Decrease In Elastic Modulus Research Articles

Eupatorium Adenophorum Spreng as a green additive in cementitious materials for sustainable infrastructure

The use of natural admixtures as a sustainable alternative to cement and chemical admixtures in concrete has gained significant attention. Eupatorium adenophorum Spreng (EAS), commonly known as the ‘forest killer’ in Nepal, is a perennial and herbaceous invasive plant. This prompted an experimental investigation aimed at assessing the potential utilization of its liquid and burnt ashes as additives in cement mortar. EAS leaves were dried, burnt at wooden coal fire, and sieved through a 90 μm sieve to obtain EAS powder. EAS liquid was produced by hammering the fragmented leaves, followed by squeezing and filtering. The control mortar had a water-cement ratio of 0.35 and a cement-sand ratio of 1.0. EAS powder content ranged from 0 % to 15 % and EAS liquid from 0 % to 0.4 %, by weight of cement. The optimal content (10 %) of EAS powder resulted in decreases in flow table value, density, and elastic modulus of mortar by 2.3 %, 4.2 %, and 10.6 %, respectively, while increasing compressive strength and water absorption by 2.3 % and 14.6 %, respectively. As for EAS liquid, its optimal content (0.3 %) led to increases in flow table value, density, compressive strength, elastic modulus, flexural strength, and splitting tensile strength by 11.0 %, 1.4 %, 13.0 %, 25.4 %, 28.4 %, and 33.0 %, respectively, while decreasing water absorption by 2.7 %. The observed increase in the compressive strength of mortar with the incorporation of EAS powder suggests its potential to substitute mineral admixtures. This can be achieved through improvements in the burning process, grinding to finer particles, and thorough micro-characterization, followed by detailed investigations into mortar properties. Additionally, the effectiveness of EAS liquid in replacing chemical admixtures to enhance various mortar properties has been confirmed. The collaborative use of EAS powder and liquid holds promise for supporting future sustainable infrastructure development, facilitating the production of eco-friendly green concrete.

Experimental and Numerical Simulation Investigation of Cement Sheath Integrity during Multi-Stage Fracturing in Offshore Tight Oil Reservoir

The integrity of the cement sheath is susceptible to failure during multi-stage fracturing. In this study, the failure mechanisms of cement sheath integrity during multi-stage fracturing in the A offshore tight oil reservoir wells were investigated. The cement samples were subject to triaxial compression test (TCT), triaxial cyclic loading test (TCLT), and permeability test. A full-scale device was constructed for cement sheath integrity experiments. Additionally, a 3-D finite element model was developed to simulate the interface debonding and the subsequent growth of micro-annuli throughout multi-stage fracturing. The results revealed that TCLT induced cumulative plastic deformation in the cement samples, resulting in a 10.7% decrease in triaxial compressive strength, an 8.3% decrease in elastic modulus, and a 150% increase in permeability. Despite these significant variations, no serious damage was caused to the cement sheath matrix. It was observed that gas leakage occurred at the 8th, 10th, and 14th cycles under cyclic loading with upper limits of 70 MPa, 80 MPa, and 90 MPa, respectively. After 15 cycles, the experimentally measured widths of micro-annuli were 117 μm, 178 μm, and 212 μm, which were in good agreement with simulation results of 130 μm, 165 μm, and 205 μm, respectively. These findings elucidate the causes of cement sheath integrity failure, providing insights into the failure mechanisms of cement sheath integrity during multi-stage fracturing.

Effect of Nano-TiO2 and Polypropylene Fiber on Mechanical Properties and Durability of Recycled Aggregate Concrete

In order to promote the engineering application of recycled concrete, the effects of PPF and nano-TiO2 dioxide on the mechanical properties and durability of recycled concrete were studied.Polypropylene fiber recycled concrete(PRAC) and nano-TiO2 recycled concrete(TRAC) were prepared by adding different volume contents of PPF and nano-TiO2. The experimental findings demonstrated that the PPF and nano-TiO2 improved the splitting tensile strength of RAC better than the compressive strength. When the volume content of nano-TiO2. and PPF is 0.8% and 1.0%, respectively, the corresponding splitting tensile strength of concrete reaches the maximum value(3.4 and 3.7 MPa). The contribution rates of nano-TiO2 and PPF with different volume contents to the mechanical properties of RAC have optimal values, which are 0.4 and 1.0%, respectively. The incorporation of nano-TiO2 and PPF can effectively inhibit the loss of RAC mass and the generation of pores under freeze–thaw conditions, and slow down the decrease of dynamic elastic modulus. When the volume content of PPF is 1.0% and the volume content of nano-TiO2 is 0.4%, the protection effect on the internal structure of RAC is better, and its carbon resistance is better. The results of RSM model analysis and prediction show that both PPF and nano-TiO2 can be used as admixture materials to improve the mechanical properties and durability of RAC, and the comprehensive improvement effect of PPF on RAC performance is better than that of nano-TiO2.

Characterization of fly ash reinforced wood polypropylene composites

In this study, fly ash, which is released as waste from thermal power plants and has negative effects on the environment, was evaluated as a filler in wood-plastic composite materials (WPC). For this purpose, inorganic fly ash from thermal power plants was mixed with polypropylene (PP) thermoplastic polymer at 10%, 20%, 30%, 40%, and 50% by extrusion method instead of wood flour used in wood plastic composite materials. Maleic anhydride-treated polypropylene (MAPP) was used to strengthen the bonding during WPC production. The material mixed in extrusion was passed through a crusher and turned into pellets. Test samples were prepared using injection molding of pelletized WPC material. Density, thickness swelling, water absorption, modulus of rupture, impact strength, modulus of elasticity in bending, tensile strength, janka hardness, differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA) were performed on the prepared test samples. The results indicated that as the amount of fly ash used in the wood-plastic composite material increases, the density increases but the thermal degradation temperature of the material, water uptake, the swelling ratio to its thickness, tensile strength, impact strength, janka hardness, modulus of rupture, and modulus of elasticity decrease.

High-temperature transient-induced thermomechanical damage of fiber-reinforced ceramic-matrix composites in supersonic wind tunnel

This article is based on the supersonic directly connected wind tunnel. Through a specially designed experimental chamber, combined with infrared temperature measurement, high-speed camera, etc., in-situ monitoring of composite materials under airflow at Ma 3.0 with a total temperature of 950 ∼ 1473K was carried out. The dimensional analysis method was used to propose dimensionless parameters to characterize the thermal coupling caused by high-speed airflow thermal shock. Research has shown that the thermal coupling effect of supersonic airflow causes uneven temperature inside the material, and the thermal stress caused by temperature gradient changes (including increasing and decreasing processes) is the main reason for material damage. The damage of ceramic matrix composites under thermal shock mainly manifests as a decrease in surface roughness, surface fiber fracture and a decrease in elastic modulus. In addition, the study also found that there are damage thresholds for the thermal shock effect of airflow at different total temperatures, which helps to further understand the thermomechanical damage mechanism and degradation law of composite structure under high-temperature transient conditions.

Study of Surface Chemistry, Temperature and Strain Rate on the Tensile Properties of Monolayer Graphene Oxide

The mechanical properties of graphene oxide (GO) during tensile fracture were studied using molecular dynamics methods, and the influence of hydroxyl and epoxy groups on the mechanical properties of GO was explored. In addition, the changes in mechanical properties of GO under different temperatures and strain rates were studied to gain a deeper understanding of its mechanical behavior. The results indicate that hydroxyl and epoxy groups have a significant influence on the elastic modulus, ultimate stress, and ultimate strain of GO. The presence of hydroxyl and epoxy groups can alter the molecular structure of GO, thereby affecting its ultimate stress and strain. When the number of hydroxyl groups is 16 and the number of epoxy groups is 20, the ultimate stress decreases by about 31% and the elastic modulus decreases by about 20%. The variation of elastic modulus, ultimate stress, and ultimate strain of GO with temperature was studied at three temperatures: 300[Formula: see text]K, 500[Formula: see text]K, and 800[Formula: see text]K. As the temperature increases, the amplitude of atomic vibration increases and internal defects and cracks in GO continue to form and expand. At the same time, its coefficient of thermal expansion also increases, causing deformation and loosening of the crystal structure, resulting in a decrease of about 10% in the ultimate stress of GO, and a slight decrease in the ultimate strain and elastic modulus. Finally, the influence of different strain rates on the mechanical properties of GO was studied. As the strain rate increases, the intermolecular interactions within GO are rapidly altered, and the previously loose structure gradually becomes tightly ordered, resulting in an increasing trend in the elastic modulus, ultimate stress, and ultimate strain of GO.

Strain rate-dependent tensile deformation and failure behavior in single-crystal β-Sn

Given that electronic components often undergo intricate thermal and mechanical loads during operation, comprehensively understanding lead-free solder, particularly solder based on [Formula: see text]-Sn, in various complex load conditions, plays a crucial role in ensuring the structural integrity and functional reliability of integrated circuits. Therefore, investigating the mechanical properties and fracture behavior of [Formula: see text]-Sn as a solder material holds paramount importance. In this study, we performed molecular dynamics simulations using the modified embedded atom method to investigate the mechanical properties and crack propagation of single-crystal [Formula: see text]-Sn under different strain rates. The research findings demonstrate that as the strain rate increases, the single-crystal [Formula: see text]-Sn exhibits elevated yield strength, fracture strength, and strain, while the elastic modulus decreases. Under higher strain rates, the relationship between dislocation density and strain rate in single-crystal [Formula: see text]-Sn is quantitatively elucidated. The substantial increase in internal dislocation density imparts conspicuous strain hardening to the material, rendering plastic deformation more challenging. This observation sheds light on the microscale mechanism of strain hardening at the atomic level. Our results shall facilitate a deeper investigation into the mechanical behavior of single-crystal [Formula: see text]-Sn while also paving the path for optimizing the design and application of lead-free solder materials in the electronics industry.

Xyloglucan deficiency leads to a reduction in turgor pressure and changes in cell wall properties, affecting early seedling establishment

Xyloglucan is believed to play a significant role in cell wall mechanics of dicot plants. Surprisingly, Arabidopsis plants defective in xyloglucan biosynthesis exhibit nearly normal growth and development. We investigated a mutant line, cslc-Δ5, lacking activity in all five Arabidopsis cellulose synthase like-C (CSLC) genes responsible for xyloglucan backbone biosynthesis. We observed that this xyloglucan-deficient line exhibited reduced cellulose crystallinity and increased pectin levels, suggesting the existence of feedback mechanisms that regulate wall composition to compensate for the absence of xyloglucan. These alterations in cell wall composition in the xyloglucan-absent plants were further linked to a decrease in cell wall elastic modulus and rupture stress, as observed through atomic force microscopy (AFM) and extensometer-based techniques. This raised questions about how plants with such modified cell wall properties can maintain normal growth. Our investigation revealed two key factors contributing to this phenomenon. First, measurements of turgor pressure, a primary driver of plant growth, revealed that cslc-Δ5 plants have reduced turgor, preventing the compromised walls from bursting while still allowing growth to occur. Second, we discovered the conservation of elastic asymmetry (ratio of axial to transverse wall elasticity) in the mutant, suggesting an additional mechanism contributing to the maintenance of normal growth. This novel feedback mechanism between cell wall composition and mechanical properties, coupled with turgor pressure regulation, plays a central role in the control of plant growth and is critical for seedling establishment in a mechanically challenging environment by affecting shoot emergence and root penetration.

ТЕХНОЛОГІЇ ОДЕРЖАННЯ ПОЛІМЕРНИХ КОМПОЗИЦІЙ ДЛЯ ВИГОТОВЛЕННЯ ПОГОНАЖНИХ ВИРОБІВ

The work is devoted to the characteristics of the technologies for obtaining a polymer composition for the manufacture of decorative products. Research is focused on the technology of manufacturing polymer composite material based on polyvinyl chloride for the production of rigid pipes, fittings, sidings, windows and doors, profiles, fences, railings, various devices, valves, housings of inspection lights, ventilation ducts, fans, heat exchange equipment, parts of chemical equipment , laboratory devices and other products. The paper describes the manufacturing technology of the PVC composition and investigates the important performance characteristics of the polymer melt. Three common technologies are presented, they are rolling, calendering and extrusion. The most common material for the manufacture of polymer. This composition is most often obtained by the extrusion method, so this section focuses on this technology in more detail resin products is a polyvinyl chloride composition. The stiffness of the polymer is characterized by the modulus of elasticity during bending. To determine this indicator, samples of polymer material without irradiation and with UV irradiation for a certain period of time were used. When the content of chalk in the recipe increases, the hardness increases. All compositions are characterized by approximately the same character - with exposure to six hours, the modulus of elasticity decreases, and with further exposure, it begins to gradually increase. The combination of а filler and a polymer is the most powerful for use in PVC compositions in the manufacture of decorative products.

Effect of high temperature thermohydrogen treatment on the microstructure, martensitic transformation, and mechanical and corrosion behaviors of Ti-V-Al lightweight shape memory alloy

In the present study, hydrogenation treatment was adopted to tailor the phase constituents of the Ti-V-Al shape memory alloy, further optimizing its performances. It can be found that hydrogenation treatment induced the transition from the α″ martensite phase to the β parent phase. Moreover, large amounts of hydride precipitates can be observed in the hydrogenation treated Ti-V-Al shape memory alloy with longer time of 5h. Meanwhile, the grain size of the Ti-V-Al shape memory alloy was reduced as a result of hydrogenation treatment. The interstitial atom H serving as a β-stabilizing element led to the reduction of martensitic transformation temperature. In proportion, hydrogenation treatment caused the enhancement of yield strength and decrease of elastic modulus, which promoted its application in biomedical fields. Besides, by optimizing the time of hydrogenation treatment, the hydrogenation treated Ti-V-Al shape memory alloy with 1 h possessed the superior corrosion resistance.

Experimental Study on Mechanical Properties of Highway Subgrade in Cold Regions under Different Conditions

In order to study the changes in the mechanical properties of road subgrade in cold areas after the freezing and thawing of highways in cold areas, indoor mechanical tests were carried out to investigate the effects of the number of freeze–thaw cycles, freezing temperature, water content, and circumferential pressure on the mechanical properties of road subgrade soil in cold areas after thawing. The mechanical properties of road subgrade soil in cold areas after thawing were measured under different conditions. The test results show that, within the study range: (1) After 7 freeze–thaw cycles, the destructive stress of the subgrade soil decreased from 321.7 kPa to 289.9 kPa, a decrease of 9.9%, and the elastic modulus decayed by 19.9%. (2) When the freezing temperature was reduced from −5 °C to −15 °C, the destructive stress of the subgrade soil decreased from 303.9 kPa to 290.1 kPa, a decrease of 13.8 kPa, approximately 4.5%, and the decrease in modulus of elasticity was about 1.6%. (3) The water content increased from 6% to 12%, and the destructive stress decreased from 405.43 kPa to 288.4 kPa, a decrease of 29.1%, and the modulus of elasticity decreased approximately linearly, with an attenuation of 50.4%. (4) The peripheral pressure increased from 50 kPa to 150 kPa, and the destructive stress increased from 194.7 kPa to 367.7 kPa, a growth of 88.8%, and its modulus of elasticity increased with the increase in peripheral pressure, an increase of 154.1%. The results of this research can provide a reference for highway and engineering construction in the western silt–soil distribution area.

Numerical investigation of mechanical responses and failure features of coal measure strata using combined finite-discrete element method

Investigating the mechanical responses and failure features of the deep coal measure strata (CMS) is essential for designing hydraulic fracturing treatments and preventing geological dynamic hazards in underground engineering. In this paper, a three-dimensional CMS model is established by the combined finite-discrete element method (FDEM). The mechanical properties, stress evolutions and failure features of the CMS with different lithological combinations (sandstone-coal-sandstone (SCS), sandstone-coal-mudstone (SCM) and mudstone-coal-mudstone (MCM)) and thickness ratios are investigated under the uniaxial compressive condition. Results indicate that the SCS combination exhibits the highest uniaxial compressive strength (UCS) and elastic modulus, followed by the SCM and MCM combinations. The mechanical properties of the CMS are predominantly determined by the softer coal layer. The mechanical contrasts in elastic modulus and Poisson’s ratio between adjacent layers cause the generation of additional compressive stress in the softer layer and additional tensile stress in the stiffer layer. Therefore, the softer coal layer exhibits the shear-dominated failure pattern while the stiffer sandstone/mudstone layer displays the tensile-dominated failure pattern in the CMS. Furthermore, as the thickness ratio of the coal layer increases, the UCS, elastic modulus, and interfacial constraint stress decrease in the CMS. Additionally, the UCS and stress–strain relationship in the post-peak stage exhibit the noticeable size effect, whereas the mechanical behaviors in the pre-peak stage and the ultimate fracture patterns show the opposite. The elastic modulus and interfacial constraint stress obtained by the FDEM simulation match well with those calculated by theoretical models. The key findings of this paper can provide fundamental understanding and reliable parameters for multi-scale geomechanical modeling in petroleum and mining engineering.

A Study on the Cavitation Effect of Elastic Material with Textured Surfaces under Fluid Lubrication Conditions

This study investigates the effect of the elastic surface micro-texture on the cavitation and lubrication characteristics of the friction pairs through theoretical and experimental research. Through numerical simulations and experiments, the influences of the elastic modulus and sliding speed on the lubrication performance of the friction pair are studied. The results show that under certain speed and load conditions, the friction coefficient of the elastic texture is smaller, and the lubrication performance is better than that of the rigid texture. Increasing the sliding speed and texture spacing properly can improve the lubrication performance of elastic friction pairs. In addition, as the elastic modulus decreases, the elastic deformation and oil film thickness increase, and the cavitation phenomenon becomes more significant. Thus, the lubrication performance of the friction pair is improved.

Compressive Behaviors of High-Strength Geopolymeric Concretes: The Role of Recycled Fine Aggregate

In this study, natural fine aggregates (NFAs) in high-strength fly ash (FA)/ground granulated blast furnace slag (GGBFS)-based geopolymer concretes were both partially and completely replaced by RFAs to prepare geopolymer recycled fine aggregate concrete (GRFC). Herein, the impacts of RFA content (0%, 25%, 50%, 75%, and 100%) on the fresh and hardened performance and microstructural characteristics of a GRFC were investigated. The results indicated that with increasing RFA substitution ratio, the setting time of the GRFC decreases. In addition, the compressive strength and elastic modulus decrease. However, owing to the enhanced adhesion of the geopolymer matrix and recycled aggregate, RFA has a relatively small impact on the compressive strength, with a maximum strength loss of 9.7% at a replacement level of 75%. When the RFA content is less than 75%, the internal structure of the concrete remains relatively compact. The incorporation of RFA in concrete has been found to adversely affect its compressive strength and elastic modulus, while simultaneously increasing its brittleness. The increase in dosage of RFA leads to a reduction in the compressive strength and elastic modulus of concrete, while partial failure occurs when the GRFC constitutes 100% of the RFA. The existing stress–strain model for conventional concrete is recalibrated for the GRFC. Observed by SEM, with increasing RFA, the damage is mainly concentrated at the interface associated with the attached cement. Although the recalibrated model predicts the stress–strain responses of the GRFC reasonably well, an acceptable range of deviation is present when predicting the residual stress due to the relatively high strength and brittle behavior of the GRFC during compression. Through this research, the applicability of RFA is expanded, making it feasible to apply large quantities of this material.

Study on Microstructure, Mechanical Properties, Tribological Properties and Service Performance of CrAlN and CrAlBN Coatings Deposited on Powder Metallurgy High-Speed Steel (PM-HSS) and Shaper Cutter by Arc Ion Plating Technique

CrAlN and CrAlBN coatings were prepared on the surface of high-speed steel and shaper cutter by physical vapor deposition (PVD) technique using arc ion source. In the process of coating preparation, the adhesive layers were deposited by low bias voltage (−40 V) and the working layers are deposited by high bias voltage (−130 V). The effects of the addition of B element on the microstructure, hardness, elastic modulus and wear resistance of CrAlBN coating were studied. The results show that B element and its compounds exist in amorphous form in the coating, resulting in lattice distortion of the coating, increase of coating hardness to 37.1 GPa, and decrease of elastic modulus to 406.2 GPa. The addition of B element increases the uniformity of the columnar structure distribution and decreases the width of the columnar structure and grain size. The resistance to elastic deformation and plastic deformation of CrAlBN coating is improved, the wear resistance is improved. The performance of CrAlN and CrAlBN coatings on shaper cutter was studied. It was found that the main failure mode of shaper cutters is boundary wear and the wear mechanism of coatings had changed obviously. CrAlBN coating is mainly due to fatigue induced failure, accompanied by some diffusion wear. The addition of B element makes the CrAlBN coating have excellent resistance to oxidative wear, abrasive wear and diffusion wear during cutting. The results show that the addition of B element can improve the microstructure and mechanical properties of CrAlN coating, and the preparation of CrAlBN coating on the surface of the shaper cutter can significantly improve the service life of the coated shaper cutter, which has significance for the development of the shaper cutter industry.

Experimental investigation on the mixture optimization and failure mechanism of cemented backfill with coal gangue and fly ash

Using coal gangue and fly ash for mining backfill materials can create a win-win situation for safe mining and waste disposal, with the critical challenge being the optimization of coal gangue grading and fly ash proportions. Uniaxial compression tests and scanning electron microscopy (SEM) observation were conducted on backfill specimens with different coal gangue grading and fly ash proportions, and in-situ monitoring of acoustic emission (AE) parameters and infrared radiation temperatures (IRT) was carried out. The elastic modulus, uniaxial compressive strength (UCS), failure pattern, infrared temperature, AE ringing count and energy evolution of the backfill were discussed. Further, the b-value and entropy-value of AE during the loading were analyzed. The results show that the UCS and elastic modulus decrease with the increase in the proportions of fly ash and large-size gangue. Tensile cracks generally dominate the failure of specimen under unaxial compressive load but shear cracks are more prone to occur for specimens with high proportions of fly ash and large-size gangue. The inner defects and weak interfaces between large-size gangue and cement pastes significantly affect the mechanical performance for specimens with high proportions of fly ash and large-size gangue. A sudden drop of the b-value occurs before the peak stress while the AE entropy-value reaches maximum at the peak stress. The methods and findings can guide the mixture optimization and mechanical failure analysis for backfill mining.

Tuning the mechanical characteristics of ZnO nanosheets via C, F, and P doping: A DFT approach

This study investigates the impact of doping with carbon (C), fluorine (F), and phosphorus (P) atoms on the structural and mechanical properties of 2 × 2 and 3 × 3 ZnO monolayers using Density Functional Theory (DFT) calculations. Our analysis reveals a notable decrease in both the elastic and bulk moduli of the monolayers upon doping, with the most significant reduction observed in the P-doped structure. For the pristine structure, the elastic modulus is measured at 78.84 N/m for the 2×2 monolayer and 79.46 N/m for the 3×3 monolayer, while the bulk modulus is 62.47 N/m and 63.94 N/m, respectively. Following P doping, the elastic modulus decreases by 56.02 % (34.67 N/m) in the 2 × 2 monolayer and 46.40 % (42.59 N/m) in the 3 × 3 monolayer. Similarly, the bulk modulus experiences substantial decreases of 53.09 % (29.30 N/m) in the 2 × 2 monolayer and 42.96 % (36.47 N/m) in the 3×3 monolayer upon P doping. Additionally, C and F doping result in reductions of 26.10 % and 11.04 % in the elastic modulus of the 2×2 monolayer and 26.27 % and 10.92 % in the 3×3 monolayer, respectively. The corresponding bulk modulus reductions are 14.51 % and 10.79 % in the 2×2 monolayer and 20.12 % and 11.15 % in the 3×3 monolayer, respectively. These findings underscore the considerable influence of various dopants on the mechanical characteristics of ZnO nanosheets, with P doping inducing the most significant reductions in both elastic and bulk moduli, suggesting its efficacy in tuning the mechanical properties of ZnO nanosheets for diverse applications.

Investigating the effect of Persian gum on physicochemical, textural and rheological characteristics of UF white brined cheese during ripening

In this research, the effect of Persian gum at concentrations of 0, 0.03%, 0.05%, and 0.1% on syneresis, textural, and rheological properties of UF white brined cheese was investigated during ripening on days 3, 45, and 90. According to the results, the use of Persian gum led to a reduction of 26% to 44% in syneresis of samples containing gum compared to the control at the end of ripening. The increase in gum concentration resulted in a significant decrease (p ≤ 0.05) in syneresis, hardness, cohesiveness, elastic modulus, and viscous modulus of the cheeses, while their springiness showed a significant increase (p ≤ 0.05). Samples containing Persian gum exhibited the highest values of hardness and elastic and viscous moduli on day 45 of ripening, while cohesiveness and springiness showed a decreasing trend during ripening. Ultimately, the utilization of Persian gum resulted in increased production yield and improved texture of the produced cheese.

Experimental study on cyclic axial tensile mechanical properties of SAP-PVA fiber concrete at different temperatures

This study conducted uniaxial cyclic axial tests on internally cured SAP-PVA fiber reinforced concrete specimens at different temperatures using an MTS universal hydraulic servo machine, obtaining the failure modes and uniaxial cyclic stress-strain curves of concrete with different mix proportions. Utilizing the experimental data, characteristic points of the cyclic stress-strain curves, including loading and unloading, were obtained for different SAP-PVA fiber reinforced concretes. Subsequently, the variations in mechanical parameters such as plastic strain and elastic modulus were analyzed, and the relationship between unloading strain, reloading strain, and plastic strain was investigated. Corresponding regression models for the relationship between plastic strain and loading and unloading strain were established, and the accuracy of the model was validated using various experimental data. The results indicated a continuous decrease in the secant elastic modulus and peak stress but increase in the peak strain of SAP-PVA concrete with increasing temperature, indicating a significant negative impact of high-temperature effects on the mechanical properties of concrete. As the cyclic load increased, plastic strain accumulated, and the cumulative relationship between unloading strain and plastic strain showed weak correlation with high-temperature effects. The unloading model parameters of SAP-PVA concrete were independent of temperature load and only influenced by the degree of damage. With an increase in material damage, the nonlinearity of the unloading curve increased. Compared to the unloading curve, temperature load significantly affected the nonlinearity of the reloading curve. This study revealed the cyclic tensile mechanical properties of SAP-PVA fiber concrete at different temperatures, providing experimental and theoretical references for the practical application and calculation of such concrete in engineering projects.

Physical and Mechanical Properties of Butt Welded Joints of Aluminum Alloys

Along with the improvement of joining technologies with argon arc, plasma and laser welding for aluminum alloy elements, high efficiency of joints made with the use of friction stir welding (FSW), which has low energy consumption and is almost equally strong as base metal, has been achieved. However, the processes of friction stir welding have not been sufficiently studied and can lead to softening of aluminum alloy welds up to 0.65 of base metal strength. When studying the effect of friction stir welding and mechanized electric arc welding in argon medium, welded joints of aluminum alloys of Al-Si-Mg (AD35T1, 6082-T6) and Al-Zn-Mg alloying systems (1915T) were subjected to tensile and impact tests. The values of strength, elastic and plastic characteristics of argon arc welded specimens of 1915T, AD35T1 and 6082-T6 alloys were obtained. For alloy 6082-T6, the same characteristics are presented for FSW welded specimens. Decrease in strength and ductility in the zones of welded joints for both welding methods is observed. At the same time, the highest relative values of strength and offset yield strength of the welded joint are fixed for friction stir welding. Slight decrease in modulus of elasticity obtained for argon-arc welded specimens was recorded. The impact strength is constant for each welded joint zones in the temperature range of +20 – -60оC and increased in weld metal of FSW butt joints of alloy 6082-T6.