Distortions and Residual Stresses at Layer-by-Layer Additive Manufacturing by Fusion

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
V. A. Safronov ◽  
R. S. Khmyrov ◽  
D. V. Kotoban ◽  
A. V. Gusarov
Keyword(s):  
Residual Stresses ◽  
Layer Thickness ◽  
Rectangular Cross Section ◽  
Thermal Shrinkage ◽  
Curvature Radius ◽  
Layer By Layer ◽  
Proposed Model ◽  
Sequential Addition ◽  
Beam Height ◽  
Elastic Layers

Thermal shrinkage of the added material can distort the manufactured part and generate residual stresses. Experiments are carried out on growing the beams of rectangular cross section. The beams bend with formation of a concave top surface. The distortion is characterized by the curvature radius. The curvature radius significantly increases with the beam height, however, its variation with the layer thickness is within the experimental uncertainty. The proposed mathematical model assumes sequential addition of thermally expanded elastic layers. It explains the experiments and indicates the existence of finite limits for the stress and the deformation fields and the curvature radius at small layer thickness. The proposed model can be applied to predict residual stresses and deformations arising in complicated parts.

Edgewise Bending Vibration Analysis of a Rotating Sandwich Beam with Magnetorheological Elastomer Core

2018 ◽  
Vol 18 (11) ◽  
pp. 1850134 ◽  
Author(s):  
S. Bornassi ◽  
H. M. Navazi ◽  
H. Haddadpour
Keyword(s):  
Magnetic Field ◽  
Layer Thickness ◽  
Rectangular Cross Section ◽  
Ritz Method ◽  
Sandwich Beam ◽  
Beam Theory ◽  
Core Layer ◽  
Magnetorheological Elastomer ◽  
Bending Vibration ◽  
Elastic Layers

The vibration of a rotating sandwich beam with magnetorheological elastomer (MRE) as a core between two elastic layers is theoretically analyzed in this paper. This study is focused on the bending vibration along the edgewise direction of a sandwich beam of rectangular cross-section, which, to the best of our knowledge, has not been addressed yet. The classical Euler–Bernoulli beam theory is used to model the dynamic behavior of the elastic layers. In the modeling, the effect of the MRE layer is considered by incorporating its shear strains and the inertia due to shear deformation and bending motion. The governing equations of motion of the rotating sandwich beam are derived by using the Ritz method and the Lagrange’s equations. The effects of the applied magnetic field, core layer thickness, rotational speed, setting angle and hub radius on the natural frequencies and the corresponding loss factors are investigated parametrically. The results show the significant effect of the magnetic field intensity and the MRE layer thickness on the modal characteristics of the MRE sandwich beam.

Thermomechanical Model of Spot Welding for Calculating Residual Stresses

2003 ◽  
Author(s):  
Lijun Xu ◽  
Jamil A. Khan
Keyword(s):  
Residual Stresses ◽  
Heat Generation ◽  
Spot Welding ◽  
Welding Process ◽  
Mechanical Analysis ◽  
Temperature Dependent ◽  
Thermomechanical Model ◽  
Faying Surface ◽  
Proposed Model ◽  
Electrode Interface

A comprehensive axisymmetric model of the coupled thermal-electrical-mechanical analysis predicting weld nugget development and residual stresses for the resistance spot welding process of Al-alloys is developed. The model estimates the heat generation at the faying surface, the workpiece-electrode interface, and the Joule heating of the workpiece and electrode. The phase change due to melting in the weld pool is considered. The contact area and its pressure distribution at both the faying surface and the electrode-workpiece interface are determined from a coupled thermal-mechanical model using a finite element method. The knowledge of the interface pressure provides accurate prediction of the interfacial heat generation. For the numerical model, temperature dependent thermal, electrical and mechanical properties are used. The proposed model can successfidly calculate the nugget diameter and thickness, and predict the residual stresses and the elastic-plastic deformation history. The calculated nugget shape and the deformation of sheets based on the model are compared with the experimental data. The computed residual stresses approach the distribution of experimental measurement of the residual stress.

DESTRUCTIVE METHODS FOR DETERMINING RESIDUAL STRESSES (review)

2021 ◽  
pp. 95-104
Author(s):  
A.D. Monakhov ◽  
◽  
N.O. Yakovlev ◽  
V.V. Avtaev ◽  
E.A. Kotova ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Residual Stresses ◽  
Speckle Interferometry ◽  
Image Correlation ◽  
Strain Gauges ◽  
Contact Method ◽  
Layer By Layer ◽  
Deep Hole ◽  
Destructive Methods

The paper presents an overview of methods for determining residual stresses. Methods such as splitting and segmentation, layer-by-layer removal, slitting (cutting, pliability), profiling, drilling holes (including a «deep» hole) are considered. The description of the methods for mea-suring the deformation used in the determination of residual stresses is given. The most common contact method using strain gauges, as well as non-contact methods: polarization-optical (photo-elasticity), optical speckle interferometry, digital image correlation.

Residual Stress Effect on Performance of Diaphragm-Based MEMS Pressure Transducers

2000 ◽  
Author(s):  
Meng-Nian Niu ◽  
Eun Sok Kim
Keyword(s):  
Residual Stress ◽  
Theoretical Analysis ◽  
Layer Thickness ◽  
Compressive Residual Stress ◽  
Stress Effect ◽  
Layer By Layer ◽  
Pressure Transducers ◽  
Before And After ◽  
Supporting Layer ◽  
Residual Stress Effect

Abstract We experimentally and theoretically confirm that residual stress within a diaphragm is critical in limiting the performance of diaphragm-based piezoelectric microphones even if the stress is low (around 50 MPa). We have fabricated and studied microphones with Al/parylene/ZnO/SiN2/poly-Si/SiN1 (from top to bottom) diaphragm. As the SiN1 supporting layer is removed layer by layer from the backside with CF4 plasma (in an RIE system), we measure both the sensitivity and center displacement of the microphone before and after each RIE etching of the SiN1 from the microphone diaphragm, and find the sensitivity increasing about 5–16 times with the best sensitivity reaching 11 μV/μbar from a mere 0.6 μV/μbar. The center displacement increases very moderately as the SiN1 layer thickness decreases from 0.8 to 0.2 μm. However, the center displacement starts to increase greatly as the SiN1 layer thickness goes below 0.2 μm, which compares with our theoretical analysis well. In the case of the SiN1 layer having compressive residual stress, the compressive stress can enhance the microphone sensitivity and center displacement to a certain extent.

Theoretical prediction of residual stresses induced by cold spray with experimental validation

2019 ◽  
Vol 15 (3) ◽  
pp. 599-616 ◽  
Author(s):  
Dibakor Boruah ◽  
Xiang Zhang ◽  
Matthew Doré
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Cold Spray ◽  
Residual Stress Distribution ◽  
Thermal Mismatch ◽  
Individual Layer ◽  
Content Type ◽  
Layer Height ◽  
Proposed Model

PurposeThe purpose of this paper is to develop a simple analytical model for predicting the through-thickness distribution of residual stresses in a cold spray (CS) deposit-substrate assembly.Design/methodology/approachLayer-by-layer build-up of residual stresses induced by both the peening dominant and thermal mismatch dominant CS processes, taking into account the force and moment equilibrium requirements. The proposed model has been validated with the neutron diffraction measurements, taken from the published literature for different combinations of deposit-substrate assemblies comprising Cu, Mg, Ti, Al and Al alloys.FindingsThrough a parametric study, the influence of geometrical variables (number of layers, substrate height and individual layer height) on the through-thickness residual stress distribution and magnitude are elucidated. Both the number of deposited layers and substrate height affect residual stress magnitude, whereas the individual layer height has little effect. A good agreement has been achieved between the experimentally measured stress distributions and predictions by the proposed model.Originality/valueThe proposed model provides a more thorough explanation of residual stress development mechanisms by the CS process along with mathematical representation. Comparing to existing analytical and finite element methods, it provides a quicker estimation of the residual stress distribution and magnitude. This paper provides comparisons and contrast of the two different residual stress mechanisms: the peening dominant and the thermal mismatch dominant. The proposed model allows parametric studies of geometric variables, and can potentially contribute to CS process optimisation aiming at residual stress control.

The Effects of Layer-by-Layer Thickness and Fiber Volume Fraction Variation on the Mechanical Performance of a Pressure Vessel

2018 ◽  
Author(s):  
Emre Özaslan ◽  
Ali Yetgin ◽  
Volkan Coşkun ◽  
Bülent Acar ◽  
Tarık Olğar
Keyword(s):  
Finite Element ◽  
Layer Thickness ◽  
Pressure Vessel ◽  
Fiber Volume Fraction ◽  
Mechanical Performance ◽  
Volume Fraction ◽  
Element Model ◽  
Layer By Layer ◽  
Fiber Volume ◽  
Filament Wound

Due to high stiffness/weight ratio, composite materials are widely used in aerospace applications such as motor case of rockets which can be regarded as a pressure vessel. The most commonly used method to manufacture the pressure vessels is the wet filament winding. However, the mechanical performance of a filament wound pressure vessel directly depends on the manufacturing process, manufacturing site environmental condition and material properties of matrix and fiber. The designed ideal pressure vessel may not be manufactured because of the mentioned issues. Therefore, manufacturing of filament wound composite structures are based on manufacturing experience and experiment. In this study, the effect of layer-by-layer thickness and fiber volume fraction variation due to manufacturing process on the mechanical performance was investigated for filament wound pressure vessel with unequal dome openings. First, the finite element model was created for designed thickness dimensions and constant material properties for all layers. Then, the model was updated. The updated finite element model considered the layer-by-layer thickness and fiber volume fraction variation. Effects of the thickness and fiber volume fraction on the stress distribution along the motor axial direction were shown. Also hydrostatic pressurization test was performed to verify finite element analysis in terms of fiber direction strain through the motor case outer surface. Important aspects of analyzing a filament wound pressure vessel were addressed for designers.

Six Sigma Robust Design of Composite Hand for LCD Glass Transfer Robot

2008 ◽  
Vol 33-37 ◽  
pp. 1451-1456 ◽  
Author(s):  
Hyun Wook Nam
Keyword(s):  
Layer Thickness ◽  
Robust Design ◽  
Six Sigma ◽  
Design Parameter ◽  
Beam Width ◽  
Coefficient Of Determination ◽  
Stacking Sequence ◽  
Pareto Chart ◽  
Sigma Level ◽  
Beam Height

This research studied robust design of composite hand for LTR (LCD glass Transfer Robot). 1st DOE (Design of Experiment) was conducted to find out vital few Xs. 108 experiments were performed and their results were statistically analyzed. Pareto chart analysis shows that the geometric parameters (height and width of composite beam) are more important than material parameters (E1, E2) or stacking sequence angle. Also, the stacking sequence of mid-layer is more important than that of outer-layer. The main effect plots show that the maximum deflection of LTR hand is minimized with increasing height, width of beam and layer thickness. 2nd DOE was conducted to obtain RSM (Response Surface Method) equation. 25 experiments were conducted. The CCD (Central Composite Design) technique with four factors was used. The coefficient of determination (R2) for the calculated RSM equation was 0.989. Optimum design was conducted using the RSM equation. Multi-island genetic algorithm was used to optimize. Optimum values for beam height, beam width, layer thickness and beam length were 24.9mm, 186.6mm, 0.15mm and 2402.4mm, respectively. An approximate value of 0.77mm in deflection was expected to be maximized under the optimum conditions. Six sigma robust design was conducted to find out guideline for control range of design parameter. To acquire six sigma level reliability, the standard deviation of design parameter should be controlled within 2% of average design value

scholarly journals Taking into account thermal residual stresses in topology optimization of structures built by additive manufacturing

2018 ◽  
Vol 28 (12) ◽  
pp. 2313-2366 ◽  
Author(s):  
Grégoire Allaire ◽  
Lukas Jakabčin
Keyword(s):  
Topology Optimization ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Heat Fluxes ◽  
Powder Layer ◽  
Layer By Layer ◽  
Thermal Deformations ◽  
Thermal Residual Stresses ◽  
Structural Design Optimization ◽  
Manufacturing Techniques

We introduce a model and several constraints for shape and topology optimization of structures, built by additive manufacturing techniques. The goal of these constraints is to take into account the thermal residual stresses or the thermal deformations, generated by processes like Selective Laser Melting, right from the beginning of the structural design optimization. In other words, the structure is optimized concurrently for its final use and for its behavior during the layer-by-layer production process. It is well known that metallic additive manufacturing generates very high temperatures and heat fluxes, which in turn yield thermal deformations that may prevent the coating of a new powder layer, or thermal residual stresses that may hinder the mechanical properties of the final design. Our proposed constraints are targeted to avoid these undesired effects. Shape derivatives are computed by an adjoint method and are incorporated into a level set numerical optimization algorithm. Several 2D and 3D numerical examples demonstrate the interest and effectiveness of our approach.

Modelling of Residual Stresses in Dental Restorative Polymer Based Materials

2015 ◽  
Vol 760 ◽  
pp. 251-256
Author(s):  
Giuseppe Lamanna ◽  
Raffaele Sepe
Keyword(s):  
Residual Stresses ◽  
Coming Out ◽  
Input Data ◽  
Thermal Shrinkage ◽  
Test Case ◽  
Chemical Shrinkage ◽  
Thermal Contraction ◽  
Curing Shrinkage ◽  
Photo Curing ◽  
Dental Restorative

A methodology for residual stresses calculations is proposed. Common photo-curing dental restorative materials under different C-factors are considered as case studies. Reaction kinetics, curing shrinkage, and viscoelasticity map were required as input data on a structural FE solver. Post cure effects were considered in order to quantify the residual stresses coming out from natural contraction with respect to those debited to the chemical shrinkage. The analysis showed for a given test case that stresses build-up due to the thermal contraction (after the completion of restoration) are comparable with those emerging due to thermal shrinkage.

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