Equivalent Tensile Stress Research Articles

Pulsed laser cleaning of C contamination on a glass insulator surface.

When a pulsed laser cleans a glass insulator, the laser power, scanning speed, and repetition frequency affect the laser-cleaning effect. Herein, we considered glass insulators and their surface contaminations as objects, established a finite element model, analyzed the influence of these parameters on the temperature and stress fields, and explored the optimal cleaning parameters for glass insulator surface contamination. In addition, a laser test platform was constructed to verify the cleaning effect. The results indicated that the difference in the cleaning effect was negligible for lasers at repetition frequencies of 10-75kHz. When the power increased, the scanning speed decreased and the temperature of the fouled layer increased. When the power was 60-70W and the scanning speed was 240mm/s, the equivalent tensile stress did not exceed the tensile strength of the insulator. The ablation reaction can remove the fouling part, and the tensile stress can overcome the adhesion force generated between the dirt and glass insulator to achieve effective cleaning. Experiments confirmed that the surface dirt removal rate of glass insulators can be approximately 99% at 60-70W (laser power) and 240mm/s (scanning speed).

Influence of self-healing property of Ultra-High Performance Concrete under aggressive environment

This paper investigates the evolution of self-healing properties of ultra-high performance concrete exposed to aggressive environments. Double edge wedge splitting UHPC specimens with 0.8% crystalline admixture and 1.5% steel fibre by volume have been first pre-cracked up to a average 0.30 mm crack opening displacement (COD) obtained by two linear variable differential transformers attached to both sides of the sample surface. Then, the pre-cracked samples have been exposed to three different environments: tap water, salt water (a NaCl aqueous solution at 3.3% concentration) and geothermal water obtained from a geothermal power plant. After one month exposure, samples were carried out re-crack to know the self-healing properties. The results from ultrasonic pulse velocity tests (UPV) reveal that the samples exposed to tap water exhibit the highest rate of recovery along the exposure time, while those exposed to geothermal water show the lowest. The calculated indexes of cracking self-healing (ICS) show a 73.8% closure in tap water, 58.4% in salt water 43.9% in geothermal water. Additionally, the index of damage recovery, evaluated from UPV frequencies as well as from the stress vs. COD curves of pre-cracking and post-healing re-cracking tests on specimens, and the equivalent tensile stress also indicate a higher level of healing capable of inducing a significant recovery of mechanical properties.

Movement of flexible filter media under pulse-jet filter cleaning conditions

Reverse pulse-jet cleaned bag filters are widely used for the removal of fine particles from gas streams. Based on the material properties of a single fiber, the entire filter medium is modeled which shows an elastic and apparent viscous property mainly due to the restoration of the weaving pattern. Thus, for the pulse-jet cleaning, the actual transient pressure difference can be linked directly to the deflection of the filter medium. The filter medium displacement is simulated for the filtration and cleaning measures by finite element method (FEM) for a clamped filter test sample and the large-scale bag filter situation, respectively. As expected a high curvature of the filter medium coincides with a high equivalent tensile stress which in turn is a pre-curser for the probability for cake breakage.

Insulation degradation and fracture cracks of mechanical impacted thermal‐ageing oil‐impregnated papers

In order to elucidate mechanical impacts affecting the insulation strength of thermal-ageing oil-impregnated pressboards, we perform mechanical degradation experiments of impacting forces that are represented as the winding-suffered stresses on thermal-ageing oil-paper insulation in transient short-circuit of transformer. Water content, degree of polymerisation (DP), partial discharge inception voltage and AC breakdown field strength are tested and analysed for diverse thermal-ageing levels. An analytical model of mechanical degradation is established by relating dielectric breakdown strength to mechanical impact. Mechanical impacts result in less water content in thermal-aging oil-impregnated pressboards while causing reduction and increment of DP, respectively, in mildly and severely aged oil-impregnated pressboards. Partial discharge inception voltage and dielectric breakdown strength vary significantly with the numbers of impact cycles, showing a maximum value under low-intensity impact and decreasing monotonously under high-intensity impact. High-intensity mechanical impacts will evidently exacerbate the thermal deterioration process of oil-impregnated pressboards, which is primarily attributed to cellulose fibre fractures in pressboard cracks produced by equivalent tensile stress of mechanical impacts. It is acceptable for mildly aged oil-impregnated pressboards to suffer low-intensity mechanical impacts that will alleviate insulation degradation by restraining partial discharge in smaller oil-gaps and prolonging breakdown discharge pathways along impact-caused cracks.

Experimental Study on Dynamic Mechanical Properties and Fracturing Behavior of Granite CSTFBD Specimens in SHPB Tests

Abstract The purpose of this paper is to study the dynamic fracture mechanics characteristics and fracturing behavior of cracked-straight-through flattened Brazilian disk specimens using the Split Hopkinson Pressure bar system. The researchers also used Particle Flow Code 2D for simulating the crack process and achieved consistent outcomes. In this experiment, rock specimens were made from Beijing Fangshan granite. The results of the experiment determined the effects of impact pressures and loading angles on the crack mode and mechanical properties of the specimens. These specimens have attained the stress equilibrium state prior to failure. With greater impact pressure, there will be faster changes in the corresponding equivalent tensile stress, while the peak value remains relatively high under the same loading angle. With different loading angles, the change rate of the equivalent tensile stress remains the same; however, the time required to reach the maximum stress becomes different. For a 30° loading angle, the energy dissipation ratio in accordance with the same impact pressure is lower than compared to that of a 0° loading angle. In this experiment, several cracks have been produced under a different range of impact pressures and loading angles, which can be classified into six types. They include two types of tensile cracks, shear cracks, and tensile-shear cracks. At a 0° loading angle, mode I fracture occurs, and at 15° and 30° loading angles, a mixed-mode I-II fracture occurs on the specimen. Furthermore, triangular fracture zones occur on the two end faces of the specimens under the loading force due to the concentration of local stress during the force process.

Testing the State of Internal Load and Strength of the Facade Mesh Wire Subjected to the Corrugation Process

Abstract The article presents an example of a structural solution of a mesh facade installed on a public building. The types of loads that can affect the structure of such a mesh have been characterized. The course of the wire shaping process used to produce the described mesh was reported. A finite element method (FEM) model was developed to simulate mechanical phenomena occurring during the technological process of crimping stainless-steel wire. Material model parameters have been defined. The developed model was verified in production conditions. Relations between wire-forming loads and tensile limit loads, as well as the distribution of equivalent tensile stress forced by the crimping process and internal stresses after crimping, were determined. The description of the technological process was presented in a form of a graph. The work contains the results of strength tests of wire materials and shaping tools.

TENSILE STRENGTH ANALYSIS OF WELDED JOINTS OF CARBON/PPS COMPOSITES

The growing use of thermoplastic polymers in structural composites are mainly due to their intrinsic properties. The joining of these composite structures plays a crucial role in determining its performance. Welding is considered one of the efficient techniques to join thermoplastic polymer composites. In the present work, the weld strength of the carbon fiber polyphenylene sulphide composite using electrical resistance welding is analyzed using the finite element method. The proposed model is validated for the shear strength of the weld joint and equivalent tensile strength is analyzed using the validated numerical model. The result shows that the proposed-model exhibits a shear stress value of 18.29 Mpa, which is almost closer to the experimental lap shear and the equivalent tensile stress simulated is 47.39 Mpa.

Research on reinforcement at the RCC dam toe of a hydropower station

The dam of a hydropower station is a RCC arch dam. Based on relevant tests and monitoring data, the compression strength of the dam concrete and the temperature of grouting of the transverse joints in some areas do not meet the design standard. To solve those quality problems, this paper evaluated the stress and deformation of the present dam and checked the safety of the dam. In addition, by analyzing the reinforcement body of the dam, the paper assessed the safety of the reinforced dam. According to the calculating results by FEM, the maximum equivalent tensile stress exceeds the allowable tensile stress and the exceeding area mainly locates on the dam heel of upstream face, which extends about 5.20 meters upward from the foundation. The effect of the reinforcement at the dam toe is obvious and the tensile stress after reinforcement meets the standard under the condition that the shear strength between the reinforcement and the dam body is not reduced or is reduced by less than 30%.

Multiaxial fatigue of in-service aluminium longerons for helicopter rotor-blades

Fatigue cracking of longerons manufactured from Al-alloy AVT-1 for helicopter in-service rotor-blades was considered and crack growth period and equivalent of tensile stress for different blade sections were estimated. Complicated case of in-service blades multiaxial cyclically bending-rotating and tension can be considered based on introduced earlier master curve constructed for aluminum alloys in the simple case of uniaxial tension with stress R-ratio near to zero. Calculated equivalent tensile stress was compared for different blade sections and it was shown that in-service blades experienced not principle difference in this value in the crack growth direction by the investigated sections. It is not above the designed equivalent stress level. Crack growth period estimation in longerons based on fatigue striation spacing or meso-beach-marks measurements has shown that monitoring system introduced designer in longerons can be effectively used for in-time crack detecting independently on the failed section when can appeared because of various type of material faults or in-service damages.

Influence of solute partitioning on the microstructure and growth stresses in nanocrystalline Fe(Cr) thin films

This paper addresses how solute segregation and phase separation evolves the intrinsic growth stresses for Fe-4Cr and Fe-16Cr (at.%) nanocrystalline films. Ambient temperature deposition resulted in both alloys exhibiting a near equivalent tensile stress though the average grain sizes were approximately 50 nm and 100 nm respectively. Upon heating during deposition to 523 K and 673 K, the tensile stress was reduced in each film and it eventually became compressive for the higher deposition temperature. Interestingly, the Fe-16Cr film, at the higher heating temperature, diverted from the steady state compressive stress towards a tensile stress after approximately 150 nm of growth. The collective stress evolution of these films is discussed in terms of their phase separation, which can include spinodal deposition, as a function of Cr content and processing temperature. It was found that Cr acted as a grain refiner which appeared to dominate the film microstructure and associated stress response.

Multiaxial fatigue of in-service aluminium longerons for helicopter rotor-blades

Fatigue cracking of longerons manufactured from Al-alloy AVT-1 for helicopter in-service rotorblades was considered and crack growth period and equivalent of tensile stress for different blade sections were estimated. Complicated case of in-service blades multiaxial cyclically bending-rotating and tension can be considered based on introduced earlier master curve constructed for aluminum alloys in the simple case of uniaxial tension with stress R-ratio near to zero. Calculated equivalent tensile stress was compared for different blade sections and it was shown that in-service blades experienced not principle difference in this value in the crack growth direction by the investigated sections. It is not above the designed equivalent stress level. Crack growth period estimation in longerons based on fatigue striation spacing or meso-beach-marks measurements has shown that monitoring system introduced designer in longerons can be effectively used for in-time crack detecting independently on the failed section when can appeared because of various type of material faults or in-service damages.

Analytical solution for transient temperature and thermal stresses within convective multilayer disks with time-dependent internal heat generation, Part I: Methodology

ABSTRACTThis work deals with the exact solution for asymmetric transient problem of heat conduction and accordingly thermal stresses within multilayer hollow or solid disks which lose heat by convection to the surrounding ambient. The combination of the separation of variables method (SVM) and Duhamel's theorem is applied to the heat conduction problem which provides a versatile technique. The temperature distribution is obtained by the SVM which concerns the heat conduction problem with time-independent internal heat generation. Applying Duhamel's theorem on the previous solution, temperature distribution with time-dependent internal heat generation can be achieved. Accordingly, assuming plane stress condition, radial and tangential stresses are obtained which are incorporated into the equivalent tensile stress formulation to calculate von Mises stress. The comprehensive methodology described here can be useful addition for many new emerging fields in which both transient and steady-state temperature distributions and thermal stresses for composite disks are important.

Stress from NaCl crystallisation by carbon dioxide injection in aquifers

The goal of this paper is to identify the mechanical impact of water evaporation and salt crystallisation during supercritical carbon dioxide injection (drying-out process) in aquifer rocks. The precipitation of salt and the resulting crystallisation pressure are inferred from the chemical equilibrium of the carbon dioxide-rich gas phase, the in-pore brine and the crystal. The induced rock strain and equivalent tensile stress are then estimated within the framework of isotropic linear poroelasticity. A one-dimensional numerical simulation is conducted to illustrate the ability of the model to estimate the poromechanical behaviour of a structure submitted to a constant flow of nearly dry supercritical carbon dioxide.

Analytical solution for decelerated mechanochemical corrosion of pressurized elastic–perfectly plastic thick-walled spheres

The paper presents benchmark solutions for the mechanochemical corrosion of an elastic–perfectly plastic thick-walled spherical shell under internal and external pressure with possible inhibition of corrosion being taken into account. The rates of inner and outer corrosion are linear with equivalent tensile stress at the related surface when the stress increases beyond a certain threshold. The time of initial and complete yielding is determined and compared with the same results for a cylindrical tube that were obtained earlier.

Analytical solution for the general mechanochemical corrosion of an ideal elastic–plastic thick-walled tube under pressure

The paper presents analytical solutions for the equal-rate mechanochemical wear of an ideal elastic–plastic thick-walled cylindrical tube subjected to any combination of internal and external pressure. The rates of corrosion at the inner and outer surfaces are supposed to be proportional to the equivalent tensile stress at the surface involved when it exceeds a given threshold. Furthermore, the corrosion rate can decay exponentially with time. The obtained solutions allow to assess the time of the initial yielding at the bore of the tube and the time of fully plastic yielding. Calculations showed that the time of plastic-zone propagation throughout the tube wall can be much greater than the length of the pure elastic stage. The proposed analytical solutions are to be used for design purposes and as benchmark solutions for numerical analysis.

An analysis of microband orientation in a commercial purity aluminium alloy subjected to forward and reverse torsion using Electron Backscatter Diffraction (EBSD)

High-resolution electron backscatter diffraction has been used to study the effects of strain reversal on the evolution of microbands in commercial purity aluminium alloy AA1200. Deformation was carried out using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300 degrees C and strain rate of 1 s(-1) to a total equivalent tensile strain of 0.5. In both cases, microbands were found in the majority of grains examined with many having microband walls with more than one orientation. For the forward/forward condition, the microband clusters were centred around -20 degrees and +45 degrees to the equivalent tensile stress axis, whereas for material subjected to a strain reversal, the clusters were at -65 degrees and -45 degrees . There was no evidence of microbands that were formed in the forward deformation step in the reversed material, which would suggest that a strain of 0.25 is sufficient to dissolve any microstructure history generated by the first step. Furthermore, the microbands within the strain-reversed material had a reduction in misorientation compared with the lineally strained material, suggesting that these microbands only formed at the onset of the second deformation step. This confirms that microband formation is complex and sensitive to strain path; however, it is still unclear to what extent microband formation is dependent on strain path history compared with the instantaneous deformation mode.

Plastic and magnetoplastic deformation of Dy single crystals

Several authors have published reports of plastic deformation in Dy and Tb single crystals magnetized in fields of about 100 kOe parallel to the magnetically hard direction at cryogenic temperatures [1–3]. The mechanism for this deformation has not been described in literature. We have investigated the nature of this phenomenon in Dy crystals, using optical and scanning electron microscopy. X-ray diffraction, and magnetic measurements. Plastic deformation was generally found to occur at 70–90 kOe at 4.2 K in Dy and the mechanism is {101̄2} 〈101̄1̄〉 mechanical twinning, which was determined by independent mechanical tests to be a primary twinning system. The most likely driving force for the deformation appears to be the decrease in magnetostatic and magnetocrystalline anisotropy energies on twinning, since a relatively easy 〈101̄0〉 direction in the twinned region lies almost colinear with the field. A simple calculation shows that this energy difference leads to an equivalent tensile stress comparable to the yield stress of Dy.