Decrease In Elastic Modulus Research Articles

Effect of Different Essential Oils on the Properties of Edible Coatings Based on Yam (Dioscorea rotundata L.) Starch and Its Application in Strawberry (Fragaria vesca L.) Preservation

Every year the world loses about 50% of fruits and vegetables post-harvest and in the supply chain. The use of biodegradable coatings and films with antioxidant properties has been considered an excellent alternative to extend the shelf life of food. Therefore, the objective of this work was to develop a coating based on yam (Dioscorea rotundata L.) starch-containing lime, fennel, and lavender essential oils to extend the shelf life of strawberries (Fragaria vesca l.). The tensile properties, barrier properties (water vapour permeability (WVP) and oxygen permeability (OP)), moisture content, water-solubility, absorption capacity, water contact angle, optical properties, the antioxidant activity of the resultant starch-based coatings were evaluated. After that, the active properties of the coatings were assessed on strawberries inoculated with Aspergillus niger during 14 days of storage at 25 °C. The results showed that the incorporation of essential oils improved the elongation and WVP and provided antioxidant capacity and antimicrobial activity in the films. In particular, the essential oil of lime showed higher antioxidant activity. This fact caused the unwanted modification of other properties, such as the decrease in tensile strength, elastic modulus and increase in OP. The present study revealed the potential use of lime, fennel, and lavender essential oils incorporated into a polymeric yam starch matrix to produce biodegradable active films (antioxidant and antimicrobial). Obtained films showed to be a viable alternative to increase the shelf life of strawberries and protect them against Aspergillus niger.

Investigation of biaxial strain behavior and phonon-limited mobility for γ graphyne: First-principles calculation

γ graphyne is a new allotrope of carbon that has attracted interest because of its semiconductor characteristics and high mobility. This work investigates the biaxial strain behavior and phonon-limited mobility for single-layer γ graphyne by using first-principles calculations. Ab initio molecular dynamics calculations reveal that γ graphyne is thermodynamically stable at 300 K and can withstand a biaxial strain of ε=10%. The mobility is investigated by using the deformation potential method. We consider the contribution to mobility of three equivalent valence-band maxima and conduction-band minima, which correct the prediction of carrier mobility. The mobility significantly decreases with the biaxial strain. When under strain, the effective mass gradually increases and the elastic modulus decreases. The mobility is mainly determined by scattering from acoustic phonons. With increasing strain, optical phonons play a decisive role in carrier scattering. Finally, phonon-limited mobility is investigated by using the electron–phonon coupling method within the framework of the Boltzmann transport equation. At 300 K, the predicted mobility is as high as 9.04×103cm2V−1s−1 for electrons and 8.64×103cm2V−1s−1 for holes. The results thus give the upper limit of γ graphyne’s mobility.

Influence of Microfibrillated Cellulose Additive on Strength, Elastic Modulus, Heat Release, and Shrinkage of Mortar and Concrete.

This work aimed to study the effect of a microfibrillated cellulose additive on strength, elastic modulus, heat release, and shrinkage of mortar and concrete. The dosage of the additive varies from 0.4 to 4.5% by weight of the cement. The change in strength with an increase in the dosage of the additive occurred in a wave-like manner. The uneven character of the change in the results also took place in the determination of heat release and shrinkage. In general, heat release and shrinkage decreased at increasing additive dosage. The additive showed the greatest decrease in the heat release of concrete at a content of 2%. The heat release of concrete practically differed little from the exotherm of the standard at an additive content of 1 and 1.5%. The addition of microfibrillated cellulose additive in small (0.5%) and large (1.5%) amounts reduced shrinkage compared to the reference, and at an intermediate content (1%), the shrinkage was higher than in the reference specimens. In this case, the water evaporation rate from concrete increased with an increase in the additive. With an increase in the additive dosage, the modulus of elasticity decreases. Thus, the microfibrillated cellulose additive provides concrete with lower values of the modulus of elasticity, heat release, and shrinkage, and the additive is recommended for use in concretes with increased crack resistance during the hardening period. The recommended additive content is 0.5% by weight of cement. At the specified dosage, it is possible to provide the class of concrete in terms of compressive strength C35/45.

Experimental Study on Mechanical Properties of Freeze-Thaw Damaged Red Sandstone under Combined Dynamic and Static Loading

Using the freeze-thaw cycle test chamber, the red sandstone samples are subjected to cyclic freeze-thaw tests. The physical properties, static mechanical properties of freeze-thaw damage rocks, and the compressional wave velocity at specific axial pressure are measured using conventional physical tests and uniaxial compression tests. The mechanical properties of freeze-thaw damage rocks under dynamic and static loading were studied using Hopkinson pressure bar which can exert axial pressure. The studies show that, with the increase of freeze-thaw cycles, the surface layer of the rock sample undergoes spalling phenomenon, the weight gradually decreases, the sample compactness becomes worse, there are microcracks between the cemented particles, and the compressive strength and elastic modulus decrease. Under the static loading, the longitudinal wave velocity of freeze-thaw damaged samples change significantly compared with that of samples without freeze-thaw. The freeze-thaw damage degree, axial pressure, and strain rate are coupled with each other, which together affect the dynamic mechanical properties of samples, and make the variation of mechanical parameters, such as dynamic peak strength and dynamic elastic modulus of rock. The combined action of freeze-thaw damage and axial pressure weakens the strain rate effect of samples, but when the incident wave of SHPB test is same, the dynamic strength and elastic modulus of freeze-thaw damaged samples are reduced compared with those without freeze-thaw. Combining with strain equivalence principle, the constitutive relation of freeze-thaw damage of red sandstone under dynamic and static combined loading can reflect the influence of coupling damage of axial pressure and freeze-thaw, dynamic impact parameters, and other factors, which are in good agreement with the test results.

Orientation dependence of microstructure deformation mechanism and tensile mechanical properties of Nickel-based single crystal superalloys: A molecular dynamics simulation

In this paper, molecular dynamics (MD) simulations are performed to investigate the tensile deformation mechanisms and mechanical properties of superalloys with different orientations. The research results show that the superalloys exhibit anisotropy of mechanical properties and are consistent with previous experimental research results. The anisotropy of mechanical properties is related to the differences of stability at the interfacial dislocation network and the 1/6〈112〉{111} slip system startup of superalloys with different orientations. When the yield point is reached, dislocations and stacking faults on both sides of the slip plane will contact each other and merge into a stacking fault band to penetrate into the γ' precipitates. Meanwhile, the dislocation density and the proportion of face-centered cubic (FCC) structure with different orientation models have a sudden change at the yield point. As the temperature increases, the yield strength and elastic modulus decrease in the (110) and (111) orientation models, whereas the (100) orientation model has an anomalous yield behavior. This is mainly related to the destruction of dislocation network, the change of deformation mechanism and the thermally activated cross-slip mechanism when the temperature increases.

Experimental study on the effect of water on mechanical properties of swelling mudstone

Water has a significant effect on the mechanical properties of rocks, especially for rocks containing swelling clay minerals. The clay minerals in swelling rocks will lead to volume expansion and disintegration of rocks after encountering water. In order to further study the water effect on mechanical properties of swelling mudstone, the swelling property of samples was first evaluated by the oedometric swelling test. Then, uniaxial compression tests, Brazilian disc tests, triaxial compression tests, and scanning electron microscope tests were carried out on the swelling mudstone samples (from Xinjiang, China) with different water content. The results showed that the various strengths (uniaxial compressive strength, tensile strength and triaxial compressive strength) of the mudstone samples all decreased with the increase of water content. Furthermore, with increasing water content, the elastic modulus decreases, while the peak strain decreases first and then increases. The strength envelope under each water content was constructed and the relevant parameters were obtained. It was found that the internal friction angle did not change with the water content, but the cohesion decreased with the increase of water content. The reasons of the deterioration of cohesion were explained by scanning electron microscopy tests. Finally, a complete empirical formula for predicting the mechanical properties of swelling mudstone is established.

Effect of recycled powders on the mechanical properties and durability of fully recycled fiber-reinforced mortar

Recycled powders from construction and demolition wastes are rarely applied due to their low additive value. This study used recycled concrete powder (RCP) and recycled brick powder (RBP) as fine particles to partly replace cement, which represents a novel application of recycled powder. Fully recycled fiber-reinforced mortar with recycled sand, recycled fiber and RCP/RBP with replacement ratios of 10%, 20% and 30% was prepared. The mechanical properties and durability, including compressive and flexural strength, dynamic elastic modulus, capillary water absorption, freeze-thaw resistance and carbonization were tested. In addition, XRD and TGA tests were carried out to reveal the mechanism of the RBP/RCP's influence on the properties of fully recycled fiber-reinforced mortar. The results show that there is a greater reduction in strength in mortars with RCP when the curing age is 3 d. When the replacement ratio is 30%, the compressive strengths of mortar with RCP/RBP reach 75.73% and 79.95% of that of cement mortar, respectively. With the addition of RCP/RBP, the capillary water absorption decreases and the carbonization depth increases. In addition, a clear increase in mass loss and decrease in dynamic elastic modulus after 50 freeze-thaw cycles are noted. The mortar with RBP has better performance than that with RCP. The XRD and TGA results show the low activity and secondary hydration of RCP/RBP.

The pore-forming activity of sticholysin I is enhanced by the presence of a phospholipid hydroperoxide in membrane

Sticholysin I (StI) is a pore-forming toxin (PFT) belonging to the actinoporin protein family characterized by high permeabilizing activity in membranes. StI readily associates with sphingomyelin (SM)-containing membranes originating pores that can lead to cell death. Binding and pore-formation are critically dependent on the physicochemical properties of membrane. 1-palmitoyl-2-oleoylphosphatidylcholine hydroperoxide (POPC–OOH) is an oxidized phospholipid (OxPL) containing an –OOH moiety in the unsaturated hydrocarbon chain which orientates towards the bilayer interface. This orientation causes an increase in the lipid molecular area, lateral expansion and decrease in bilayer thickness, elastic and bending modulus, as well as modification of lipid packing. Taking advantage of membrane structural changes promoted by POPC-OOH, we investigated its influence on the permeabilizing ability of StI. Here we report the action of StI on Giant Unilamellar Vesicles (GUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and SM containing increasing amount of POPC-OOH to assess vesicle permeability changes when compared to OxPL-lacking membranes. Inclusion of POPC-OOH in membranes did not promote spontaneous vesicle leaking but resulted in increased membrane permeability due to StI action. StI activity did not modify the fluid-gel phase coexistence boundaries neither in POPC:SM or POPC-OOH:SM membranes. However, the StI insertion mechanism in membrane seems to differ between POPC:SM and POPC-OOH:SM mixtures as suggested by changes in the time course of monolayer surface tension measurements, even though a preferable binding of the toxin to OxPL-containing systems could not be here demonstrated. In summary, modifications in the membrane imposed by lipid hydroperoxidation favor StI permeabilizing activity.

From mango by-product to food packaging: Pectin-phenolic antioxidant films from mango peels

The objective of the study was to prepare active films based on pectin and polyphenol-rich extracts from Tommy Atkins mango peels. Aqueous and methanolic extracts showed a variety of phenolic compounds that were identified by UPLC-MS analysis, and a high content of total phenolics that were quantified by the Folin-Ciocalteau method. The methanolic extract showed better results in antioxidant tests and was more effective in inhibiting the growth of Gram-positive and Gram-negative bacteria. The pectin extracted from mango peels showed good thermal stability and a degree of methoxylation of 58.3% by 1H NMR. The films containing the phenolic extracts showed lower water vapor permeability when compared to the control film (without any phenolic extracts). The incorporation of the extracts led to an increase in elongation (ε) and a decrease in tensile strength (σ) and modulus of elasticity (Y). The films with aqueous or methanolic extracts showed higher antioxidant activity in terms of inhibition of the DPPH radical. Therefore, the films developed in this work are presented as a promising alternative for food packaging and/or coating applications.

Intercalated water mediated electromechanical response of graphene oxide films on flexible substrates

The confinement of water between sub-nanometer bounding walls of layered two-dimensional materials has generated tremendous interest. Here, we examined the influence of confined water on the mechanical and electromechanical response of graphene oxide films, prepared with variable oxidative states, casted on polydimethylsiloxane substrates. These films were subjected to uniaxial strain under controlled humid environments (5 to 90% RH), while dc transport studies were performed in tandem. Straining resulted in the formation of quasi-periodic linear crack arrays. The extent of water intercalation determined the density of cracks formed in the system thereby, governing the electrical conductance of the films under strain. The crack density at 5% strain, varied from 0 to 3.5 cracks mm−1 for hydrated films and 8 to 22 cracks mm−1 for dry films, across films with different high oxidative states. Correspondingly, the overall change in the electrical conductance at 5% strain was observed to be ∼5 to 20 folds for hydrated films and ∼20 to 35 folds for the dry films. The results were modeled with a decrease in the in-plane elastic modulus of the film upon water intercalation, which was attributed to the variation in the nature of hydrogen bonding network in graphene oxide lamellae.

Influence of the anomalous elastic modulus on the crack sensitivity and wear properties of laser cladding under the effects of a magnetic field and Cr addition

Laser cladding layer with high hardness (H) and toughness have been the focus of surface science research because of their remarkable resistance to cracking and wear. This laser cladding experiment is performed in a magnetic field to fabricate alloy cladding layers. This paper presents the research on the magnetostrictive effects of laser cladding with regard to improvements in crack and wear resistance. The microstructural evolution, mechanical properties, lattice constant changes, and frictional wear properties are also investigated. The magnetostriction generated by the magnetic field reduces the elastic modulus (E). This work presents that cracking and wear resistance can be improved by reducing the elastic modulus while ensuring high hardness. The addition of different Cr contents reveals that the magnetostrictive effect relies on elemental content. Ratio of hardness and elastic modulus can characterize the wear and crack resistance of the coating well. In this study, we discussed the influence of the magnetostrictive effect on the wear resistance, which is related to H/E, and crack sensitivity, which is related to H3/E2, of the laser cladding layer. High H/E and H3/E2, that are obtained by the decrease in elastic modulus through the magnetostriction effect, is an effective method for increasing wear and crack resistance, respectively.

Effects of high temperatures and unloading confining pressures on granite

The mechanical and permeability properties of rocks under unloading stress path and high temperature are critically important for hot dry rock. A series of unloading confining pressure and gas permeability tests were conducted on granite samples after heating and rapid cooling treatment. Five levels of temperature and three levels of confining pressures were used. The stress–strain curves of unloading confining pressure were obtained. The strength parameters and deformation parameters were further discussed and analysed. When the heat treatment temperature is higher than 600°C, the granite samples experience a significant degree of thermal damage. With the increase in heat treatment temperature and the decrease in confining pressure, the gas permeability increases. Beyond 600°C, the gas permeability of the samples increases significantly. With the increase in temperature, the internal friction angle decreases slightly from 25 to 400°C, while it increases beyond 400°C. The cohesion exhibits an inverse evolution. The initial unloading elastic modulus and deformation modulus decrease gradually during relief of confining pressure. The decrease rate of the deformation modulus increases with the increase in heating temperature. The experimental results could improve knowledge about the effect of thermal shock and stress on the physico-mechanical properties of granite.

Effect of water on mechanical behavior and acoustic emission response of sandstone during loading process: phenomenon and mechanism

In this paper, a series of uniaxial compression experiments were carried out on sandstone with varying water contents, and acoustic emission (AE) signals were synchronously collected in the experimental process. It reveals that water content has a significant effect on the mechanical behavior and AE signals of sandstone. As the water content increases, both the uniaxial compression strength and the elastic modulus decrease while the peak strain and energy dissipation increase. In the perspective of AE signals, both the peak and the cumulative AE energy drop with the water content, and an exponential empirical function was proposed to describe their relationships. Multi-fractal analyses of AE signals were also performed. The uniformity of signal distribution (∆a) and the difference between frequencies of largest and smallest signals (∆f) also decrease with the increase of water content. All these phenomena can be explained by the fact that more and more intergranular fractures occur at the higher water content condition. Moreover, a sudden increase of ∆a and a sudden decrease of ∆f in time series can be used as the precursor of rock destabilization and failure which have potential engineering application value.

Durability of a New Thermal Aerogel-Based Rendering System under Distinct Accelerated Aging Conditions.

The widespread application of innovative thermal enhanced façade solutions requires an adequate durability evaluation. The present work intends to assess the durability of a new aerogel cement-based rendering system through the adaptation of different accelerated aging cycles, such as heating–freezing, freeze–thawing, and heat–cold. Several mechanical properties and also capillary and liquid water absorptions were tested for uncoated and coated specimens. A decrease in the mechanical strength, especially after freeze–thaw cycles, was observed. However, the water action promoted the late hydration of the cement paste contributing to the densification of the matrix and, consequently, the increase of the adhesive strength. Additionally, a decrease in the dynamic modulus of elasticity and an increase in the Poisson’s ratio were observed after aging, which indicates a higher capacity of the render to adapt to substrate movements, contributing to a reduction of cracking.

Damage Evolution of Concrete Piles Mixed with Admixtures in Marine Corrosion and Freeze-Thaw Environment

Marine corrosion and freeze-thaw environment will bring serious damage to marine concrete structures, leading to affect the safety and service life of structures. With the help of artificial climate and environment simulation laboratory, the variation of the compression strength and elastic modulus of concrete with the number of freeze-thaw cycles and corrosion time under the corrosion and freeze-thaw environment is studied. The results show that both of them firstly increase and then decrease with corrosion time. When the corrosion time is 270 d and the freeze-thaw time is 90 times, the strength of concrete decreases by 13% and the elastic modulus decreases by 5%. Then, based on the theory of damage mechanics, the damage evolution and constitutive model of concrete under the marine corrosion and freeze-thaw environment are established. Compared with the experimental results, it is found that the model can well describe the damage evolution characteristics of concrete under marine corrosion and freeze-thaw environment. Finally, a numerical model is established on the basis of elastic modulus and strength degradation model of concrete under marine corrosion and freeze-thaw environment. Elevated pile caps of concrete pile component are taken as an example to analyze the process of damage, and the change rules of displacement, deformation, and damage of concrete pile are obtained.

Testing method for evaluating mechanical properties of 3D printed CFRP with curved fibers by four-point bending test of L-shaped specimen

In this study, we propose a method to evaluate the mechanical properties (circumferential fracture stress, circumferential elastic modulus) of 3D printed carbon fiber reinforced plastics with a curved section by a four-point bending test of an L-shaped specimen. Several L-shaped specimens with different radii were printed to evaluate the relation between the radius and mechanical properties. Additionally, the internal structure was observed by X-ray CT, and the fiber orientation angle was examined by cross-sectional observation of the curved section to clarify the fracture mechanism and causes that affect the mechanical properties.In the four-point bending test of the L-shaped specimen, a compressive fracture first occurs at the outer surface of the curved section, and the compressive fracture stress and the elastic modulus decrease with the inner radius are less than 10 mm and 5 mm, respectively. The evaluation of the fiber orientation angle suggests that the decrease in the elastic modulus is caused by the fiber bundle twisting that deviates the fiber direction from the circumferential direction. Furthermore, the fiber breakage and voids generated in the curved section can affect its mechanical properties.

Material study of photovoltaic modules with silicone encapsulation after long-term outdoor exposure

In this study we analyze the properties of silicone elastomers used in the fabrication of PV modules in the early 1980's, which were in operation outdoors in a semi-tropical climate for more than 20 years. We observe that the silicone materials have very similar properties to recent, freshly cured silicone. The information gathered gives evidence that silicone elastomers undergo only very limited degradation after years of exposure in the field in operating PV modules. A moderate decrease in elastic modulus was observed, but further studies are needed to determine whether this effect is real. The very limited degradation of silicone encapsulant is consistent with the low performance decrease reported in other studies. - Insights into nineteen eighties module designs - Material analysis of solar cell encapsulant after 20 years of outdoor exposure - Properties of the silicone materials under study are very similar to those of recent, freshly cured material - Correlation between limited encapsulant material degradation and limited power output degradation - Direct comparison between fresh silicone encapsulant and same material after 20 years of exposure in modules in operation

Pilot plant scale-up of the production of optimized starch-based biocomposites loaded with cellulosic nanocrystals from Posidonia oceanica waste biomass

Posidonia oceanica biomass has been valorized to produce cellulosic nanocrystals with different purification degrees at lab- and pilot plant-scale. The cellulosic nanocrystals (10 % and 20 % (w/w)) were incorporated into corn starch, producing biocomposite films by melt mixing and hot-pressing at lab-scale. Biocomposite films showed remarkable improvements on the mechanical and water barrier performance (up to 10-fold increase in the elastic modulus and 2-fold decrease in the water permeability). Biocomposite packaging structures were also produced at pilot plant-scale by extrusion and thermoforming. Adjusting the plasticizer formulation and increasing the nanocrystals’ loading up to the maximum enabling good processability (10 % (w/w)) allowed the production of trays with enhanced water barrier and mechanical performance, which, unlike the pure starch, kept their shape upon storage. These results highlight the potential of P. oceanica nanocrystals to improve the performance of starch-based packaging structures and demonstrates the potential of the production process to be industrially applied.

Effect of fictive temperature on tribological properties of Zr44Ti11Cu10Ni10Be25 bulk metallic glasses

Zirconium (Zr) based bulk metallic glasses (BMGs) have emerged as a potential material for various engineering applications due to their unique and tunable mechanical properties. Heat treatment of the BMGs plays a vital role in changing the mechanical as well as tribological properties. In the present work, the effect of the fictive temperature (Tf) on the mechanical and tribological behavior of Zr based BMGs with a glass transition temperature (Tg) of 352 °C has been studied by nanoindentation and micro-scratch testing at constant (load 10 N) and progressive (0.5–25 N) loading conditions. The BMGs were heat treated at three different fictive temperatures ranging from 0.91Tg (320 °C) to 1.05Tg (370 °C). Hardness and effective elastic modulus were observed to be highest (8.3 GPa and 128 GPa, respectively) for the metallic glass with a fictive temperature of 0.91Tg (320 °C). With an increase in fictive temperature, hardness and effective elastic modulus decrease due to decreased short-range ordering and more free volume (density fluctuations) in the internal structure, which enhances atomic and plastic flow in the material. For constant loading, wear resistance is observed to be similar for as-cast BMG and BMG with Tf = 1.05Tg, but increases by 65% and 40% from as-cast to BMGs with Tf's of 0.91Tg and 0.99Tg, respectively. For progressive loading, the wear resistance increases by 10% from as-cast to 0.91Tg, whereas it decreases by 75% and 76% as Tf increases to 0.99Tg and 1.05Tg, respectively. BMGs with Tf = 0.91Tg are observed to be the most wear resistant in both the loading conditions, making it a viable candidate for biomedical applications, machine tools, and engine parts where wear resistance of the component during service is a dominating factor.

Temperature- and Defect-Induced Uniaxial Tensile Mechanical Behaviors and the Fracture Mechanism of Two-Dimensional Silicon Germanide.

Recently, monolayer silicon germanide (SiGe), a newly explored buckled honeycomb configuration of silicon and germanium, is predicted to be a promising nanomaterial for next-generation nanoelectromechanical systems (NEMS) due to its intriguing electronic, optical, and piezoelectric properties. In the NEMS applications, the structure is subjected to uniaxial tensile mechanical loading, and the investigation of the mechanical behaviors is of fundamental importance to ensure structural stability. Here, we systematically explored the uniaxial tensile mechanical properties of 2D-SiGe through molecular dynamics simulations. The effects of temperature ranges from 300 to 1000 K and vacancy defects, for instance, point and bi vacancy, for both armchair and zigzag orientations of 2D-SiGe were investigated. In addition, the influence of system areas and strain rates on the stress–strain performance of 2D-SiGe has also been studied. With the increase in temperature and vacancy concentration, the mechanical properties of 2D-SiGe show decreasing behavior for both orientations and the armchair chirality shows superior mechanical strength to the zigzag direction due to its bonding characteristics. A phase transformation-induced second linearly elastic region was observed at large deformation strain, leading to an anomalous stress–strain behavior in the zigzag direction. At 300 K temperature, we obtained a fracture stress of ∼94.83 GPa and an elastic modulus of ∼388.7 GPa along the armchair direction, which are about ∼3.17 and ∼2.83% higher than the zigzag-oriented fracture strength and elastic modulus. Moreover, because of the strong regularity interruption effect, the point vacancy shows the largest decrease in fracture strength, elastic modulus, and fracture strain compared to the bi vacancy defects for both armchair and zigzag orientations. Area and strain rate investigations reveal that 2D-SiGe is less susceptible to the system area and strain rate. These findings provide a deep insight into controlling the tensile mechanical behavior of 2D-SiGe for its applications in next-generation NEMS and nanodevices.