Minimal Residual Stress Research Articles

Design for additive manufacturing of topology-optimized structures based on deep learning and transfer learning

PurposeThis paper aims to improve the manufacturability of additive manufacturing (AM) for topology-optimized (TO) structures. Enhancement of manufacturability focuses on modifying geometric constraints and classifying the building orientation (BO) of AM parts to reduce stresses and support structures (SSs). To this end, artificial intelligence (AI) networks are being developed to automate design for additive manufacturing (DfAM).Design/methodology/approachThis study considers three geometric constraints for their correction by convolutional autoencoders (CAEs) and transfer learning (TL). Furthermore, BOs of AM parts are classified using generative adversarial (GAN) and classification networks to reduce the SS. To verify the results, finite element analysis (FEA) is performed to compare the stresses of modified components with the original ones. Moreover, one sample is produced by the laser-based powder bed fusion (LB-PBF) in the BO predicted by the AI to observe its SSs.FindingsCAE and TL resulted in promoting the manufacturability of TO components. FEA demonstrated that enhancing manufacturability leads to a 50% reduction in stresses. Additionally, training GAN and pre-training the ResNet-18 resulted in 80%, 95% and 96% accuracy for training, validation and testing. The production of a sample with LB-PBF demonstrated that the predicted BO by ResNet-18 does not require SSs.Originality/valueThis paper provides an automatic platform for DfAM of TO parts. Consequently, complex TO parts can be designed most feasibly and manufactured by AM technologies with minimal material usage, residual stresses and distortions.

Numerical Simulation-Based Study on the Microstructure of TC4 Titanium Alloy in CMT Additive Manufacturing

This thesis explores the thermal and mechanical phenomena occurring during the Cold Metal Transfer (CMT) additive manufacturing process of TC4 titanium alloy. The investigation delves into the effects of layer-by-layer deposition on the thermal cycles, stress distribution, and microstructural evolution of the additive manufactured specimens. Key findings include the identification of thermal accumulation with increasing deposition layers, leading to a decrease in cooling rates and a slight increase in the peak molten pool temperatures. The temperature profiles on the substrate exhibit cyclic patterns of peaks and troughs, which become smoother and exhibit less variance between maximum and minimum temperatures as deposition progresses. Stress analysis reveals that equivalent stress within the deposited layers decreases with the number of layers. This is attributed to the thermal stress accumulation and stress cycles induced by multiple thermal cycles, which initially increase the equivalent stress. However, a reduction in cooling rates over time and the effects of remelting facilitate the release of interlayer stress, resulting in minimal residual stress within the cooled specimens. Microstructurally, the TC4 titanium alloy specimens are characterized by the presence of primary β phase spanning across multiple deposition layers, growing in the direction of additive manufacturing. The accumulated heat input from increased layering enhances the growth of the primary β phase.The specimens' microstructure features a basketweave pattern comprised of α' martensite, α, and β phases, with α' martensite directly transformed from the primary β phase. Repeated heating cycles foster diverse pathways for the secondary α phase's formation, leading to more pronounced, directionally parallel α phases and extensive basketweave structures within the specimen layers. Higher temperature gradients at specimen edges encourage the formation of needle-like α' martensite. This thesis contributes to the understanding of the thermal behavior, stress dynamics, and microstructural characteristics in TC4 titanium alloy during CMT additive manufacturing, highlighting the interplay between process parameters, thermal management, and material response.

Effects of forming techniques on residual stresses in stiffening ribs of sandwich panels

This study investigates residual stresses in stiffening ribs of composite materials formed by stamping in a punch-die system. Using two-dimensional X-ray diffraction (XRD), we measured residual stresses on both the anterior and posterior sides. Three LITECOR® composite types, with core thicknesses of 0.8, 1.25, and 1.6 mm, were examined. Results indicate that as core thickness increases, residual stress values decrease on both sides. Notably, anterior side stresses on the y-axis are relatively higher (1027–1199 MPa) compared to the x-axis, exceeding posterior side values (998–1083 MPa) at 0.8 mm core thickness. Moreover, the study compares these values with Single Point Incremental Forming (SPIF) and finds that SPIF generally yields lower stress values for all core thicknesses. These findings suggest that SPIF is favourable for achieving minimal residual stress in LITECOR® composites. Addressing residual stresses is crucial for enhancing structural integrity and extending the service life of sandwich panels and composite materials.

Phase Structure, Microstructure, Corrosion, and Wear Resistance of Al0.8CrFeCoNiCu0.5 High-Entropy Alloy

This study investigates the structure and corrosion behavior of the Al0.8CrFeCoNiCu0.5 high-entropy alloy prepared using non-consumable vacuum arc melting. XRD analysis identified BCC1 and BCC2 phases corresponding to (Fe-Cr) and Al-Ni, respectively, while the FCC phase aligned with Cu. SEM and EBSD observations confirmed an equiaxed grain structure with fishbone-like morphology at grain boundaries and modulated structures within the grains. The alloy exhibited minimal residual stress and strain. The alloy demonstrated a preferred orientation of grain growth along the <001> direction. Electrochemical testing in a 3.5% NaCl solution revealed a corrosion potential of −0.332 V and a corrosion current density of 2.61 × 10−6 A/cm2. The intergranular corrosion regions exhibited significant depletion of Al and Cu elements, with the corrosion products primarily consisting of Al and Cu. Al and Cu elements are susceptible to corrosion. The wear scar width of Al0.8CrFeCoNiCu0.5 high-entropy alloy is 1.65 mm, which is less than 45# steel, and high-entropy alloy has more excellent wear resistance. Given its unique attributes, this high-entropy alloy could find potential applications in high-end manufacturing industries such as the aerospace engineering, the defense industry, energy production, and chemical processing where high corrosion resistance and wear resilience are crucial.

Evaluation of residual stresses in CO2 laser beam welding of SS316L weldments using FEA

Laser welding is used in critical component production when tight tolerances like minimal distortions and residual stresses are required. Laser beam welding offers a lower heat input, a smaller heat affected zone, lower residual stresses, minimum distortions, and greater mechanical joint characteristics than conventional welding does. In order to simulate the laser welding process used on SS316L plates, the Gaussian heat source model was used. The model is developed and simulated with volumetric heat source model with APDL coding using ANSYS. The thermal profiles at the joint cross sections via welded area, interface across joints is taken for the analysis. The maximum temperature was observed at the fusion zone and associated zones. The residual stresses are analysed in the same path and found the stresses are in safe limits of base material. Predicted and experimentally measured residual stresses are close agreement with 10%.

Effect of patch length and elevated temperature on fatigue behaviour of repaired aluminium panels with a CFRP patch

ABSTRACT Thin panels of aluminium alloy 6061-T6 with a centre pre-crack were repaired with a one-sided asymmetrical CFRP patch through co-curing of epoxy at the room temperature to have minimal residual stresses. The specimens were tested with a tension-tension fatigue load. The numerical simulation as well as the experiments showed that the fatigue life was improved considerably with the increasing patch length when tested at room temperature. In the asymmetrical repair with a single patch, a bending moment was induced whose magnitude decreased with the increasing patch length, resulting into longer fatigue life. The specimens failed through the growth of the pre-crack in the skin. However, the crack in the skin did not grow in case of the specimen with the longest patch length and the failure occurred at substantially higher number of fatigue cycles through a different mechanism in the bare portion of the aluminium alloy skin. Experiments were also conducted at the elevated temperature of 80°C. Thermal compressive stresses were developed in the aluminium alloy panel due to the vast difference in the coefficient of thermal expansion of the aluminium alloy and the CFRP patch. Consequently, the stress intensity factor of the crack in the aluminium panel was reduced considerably, resulting into the increase of the fatigue failure life significantly.

Additively manufactured Haynes-282 monoliths containing thin wall struts of varying thicknesses

Magnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations of them may occur within the complex geometry of a component, due to inherent variations of thermal signatures and the evolution of section modulus along the build direction. This work reveals the residual stress distribution, characterised from neutron diffraction, of an as-fabricated Haynes 282 monolith containing internal cube voids and thin wall struts of varying thicknesses. Complementary local hardness measurements and multi-scale microscopy were used to investigate the geometry-structure-property relationships. Observed variations in hardness were attributed to a combination of type I macro-scale residual stresses and variations in bimodal γ′ precipitation behaviour. The results highlight the influence of residual stresses and microstructure on the mechanical properties of E-PBF Haynes 282.

Effect of substrate condition on wire fed electron beam additive deposition

Electron beam wire fed (EB-WF) additive manufacturing (AM) can be utilised for cost-effective part repair in the aerospace industry and, especially for titanium alloys, the vacuum processing effectively mitigates high temperature contamination for enabling reliable high-performance. This research advanced EB-WF additive processing and simulation for depositing Ti–6Al–4V thin walls (3 mm in thickness) that emulates repair of damaged fan and compressor blades. The main focus of this research was to understand the effect of the initial substrate microstructure and residual stress profile on the final deposit properties. The results revealed that the EB-WF additive repair process for depositing Ti–6Al–4V yielded minimal distortion (<350 μm) and residual stresses (<150 MPa (0.15σys)). The initial residual stress states of the substrate were found to have a negligible effect on the final residual stress profiles, from the stress relaxation effect during EB-WF AM. Although significant variance in the microstructure for each substrate condition was present after deposition, their mechanical properties were similar. Deposited test specimens had tensile yield and ultimate strength values ranging between 800-830 MPa and 860–880 MPa, respectively. The similar mechanical properties of the interface were correlated with the microstructural features such as layer bands and titanium alpha (α) colonies.

An intelligent process parameters determination method based on multi-algorithm fusion: a case study in five-axis milling

• An intelligent parameters determination method is proposed based on multi-algorithm. • An improved GRNN with high accuracy is proposed for small batch of experiments. • An improved NSGA-II is proposed to generate the Pareto frontier with good uniformity. Process parameters have a significant effect on surface integrity, which determines the service performance of the parts. To improve surface integrity, the process parameters are determined: 1) by experienced engineers directly, 2) based on the Pareto frontier automatically constructed by swarm intelligence algorithms. However, as the Pareto frontier contains many non-dominated solutions, the final parameters are still determined by experienced engineers, which reduces the intelligence level. Therefore, an intelligent process parameters determination method based on multi-algorithm fusion is proposed towards minimal surface residual stress in feed or transverse direction ( Rs f , Rs t ) and surface roughness ( Ra ) in five-axis milling. Firstly, the Improved Generalized Regression Neural Network ( IGRNN ), which enhances the nonlinear mapping capability even in dealing with a small batch of experiments, is proposed to predict the Rs f , Rs t , and Ra with certain inputs (including lead angle, tilt angle, cutting depth, feed speed, and spindle speed). Then based on the proposed model, the Improved Non-dominated Sorted Genetic Algorithm-II ( INSGA-II ), which improves the uniformity of the Pareto frontier, is used to obtain a series of non-dominated process parameters. Finally, the optimal parameters are determined by the Principal Component Analysis ( PCA ) without manual weight assignment for Rs and Ra . By comparing with the second-best one, although the Rs f decreases by 0.33%, which is still able to obtain negative residual stress, the Rs t and Ra are greatly improved by 9.3% and 47.94%, respectively. The proposed method could improve the intelligent level of process parameters determination and the service performance of the parts. Furthermore, it lays a foundation for the realization of intelligent manufacturing.

Effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the contact zone with a cylindrical surface

This paper aims to determine the effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the center of elastoplastic deformation and residual stresses in the hardened zone of the surface layer of cylindrical workpieces. A mathematical model of local loading was constructed using the finite element method and AN-SYS software. This model was used to determine the values of temporary and residual stresses and deformations, as well as the depth of plastic zone, depending on the sector radius of the working tool. The simulation results showed that, under the same loading of a cylindrical surface, working tools with different sector radii create different maximum tempo-rary and residual stresses. An assessment of the stress state was carried out for situations when the surface layer of a product is treated by workpiece-deforming tools with a different shape of the working edge. It was shown that, compared to a flat tool, a decrease in the radius of the working sector from 125 to 25 mm leads to an increase in the maximum temporary and residual stresses by 1.2–1.5 times, while the plastic zone depth increases by 1.5–2.4 times. The use of a working tool with a flat surface for hardening a cylindrical workpiece ensures minimal temporary residual stresses, com-pared to those produced by a working tool with a curved surface. A decrease in the radius of the working sector leads to an increase in temporary residual stresses by 2–7%. The plastic zone depth ranges from 1.65 to 2.55 mm when chang-ing the sector radius of the working tool.

Topology optimization of aerospace part to enhance the performance by additive manufacturing process

Additive Manufacturing (AM) technology is an advanced manufacturing process implemented for the manufacture of biomedical, automobile, and aerospace parts. The main advantages of AM process is having a freedom to design any complex structures, low material waste, and production time. Currently, metal AM process is expensive due to its powder cost. The cost of production can be minimized by reducing the material usage with the help of topology optimization. Topology optimization is a process of estimating optimum material distribution in a given design space of a product. In the present study the aerospace bracket was redesigned using topology optimization. In topology optimization to minimize residual stresses were also considered as they are more in the AM process due to the high thermal gradient. The bracket was redesigned using CAD and topology optimization was accomplished using numerical simulation. The part material distribution was redesigned using the level set-based topology optimization approach in numerical simulation and analyzed for factor of safety. The topology optimization reduces 44.8% weight of the part and achieves a factor of safety of 2.3. The AlSi12Mg alloy material data is considered for numerical analysis. The optimized part printing conditions were numerically simulated to minimize manufacturing time with minimal residual stresses. The simulated SLM process parameters are 80 W of laser power with a scan speed of 1000 mm/sec, and hatch spacing of 90 µm confers minimal residual stresses. The obtained results were validated with published research data of different kinds of brackets and which are inline. Hence, integration topology optimization design and additive manufacturing can be an efficient tool for lightweight structures considerations.

Optimization of fused deposition modelling process parameters and the effect on residual stresses of built parts

Fused deposition modelling (FDM) is one of the most used additive manufacturing techniques for the fabrication of functional parts from composite filaments. Despite the widespread application spectra, FDM is still limited in its applicability due to inherent problems, one of which is the significant accumulation of residual stresses during part building. Residual stresses are generated due to thermo-cyclic loading in subsequent layers. The effect of residual stresses is significant for the mechanical integrity of the manufactured parts. Since it is impossible to manufacture parts without internal residual stresses, it is prudent to optimize the process parameters that would result in minimal residual stresses. In this study, Digimat additive manufacturing 2020 software with Taguchi design of experiment was used to predict the effect of printing temperature, layer thickness, and print speed on the generated residual stresses. Generic algorithm was used to determine the optimum combination levels for the minimum residual stresses. Results showed a near convergence between simulation and experimental residual stress values with an error of 3.7 %. The mechanical properties of 3D printed carbon fiber composite products were found to have tensile strength; 71.48 MPa, compressive strength; 135.8 MPa, Young’s Modulus; 7.6 GPa, and percentage elongation; 1.86 %. These properties fell within the acceptable range for the actual parts to be replaced. The results of this study will serve as a pragmatic approach to 3D printing of components devoid of trial and error strategies that have currently slowed the adoption of the FDM technique as a rapid prototyping tool for enhanced manufacturing.

Рост тонкопленочных AlGaN/GaN эпитаксиальных гетероструктур на гибридных подложках, содержащих слои карбида кремния и пористого кремния

We carried out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen plasma activation on a hybrid substrate containing layers of silicon carbide and porous silicon. Using X-ray diffractometry, Raman and photoluminescence spectroscopy, it is shown that thin films formed on a hybrid substrate have minimal residual stresses and intense photoluminescence.

Deep borehole disposal of intermediate-level waste

Abstract. Around the world, deep borehole disposal is being evaluated for intermediate-level waste (ILW), high-level waste (HLW), spent nuclear fuel (SNF), separated plutonium waste and some very high specific activity fission product waste. In Australia, long-lived ILW from research reactors and radiopharmaceutical production represents the principal waste stream that requires deep geologic disposal. Whilst the Australian government has not yet made a decision on its preferred strategy for ILW disposal, deep borehole disposal of small volumes of ILW would be a more cost-effective and modular solution compared to a conventional geologic disposal facility (GDF). CSIRO, ANSTO and SANDIA have created an international partnership to execute a full-scale borehole research, development and demonstration (RD&amp;amp;D) project in Australia. The project will demonstrate the technical feasibility of the long-term safety of borehole disposal in deep geological formations. The execution of this project could also demonstrate options for nuclear waste disposal that would reduce proliferation risks, potentially up to the termination of compliance with international safeguards requirements. The RD&amp;amp;D includes demonstration of surface handling and waste/seal emplacement capabilities, basic research on foundational science areas, and full-scale field testing in both a deep characterization borehole and a larger-diameter (0.7 m or 27.5 inch) 2000 m deep demonstration borehole. The multi-barrier system designed for such a deep disposal borehole concept places much less reliance on engineered barriers at the disposal zone to achieve safety as compared to a conventional GDF. It rather relies on geological features for waste containment. The concept being explored uses disposal containers with primary waste packages, such as vitrified waste canisters, inside; to be both cost effective and fit for purpose, such a container could have a mild steel-based structural component with copper coating. A critical review of six coating technologies showed that cold spray has the greatest advantages, such as minimal porosity and compressive residual stress. The RD&amp;amp;D has delivered novel enabling tools that assist with site screening, borehole design and post-closure safety assessments. For instance, an automated geological fault mapping and meshing tool was developed that assists with ranking the suitability of potential disposal sites based on proximity to faults. New codes were developed for better representation of fault zones in 2D/3D numerical flow and transport models, while also being more efficient to execute. Post-closure safety assessments tested the sensitivity of long-term safety with respect to disposal depth, rock permeability and sorption. Heat transport calculations explored the sensitivity of temperature evolution within the borehole to parameters such as heat load, borehole depth, geothermal gradients and rock thermal conductivity. For verification of host rock tightness while also demonstrating the absence of recent groundwater, a new noble gas analytical facility has been established for measuring rare noble gases in mineral fluid inclusions as indicators of very old pore fluids.

Experimental investigation of Al7075 reinforced with WC and SiC metal matrix composites

This study proposed the methodology to produce silicon carbide particulate MMCs based on aluminum to create typical low-cost MMCs and achieve a homogeneous scattering of ceramic material. The trial was done with a different weight fraction of Silicon Carbide (2%, 3%) and Tungsten Carbide (2%, 3%) with all other parameters being maintained. A growing hardness was noticed with the rise in SiC & WC weight 2 to 3%. The advantages of this technique include improved mechanical characteristics, minimal residual stress and deformation, and fewer flaws. Although casting technique poses numerous technical obstacles, this problem can nevertheless be addressed. Aluminum materials with high strength to weight and low density have been proven to be the best option. As lightweight materials are developed, weight reduction has been offered several alternatives through conducting different tests to analyze different features such as mechanical and metallurgical characteristics.

Modelling and Simulation of Mechanical Loads and Residual Stresses in Deep Rolling at Elevated Temperature

Based on the concept of Process Signatures, the deep rolling process is analyzed, aiming at functional relationships between material modifications and internal material loads during the process. The focus of this work is to investigate the influence of the workpiece temperature on the generated residual stress components. For this purpose, extensive finite element simulations of deep rolling were conducted, taking into account the effect of neighboring tool paths on the internal material loads and residual stress. A kinematic strain hardening model was parameterized and utilized and the simulations were validated experimentally. Simulated residual stresses agree qualitatively well with measurements and show a strong influence of the workpiece temperature as expected. Process Signature Components were generated, taking into account the maximal and minimal residual stress as well as their respective positions beneath the workpiece surface.

Application of Bat algorithm for Improvement of Surface Integrity in Turning of AISI 304 Austenitic Stainless Steel

Improving product quality is a crucial factor in determining the competitiveness and business efficiency of enterprises. This study investigates the influence of the cutting parameters, including the cutting speed, the depth of cut, and the feed rate on the surface roughness and the residual stress during the turning of AISI 304 austenitic stainless steel. Moreover, the work aims to determine optimal cutting parameters to satisfy both surface roughness and residual stress requirements. The mathematical model of the relationship between the machining parameters and the performance characteristics was formulated based on the response surface methodology (RSM) and the Box-Behnken design of the experiments. Pareto optimal solution applying natural-inspired algorithm (Bat Algorithm) is proposed to solve the bi-objective optimization problem to obtain the lowest surface roughness and minimal residual stress. The optimum cutting parameters selected by the manufacturing planners from the Pareto optimal fronts are calculated to comply with the production requirements.

Consumable development to tailor residual stress in parts fabricated using directed energy deposition processes

Distortion and residual stresses are major challenges that limit the ability to fabricate large scale structures using Additive Manufacturing (AM). Researchers worldwide are evaluating techniques to induce compressive residual stress in the parts via intermittent rolling. While reasonable success has been documented, the idea of lowering the martensite start temperature to induce compressive stresses has not been evaluated in the context of AM, despite demonstrated success by the welding community. This study validates the hypothesis that, by a proper selection of materials and process parameters, one may effectively reduce distortion and induce a compressive residual stress in AM parts. Using neutron diffraction to measure residual stresses in parts, we demonstrate that, in addition to selection of the correct materials, the inter pass temperature plays a major role in controlling the residual stress evolution. The observations relating to the residual stresses are rationalized based on a microstructural evolution in these samples. Based on this preliminary study, a strategy to fabricate large structures with minimal distortion and residual stress is outlined.

Modeling the stress state of steel strip at roller levelling machine under cyclic alternating deformations

The final stage in the production of hot rolled steel is leveling on roller levellers under cyclic alternating deformation. When laser is cutting a sheet it may bend due to the release of residual stresses that are unevenly distributed over the volume. The majority of roller leveller models for calculating the process under cyclic alternating deformation does not provide an adequate assessment and prediction of residual stresses in a steel sheet. On the basis of finite element analysis, formation of residual stresses owing to roller levelling of hot rolled strip is disclosed. The implementation of a model of the levelling process was performed in SIMULIA Abaqus. Models are verificated by comparing forces under the rollers. We have experimentally confirmed the convergence of the simulation results with the measurements of the strip flatness obtained after sheets plasma cutting. It was found that after levelling, tensile longitudinal residual stresses remain on the upper surface of the sheet, compressive ones remain on the lower surface, stresses are zero in the middle in thickness, and the stress values are opposite in sign in the remaining parts of the section. It was established that the same parameters of the levelling process of different strength categories lead to different deviations of stresses. An increase in yield strength of the strip leads to an increase in the deviation of residual stresses along the strip thickness. The proposed method of simulation of roller levelling process should be used to study the stress-strain state of hot-rolled steel and to design improved strip levelling setting modes with minimal residual stress deviations.

Modeling the Stress State of a Steel Strip with a Roller Leveling Machine under Cyclic Alternating Deformations

The final stage in the production of hot rolled steel is leveling on roller levelers under cyclic alternating deformation. When laser cuts a sheet, it may bend due to the release of residual stresses that are unevenly distributed over the volume. The majority of roller leveler models for calculating the process under cyclic alternating deformation does not provide an adequate assessment and prediction of residual stresses in a steel sheet. On the basis of finite element analysis, formation of residual stresses due to roller leveling of hot rolled strip is disclosed. The implementation of a leveling process model was performed in SIMULIA Abaqus. Models are verified by comparing forces under the rollers. We have experimentally confirmed the convergence of the simulation results with the measurements of the strip flatness obtained after sheets plasma cutting. It was found that after leveling, tensile longitudinal residual stresses remain on the upper surface of the sheet, compressive ones remain on the lower surface, stresses are zero in the middle in thickness, and the stress values are opposite in sign in the remaining parts of the section. It was established that the same parameters of the leveling process of different strength categories lead to different deviations of stresses. An increase in yield strength of the strip leads to an increase in the deviation of residual stresses along the strip thickness. The proposed method of simulation of roller leveling process should be used to study the stress-strain state of hot-rolled steel and to design improved strip leveling setting modes with minimal residual stress deviations.