Process-induced Residual Stresses Research Articles

Reduction in residual stress and distortion of thin-walled inconel 718 specimens fabricated by selective laser melting: Experiment and numerical simulation

Residual stresses were induced in the fabrication of thin-walled Inconel 718 specimens through selective laser melting (SLM) due to rapid heating and cooling, which yield distortion and have a detrimental impact on their mechanical performance. Reducing the process-induced residual stress and distortion is of great importance for practical applications. For achieving this aim, accurate measurement of residual stress and distortion is required. In the present work, residual stresses of SLMed samples were measured through hole drilling method (HDM), taking into account their anisotropic features. The distortion induced by the release of residual stress after manufacturing was measured using digital image correlation (DIC). The effect of thickness of thin-walled samples on residual stress and distortion was investigated. The results indicate that by reducing the thickness of sample, the residual stress could be reduced, whereas the distortion was increased. Furthermore, it was revealed that by manufacturing a pair of side samples in one printing job, the distortion and residual stress of the thin-walled component fabricated by SLM can be evidently reduced. The obtained results were clarified by using thermal-mechanical simulations of SLM.

Optimisation of process-induced residual stresses in composite laminates by different genetic algorithm and finite element simulation coupling methods

To address the residual stress induced during the cure of fibre reinforced thermoset polymer composites, two different approaches were suggested for coupling a non-dominated sorting genetic algorithm (NSGA-II) with finite element (FE) simulations based on a viscoelastic constitutive law. These two approaches were proposed with consideration of different ways of integrating NSGA-II and the FE model. In Approach A, NSGA-II was performed based on results from a series of simulations under various combinations of cure variables. Alternatively, Approach B employed NSGA-II to iteratively update and optimise the cure profile for subsequent simulations. Results indicated that both approaches achieved simultaneous reductions in cure time and macroscale residual stress, with Approach B showing further improvements due to the direct coupling between the NSGA-II and simulations. Specifically, the maximum residual stress and cure time optimised by Approach A were reduced by 5%–9% and 22%–50% respectively, while those obtained by Approach B were reduced by 7%–10% and 32%–49% respectively, compared to those based on the manufacturer recommended cure profile. The evolution of stress in composites based on optimised cure profiles from these two approaches was also elucidated. Additionally, microscale modelling further revealed a 3%–5% reduction in the average residual stress within a representative volume element (RVE) model was also shown, depending upon the approach adopted. Ultimately, by combining a NSGA-II and FE simulations, the optimisation of cure time and residual stress at the macroscale and cure time together with a reduction of microscale stress could be realised.

Enhanced prediction of reflected spectrum for FBG sensors with metallic coating embedded in CFRP composites: Unveiling the impact of process-induced residual stress and coating thickness

The occurrence of peak-split or distortion in the reflected light of fiber Bragg grating (FBG) sensors with metallic coatings embedded in composites is inevitable during the curing process, regardless of protection layers. In this study, we present a comprehensive methodology to numerically predict the reflected spectrum of metallic-coated FBG sensors, considering the process-induced residual stress in carbon fiber/epoxy composites. The finite element analysis was utilized to simulate the residual stress, which primarily arises from mechanical, thermal, and chemical cure mechanisms of the composites, including the thermosetting resin. Subsequently, the reflected spectra were calculated using the coupled mode theory. Contrary to common expectations, our findings indicate that the coating thickness has minimal influence on the reflected spectrum, while the residual stress and embedding position significantly impact it. By employing this proposed methodology, the number of experimental trials can be reduced, enabling the development of robust structural and state monitoring systems for composites using metallic-coated FBG sensors.

Impact of process parameters on the dynamic behavior of Inconel 718 fabricated via laser powder bed fusion

In this research, we investigate the dynamic behavior of Inconel 718 fabricated through laser powder bed fusion (L-PBF), addressing a notable knowledge gap regarding the correlation between process parameters and dynamic properties. The process parameters adopted are deducted from an extension of the Rosenthal solution, formulated to increase the process productivity while avoiding the typical production process defects. The dynamic Young modulus and the structural damping of the material are estimated as a function of the process parameters through ping tests reproducing the flexural vibrations of the specimens in as-built, solutioned, and aged conditions. The microstructure and porosity are investigated through metallographic analyses. The results show a substantial influence of the L-PBF process parameters on the dynamic Young modulus, which markedly increases as the energy density is reduced (23%) and progressively becomes more similar to the conventionally produced material. This influence stands in stark contrast to the relatively modest impact of heat treatments, which underlines a negligible effect of the process-induced residual stress. The structural damping remained approximately constant across all test conditions. The elastic response of the material is found to be primarily influenced by the different microstructures produced as the L-PBF process parameters varied, particularly in terms of the dimensions and shape of the solidification structures. The unexpected relationship between the dynamic Young modulus, energy density, and microstructure unveils the potential to fine-tune the material’s dynamic behavior by manipulating the process parameters, thereby carrying substantial implications for all the applications of additively manufactured components susceptible to significant vibratory phenomena.

Process-induced residual stress in a single carbon fiber semicrystalline polypropylene thin film

During the processing of semicrystalline thermoplastic composites, various models for the prediction of residual stress have been proposed but experimental validation is limited. In this study, a modeling framework is developed to predict the evolution of residual stress in a single carbon fiber embedded in a semicrystalline polypropylene thin film subjected to non-isothermal cooling. Validation is based on in-situ measurement of axial fiber strain after processing using micro-Raman Spectroscopy. A material model for polypropylene (50% equilibrium crystallinity) is presented that incorporates the effects of non-isothermal cooling on crystallinity-dependent resin shrinkage and crystallinity-dependent resin modulus from the amorphous polymer melt to room temperature. The evolution of residual stress is calculated using a finite element (FE) model with a user-developed subroutine incorporating the resin material models. Single-fiber polypropylene films are fabricated using a range of fiber pretension levels to prevent fiber waviness during cooling and to induce a wide range of axial strain levels in the fiber for model validation. The fiber axial strain was measured over the length of the fiber, from the free edge into the bulk, capturing the ineffective length region where strain builds up and plateaus. A good correlation has been obtained between the model results and the in-situ measurements of axial compression strain in the fiber. A key finding was the importance of including temperature-dependent resin modulus and that the contribution of crystallinity shrinkage to residual strain in the carbon fiber is relatively low. The model developed in this study is also compared to residual stress models in the literature which shows the importance of including the effects of crystallization and cooling rate on temperature and crystallinity-dependent modulus and resin shrinkage for accurate predictions.

Effective Platform Heating for Laser Powder Bed Fusion of an Al-Mn-Sc-Based Alloy.

Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treatment typically needed for LPBF Al-Sc alloys without compromising the mechanical properties. We systematically investigated the effects of LPBF platform heating at 200 °C on the residual stress relief, microstructure, and mechanical performance of a high-strength Al-Mn-Sc alloy. The results reveal that LPBF platform heating at 200 °C is sufficient to largely relieve the process-induced residual stresses compared to parts built on an unheated 35 °C platform. Meanwhile, the platform heating triggered the dynamic precipitation of uniformly dispersed (1.5-2 nm) Sc-rich nano-clusters. Their formation in a high number density (1.75 × 1024 m-3) resulted in a ~20% improvement in tensile yield strength (522 MPa) compared to the build on the unheated platform, without sacrificing the ductility (up to 18%). The improved mechanical properties imply that platform heating at 200 °C can strengthen the LPBF-synthesised Sc-containing Al alloys via in situ aging, which is further justified by an in situ measurement study revealing that the developing temperatures in the LPBF part are within the aging temperature range of Al-Sc alloys. Without any post-LPBF treatments, these mechanical properties have proven better than those of most Al-Sc alloys through long-time post-LPBF heat treatment.

Numerical study of the axial compression strength for nano-reinforced filament-wound riser considering curing residual stress

The present study is dedicated to the numerical analysis of progressive failure damage in multiangle nano-reinforced filament wound risers, with due consideration for process-induced residual stresses. Utilizing a multi-model coupling strategy, we introduce an integrated methodology predicated upon the time-varying material characteristics at a macroscopic scale. Initially, the process-induced residual stresses are anticipated via a sequential coupled numerical simulation methodology based on the time-varying attributes of the material. Subsequently, the curing residual stresses serve as the initial stress for the composite wound riser to prognosticate its axial compressive strength, grounded in the progressive damage model. Finally, the multiparametric effects on the strength properties of the composite risers are further investigated to reveal the intrinsic mechanism. The numerical findings evince that curing-induced residual stress retards both fiber and matrix failure while augmenting the axial compressive strength of the composite riser. Furthermore, the escalation in nanoparticle content diminishes the process-induced residual stresses. Additionally, the incorporation of 5 % nanoparticles yields an enhancement in the strength of the composite risers by approximately 16.26 % relative to those devoid of nanoparticles.

Recent advanced thermal interfacial materials: A review of conducting mechanisms and parameters of carbon materials

Understanding the effect of process-induced residual stresses on the final shape of fiber-reinforced polymer composites is critical due to their widespread use in structural applications. It is crucial for more dependable composite production, as residual stresses change the internal stress level of the composite component during service life, and residual shape distortions may prevent the part from achieving the required geometrical tolerances. Residual strains are the result of many interplays among physical processes, such as heat transfer, material flow, polymerization, crystallization, or heat transfer. Numerical process models must be constructed instead of time-consuming and inefficient trial-and-error procedures to design and optimize the composite manufacturing process digitally. This study aims to review the model creation and applications for predicting residual stresses and form distortions in composite manufacturing. Uses for both thermoset and thermoplastic composites are investigated in detail. Predictions of the process-induced deformations of laminated composite structures have been made using elastic constitutive models, such as a plane strain finite element model with a cure-hardening, instantaneous linear elastic constitutive model. to learn more about the factors that lead to shape distortion and how they can be reduced, such as by adjusting cure cycles, tool surfaces, geometry, or lay-up.

Dynamic 3D effects of single fiber tensile break within unidirectional composites including resin plasticity, residual stress, interfacial debonding and sliding friction

To study the dynamics of a single fiber tensile break within an S-Glass/epoxy composite and the associated effects of stress wave propagation in the fibers, interface and matrix, a 3D micromechanical Finite Element (FE) model with a hexagonal packing of parallel fibers is developed. The effects of a dynamic fiber break on energy dissipation associated with resin plasticity and interface debonding using cohesive traction laws are included. The 3D FE model also incorporates process-induced residual stresses that induces radial compression at the fiber-matrix interface due the mismatch in CTE and Poisson’s ratios between the fiber and matrix. During dynamic fiber failure where interface debonding occurs, radial compressive residual stresses lead to additional frictional energy dissipation in the debond region of the interface. A map of the dynamic stress concentration factor (SCF) values on the surface (along the axial as well as circumferential directions) of the fibers which are neighboring the fiber break is generated. A stability criterion based on an energy balance between elastic strain energy released by the fiber and energy dissipation (resin plasticity, interphase debonding and frictional sliding) is established to predict maximum fiber strength that initiates unstable debonding of the interface characteristic of axial splitting of the unidirectional composite loaded in tension. The FE modeling results also indicate that the dynamic fiber break introduces strain rates on the order of 106/s in the fiber and matrix, and up to 1012/s in the interphase.

Understanding the Interplay between Electrochemistry and Mechanics at Dendrite Tips in Sulfide and Oxide Electrolytes

Dendrite-induced short circuits threaten the deployment of solid-state batteries with metal anodes. Whether dendrites grow by internal chemical reduction of lithium or because of mechanical stresses has been a topic of debate. For both oxide and electrolyte electrolytes, we address this question by conducting operando microscopy to observe mechanical and electrochemical phenomena underlying dendrite growth. Here, we build upon the method from Athanasiou-Fincher et al. to observe stress-optic couplings around dendrite tips in thin oxide electrolytes[1]. Specifically, operando measurements of dendrite-induced stress fields are measured as a function of applied potential, and then the images are quantitatively analyzed to measure the mechanical driving forces underlying failure (i.e., the energy release rate). These operando measurements demonstrate a complex interplay between electrochemistry and mechanics. We develop a mechanistic framework to describe the observed behavior, discussed in juxtaposition with stress-corrosion cracking and linear elastic fracture mechanics. The resulting implications for electrolyte testing and design are discussed. Lastly, we assess whether mechanical stresses in electrolytes can be used to “steer” the dendrite growth directory. By dynamically applying mechanical loads to growing dendrites in LLZTO, we show that dendrite growth trajectory can be deflected to avoid short-circuit failures in oxide electrolytes[2]. Together, these results demonstrate a complex relationship between electrochemical and mechanical driving forces. Despite the observed complexity, processing-induced residual stresses can deflect dendrites and avert short circuits.[1] CE Athanasiou=, CD Fincher=, C Gilgenbach, WC Carter, H Gao, YM Chiang, BW Sheldon. Manuscript in preparation. “On the Use of Photoelasticity for Operando Dendrite-Induced Stress Quantification in Ceramic Electrolytes,” 2022 Materials Research Society Fall Conference; manuscript in preparation.[2] CD Fincher, CE Athansiou, C Gilgenbach, MJ Wang, BW Sheldon, WC Carter, YM Chiang, “Controlling dendrite propagation in solid-state batteries with engineered stress,” Joule, in press. DOIs: 10.1016/j.joule.2022.10.011

Evaluating Residual Stress in Carbon Fiber-Reinforced Polymer (CFRP) at Microscale Using Fiber Push-Out Experiment and Finite Element Modeling.

Microscale residual stress may develop during the manufacturing of Carbon Fiber-Reinforced Polymer (CFRP) composites and negatively affect apparent macroscale mechanical properties. Accordingly, accurately capturing residual stress may be essential in computational methods used for composite material design. This work presents a new data-driven methodology for the evaluation of microscale residual stress in CFRPs using fiber push-out experiments with in situ scanning electron microscopy (SEM) imaging. SEM images reveal significant through-thickness matrix sink-in deformation in resin-rich areas after nearby fibers are pushed out, which is attributed to the release of microscale process-induced residual stress. The sink-in deformation is measured experimentally, and a Finite Element Model Updating (FEMU) method is used to retrieve the associated residual stress. The finite element (FE) analysis includes simulation of the curing process, test sample machining, and fiber push-out experiment. Significant out-of-plane matrix deformation larger than 1% of the specimen thickness is reported and associated with a high level of residual stress in resin-rich areas. This work emphasizes the importance of in situ data-driven characterization for integrated computational materials engineering (ICME) and material design.

Investigations on the mechanical behavior of composite pipes considering process-induced residual stress

Hydrogen, as a clean energy source, has gained worldwide attention due to its high energy density and diverse manufacturing methods. Pipeline transportation is the most important way for long-distance transportation of hydrogen. However, hydrogen embrittlement due to hydride formation in metals will induce cracking in the pipeline structures. Composites pipes are good alternatives to metals as their excellent compatibility with hydrogen. This paper aims to carry out the preliminary design of composite hydrogen transportation pipelines. Firstly, the Thermo-Consolidation/Curing-mechanical analysis models for the thermosetting composites (T700/3501-6) and thermoplastic composites (T700/HDPE) were established, respectively. The process-induced residual stress of the composite pipelines was predicted by the models. Subsequently, a criterion of hydrogen leakage for the composite pipelines was proposed, and the load-bearing capacity analysis of the composite pipelines was carried out based on the progressive damage model. The simulation results emphasize that the predicted leakage pressure would be overestimated without considering the process-induced residual stress. The leakage pressures of composite pipelines with and without liner are calculated and compared, the results showed that the thermoplastic composite pipes with liner are the most suitable for hydrogen transportation.

Effect of carbon fiber reinforcement on dimensional variations of 3D printed polyamide-6 composites: A simulation study.

Due to material design and fabrication flexibility, additive manufacturing (AM) or 3D printing (3DP) processes and polymer composites have paved their way into several industrial sectors. The quality of 3D printed polymer composites is highly dependent on the reinforcement content of polymers and 3DP process parameters. Several experimental studies are performed to optimize the reinforcement contents and process parameters; however, exploring the numerical modeling and simulation techniques is vital to lower the research and development costs. In the study, the numerical simulations for the 3DP process were performed using Digimat® software for carbon fiber-reinforced polyamide-6 (PA6) composites fabricated via the fused filament fabrication (FFF) process to evaluate the effect of reinforcement content on deflections, warpages, and process-induced residual stresses. The FFF process simulations were performed to fabricate tensile testing coupons with pure PA6 and 10%-28% CF-reinforced PA6 composites. A significant impact of CF-reinforcement was observed on the deflections, warpages, and residual stresses. The maximum displacement of 4.518 mm and critical warpage of 3.012 was observed for pure PA6 material. However, with the addition of CF reinforcement, a maximum deflection of 3.369 mm and critical warpage of 2.246 was achieved for PA6 reinforced with 28% CF (PA6-CF28). The improved 3D printed specimen quality was acquired at the cost of increased residual stresses of 14.53 MPa compared to 11.75 MPa in pure PA6 specimen. The CF reinforcement significantly improved the 3DP manufacturing performance of PA6/CF composites, reducing deflections and warpages.

Warpage and residual stress analyses of post-mold cure process of IC packages

To improve the production yield rate, reliability is one of the important indicators of electronic packaging products. In past research, however, the influence of the fabrication process was rarely taken into consideration. In this thesis, mold flow analysis software Moldex3D is used to develop a series analysis procedure for IC package products. The effects of many factors, including process, structure, and materials were being taken into account. Especially for epoxy molding compound, namely EMC, is studied on its properties during the molding and post-mold cure (PMC) processes. This paper adopted P–V-T-C equations, which consider both volume shrinkage due to thermal mismatch and chemical shrinkage to predict the amount of warpage and residual stresses after the mold filling process. Next, dual shift factor model for viscoelastic analysis was used to model the PMC process and predict the amount of warpage and residual stresses after PMC. And the influence of different PMC process conditions and loading conditions on the warpage results is discussed. The residual stresses after PMC simulation are set as the initial conditions for reliability analysis and then the stress distribution after two thermal cycles is analyzed. It is observed that the deformed shape of the simulation and experiment results after PMC were consistent. Both are concave downwards. In comparison with experiment results, the error of warpage simulation results was between 10% and 50%. The biggest error was found in the short direction. During two thermal cycles, it is can be found that the maximum stress of the lead frame is 505.7 MPa and the location of the possible failure is at the top left of the die. In addition, when considering or not considering the process-induced residual stress in the thermal cycle analysis, the stress states are very different.

Very low levels of n-butyl acrylate comonomer strongly affect residual stress relaxation in styrene/acrylic random copolymer films

Processing-induced residual stresses in polymer films can cause microscopic defects and macroscopic dimensional changes. Although stress relaxation behavior of polymer films has been studied for several decades, little work has addressed random copolymers. We probed the residual stress relaxation in non-equilibrated random copolymer films of styrene (S) and n-butyl acrylate (nBA) using two optical techniques, ellipsometry and fluorescence. Both techniques show that incorporation of very low levels of nBA (2 mol% to 5 mol%) in S/nBA random copolymers can lead to dramatic increases in stress relaxation time of copolymer films relative to neat polystyrene films. For example, relative to polystyrene, the bulk-film stress relaxation time at 130 °C of 95/5 mol% S/nBA copolymer increases by factors of at least six as determined by ellipsometry and three as determined by fluorescence. Nanoconfined, 25-nm-thick films exhibit similar differences. This work provides implications for how low comonomer levels may deleteriously affect stress relaxation in polymer films, and we highlight that these findings are important for applications in which thin polymer films are required.

Benchmark of a probabilistic fatigue software based on machined and as-built components manufactured in AlSi10Mg by L-PBF

The possibility to obtain optimized components with a reduced weight is the main driver of space and aeronautic industries in seriously considering the metal additive manufacturing (AM) technology for production. Despite the incontrovertible advantages offered by this manufacturing technique, the material produced is usually affected by the presence of internal defects, a poor surface quality, and process-induced residual stresses. These features strongly affect the fatigue performance and reproducibility of AMed parts, limiting the adoption of deterministic criteria for fatigue assessment. A probabilistic approach is therefore needed for the analysis of critical and structural components. To this aim, a fully probabilistic finite element (FE) post-processor, ProFACE, was developed by part of the authors to assess the fatigue strength and critical locations of complex components in the presence of process-induced defects. A wide benchmark activity was supported by the European Space Agency (ESA) to test the software capabilities for the life prediction of components manufactured in AlSi10Mg by L-PBF. After tuning ProFACE parameters based on the results obtained on standard fatigue specimens, the software was used to estimate the fatigue life of the components obtaining a good description of the experimental dataset for both volumetric and surface defects. The software was then used to explore the effect of the variability of the most significant parameters affecting fatigue strength of AlSi10Mg AMed components.

Metal Forming-Induced Residual Stresses and Rule of Mixtures’ Prediction of Tensile Behavior of Bimetallic Wires

The present study investigates the tensile behavior of the two bimetallic composite wires Cu-Al and Fe-Al. The purpose is to understand the deviation their tensile strengths show from the Rule of Mixtures’ prediction. To that end, an experimental-numerical approach was adopted. Following tensile testing of the above cold-drawn composite wires, the manufacturing process (wire drawing) was simulated via finite element analysis. The prominent role of processing-induced residual stresses on the yield strength of cold-drawn products is known. Therefore, a discussion based on the axial tensile residual stress profile was developed. It was concluded that the higher-magnitude-near-surface tensile residual stresses in the Fe-Al wire causes its tensile curve to show a negative deviation from the Rule of Mixtures (RoM). The Cu-Al wire, on the contrary, exhibits a slight positive deviation.

Evaluation of process-induced residual stresses in orthogonal 3D woven composites via nonlinear finite element modeling validated by hole drilling experiments

Effects of matrix material constitutive model and presence of defects on development of manufacturing induced residual stresses are studied using Finite Element (FE) analysis in an orthogonal 3D woven composite. The residual stresses are assumed to arise from a difference in the coefficients of thermal expansion between the reinforcement and the matrix. Numerical results are compared with experimentally observed surface displacements resulting from blind hole drilling and measured via electronic speckle pattern interferometry. It is demonstrated that for accurate reproduction of the residual stress fields using FE modeling, viscoelastic matrix properties should be used and possible presence of cracks at the tow/matrix interface should not be neglected.

Evolution analysis of process-induced residual stress during the manufacture of diesel engine block

Evolution analysis of process-induced residual stress during the manufacture of diesel engine block

Optimization of process-induced residual stresses in automated manufacturing of thermoset composites

The present study investigates the effect of automated fiber placement process on the induced residual stresses in polymer-matrix composites. The robotic fiber placement is utilized to fabricate a total of 150 flat specimens. The specimens are then cured inside an autoclave. The incremental hole-drilling method is applied to estimate the maximum stresses induced in the laminates. Further, an optimization process is conducted based on the response surface method to minimize the generated stresses, while maintaining the highest production rate. A mathematical modeling of the relationship between the process parameters and the residual stresses is generated. The statistical analysis (ANOVA test) and sensitivity analysis are conducted to evaluate the generated model. The results show considerable effect on the stresses when changing the manufacturing process parameters due to the existence of in-situ curing and the change in material porosity. The optimization strategy could significantly decrease the stresses with maximizing the fabrication speed.