Changes In Elastic Modulus Research Articles

Experimental study on axial compressive properties of bamboo scrimber after high temperature

This study examines the uniaxial compressive mechanical properties of after high temperature bamboo scrimber, taking into account the combined effects of temperature, constant temperature duration, and moisture content. A series of 46 uniaxial compression tests were conducted on bamboo scrimber under various conditions to investigate the failure modes after high temperatures. The analysis focuses on the changes in compressive elastic modulus and peak stress of bamboo scrimber parallel and perpendicular to the grain, in relation to temperature, constant temperature duration, and moisture content. The findings reveal that below 180℃, diagonal shear failure and Y-type shear failure are the primary failure modes for specimens parallel to the grain, while diagonal shear failure predominates for specimens perpendicular to the grain. Above 180℃, bond failure and eccentric crushing become the main failure modes for specimens parallel and perpendicular to the grain, respectively. The peak compressive stress decreases significantly beyond 180℃, with a slower decrease observed as moisture content increases. Constant temperature duration has a notable impact on peak stress, with longer durations resulting in lower peak stress at the same temperature. Although temperature has a lesser effect on the elastic modulus compared to peak stress, empirical formulas were derived to establish the relationship between compressive elastic modulus and peak stress reduction coefficient with variations in temperature, constant temperature duration, and moisture content based on the experimental data.

Mechanical properties of reactive powder concrete under compression at ultra-low temperatures

In this paper, the mechanical properties of reactive powder concrete (RPC) at ultra-low temperatures were studied. RPC prisms (300 mm × 100 mm × 100 mm) were tested at ultra-low temperatures (20 °C, 0 °C, −20 °C, −40 °C, −80 °C, −120 °C, −165 °C) and resulting prism compressive strength, compressive stress-strain curve, and toughness were determined. The increase in prismatic compressive strength of RPC at ultra-low temperatures is greater than that of ordinary concrete, with an overall strength of about 2.12 times that of ordinary concrete. Pore water freezing behavior was also studied to assess the effects on the mechanical properties of RPC in ultra-low temperatures. The water-ice phase transition further improved the RPC strength. With the reduction in temperature, The change in elastic modulus of RPC change is small, the peak strain of specimens at different temperatures increases with the decrease in temperature. The peak strain of RPC showed an overall linear increase with decreasing temperatures, and the water-ice phase transition at negative temperature increases the peak strain of RPC, adding steel fibers improves the RPC ductility, limiting the fracture. With the temperature reduction, RPC toughness first increases and then decreases. The toughness is lowest at room temperature, and highest at −120 °C, which is 2.26 times higher than at room temperature. RPC has better toughness than normal concrete at different temperatures, the reduction of temperature relatively improves the toughness of RPC, and the addition of steel fibers plays a vital role in improving the toughness. This study can serve as technical support for using RPC to design liquefied natural gas full-capacity tanks.

The effect of rock mechanical heterogeneity on induced stress and initiation pressure of multi-cluster fracturing

The stress interference between fracturing clusters in horizontal wells is key in affecting the initiation and propagation of multi-cluster fractures. However, in reservoirs such as shale, there are often changes in the mechanical properties of the rock along the direction of the wellbore. Such changes are often not considered in models for multi-fracture propagation. As a result, the impact of rock mechanical heterogeneity on induced stress is not fully understood. Therefore, in this paper, a prediction model of the three-dimensional induced stress field of hydraulic fractures is established, taking into account mechanical heterogeneity. Combined with the prediction model of fracturing pressure, the changes in induced stress and initiation pressure under different conditions are analyzed. The results indicate a significant difference between the induced stress results considering mechanical heterogeneity and those considering only a single homogeneous region. The change in elastic modulus has a profound influence on induced stress and initiation pressure. Perforating at locations with low elastic modulus in situ can help reduce initiation pressure. Additionally, temporarily blocking the wellbore and reducing the flow rate to decrease the net pressure in the fractures can facilitate more fractures to initiate.

Elastic modulus, water stability and resistivity for loess solidified with white mud based solid waste cementing material: Mechanism analysis and relationship establishment

To increase the engineering application value of white mud based solid waste cementing materials: white mud-slag and white mud-slag-Calcium Carbide Residue (CCR), this paper explored the changes in elastic modulus, water stability and resistivity of loess solidified with white mud based solid waste cementing material. Furthermore, relationships between elastic modulus, water stability and resistivity were established. The following conclusions can be obtained: The alkaline activation effect of CCR was stronger than white mud, therefore the formation rate of C-S-H and C-A-(S)-H cementitious products in CCR-containing solidified loess was more faster than that without CCR. At the same time, white mud not only served as an alkaline activator, but its finer CaCO3 components also helped fill pores, while the irregular fine particles provided nucleation sites for the formation of cementitious products. Consequently, slag-white mud-CCR solidified loess exhibited the best performance in terms of elastic modulus and water stability coefficient. This was followed by slag-white mud solidified loess and lime solidified loess. In addition, the analysis of the relationship between the resistivity of solidified loess and factors such as curing age, dry density, water content, elastic modulus, and water stability coefficient revealed that the main reasons for the increased resistivity of solidified loess were the consumption of internal water and the increase in cementitious products with poor conductivity. Furthermore, the modified resistivity formula was applied to establish the fitting relationships between the resistivity of solidified loess and various parameters. The formula has been successfully applied in the slag-white mud-CCR solidified loess, where the fitting of resistivity with various parameters yielded an R2 of 0.94. This paper facilitates the resistivity method (non-destructive testing) of loess treated with slag, white mud, CCR and promotes the application of these curing agents, contributing to their broader adoption in geotechnical engineering.

Experimental study on fracture failure characteristics evaluation of wooden pallets in humid-cold environment based on piezoelectric technology

Wooden pallets often suffer mechanical damage during transportation, stacking, forklifting, and on-site handling in cold supply chain logistics. In humid-cold environments, the fracture properties of wooden pallets change, increasing the risk of sudden fracture failure. Understanding the fracture failure characteristics of wooden pallets is essential to prevent further damage to goods. Nevertheless, evaluating and identifying these characteristics currently presents significant challenges. This study investigates the changes in modulus of elasticity (MOE) and fracture failure characteristics including modulus of rupture (MOR), brittleness and toughness of wooden pallets and impact toughness of wood material under humid-cold conditions. The piezoelectric technology was applied to evaluate and identify fracture risk of wooden pallets used in various humidity and cold conditions. Quarter-sized wooden pallets and standard wood specimens were examined by laboratory study. The experimental results showed that the MOE, MOR, toughness of wooden pallets and impact toughness of wood with higher moisture content (MC) increased with decreasing temperature, while brittleness increased as temperature decreased. These results indicate that the maximum carrying ability of wooden pallets increases in humid-cold environments while the ability to resist fracture was reduced with a higher brittle rupture risk. The toughness and its corresponding piezoelectric voltage exhibited good consistency with changes in temperature and MC. The relationship between toughness and piezoelectric voltage was established with good coefficient of determination (over 0.81). It indicates that the risk of wooden pallets could be predicted effectively using piezoelectric technology.

Understanding mechanism on carbonation curing for Portland cement through phase profiling via QXRD analysis and thermodynamic modeling

The mechanism of early age accelerated carbonation cured ordinary Portland cement mixtures is evaluated using experimental and thermodynamic modeling. This study considered three early precuring conditions, two carbonation curing periods, four CO2 concentrations, and a 0.5 w/c ratio. The investigation was conducted using phase profiling of mixtures based on QXRD results and developed a thermodynamic model that simulated the experimental conditions. The mechanical characteristics of carbonation-cured mortar specimens, including compressive strength, elastic modulus, shrinkage, and mass change, were evaluated. The results revealed that short precuring durations hindered carbonation, resulting in lower CO2 uptake, strength, elastic modulus and higher shrinkage. Increasing the precuring period from six-hours to one or three days resulted significant amount of CaCO3 precipitation on the surface of the specimen and appropriate mechanical properties. One day precuring followed by one day carbonation with a 10 % CO2 exposure resulted in a higher calcite precipitation on the surface with less depth of penetration. It was found that a balance between drying-induced degradation and microstructure densification due to calcite precipitation is crucial. An appropriate precuring duration, for each binder type and mix proportion, should be applied to achieve desired properties and CO2 uptake in carbonation-cured cementitious materials.

Micro-morphology and fractal characteristics of pore structure of aeolian sand concrete under long-term semi-immersion with chloride solution

To investigate the influence of chloride exposure on hydraulic concrete, we investigated the microstructural changes and pore evolution of aeolian sand concrete (ASC) during prolonged semi-immersion in chloride solution. Our analysis included examining the mass loss rate, relative dynamic elastic modulus, and maximum depth of chloride erosion. Utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR), we assessed the microscopic morphology and pore structure evolution. Additionally, we employed fractal theory to evaluate pore structure heterogeneity in ASC before and after exposure to chloride erosion. After 450 days of chloride erosion, ASC displayed minimal changes in mass loss rate and relative dynamic elastic modulus, with a maximum erosion depth of 9.8 mm. Chlorides adhered to the immersed end at the concrete's base and migrated from the surface to the exposed top end during erosion. The erosion depth at the top end ranged from 23.9 % to 25.9 % of that at the bottom end. Within ASC, hydration products reacted with chlorides, resulting in the formation of Friedel's salt, a characteristic corrosion crystal. Following erosion, the total porosity of ASC increased, accompanied by shifts in pore size distribution. The internal structure of ASC underwent distinctive evolution, transitioning from small to large pores. ASC consistently exhibited fractal properties both before and after erosion. The fractal dimension D1 demonstrated an inverse relationship with pores of radius (r) less than 0.01 μm, while D2 was directly proportional to pores with r ≤ 0.01 μm and 0.01 <r ≤ 0.1 μm, and inversely proportional to pores with 1 <r ≤ 10 μm and r > 10 μm. This study significantly contributes to the theoretical understanding of ASC's endurance mechanisms in chloride environments.

Experimental Evaluation of Compressive Properties of Early-Age Mortar and Concrete Hollow-Block Masonry Prisms within Construction Stages.

Early-age masonry structures require temporary support until they achieve full strength. Nevertheless, there is a limited understanding of the properties of freshly laid masonry and the design of newly constructed, unsupported masonry walls. This situation has led to numerous instances of structural damage and injuries to workers, prompting conservative construction bracing techniques. This paper presents comprehensive experimental studies on early-age mortar cubes and masonry prisms to assess the effects of curing time on the compressive properties of masonry assemblies, which is necessary for the design of temporary bracing. The change in modulus of elasticity and compressive strength of masonry prisms and mortar with curing time has been experimentally assessed. The results indicate that the compressive strength of freshly cast mortar cubes is relatively insignificant until approximately 24 h after construction, when it was observed to increase logarithmically. Regarding the performance perspective, the compressive strength of early-age masonry prisms is inconsiderable, less than 15% of full strength during the first day after construction. By contrast, regarding the life safety perspective, the compressive properties of a mortar joint within a masonry assembly (which is of more practical interest) appear to have no effect on the failure strength of concrete masonry prisms over the range of ages tested. The failure modes of the early-age mortar cubes and early-age masonry prism samples depend on the curing time, and different failure modes occurred before and after the start of the primary hydration phase, which is 20.8 h after construction. It is anticipated that the proposed research will provide valuable material properties leading to efficient design of control devices (e.g., temporary bracing) and improved guidelines for concrete-block masonry construction.

Nano-, micro- and macro-indentation tests of thermal spray WC-Ni coatings with lamellar microstructure at different particle deposition temperatures

The mechanical properties of WC-Ni coatings by HVOF thermal spraying were comprehensively evaluated by indentation tests at a wide load range of 10−1-103 N, i.e. nano-, micro- and macro-indentations. The correlation between process parameters and coating microstructure and mechanical properties was characterized via particle deposition temperature. The coating microstructure changes in reduced porosity, enhanced WC phase decomposition and better splats flattening were correlated to the particle deposition temperature rising. A porosity divergence between coating surface and cross-section was found as a quantitative anisotropy indicator to coating intrinsic lamellar microstructure formed by the splats flattening and piling up. Considering the lamellar microstructure, indentation responses on coating surface and cross-section were compared for hardness and elastic modulus evaluation below 3 N. The surface hardness is higher than that of cross-section, and both increased correlatively to the particle deposition temperature rising except for the almost constant surface hardness below 1 N. An analogous particle temperature-dependent behavior was also manifested for the elastic modulus by nano-indentation below 1 N. Interestingly, the elastic modulus by coating surface micro-indentation at 30 N presented identical particle temperature dependence to that by coating cross-section nano-indentation, both consistently representing the overall coating elastic modulus change trend verified by non-destructive ultrasonic test. Indentation fracture toughness on coating surface under 1.96 kN and on coating cross-section under 49 N was comparatively evaluated, and the values had a reverse trend of dependence on the particle deposition temperature. The particle-deposition-temperature dependent mechanical properties were interpreted by the coating intra-splats and inter-splats defects reduction with enhanced carbide-metal bonding essentially determined by the melting state of the metal binder phase, providing an insight to utilize indentation tests for characterizing thermal spray coatings.

Study on updating finite element model of steel truss structure based on knowledge-enhanced deep reinforcement learning

Accurate assessment of the damage to a structure is the key to structural health monitoring. Among them, one effective means to assess the real-time status of the structure is by establishing a finite element model (FEM) of the structure and updating it synchronously. Previous research mainly updates the FEM of the structure with a certain moment in time without considering the continuous changes of structural parameters over a longer time. In this paper, we propose a FEM updating method for steel truss structure based on knowledge-enhanced deep reinforcement learning, which introduces long short-term memory (LSTM) network based on a deep deterministic policy gradient (DDPG) algorithm and constructs a knowledge-enhanced noise function (NF) module based on parametric analysis. The NF-LSTM-DDPG algorithm can fit a continuous variation of structural parameters. The ablation experiments revealed that the LSTM network and the NF module facilitate the exploration and learning ability of the DDPG algorithm. The NF-LSTM-DDPG algorithm is used in an actual steel truss structure case, and the variation rules of the elastic modulus and support deviations obtained from the solution are consistent with the actual situation. The average relative error of the 34 strain measurement points after updating is 14.147 %, and the relative error is higher than 20 % in only 13 days out of 187 days of continuous monitoring. Five days were selected for the comparative study, and the experimental results show that the relative error of the NF-LSTM-DDPG algorithm is 13.206 %, which is higher than that of the particle swarm optimization algorithm and the simulated annealing algorithm. The change of elastic modulus updated based on the NF-LSTM-DDPG algorithm is more reasonable than other algorithms.

Mechanical properties of recycled aggregate concrete containing brick particles

To investigate the mechanical properties of recycled aggregate concrete containing brick particles (RACB), compressive strength tests were conducted on RACBs with different water/cement ratios and recycled fine aggregate substitution rates. The changes in compressive strength, elastic modulus and peak strain of RACB were analysed as a function of the proportion of substituted recycled fine aggregate, and a stress–strain equation was established. A damage model was established using ultrasonic non-destructive testing technology to reveal the damage mechanism of RACB. Results show that the basic mechanical properties of RACB are best when the replacement proportion of recycled fine aggregate (r) is 30%. The model parameter a of the stress–strain curve equation is consistent with the change of elastic modulus with r. The model parameter b has a quadratic function relationship with r, reflecting the brittleness of RACB. The initial damage of RACB is relatively large, and cracks penetrate the recycled coarse aggregate, leading to specimen failure.

Magneto-Acoustic Theranostic Approach: Integration of Magnetomotive Ultrasound Shear Wave Elastography and Magnetic Hyperthermia.

Although magnetically induced hyperthermia has shown great efficiency in the treatment of solid tumors, it is still a challenge to avoid incomplete ablation or overtreatment. In this study, we applied magnetomotive ultrasound shear wave elastography (MMUS-SWE) as a tool for real-time image guidance and feedback in the magnetic hyperthermia (MH) process. We called this new method as magneto-acoustic theranostic approach (MATA). In MATA, a ferromagnetic particle (fMP) was simultaneously used as a thermoseed for MH and a shear wave source for MMUS-SWE. The fMP was excited by a high-frequency magnetic field to induce the heating effect for MH. Meanwhile, the fMP was stimulated by a pulsed magnetic field to generate shear wave propagation for MMUS-SWE. Thus, the changes in elastic modulus surrounding fMP can be used to estimate the therapy effect of MH. The phantom and in vitro experiments were conducted to verify the feasibility of MATA, which has good performance in magnetothermal conversion and treatment efficacy feedback. The shear wave speed of the isolated pork liver changed significantly after the MH process, which varied from about 1.36 to 4.85 m/s. Preliminary results proved that changes in elastic modulus could be useful to estimate the therapy effect of MH. We expect that MATA, which is the integration of MMUS-SWE and MH, will be a novel theranostic method for clinical translation.

Preparation of Gradient Polyurethane and Its Performance for Flexible Sensors.

Flexible sensors are prone to the problems of slow recovery rate and large residual strain in practical use. In this paper, a polyurethane functional composite with a gradient change in elastic modulus is proposed as a flexible sensor to meet the recovery rate and residual strain without affecting the motion. Different hard and soft segment ratios are used to synthesize a gradient polyurethane structure. The conductive percolation threshold was obtained between 45 wt% and 50 wt% of flake silver powder. Both gradient polyurethane and gradient polyurethane composites demonstrated that gradient materials can increase the recovery rate and reduce residual strain. The gradient polyurethane composites had a tensile strength of 3.26 MPa, an elastic modulus of 2.58 MPa, an elongation at break of 245%, a sensitivity coefficient of 1.20 at 0-25% deformation, a sensitivity coefficient of 11.38 at 25-75% deformation, a rate of recovery of 1.95 s at a time, and a resistance to fatigue (over 1000 cycles at a fixed strain of 20% showed a stable electrical response). The sensing performance under different cyclic strain frequencies was also investigated. The process has practical applications in the field of wearable skin motion and health monitoring.

Changes in mechanical properties and surface microstructure of shale organic matter after coupling supercritical carbon dioxide with water

Supercritical carbon dioxide (ScCO2) fracturing technology has been increasingly emphasized in the development of unconventional oil and gas resources due to its advantages of anhydrous fabrication of complex seam networks and geological sequestration of CO2. However, previous studies have mostly focused on the geometry, number, and type of inorganic mineral fractures, and rarely paid attention to the changes in the seepage structure within organic matter (OM). To characterize the nanoscale microstructural changes of OM induced by H2O-ScCO2, this study obtained the variation rule of mechanical properties of OM with adsorbed water saturation based on nanoindentation test, and the continuous change of elastic modulus and morphology of the OM in the same region after dry, water-wet, and water-ScCO2 treatments was compared by atomic force microscopy (AFM). Elastic modulus and hardness of OM were calculated by Oliver-Pharr and Hertz methods, and the average roughness, root mean square roughness, and kurtosis were obtained based on 3D morphology. The results showed that elastic modulus and hardness were negatively and nonlinearly correlated with water saturation. Although the AFM-measured elastic modulus of OM microphases of the dry, water-wet, and water-ScCO2-treated shale were all highly discrete and non-homogeneous, they were generally normally distributed, and the mean values of the elastic modulus decreased sequentially. It is determined that water-ScCO2 coupling make OM matrix undergo superimposed dissolution. It is shown that ScCO2 and water synergistically change the microstructure of shale OM, and the weakening of mechanical properties and the increase of surface roughness are very favorable for geological sequestration and long-term storage of CO2.

Hydrogen charging can relax compressive residual stresses caused by shot peening

Surface engineering to generate compressive stresses via processes such as shot peening is commonly employed to mitigate fracture or fatigue failures in metallic systems. Localized plastic deformation is used to generate the generally biaxial compressive elastic stresses. This study examined the residual stress conditions and local mechanical performance of medium carbon steel in a quenched and tempered state. Electrolytic hydrogen charging of peened samples led to a permanent reduction in the compressive surface stress while concurrently hardening the surface. Slight changes in elastic modulus when solute hydrogen was present could not explain the resulting change in the measured residual stress; a reduction in X-ray peak breadth suggests that the combined effects of elastic stresses and solute hydrogen caused local dislocation annihilation and re-organization of the dislocation structure in the severe plastically deformed layer, leading to a lower magnitude and shallower depth of compressive residual stress on the peened surface after hydrogen charging.

A prediction method for salt frost resistance of dam rock foundation based on improved BP neural network

Hydraulic resources can be utilized in a cascade manner, with the advantages of energy conservation, economy, and environmental protection. In order to study the anti salt freezing performance of rock foundation in hydroelectric power dams and accurately predict the degree of rock and soil freeze-thaw damage under salt freezing conditions, this paper proposes a prediction method for the anti salt freezing performance of dam rock foundation based on an improved BP neural network. Firstly, freeze-thaw cycle tests were conducted on the rock foundation materials of dams poured with different proportions of fiber reinforced concrete to study the changes in soil mass loss rate and dynamic elastic modulus; Then, based on BP neural network and particle swarm optimization algorithm, a prediction model for rock and soil freeze-thaw damage is established; Finally, using the historical data of the Baihetan hydropower station, optimization was carried out and model prediction errors were compared and analyzed. The method proposed in this article has been verified to have good accuracy and stability, providing guidance for the operation and construction design of hydropower projects.

Beyond static: Tracking the dynamic nature of water absorption and Young's modulus in IPMC devices

AbstractIonomeric polymer‐metal composites (IPMC) are advanced materials designed to mimic biological systems. Their performance depends on various factors, including electrical stimulus intensity, membrane hydration, ionic migration, and Young's modulus. However, there is a lack of studies in the literature investigating how the water absorption capacity and elastic modulus change over time in IPMCs. Understanding the hydration level variation as a function of time is essential because as this parameter deviates, the ionic migration capacity and Young's modulus also change, altering the device's electromechanical efficiency over time. To address this research gap, Nafion/Pt‐based IPMC devices exchanged with four monovalent cations (H+, Li+, Na+, and K+) and one ionic liquid (1‐butyl‐3‐methylimidazolium—BMIM+) were prepared, and a comprehensive investigation on how the water absorption capacity and Young's modulus vary as a function of time, relative humidity (RH), and counterion size was performed. The results revealed that the water uptake capacity is significantly higher and occurs more rapidly at higher RH levels and when the counterion's ionic radius decreases. Consequently, the time required for the device to reach osmotic equilibrium can range from 40 to 270 min, depending on the RH and counterion used. Furthermore, it was observed that the first natural frequency and Young's modulus also exhibit time‐dependent behavior. Under constant RH conditions, the mechanical properties of the IPMC can vary by up to 50% in less than 60 min. Notably, the combined results from water uptake capacity, Young's modulus, electrochemical impedance spectroscopy, and electromechanical response analyses (including blocking force, displacement, displacement rate, current, coulombic efficiency, and voltage) suggest that a morphological transformation within the polymer is likely to occur once RH exceeds 60%. This finding strengthens the hypothesis that ion migration is mainly influenced by their movement through Nafion's ionomeric channels rather than the filling of ionic agglomerates.

Strain-modulated defect engineering of two-dimensional materials

Strain- and defect-engineering are two powerful approaches to tailor the opto-electronic properties of two-dimensional (2D) materials, but the relationship between applied mechanical strain and behavior of defects in these systems remains elusive. Using first-principles calculations, we study the response to external strain of h-BN, graphene, MoSe2, and phosphorene, four archetypal 2D materials, which contain substitutional impurities. We find that the formation energy of the defect structures can either increase or decrease with bi-axial strain, tensile or compressive, depending on the atomic radius of the impurity atom, which can be larger or smaller than that of the host atom. Analysis of the strain maps indicates that this behavior is associated with the compressive or tensile local strains produced by the impurities that interfere with the external strain. We further show that the change in the defect formation energy is related to the change in elastic moduli of the 2D materials upon introduction of impurity, which can correspondingly increase or decrease. The discovered trends are consistent across all studied 2D materials and are likely to be general. Our findings open up opportunities for combined strain- and defect-engineering to tailor the opto-electronic properties of 2D materials, and specifically, the location and properties of single-photon emitters.

Calculation of the elastic modulus of steel during tensile

The rational use of resources in the design of vessels and devices and ensuring their growing needs requires the performance of strength and stability calculations, which require the use of appropriate values of the modulus of elasticity during tension E. The purpose of the article is to improve the definition of the modulus of elasticity of steels during tension, the value of which is normalized by the current in Ukraine by regulatory documents. On the basis of standard tables, dot graphs of changes in modulus of elasticity of carbon, low-alloy, heat-resistant, corrosion-resistant chromium, heat-resistant and heat-resistant austenitic steels and iron-nickel-based alloys during tension E depending on temperature t were constructed and analyzed. It is proposed to approximate these dependencies with simple mathematical equations. As a result, it was determined that the dependence E = f (t) for carbon and low-alloy steels in the range of changing t from 20 oС to 300 oС is described by a simple linear equation E = – 100t + 2.01.105. When changing t from 300 oС to 450 oС inclusive, it is proposed to apply cubic regression E = – 5.33.10–3t3 + 5.2t2 – 1.827.103t + 3.95.105. In the above and further proposed formulas, the temperature t is substituted in °C, and the result is obtained in MPa. Heat-resistant and corrosion-resistant chromium steels in the temperature range t from 20 oС to 100 oС inclusive are characterized by the same modulus of elasticity during tension E = 2.15.105 MPa. The dependence of E = f (t) in the range of changing t from 100 oС to 250 oС inclusive can be described by the cubic regression E = 1.33.10–3t3 – 2.63.102t + 2.4.105, and when changing t from 250 oС to 600 oС inclusive – by cubic regression E = – 7.5.10–4t3 + 0.722t2 – 3.426.102t + 2.4748.105. The value of the modulus of elasticity during tension for heat-resistant and heat-resistant austenitic steels and iron-nickel-based alloys E = 2.15.105 MPa in the temperature range t from 20 oС to 100 oС. The dependence of E = f (t) in the range of changing t from 100 oС to 700 oС inclusive is described by the quadratic regression E = – 0.152t2 + 9.101t + 2.009.105. The obtained formulas make it possible to abandon the use of standard tables and additional interpolation of intermediate values of the modulus of elasticity of steels during tension when performing calculations, which in turn simplifies both the calculation itself and the development of appropriate computer programs. The average error value of the performed approximations is in the range from 0 % to 0.218 %, which indicates a high level of coincidence of the regression equations with the actual values. The use of the proposed formulas for calculating the modulus of elasticity of steels during tension makes it possible to simplify the calculation of vessels and devices for strength and stability.

Impact of internal pre-damage due to drying shrinkage under various humidity conditions on DEF expansion in cement paste and mortar

This study explores the impact of internal pre-damage from early drying shrinkage on the delayed ettringite formation (DEF) expansion behavior of cement-based materials subjected to high-temperature processes. Specimens of cement paste and mortar with water-cement (W/C) ratios of 0.4, 0.5, and 0.6 were characterized after curing under relative humidity (RH) conditions of 50, 70, and 100 for 56 days. The parameters assessed were drying shrinkage, dynamic elastic modulus, and free water content. Subsequent DEF expansion over time was quantified, and the underlying mechanism was analyzed using XRD and SEM techniques after 270 days of underwater curing. Results indicate that: (1) a lack of adequate early curing humidity significantly reduces the dynamic elastic modulus with more than a 10% drop in cement paste following 56 days at RH50; (2) a higher W/C ratio and lower early curing humidity lead to more internal damage due to shrinkage, thereby promoting DEF expansion; (3) drying intensifies internal pre-damage in the interfacial transition zone (ITZ), causing an earlier deterioration of DEF expansion in mortar compared to cement paste. However, the presence of aggregates constrains this, leading to lesser DEF expansion in mortar; (4) dynamic elastic modulus changes as measured by ultrasonic methods can quantitatively characterize the extent of deterioration caused by DEF expansion, thus offering a tool for non-destructive testing and DEF expansion deterioration analysis.