Increase In Tensile Stress Research Articles

Comprehensive understanding of horizontal and vertical crack effects on failure mechanism of lamellar structured thermal barrier coatings

The local spalling induced by the propagation and coalescence of cracks in the ceramic layer is the fundamental reason for the thermal barrier coatings (TBCs) failure. To clarify the effects of horizontal and vertical cracks on the coating failure, an integrated model combining dynamic TGO growth and ceramic sintering is developed. The effects of cracks on the normal and shear stress characteristics are analyzed. The driving force and propagation ability of cracks under different configurations are evaluated. The interaction between horizontal and vertical cracks is explored by analyzing the variation of the crack driving force. The results show that TGO growth causes the ratcheting increase of σ22 tensile stress above the valley, and the σ12 shear stress is on both sides of the peak. Ceramic sintering mainly contributes to the ratcheting increase of σ11 tensile stress. There is minimum strain energy when the horizontal crack extends to the peak. The vertical cracks on the surface of the ceramic layer are easier to propagate through the coating than that of other locations. When the horizontal and vertical cracks simultaneously appear near the valley, they can promote the propagation of each other. The present results can offer theoretical support for the design of an advanced TBC system in the future.

Influences of strain rate, Al concentration and grain heterogeneity on mechanical behavior of CoNiFeAlxCu1-x high-entropy alloys: a molecular dynamics simulation

High-entropy alloys (HEAs) with a heterogeneous grain structure have been revealed to possess excellent combination of strength and toughness. However, the atomic-level deformation mechanisms of the heterogeneous HEAs were not reported yet. In this work, physical models were constructed based on the experimental observation and atomic simulations are performed to investigate the tensile behavior of face centered cubic (FCC) heterogeneous CoNiFeAl x Cu 1-x HEAs at different strain rates (5 × 10 7 –1 × 10 10 s −1 ), Al concentration (x = 0.1, 0.2, 0.3 and 0.4) and degrees of grain heterogeneity. Result analysis reveals the multiple deformation mechanisms including dislocation motion, diffusion from grain interior to grain boundary and stacking faults (SFs) as well as their interaction. The strain rates seriously influence the body centered cubic (BCC) transformation from FCC in the large grains. Besides, with the reduction of Al concentration, the value of stable stacking fault energy (SFE) raises, while the tensile yield stress increases. Finally, increasing the large grain size (D G ) of the heterogeneous grain structure improved the plasticity due to the combination of enhanced FCC to BCC phase transformation and high uniform ductility of large grains. This work provides a micromechanical understanding for designing the excellent mechanical property of HEAs by optimizing material structure parameters of heterogeneous grain structure HEAs.

SH wave propagation in a periodic cement-based piezoelectric layered barrier

The purpose of this study is to investigate SH wave in the periodic cement-based piezoelectric layered barrier to meet the needs of vibration control in complex engineering environments and improve the application of periodic vibration isolation barrier in civil engineering. The governing equation of SH wave in periodic barrier is established based on the periodic theory of phononic crystals. The band structures are calculated by plane wave expansion method, the transmission characteristics are computed by transfer matrix method, and the attenuation effect of the periodic barrier is verified by finite element method. The effects of geometric parameters, material parameters and initial stress on band structures are analyzed in details. The numerical results show that the number of unit cells, initial stress and material parameters of the periodic barrier have significant effects on the band gap. As the lattice constant of the structure increases and the equivalent elastic modulus decreases, the lower boundary and the width of the band gap decrease. With the increase of tensile stresses, whether the lower and upper boundary or the width of the band gap will all increase, while they are decrease with the increase of compressive stresses. This work provides an alternative avenue for the design of periodic layers as wave barriers.

Effect of backside dry etching on the device performance of AlGaN/GaN HEMTs

AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) have significant advantages of high carrier concentration, high electron mobility, and large breakdown voltage, and show promising potential as power devices. Being widely used in semiconductor manufacturing, dry etching process is capable of fabricating microstructures and thinning substrate from backside, which is good for developing flexible devices. Here, we investigate the effect of backside dry etching of Si substrate on the physical and electrical properties of AlGaN/GaN HEMTs. The physical properties were characterized by scanning electron microscope, Raman spectra, and x-ray diffraction (XRD). After the dry etching process, the peak red-shift of GaN E 2 mode indicates an increase of tensile stress, and the XRD rocking curve of GaN film shows to a certain extent decreased dislocation density. Furthermore, the maximum saturation current density and maximum transconductance of the HEMTs are improved by 21.1% and 25.5%, respectively. The approach of backside dry etching for thinning Si substrate would contribute to the optimization of GaN heterojunction-based devices, and also provide inspirations for the development of flexible and robust power devices.

Electronic and magnetic properties of single-layer and double-layer VX 2 (X = Cl, Br) under biaxial stress* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11904312 and 11904313), the Project of Hebei Educational Department, China (Grant Nos. ZD2018015 and QN2018012), and the Natural Science Foundation of Hebei Province, China (Grant No. A2019203507).

First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX 2 (X = Cl, Br) can be tuned from antiferromagnetic (AFM) semiconductors to ferromagnetic (FM) state when biaxial tensile stress is applied. Their ground states are all T phase. The biaxial tensile stress at the phase transition point of the double-layer VX 2 is larger than that of the single-layer VX 2. The direct band gaps can be also manipulated by biaxial tensile stress as they increases with increasing tensile stress to a critical point and then decreases. The Néel temperature (T N) of double-layer VX 2 are higher than that of single-layer. As the stress increases, the T N of all materials tend to increase. The magnetic moment increases with the increase of biaxial tensile stress, and which become insensitive to stress after the phase transition points. Our research provides a method to control the electronic and magnetic properties of VX 2 by stress, and the single-layer and double-layer VX 2 may have potential applications in nano spintronic devices.

Interface engineering of graphene oxide containing phosphorus/nitrogen towards fire safety enhancement for thermoplastic polyurethane

The high flammability and generation of toxic volatiles during combustion are big obstacles for thermoplastic polyurethane (TPU). In this work, a 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivate containing phosphorus and nitrogen was synthesized and then grafted onto the surface of graphene oxide (GO-DOPO) by using a silane agent [(3-glycidyloxypropyl)trimethoxysilane] as the chemical bridge. Then the GO-DOPO was mixed with TPU by melt compounding to improve its flame retardancy. Tensile tests exhibited that the TPU/GO-DOPO nanocomposite maintained high ductility with a slight increase in tensile stress. The cone calorimeter tests exhibited that the incorporation of 2 wt% GO-DOPO into TPU presented a significant reduction in peak heat release rate (35.8%) and peak smoke production rate (50%), respectively, as compared with those of pure TPU. Meanwhile, the peak of CO production rate and the peak of CO2 production rate decreased by 57.1% and 35.9%, respectively. The investigation of the flame retardant mechanism for TPU nanocomposites revealed that the presence of GO-DOPO in TPU contributed to generating the compact, continuous and higher graphitized char layer exerted barrier effect in condensed phase, protecting the underlying TPU matrix. This work provides a feasible functionalization approach of GO to enhance the fire safety of TPU nanocomposites without sacrificing the superior mechanical properties, which facilitates the promising applications of TPU in various fields.

Behaviour of macro-synthetic fibers reinforced concrete: Experimental, numerical and design code investigations

Fiber-reinforced concrete (FRC) is increasingly used in various civil engineering applications. Compared to conventional reinforced concrete (rebars or welded mesh), the FRC has very high ductility in the post-cracking phase and allows more distributed cracks with a smaller opening. The FRC post-cracking behaviour depends on the fiber type (properties of fibers) used and the fiber content. Therefore, the characterization of fiber-reinforced concrete material behaviour under tension is important. In this study, the post-peak behaviour of the FRC using polypropylene macro-synthetic fiber (SikaFiber Force-60 brand) was characterized. According to the European test recommendation (EN 14651, 2005), notched 3‐point bending tests were conducted on 36 prismatic notched beams (dimensions of 600 mm × 150 mm × 150 mm) to identify the stress/crack opening law of FRC. The influence of the fiber dosage was evaluated with six fiber volume fractions of 0.33%, 0.49%, 0.66%, 0.82%, 0.99% and 1.26% corresponding to dosages of 3.0 kg/m3, 4.5 kg/m3, 6.0 kg/m3, 7.5 kg/m3, 9.0 kg/m3 and 11.5 kg/m3 respectively. It was found that the increase of the fiber dosage has no significant influence on the ultimate bending strength, but a substantial increase in the residual tensile flexural stresses was found. A numerical model using the inverse method was also used to reproduce the stress/crack opening behaviour of FRC obtained in the experimental tests. A new approach was proposed to define the post-cracking diagram adapted for the macro-synthetic FRC used. Fib Model Code 2020 approach was also conducted and compared with. The Model Code requirements for FRC’s use in structural applications have also been adapted to the case of macro-synthetic FRC following Hillerborg's concept of fracture energy and a new proposal was made.

Tensile Mechanical Behavior and Spall Response of a Selective Laser Melted 17-4 PH Stainless Steel

The tensile mechanical behavior and spall response of a selective laser melted (SLM) 17-4 precipitation-hardening (PH) stainless steel were studied comprehensively through tensile test, plate impact experiment and microstructure characterization in the present study. The results reveal a steel with significant strain rate dependence on the tensile mechanical behavior and spall response. As the strain rate increases, the tensile yield stress increases, but there is no monotonic variation trend for the peak stress; grain structure remains unchanged first and then becomes fine; high-angle grain boundaries (HAGBs) increase; the martensite phase decreases at first and then increases. There is a close correlation among impact velocity, strain rate, peak stress, Hugoniot elastic limit (HEL) and spall strength. Strain rate, peak stress and HEL increase, while spall strength remains almost constant with the increase of impact velocity. As impact velocity increases, grain structure becomes fine, HAGBs increase and the martensite phase increases. The significant phase transformation is responsible for the tensile mechanical behavior and spall response, and the temperature rise was calculated to analyze its effect on phase transformation. Whether the preferred orientations are along the building direction or tensile direction is dependent on strain rate. Tensile and spallation specimens exhibit the ductile fracture mode and the damage originates from voids. It is interesting that the voids always tend to nucleate at melt pool boundaries. A spall damage evolution model is illustrated to describe the damage process.

Study on a stress-magnetic relationship of DO3 based on first principles

Based on the first principles, in this paper the stress-magnetic relationship model of the Fe3Si (DO3) phase in silicon steel was analyzed, and the band structure and electronic density states were calculated. The experimental results show that the atomic magnetic moment would increases with the increase of tensile stress, and decreases with the increase of compressive stress. The linear compressive strength of the DO3 crystal is stronger than the linear tensile strength, and this phenomenon could be explained by the band structure and electronic density states. In addition, the macro verification experiment is designed. The silicon steel plate is used as the verification experiment sample, the change of silicon steel magnetic properties during the tension and compression process is measured. The experimental results show that the magnetic properties of silicon steel show an increasing trend in the tension process and a decreasing trend in the compression process, which qualitatively proves the correctness of the first principle calculation results. The MFM measurement results confirm that the stress would affect the magnetic domain. The stress-magnetic relationship of DO3 would provide theoretical support for electromagnetic detection and reduction of residual stress in silicon steel.

Experimental and numerical investigation on the fretting fatigue behavior of cold expanded Al-alloy 2024-T3 plates

In this paper, fretting fatigue behavior of the cold expanded plates have been studied both numerically and experimentally. For this purpose, fretting fatigue testing fixture has been designed and fabricated for simulating fretting condition on the holed plates. The test specimens were cut from aluminum alloy 2024-T3 plate and have been cold expanded at two sizes of 1.5% and 4.7% before fretting fatigue tests. Two values of cyclic longitudinal load and normal contact force were applied to the specimens. The results of the experiments revealed that applying high level of cold expansion affects the frictional force on the contact interface. Moreover, cold expansion makes the fretting fatigue phenomenon to be likely to occur at locations away from the hole. The obtained numerical results indicated that tensile residual stress would be generated at areas away from the hole edge by cold expanding the holes. During fatigue loading, the tensile residual stress is superimposed to the tensile fatigue load which intensifies the stress severity and reduces the fretting fatigue life. The intensity of the tensile residual stress increases by increasing the level of cold expansion. As a result, lower fretting fatigue life is expected on higher size cold expanded plates.

Combining TGF-β1 and Mechanical Anchoring to Enhance Collagen Fiber Formation and Alignment in Tissue-Engineered Menisci.

Recapitulating the collagen fiber structure of native menisci is one of the major challenges in the development of tissue-engineered menisci. Native collagen fibers are developed by the complex interplay of biochemical and biomechanical signals. In this study, we optimized glucose and transforming growth factor-β1 (TGF-β1) concentrations in combination with mechanical anchoring to balance contributions of proteoglycan synthesis and contractile behavior in collagen fiber assembly. Glucose had a profound effect on the final dimensions of collagen-based constructs. TGF-β1 influenced construct contraction rate and glycosaminoglycan (GAG) production with two half-maximal effective concentration (EC50) ranges, which are 0.23 to 0.28 and 0.53 to 1.71 ng/mL, respectively. At concentrations less than the EC50, for the GAG production and contraction rate, TGF-β1 treatment resulted in less organized collagen fibers. At concentrations greater than the EC50, TGF-β1 led to dense, disorganized collagen fibers. Between the two EC50 values, collagen fiber diameter and length increased. The effects of TGF-β1 on fiber development were enhanced by mechanical anchoring, leading to peaks in fiber diameter, length, and alignment index. Fiber diameter and length increased from 7.9 ± 1.4 and 148.7 ± 16.4 to 17.5 ± 2.1 and 262.0 ± 13.0 μm, respectively. The alignment index reached 1.31, comparable to that of native tissue, 1.40. These enhancements in fiber architecture resulted in significant increases in tensile modulus and ultimate tensile stress (UTS) by 1.6- and 1.4-fold. Correlation analysis showed that tensile modulus and UTS strongly correlated with collagen fiber length, diameter, and alignment, while compressive modulus correlated with GAG content. These outcomes highlight the need for optimization of both biochemical and biomechanical cues in the culture environment for enhancing fiber development within tissue-engineered constructs.

Co2YZ (Y= Cr, Nb, Ta, V and Z= Al, Ga) Heusler alloys under the effect of pressure and strain

Full Heuslers alloys are a fascinating class of materials leading to many technological applications. These have been studied widely under ambient conditions. However, less attention been paid to study them under the effect of compression and strain. Here in this work Co2YZ (Y= Cr, Nb, Ta, V and Z = Al, Ga) Heusler alloys have been studied comprehensively under pressure variations. Calculated lattice constants are in reasonable agreement with the available data. It is determined that lattice constant deceases with the increase in tensile stress and increases by increasing pressure in reverse direction. Band profiles reveals the half metallic nature of the studied compounds. The bond length decreases while band gap increases in compressive strain. The compounds are found to be reflective in visible region, as characteristics of the metals. The magnetic moments reveal the half-mettalic ferromagnetic nature of the compounds.

Changes of mechanical properties of protective polyethylene films applied in transport bottles and containers for liquid media after exposure to selected liquid media

Polymers have effectual applications in many industrial branches. Especially in the automotive and food industry polymers are frequently applied. Thermoplastics can be used also including the transport of specific liquids. This study deals with an investigation of the mechanical properties of polyethylene film made of low-density polyethylene (LD-PE), which has a low density and high degree of chain branching. LD-PE film was exposed to chemical influences of selected liquid media (Savo disinfection, Savo Saponate, and Coca-Cola) for three months. Those media have a different value of potencia hydrogeni (pH). Degradation of mechanical properties of LD-PE film by selected media was monitored. Using tensile test important parameters: σB, εB and E for polymers were evaluated. After exposure, those values of parameters increased in comparison with values of original LD-PE film in the longitudinal direction. The increase of tensile stress at break (σB) in comparison with original LD-PE film was as following: for Savo disinfection - increase of 83.43 %, Savo Saponate - increase of 68.60 %, and Coca-Cola - increase of 67.63 %. In the transversal direction, the exposure in media has a different impact on investigated parameters. The increase of tensile stress at break (σB) in comparison with the original LD-PE film was as following: for Savo disinfection - increase of 14.06 %, and Savo Saponate - increase of 33.02 %. For Coca-Cola was recorded a reduction of 36.90 % in comparison with original LD-PE film. Savo disinfection and Savo Saponate have the most suitable influences on the mechanical properties of LD-PE film for the transport of those liquids after three months.

Реакционная экструзия нанокомпозитов на основе этиленовых сополимеров и минеральных наполнителей

The paper presents the results of a study of the influence of the temperature regime of reaction extrusion on the main physicomechanical characteristics of nanocomposites based on copolymers of ethylene with butylene and ethylene with hexene and natural minerals - clinoptilolite and vesuvian. The optimal temperature regime of extrusion of nanocomposites based on copolymers of ethylene and natural minerals was established. At a maximum extrusion temperature of 230 °C in the dosing zone, counterflow increases, which contributes to an increase in the residence time of the nanocomposite melt and, accordingly, to a decrease in extruder productivity. The possibility of mechanochemical synthesis of nanocomposites vulcanized with dicumyl peroxide on an extruder using monotreme technology has been proved. It was found that as a result of vulcanization of nanocomposites based on ethylene copolymers, a significant increase in the ultimate tensile stress and a decrease in the elongation at break are observed. With an increase in the maximum extrusion temperature in the extruder head to 230 °C, it does not lead to the appearance of a counterflow. At the same time, it was shown that with an increase in the temperature regime of extrusion of vulcanized nanocomposites over 200 °C, the time spent by the melt in the material cylinder practically does not undergo changes. A fundamental feature of the effect of chemical crosslinking with dicumyl peroxide on the processing process and the regularity of changes in the properties of nanocomposites are established. The probable mechanism of the vulcanization process in the melt of the polymer matrix and its selective effect on the reaction extrusion process, structural features and properties of nanocomposites are presented.

Effects of tensile stress on oxidation behavior of a Ferrite-martensite steel in supercritical water

ABSTRACT The oxidation behaviour of ferritic-martensitic steel P92 with different tensile stress conditions has been investigated in supercritical water at 600°C for up to 1000 h. The results indicated that the oxidation rate increased with an increase in tensile stress. The thickness of the oxide scale with atensile stress of 30 MPa is about 1.22 times greater to that at without stress, while the ratio of the thickness of oxide scale to that observed at 60 MPa is 1.73 times greater to that at 0 MPa. The thickness ratio of the outer and inner layer increased with the increasing tensile stress. Crack develops in all cases and is affected by the tensile loading. Furthermore, the thickness of the diffusion layer increased with an increase in tensile stress. The related mechanism has been discussed in this paper.

Evaluation of material degradation using phased array ultrasonic technique with full matrix capture

This paper presents a new approach based on phased array ultrasonic technique (PAUT) with full matrix capture (FMC) to effectively measure acoustic properties such as ultrasonic wave velocity and attenuation coefficient and to evaluate material degradation. This paper also proposes the use of PAUT with FMC, to simultaneously generate and detect ultrasonic waves such as longitudinal, shear, and Rayleigh waves in the material. A theoretical model is developed to derive the analytical solution of ultrasonic waves induced in the material by an ultrasonic phased array probe. Based on the theoretical prediction, experiments are carried out on AISI 316L stainless steel specimen of 3 mm thickness, and a 2D finite element model is built to verify the generation and detection of these waves. Furthermore, measurements of acoustic properties are carried out on the specimen using the proposed approach as well as the conventional ultrasonic testing (CUT) technique and their sensitivities are compared. The measurements of time-of-flight and back-wall echo amplitude are more accurate with the proposed approach than the CUT technique, which makes the former technique better than the latter for the evaluation of material degradation. Finally, experiments are performed on AISI 316L specimen degraded with different levels of tensile stress to verify the capability of PAUT with FMC. The results show that the velocities and attenuation coefficient increase with an increase in tensile stress until material fracture. This phenomenon is interpreted as resulting from microstructural changes such as dislocations during material degradation. From the experimental results, it is proposed that PAUT with FMC can potentially be used to evaluate early-stage materials degradation.

Effect of tensile stress on metal magnetic memory signals during on-line measurement in ferromagnetic steel

Metal magnetic memory testing (MMMT) is a promising nondestructive technique for early damage evaluation of ferromagnetic materials due to its high sensitivity to the stress state. An experimental investigation of the effect of axial applied stress on MMMT signals, both the normal component Bz and the tangential component Bx, under on-line loaded and unloaded measurement condition has been carried out during the whole tensile test in 0.45%C steel. In the elastic deformation stage, Bz signal kept rotating counterclockwise while Bx signal kept moving upward under on-line measurement both when loaded and unloaded, but the MMMT signals measured unloaded tended to resume the initial state compared those measured loaded. In the plastic deformation stage, Bz signal rotated clockwise while Bx signal moved downward under on-line loaded measurement with the increase of tensile stress, while the MMMT signals measured unloaded reversed compared those measured loaded. The results of the present work indicate that MMMT is a feasible solution for stress state on-line monitoring of ferromagnetic components.

The effect of graphene oxide on the mechanical, thermal characteristics and flame retardancy of polyurethane

ABSTRACT Presence of GO in PU muffles discharge of heat, smoke and CO and CO2 into atmosphere. The maximum improvement in mechanical properties achieved by including 2.0 wt-% of GO in PU framework, indicating an increase in tensile stress and elongation at break of 155.1% and 27.7% compared to PU. Primary temperature of thermal degradation of PU/GO nanocomposite increased by 36.5°C with 3.0 wt-% of GO. Charred yield of PU/GO composites augmented due to GOs’ physical hindrance which limits diffusion of flammable gas. Muffling effect of GO in danger of flame and smoke exposure of polymer composites decreased by introduction of 3.0 wt-% of GO. Uniform distribution of GOs within PU matrix formed a strong, twisted route and sticky char in PU/GO composites and delayed thermal deterioration process. Thereby, this work introduces an important method for improving thermal stability and fire protection of PU providing an effective application for coating industry.

The ammonite septum is not an adaptation to deep water: re-evaluating a centuries-old idea.

The shells of ammonoid cephalopods are among the most recognizable fossils, whose fractally folded, internal walls (septa) have inspired many hypotheses on their adaptive value. The enduring explanation for their iterative evolution is that they strengthen the shell against pressure at increasing water depths. The fossil record does not definitively support this idea and much of the theoretical mechanical work behind it has suffered from inaccurate testing geometries and conflicting results. By using a different set of mathematical methods compared with previous studies, I generate a system of finite-element models that explore how different parameters affect the shell's response to water pressure. Increasing the number of initial folds of the septa ultimately has little to no effect on the resulting stress in the shell wall or the septum itself. The introduction of higher-order folds does reduce the tensile stress in the shell wall; however, this is coupled with a higher rate of increase of tensile stress in the septum itself. These results reveal that the increase in complexity should not be expected to have a significant effect on the shell's strength and suggests that the evolution of ammonitic septa does not reflect a persistent trend towards deeper-water habitats.

Cathodoluminescence Spectroscopic Stress Analysis for Silicon Oxide Film and Its Damage Evaluation.

We describe the stress analysis of silicon oxide (SiO2) thin film using cathodoluminescence (CL) spectroscopy and discuss its availability in this paper. To directly measure the CL spectra of the film under uniaxial tensile stresses, specially developed uniaxial tensile test equipment is used in a scanning electron microscope (SEM) equipped with a CL system. As tensile stress increases, the peak position and intensity proportionally increase. This indicates that CL spectroscopy is available as a stress measurement tool for SiO2 film. However, the electron beam (EB) irradiation time influences the intensity and full width at half maximum (FWHM), which implies that some damage originating from EB irradiation accumulates in the film. The analyses using Raman spectroscopy and transmission electron microscopy (TEM) demonstrate that EB irradiation for stress measurement with CL induces the formation of silicon (Si) nanocrystals into SiO2 film, indicating that CL stress analysis of the film is not nondestructive, but destructive inspection.