Influence Of Residual Stresses Research Articles

Size dependent mechanical properties and deformation mechanisms in Ti and Zr films

The nanometallic Ti and Zr monolayer films with various thicknesses ranging from 600 to 2200 nm were prepared by using magnetron sputtering technique. The microstructure results demonstrated that Ti films transformed from hcp to fcc at t ≤ 600 nm, while Zr films were grown with hcp structure of nanocolumnar grain. Moreover, the grain orientation of hcp Ti films changed from (0002) preferred orientation at t = 1200 nm to random orientation at larger thickness. Subsequently, the hardness and strain rate sensitivity of films were explored by nanoindentation. The Hall-Petch relationship is obviously invalid to explain the film thickness dependent hardening behaviors in Ti and Zr films, and the influence of phase structure, orientation and residual stress on nanoindentation hardness was discussed. It seems that residual stress plays an important role in the determination of hardness in present Ti and Zr films. The negative strain rate sensitivity m appeared during the plastic deformation of fcc Ti films, which is caused by the phase transformation. The underlying deformation mechanism of hcp Ti and Zr films was also discussed.

Influence of initial state and residual stresses on the modulus-density relationship of geomaterials: insights from multiple experimental setups

ABSTRACT Quality control in pavement construction traditionally relies on density measurements of geomaterials. With the introduction of modulus measurement methods, a shift has occurred due to the operational advantages of modulus-estimating devices over conventional density measurement techniques. Modulus-based methods also provide valuable information for the mechanistic-empirical (ME) design of pavement layers. However, a challenge emerges as a single modulus measurement does not directly correspond to a specific density measurement, leading to concerns about replacing density measurements in quality control processes. While it is generally accepted that a geomaterial's modulus primarily depends on its moisture content and density or void ratio, this study explores the complex relationship between modulus and density, particularly in field scenarios with consistent moisture content. Using three different laboratory-scale test set-ups, characterised by unique loading and boundary conditions, the research highlights the significant role of a geomaterial's initial state in obtaining accurate modulus estimates. The results reveal that identical densities can exhibit variations in modulus due to differences in initial densities and the development of residual lateral stresses. These variations in field conditions often stem from different paving or spreading techniques, emphasising the need for a comprehensive approach when establishing density-modulus correlations..

Investigation of the influence of initial residual stress and toolpaths on milling deformation of titanium alloy

Titanium alloy structural components are widely used in the aerospace industry due to their excellent physical properties. However, their susceptibility to machining deformation during milling, attributed to the presence of initial residual stress, poses a significant challenge. Therefore, this paper proposes a finite element model for predicting milling deformation in Ti6Al4V titanium alloy structural parts, considering initial residual stress. The methodology involves establishing the initial residual stress field of titanium alloy components based on a mathematical model of annealing heat transfer and a theoretical study of thermal elasto-plastic constitutive relation, with experimental confirmation of model accuracy. Based on the initial residual stress, a finite element model was developed to predict the maximum deformation under different toolpaths. Finally, a comparative analysis with milling experiments validated the proposed models. The experimental results demonstrated a remarkable alignment with the finite element model, showcasing the correctness of the developed models. The maximum deviation in deformation observed was within the range of 0.003 mm–0.011 mm. This study is the first to comprehensively consider the effects of initial residual stress and toolpaths on titanium alloy milling deformation, and to experimentally verify the proposed model’s accuracy and practicality. It provides a new theoretical basis and technical guidelines for titanium alloy milling deformation.

Exploring Fatigue Crack Initiation in Helical Gears: Impact of Carburization and Frictional Influences

A computational model is presented to analyze the fatigue crack initiation period in helical gears, incorporating considerations for heat treatment via carburization and friction effects. The aim is to determine the number of stress cycles necessary for the initiation and growth of initial cracks, while investigating the impact of dynamic behavior. This study employs a dynamic gear model with two degrees of freedom in torsion, developed using MATLAB, and incorporates the Papadopoulos criterion for fatigue analysis. The computational results are benchmarked against the strain-life method. The findings underscore the significant influence of the friction coefficient between surfaces, heat treatment, and dynamic loads on the growth of initial fatigue cracks. For instance, with a friction coefficient (μ) of 0.5, the initial crack forms on the tooth surface (y=0) in both methods, with the (ε-N) method suggesting 28-65 cycles and the Papadopoulos criterion indicating 101-156 cycles. The latter accounts for the greater influence of residual stresses. Additionally, untreated gears exhibit a minimum number of loading cycles for initial crack appearance at 1.07 × 104 cycles. In contrast, carburized gears demonstrate an extended lifespan, requiring 1.45 × 105 loading cycles for crack initiation in our example. This emphasizes the efficacy of carburization in enhancing gear durability.

Control strategy of reducing hydrogen enrichment in heat-affected zone during welding for ultra-high strength steels

The hydrogen diffusion behaviors in welded joints of ultra-high strength steel (UHSS), which are related to hydrogen-induced cracks (HIC) in welding, are not yet fully understood due to the lack of in-situ observation techniques for hydrogen during welding. An improved microphotography technique is proposed to visualize the hydrogen distribution within the as-welded joint. When UHSS is welded using traditional welding materials, the transformation temperature from γ to α phase (TF) of the weld metal (WM) is higher than that (TB) of the heat-affected zone (HAZ), resulting in the observed hydrogen enrichment in the HAZ. We developed a low transformation temperature (LTT) welding material. This material is designed so that the TF of WM is lower than the TB of HAZ, facilitating hydrogen back-diffusion from the HAZ to the WM. This back-diffusion effectively reduces the hydrogen concentration in the HAZ. Additionally, a thermo-mechanical hydrogen diffusion sequentially coupled finite element procedure was utilized to simulate hydrogen concentration evolution during welding, revealing the control process of phase transformation temperature differences (ΔT = TF - TB) on hydrogen diffusion behavior and the influence of residual stress on the accumulation of hydrogen. The microphotography technique has successfully validated these findings, which can help to mitigate the risk of HIC in the HAZ during welding of UHSS.

Influence of residual stress on the high-temperature tribological performance of nickel-based superalloy

This study introduces a method for generating residual compressive stress by utilizing differences in thermal expansion coefficients of materials. A corresponding experimental device has been developed. Using this method, experiments were conducted to investigate the effects of residual compressive stress on the tribological properties of the nickel-based superalloy Ni16Cr13Co4Mo. The results indicate that residual stress significantly affects the friction behavior and wear resistance of the superalloy. The stabilization time of the friction coefficient as well as the wear rate reaches a minimum under moderate residual compressive stresses. Moderate residual compressive stress can facilitate the formation of a tribo-oxide layer and enhance its bonding strength with the substrate, thereby shortening the time for stabilization of the friction coefficient and reducing the wear rate. Finite element simulation of static ball-on-disc contact model also shows that residual stress alters the internal stress distribution inside the alloy, and changes its yield and plastic behavior. Under moderate residual compressive stress, a reduction in maximum von Mises stress can be achieved, which is consistent with the variation rule of friction coefficient and wear rate in the tests.

Multiscale study of interfacial properties of carbon fiber reinforced polyphthalazine ether sulfone ketone resin matrix composites

In view of the limitations of traditional research tools on interfacial failure mechanisms in fiber/PPESK composites, this work proposes a multiscale research tool to carry out an in-depth study of the interfacial behavior between fibers and matrix. Based on microdroplet debonding tests, at the mesoscopic scale, the influence of residual thermal stress on the interface damage mode is explored through finite element (FEM) simulations. The evolution mechanism of composite material interfaces in spatial and temporal dimensions is examined based on changes in interfacial stress distribution, energy dissipation, and damage morphology during the debonding process, which can be summarized as follows: accompanied by elastic-plastic deformation and friction effects, the progressive process from localized to complete failure presents a dominant Type II damage mode at the interface. To further explore the interface failure mechanism at the molecular level, an interface model of CF/PPESK composite materials was established using molecular dynamics (MD) method. By monitoring the atom movement trend, the “fiber-matrix displacement synergistic effect" in the interfacial shear damage process was revealed, thereby establishing a multiscale mapping relationship of composite material interface. Based on this, the combination of FEM and MD was utilized to investigate the interface damage process of composite materials under different service conditions and to reasonably predict the initiation and expansion of microcracks. This study provides a pioneering perspective on interface damage research in composite materials with a “top-down” multiscale approach.

Correlation of residual stress on piezoresistive properties of boron-doped diamond films

To investigate the influence of residual stress on the piezoresistive behavior of boron-doped diamond (BDD) films, BDD films with varying doping concentrations were synthesized using a hot-filament chemical vapor deposition (HFCVD) system on silicon and diamond substrates. The relationship between the surface morphology, structural composition, resistivity, and piezoresistive properties of BDD electrodes was examined, along with an in-depth analysis of the impact of boron doping level on these properties. The microstructure and bonding state of the BDD films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. The piezoresistive properties of the BDD films were evaluated employing a cantilever beam bending method. Our findings demonstrate that the level of boron doping not only affects resistivity but also directly influences residual stress in BDD films, both factors having an impact on their piezoresistive properties. Despite significantly larger grain sizes observed in BDD films grown on diamond substrates compared to those grown on silicon substrates at identical boron doping concentrations, they exhibit consistent variations in residual stress and gauge factor (GF) values. With increasing doping levels, the absolute residual stress decreases initially before increasing again; moreover, at 2000 ppm doping level, it transitions from compressive to tensile stress. The GF value is closely associated with both the magnitude and type of residual stress. By utilizing a doping concentration of 2000 ppm for growth on diamond substrates, we achieved a peak GF value of 257 for BDD films which highlights their promising potential for pressure sensor applications.

Fatigue reliability analysis methodology based on fatigue life and failure mechanism for carburized gear

Gears are one of the important components in mechanical products, and their fatigue reliability determines the safety performance of mechanical products. In this paper, the fatigue characteristics of carburized gears under different torque and constant rotational speed conditions are investigated by using a gear contact fatigue testing machine, and combined with the dynamic maximum contact stress distribution on the subsurface of the meshing gears, the very-high cycle fatigue P-S-N curves of carburized gears under a stress ratio of −1 is established. Local stress concentration in the surface or subsurface of carburized gears causes grain dislocation movement under the combined influence of maximum contact and residual stresses, and then causes dislocation pileup and transcrystalline rupture after being hindered by grain boundaries, ultimately leading to pitting and fatigue failure of gears. Based on the dislocation energy method and combined with the fatigue failure mechanism of gears, a life prediction model of gears with good prediction results is established by considering the interaction of factors such as dynamic load, grain size, initial crack length, residual stress, slip band length and width. A fatigue reliability analysis method of gears is established based on the life state equation of gears considering the life prediction model. Further analyses of the influence of rotational speed, grain size, residual stress, slip band width, slip band length and initial crack size on the fatigue life reliability index of the gears resulted in the conclusion that the fatigue reliability of the gears not only decreases with the increase of the above-mentioned parameters, but also shows decreasing trend with the increase of time. This is of significance for evaluating the fatigue reliability of gears under very-high cycle fatigue conditions.

Reasons for Depressurization of a High-Pressure Cylinder

High-pressure cylinders are vessels for storing and transporting compressed gases under high pressure, which are necessary for use in various technological processes. These vessels are mainly made of steel or aluminum and have significant strength to withstand high (more than 400 kgf/cm2) pressure. Such cylinders have a wall of sufficiently large thickness and are used in various industries. The object of the study is a one-piece forged cylinder made of 38ХН3МФА steel. The purpose of this study is to determine the causes of cylinder depressurization, which occurred during filling the cylinder with helium at a speed of 7.5 m3/h at an operating pressure of 365 kgf/cm2. As is known, when operating process equipment operating under excess pressure, damage may occur due to the structure of the material and the features of its mechanical properties. This damage can lead not only to the failure of the vessel itself, but also to damage to other units and parts located nearby. And if people are working nearby, the cost of such an accident will be even higher. Therefore, the study in this article of the causes of destruction of a high-pressure cylinder is very relevant. A set of studies (visual and measuring control, factographic, metallographic and spectral analysis) was carried out, which helped to establish the cause of the destruction of the vessel body at the neck of the cylinder. The main conclusion on the causes of depressurization of the vessel in question is the presence of a stress concentrator, namely, a depression of the folds of the cylinder, which was formed during the formation of the neck of the cylinder in the transition area from the cylindrical part to the neck. During long-term operation, under the influence of residual technological stresses, a crack was formed, which spread from the inner surface of the cylinder to the outer one, up to its through damage, which led to depressurization.

Effect of impact angle on hot corrosion resistance of abrasive water jet peened Ti-6Al-4V alloy

The effect of peening angle (10° to 40°) on NaCl induced hot corrosion behavior of Ti-6Al-4V alloy was evaluated at 750 °C for 100 h. Peening at higher impact angles progressively increases the surface roughness, number of sub-grains, magnitude of compressive residual stresses and hardness of the alloy. During hot corrosion, the surfaces of Ti-6Al-4Al, irrespective of the peened condition, develops oxide scales that contain oxides of Ti, Al and V. Hot corrosion rate, measured in terms of rate of mass gain and the rate constant, Kp, was highest for the unpeened alloy but decreased for surfaces subjected to AWJ peening. Surfaces peened at increasing impact angles have smaller mass gain rate and the one peened at the impact angle of 30° exhibited the lowest corrosion rate and a lowest Kp of ∼0.08 mg2/cm4/h. The surface peened at 40° is, however, not as corrosion resistant. The mechanism of corrosion was discussed in the context of corrosion products formed and the opposing influences of initial roughness and compressive residual stresses. While higher roughness promotes hot corrosion by facilitating sites for corrosive attack, higher compressive residual stresses retard the diffusion of corrosive species into the Ti-6Al-4V surface. Based on these discussions, the optimum impact angle for AWJ peening for imparting maximum hot corrosion resistance on Ti-6Al-4V was determined to be ∼30°.

An alternative stress boundary condition in small deformations and its application to soft elastic composites and structures

Linear elasticity theory has been used extensively in the study of the elastic behavior of various perforated structures and composite materials requiring the accompaniment of appropriate boundary conditions to derive qualitatively correct and quantitatively referential solutions. When incorporating conventional boundary conditions, however, linear elasticity theory fails to predict certain essential phenomena associated with perforate structures and composite materials even when they undergo small deformations. For example, a soft elastic porous medium is appreciably stiffened when inflated despite the fact that the internal air pressure is significantly lower than the modulus of the medium itself. In this paper, we propose an improved stress boundary condition by simply incorporating a small change in the normal to the boundary during deformation. We show via numerical examples that in the context of linear elasticity theory, the use of this improved boundary condition offers the possibility of predicting the influence of initial or residual stress in a perforated structure on the elastic response of the structure to external loadings (which can never be captured with the use of conventional boundary conditions). We perform also large-deformation-based finite element simulations to verify the accuracy of the closed-form results obtained from the improved boundary condition for a soft elastic perforated structure with initial internal pressure. We believe that the idea presented in this paper will extend the applicability of linear elasticity theory and yield more accurate referential analytic results for soft elastic structures and composites.

Structural Design and Mechanical Properties Analysis of Laminated SiAlON Ceramic Tool Materials

Based on finite element simulation analysis, laminated ceramic tool materials with different structures were designed and the effect of laminated structure on tool state was investigated. Residual stresses in ceramic tool materials increase with the number of layers and layer–thickness ratio. Based on the simulation results, SiAlON-SiC-SiCw/SiAlON-Al2O3 ceramic tool materials (SCWAs) were prepared using the spark plasma sintering process, and the influence of residual stress on the mechanical properties and microstructure of laminated ceramic tool materials was studied. The mechanical properties of ceramic materials were significantly improved under the effect of residual stresses. The fracture toughness of SCWA4 with 7 layers and a layer–thickness ratio of 6 was 6.02 ± 0.19 MPa·m1/2, and the front and side flexural strengths were 602 ± 19 MPa and 595 ± 17 MPa, 36.3% and 39.0% higher than homogeneous SiAlON ceramics, respectively.

Improved buckling reduction factors for existing steel columns accounting for different imperfections

The presented research aims to develop global and local buckling reduction factors that account for the impact of amplified geometrical imperfections and the variability of residual stresses on the buckling resistance. The improved buckling coefficients might be necessary for analysing existing structures, which often have larger imperfections than the manufacturing tolerances. Advanced GMNI analyses are employed to investigate pure local and global buckling resistances of I- and box-section columns, incorporating accurate non-amplified local and global imperfections. A parametric study is conducted to systematically investigate the impact of enlarging the imperfection factors and varying residual stresses. The local and global buckling formulas specified in EN1993-1-5 and EN1993-1-1 are calibrated against laboratory test results and/or GMNI analyses to account for the influence of imperfections and residual stresses. Similar calibration process is performed within the current study by modifying the imperfection factor α in the buckling formulas taking into account the enlarged imperfection magnitude. The result of the current study enables designers to refine the estimation of the buckling capacity when actual imperfections and residual stresses deviate from those employed during the design phase.

The impact of welding residual stresses on fatigue crack growth behaviour in aluminium alloy plates: a numerical and experimental investigation

ABSTRACT This paper presents the findings of an investigation into fatigue crack growth in Compact Tension (CT) samples made of an aluminium alloy that contains welding residual stresses. The samples were welded using the TIG welding process, and the fatigue crack growth was measured through experimental means. To model the welding process and resulting residual stresses, as well as their impact on the rate of fatigue propagation, 3-D thermal-mechanical finite element (FE) analyses were conducted. The simulations revealed that the residual stresses induced by welding relaxed during fatigue loading. Both the experimental and FE results demonstrated similar relaxation behaviour of the specimens under fatigue loading. This study highlights the significant influence of residual stresses on the propagation of fatigue cracks in aluminium alloy specimens. By combining experiments and numerical simulations, a comprehensive understanding of how welding residual stresses evolve during fatigue loading and affect crack growth rates is achieved. The agreement between the experimental and FE models confirms the effectiveness of the finite element method in investigating the influence of residual stresses on the behaviour of fatigue crack propagation in structures fabricated through welding processes.

Использование новых видов технологической оснастки при изготовлении нежестких плоскостных алюминиевых деталей методом волновых технологий

It has been suggested that wave technologies in non-rigid plane parts production should be used with the introduction of ultrasonic range vibrations into the shaping zone in combination with technological equipment, i.e. it is- a zero-base system. The traditional technique used in domestic enterprises implies a high probability of out-of-flat conditions and deformations due to the influence of technological residual stresses (TRS) in the process of stock removal or force stresses under plastic deformation of the part when fixing blanks. Using modern universal software systems such as Simulia Abaqus, ANSYS, etc., it was possible to determine the magnitude of deformations, aligment errors caused by residual stresses. The data obtained were used to calculate rational ways for fixing some typical non-rigid plane aluminum blanks on a technological equipment - a zero-based system of German production SCHUNKVERO–SAviation (VSA). The research was aimed at determining the manufacturability for the use of such equipment when making a particular non-rigid blank made of aluminum alloys and finding the most optimal way of its fixing. The estimated values of the TRS were determined by mechanical and X-ray methods. The calculations were performed using real parts of aircraft equipment of the "beam" type and blanks made of aluminum rolled products. The proposed method for determining the maximum amount of deformation of the workpiece under machining is applicable to the most optimal placement of the support and clamping modules of the zero-based system (VSA). In combination with a certain strategy of wave mechanical processing, it makes a practically complete compensation for deformations possible and allows obtaining a suitable product from the first presentation without performing an additional correction operation.

Effect of residual stress on mechanical properties of Triply periodic minimal surface lattice structures in Additive manufacturing

Due to its special porous structure with smooth continuous surface and high specific surface area, the triply periodic minimal surface (TPMS) lattice structure exhibits excellent properties such as strong bearing capacity, high energy absorption rate and good fatigue performance. The residual stresses generated during the additive manufacturing (AM) process can have a significant impact on the mechanical properties of the TPMS structure. In this paper, the AM process of four typical TPMS structures are investigated by the thermal–mechanical coupling model. The mechanism of residual stress generation is analyzed, and an optimized preparation process scheme is proposed to reduce the residual stress. Furthermore, the effects of residual stresses on the mechanical properties of TPMS structures are investigated for different types, volume fractions and compression directions. Results show that the influences of scanning speed and hatch spacing on the residual stress are not significant with constant laser power, but the deposition thickness should be adjusted according to the characteristics of the structure. The residual stress will reduce the elastic modulus and yield strength, while no obvious effect on the plastic behavior is observed. Importantly, the residual stress has the greatest influence on the mechanical properties of I-WP-type among the four investigated types, which becomes more pronounced with the increase of volume fraction. Moreover, the influence of residual stress on the mechanical properties of TPMS structures depends on the compression direction. Our results give a comprehensive understanding of the residual stress distribution and impact on the mechanical properties of TPMS structures, providing guidance to the rational design and optimization of TPMS structures in engineering applications.

Nonlocal dynamic response of FGP sandwich microbeam with 2D PSH network incorporating adatoms-surface interactions energy under magnetic field

The present work models and studies the resonance frequency change due to adsorption phenomena in a simply-supported adatom-microbeam system under an axial magnetic environment. The microbeam structure is a functionally graded (FG) sandwich that includes a rectangular configuration and a ceramic perforated core with periodic square holes network and FG porous material faces. To evaluate the adsorption-induced energies produced by van der Waals interaction (vdW), the Morse and Lennard-Jones (6–12) potentials are included in conjunction with nonlocal material elasticity to adopt the small-scale impact. Moreover, the explicit formulas for the inertia moments and shear force are developed by the Timoshenko beam equations, considering the residual stress influence as an additional axial load. The Navier-type solution and the differential quadratic method (DQM) are implemented to compute the solution of the governing equations. It is established that the resonance frequency change for the O/Si (100) and H/Si (100) is dependent on the geometrical, perforation, and porosity parameters, adsorption density, mode number, and the magnetic field intensity as well. Therefore, these numerical results have been discussed in detail to properly examine dynamic vibration behavior and a suitable mass detection design of M/NEMS structures.

A study of fatigue property enhancement of 1045 steel processed by surface mechanical rolling treatment with an emphasis on residual stress influence

Several factors contribute to the observed bulk mechanical properties enhanced by surface mechanical rolling treatment (SMRT), and it is important to distinguish the influences of each major factor. A commonly used engineering carbon steel, 1045 steel, was chosen for the current study because the material does not have stress-induced phase transformation. A fully reversed strain-controlled gradual decreasing amplitude loading spectrum (ENV) was employed to release the residual stresses induced by SMRT. Fatigue experiments were conducted on the 1045 steel specimens with and without ENV to assess the influences of grain refinement and the residual stress on fatigue. It was found that SMRT refined and recombined the microstructures in the surface layer through deformation and fragmentation of brittle cementite, and extrusion of ductile ferrite between adjacent cementite layers. In the high cycle fatigue regime, both the SMRT induced residual stresses and the refined/recombined microstructures contributed to the enhancement of fatigue strength and fatigue ductility but the gradient microstructure contributed significantly more than do the residual stresses. Unlike stainless steels processed by SMRT, the carbon steel does not display a kink point in the strain-life fatigue curve, and all the crack initiations were found to occur on the specimen surface.

Pipeline Circumferential Cracking in Near-Neutral pH Environment Under the Influence of Residual Stress: Crack Growth

Pipeline Circumferential Cracking in Near-Neutral pH Environment Under the Influence of Residual Stress: Crack Growth