion model is suitable for the new high-performance steel under atmospheric corrosion.

Legume re-establishment in northern temperate grasslands following application of aminocyclopyrachlor and aminopyralid

Herbicides with residual properties are often used for broadleaf weed control in pastures but can remove desirable legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.). Field trials at five sites within central Alberta, Canada were used to assess legume population dynamics during recovery after spraying. Medicago sativa and T. repens populations were monitored for three years following application of aminopyralid (AMP) at 120 g a.i. ha−1, or aminocyclopyrachlor (AMCP) at 60 g a.i. ha−1, in combination with repeated mowing and legume over-seeding. Bioassays were performed twice a year (spring and fall) using M. sativa and T. repens seeded into soil sourced from each plot up until 26 months-after-spraying (MAS) and grown in a greenhouse. Medicago sativa and T. repens densities in the field remained below non-sprayed control levels throughout the study (26 MAS). In contrast, bioassay results indicated a shorter time than the field trial for legume recovery, with recovery occurring in soil from treated grassland as soon as 14 MAS. There were no differences between AMCP and AMP in the time required to facilitate legume establishment. Critically, legume establishment in the field depended on intermittent mowing, particularly for T. repens, which failed to persist in the absence of mowing at 22 MAS regardless of herbicide application. Medicago sativa had a high potential to establish from the natural seed bank, while T. repens depended on over-seeding. These findings indicate it may be possible to reintroduce legumes to temperate pastures as early as the second growing season after herbicide application, though field trials indicate legume population recovery will depend on seeding and secondary disturbances to reduce competition.

Effect of volume ratio and hybrid mode on low-velocity impact properties of unidirectional flax/carbon fiber hybrid reinforced polymer composites

Hybrid fiber reinforced polymer composites have attracted widespread attention because they can fully utilize the advantages of two different types of fibers. To produce fiber reinforced polymer composites with excellent impact properties, unidirectional carbon/flax hybrid fiber reinforced polymer composite (HFRP) plates were developed using a filament-winding technique. The effects of the carbon fiber content and hybrid mode (a carbon–flax–carbon or flax–carbon–flax structure) on the impact properties and residual compressive properties of the HFRP plates were studied. Acoustic emission tests were performed to characterize the damage during impact, and the K-means cluster analysis method was used to investigate the HFRP damage development during post-impact compression. The test results indicate the higher carbon fiber contents enhanced their specific energy absorption (SEA), as the impact-induced brittle fracturing of the carbon-fiber layers was more severe. The hybrid mode and impact energy level critically influenced the HFRP SEA behavior. The HFRP plate with flax skin exhibited high SEA at a low impact energy, whereas that with carbon fiber skin exhibited high SEA at a high impact energy along with perforation. A more severe extension of the damage caused by the original impact occurs in the impacted HFRP under a compressive load.

The Correlation between the Structure Characteristics and Gasification Characteristics of Tar Residue from Pyrolysis

Pyrolysis is an efficient method for utilizing tar residue as a resource, and the structural properties of tar residue from pyrolysis (TRP) significantly impact subsequent gasification. The study examines the changes in the microscopic morphology, surface area, and carbon structure characteristics of TRPP as a function of pyrolysis temperature to elucidate the influence of pyrolysis temperature on the CO2 gasification characteristic parameters of TRP. Additionally, the investigation explores the relationship between surface structure and carbon structure characteristic parameters and gasification parameters at various stages. The findings indicated that the surface morphology of TRP synthesized at different pyrolysis temperatures (500–900 °C) was divided into two stages: the development of pores and the jamming of pores. With increasing pyrolysis temperature, the bigger aromatic nucleus was formed in the TRP without complete graphitization, and more amorphous carbon was consumed. TRP prepared at a pyrolysis temperature of 700 °C had the best gasification reactivity. By combining XRD, Raman, and gas adsorption techniques, the correlations between the surface structure and carbon structure parameters and the gasification characteristic parameters were established to evaluate the main factors influencing the gasification reaction. In the early stage of the gasification reaction, the carbon structure played a more important role than the surface structure. As the gasification reaction proceeded, the relationship between the surface structure and the gasification reaction was closer.

On residual implications derived from 2-uninorms

Residual implications are one of the most important families of fuzzy implications, which are related to the concept of residuation in intuitionistic logic. In this paper, we focus on residual operators derived from 2-uninorms and study necessary and sufficient conditions for such operators being fuzzy implications, called RU2-implications. What is remarkable is that the RU2-implication is a generalization of residual implications generated by some popular fuzzy logic operations such as t-norms, uninorms and uni-nullnorms. Then, we obtain the block structures for RU2-implications, especially for ones generated by two special classes of conjunctive 2-uninorms. Moreover, the main properties of RU2-implications and their natural negations are discussed. Finally, we give a characterization of residual implications derived from left-continuous 2-uninorms, which preserve the residuation property.

Mechanical Properties Degradation of Fiberglass Tubes during Biaxial Proportional Cyclic Loading.

Composite structures during an operation are subjected to various types of external loading (impact, vibration, cyclic, etc.), which may lead to a decrease in mechanical properties. Previously, many experimental investigations of the mechanical behavior of composites under uniaxial cyclic loading were carried out. Acquisition of new data on the reduction of composite materials' mechanical characteristics under conditions of multiaxial cyclic loading, as well as verification of existing models for calculation of the residual properties, are relevant. Therefore, this work is devoted to the experimental investigation of the mechanical behavior of fiberglass tubes under proportional cyclic loading. Static and fatigue tests were carried out under tension with torsion conditions. Inhomogeneous strain fields were obtained using a non-contact optical video system VIC-3D. The structural damage accumulation processes were analyzed by an AMSY-6 acoustic emission signals recording system. Surface defects were determined using a DinoLite microscope. Residual dynamic elastic modules were calculated during fatigue tests, and fatigue sensitivity curves were built. Data was approximated using various models, and their high descriptive capability was revealed. Damage accumulation stages were determined. The dependence of the models' parameters on a stress state were observed. It was concluded that multiaxial cyclic loading leads to a significant decrease in mechanical properties, which should be taken into account in composite structure design.

Effect of ground granulated blast furnace slag on the properties of hybrid‐fiber‐reinforced high‐strength concrete under normal and high temperatures

AbstractIn this paper, the residual mechanical properties, mass loss, and cracking behavior of hybrid‐fiber‐reinforced high‐strength concrete (HFRHSC) containing 0%, 30%, and 60% ground granulated blast furnace slag (GGBFS) in normal and high temperatures have been investigated. Chopped aramid and steel fibers at 0%, 0.5%, and 1% by volume, either individually or in different combinations, were used to reinforce the HSC. In total, 24 different mix proportions were designed. The experimental results showed that the residual compressive strength of the majority of specimens increased at 400°C while this property of all of them decreased at 800°C. Also, the test indicated that the use of GGBFS did not reduce flexural and compressive strength of HSC significantly, and in some mixed designs, the presence of GGBFS slightly increases the strength. Moreover, another result that can be inferred is that although the utilization of hybrid fibers in concrete increases flexural strength, it may decrease its compressive strength. In addition, the residual flexural strength of most specimens was reduced at 400°C, but this property of all samples decreased at 800°C. The results showed that the simultaneous presence of GGBFS and hybrid fibers can improve the flexural strength of most specimens at different temperatures.

Residual compressive strength of filament wound hybrid glass/carbon fibre reinforced polymer tubes after exposure to elevated temperature

Fibre hybridisation is used to balance the high cost of carbon fibres and the low durability performance of glass fibres. This study investigates the residual compressive mechanical properties of filament-wound hybrid glass/carbon Fibre Reinforced Polymer (FRP) tubes after exposure to elevated temperatures. Effects of temperature exposure and fibre orientation on compressive properties have been investigated. Tubes were exposed to temperatures ranging from ambient to 350 °C. Two fibre orientation configurations, including hoop (89°) and cross-ply (20% at 15°, 40% at 40°, and 40% at 75°) were used to study the effect of fibre orientation. Compression tests were carried out to study the compressive mechanical properties of FRP tubes, while Digital Scanning Calorimetry and Thermal Gravimetry Analysis were conducted to study the thermomechanical characteristics of the specimens before and after exposure to the elevated temperatures. Finally, the level of damage and its mechanisms were investigated using Scanning Electron Microscopy. The experimental test results indicate that hybrid carbon/glass FRP (C/GFRP) tubes exhibit a performance closer to the weaker tube type, i.e. CFRP tubes rather than GFRP tubes. Moreover, when subjected to elevated temperature, tubes with cross-ply fibre orientations showed slightly better compressive performance compared to the tubes with a hoop fibre orientation.

Modified Residual Property Model For Fracture Mechanics

In this paper, the application requirement of the Residual Property Model based on the decrescent exponential function is reduced to only one mechanical test data. For this, by using Creager and Paris's elastic stress field equation in front of the blunt elliptical hole, the theoretical radius was chosen for the tip curvative and the maximum stress in the load direction at the tip is ensured to be equal the fracture toughness. Thus, the workload of the model is reduced by making the u exponent in the e-u function dependent on the geometric correction factor and the crack length. It was applied to the laminated composite specimens with three-point bending and the specimens including circular hole, and critical fracture stress values close to actual values were achieved.

Effects of Stress-Relieving Temperature on Residual Stresses, Microstructure and Mechanical Behaviour of Inconel 625 Processed by PBF-LB/M

Inconel 625 (IN625) superalloys can be easily fabricated by the laser-based powder bed fusion (PBF-LB/M) process, allowing the production of components with a high level of design freedom. However, one of the main drawbacks of the PBF-LB/M process is the control over thermally induced stresses and their mitigation. A standard approach to prevent distortion caused by residual stress is performing a stress-relieving (SR) heat treatment before cutting the parts from the building platform. Differently from the cast or wrought alloy, in additively manufactured IN625, the standard SR at 870 °C provokes the early formation of the undesirable δ phase. Therefore, this unsuitable precipitation observed in the PBF-LB/M material drives the attention to develop a tailored SR treatment to minimise the presence of undesirable phases. This work investigates SR at lower temperatures by simultaneously considering their effects on residual stress mitigation, microstructural evolution, and mechanical properties. A multiscale approach with cantilever and X-ray technologies was used to investigate how the residual stress level is affected by SR temperature. Moreover, microstructural analyses and phase identifications were performed by SEM, XRD, EBSD, and DSC analyses. Finally, mechanical investigations through microhardness and tensile tests were performed as well. The results revealed that for the additively manufactured IN625 parts, an alternative SR treatment able to mitigate the residual stresses without a massive formation of δ phase could be performed in a temperature range between 750 and 800 °C.

Rheological and physicochemical properties of Spirulina platensis residues-based inks for extrusion 3D food printing

Novel food matrices (such as microalgae, plants, fungi, and microbial proteins) with high protein content and biological value, good amino acid profile, and functionality have been explored. Phycocyanin and active polysaccharides extracted from Spirulina platensis are used as food additives, treatment of colitis, as well as obesity prevention. However, most of the remaining Spirulina platensis residues are mainly used as fish feed at present. 3D food printing is one of the promising development techniques used in the food industry. The aim of this study was to develop a novel 3D printing material of Spirulina platensis residues with shear thinning characteristics, high viscosity and rapid recovery. The effects of moisture content and pretreatment method on the rheological properties of Spirulina platensis residues were clarified. Scanning electron microscopy was used to observe the microstructure and texture profile analysis was used to determine the texture characteristics of Spirulina platensis residues, rheology was used to determine the key 3D printing factors such as viscosity and modulus of Spirulina platensis residues. More importantly, the printing process could be realized under ambient conditions. The development of microalgae residue ink promoted the high-value and comprehensive utilization of microalgae, and also broadened the application of microalgae in the food field.

Effect of fire exposure on the bonding behavior of hybrid engineered composite systems

When used with self-compacting concrete (SCC) in a fresh state, engineered cementitious composites (ECC) can enhance flexural properties and durability. There is, however, some uncertainty as to whether the composites and their related interfacial bonds will endure high temperatures. This article investigates how fire exposure affects hot-jointed concrete systems (CS) that combine SCC and ECC. Residual flexural and tensile properties and possible degradation/debonding of the interfacial zone after exposure to 800 °C were examined, considering the effect of three different fiber types (i.e. polyvinyl alcohol (PVA), steel (SF), and hybrid PVA/steel fibers) in the tension ECC layer. Visual, microstructural, ultrasonic pulse velocity and mass loss properties were assessed for air- and water-cooled specimens. Also, mathematical models were proposed based on the results of each concrete composite. ECC added to SCC at fresh-to-fresh state significantly increased its flexural and splitting tensile resistance, as well as thermal integrity. All composites were negatively affected by fire, but composite systems maintained their interfacial bond without excessive degradation. It was also determined that fibers at the interface area of composite systems are crucial to preserving their mechanical and physical bonding under fire, thus SF resulted in higher thermal resistance compared to PVA.

Fluid phase behavior during multi-cycle injection and production of underground gas storage based on gas-condensate reservoirs with oil rim

Underground gas storage (UGS) plays an important role in energy supply and peak shaving of urban natural gas. Fluid phase behavior and mass transfer are complicated during multi-cycle injection and production of UGS especially based on gas-condensate reservoirs with oil rim, which will impact the fluid properties, gas-oil recovery factor and stability of UGS. This work innovatively develops an experimental approach to investigate the phase behavior during multi-cycle gas injection and production in a UGS based on gas-condensate reservoir with oil rim in Bohaiwan basin, China. The produced fluid composition, residual fluid properties and oil recovery factor are analyzed. Results indicated that the condensate oil recovery factor is only 24.12% and the oil rim influences condensate oil recovery factor during primary depletion. The oil recovery factors of individual cycles are 8.33%, 5.79%, 3.83%, 1.92% and 0.88%, respectively. The total condensate oil recovery is 20.75% after five cycles, indicating multi-cycle gas injection and production can effectively extract and evaporate oil phase especially in the first and second cycles. As the cycles increase, the composition difference between injected gas and oil rim becomes larger and the evaporation of oil rim by gas injection is weakened. The GOR of oil rim under the 24 MPa decrease from 190.5 to 162.5 m3/m3, indicating gas dissolving ability of oil rim decrease. The remaining oil saturation is 1.7% after five cycles, lower than the primary depletion (3.8%), indicating part of oil rim is also produced and the gas storage capacity is enhanced after multi-cycle injection and production. This work provides an approach to understand the phase behavior of UGS in condensate gas reservoirs with oil rim and is beneficial for the efficient operation of UGS.

Residual Mechanical Properties of Corroded Steel Bars after High-Temperature Exposure

Accidental fires in aged concrete structures can lead to combined damage from corrosion and fire. In this study, we aimed to explore the effects of corrosion and high temperature on the residual mechanical properties of hot-rolled plain and ribbed bars. The results indicated that the corroded steel bars still exhibited ductile failure after high-temperature exposure. Moreover, the combined action of high temperature and corrosion has little effect on the elastic modulus. The residual bearing capacity of the hot-rolled steel bar became smaller under the condition of temperatures above 600°C. When the temperatures experienced by the plain and ribbed steel bars were less than 600°C and 500°C, respectively, the high temperature accelerated the decrease in the nominal yield and ultimate strength. However, the yield and ultimate strengths based on the minimum cross-sectional area remained unchanged with an increase in the cross-sectional loss ratio. Similar to that at room temperature, the ultimate strain of steel bars subjected to high-temperature exposure decreased exponentially with an increase in the cross-sectional loss ratio. The new findings of this study can provide a theoretical basis for the safety assessment of aged reinforced concrete structures after exposure to fire.

Effect of multiwalled carbon nanotubes on compressive behavior of concrete at elevated temperature for mass concreting

In this article, CNTs have been used in concrete, and the resulting properties are evaluated. Also, the CNT-reinforced concrete was exposed to elevated temperature, and the corresponding change in mechanical performance was investigated. Mechanical properties were studied, such as compressive and flexural strengths, stress-strain response, elastic modulus, compressive toughness, mass loss, and deterioration caused by exposure to elevated temperatures. Concrete specimens were heated to 200, 400, 600, and 800 °C at a heating rate of 5 °C/min and then tested for residual properties. CNT-reinforced concrete showed a higher compressive strength, elastic modulus, flexural strength, and compressive toughness than the control specimens. 0.15-CNT reinforced samples showed an increase of nearly 33% in Compressive strength and 50% in flexural strength. From the visual inspection, CNT-reinforced specimens showed less cracking at higher temperatures. Moreover, the effect of plastering concrete with CNTs was studied, which depicted better strength retention on exposure to fire. At 600 °C, 0.3 P-CNT plaster samples retained up to 43% of compressive strength and 46% of flexural strength, whereas control samples only retained up to 29% and 34% of their original strengths, respectively. Thus, it can be concluded that CNTs utilization in concrete is efficient for improved concrete fire resistance.

Progressive damage and residual strength of open-hole thin-ply CFRP laminates under tensile fatigue loading

Thin-ply composites are promising structural materials because of their excellent damage resistance and fatigue properties, as well as the advantage of improved design freedom in composite structures. In this study, open-hole tensile fatigue tests were performed on carbon-fiber-reinforced polymer laminates using thin-ply prepregs to investigate the effects of varying ply thickness. Fatigue tests were performed on three types of quasi-isotropic laminates with different ply thicknesses (thin-ply, intermediate-ply, and thick-ply) at several stresses. Fatigue damage growth around a circular hole was examined by evaluating stiffness degradation and internal damage using X-ray radiography. Additionally, the fatigued specimens were subjected to static tensile tests to evaluate the effect of fatigue damage on the residual strength after fatigue tests. The thin-ply laminates can suppress fatigue damage growth and retain the residual strength properties under high-cycle fatigue at high stress level, thus validating their superiority over thick-ply laminates.

Enhancing bauxite residue properties for plant growth: Gypsum and organic amendment effects on chemical properties of soil and leachate

Here, we assess the effects of gypsum and local organic waste as amendments to non-weathered, filter-pressed bauxite residue (BR) to improve its properties and support plant growth. In addition, we monitored the leachate quality of the amended BR under progressive leaching that simulated precipitation conditions in Northern Brazil. Free-draining column tests consisting of BR amended with gypsum and organic waste, at 5% and 10% w/w, respectively, were leached for 8 weeks to assess the effects on the chemical composition of BR and the leachates. Adding gypsum to BR reduced the exchangeable sodium (Na) percentage (ESP) from approximately 79%–48%, whereas adding only organic waste had smaller effects on ESP (from ∼79% to ∼ 70%). The mean leachate pH ranged from 8.7 to 9.4 for the gypsum, and organic waste amended BR, while this was 10.3 in the leachate of the unamended BR. The treatments had similar trends of electrical conductivity throughout the experiments and were below 2 dS/cm after 8 weeks, when ∼1.700 mm simulated precipitation had leached. Aluminium (Al), Arsenic (As), and Vanadium (V) concentrations in leachates of BR with gypsum, either alone or in combination with organic waste, were significantly lowered than in leachate of non-amended BR. By contrast, metal concentrations increased if organic waste was added to BR. We conclude that amending BR with gypsum, in combination with organic waste, significantly improves the chemical properties of the solid phase and achieved rehabilitation goals for SAR and EC of the leachates after 8 weeks of leaching. However, despite high leaching rates, rehabilitation goals for pH and ESP were not achieved with gypsum either alone or combined with organic waste.

Residual mechanical properties of hollow concrete blocks with different aggregate types after exposure to high temperatures

The exposure of concrete to high temperatures negatively affects its mechanical properties, and the factors that reduce these properties have been the subject of several studies over the years. Nevertheless, there are few studies on concrete for manufacturing blocks for structural masonry of very dry and vibro-pressed consistency. This paper shows the results of an experimental study on the mechanical strength and residual deformability modulus of hollow concrete blocks when exposed to temperatures from 100 to 800 °C. Three types of coarse aggregates—basalt, gneiss, and calcareous—were used, also varying the resistance of the inspected blocks − 12 MPa, 24 MPa, and 48 MPa. The differences in thermal and mechanical properties between concrete produced from a fluid mixture formed and consolidated in a mold, and concrete made of blocks for load-bearing masonry of very dry consistency and vibro-pressed are highlighted. The results also confirmed the low-level influence of compressive strength on the evolution of residual mechanical strength and the strong influence of the type of aggregate on this behavior. It was also found that the evaluation of residual thermal and mechanical properties of a wet-shaped concrete mixture to represent the behavior of dry and vibrated concrete, used in the manufacture of blocks for load-bearing masonry, can lead to unrepresentative results. There is no precedent for a study conducted with these parameters for this purpose that has applied such international recommendations.