Stress In Additive Manufacturing Research Articles

Estimation of stresses in 1D structures via inverse wavenumber analysis

The ANR ITHERATE project proposes to develop identification procedures of residual stresses in additive manufacturing via in-situ and non destructive methods using the wide band wave response of structures. This work presents a proof on concept on one-dimensional waveguides, as a preliminary results to more complex configurations. An original experimental setup is implemented using a cylindrical lens to optically amplify the vibrations of the structure in the transverse direction, allowing to resolve the wave propagation with a high-speed low-resolution camera. The dispersion of the wave velocity with the frequency, obtained via high-resolution wavenumber analysis (HRWA), is compared to predictions given by the acousto-elastic theory. In particular, the effects of the quasi-static initial stress and the elasticity of the material can be separated and estimated seperately via an inverse method that is independent from the boundary conditions and applied loads. Interestingly, this wave-based estimation does not necessitate an a-priori knowledge of the material constitutive law, overcoming the limitations of most stress estimation techniques of the state of the art, that are based on a measurement of the strain. Finally, perspectives for the generalization of the method to more complex situations, as plates under thermal loads, will be presented.

Development of Diffraction Research Methodologies for Mediloy S-CO Alloy Speciments Made Using LPBF Additive Manufacturing

Abstract This study focuses on the application and improvement of diffraction measurement methodologies for the optimization of manufacturing parameters of CoCr alloy components made by additive manufacturing (AM) – particularly for Mediloy S-Co alloy specimens made using Laser Powder Bed Fusion (LPBF) additive manufacturing. We measured the phase composition of specimens obtained in AM processes, the measurement of residual stresses resulting from the manufacture of these printed parts, as well as the effectiveness of stress relaxation through the use of heat treatments dedicated to this type of material. Findings reveal several insights into how printing strategies affect the porosity and residual stresses in additive manufacturing. Specimens with higher porosity, particularly those created using specific strategies that resulted in lower energy densities, exhibited lower residual stresses. Notably, printing direction and energy density were found to significantly affect the mechanical stresses within the specimens, with directional choices playing a critical role in the final properties of the parts. Additionally, our findings underscore the complex relationship between various printing parameters and the development of mechanical stresses, highlighting the impact of adjustments in printing strategy on the properties of printed components.

Efficient prediction of residual stress in additive manufacturing based on semi-analytical solution

Efficient prediction of residual stress in additive manufacturing based on semi-analytical solution

A Review on Thermal Modelling of Residual Stresses during Additive Manufacturing

Additive Manufacturing (AM) has received interest since it is simpler to manufacture complicated 3D component without the requirement for casting moulds than convective fabrication. AM has a lot of significance in fields like aerospace, medicine, and more to make parts of any kind of complex shape. Since the finished products are subjected to repeated cycles of heating and cooling, there will always be some residual stresses present in them. During layer-over-layer deposition, the large difference in temperature between the layers causes residual stresses, which hurt the performance of the products. As far as the author’s knowledge, there is no thorough review of the thermal modelling of residual stress in AM. In this review paper, the goal is to first get a good understanding of how residual stresses are developed, and then to look at how different models measure them. So, residual stresses can be seen as a key factor in controlling costs, performance, and quality standards of the finished component. This paper does a thorough review of the field to give engineers and researchers up-to-date information and advice about residual stresses.

Evolution, Control, and Mitigation of Residual Stresses in Additively Manufactured Metallic Materials: A Review

Powder bed fusion (PBF) and directed energy deposition (DED) are the two major types of metal additive manufacturing (AM) processes, in which significant residual stresses could be generated in the as‐deposited materials and in turn affect part quality and performance. Therefore, how to control and mitigate residual stress has been a most pressing challenge for metal AM. Herein, the significant efforts made in literature to address this challenge for both PBF and DED processes are reviewed. The extensive survey covers the formation of residual stress in AM, influence of various AM process parameters, modeling techniques for predicting residual stresses, and post and in situ treatments for mitigating unfavorable residual stress distributions. More importantly, a critical analysis is provided to discuss the research gaps and opportunities, such that more exciting research will be stimulated to address the outstanding issues in this area and improve the quality and service life of AM‐produced components. As a result, once being better equipped with residual stress control knowledge and tools, the industry will be more confident in adopting metal AM techniques.

Correlation Between Printing Parameters and Residual Stress in Additive Manufacturing: A Numerical Simulation Approach

Abstract Fused Deposition Modeling (FDM) is a widely used 3D printing technology that can create a diverse range of objects. However, achieving the desired mechanical properties of printed parts can be challenging due to various printing parameters. Residual stress is a critical issue in FDM, which can significantly impact the performance of printed parts. In this study, we used Digimat-AM software to conduct numerical simulations and predict residual stress in Acrylonitrile Butadiene Styrene (ABS) material printed using FDM. We varied six printing parameters, including printing temperature, printing speed, and infill percentage, with four values for each parameter. Our results showed that residual stress was positively correlated with printing temperature, printing speed, and infill percentage, and negatively correlated with layer thickness. Bed temperature did not have a significant effect on residual stress. Finally, using a concentric infill pattern produced the lowest residual stress. The methodology used in this study involved conducting numerical simulations with Digimat-AM software, which allowed us to accurately predict residual stress in FDM-printed ABS parts. The simulations were conducted by systematically varying six printing parameters, with four values for each parameter. The resulting data allowed us to identify correlations between residual stress and printing parameters, and to determine the optimal printing conditions for minimizing residual stress. Our findings contribute to the existing literature by providing insight into the relationship between residual stress and printing parameters in FDM. This information is important for designers and manufacturers who wish to optimize their FDM printing processes for improved part performance. Overall, our study highlights the importance of considering residual stress in FDM printing, and provides valuable information for optimizing the printing process to reduce residual stress in ABS parts.

Topology optimization of continuous fiber-reinforced composite (CFRC) structures considering the residual stress in additive manufacturing

This work proposes a topology optimization method for continuous fiber-reinforced composite (CFRC) structures with additive manufacturing (AM), which realizes the concurrent optimization of material layout and fiber orientation. The residual stress caused by AM process is constrained to avoid the failure of warpage and distortion. The inherent strain method (ISM) is applied to simplify the calculation of residual stress, the Tsai–Wu criterion and P-norm are incorporated to realize structural failure prediction and local constraint aggregation. Several typical instances are adopted to verify the effectiveness of proposed method, which provides a novel solution for the optimization of CFRC structures fabricated by AM.

Modeling the thermomechanical processes and residual stresses in additive manufacturing of metallic components

AbstractIn additive manufacturing of metallic components and fusion welding, undesirable deformations and residual stresses are common drawbacks, which directly influence the performance and functionality of the manufactured components. In this work, a thermomechanical continuum model is developed by using the phase‐field method to track the evolution of the melting/remelting‐solidification occurring due to the incident of localized heat input sources, e.g, by means of a laser heat source. The result of the thermal analysis is then employed for the mechanical analysis to predict the residual stresses. In the thermal and mechanical analysis, the thermomechanical properties are considered to evolve with the phase‐field variable. In addition, a scalar‐valued history variable is introduced to distinguish between consolidated and loose powder materials. This enables single‐track additive manufacturing simulations with a possible extension to multi‐layer and multi‐track simulations. To verify and validate the modeling approach, the coupled system of equations is implemented in the open‐source FEniCS project and a numerical example for additive manufacturing is solved and compared qualitatively and quantitatively with reference results from the literature.

Dislocation structures formation induced by thermal stress in additive manufacturing: Multiscale crystal plasticity modeling of dislocation transport

The motion of dislocations governs the plastic deformation of crystalline materials, which in turn determines the mechanical properties. The complex thermal history, large temperature gradients and high cooling rates during the process of additive manufacturing (AM) can induce high dislocation density and unique dislocation structures in the material. The origin of these dislocation structures and their stability during mechanical loading are debated. A novel temperature dependent continuum dislocation dynamics (CDD) model is developed, in which four state variables are used for each slip system representing the total dislocation density, edge and screw geometrically necessary dislocation densities and dislocation curvature. The CDD model is fully coupled with a crystal plasticity solver, which captures the plastic deformation induced by the dislocation motion. A hybrid continuous and discontinuous Galerkin formulation is developed to accurately reproduce the dynamics of highly discontinuous dislocation density fields that are typical of dislocation structures. A multiscale modeling approach is used, in which the thermally induced deformation in specific grains of a polycrystal is extracted from larger scale crystal plasticity simulations of the laser powder-bed fusion process, and is then used for single crystal scale dislocation dynamics simulations. Simulation results reveal the dynamics of dislocation structure formation in grains at different positions during laser scanning and cooling stages. The effect of the cyclic thermal stress during multi-layer AM fabrication is also investigated. The simulations provide a new perspective on the specific conditions that should be satisfied during AM process for the formation of stable dislocation structures.

Development of a calibration technique of a finite element model for calculating compensation of deformations from the action of residual stresses in additive manufacturing

In additive manufacturing, it is necessary to take into account and compensate for the warping of the part due to the action of residual stresses. One of the effective fast methods for calculating the magnitude of deformations in CAE-systems is mechanical finite element analysis, which does not require numerous iterations. To ensure the accuracy of calculations in CAE-systems, they must be calibrated on special samples. The paper proposes a method of such calibration on annular samples for the process of direct metal deposition (DMD), the result of which are the values of internal deformations necessary to calculate the deformations of parts during DMD. With the help of the Simufact Additive CAE system, a digital model of the DMD process was designed and the effect of residual stresses was simulated. Based on the obtained results of comparison with full-scale samples, the calculated parameters have been adjusted, which can be applied to optimize the geometry of the workpiece parts, taking into account the features of the DMD process.

Внутрішні залишкові напруження в адитивному виробництві. (Огляд)

Additive manufacturing (AM) is a modern set of technologies that make it possible to quickly and qualitatively create products with a unique geometry that are impossible or difficult to manufacture by traditional methods of production. Currently, researchers pay attention to two major areas, namely AM quality systems and the search for new regularities in already well-known materials that were produced in a traditional way. Internal residual stresses in polycrystalline materials are classified according to three main classes, namely: stress of type I (macrostress), type II (microstress) and type III (intracrystalline residual stress). Accumulation of internal residual stresses generated during the manufacturing process as a result of local heating and cooling (cooling rates from 103 to 108 K/s) can cause damage and possible failure of parts during service. Thus, the reduction of residual internal stresses is considered one of the most urgent and important problems in the field of AM. As a result of the analysis of the works, it was established that during the process of manufacturing parts with the help of SLP, it is actually characteristic that tensile internal stresses develop on the surfaces, which are balanced by compressive internal stresses in the volume. Since the research was carried out on samples of a simple shape, the obtained results are difficult to compare with the details of products of a complex geometric shape, which have significant changes in the geometric dimensions of the cross-section.

Effect of preheating during laser metal deposition on the properties of laminated bending dies

Metal-laminated tooling provides a fast and cheap manufacturing concept. In this study, laser metal deposition (LMD) is used for reducing and eliminating the stair step effect in a metal-laminated bending die. Preheating could decrease the undesired residual stresses in additive manufacturing, thus a systematical analysis of the effect of preheating of the laminae on the surface quality and mechanical properties of the bending die is performed. Ferritic steel sheets (S355 MC) with a thickness of 2 mm are laser cut and stacked up to manufacture the laminated bending die with a radius of 6 mm. The sheets are joined and the stair steps are filled with LMD with stainless steel powder 316L-Si. The initial temperature of the tool sheets (substrates), beside room temperature, is elevated up to 300 °C. The effect of the preheating on the surface roughness, shape deviation, hardness, and residual stresses of the die are investigated. The mean height of the surface increases by 59% at elevated temperatures. However, the tensile residual stress parallel to the weld direction at the middle of the deposited area decreases only around 25%. The functionality of the forming tools manufactured by this method is proven by bending of DC06 and HC380LA sheets.

Analysis of the residual stress in additive manufacturing of Ti-6Al-4V

Minimizing the residual stress build-up in metal-based additive manufacturing plays a pivotal role in selecting a particular material and technique for making an industrial part. However, there are still some limitations for this application, especially the unfavourable final shape and undesired macroscopic properties of metallic parts built in additive manufacturing systems. The distortion or crack due to the residual stress of these parts leads usually to severe problems for some kinds of metal additive manufacturing technology. Therefore, it is necessary to study the distribution of residual stress in the process, which can provide an important reference for the process control of laser cladding. Taking Ti-6Al-4V (TC4) alloy as the research object, a nonlinear sequential thermal mechanical coupling model is established by combining the finite element numerical simulation and experimental deformation measurement. A least squared cost function between the Finite Element Cladding model and the experimental deformation measurement is proposed, and the finite element model updating method is constructed to retrieve the heat source parameters of TC4 Alloy in laser cladding. By comparing the numerical results with the experiment, the rationality of the inversion results of heat source parameters is verified. After that, the stress near the cladding layer is analyzed, and the influence of temperature field on the mechanical field distribution is further studied through the affects of stress distribution.

Residual Stresses Control in Additive Manufacturing

Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM), since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered. To date, several strategies based on reducing the thermal gradients have been developed to mitigate the manifestation of residual stresses in AM; however, how to choose the optimal processing plan is still unclear for AM designers. In this regard, the concept of the yield temperature, related to the thermal deformation and the mechanical constraint, plays a crucial role for controlling the residual stresses, but it has not been duly investigated, and the corresponding approach to control stresses is also yet lacking. To undertake such study, a three-bar model is firstly used to illustrate the formation mechanism of the residual stress and its key causes. Next, an experimentally calibrated thermomechanical finite element model is used to analyze the sensitivity of the residual stresses to the scan pattern, preheating, energy density, and the part geometry and size, as well as the substrate constraints. Based on the numerical results obtained from this analysis, recommendations on how to minimize the residual stresses during the AM process are provided.

A bead sequence-driven deposition pattern evaluation criterion for lowering residual stresses in additive manufacturing

Deposition patterns can significantly influence the distribution and magnitude of residual stress in additively manufactured parts. Time-consuming thermal-mechanical simulations and costly experimental studies are often required to identify the optimal patterns. A simple and generic method to evaluate and optimize the deposition pattern for the purpose of minimizing residual stress is in urgent need. To overcome the shortcomings of the current practice, here we propose a novel pattern evaluation criterion. Starting from the discretization of the deposition pattern by a series of sequence numbers, we introduce two interconnected concepts. The first is called “equivalent bead sequence number” which can be physically interpreted as an index of the localized heat accumulation induced by the deposition process. Based on this point-wise “equivalent bead sequence number”, the second concept called “bead sequence number dispersion index” which can be considered as a representation of the global heat accumulation gradient, is proposed as a criterion for assessing the resulting residual stress. The temperature fields and residual stresses of a square part with six typical deposition patterns predicted by thermo-mechanical finite element simulations are used to develop and verify the proposed criterion. It is found that the “equivalent bead sequence number” of a given pattern is closely correlated to the distribution of the associated temperature and residual stress. More interestingly, both the highest equivalent and highest maximum principal residual stress of a pattern linearly increase with its corresponding value of “bead sequence number dispersion index”. Guided by this relation, two new patterns with lower residual stress are developed and evaluated. Among all the patterns considered, the so-called S pattern shows the lowest value of the “bead sequence number dispersion index” which corresponds to the lowest residual stress. The proposed sequence-driven approach provides a new candidate for real-time evaluation and optimization of the deposition pattern in additive manufacturing.

Crystal plasticity model of residual stress in additive manufacturing using the element elimination and reactivation method

Selective laser melting is receiving increasing interest as an additive manufacturing technique. Residual stresses induced by the large temperature gradients and inhomogeneous cooling process can favour the generation of cracks. In this work, a crystal plasticity finite element model is developed to simulate the formation of residual stresses and to understand the correlation between plastic deformation, grain orientation and residual stresses in the additive manufacturing process. The temperature profile and grain structure from thermal-fluid flow and grain growth simulations are implemented into the crystal plasticity model. An element elimination and reactivation method is proposed to model the melting and solidification and to reinitialize state variables, such as the plastic deformation, in the reactivated elements. The accuracy of this method is judged against previous method based on the stiffness degradation of liquid regions by comparing the plastic deformation as a function of time induced by thermal stresses. The method is used to investigate residual stresses parallel and perpendicular to the laser scan direction, and the correlation with the maximum Schmid factor of the grains along those directions. The magnitude of the residual stress can be predicted as a function of the depth, grain orientation and position with respect to the molten pool. The simulation results are directly comparable to X-ray diffraction experiments and stress–strain curves.

Investigating the residual stress in additive manufacturing of repair work by directed energy deposition process on SS316L hot rolled steel substrate

The aim of this research is to conduct a systematic investigation of the directed energy deposition of stainless steel 316L powder in order to evaluate and investigate residual stresses caused by the laser deposition process. In metal additive manufacturing, predicting residual stress is critical for ensuring the quality of the fabricated part. Stainless steel 316L cubes were prepared by directed energy deposition process on hot rolled steel substrate for the repair work purpose. To evaluate the effect of the residual stress of sandwich samples, which can be compressive or tensile. Also, to investigate the residual stresses developed on the interface region for between the directed energy deposition, and hot rolled steel sample. Finally, it is found that the residual stresses on the hot rolled steel surfaces in the compressive stress (-855 MPa), on other hand compressive stress has obtained in the directed energy deposition surface (-822 MPa). The residual stresses were determined experimentally using X-Ray Diffraction (XRD) residual stress measurements.

Investigating the residual stress in additive manufacturing of combined process in powder bed fusion and directed energy deposition

Residual stress is the secondary stress that still exists even after removing all loads. Parts manufactured by directed energy deposition on powder bed fusion contain residual stress, which can be compressive or tensile. When performing directed energy deposition processing on a powder bed fusion substrate, if these residual stresses are not considered, it may cause stress fatigue cracks, deformation, corrosion cracks, design examples, and premature component failure. Residual stress calculation is very important for deformation analysis, life prediction, and evaluation of failure causes. The purpose of this study is to understand the residual stress evaluation of powder bed fusion substrate additives made of stainless steel 316L powder in directed energy deposition treatment. In order to evaluate the residual stress value in additive manufacturing, the value can be obtained by X-ray diffraction technique.

A fast matrix-free elasto-plastic solver for predicting residual stresses in additive manufacturing

Process planning for additive manufacturing (AM) today relies heavily on multi-physics, multi-scale simulation. The focus of this paper is on one aspect of AM simulation, namely, part-level elasto-plastic simulation for residual stress and distortion predictions. This is one of the crucial steps in AM process optimization, but is computationally expensive, often requiring the use of large computer clusters.The primary bottleneck in elasto-plastic simulation is the repeated solution of large linear systems of equations. While there is a wide range of linear solvers, most cannot exploit the unique structured nature of the mesh underlying AM simulation. Here, we revisit a specific matrix-free solver, namely rigid-body deflated solver that has been successfully deployed for solving large linear elastic problems in such scenarios. The salient feature of this solver is that the stiffness matrix is never assembled, thereby reducing the memory requirements significantly, leading to large computational gains.The objective of this paper is to extend the above solver to elasto-plasticity by efficiently updating the element tangent stiffness matrices, and the corresponding deflation matrix. The performance of the proposed method is evaluated on a benchmark problem using multi-core CPU and GPU architectures, and compared against ANSYS. Then, part-level residual stresses and distortion are predicted using the proposed solver. The present work is restricted to associative plasticity with von-Mises yield criteria, but can be extended to other plasticity models.

A new method to estimate the residual stresses in additive manufacturing characterized by point heat source

Residual stress in additive manufacturing (AM) is one of the key challenges in terms of structural integrity and the finish quality of printed components. Estimating the distribution of residual stresses in additively manufactured components is complex and computationally expensive with full-scale thermo-mechanical FE analysis. In this study, a point heat source is utilized to predict the thermal field and residual stress distribution during the manufacturing processes. Numerical results show that the residual stress at a single material point can be expressed as a function of its spatial position and the peak nodal temperature it has experienced during thermal cycles. The distribution of residual stress can be divided into three segments according to the peak nodal temperature. The peak nodal temperature only depends on the heat flux and the distance to the point heat source center. A semi-analytical approach to predict the peak nodal temperature and residual stresses, once the heat flux is known, is proposed. The proposed approach is further validated by a numerical case study, and a very good agreement has been achieved. Compared with traditional thermo-mechanical FE analysis of additive manufacturing, the proposed method significantly improves the computational efficiency, showing great potential for prediction of residual stresses and distortion.