Residual Microstresses Research Articles

Investigating the Effects and Mechanisms of Thermal–Vibration-Coupled Stress Relief Treatment on Residual Stress in SiC/Al Composites

Aluminum matrix composites reinforced with particles (PRAMCs) frequently develop considerable residual stresses post-quenching, which can negatively affect fatigue life and dimensional accuracy. Traditional stress relief methods for aluminum alloys are only partially effective. This study examined thermal stress relief (TSR), vibratory stress relief (VSR), and a combined thermal–vibratory stress relief (TVSR) approach for SiC/Al composites. All treatments proved successful in diminishing residual stresses, with the most significant reduction along the direction of peak dynamic stress. Additionally, this study analyzed micro-residual stresses via a macro–micro-residual stress finite element model to understand differences in stress relief outcomes. Optimizing the TVSR process could be key to more effectively reducing residual stresses in SiC/Al composites.

Hydrogen-induced cracking of longitudinally submerged arc welded HSLA API 5L X65 carbon steel pipeline

This study investigates the hydrogen-induced cracking (HIC) of a thermomechanical controlled processed (TMCP) API 5L X65 steel pipe fabricated using the JCOE forming process. Despite passing HIC testing as a plate, the final pipe exhibited unexpected failure, highlighting the critical influence of pipe fabrication on material performance. In this study, failed pipes were subjected to heat treatment, and HIC testing following NACE TM 0284 standard, SEM, and EDX examinations. The effect of heat treatment on the grain size, residual stress and susceptibility to HIC was investigated. The findings revealed that welding played a detrimental role, as all the HIC failures occurred at the welded area (0° orientation) due to welding-induced stresses and potential microstructural changes. It is believed that the welding process imposed reversible hydrogen traps in the HIC resistance plate ultimately reducing the HIC resistance. The heat treatment proved an effective method for relieving the applied micro-residual stresses that resulted in enhanced HIC resistance of the material.

Experimental study of residual stress distribution in interfacial micro-region of SiCf/Ti17 composites via micro-slotting method

Residual stresses in the interface layer significantly affects the mechanical properties of SiCf/Ti17 composites, which inevitably occurs due to the difference in the thermal expansion coefficient during the fabrication process. Therefore, the micro-residual stress at interface layer of SiCf/Ti17 composites should be quantitatively characterized. In this study, the micro-residual stresses at the interface of the composite are released and mapped via micro-slotting method and subset geometric phase analysis (S-GPA). Based on the material microstructure, a residual stress measurement scheme is designed for the interface layer in the radial and tangential directions. And the deformation field, which is calculated via S-GPA, is released, while the corresponding deformation field is obtained via finite element analysis, so that the residual stress can be fitted by above two deformation fields. The results indicate that, in the cross-setion of the fiber, the residual stresses at carbon interface are tensile, which may be beneficial to improve the mechanical properties of the materials. Meanwhile, tensile residual stresses, instead of compressive stresses in the interface layer, do not inhibit energy dissipation during the fracture of the composite.

Experimental characterization and numerical analysis of CFRPs at cryogenic temperatures

The thermo-mechanical performance of carbon fiber reinforced polymers (CFRPs) is affected by temperature changes due to the dissimilar nature of the constituents and dissimilar properties. For instance, under cryogenic conditions, the effective mechanical performance of the composite system can be significantly reduced. In this work, dynamic mechanical analysis (DMA) tests and coupon mechanical tests at room and cryogenic temperatures (through immersion in liquid nitrogen), are combined with computational micromechanics to analyze the development of micro-residual stresses from curing to cryogenic conditions, and their influence on the mechanical performance of a unidirectional CFRP. The results confirm the stiffness increase in the matrix and in the composite under cryogenic conditions, but the high tensile triaxial stress state that is developed during cooling reduces the overall composite strength, despite the increase of the matrix strength with decreasing temperature. To capture the failure modes and the evolution of the properties appropriately, the elastic-plastic response and the pressure dependent failure model are formulated to appropriately represent the shear response of the composite system and matrix failure under complex triaxial stress states, enabling a complete analysis and the identification of effective material properties, based on a reduced number of simple tests on the neat resin and on the composite system at different temperatures, which otherwise would be impossible to obtain considering the dimensional and technological restrictions of performing mechanical tests at cryogenic conditions.

Rapid microstructure modification of laser powder-bed fused superalloy IN718 using high-density pulsed electric current

A novel high-density pulsed electric current (HDPEC) method is developed to modify the grain-scale microstructure of laser powder-bed fused Ni-based superalloy IN718, which has not been reported in other studies. Rapid micro-residual stress relief and micro-segregation alleviation were achieved without significant grain coarsening which is common in conventional heat treatment. This technique can be an alternative energy-saving post-treatment method for additively manufactured metallic materials, enabling rapid and efficient annealing and solution treatment.

Micro-mechanical analysis of the effect of ply thickness on curing micro-residual stresses in a carbon/epoxy composite laminate

During the manufacturing of thermoset-based carbon fiber reinforced polymers (CFRPs), micro-residual stresses are developed in the material, due a mismatch of the chemical-thermal-mechanical properties of the fibers and the polymer matrix. This ultimately leads to a reduction in the mechanical performance of the composite material. In this work, a representative volume element (RVE) of a composite sub-laminate with a 90° ply discretized at micro-scale level, stacked within homogenized plies, is proposed to study the micro-residual stresses and the ply mechanical response considering the in-situ effect caused by the constraining adjacent layers. A model framework is developed using finite elements in Abaqus®/Standard with user-subroutines. The retrieved micro-residual stresses in the 90° layer are generated by the dissimilar chemical shrinkage and thermal expansions, plus the additional residual meso-scale stresses caused by the constraining effect of adjacent plies. The residual stresses in the constrained condition can achieve almost 80 % of the ply failure load for the 0/90/0 sub-laminate, meaning lower sub-laminate strain to failure. Thick laminates retrieve more residual stresses in the transverse 90° layer and exhibit lower constrained strength and more unstable post-failure response, demonstrating that thin-ply laminates exhibit beneficial constraining effects during the curing process.

Preparation of SiC/SiC composites with high toughness by reaction of the SiCP+C double-cladding layer with liquid silicon

SiC/SiC composites prepared by liquid silicon infiltration (LSI) have the advantages of high densification, matrix cracking stress and ultimate tensile strength, but the toughness is usually insufficient. Relieving the residual microstress in fiber and interphase, dissipating crack propagation energy, and improving the crystallization degree of interphase can effectively increase the toughness of the composites. In this work, a special SiC particles and C (SiCP +C) double-cladding layer is designed and prepared via the infiltration of SiCP slurry and chemical vapor infiltration (CVI) of C in the porous SiC/SiC composites prepared by CVI. After LSI, the SiC generated by the reaction of C with molten Si combines with the SiCP to form a layered structure matrix, which can effectually relieve residual microstress in fiber and interphase and dissipate crack propagation energy. The crystallization degree of BN interphase is increased under the effects of C-Si reaction exotherm. The as-received SiC/SiC composites possess a density of 2.64 g/cm3 and a porosity of 6.1%. The flexural strength of the SiC/SiC composites with layered structure matrix and highly crystalline BN interphase is 577 MPa, and the fracture toughness reaches up to 37 MPa·m1/2. The microstructure and properties of four groups of SiC/SiC composites prepared by different processes are also investigated and compared to demonstrate the effectiveness of the SiCP +C double-cladding layer design, which offers a strategy for developing the SiC/SiC composites with high performance.

Laser In Situ Synthesis of Gradient Fe-Ti Composite during Direct Energy Deposition Process

The suitability of the direct energy deposition process of exothermic powders Fe-Ti in joining dissimilar metals to produce small parts of a complete shape for various applications is considered. The procedure of the direct energy deposition of commercial pure iron and titanium in various proportions and the modes of the process are described. Optical microscopy and SEM with EDX analysis, X-ray analysis, and microhardness measurements of laser-fabricated intermetallics are applied. Intermetallic compounds of FeTi, Fe2Ti, eutectoids, complex titanium oxides and nitrides, and iron carbides are found. Interlayer and trans-layer cracks and pores are observed. A microhardness growth from 150 HV to 900 HV was obtained for all samples due to the precipitation of brittle intermetallic phases in the gradient Fe-Ti system during the DED. The dispersion of microhardness values becomes significant in Ti-rich areas; there, pores and cracks are found. The revealed structure features are considered in relation to published results and explained. Increased concentrations of Ti to Ti + Fe = 3:1 on the Fe- and Fe + Ti -substrate with concentrations of Ti + Fe = 1:1 and Ti + Fe = 1:3 lead to increasing hardness and its distribution, but also increases in residual microstress. Recommendations are given to reduce the power during the direct energy deposition of titanium layers and to apply Fe-substrate, which can reduce residual stress, pores, and cracks.

Formation of Thick Immersion Coatings and Residual Stress Evaluation in the System ZrB2-ZrO2: Experimental and Numerical Investigation.

The combination of various oxide ceramics in layered and functionally graded composites allows for the development of novel materials, including for high-temperature applications. This study demonstrates the possibility of obtaining a thick ZrO2-based coating on a ZrB2-SiC ceramic substrate by the immersion method. For better wettability, the porous ZrB2-SiC substrate is treated with cold plasma without changing the structure and phase composition of the surface. Immersion of the substrate in a ZrO2-based slurry results in the formation of a gradient transition layer due to ZrO2 particle penetration into the pore volume. The interfacial residual microstresses are evaluated experimentally. The residual macrostresses in the samples are calculated by finite element simulation. It is shown that the thermal residual stresses in the ZrB2-SiC substrate are compressive and do not exceed 43 MPa. In the ZrO2 coating and transition layers of the composite, the residual stresses are tensile. Their values increase as they get closer to the outer layer of the ZrO2 coating and reach 1525 MPa. This confirms the conclusions about the presence of tensile residual stresses made in the experimental part of the work when observing crack propagation in the surface layers during indentation.

Influence of Tempering on Macro- and Micro-Residual Stresses and Yield Stress of Ferritic-Pearlitic Drawn, Coiled, and Straightened Wires

Influence of Tempering on Macro- and Micro-Residual Stresses and Yield Stress of Ferritic-Pearlitic Drawn, Coiled, and Straightened Wires

A New Stored Energy Model Based on Plastic Work of Back Stress during Cyclic Loading in Polycrystalline Metal.

Two mesomechanics models were analyzed in an attempt to reveal the relationship between stored energy and back stress. It has been indicated that the portion of elastic stored energy due to residual microstresses (ESR) is closely related to intergranular back stress (Xinter), and the stored energy of dislocations inside grains (ESD) can be estimated with the plastic work of intragranular back stress (Xintra). Then, the evolution of back stress during cyclic loading was studied, and the plastic work of back stress (WpB) was calculated with the low cycle fatigue experimental data of Ti-6Al-4V. The result shows that WpB is partially released at every reverse loading, sufficient to reproduce the evolution of stored energy correctly under cyclic loading. The study also reveals that partially released energy is related to the decrease of Xinter at the initial state of reversal loading resulting from the reduction of the plastic strain incompatibility between grains.

Numerical Analysis of Micro-Residual Stresses in a Carbon/Epoxy Polymer Matrix Composite during Curing Process.

The manufacturing process in thermoset-based carbon fiber-reinforced polymers (CFRPs) usually requires a curing stage where the material is transformed from a gel state to a monolithic solid state. During the curing process, micro-residual stresses are developed in the material due to the different chemical–thermal–mechanical properties of the fiber and of the polymer, reducing the mechanical performance of the composite material compared to the nominal performance. In this study, computational micromechanics is used to analyze the micro-residual stresses development and to predict its influence on the mechanical performance of a pre-impregnated unidirectional CFRP made of T700-fibers and an aeronautical grade epoxy. The numerical model of a representative volume element (RVE) was developed in the commercial software Abaqus® and user-subroutines are used to simulate the thermo-curing process coupled with the mechanical constitutive model. Experimental characterization of the bulk resin properties and curing behavior was made to setup the models. The higher micro-residual stresses occur at the thinner fiber gaps, acting as triggers to failure propagation during mechanical loading. These micro-residual stresses achieve peak values above the yield stress of the resin 55 MPa, but without achieving damage. These micro-residual stresses reduce the transverse strength by at least 10%, while the elastic properties remain almost unaffected. The numerical results of the effective properties show a good agreement with the macro-scale experimentally measured properties at coupon level, including transverse tensile, longitudinal shear and transverse shear moduli and strengths, and minor in-plane and transverse Poisson’s ratios. A sensitivity analysis was performed on the thermal expansion coefficient, chemical shrinkage, resin elastic modulus and cure temperature. All these parameters change the micro-residual stress levels and reduce the strength properties.

On the effect of microplasticity on crack initiation from subsurface defects in rolling contact fatigue

This work demonstrates numerically how microplasticity, i.e. the yielding behavior below the conventional 0.2% plastic strain threshold, can lead to initiation of cracks at subsurface defects, in rolling contact applications operating under realistic loads. A 3D elasto-plastic finite element model is employed to perform shakedown analysis of the bearing steel around a small spherical void with two different approximations of the steel constitutive behavior at the plastic micro-strain regime. When non-linear kinematic hardening is used to model a fast but smooth onset of plasticity, the fields of plastic strains and micro-residual stresses around the void evolve very distinctly to the case where a sharp transition is assumed. To further investigate the role of the tensile micro-residual stresses occurring in the former case on crack initiation, a planar circular crack is inserted at the equator of the void and an entire overrolling cycle is investigated by means of linear elastic fracture mechanics (LEFM). This analysis is repeated for different crack sizes and the respective stress intensity factors and their amplitudes, relevant for crack growth, are reported. The work also reports implementation details for the coupling of a 3D elasto-plastic model for shakedown analysis to a subsequent LEFM analysis model.

The influence of Nd: YAG pulsed laser treatment on the structure, morphology and hardness of e.max ceram dental material

The use of ceramics in dentistry is increasing day by day owing to their more aesthetic look, better mechanical properties, and easy-to-fit approach. The material used in the study is IPS e.max Ceram by Ivoclar Vivadent which has been widely adopted as the ceramic of choice by many dentists as it is ideally suitable for the veneering of more opaque substructures. The study aims to elucidate the result of Nd: YAG pulsed laser irradiation at different numbers of pulses on structure, surface morphology, and hardness of e.max Ceram dental material. XRD shows the amorphous nature of the material before the laser irradiation, whereas the crystallinity in the material is slightly induced after the exposure of e.max Ceram with 150 laser shots. The surface morphology and hardness degradation are attributed to the swelling potential of the material and induced increase of the residual micro-stresses during laser irradiation. This technique could provide more ease for bonding and de-bonding of orthodontic brackets and might be used as a chairside tool.

Physical principles of radio-frequency magnetron sputter deposition of calcium-phosphate-based coating with tailored properties

The influence of radio-frequency (RF) magnetron sputter deposition conditions (RF power discharge density, working gas atmosphere, deposition time, and electrical substrate bias) on the properties (microstructure, texture, Ca/P ratio) of nanocomposite calcium-phosphate (CaP) coatings has been reported. A phenomenological model was developed to explain the formation of the RF magnetron sputter-deposited hydroxyapatite (HA) coating depending on the various deposition conditions. In the initial deposition stages, a nanocrystalline or quasi-amorphous CaP layer is formed. As both the film thickness and temperature gradient across the film thickness increased, the crystallisation of the HA phase occurred, which led to the formation of the fibre 〈002〉 texture in the films. The increase in the coating thickness also resulted in an increase in the grain size and a decrease in the residual microstress. The cross-section of the coating revealed a polycrystalline fibre structure with wedge-shaped columns. The addition of water vapour to an Ar atmosphere allowed to restore the hydroxyl groups in the composition of the HA coatings. The topography of the СaP coating surface that had irregular grains with different form and shape grown out of the coating plane was established, which extended the well-known structural zone models (Thornton, Monsieur, Movchan and Demchishin, Anders, etc.) and was formed both at a relatively low substrate temperature of 160–200 °С and RF power level when the substrate was bombarded with positive ions with an energy of ~100 eV, regardless of the working gas atmosphere used (argon or oxygen), resulting in a the growth of a coating with a preferably amorphous or nanocrystalline structure.

Особенности замедленного разрушения мартенситных сталей при наводороживании в зависимости от размеров исходных аустенитных зерен

The effect of the size of the initial austenite grains on the local characteristics of delayed fracture of martensitic steel with high and low levels of residual internal microstresses under hydrogenation conditions has been studied. The contribution of hydrogen and residual internal microstresses to the decrease in local strength of the boundaries of the original austenite grains during hydrogenation during the incubation period is divided.

Anomalous Dilatometric Response of Hot-Worked Ti-5Al-5Mo-5V-3Cr Alloy: In Terms of Evolution of Microstructure, Texture and Residual Stress

The Ti-5553 alloy has high strength close to that of the β Ti alloy for applications in high-strength structural components. In this article, results of detailed investigations of dilatometric responses of this alloy are presented. A Ti-5553 alloy ingot (150 mm diameter and 250 mm length) was double vacuum arc remelted (VAR), homogenized, forged and rolled. A very interesting dilatometric response was observed in this deformed material during heating in a dilatometer. Monitoring the sample length during continuous heating at a constant heating rate showed expansion and contraction in different temperature ranges. The observed contraction could not be attributed to any known phase transformation feasible in this alloy over the corresponding temperature range. Interestingly, the dilatometric contraction during heating was found to be orientation dependent. Precise lattice parameter measurements done on the basis of synchrotron data showed that the α to β phase transformation is associated with a slight expansion. To understand physical phenomena causing the dilatometric expansion/contraction, evolutions of microstructure and texture were investigated by intermittent sample removal at various intermediate temperatures along the heating path. Dilatometric responses were analyzed in terms of α phase dissolution, recovery, recrystallization of both α and β phases and release of anisotropic residual stress present in the starting material. The present investigation showed that the dilatometric examination coupled with microscopic observations can be employed for identifying the temperature ranges over which these processes occur—the information relevant for devising thermomechanical treatments of this alloy. This article also describes a method of assessing micro-residual stresses present in the two-phase Ti alloys from the dilatometric response of a small sample from the thermomechanically processed material.

Investigation on micro-residual stress distribution near hole using nanoindentation: Effect of drilling speed

Residual stresses are induced in the material during manufacturing operations, which considerably affect the fatigue performance and the lifespan of a mechanical work piece. The nature, magnitude, and distribution of residual stresses decide their beneficial or detrimental effects. Past research efforts concluded that mechanical process parameters influence residual stress nature, distribution, and the magnitude. Nevertheless, how residual stress generation depends on the process parameters, is not well investigated especially in the case of a drilling operation. In fact, the residual stress field is required to be regulated near drilled holes to improve the fatigue strength of structural joints, especially in the aircraft industry. Accordingly, this work attempts to estimate the drilling-induced micro-residual stress distribution near the drilled hole. In addition, the effect of drilling speed on residual stress distribution has also been studied. A nanoindentation technique is used to follow-up precise distribution of micro-residual stresses near the holes drilled at three different drilling speeds of 700, 900, and 1100 r/min. The outcomes indicate the presence of compressive residual stresses near the hole. In addition, an increase in residual stress level is noticed with an increase in the drilling speed up to 900 r/min. A uniform distribution of residual stresses is observed near the hole when drilled at a higher drilling speed of 1100 r/min. These findings may be useful in planning an improved drilling operation to produce beneficial residual stress distribution. This may ultimately improve the fatigue strength and the service life of mechanical components or structures with drilled holes.

Micro-Residual Stress Measurement in Nanocomposite Reinforced Polymers

Abstract In the present study, residual stress is measured in fiber-reinforced SWCNT/epoxy at weight fractions of 0.1% and 0.5% with a cross-ply layup on a micro-scale. The mechanical properties of the SWCNT/epoxy composites were determined by tensile testing and the Young's modulus of the epoxy increased moderately with the addition of CNTs. The micro-residual stress of the cross-ply CF/epoxy and CNF-reinforced CF/epoxy laminates were measured using a new experimental approach. The micro-hole was milled by laser beam and the surface displacement was recorded by SEM after milling. In order to determine the residual stress from the recorded strain, the calibration matrix was calculated using the finite element method. The residual stress was obtained at a certain hole depth of specimens. The reliability of this approach was assessed by comparing the residual stress measurements from this method and from the standard hole-drilling method. The experimental results of the present approach confirmed that laser hole drilling SEM-DIC has excellent potential as a reliable method for measuring residual stress in polymer nanocomposites. Generally, CNT agglomerates, especially in high weight fractions, increased the micro-residual stress. An analytical method based on classical theory was used to calculate the residual stress and was compared with the experimental results. Good agreement was found between the results of the analytical methods and the experimental measurement.

Elastoplastic bend of round steel beam. Message 2. Residual stresses

The residual stresses in metals can lead to the defects in metals during their forming and to destruction of metal structures during their long-term operation. The resulting residual stresses during metal forming can be of plastic nature, as in the malleable metals, or caused by a slow irreversible creep at the increased temperatures and prolonged action of loads. In the viscoelastic mediums, it can be caused by the viscous parts of deformation that can accumulate when the body is deformed for a long period of time. The residual stresses also have an effect on the metals microstructure and can present inside and around the crystalline grains as the micro-residual stresses, which are called the hidden elastic stresses. Sometimes the residual stresses are called the eigenstresses by an analogy with the eigenfunctions, introduced by the mathematicians to denote the functions that correspond to the certain values (the eigenvalues) of parameters of the differential equation under the given boundary conditions. The concept of the internal stresses was proposed as a general concept for this type of stresses, created by the body itself; the term residual stresses is assigned to the case, when the internal stresses are caused by the irreversible deformation. In addition to the emergence of favorable system of residual stresses in the discs of malleable metals with a pronounced deformation hardening, there will also be a local increase in strength, provided that the Bauschinger’s effect does not negate the achieved advantages. The extreme values of residual stresses of a straight cylindrical steel rod (beam) during bending are studied below.