Elastic Tensile Stress Research Articles

Influence of the applied elastic tensile and compressive stress on the hysteresis curves of Fe-3%Si non-oriented steel

The influence of applied elastic tensile stress up to 120MPa and compressive stress up to 35MPa on the magnetic hysteresis curves of non-oriented Fe-3%Si steel is studied. In two tensile stress ranges the hysteresis loop changed monotonously – low stress below 10MPa facilitated the magnetization process, while above 15MPa tension deteriorated magnetic properties. This difference in behavior corresponds to two different mechanisms – 1) favoring by tensile stress magnetic easy axes closest to the filed direction and 2) appearance of large demagnetizing fields at grain boundaries and the sample surface. Compression continuously deteriorated magnetic properties and made the hysteresis loop constricted above a few MPa. The effective field as a product of two functions – of the magnetization and of the stress gave excellent agreement with experimental curves for both tensile stress ranges and for compression. The sensitivity of magnetization to compression was approximately five times larger than to tension. The complex hysteresis loop behavior under tension and compression was explained on the basis of our previous results on stressed grain-oriented steel of the same composition, in which the magnetic domains were also studied.

Preparation and Characterization of Cassava Starch/Peel Composite Film

This work is focused on the use of cassava peel as a natural fiber for thermoplastic starch (TPS) based on the cassava starch. Starch was extracted from the cassava tuber and the peel was used as a film fiber in order to obtain fully biodegradable composites. The composite films were prepared using casting technique. The addition of peel results in an increase in the thickness, water content, and water absorption of the films while decreasing the density and water solubility. Moreover, no significant effect was noticed on the thermal properties of the composite films. Scanning electron microscopy showed that the films containing a small size of peel had a better compact structure and a homogeneous surface without pores. The addition of 6% peel increased the elastic modulus and tensile stress up to 449.74 and 9.62 MPa, respectively, this being the most efficient reinforcing agent. Also the temperature variation of the dynamic‐mechanical parameters of cassava starch/peel composites was investigated using DMA test. It was observed that the incorporation of peel increased the tensile strength and modulus. In conclusion, of all‐plant composites can be prepared using cassava as both the matrix and the reinforcement, adding value to the residue of starch extraction. Based on its excellent properties, cassava starch/peel composite films are suitable for various purposes such as packaging, automotive and agro‐industrial application, at lower cost. POLYM. COMPOS., 39:1704–1715, 2018. © 2016 Society of Plastics Engineers

(Invited) Effect of Mechanical Stress on the Passivity of Steel

The influence of the elastic and plastic tensile stress on the electrochemical properties of mild carbon steel and austenitic stainless steel was studied using Scanning Kelvin Probe (SKP) and Localized Electrochemical Impedance Spectroscopy (LEIS) techniques. These two methods give complementary information on the surface of the stressed electrode. SKP characterizes the thermodynamic (surface potential) and LEIS is informative on the conditions of the passive oxide (capacitance of the film). The Volta potential and the admittance were mapped across an area with stress concentrator (notch) “in situ” under load. It was found that the elastic deformation slightly influences both the potential and the capacitance. The plastic strain decreases the potential measured in the lab air for both steels by 150 to 300 mV. LEIS shows an increase of the capacitance measured in borax electrolyte above the yielded surface in the notch relatively to the surrounding surface. Thus, the change inf the potential is reciprocal to the change of the capacitance. After straining, in load free conditions, stainless steel saved low potentials in the area containing residual stresses. It corresponds to LEIS data that shows an increased capacitance. In opposite, unloading of strained mild steel redistributes the surface potential. Mainly the surface increased the potential showing the passivation. However, low potential locations related to residual stress were also found by SKP. Mapping of the capacitance by LEIS also shows partial passivation of the steel. Thus, locations with concentrated stress, which are prone to localized corrosion can be recognized using local electrochemical techniques.After experiments, the strained surfaces were characterized by XPS and AFM. The effect of the plastic tensile strain was explained by the formation and emerging of dislocations and dislocations pile-ups. The dislocations rupture the oxide film making it more defective that weaken the steel passivity. On the other hand, the formation of the stepped surfaces decreased the potential that decreased the activation energy of anodic dissolution of the steel.

Electrochemical behavior of tensile stressed P110 steel in CO2 environment

An investigation on the electrochemical behavior of P110 steel loaded with different tensile stresses in CO2 corrosion environment was conducted using electrochemical measurement and surface analysis. The results show that both elastic tensile stress and plastic tensile stress enhance the surface thermodynamic activity of P110 steel. Tensile stress accelerates the cathodic reaction more obviously than the anodic reaction. The corresponding corrosion mechanisms to elastic tensile stressed and plastic tensile stressed P110 steels are separately proposed by “local melting zone” and slip planes according to the different features of corrosion product nucleation along with the electrochemical data.

Magnetoimpedance of cobalt-based amorphous ribbons/polymer composites

The combined influence of the temperature, the elastic tensile stress and the external magnetic field on the total impedance and impedance components were studied for rapidly quenched amorphous Co75Fe5Si4B16 ribbons. Both as-cast amorphous ribbons and Co75Fe5Si4B16/polymer amorphous ribbon based composites were considered. Following polymer coverings were studied: modified rubber solution in o-xylene, solution of butyl methacrylate and methacrylic acid copolymer in isopropanol and solution of polymethylphenylsiloxane resin in toluene. All selected composites showed very good adhesion of the coverings and allowed to provide temperature measurements from 163K up to 383K under the applied deforming tensile force up to 30N. The dependence of the modulus of the impedance and its components on the external magnetic field was influenced by the elastic tensile stresses and was affected by the temperature of the samples. It was shown that maximal sensitivity of the impedance and its components to the external magnetic field was observed at minimal temperature and maximal deforming force depended on the frequency of an alternating current.

Evolution of precipitate microstructure during stress aging of an Al–Zn–Mg–Cu alloy

The effect of elastic tensile stress on the microstructure of 7075 aluminum alloy aged at 433K for 1h has been investigated in this paper. It was found that double peaks occur in hardness after various aging treatments. The peak microhardness of the stress-aged specimens reaches 178HV, much higher than that of the conventional aged sample. The stress aging exhibits a diverse microstructure: the GPII zones and various sizes of η precipitates are just identified in the stress-free aged sample; the main hardening η′ precipitates, with the highest and lowest degree of dispersion, are formed after 25 and 50MPa stress-aged respectively; a finer aging precipitate size distribution, a larger grain boundary precipitate size and spacing and a wider precipitate free zone are represented in the stress-aged specimens. After the 25MPa stress aging treatment, a preferential growth orientation of the larger-size MgZn2 phase is observed in 7075 aluminum alloy. During aging, the external stress accelerates the growing of the larger-size MgZn2 phase, promotes the formation of the η′ precipitate and inhibits the formation of the η phase. Our study provides a new process to improve the comprehensive properties of Al–Zn–Mg–Cu alloys.

Mechanical properties of the cement of the stalked barnacleDosima fascicularis(Cirripedia, Crustacea)

The stalked barnacle Dosima fascicularis secretes foam-like cement, the amount of which usually exceeds that produced by other barnacles. When Dosima settles on small objects, this adhesive is additionally used as a float which gives buoyancy to the animal. The dual use of the cement by D. fascicularis requires mechanical properties different from those of other barnacle species. In the float, two regions with different morphological structure and mechanical properties can be distinguished. The outer compact zone with small gas-filled bubbles (cells) is harder than the interior one and forms a protective rind presumably against mechanical damage. The inner region with large, gas-filled cells is soft. This study demonstrates that D. fascicularis cement is soft and visco-elastic. We show that the values of the elastic modulus, hardness and tensile stress are considerably lower than in the rigid cement of other barnacles.

Structure-Property Relationship of Layered Metal Oxide Phosphonate/Chitosan Nanohybrids for Transducer in Biosensing Device

A candid approach to analyze the performance characteristics of phenyl phosphonate-functionalized zirconium oxide and pure zirconium oxide (ZrO2) fillers reinforced chitosan nanocomposites and their suitability as a potential biomaterial for the development of transducer surface in biosensing device has been investigated in this communication. Functionalization of ZrO2 has been carried out using sulfophenylphosphonate which was confirmed using Fourier transform infrared spectrographs. The electrostatic intercalation of chitosan with filler particles was monitored using electrochemical impedance analyzer which exhibits lowest bulk resistance which is highly effective for ionic switching. Incorporation of zirconium sulfophenylphosphonate (ZrSP) the ionic conductivity of the chitosan film attained a value of 1.2 × 10−6 S/cm as compared to the unmodified one which is a prefeasibility work for the fabrication of biosensing platform. Variation in performance characteristics has been evaluated through morphological and thermal characterization. TGA and DSC analysis reveal that the thermal stability and decomposition temperature of the nanocomposites were improved by the addition of reinforcing filler particles. XRD and SEM and TEM results support the above assumption. The continuous alignment of the proton transfer channels of the nanocomposites was thoroughly investigated by AFM analysis which revealed phase morphology for improved enzyme entrapment. Further, surface functionalized nanofillers result considerable increment of mechanical properties in terms of elastic modulus and tensile stress.

An Investigation of the Nanomechanical Properties of 0.5Ba(Ti0.8Zr0.2)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films

For practical application, the functional piezoelectric film in microelectromechanical systems should meet the requirement of physical properties, as well as the mechanical properties. In this article, 0.5Ba(Ti0.8Zr0.2)O3–0.5(Ba0.7Ca0.3)TiO3 (0.5BZT–0.5BCT) thin films with varied properties were prepared on (100) Si substrates via a sol–gel technique at different annealing temperatures. The effects of the annealing temperature on the morphology, piezoelectricity, hardness, and elastic modulus were studied. Particular attention was paid to the surface frictional behavior of films, and the changes in the friction force can be radically explained in terms of differences in the hardness/elastic modulus ratio and the residual stress of films. And, it reveals that the higher ratio of hardness to elastic modulus and tensile residual stress can contribute to a lower friction force for 0.5BZT–0.5BCT film during sling friction.

Percolation of the interacting elastic stress fields of aligned cracks as an alternative explanation of critical crack densities

Abstract The concept that the lithosphere is in a general critical, or near-critical, mechanical state has previously assumed spatial intersection of fractures at the critical point. This paper provides an initial basis for an alternative mechanism in which elastic interactions between aligned, open, spatially separated (micro-)cracks in rock can, by themselves, lead to a continuous phase change at a critical threshold of crack density lower than that required for crack coalescence. The existence of a critical density of aligned cracks is first demonstrated on a regular 2D hexagonal grid when subjected to a central stress perturbation; at this critical density the elastic tensile stress interactions have a long-range effect. From the results of those calculations an approximation of the tensile stress field around a crack in 3D is provided. The percolation behaviour of such 3D bodies is discussed and a critical crack density in 3D for elastic interaction of 0.035 is deduced. This falls within the range of crack densities (0.015–0.045) interpreted from observations of shear-wave splitting in many different rocks. The possibility that critical crack interactions can be mostly elastic provides one explanation of the long-range nature of correlations in flowrate fluctuations in oilfields without large-scale seismicity.

The influence of hydrostatic stress states on the hydrogen solubility in martensitic steels

A specific dependency of elastic tensile stress on the hydrogen solubility is identified for martensitic steels. The lattice hydrogen concentration under applied stress may be underestimated when predicted by a classical law which associates hydrostatic stress with the partial molar volume of hydrogen. We have explored the impact of elastic distortions on hydrogen solubility from two different sources: internal stresses arising from heterogeneous microstructures and elastic fields around vacancy clusters. Only the latter seems to be in reasonable agreement with our results.

Performance of Precipitates in the Stress Aging Treatment of 7075 Al Alloy

The effect of elastic stress on the precipitation process of 7075 Al alloy aged at 438 K for 1 hour has been investigated in this paper. The mechanical properties have been measured by hardness testing and scanning electron microscopy (SEM) and the microstructures have been characterized by optical microscopy (OM), together with transmission electron microscopy (TEM). Results indicate that the microhardness can reach 180 HV after a 25 MPa elastic tensile stress aging treatment, much higher than the stress-free ones'. The fracture is more brittle and the formation of the precipitates is promoted in the case of the stress-aged specimen. Our study provides a new process to bring down the energy consumption.

Influence of elastic tensile stress on aging process in an Al–Zn–Mg–Cu alloy

The effect of elastic tensile stress on the microstructure of 7075 Al alloy aged at 393–453K for 1h has been investigated in this paper. It was found that during the low temperature aging, the external stress lessens the size of the GPI zones. GPII zones are just identified in the stress-free aged condition. A new edge-on η′ platelet is observed in the stress-aged specimen. During the high temperature aging, the external stress promotes the formation of MgZn2 precipitates without changing the type of it. The peak microhardness value of the stress-aged specimens reaches 180HV. The aging period of this alloy is shortened using the stress aging treatment.

Anisotropic hydrogels fabricated with directional freezing and radiation-induced polymerization and crosslinking method

Biological gels are generally anisotropic in both structures and mechanical properties, but conventional synthetic hydrogels are generally isotropic. We developed a directional freezing and radiation-induced polymerization and crosslinking (DFRPC) method to fabricate anisotropic hydrogels starting from monomers. The obtained poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels show significant anisotropy in both microstructures and mechanical properties. The hydrogels exhibit an aligned porous structure along the freezing direction and an irregular porous structure in the vertical direction. Their elastic modulus and tensile stress in the parallel direction are significantly higher than those in the vertical direction, and the difference between the two directions decreases as the increase of HEMA concentration. This novel methodology offers a promising way to fabricate a wide variety of anisotropic hydrogels, and the anisotropic hydrogels may find practical applications in biomedical fields.

Thermo-mechanical properties of high density polyethylene – fumed silica nanocomposites: effect of filler surface area and treatment

High density polyethylene was melt compounded with various untreated (hydrophilic) or surface treated (hydrophobic) fumed silica nanoparticles, having different surface areas. The thermo-mechanical properties of the resulting nanocomposites have been thoroughly investigated. Field emission scanning electron microscopy revealed that nanofiller aggregation was more pronounced as the silica surface area increased, while nanofiller dispersion improved with a proper filler functionalization. The homogeneous distribution of fumed silica aggregates at low filler content allowed us to reach remarkable improvements of thermal stability, evidenced by an increase of the degradation temperature and a decrease of the mass loss rate with respect to neat matrix, especially when surface treated nanoparticles were utilized. Interestingly, the stabilizing effect produced by fumed silica nanoparticles was accompanied by noticeable enhancements of the ultimate tensile mechanical properties, both under quasi-static and impact conditions. Concurrently, a progressive enhancement of both elastic modulus and tensile stress at yield with the filler amount, was observed.

Study on carvacrol and cinnamaldehyde polymeric films: mechanical properties, release kinetics and antibacterial and antibiofilm activities

Polyethylene-co-vinylacetate (EVA) films with different concentrations (3.5 wt% and 7 wt%) of essential oil constituents, carvacrol or cinnamaldehyde, were prepared and characterized by mechanical, antibacterial and antibiofilm properties. The incorporation of the compounds into copolymer films affected their elastic modulus, tensile stress and elongation at break. Carvacrol and cinnamaldehyde act as plasticizers which reduce the intermolecular forces of polymer chains, thus improving the flexibility and extensibility of the film. The analysis of the surface characteristics demonstrated that essential oil constituents lowered the contact angle values without causing any remarkable variation of the surface roughness. The films allowed progressive diffusion of the bioactive molecules and the kinetic of release was correlated with the damaging effect on bacterial growth. The kill curves proved that the film with essential oil constituents (7 wt%) had a significant bactericidal effect (reduction of 4 and 2 log CFU) against Staphylococcus aureus and Escherichia coli and a bacteriostatic effect against Staphylococcus epidermidis and Listeria monocytogenes (reduction of about 1 log CFU). With regard to biofilm formation the biomass formed on polymeric films surface was significantly reduced if compared with the pure copolymer control. The results were confirmed by fluorescence microscopy images by Live/dead staining. The reduction in the surface tension coupled to an inherent bactericidal property of carvacrol and cinnamaldehyde could in turn affect the initial attachment phase of bacteria and compromise the normal biofilm development.

An experimental investigation of corrosion of X100 pipeline steel under uniaxial elastic stress in a near-neutral pH solution

In this work, the effect of uniaxial elastic stress on corrosion of X100 pipeline steel in a near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS), corrosion potential and electrochemical impedance measurements, surface analysis techniques as well as finite element analysis. No effect of the static elastic stress on electrochemical corrosion potential of the steel is detected. The critical failure strain of corrosion scale formed on the steel surface is calculated to be 0.00357–0.00417, which is higher than the maximum strain of 0.0029 generated on the specimen. Thus, corrosion scale does not fracture during loading. No difference in the steady-state corrosion potential could be detected upon application of an elastic tensile or compressive stress. If the scale is pre-formed on the steel surface, the applied dynamic elastic load would “weaken” the scale by expanding its pores, and thus, increase the steel corrosion. While a dynamic tensile stress enhances the steel corrosion, the dynamic compressive stress would inhibit corrosion of the steel. This work provides important recommendations for pipeline safety design, where the corrosion enhancement due to the dynamic elastic stress should be considered.

Modeling and stress–strain characteristics of the mechanical properties of carbon‐nanotube‐reinforced poly(vinyl acetate) nanocomposites

AbstractPolymer/carbon nanotube (CNT) composites are one of the most perspective advanced materials developed in recent years. The properties of CNT‐reinforced polymer composites, however, strongly depend on structural aspects of the nanostructured filler and on its dispersion quality in a polymer matrix. Consequently, this research was devoted to the investigation of multiwalled‐CNT‐modified poly(vinyl acetate) (PVAc) composites with respect to the mechanical property dependence on some structural characteristics of CNTs. PVAc/CNT nanocomposites were obtained with a solution casting technique. The amount of CNTs was changed from 0.01 up to 2 wt %. The stress–strain characteristics of PVAc/CNT nanocomposites clearly revealed remarkable reinforcing effects of the CNT additions already at 0.01 wt %. At this CNT concentration, the elastic modulus (E) and tensile yield stress increased by 12.5 and 60%, respectively. Special attention was paid to the change of E with respect to some structural characteristics of CNTs. A corresponding mathematical model for the prediction of the elastic properties of CNT polymer nanocomposites is proposed, showing that elastic constants of the nanocomposites largely depend on the agglomeration of CNTs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Biodegradable polyurethanes: Comparative study of electrospun scaffolds and films

AbstractThe development of elastomeric, bioresorbable, and biocompatible segmented polyurethanes (SPUs) for use in tissue‐engineering applications has attracted considerable interest in recent years. In this work, nonporous films and microfiber/nanofiber scaffolds, which were prepared from two different poly(ϵ‐caprolactone)‐based SPUs previously synthesized from 1,6‐hexamethylene diisocyanate and novel chain extenders containing urea groups or an aromatic amino acid derivative, were studied. Their thermal properties were influenced by both the different chemical structures of the hard segments and the processing conditions. The mechanical properties of the scaffolds (the elastic modulus, ultimate strain, and tensile stress) were adequate for engineered soft‐tissue constructs (e.g., myocardial tissue). The film samples displayed a low swelling degree (<2 wt %) in a phosphate‐buffered solution at 37°C. The introduction of the amino acid derivative chain extender with hydrolyzable ester bonds contributed to greater degradation. The fibrous scaffolds exhibited higher hydrolytic stability than the films after short assay times because of their more crystalline structures and higher degrees of association by hydrogen bonding, but they also experienced higher mass losses under accelerated conditions (70°C). This suggested that the degradation rate was not constant but depended on the degradation time and the processing technique. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Modification of the structural lattice parameters and electron spectra of n-GaAs films on sapphire on irradiation with reactor neutrons

Changes in the structural parameters of epitaxial GaN films on sapphire (n-GaN/Al2O3(0001)) induced by irradiation with reactor neutrons with integrated fluences up to 7.25 × 1019 fn cm−2 (φfn/φtn ≈ 1) and subsequent isochronal annealing at temperatures up to 1000°C are studied. Measurements of the lattice parameters a and c of the irradiated n-GaN films show that the parameter c increases by 0.38% and the parameter a remains almost unchanged. From theoretical estimations, it follows that, in the irradiated n-GaN film, the elastic tensile stress along the c axis is as high as ∼1.5 GPa, whereas the compression stress in the basal plane of the unit cell is about −0.5 GPa. The tension of the irradiated GaN film along the hexagonal axis induces a decrease in the band gap Eg by 37 meV and a lowering of the charge neutrality level by 22 meV with respect to the corresponding parameters in the initial GaN film on sapphire. The parameter c changed by irradiation with reactor neutrons by Δc can be recovered by annealing in the temperature range 100–1000°C, with the basic stage of annealing at about 400°C.