Inherent Strain Research Articles

Deformation Prediction of Aluminum Thick Plate Products Using Friction Stir Welding by Inherent Strain Method

Deformation Prediction of Aluminum Thick Plate Products Using Friction Stir Welding by Inherent Strain Method

Reducing hot tearing by grain boundary segregation engineering in additive manufacturing: example of an AlxCoCrFeNi high-entropy alloy

One major hindrance that alloy design for additive manufacturing (AM) faces nowadays is hot tearing. Contrary to the previous works which either try to reduce solidification range or introduce grain refinement, the current work presents a new approach of employing segregation engineering to alter the residual stress states at the interdendritic and grain boundary regions and consequently prevent hot tearing. Here, in situ Al alloying is introduced into an existing hot-cracking susceptible high-entropy alloy CoCrFeNi. It is found that within a certain range of compositions, such as Al0.5CoCrFeNi, the hot crack density was drastically decreased. During the solidification of this specific alloy composition, Al is firstly ejected from the primary dendritic face-centred cubic (FCC) phase and segregates into the interdendritic regions. Spinodal decomposition then occurs in these Al-enriched regions to form the ordered B2 NiAl and disordered body-centred cubic (BCC) Cr phases. Due to the higher molar volume and lower homologous temperatures of these B2/BCC phases, the inherent residual strain is accommodated and transformed from a maximum 0.006 tensile strain in CoCrFeNi to a compressive strain of ~0.001 in Al0.5CoCrFeNi. It is believed that this grain boundary segregation engineering method could provide a new pathway to systematically counteract the hot tearing problem in additive manufacturing of metals and alloys, using available thermodynamic and kinetic database information.

Effect of residual stress distribution in a log on lumber warp due to sawing: a numerical simulation based on the beam theory

When a squared lumber such as a beam and/or a bearer is produced from a log, they often show warps. Warp of the sawn lumber is practically not serious when the pith is located at the center of the cross-section, as in the lumber-with-pith, but causes serious problems in the lumber-without-pith. In the present study, a mechanical model was introduced to explain lumber warping based on beam theory, and a numerical simulation using the introduced model examined how the magnitude and type of the residual stress distribution would affect the warps of the lumbers sawn from the four-sided cants with various sizes and shapes in their cross-sections, and how the different sawing patterns would affect the production efficiency of the straight lumber, which is manufactured from the four-sided cant by quartering and subsequent correction sawing. As a result, the following suggestions were obtained. The warp of the sawn lumber is affected by the type and the magnitude of the inherent strain distribution in the log and furthermore by the cross-sectional shape and/or size of the four-sided cant. Production efficiency of the straight lumbers differs depending on the sawing patterns. In the present study, two types of sawing patterns (a) and (b) were assumed. The sawing pattern (a) gave better production efficiency than the sawing pattern (b) in the sense that straight lumbers are produced with higher volumes as well as with less variation in dimension of the cross-section.

On incorporating scanning strategy effects into the modified inherent strain modeling framework for laser powder bed fusion

Laser powder bed fusion ( L -PBF) has been the most popular metal additive manufacturing (AM) process thus far. However, residual deformation of the metal builds has been a significant issue. Laser scanning strategies adopted in the laser-assisted fabricating process have proved to have important influence on the residual stress and deformation. As the main contribution of this paper, the effects of different laser scanning strategies are incorporated into the modified inherent strain modeling (MISM) framework for the first time to enable accurate simulation for residual deformation of the L -PBF metal parts. Anisotropy in mechanical property of the fabricated components caused by the laser scanning strategies is also fully considered. For the rotational laser scanning strategies, only a small-scale representative volume element (RVE) is modeled by employing both the inherent strains and asymptotic homogenization. By employing the homogenized inherent strains, residual deformation can be predicted for the L -PBF manufactured components using different rotational scanning strategies accurately. Regarding the unidirectional parallel line scanning strategy, the directional inherent strain vector and orthotropic mechanical properties are used in the MISM-based layer-wise simulation. Good accuracy of the proposed framework is fully validated through comparing the simulated residual deformations with the experimental results for Inconel 718 parts produced by different laser scanning strategies. Thus, it is demonstrated that the effects of both parallel line and rotational laser scanning strategies have been successfully integrated into the MISM framework for predicting residual deformations of the L -PBF builds.

Nucleophilic Transformations of Lewis Acid-Activated Disubstituted Epoxides with Catalyst-Controlled Regioselectivity.

Due to their inherent ring strain and electrophilicity, epoxides are highly attractive building blocks for fundamental organic reactions. However, controlling the regioselectivity of disubstituted epoxide transformations is often particularly challenging. Most Lewis acid-mediated processes take advantage of intrinsic steric or electronic substrate bias to influence the site of nucleophilic attack. Therefore, the scope of many of these systems is frequently quite limited. Recent efforts to generate catalysts that can overcome substrate bias have expanded the synthetic utility of these well-known reactions. In this Perspective, we highlight various regioselective transformations of disubstituted epoxides, emphasizing those that have inspired the production of challenging, catalyst-controlled processes.

A comparative structural and photocatalytic study on SnO2 nanoparticles fabricated in batch reactor and microreactor

Controlling of scalability, agglomeration and monodispersity of nanoparticles are fundamental to be exploited in diverse application-based fields such as catalysis, sensing, drug delivery, bio-imaging etc. Currently fabrication of scalable, non-agglomerated and monodispersed nanoparticles by using continuous flow microreactor technology pay severe consideration as it offers a variety of advantages such as competent heat transfer and better intermixing of the reactants compare to the conventional batch reactor technology. In this contribution, we advance the prior art by introducing a straightforward, scalable, cost-effective and environmentally benign continuous flow microreactor synthetic approach for the fabrication of pristine SnO2 nanoparticles at a reasonably low reaction temperature and short reaction period. A PTFE (polytetrafluoroethylene)-based helical tubular microreactor is being exploited that comprises compact structure and offers enhanced heat and mass transport as well as better intermixing among the reactants. To discriminate this technique with the conventional batch reactor method herein SnO2 nanoparticles have been synthesized by using both techniques by maintain the identical reaction temperature and reaction time in both cases. Inherent crystal phases, lattice strain, lattice parameters and oxygen vacancies of the as-synthesized SnO2 nanoparticles have been investigated by using XRD/Rietveld analysis. High resolution (HR) -Transmission electron microscopy (TEM) is carried out to investigate the size, shape, crystallinity and agglomeration behaviour of the SnO2 nanoparticles fabricated by each method. SnO2 nanoparticles fabricated by microreactor technology demonstrate excellent activity in the degradation of methylene blue (MB) dye and good stability in response to irradiation. Results demonstrate that altering the synthetic technique amends both surface properties (extent of oxygen vacancies and defects at the surface) and optical band gaps and that these alterations are eventually reflected in the photocatalytic properties of the SnO2 nanoparticles.

Artificial thermal strain method: A novel approach for the analysis and fast prediction of the thermal distortion

Abstract Understanding the thermal distortion induced by arc welding, laser, or induction heating is a challenge in academia and industry. This study presents the artificial thermal strain (ATS) method which was modified from strain as boundary (SDB) method, based on inherent strain theory, and its equivalent mechanical model to analyse the distortion mechanism. Experiments and numerical simulation of multi-pass laser bending of alloy 304 L were conducted, wherein the various kinds of inherent strain distributions and the boundary of effective inherent strain were examined. Further, the mechanism of bending angle reduction under lower line energy was evaluated by considering the inherent strain redistribution at each pass. The results indicate that the bending angle reduction in multi-pass laser scanning is determined by the size of the inherent strain area at low line energy. Moreover, a simplified plastic finite element model based on the ATS method was developed to predict the welding deformation of plate curvature induced by parallel laser scanning. Additionally, only 210 elements and 7 s was cost to perform with the deformation analysis, which indicates that the ATS model is effective in predicting thermal distortion. Meanwhile, the ATS method can provide theoretical guidance and fast prediction for the actual thermal processing in large welded structure and additive manufacturing in the future.

Graphene as a nanoelectromechanical reference piezoresistor

Motivated by the recent prediction of anisotropy in piezoresistance of ballistic graphene along longitudinal and transverse directions, we investigate the angular gauge factor of graphene in the ballistic and diffusive regimes using highly efficient quantum transport models. It is shown that the angular guage factor in both ballistic and diffusive graphene between $0^{\circ}$ to $90^{\circ}$ bears a sinusoidal relation with a periodicity of $\pi$ due to the reduction of six-fold symmetry into a two-fold symmetry as a result of applied strain. The angular gauge factor is zero at critical angles $20^{\circ}$ and $56^{\circ}$ in ballistic and diffusive regimes respectively. Based on these findings, we propose a graphene based ballistic nano-sensor which can be used as a reference piezoresistor in a Wheatstone bridge read-out technique. The reference sensors proposed here are unsusceptible to inherent residual strain present in strain sensors and unwanted strain generated by the vapours in explosives detection. The theoretical models developed in this paper can be applied to explore similar applications in other 2D-Dirac materials. The proposals made here potentially pave the way for implementation of NEMS strain sensors based on the principle of ballistic transport, which will eventually replace MEMS piezoresistance sensors with a decrease in feature size. The presence of strain insenstive ``critical angle'' in graphene may be useful in flexible wearable electronics also.

Optimal simultaneous welding to minimise welding deformation of a general ship grillage structure

ABSTRACT A precise estimation of the welding deformation is an essential process in improving steel fabrication processes for building ships and offshore structures. This study validated the effect of the optimal simultaneous welding on the mitigation of welding displacements. Most previous studies on the optimised welding sequence for the reducing welding displacements have focused on one welding line at each order. However, in heavy industries, several welders or robotic welding machines generally work together to efficiently spend work time. Herein, inherent strain theory is introduced to calculate the complex mechanical behaviour during a welding operation using the elastic finite element method (FEM). Multipoint constraint function and the interface element theory are employed to consider the relationship of the different welded parts. The impact of the optimal simultaneous welding in the sequence on the reduction of welding displacement is validated by using the proposed numerical method in the present study.

Efficient prediction of cracking at solid-lattice support interface during laser powder bed fusion via global-local J-integral analysis based on modified inherent strain method and lattice support homogenization

Residual stress induced cracking at the solid-lattice support interface is often observed in laser powder bed fusion (LPBF) additive manufactured metals. Therefore, it is crucial to predict possible cracking before printing a part especially when it is large and complex. Previously, a method has been proposed to predict interfacial cracking during LPBF processing based on performing inherent strain simulations and evaluating J-integral at the critical point in a single model. However, that method is limited to application to small parts due to the high computational cost of explicit modeling of the lattice structure. In the present work, a more robust method based on the global-local technique is proposed to perform homogenized inherent strain analysis for the entire part (global) first, followed by J-integral analysis at several suspected critical locations (local). The proposed local-global analysis technique is validated both numerically and experimentally that it is both efficient and accurate in predicting interfacial cracking in as-built LPBF processed parts.

Stabilizing Ni‐Rich LiNi0.92Co0.06Al0.02O2 Cathodes by Boracic Polyanion and Tungsten Cation Co‐Doping for High‐Energy Lithium‐Ion Batteries

AbstractLayered nickel‐rich transition metal oxide has been receiving much attention as high‐energy‐density cathode materials for rechargeable lithium‐ion batteries. However, the severe capacity fading caused by bulk structural degradation of Ni‐rich cathodes during lithiation/delithiation obstructs their commercialization. Herein, we modify the LiNi0.92Co0.06Al0.02O2 (NCA92) cathode materials by W6+ cation and BO33− polyanion co‐doping to improve the structural stability and upgrade the electrochemical reversibility. The co‐doped NCA92 materials show remarkably improved cycling stability at 1 C with a capacity retention of 93.4 % after 100 cycles, whereas the pristine cathodes exhibit poor capacity retention of 53.0 % and suffer severe structural deterioration. Further studies reveal that the particle fragmentation resulted from the inherent internal strain and the structural degradation upon cycling can be effectively mitigated by W6+ cation and BO33− polyanion co‐doping. Besides, W6+ and BO33− co‐doping could enlarge the interlayer spacing of NCA92, thus increasing lithium‐ion diffusion coefficient, which is conducive to enhancing the rate capability. The present work demonstrates that cationic‐anionic co‐doping is an effective strategy to maintain the structural stability of Ni‐rich cathode materials, and it promotes the development of stable cathode materials for high energy density lithium‐ion batteries.

Modeling the non-linear rheological behavior of magnetorheological gel using a computationally efficient model

Magnetorheological (MR) gel is a novel generation of smart MR material, which has the inherent hysteretic properties and strain stiffening behaviors that are dependent on applied excitation, i.e. magnetic field. The main challenge for the application of the MR gel is the accurate reproduction of the above characteristics by a computationally efficient model that can predict the dynamic stress-strain/rate responses. In this work, parametric modeling on the non-linear rheological behavior of MR gel is conducted. Firstly, a composite MR gel sample was developed by dispersing carbon iron particles into the polyurethane matrix. The dynamic stress-strain/rate responses of the MR gel are obtained using a commercial rheometer with strain-controlled mode under harmonic excitation with frequencies of 0.1 Hz, 5 Hz and 15 Hz and current levels of 1 A and 2 A at a fixed amplitude of 10%. Following a mini-review on the available mathematical models, the experimental data is utilized to fit into the models to find the best candidate utilizing a genetic algorithm. Then, a statistical analysis is conducted to evaluate the model’s performance. The non-symmetrical Bouc–Wen model outperforms all other models in reproducing the non-linear behavior of MR gel. Finally, the parameter sensitivity analysis is employed to simplify the non-symmetrical Bouc–Wen model and then the parameter generalization is conducted and verified for the modified non-symmetrical Bouc–Wen model.

A computational phase transformation model for selective laser melting processes

Selective laser melting (SLM) has gained large interest due to advanced manufacturing possibilities. However, the growing potential also necessitates reliable predictions of structures in particular regarding their long-term behaviour. The constitutive and structural response is thereby challenging to reproduce, due to the complex material behaviour. This motivates the aims of this contribution: To establish a material model that accounts for the behaviour of the different phases occurring during SLM but that still allows the use of (basic) process simulations. In particular, the present modelling framework explicitly takes into account the mass fractions of the different phases, their mass densities, and specific inelastic strain contributions. The thermomechanically fully coupled framework is implemented into the software Abaqus. The numerical examples emphasise the capabilities of the framework to predict, e.g., the residual stresses occurring in the final part. Furthermore, a postprocessing of averaged inelastic strains is presented yielding a micromechanics-based motivation for inherent strains.

Numerical prediction of deformation in thin-plate welded joints using equivalent thermal strain method

Large welding-induced distortions are inevitably generated in a thin-plate welded joint due to its weak stiffness. In this study, an equivalent thermal strain method based on inherent strain theory is proposed to predict the welding deformation of thin plates. An artificial temperature and an orthotropic thermal expansion coefficient are adopted to directly simulate the welding shrinkage and bending behavior of the cooling phase in all directions. To describe the distribution of transverse inherent strain through thickness more accurately, a composite shell element is employed, which can divide the thickness into multiple layers and set different material properties. A three-dimensional (3D) thermo–elastic–plastic finite element method (TEP-FEM) model is also developed to simulate the welding process of a thin plate and compute the inherent strain. Moreover, an experiment was performed to verify the accuracy of the numerical model. Comparing the results from experimental data, TEP-FEM, and the proposed method, it is discovered that the new method can predict the deformation of a thin-plate welded joint with good computational accuracy.

Numerical Prediction of Residual Deformation and Failure for Powder Bed Fusion Additive Manufacturing of Metal Parts

ABSTRACTResidual deformation and failure are two critical issues in powder bed fusion (PBF) additive manufacturing (AM) of metal products. Residual deformation caused by the non-uniform residual stress distribution dramatically affects the quality of AM product and can result in catastrophic failure in operation. Therefore, the development of an effective numerical approach to predict residual deformation and failure characteristics of AM product is always a major concern in industrial applications.In this paper, a numerical approach in predicting residual distortion, stress and failure in AM products is presented. The conventional inherent strain method used in welding process is modified to consider the specific characteristic of AM process, such as the influences of reheating and scanning pattern. This approach consists of three simulation steps including a detailed process simulation in small-scale, a onetime static mechanical finite element analysis in part-scale, and a material failure analysis. First, the inherent strains are calculated from a thermo-mechanical process simulation in small-scale, which considers AM process parameters, such as laser power, scanning speed and path. The physical state in deposited materials including powder, liquid and solid states are taken into account in the simulation by specifying the solidus and liquidus temperature and corresponding material properties. Then the inherent strains are applied layer by layer to the part-scale simulation, where the residual distortion and stress can be predicted efficiently. Finally, a Lagrange particle method is utilized to study the failure characteristics of AM products. Numerical examples are studied to investigate the effectiveness and applicability of present approach.

Sensitivity analysis and lattice density optimization for sequential inherent strain method used in additive manufacturing process

Compensation of the thermal distortion that occurs during the fabrication process is an important issue in the field of metal additive manufacturing. Considering the problem in forming a lattice structure inside an object to reduce the thermal distortion, we developed a lattice volume fraction distribution optimization method. Assuming that the linear elastic problem is solved using the finite element method (FEM), an inherent strain method applying a layer-by-layer process utilizing the element activation during the FEM is formed as a recurrence relation, and the sensitivity of an objective function is derived based on the adjoint method. The unit lattice shape is a simple cube with a cube or a sphere-shaped air hole, and its distribution is optimized by considering the minimum thickness of the wall surrounding it as a design variable. The effective stiffness tensor of the lattice is derived using a homogenization method. The functions of the effective properties with respect to the design variables are approximated through polynomial functions. The optimization problem is formulated as an unconstrained minimization problem. The design variables are optimized using the method of moving asymptotes. Herein, the validity of the proposed method is discussed based on quasi two-dimensional and three-dimensional numerical studies including a re-analysis through full-scale thermo-mechanical analysis.

Numerical Prediction of Welding Distortion Considering Gravity Force on General Ship Grillage Structure by Elastic Finite Element Method Using Inherent Strain

The accurate numerical prediction of welding deformation is important to improve the structural safety of ships and offshore structures in heavy industries. The precise reflection of the real working condition in the numerical prediction is an essential factor to improve its result. In the present study, the effect of the gravity force on numerical prediction of the optimal welding sequence of a general ship grillage structure was validated with the introduction of a new boundary condition in which the structure is placed over rails. Additionally, the direction of the gravity force of welded structures could be changed at the final assembly process according to the production plan. The effect of the gravitational orientation on the final welding displacements was also investigated herein. The elastic finite element method using the inherent strain, interface element, and multipoint constraint function was introduced to analyze the welding deformation. This study validated the influence of the gravity force on the numerical prediction of welding displacements in a general ship grillage structure.

Age-hardening response of AlMgZn alloys with Cu and Ag additions

A recurrent challenge with aluminum alloys is their longstanding trade-off between mechanical strength and formability. Recently recyclability has put further pressure on the development of single-alloy concepts for solving this challenge. This study addresses an AlMg-based system featuring additional elements to facilitate age-hardening but retaining a high Mg content for inherent pronounced strain hardening as a potential candidate. Age-hardening was enabled by T-phase based precipitation in the commercial alloy EN AW-5182 via the addition of 3.5 wt.% of Zn. The investigation shows that minor additions of Cu and Ag enhance and accelerate it. The study also compares single-step and double-step artificial aging. Hardness and tensile testing and scanning transmission electron microscopy methods were deployed to characterize the alloys investigated, mechanically and microstructurally. An alloy with added Zn, Cu and Ag showed improved strain hardening and reduced serrated flow in the soft state, while exhibiting an age-hardening response of up to 326 MPa in yield strength leading to an ultimate tensile strength of 550 MPa in peak-aged condition. The study discusses the evolution of the microstructure during artificial aging in the light of Zn, Cu and Ag additions and their effect on the precipitation process.

Validation of Efficient Welding Technique to Reduce Welding Displacements of Ships using the Elastic Finite Element Method

Welding is the most convenient method for fabricating steel materials to build ships and offshore structures. However, welding using high heat processes inevitably produces welding displacements on welded structures. To mitigate these, heavy industries introduce various welding techniques such as back-step welding and skip-step welding. These techniques effect on the change of the distribution of high heat on welded structures, leading to a reduction of welding displacements. In the present study, various cases using different and newly introduced welding techniques are numerically simulated to ascertain the most efficient technique to minimize welding displacements. A numerical simulation using a finite element method based on the inherent strain, interface element and multi-point constraint function is introduced herein. Based on several simulation results, the optimal welding technique for minimizing welding displacements to build a general ship grillage structure is finally proposed.

Reconstructing a 3D map of longitudinal residual stress by combining the inherent strain theory and contour method

Reconstructing a 3D map of longitudinal residual stress by combining the inherent strain theory and contour method