scholarly journals The Computation and Measurement of Residual Stresses in Laser Deposited Layers

2003 ◽  
Vol 125 (3) ◽  
pp. 302-308 ◽  
Author(s):  
S. Finnie ◽  
W. Cheng ◽  
I. Finnie ◽  
J. M. Drezet ◽  
M. Gremaud
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Metal Forming ◽  
Steel Substrate ◽  
Plane Deformation ◽  
Compressive Stresses ◽  
Out Of Plane ◽  
Simulation And Experiment ◽  
Melted Material

Laser metal forming is an attractive process for rapid prototyping or the rebuilding of worn parts. However, large tensile stress may arise in layers deposited by laser melting of powder. A potential solution is to preheat the substrate before and during deposition of layers to introduce sufficient contraction during cooling in the substrate to modify the residual stress distribution in the deposited layers. To demonstrate the value of this approach, specimens were prepared by depositing stellite F on a stainless steel substrate with and without preheating. Residual stresses were computed by numerical simulation and measured using the crack compliance method. For non-preheated specimens simulation and experiment agreed well and showed that extremely high residual tensile stresses were present in the laser melted material. By contrast, pre-heated specimens show high compressive stresses in the clad material. However, in this case the numerical simulation and experimental measurement showed very different stress distribution. This is attributed to out of plane deformation due to the high compressive stresses which are not permitted in the numerical simulation. A “strength of materials” analysis of the effect of out of plane deformation was used to correct the simulation, Agreement with experimental results was then satisfactory.

How to Combine the Parameters of the Yield Criteria and the Hardening Law

2013 ◽  
Vol 554-557 ◽  
pp. 1195-1202 ◽  
Author(s):  
Pedro Prates ◽  
M.C. Oliveira ◽  
Nataliya A. Sakharova ◽  
José Valdemar Fernandes
Keyword(s):  
Numerical Simulation ◽  
Metal Forming ◽  
Forming Process ◽  
Accurate Identification ◽  
Material Parameters ◽  
Hardening Law ◽  
Out Of Plane ◽  
Simulation Results ◽  
The Hill ◽  
Constitutive Parameters

The numerical simulation of sheet metal forming processes needs the accurate identification of the material parameters, for a given constitutive model. This identification can follow different methodologies and different sets of experimental data can be used, which lead to distinct sets of material parameters. In order to accurately compare the results of several methodologies, it is necessary to guarantee uniformity of their presentation. In this work, the correspondence between sets of parameters of the Hill’48 criterion is explored. The meaning of the “isotropic values” of the parameters associated with the out-of-plane stresses components is discussed and a required condition is proposed, in order to properly compare numerical simulation results obtained by using different input sets of constitutive parameters, identified by different procedures. Finite element simulations of complex shaped forming process, involving strain-path changes, are carried out in order to support the analysis.

Influence of Friction on Springback of Quadrangle Parts Bending

2011 ◽  
Vol 217-218 ◽  
pp. 619-624
Author(s):  
Chun Jian Su ◽  
Guang Heng Zhang ◽  
Su Min Guo ◽  
Li Gao ◽  
Rui Ma
Keyword(s):  
Numerical Simulation ◽  
Friction Coefficient ◽  
Sheet Metal ◽  
Analytical Model ◽  
Elastic Deformation ◽  
Approximate Calculation ◽  
Plane Deformation ◽  
Theoretical Formula ◽  
Simulation And Experiment ◽  
Springback Angle

Springback is the prominent problem in bending forming of sheet metal, which is difficult to control accurately, especially for the complex shaped bending parts. The change of friction conditions will cause significant changes of bending springback amount. The theoretical analytical model of quadrangle parts bending, which takes into account of the harden ability, anisotropy and elastic deformation of material, is proposed in this paper based on the plane deformation assumption and the bending theory of sheet metal, the quadrangle parts bending of wide sheet is analyzed theoretically, the approximate calculation relational expression is derived between friction coefficient and springback angle, and the influence of friction on springback is discussed. In the same conditions, the springback result deduced from theoretical formula is basically consistent with numerical simulation and experiment result.

scholarly journals Understanding the edge crack phenomenon in ceramic laminates

2015 ◽  
Author(s):  
O. Ševeek, ◽  
M. Kotoul ◽  
D. Leguillon ◽  
E. Martin ◽  
R. Bermejo
Keyword(s):  
Residual Stresses ◽  
Edge Crack ◽  
Energy Criterion ◽  
Element Model ◽  
Ceramic Materials ◽  
Brittle Behavior ◽  
Compressive Stresses ◽  
Out Of Plane ◽  
Edge Cracks ◽  
Edge Cracking

Layered ceramic materials (also referred to as “ceramic laminates”) are becoming one of the most promising areas of materials technology aiming to improve the brittle behavior of bulk ceramics. The utilization of tailored compressive residual stresses acting as physical barriers to crack propagation has already succeeded in many ceramic systems. Relatively thick compressive layers located below the surface have proven very effective to enhance the fracture resistance and provide a minimum strength for the material. However, internal compressive stresses result in out-of plane stresses at the free surfaces, what can cause cracking of the compressive layer, forming the so-called edge cracks. Experimental observations have shown that edge cracking may be associated with the magnitude of the compressive stresses and with the thickness of the compressive layer. However, an understanding of the parameters related to the onset and extension of such edge cracks in the compressive layers is still lacking. In this work, a 2D parametric finite element model has been developed to predict the onset and propagation of an edge crack in ceramic laminates using a coupled stress-energy criterion. This approach states that a crack is originated when both stress and energy criteria are fulfilled simultaneously. Several designs with different residual stresses and a given thickness in the compressive layers have been computed. The results predict the existence of a lower bound, below no edge crack will be observed, and an upper bound, beyond which the onset of an edge crack would lead to the complete fracture of the layer.

Measurement of Residual Stresses in Stainless Steel Cladded Specimens

2010 ◽  
Author(s):  
E. Kingston ◽  
M. Udagawa ◽  
J. Katsuyama ◽  
K. Onizawa ◽  
D. J. Smith
Keyword(s):  
Stainless Steel ◽  
Residual Stresses ◽  
Steel Substrate ◽  
Single Layer ◽  
304 Stainless Steel ◽  
Hole Drilling ◽  
Stress Distributions ◽  
Compressive Stresses ◽  
Three Samples ◽  
Type 304

Residual stresses were measured in cladded steel specimens using deep hole drilling (DHD) and block removal and surface layering (BRSL) techniques. The samples consisted of a A533B steel substrate and cladded with Type 304 stainless steel using two different welding techniques; electro-slag (ESW) and submerged welding (SAW). Two SAW samples were created; one with a single layer of weld and a second with a double layer of welding. Only a single weld layer of ESW was used on another sample. All three samples were subjected to post-weld heat treatment prior to measurement. The measured residual stress distributions revealed (as expected) tensile stresses in the clad. However, the DHD method measured compressive stresses in the substrate adjacent to the clad for the single layer ESW and SAW welds. In contrast, the BRSL method found that the residual stresses in the substrate were close to zero or approximately tensile. The measurements are compared with results obtained from finite element (FE) simulations of the welding and PWHT treatment. The predicted tensile residual stresses in the clad were found to be larger than the measurements while in the substrate the FE analysis did not predict the measured compressive stresses.

Integrated Design and Numerical Simulation of Stiffened Panels Including Friction Stir Welding Effects

2013 ◽  
Vol 554-557 ◽  
pp. 2237-2242 ◽  
Author(s):  
Rui Miguel Ferreira Paulo ◽  
Pierpaolo Carlone ◽  
Robertt A.F. Valente ◽  
Filipe Teixeira-Dias ◽  
Gaetano S. Palazzo
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Friction Stir Welding ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Ultimate Load ◽  
Simulation Models ◽  
Residual Stress Distribution ◽  
Stiffened Panels ◽  
Friction Stir

Stiffened panels are usually the basic structural building blocks of airplanes, vessels and other structures with high requirements of strength-to-weight ratio. They typically consist of a plate with equally spaced longitudinal stiffeners on one side, often with intermediate transverse stiffeners. Large aeronautical and naval parts are primarily designed based on their longitudinal compressive strength. The structural stability of such thin-walled structures, when subjected to compressive loads, is highly dependent on the buckling strength of the structure as a whole and of each structural member. In the present work, a number of modelling and numerical calculations, based on the Finite Element Method (FEM), is carried out in order to predict the ultimate load level when stiffened panels are subjected to compressive solicitations. The simulation models account not only for the elasto-plastic nonlinear behaviour, but also for the residual stresses, material properties modifications and geometrical distortions that arise from Friction Stir Welding (FSW) operations. To construct the model considering residual stresses, their distribution in FSW butt joints are obtained by means of a numerical-experimental procedure, namely the contour method, which allows for the evaluation of the normal residual stress distribution on a specimen section. FSW samples have been sectioned orthogonally to the welding line by wire electrical discharge machining (WEDM). Displacements of the relaxed surfaces are then recorded using a Coordinate Measuring Machine and processed in a MATLAB environment. Finally, the residual stress distribution is evaluated by means of an elastic FE model of the cut sample, using the measured and digitalized out-of-plane displacements as input nodal boundary conditions. With these considerations, the main goal of the present work will then be related to the evaluation of the effect of FSW operations, in the ultimate load of stiffened panels with complex cross-section shapes, by means of realist numerical simulation models.

scholarly journals Modification of Residual Stresses in Laser Additive Manufactured AlSi10Mg Specimens Using an Ultrasonic Peening Technique

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 455 ◽  
Author(s):  
Xiaodong Xing ◽  
Xiaoming Duan ◽  
Xiaojing Sun ◽  
Haijun Gong ◽  
Liquan Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Finite Element ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Finite Element Simulation ◽  
Residual Stress Distribution ◽  
Ultrasonic Peening ◽  
Element Simulation ◽  
Before And After

Ultrasonic peening treatment (UPT) has been proved to be an effective way of improving residual stresses distribution in weld structures. Thus, it shows a great potential in stress modification for metal parts fabricated by additive manufacturing technology. In this paper, an investigation into the ultrasonic treatment process of AlSi10Mg specimens fabricated by selective laser melting (SLM) process was conducted by means of experimental and numerical simulation. The specimens were prepared using a SLM machine, and UPT on their top surface was carried out. The residual stresses were measured with an X-ray stress diffraction device before and after UPT. Meanwhile, a finite element simulation method for analyzing the influence of UPT on the residual stress field of specimens was proposed and validated by experiments. Firstly, the thermal mechanical coupling numerical simulation of the SLM process of the specimen was carried out in order to obtain the residual stress distribution in the as-fabricated specimen. Then, the transient dynamic finite element simulation model of the UPT process of the specimen was established, and the UPT effect analysis was implemented. In the UPT simulation, the residual stress was applied as a pre-stress on the specimen, and the specimen’s material mechanical property was described by the Johnson–Cook model, whose parameters were determined by Split Hopkinson Pressure Bar (SHPB) experiment. The residual stress distribution before and after UPT predicted by the finite element model agree well with the measurement results. This paper concludes with a discussion of the effects of ultrasonic peening time, as well as the frequency and amplitude of the peening needle on residual stress.

scholarly journals Targeted adjustment of residual stresses in hot-formed components by means of process design based on finite element simulation

2021 ◽  
Author(s):  
B.‐A. Behrens ◽  
K. Brunotte ◽  
H. Wester ◽  
C. Kock
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Process Control ◽  
Residual Stresses ◽  
Experimental Studies ◽  
Residual Stress Distribution ◽  
Microstructural Properties ◽  
Compressive Stresses ◽  
Martensitic Microstructure ◽  
Scientific Challenge

AbstractThe aim of this work is to generate an advantageous compressive residual stress distribution in the surface area of hot-formed components by intelligent process control with tailored cooling. Adapted cooling is achieved by partial or temporal instationary exposure of the specimens to a water–air spray. In this way, macroscopic effects such as local plastification caused by inhomogeneous strains due to thermal and transformation-induced loads can be controlled in order to finally customise the surface-near residual stress distribution. Applications for hot-formed components often require special microstructural properties, which guarantee a certain hardness or ductility. For this reason, the scientific challenge of this work is to generate different residual stress distributions on components surfaces, while the geometric as well as microstructural properties of AISI 52100 alloy stay the same. The changes in the residual stresses should therefore not result from the mentioned changed component properties, but solely from the targeted process control. Within the scope of preliminary experimental studies, tensile residual stresses in a martensitic microstructure were determined on reference components, which had undergone a simple cooling in water (from the forming heat), or low compressive stresses in pearlitic microstructures were determined after simple cooling in atmospheric air. Numerical studies are used to design two tailored cooling strategies capable of generating compressive stresses in the same components. The developed processes with tailored cooling are experimentally realised, and their properties are compared to those of components manufactured involving simple cooling. Based on the numerical and experimental analyses, this work demonstrates that it is possible to influence and even invert the sign of the residual stresses within a component by controlling the macroscopic effects mentioned above.

The Effect of Residual Stresses on the Deformation of Semi-Circular Micromachined Beams

1999 ◽  
Author(s):  
Chingfu Tsou ◽  
Weileun Fang
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Residual Stresses ◽  
Plane Deformation ◽  
The Other ◽  
Side View ◽  
End Conditions ◽  
Out Of Plane ◽  
Circular Beam ◽  
The Mean

Abstract In this research, a semi-circular micromachined beam is proposed to reduce the out-of-plane deformation caused by the residual stresses. The side view of the semi-circular beam is similar to that of the cantilever. However, the end conditions of the semi-circular beam are similar to that of the microbridge. Although the micromachined cantilever would not be deformed by the mean compression, it is bent significantly by the residual gradient stress. On the other hand, the microbridge would not be bent by the gradient residual stress, however, it would be buckled by the mean compression. As demonstrated through the analytical and experimental results, the out-of-plane deformation due to bending and buckling is significantly reduced for the semi-circular micromachined beam. Thus, the flatness of the micromachined suspensions is improved. The more traditional techniques in which the out-of-plane deformation is reduced by lowering the net residual stresses of thin films can be supplemented by the use of semi-circular micromachined beam.

Sheet-Metal Forming

1989 ◽  
Author(s):  
Shiro Kobayashi ◽  
Soo-Ik Oh ◽  
Taylan Altan
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Plane Deformation ◽  
Sheet Thickness ◽  
Deformation Analysis ◽  
Normal Anisotropy ◽  
Metal Sheets ◽  
Stress Components ◽  
Out Of Plane

The stress-state is said to be plane when the direction normal to the plane is a principal stress direction and the magnitude of the stress in this direction is zero. This situation occurs when a sheet is loaded along its edges in the plane of the sheet. In-plane deformation of sheet metal, such as bore expanding and flange-drawing, is an example of plane-stress problems. For out-of-plane deformation of sheet metals, such as punch stretching, sheet bending, and cup drawing, a simple analytical method is the use of membrane theory. This theory neglects stress variations in the thickness direction of a sheet and considers the distribution of stress components only in the plane of the sheet. Thus, the basic formulations for the analysis of both in-plane and out-of-plane deformations contain only the stress components acting in the plane of the sheet. However, the analysis of out-of-plane deformation requires consideration of large deformation, while the infinitesimal theory is applicable for in-plane deformation analysis. Many materials employed in engineering applications possess mechanical properties that are direction-dependent. This property, termed anisotropy, stems from the metallurgical structure of the material, which depends on the nature of alloying elements and the conditions of mechanical and thermal treatments. Metal sheets are usually cold-rolled and possess different properties in the rolled and transverse directions. Therefore, in sheet-metal forming in particular, the effect of anisotropy on the deformation characteristics may be quite appreciable and important. In the past the calculation of the detailed mechanics of large plastic deformation of metal sheets has been achieved with some success by numerical methods. However, without exception, these studies have dealt with deformations that possess a high degree of symmetry, and were concerned with the anisotropy existing only in the direction of sheet thickness (normal anisotropy). Methods that are capable of solving nonaxisymmetric problems in forming of anisotropic sheet metal are still being sought. The finite-element method is one of those methods. It was applied to the elastic-plastic analysis of nonaxisymmetric configurations of sheet stretching with normal anisotropy by Mehta and Kobayashi.

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