Thermal Residual Stresses Research Articles

Integrated Control of Thermal Residual Stress and Mechanical Properties by Adjusting Pulse-Wave Direct Energy Deposition

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature–stress relationship curve of the additive manufacturing sample enters the “brittleness temperature zone”, leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

Direct formation of pure copper layer on aluminum nitride by multibeam laser deposition with blue diode lasers

A demand of power module devices has been increasing for highly energy efficient social system. The insulated heat sink printed circuit board is the key component of power module devices, which is composed of copper and aluminum nitride (AlN) due to high thermal conductivity. The conventional method of the joining between copper and AlN is active metal brazing method, but there is an issue that the high heat treatment of this method generates thermal residual stress on the board and decrease the reliability. For that reason, the development of a direct bonding process between copper and AlN has been demanded. Therefore, we focused on the laser metal deposition (LMD) method, which is a selective heating and microfabrication process. The LMD method is a method in which a powder material is supplied to the processing point and irradiated with a laser to melt the powder and form layer on the surface of the substrate. Then, a blue diode laser with a wavelength of 450 nm, which has a high absorptivity of 60% for copper, is used as a heat source. In addition, the multibeam type LMD system has been installed for the uniform heating of powder. In this study, the laser power density, laser scanning speed, and powder feeding rate were changed to explore the conditions for forming a copper layer on the AlN substrate.

Failure assessment of seam-welded pipe under fatigue and thermal loading

This paper presents an assessment of the failure of a seam-welded pipeline under fatigue and thermal loading. The investigation concentrated on analyzing several factors potentially influencing pipeline failure. Both experimental analysis and numerical simulations utilizing the finite element method (FEM) were conducted to understand potential failure modes of a seam-welded SS304L pipeline. The experimental and FEA analyses investigated various failure factors including weld defects, fatigue and thermal loading, residual stresses, and overloads. The study concludes that substandard welding procedures and inadequate post-weld treatment, coupled with elevated residual stresses in the heat-affected zone (HAZ) of the weld, were the primary contributors to failure. The paper systematically outlines the utilization of experimental and FE analyses in examining practical engineering failure instances. This approach strengthens the ability to avert failures and navigate risks with precision. Furthermore, the results highlight the critical significance of adhering to code and standard guidelines concerning pipe seam welds and post-weld treatment practices.

Numerical simulation of thermal and stress fields for multilayer and multi-pass weaving WAAM of magnesium alloy

Purpose A 3D finite element (FE) model based on the double ellipsoidal heat source was developed to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process. This paper aims to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process by developing a 3D finite element (FE) model based on the double ellipsoidal heat source. Design/methodology/approach Experimental thermal cycle curves and residual stresses were obtained by thermocouples and X-ray diffraction, respectively. The validity of the model was verified by the corresponding experimental results. Findings The deposition process of the upper pass led to the partial remelting of the lower deposited pass. The thermal process of the current-deposited pass alleviated the stress concentration in the previous-formed passes. A more uniform temperature distribution could be obtained by using the reciprocating deposition path. Compared to the reciprocating deposition path, the peak values of the transverse and longitudinal tensile residual stresses of the deposited sample under the unidirectional deposition path were reduced by 15 MPa and increased by 13 MPa, respectively. The heat conduction in the deposited passes could be improved by extending the inter-pass cooling time appropriately. With an increase in the inter-pass cooling time, the longitudinal residual stress in the middle region of sample along longitudinal and transverse directions showed increase and decrease–increase trends, respectively, while the transverse residual stress exhibited decrease trend. Originality/value This study enhances the understanding of temperature and stress fields evolution during the multilayer and multi-pass cold metal transfer-WAAM processes of magnesium alloy and provides the reference for parameter optimization.

Enhancing mechanical performance of hydroxyapatite-based bone implants via citric acid post-processing in binder jetting additive manufacturing

Binder jetting is a promising technology in the additive manufacturing of bone implants, particularly for printing brittle bioceramics that are susceptible to thermal residual stresses. However, challenges in this field include low strength and undesirable size changes due to post-sintering treatments, as well as the absence of necessary organic matter like Glycosaminoglycans, citric acid, etc. To address these issues, a novel approach was introduced using citric acid (CA) as a post-processing agent to enhance the mechanical performance of green samples and add organic matter, with boric acid (BA) as a control. A hydroxyapatite (HA) based powder mixed with 25 wt.% high-viscosity polyvinyl alcohol (PVA) was prepared and printed using a self-made printer with deionized water as the binder. The post-processing effects were analyzed in terms of mechanical properties and microstructure. The application of 5 wt.% CA solution increased the thickness of the PVA film between HA particles by 320.0%, leading to an increase in compressive strength (7.37 ± 0.28 MPa) and modulus (102.81 ± 6.74 MPa) by 840.7% and 1571.3%, respectively, achieving the mechanical standards for human trabecular bone. This work presents a simple and rapid room-temperature post-processing strategy for enhancing the mechanical properties of bone implants produced by binder jetting additive manufacturing.

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.

Microstructure and performance of compositionally graded Ta2O5/Ti thin films on Ti6Al4V alloy deposited by magnetron sputtering

Tantalum pentoxide (Ta2O5) ceramic is a promising material for modifying metal implants due to its superior wear resistance, chemical stability, and biocompatibility. However, the clinical application of Ta2O5 coatings may be limited by inadequate adhesion, resulting from performance mismatches between Ta2O5 coatings and metal substrates. In this study, a Ta2O5/Ti gradient film was developed on the Ti6Al4V titanium alloy substrate using magnetron sputtering, consisting of a Ti bonding layer, four Ta2O5-Ti composite interlayers with graded composition, and a Ta2O5 surface layer. The microstructure and properties of the Ta2O5/Ti gradient films were investigated, with a Ta2O5 monolayer coating as a reference. Results reveal that the gradient layers have higher density, lower surface roughness, diminished residual thermal stress, and improved adhesion, mechanical properties, and wear resistance compared to the Ta2O5 monolayer coating. However, the corrosion resistance of the Ta2O5/Ti gradient layer sample is inferior to that of the Ta2O5 monolayer coating sample, attributed to interphase corrosion between Ta2O5 and Ti within the interlayers. These significant findings offer a promising approach for enhancing the overall performance of Ta2O5 coating on Ti6Al4V titanium alloy surfaces, thereby opening avenues for widespread application in the biomedical industry.

An overview of tensile and shear failure mechanisms of silicon carbide-based ceramic matrix composites

The successful applications of silicon carbide-ceramic matrix composites (SiC-CMCs) in aeronautical and aerospace industries require deeper understanding of their mechanical behaviors and failure mechanisms. The overview on tension and shear is then presented from meso-mechanics perspective, including matrix cracking, interface de-bonding and sliding, matrix crack propagation as well as fiber bridging. The results reveal that the matrix cracking stress is proportional to the interface sliding stress and the matrix fracture energy. The ratio of tensile to shear stress of the matrix cracking remains constant both in tension and in shear. In addition, the deflection of matrix cracks in the interface depends on the elastic modulus matching parameter, the angle between matrix cracks and interface, as well as the residual thermal stress. The matrix cracks propagate in a random or periodic pattern, which are proportional to the sliding length at the matrix cracking stress. The fiber bridging mechanism, related to the Weibull distribution of the fiber strength, determines the tensile and shear behaviors after the saturation of matrix cracks.

Grain boundary behaviour and impact fractography of cryogenic treated AISI 316l manufactured by laser powder bed fusion

AISI 316L manufactured using laser powder bed fusion process was subjected to heat and cryogenic treatments. The effect of microstructural and mechanical properties, such as hardness, thermal residual stress, and Charpy impact, were investigated. The results indicate that after the heat and cryogenic treatment, the amount of austenite (FCC) phase increased, and the residual stress was removed after the heat and cryogenic treatment. The increase in deformation twins (Σ3) was observed after heat and cryogenic treatment. The cryogenic treatment altered the crystal lattice and orientation of crystal grains, resulting in grain refinement.

Physical properties and microstructural corrosion propertiesof Laser-bent 304 Stainless Steel Sheets

Laser treatment by laser bending is a technique of treating sheet metal by thermal residual stresses generated by laser assisted heating without any externally applied mechanical forces. The advantages of laser assisted bending over conventional bending include flexibility of non-contact processing, amenability to materials with diverse shape/geometry, and high precision/productivity. Up to now, most of previous work on laser bending was concentrated on study of bending angles/shapes with laser operating conditions, and modelling of the thermal process, however, no work has been reported on corrosion behavior of the laser-bended components. Since the laser bending is a thermal process, it is believed that the thermal process could not only alter microstructure, but also affect corrosion performances, such as intergranular corrosion, due to possible sensitisation caused by repeating laser scans. The aim of the present work is to investigate corrosion performance of laser-bent 304 austenitic-steel sheet with thicknesses of 2 mm and 1.5 mm, respectively, using a 2 kW CO2 laser. After laser treatment, the laser-bent samples were characterised in terms of microstructural change within bent zones consisting of melt-zone and heat-affected zone, using optical microscopy and scanning electron microscopy (SEM). Hardness profiles were obtained across the bent zones. Corrosion performances of the laser-bent evaluated by means of electrolytic etching in oxalic acid and double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. Laser bending is a thermal process, it is believed that the thermal process could not only alter microstructure, but also affect corrosion performances, due to possible sensitisation caused by repeating laser scans.

Finite element simulation of the effect of particle shape and thermal residual stress on the tensile properties of NbCp/Fe composites

To optimize the microstructure and properties of NbCp/Fe composites, this study considered factors such as load transfer, plastic strain, matrix damage, and interface debonding. A two-dimensional finite element model was constructed using ABAQUS software. Random adsorption algorithm was used to realize the random distribution of particles within the representative volume element, and interface damage was described using a cohesive zone model. The effects of particle shape and thermal residual stress on the tensile properties of NbCp/Fe composites were investigated. The results show that circular particles uniformly distribute the stress during the tensile process, effectively enhancing the tensile properties of the composites. Conversely, triangular particles, with obvious sharp corners, reduce their tensile properties, particularly in the presence of thermal residual stresses, which further aggravates the stress concentration between the particles and the matrix. This leads to a decrease in the strength and toughness of the material.

Multiscale shear failure mechanisms within a prestrained composite

AbstractThe elastic fiber prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite, where continuous fibers were prestretched under either constant stress or constant strain throughout the curing process. The tension was only removed after the resin was fully cured. It has been demonstrated that EFP is able to enhance the shear properties of the composite, while the underlying mechanics is still unknown. Here, we investigated the multiscale shear failure mechanisms induced by the EFP within a carbon composite. A bespoke biaxial fiber prestressing rig was developed to apply biaxial tension to a plain‐weave carbon prepreg, where the constant strain‐based EFP method was employed to produce prestrained composites with different prestrain levels. Effects of EFP on macro‐scale shear failure were subsequently characterized through mechanical tests and micro‐morphological analysis. Both the micro‐ and meso‐scale representative volume element (RVE) finite element models were established and experimentally verified. These were then employed to reveal the underlying stress evolution mechanics induced by EFP. It is found that EFP would improve the shear performance of a composite by enhancing the fiber/matrix interfacial bonding strength. This attributes to the elastic strain recoveries of the prestrained fibers locked within a polymeric composite, which generate compressive stresses to counterbalance the external loading. The multiscale shear failure mechanisms were then proposed. These findings are expected to facilitate structural design and application of the EFP for aerospace composites.Highlights Biaxial tension is applied to produce prestrained woven composite. Prestrain effects on microstructural stress evolution mechanics are revealed. Multiscale shear failure mechanisms are proposed for prestrained composites.

Combined computational-experimental investigation of residual stresses and pre-cracking in mode I behaviour of thick adhesively bonded GFRP composite joints

This paper presents a novel Finite Element (FE) simulation approach to examine the mode I fracture of thick adhesive joints used particularly in the trailing edge of the wind turbine blades. The approach involved FE models of the DCB specimens focusing on aspects overlooked in the existing literature. There has been limited investigation on residual stresses caused by thermal mismatch between composites and adhesives. Similarly, the impact of generating notches/pre-cracks in the adhesive layer during the preparation of Double Cantilever Beam (DCB) specimens on residual stresses has received minimal attention. Additionally, the Cohesive Zone Model, commonly used for simulating elastoplastic adhesives, may be inadequate due to its inability to account for the plastic deformation of the adhesive. In the present work, the pre-cracks were virtually generated in DCB FE models so that their effect on the stresses within the joint could be examined, making it a novel contribution to the field. The components were assigned with appropriate thermal expansion coefficients, and a simulation of the cool-down process was conducted to determine the thermal residual stresses. Furthermore, the Drucker-Prager plasticity criteria were used to capture the elastoplastic behaviour of adhesives in the FE simulations. Concurrently, the T-stresses were assessed through numerical investigations. For validation, experiments were conducted on DCB specimens made of two cross-ply composite laminates bonded with a ∼ 10 mm thick layer of an epoxy-based adhesive. A good agreement between computational and experimental results was observed, confirming the effectiveness and reliability of the proposed approach.

Influence of polyethylene pipe butt fusion welding in ultrasonic non-destructive testing

Abstract Butt fusion welding is a commonly used manufacturing method for polyethylene pipes. To investigate the influence of butt fusion welding on oblique ultrasonic wave in ultrasonic non-destructive testing, a numerical simulation model was established for polyethylene pipe with welding joints. Wave propagation in the polyethylene pipe was analysed, which showed that there exist longitudinal and shear waves propagating and their mode conversion. Detection signals of pipes with different defects and different acoustic attenuations were calculated. The special structure of welding joint was then modelled. Results show that the signal response declines with acoustic attenuation coefficient. Butt welding joints, especially the inner joints, would affect waves propagation. Finally, the welding process of polyethylene pipes was also simulated. The influence of cooling time was discussed, which indicated that insufficient cooling time would cause thermal residual stress and then alter the ultrasonic signal.

Finite element modeling of thermal residual stresses in functionally graded aluminum-matrix composites using X-ray micro-computed tomography

Metal-ceramic composites by their nature have thermal residual stresses at the micro-level, which can compromise the integrity of structural elements made from these materials. The evaluation of thermal residual stresses is therefore of continuing research interest both experimentally and by modeling. In this study, two functionally graded aluminum alloy matrix composites, AlSi12/Al2O3 and AlSi12/SiC, each consisting of three composite layers with a stepwise gradient of ceramic content (10, 20, 30 vol%), were produced by powder metallurgy. Thermal residual stresses in the AlSi12 matrix and the ceramic reinforcement of the ungraded and graded composites were measured by neutron diffraction. Based on the X-ray micro-computed tomography (micro-XCT) images of the actual microstructure, a series of finite element models were developed to simulate the thermal residual stresses in the AlSi12 matrix and the reinforcing ceramics Al2O3 and SiC. The accuracy of the numerical predictions is high for all cases considered, with a difference of less than 5 % from the neutron diffraction measurements. It is shown numerically and validated by neutron diffraction data that the average residual stresses in the graded AlSi12/Al2O3 and AlSi12/SiC composites are lower than in the corresponding ungraded composites, which may be advantageous for engineering applications.

A novel meshless radial basis reproducing kernel particle approach for 3D thermo-mechanical analysis of mushy zone phase-change problems

This paper presents a three-dimensional thermo-elastoplastic computational model for the analysis of phase change problems involving the mushy zone. The model utilizes a novel meshless radial basis reproducing kernel particle approach, incorporating a high-order kernel that integrates Gaussian and cosine functions. An energy balance equation for the entire domain is formulated using the effective heat capacity method, based on the enthalpy formulation. The governing equations are discretized using the Galerkin weak form to compute thermal residual stresses, with essential boundary conditions enforced through the penalty method. Plastic deformation is characterized using the von Mises criterion with isotropic hardening, and the strain term resulting from temperature-dependent material properties is incorporated into the incremental solution process. Determination of the plastic strain increment is based on the Prandtl–Reuss flow rule. The accuracy and efficiency of the proposed meshless approach were rigorously evaluated through numerical examples encompassing two- and three-dimensional problems. The computational results were compared against available analytical and validated numerical solutions. This comprehensive assessment substantiated the robustness and precision of the developed technique. The case studies presented elucidate the capacity of the novel meshless model to effectively predict temperature distributions and residual stress fields within mushy zone phase change phenomena, accommodating both regular and irregular geometries under various boundary conditions. Notably, the model demonstrated consistent stability and high accuracy across the spectrum of simulated scenarios, thus underscoring its potential as a valuable tool for investigating complex phase change processes.

High-strength joining of WC-Si3N4 composite via spark plasma sintering and functionally graded material (FGM) bonding

Joining of large aspect ratio WC-based cemented carbide and Si3N4-based ceramic at 1650 °C was achieved via spark plasma sintering by using functionally graded material (FGM) as a bonding layer. The influence of FGM layer numbers on the bonding quality of the large aspect ratio WC-FGM-Si3N4 composite materials was assessed based on thermal expansion coefficient and residual stress data. The microstructure analysis of the interface between adjacent layers revealed the formation of a structure with grain bidirectional anchoring, which promoted the enhancement of the bonding strength. High-strength joining of the large aspect ratio WC-FGM-Si3N4 composite rods with the average shear strength of 210.5 MPa was successfully realised. Furthermore, the rod was ground into an end mill, and the obtained end mill connection strength fulfilled the stringent machining conditions for dry milling of nickel-based superalloys.

Effect of foam interlayer thickness and pore size on the microstructure and properties of brazed joints

Ni foam was introduced as an interlayer to improve the performance of the brazed C/C composite-TC4 titanium alloy joint, and high-quality brazed connections of c/c composites and TC4 were realized. Compared to a brazing joint without foam, the introduction of a foam Ni interlayer can achieve a more uniform bonding interface. The effects of the thickness and pore size of the foam Ni interlayer on the microstructure, mechanical properties and residual stresses of the joints were investigated. With increasing thickness and pore diameter, Ag-based solid solutions and Ti–Cu intermetallic compounds first become more dispersed and smaller at the center of the brazed joints, and then aggregate to become larger. The brazed interface microstructure with a 0.4 mm thick foam Ni interlayer with a pore size of 0.5 mm was more uniform, and the shear strength of the joint reached 21.23 MPa, representing an 85.96 % increase compared to the joint without the foam Ni interlayer. The residual stress and its distribution calculated by finite element method (FEM), and the residual stress of the brazed joint decreased from 467 MPa/-289.53 MPa to 457.96 MPa/-234.98 MPa. These results indicated that the Ni foam could act as a buffer layer to reduce the residual thermal stress, and improve the mechanical properties of C/C composite-TC4 titanium alloy joint.

Gradient ceramic structures via multi-material direct ink writing

Dense boron carbide-silicon carbide specimens with composition tailored at the mesoscale were produced by direct ink write additive manufacturing in three configurations: I, 2 % and II, 10 % compositional layer-to-layer steps, and III, homogeneous composition throughout. Flexural strength, indicative of tensile failure, is the highest for the Type-II design (366 MPa) due to its compressive residual stress state in the surface layers. Analysis of thermally-induced residual stresses predicts the ranking of the flexural strengths obtained for Type-II (highest), Type-I (intermediate), and Type-III (lowest) specimens. Compressive strength is load-orientation independent, highly strain-rate dependent, and reduced for specimens with thermal residual stress. Mechanical tests were performed in cube and dumbbell geometries. Dumbbell geometry compression specimens have a compressive strength that is 68 % (quasistatic) and 86 % (dynamic) higher than that of cube geometry and show a greater strain rate dependence. The rate dependency is attributed to the competition between crack propagation and loading velocities. Type-I dumbbells show the highest mean compressive strength of 3.96 GPa (quasi-static) and 5.11 GPa (dynamic). The failure mode evolves from mixed intergranular/transgranular at low strain rates to transgranular at high strain rates. High-speed video analysis indicates that dumbbell geometry specimens fail in compression due to microcrack growth and coalescence, while cubes fail due to the axial macrocracks that develop at the specimen/load platen interface and propagate into the specimen parallel to the loading direction (end splitting). This work demonstrates the impact of compositional variation, tailored by additive manufacturing, on the mechanical performance of ceramic composites.

Influence of Process Parameters on Residual Stresses in Dissimilar Friction Stir Welding of Aluminum Alloys

Foreseeing how welded structures will behave requires careful consideration of the residual stresses that the friction stir welding (FSW) process introduces. These residual stresses can cause severe deformation and compromise the ability of friction stir welded structures to bear imposed external loads. This work uses a Sequentially Coupled Thermo-mechanical finite element simulation to quantitatively evaluate the influence of such residual stresses coming from the FSW process. This modelling method examines the thermal and post- weld stress distributions during the friction stir welding of dissimilar AA2024-T3 and AA5086-O alloys. The procedure entails an initial thermal analysis followed by a mechanical analysis to determine the distribution of residual stresses across the entire dissimilarly welded alloys. The study examined how alterations in FSW operational parameters, such as rotational and translational speeds, influence both the thermal conditions and residual stress distribution. The findings highlighted that both temperature and residual stress exhibited higher values on the retreating side of the specimen compared to the intended advancing side. As the tool rotational speed rose, the magnitude of longitudinal residual stress dropped, however it showed an increase with greater tool translational speeds. Moreover, the simulated outcomes demonstrate the substantial impact of welding fixtures on the profiles and magnitudes of residual stresses.