Decrease In Elastic Modulus Research Articles

First-Principles Study of Mechanical Properties of Pb(ZrxTi1−x)O3 in the Cubic and Tetragonal Phase

In this study, we employed the first-principles method based on density functional theory to calculate the elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and density of states for both cubic and tetragonal phases of Pb(ZrxTi1−x)O3. The structural model of Pb(ZrxTi1−x)O3 was established using the virtual crystal approximation (VCA). Our results demonstrate that the VCA-calculated properties are in excellent agreement with other theoretical predictions and experimental data. As the Zr content increases, the lattice constants of both cubic and tetragonal Pb(ZrxTi1−x)O3 increase, while the c/a ratio initially decreases and subsequently increases. Both cubic and tetragonal Pb(ZrxTi1−x)O3 satisfy the Born stability criteria, indicating mechanical stability. For the cubic phase, the elastic constants, bulk modulus, and shear modulus decrease with increasing Zr content. In contrast, for the tetragonal phase, the elastic and shear moduli exhibit a non-monotonic trend, peaking at a Zr content of 0.5, where Pb(Zr0.5Ti0.5)O3 demonstrates superior mechanical properties. A comparative analysis reveals that as Zr content increases, the cubic phase exhibits enhanced structural resilience, greater electronic structure stability, and increased anisotropy. These characteristics make cubic Pb(ZrxTi1−x)O3 more suitable for advanced manufacturing techniques such as additive manufacturing, offering enhanced design flexibility for ferroelectric materials.

Mechanical properties and macro–micro failure mechanisms of granite under thermal treatment and inclination

The coupling effects of inclination angle (θ) and high temperature (T) on rock degradation present significant construction challenges for underground engineering projects, such as underground coal gasification, inclined mining pillars, and nuclear waste repositories. This study is built on a novel combined compression and shear test system, investigating granite’s physical and mechanical properties and macroscopic failure characteristics under varying temperatures and inclination angles. Additionally, acoustic emission technology was used to analyze the impact of inclination and temperature on the micro-failure behavior of the specimens. The experimental results indicate that as the inclination angle increases, the specimens’ peak compressive strength and elastic modulus decrease linearly. In contrast, the shear stress increases non-linearly, suggesting that additional shear stress accelerates the initiation and propagation of cracks. Furthermore, these mechanical parameters initially increase with rising temperatures before decreasing, with a temperature threshold identified at 400 °C. The effect of inclination angle on the failure mode of the specimens is more pronounced than that of temperature; as the inclination angle increases, the failure mode transitions from splitting failure to shear failure at any given temperature. Acoustic emission results reveal that the specimens’ microcrack initiation (CI) and damage (CD) thresholds reduce with increasing inclination, while the corresponding shear stress increases. As temperature rises, the CI and CD thresholds exhibit an initial increase attended by a decrease. Finally, founded on the experimental findings, a multivariate equation was established to accurately predict the peak compressive strength and elastic modulus about θ and T. The results of this study provide valuable insights and references for the construction of underground thermal engineering under complex conditions.

Numerical simulation of cementing seal integrity during electric heating of oil shale

Electric heating technology is a vital method for in-situ modification and exploitation of oil shale. This process subjects the wellbore and cement sheath to prolonged exposure to high temperature and pressure environments, posing significant challenges to the integrity of the cementing seal. To investigate the thermally induced changes during the electric heating process of cement sheath and oil shale, a combined model of cement sheath and oil shale was established using the discrete element method. The combined model was calibrated based on macroscopic mechanical experiments of cement sheath and oil shale. Subsequently, the thermal-mechanical coupling problem and thermal cracking phenomenon of the combined model under high temperature and high pressure environments were examined. The results revealed that thermal cracks begin to emerge at the onset of heating at around 150 °C, leading to a decrease in compressive strength and elastic modulus of the combined body. As the temperature reaches 400 °C to 500 °C, the number of thermal cracks peaks. The underground high-pressure environment impedes the thermal expansion of combined body particles, thereby inhibiting the development of thermally induced cracks. The addition of steel fibers to the cement sheath significantly reduces thermal cracking and effectively enhances the sealing performance of the cement sheath.

Macro–Micro Properties of Remodeled Waste Slurry Under Freeze–Thaw Cycles

Waste slurry, a major by-product of urban construction, is produced in rapidly increasing volumes each year. Dehydrated waste slurry has potential as a roadbed material; however, its performance in freeze–thaw environments, which can induce frost heave and thaw settlement, and the mechanism of the influence of freeze–thaw cycles on its macro and micro properties are still unclear and need thorough investigation. This study explores the macroscopic and microscopic properties of waste slurry subjected to freeze–thaw cycles. We conducted unconfined compressive strength (UCS) and triaxial unconsolidated undrained (UU) shear tests, focusing on fissure compaction, elastic deformation, plastic yielding, and strain hardening stages. The results reveal a decrease in strength and elastic modulus with increasing freeze–thaw cycles, as well as in the damage degree generated by freeze–thaw cycles. To uncover the underlying microscopic mechanisms, we performed Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) analyses. These tests highlighted the evolution of pores and microcracks during freeze–thaw cycles. These results have important reference values for the reutilization of waste slurry discharged from large-diameter bored piles for roadbed backfill materials that need to be repaired quickly in seasonally frozen areas.

Regional mechanical properties of spinal cord gray and white matter in transverse section.

Understanding spinal cord injury requires a comprehensive knowledge of its mechanical properties, which remains debated due to the variability reported. This study aims to characterize the regional mechanical properties of the spinal cord in transverse sections using micro-indentation. Quasi-static indentations were performed on the entire surface of transverse slices obtained from 10 freshly harvested porcine thoracic spinal cords using a 0.5mm diameter flat punch. No significant difference in average longitudinal elastic modulus was found between white matter (n=183, E=0.51±0.21kPa) and gray matter (n=51, E=0.53±0.25kPa). In the gray matter, the elastic modulus in the dorsal horn (0.48±0.18kPa) was significantly smaller than in the ventral horn (0.57±0.24kPa) (GLMM, p<0.05). The elastic modulus in the dorsal horn was also significantly smaller than in the lateral (0.52±0.22kPa) and ventral funiculi (0.53±0.18kPa) of the white matter (GLMM, p<0.05). However, there was no significant difference in the elastic modulus among the ventral, lateral and dorsal funiculi of the white matter (GLMM, p>0.05). The average elastic modulus strongly varies between samples, ranging from 0.23 (±0.06) kPa to 0.79 (±0.18) kPa and the testing time postmortem was significantly associated with a decrease in elastic modulus (t=-5.2, p<0.001). The spinal cord's white matter demonstrated significantly lower elastic modulus compared to published data on brain tissue tested under similar conditions. These findings enhance our comprehension of the mechanical properties of spinal cord white and gray matter, challenging the homogeneity assumption of current models.

Investigating the Effects of Metakaolin Blended With Sugarcane Bagasse Ash and Rice Husk Ash Based Geopolymer on the Engineering Properties of Geopolymer Concrete

Concrete is a major construction material, that is largely made up of cement; however, its high cost and ecological unsustainability has been a source of concern over the years in construction industry. In recent years, innovative cementitious materials that can be used as an alternative for ordinary Portland cement (OPC) with improved performance and emission, are locally source to reduce CO2 emission into the atmosphere during cement production and high cost of cement in concrete production. Therefore, geopolymer is an innovative and environmentally beneficial binder material that was developed to reduce Portland cement‘s harmful environmental consequences. Geopolymer is one of the trending research areas in composite materials; there are many areas in geopolymer that unexplored still need to be explore. This study investigates the effects of blended metakaolin concrete produced with Sugarcane bagasse ash(SCBA), Rice husk ash(RHA) and alkali solution in concrete production. The optimum percentage of Metakaolin replacement was investigated and the concrete samples were tested for strength, dry shrinkage and elastic modulus. The effectiveness of two materials was examined with Metakaolin in concrete. The percentage replacement of MK with SCBA and RHA was at 50%, 60% and 70% respectively. The ]samples of the concrete cubes were cured in ambient temperature and aging period of 7, 14, 28 and 56days were used to cure the samples. The fresh, mechanical properties, shrinkage and modulus of elasticity of geopolymer were investigated. Geopolymer was observed to have medium workability and mechanical sproperties, showed good results. The optimum mix maximum strength was observed. The target strength from the design is 25N/mm2, though; 88% of its was achieved. The strength is decreasing with increase of MK percentage and also the elastic modulus decrease; whereas the shrinkage increased as the % of MK increases. This study emphasizes, the potential for global adoption, cost saving, environmental friendly and also provide valuable insight for environmentally sustainable development.

Investigating the Effects of Metakaolin Blended with Sugarcane Bagasse Ash and Rice Husk Ash Based Geopolymer on the Engineering Properties of Geopolymer Concrete

Concrete is a major construction material, that is largely made up of cement; however, its high cost and ecological unsustainability has been a source of concern over the years in construction industry. In recent years, innovative cementitious materials that can be used as an alternative for ordinary Portland cement (OPC) with improved performance and emission, are locally source to reduce CO2 emission into the atmosphere during cement production and high cost of cement in concrete production. Therefore, geopolymer is an innovative and environmentally beneficial binder material that was developed to reduce Portland cement‘s harmful environmental consequences. Geopolymer is one of the trending research areas in composite materials; there are many areas in geopolymer that unexplored still need to be explore. This study investigates the effects of blended metakaolin concrete produced with Sugarcane bagasse ash(SCBA), Rice husk ash(RHA) and alkali solution in concrete production. The optimum percentage of Metakaolin replacement was investigated and the concrete samples were tested for strength, dry shrinkage and elastic modulus. The effectiveness of two materials was examined with Metakaolin in concrete. The percentage replacement of MK with SCBA and RHA was at 50%, 60% and 70% respectively. The ]samples of the concrete cubes were cured in ambient temperature and aging period of 7, 14, 28 and 56days were used to cure the samples. The fresh, mechanical properties, shrinkage and modulus of elasticity of geopolymer were investigated. Geopolymer was observed to have medium workability and mechanical sproperties, showed good results. The optimum mix maximum strength was observed. The target strength from the design is 25N/mm2, though; 88% of its was achieved. The strength is decreasing with increase of MK percentage and also the elastic modulus decrease; whereas the shrinkage increased as the % of MK increases. This study emphasizes, the potential for global adoption, cost saving, environmental friendly and also provide valuable insight for environmentally sustainable development.

Evaluating the impact of rock damage and induced fracture evolution on heat extraction using supercritical carbon dioxide as the working fluid: Semi-analytical model, numerical model, workflow, economic analysis, and field case

Geothermal energy, a clean and renewable source, has garnered significant attention. The excellent physical properties of supercritical carbon dioxide make it an ideal fluid for geothermal development. Fractures act as channels for the efficient seepage and heat transfer of supercritical carbon dioxide. Consequently, the macroscopic fracture damage and evolution induced by the flow of supercritical carbon dioxide impact heat extraction efficiency. Here, pseudo-pressure (multi-stage induced fracture and non-Darcy multi-stage fractured) and temperature well-testing (multi-stage induced fracture thermal and non-Darcy multi-stage fractured temperature) models are developed to monitor the fractures evolution during heat transfer. The finite element method, superposition principle, and Duhamel principle are utilized to establish the proposed models. Numerical models that either consider or disregard rock damage and fracture evolution are developed to simulate and compare the efficiency of heat extraction. The COMSOL Multiphysics 6.1 software is used to solve a heat extraction transient evaluation model. A workflow for utilizing the developed models is proposed, followed by an economic sensitivity analysis. Finally, the models are applied to field cases in the Babbage Oilfield to guide the extraction of geothermal energy. Core displacement experiments are conducted to validate its accuracy, and a differential economic analysis method demonstrates its economic benefits. Results show that the well-testing models invert parameters related to reservoir and fracture evolution. Rock damage and fracture evolution during a heat extraction process are primarily influenced by thermal stress, thermal shock, and pressure-driven effects. As production progresses, fracture permeability and porosity increase, rock elastic modulus decreases, and production temperature drops. Comparing the results with versus without considering rock damage and fracture evolution reveals that their maximum pressure difference is 14% and their maximum temperature difference is 5%. The production pseudo-pressure has the greatest impact on fracture evolution. The injection temperature has the most significant effect on heat extraction efficiency, followed by injection pressure, fracture permeability, and a mass flow rate, with elastic modulus having the least impact. The maximum differential economic benefit for a single horizontal well injection-production system reaches $293,000. Field case studies from the Babbage Oilfield demonstrate the practicality of the developed models and workflow. In summary, the models, workflow, and economic analysis methods proposed in this work provide guidance for engineers in formulating more optimized heat extraction schemes.

Influence of Aging Treatment and Volume Fraction on Nano-Indentation Behavior of Ni-Based Single Crystal Superalloys.

The effects of aging treatment and the volume fraction of precipitation particles on the nano-hardness and nano-indentation morphology of Ni-based single crystal superalloys are systematically investigated. Using nano-indentation tests and atomic force microscopy (AFM), this study examined the mechanical properties and related physical mechanisms of Ni-based superalloys that have two volume fractions of precipitation particles and four aging treatment times. Results analyzed using the Oliver-Pharr method indicate that prolonging the aging time or increasing the volume fraction of particles enhances the nano-hardness and creep resistance of Ni-based single crystal superalloys and reduces the indentation-affected area. Additionally, the nano-hardness and elastic modulus decrease gradually with increasing applied force, revealing an obvious indentation size effect. These variations are closely linked to the size and density of particles and work hardening rate, as well as to the topologically close-packed (TCP) phases, which influence dislocation movement and accumulation within the material and lead to various nano-indentation behavior in Ni-based single crystal superalloys. The related study provides theoretical guidance and experimental data to support the design and application of superalloys.

Residual reliability of a composite material subjected to buckling and post-buckling tests: the case of reinforced concrete

This article examines the residual reliability of composite materials, focusing on reinforced concrete subjected to buckling and post-buckling tests, a crucial topic in civil engineering. The main aim of the study is to assess how these loads affect mechanical properties, including compressive strength and elongation at break, while identifying associated failure mechanisms. A rigorous methodology was adopted, involving experimental tests on reinforced concrete samples, followed by microscopic analysis and comparison with literature data. The results reveal a significant decrease in compressive strength and modulus of elasticity with increasing loads and loading cycles. In addition, the study highlights a reduction in elongation at break, indicating a loss of ductility and stiffness of the material. Failure mechanisms observed include cracking and delamination, suggesting that the residual reliability of reinforced concrete is inferior to that of advanced composites. These findings underline the importance of appropriate design to ensure the durability of reinforced concrete structures, taking into account the impact of extreme loads and environmental conditions. This research contributes to a better understanding of the behavior of composite materials under critical conditions, providing recommendations for improving design and construction practices in civil engineering.

Effect of Composition on Physical, Mechanical, and Thermal Properties of Oil Palm Empty Fruit Bunch Epoxy Resin Biocomposite

Oil palm empty fruit bunches (OPEFB) are wastes from oil palm processing. The objective of this work is to study the effect of composition on the physical, mechanical, and thermal properties of OPEFB epoxy resin biocomposite. Particles of OPEFB (100 mesh) were mixed with epoxy resin with the ratio of OPEFB to epoxy resin 60/40, 70/30, 80/20, and 90/10 (vol.%/vol.%). Biocomposites were produced by a press method at room temperature with 9 tons-load. The physical properties (density, porosity, water absorption, thickness swelling) of the biocomposite were evaluated. The mechanical properties (modulus of rupture and modulus of elasticity) of biocomposite were determined by using a universal testing machine. The thermal gravimetric analyzer (TGA) was used to examine the thermal properties of the biocomposite. The results show that the density of biocomposite is 1.18 g/cm3 for 60 vol.% of OPEFB composition. It decreases significantly as the OPEFB composition increases. For 60 vol.% of OPEFB, the porosity, water absorption, and thickness swelling of biocomposite (after soaking in water for 24 hours) are 11.9%, 10.1%, and 6.5%, respectively. All these values increase significantly with the increase of OPEFB composition. For 60 vol.% of OPEFB, the modulus of rupture (MOR) and modulus of elasticity (MOE) of biocomposite are 2.31 kgf/mm2 and 267 kgf/mm2, respectively. The values of MOR and MOE decrease significantly with the increase in OPEFB composition. TGA results show that degradation of biocomposites occurs significantly at 350°C for 60 vol.% OPEFB. The degradation temperature reduces as the composition of OPEFB increases. In general, the physical, mechanical, and thermal properties of biocomposites decrease with increasing OPEFB composition. This happens because the bond between the matrix and the particles decreases as the OPEFB composition increases. The maximum OPEFB composition that can be used for particleboard applications is 80 vol.%, which meet the ANSI 208.1-2009 requirements for application as grade M-2 particleboard.

Study on the mechanical behavior and rupture characteristics of coal after thermal damage.

High temperature is a critical safety concern that poses challenges to the safe and efficient operation of coal mines. To explore the mechanical behavior and fracture mechanisms of coal exposed to high temperatures, coal samples were subjected to various thermal treatments. After cooling, uniaxial compression tests were performed using an electronic universal testing machine to assess their macroscopic properties. A discrete element numerical model, reflecting the same mineral composition, was then developed to investigate the microscopic fracture behavior of thermally treated coal under uniaxial compression. The results indicate that at high temperatures, thermal motion becomes more pronounced, leading to increased particle displacement and a transition in coal failure from brittle to ductile behavior. High temperatures intensify thermal damage, generating numerous thermal cracks, which prolong the crack closure phase and delay the onset of the elastic deformation stage. Furthermore, the formation and propagation of these thermal cracks significantly influence macroscopic mechanical properties. Peak stress and elastic modulus decrease with rising temperature, with the most pronounced reductions occurring between 200°C and 300°C, where the thermal damage factor peaks at 0.72. As the temperature increases, the proportion of tensile cracks decreases, while shear cracks become more prevalent. Under heat treatment, tensile failure dominates, whereas shear failure is predominant during uniaxial compression. These findings provide valuable insights for improving safety protocols in high-temperature coal mining environments.

Size effect on the compressive properties of neosinocalamus affinis-based bamboo scrimber

ABSTRACT Bamboo scrimber, a high-strength composite fiber material, has broad application prospects in the construction field. However, its mechanical parameters are easily influenced by the size of the test specimens, making accurate testing challenging. To investigate the impact of specimen width on the compression failure mode and compressive strength of bamboo scrimber, three sets of specimens with different slenderness ratios were prepared. Longitudinal compression tests were conducted, and the digital image correlation (DIC) system was used to observe the strain fields of the specimens and obtain stress-strain curves. The factors controlling the compression failure of bamboo scrimber were analyzed, and the size effect law of longitudinal compressive strength was studied using Weibull size effect theory. The results show that the compression failure mode, compressive strength, peak strain, and elastic modulus of bamboo scrimber exhibit significant size effects. When the specimen size is small, the bamboo scrimber is more prone to compression-shear failure. As the specimen size increases, the failure mode primarily transitions to splitting failure. For specimens with the same slenderness ratio, the compressive strength, peak strain, and elastic modulus decrease gradually with increasing size.

Mechanical properties of bridge steel Q420qE at elevated temperatures

High-temperature mechanical properties of bridge steels, which were rarely investigated, are the foundation for fire resistance analysis and design of bridges. This study investigates the high temperature mechanical properties of Q420qE bridge steel by using steady-state tensile test method. Results indicate that this steel shows no yield plateau at both room temperature and elevated temperatures. Compared with the same grade structural steels, the decrease in elastic modulus and yield strength of Q420qE with increasing temperature are slower. However, the decrease of ultimate strength is more rapid, with a maximum difference on reduction factor being about 0.327 (41.92 %). The mainstream fire resistance design standards exhibit limitations in predicting the high temperature mechanical properties of Q420qE steel. Furthermore, predictive equations of mechanical property reduction factors of Q420qE at elevated temperatures were proposed, and constitutive model of Q420qE at elevated temperatures was recommended.

Molecular dynamics analysis of iPP-polymorphs; Investigating thermal expansion and elastic properties

The elastic properties of α and β crystals of isotactic polypropylene are obtained by molecular dynamics simulations of a crystalline domain resembling an infinite crystal. The helical polymer chains are modeled with an all-atom force-field. The assessment of the pristine α2 lattice agreed with published results of structure, density, thermal expansion, and stiffness. Monoclinic α systems with particular imperfections are sampled to assess the effect of defects on conformational stability and elastic properties. The sensitivity of elastic moduli with temperature correlates with the helicity disruption: the more chain-conformational defects, the stronger the decrease in elastic modulus. The non-perfect chiral up-down α1 lattice and the arrangement with one vacancy also display a lower stiffness than α2, which can be attributed to a less dense crystal and decreased inter-chain cooperative forces due to periodicity disruption.Two variations of the metastable β modification were sampled to assess the most energetically favorable configurations. Then, both were subjected to the same procedure, validated first for α. A trigonal mono-chiral system, β2, and a stable bi-chiral one with a four-chain frustrated orthorhombic cell, β1, were found, both presenting novel characteristics. Both β structures display a less stable conformation than α2, observed by a higher specific volume, a lower transition temperature, and a more significant dependence of the elastic moduli with temperature. Remarkably, the mono-chiral β2 crystal showed higher elastic modulus than any other crystal below room temperature, related to a more efficient global methyl interlocking between chains. The fact that the experimental value for the density of the β-kind of crystal is in between the values that we obtained from the simulations of β2 and β1 implies that the experimental observations consist of both of these β crystals, where β1 might work as an interface between monochiral β2 layers.

Impact of Hexyl Branch Content on the Mechanical Properties and Deformation Mechanisms of Amorphous Ethylene/1-Octene Copolymers: A Molecular Dynamics Study.

Ethylene/1-octene copolymers exhibit enhanced flexibility and impact resistance compared to polyethylene, which makes them well suited for applications in advanced plastics and elastomers. United-atom molecular dynamics (MD) simulations were conducted to explore the mechanical behavior and deformation mechanisms of ethylene/1-octene copolymers under uniaxial tensile loading. This study systematically examined the influence of temperature, polymer chain length, chain quantity, and strain rate, with a specific focus on how hexyl branch content impacts the mechanical properties of amorphous ethylene/1-octene copolymers. The simulation results indicate that as the branch content increases, the yield strength and elastic modulus decrease, suggesting a trade-off between flexibility and mechanical strength. Energy decomposition analysis reveals that copolymers with more branched chains undergo greater changes in van der Waals energy. Additionally, as the branch content increases, the reduction in dihedral angle energy in the strain hardening region becomes more gradual, and the rate and the extent of the transition of dihedral angles from gauche to trans conformation decrease under deformation. Ethylene/1-octene copolymers exhibit higher chain entanglement parameters compared to linear polyethylene, with these parameters increasing as the branch content rises. Moreover, increasing the branch content results in a less pronounced increase in chain orientation along the loading direction.

A detailed study on the physical, mechanical, structural and gamma ray shielding properties of Al2O3–Na2O–SiO2–B2O3–Bi2O3glass system

The density, boron–boron separation, and molar volume of 4Al2O3–12Na2O-(18-x)SiO2-(64-x) B2O3-(2+2x)Bi2O3 (where x = 2, 4, 6 and 8 mol%) are increasing with the addition of Bi2O3. The addition of Bi2O3 results in an open network structure. The elastic moduli decrease from 34.711 to 29.875 GPa for Young modulus (E); 20.395 to 15.843 GPa for bulk modulus (B); from 15.257 to 13.494 GPa for shear modulus (G) and 40.738 to 33.836 GPa for longitudinal (L) respectively with increased Bi2O3 concentration. FTIR spectrainvestigation found BO3, BO4, SiO4, and BiO6 structural units to be present. The glasses' highest mass attenuation coefficient (MAC) is at 0.0395 MeV, the lowest energy value. It gradually decreases as energy increases. There is a decrease in the linear attenuation coefficient (LAC) values with energy. Sample Bi18 has the highest MAC and LAC values due to its high concentration of Bi2O3. Across the entire energy range, sample Bi18 has the highest effective atomic number, and the lowest half value layer and mean free path values across all energy values. The transmission factor (TF) values for Bi6 indicate that the required thickness for blocking 90% of the radiation must be greater than the thickness necessaryfor the attenuation of 50%. Bi18 has the lowest TF compared to other glass samples. The radiation protection efficiency values for Bi18 are highest, confirming their full protection ability. Bi18's is the best choice for radiation shielding.

Uniaxial compressive behavior and unified damage constritutive model of various types of recycled coarse aggregate concrete under freeze-thaw action

To promote the application of recycled coarse aggregates in concrete structures in cold regions, this paper focuses on the damage evolution of natural coarse aggregate concrete (NAC), recycled concrete coarse aggregate concrete (RAC) and brick-concrete mixed recycled coarse concrete (MRC) under the freeze-thaw-load coupling action. The relative dynamic modulus of elasticity is used to assess the freeze-thaw damage degree of various types of concrete after 0, 25, 50, 75, 100, 125, and 150 freeze-thaw cycles, and a freeze-thaw damage evolution model is established. Uniaxial compression tests are conducted on concretes after different freeze-thaw cycles to study the effects of freeze-thaw cycles on the failure mode, peak stress, peak strain, static elastic modulus, and toughness of the specimens. The relationship between the freeze-thaw damage variable and stress-strain characteristic parameters is analyzed, and an unified damage constitutive model for various types of concrete under the freeze-thaw-load coupling action is further established. The results show that with the increase in the number of freeze-thaw cycles, the specimens exhibit vertical splitting failure under axial compression rather than typical shear failure. The freeze-thaw cycles reduce the ability of recycled concrete to resist deformation. The peak stress and static elastic modulus decrease with the increase of freeze-thaw cycles, while the peak strain and toughness increase with the increase of freeze-thaw cycles. NAC has the best frost resistance and axial compression bearing capacity, followed by RAC and MRC. The presence of recycled brick coarse aggregate further exacerbates the freeze-thaw damage of concrete. There is an interesting finding that the water absorption of recycled aggregates is well correlated with the shape parameters of the freeze-thaw damage model and the descending section of uniaxial compression damage constitutive in recycled concrete. When the descending branch of the stress-strain curve modified by water absorption of recycled aggregates, the proposed freeze-thaw-load coupling damage constitutive model demonstrates good predictive performance for the stress-strain behavior of recycled concrete.

Impact of statistical poly(propylene co-ethylene) on the thermo-mechanical properties of high-density polyethylene

A series of high-density polyethylene and a statistical copolymer of poly(propylene-co-ethylene) blends in a wide range, namely (0, 10, 20, 30, 40, 50, 60,70, 80, 90, 100) abbreviated as HDPE/VM were systematically investigated by using a rheometer, differential scanning calorimetry (DSC) measurements, polarized optical microscopy (POM) and tensile tests. Rheometer results show that adding VM decreases dynamic viscosity, storage, and loss modulus. Han plot shows that HDPE and VM are compatible and miscible in the range from 20 to 60 VM % in the molten state. DSC results show little nucleation effect of VM on HDPE (HDPE’s melt crystallization temperature shifts 2 °C higher). Moreover, a linear composition dependence of ∆cp ∆Hc, ∆Hm shows that PE and VM are most probably compatible in the molten state in composition range from 20 to 60%. However, upon crystallization, the VM and PE domains occur distinctively. The results of the tensile tests demonstrated a decrease in elastic modulus, yield stress, and ultimate tensile strength as VM content increased. At low VM content (less than 20%), high elongation at break was detected for the blends, and very fine spherulites of HDPE were found across the sample by POM.

Flat biofilms extrusion of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) grafted with glycidyl methacrylate blends: Toward ecological packaging for sustainability

AbstractBlends of poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) grafted with glycidyl methacrylate (PBAT‐g‐GMA) were developed to produce flat and flexible biofilms through extrusion. The PLA/PBAT‐g‐GMA (90%/10%, 80%/20%, 70%/30%, and 60%/40% by mass) blends were processed in the internal mixer, injection molded, and manufactured into flat films. The optimal composition to produce flexible biofilms was PLA/PBAT‐g‐GMA (60/40%), as it demonstrated a decrease in elastic modulus of 53.2% and a significant gain in elongation at a break of 4923% about pure PLA. The incorporation of 40% PBAT‐g‐GMA in PLA increased the torque (Z) by 208%, while the melt flow index (MFI) decreased by 51.57%, compared to PLA. Additionally, the degradation rate (Rz) and molar mass loss (Rm) during processing were minimized, indicating that 40% PBAT‐g‐GMA enhanced stability of the PLA matrix. Fourier transform infrared spectroscopy indicated interactions between the GMA of PBAT‐g‐GMA and PLA, justifying the increase in viscosity and elongation at break. The PLA/PBAT‐g‐GMA (60/40%) composition showed a transmittance in the range of 20%–48% (400–800 nm) and an oxygen gas permeability of 1.56 × 10−5 cm3 STP/cm−2 h bar, indicating its potential for applications in packaging with optical barrier properties. Scanning electron microscopy (SEM) revealed ligaments in the interfacial region between PLA and PBAT‐g‐GMA, confirming the good performance in elongation at break. The results presented are essential for the plastics processing sector, aiming to develop eco‐friendly packaging.