A Numerical Investigation into Residual Stress Characteristics in Laser Deposited Multiple Layer Waspaloy Parts

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
A. M. Kamara ◽  
S. Marimuthu ◽  
L. Li
Keyword(s):  
Residual Stress ◽  
Structural Integrity ◽  
Service Failures ◽  
Number Of Layers ◽  
Multiple Layer ◽  
Combined Use ◽  
Aerospace Sector ◽  
Finite Element Package ◽  
Stress Free State ◽  
Good Agreement

This paper reports an investigation into the residual stress generated with the laser direct metal deposition (LDMD) process and particularly that which arises from the deposition of a multiple-layer wall of Waspaloy on an Inconel 718 substrate. These Ni-based superalloys possess excellent strength and creep resistance at relatively high temperatures. These are attributes contributing to their extensive utilization in various applications in modern industry and particularly in the aerospace sector. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stress generated in the combined use of these materials in an LDMD process affect interfacial bonding and structural integrity during the process, and it can also cause unpredicted in-service failures. Prediction of its distribution in the deposited structure is vital toward enhancing process optimization that could lead to its control. Using the ANSYS finite element package, this study investigated the residual stress characteristics in a 6 mm wide and 14 mm high Waspaloy wall that was built from the deposition of 20 layers each consisting of 6 parallel tracks. The predicted results were validated by published experimental data and showed very good agreement. The results indicated that irrespective of the position in the height of the wall, the stress along the length of the wall oscillates about a stress-free state. Along the height of the wall, the stress was found to vary with position. The wall is near stress-free close to the substrate, while, at positions close to the free surface, the stress was uniaxially tensile. The largely tensile stress in the beam scanning direction in the deposited wall increases with number of layers while the stress in the build-up direction in the wall is close to zero.

A METHOD FOR DEFINING INITIAL STRESS IN PROGRESSIVELY DEPOSITED FILM ON A SUBSTRATE

2014 ◽  
Vol 28 (10) ◽  
pp. 1450056
Author(s):  
KUNKUN FU ◽  
LI CHANG ◽  
BAILIN ZHENG ◽  
YONGBAI YIN ◽  
LIN YE
Keyword(s):  
Residual Stress ◽  
Initial Stress ◽  
Film Formation ◽  
Element Model ◽  
Layer Model ◽  
Multiple Layer ◽  
Stoney Formula ◽  
Deposited Film ◽  
Deposited Films ◽  
Good Agreement

The initial stress is induced during film formation and is partially counterbalanced through curvature changes. Therefore, it is commonly evaluated by the measured residual stress. Initial stress may directly affect the film formation rather than residual stress in progressively deposited films. In the present work, we introduced a multiple layer model for progressively deposited films to obtain a quantitative solution for estimating the initial stress. The results showed that residual stress in the last layer is equal to the initial stress when layer number approaches infinity. In particular, the initial stress, σi in deposited film could be determined using the equation, σi = σSt/β, in which σSt is the averaged residual stress in films calculated by Stoney formula and β is the correction factor. The value of β varied between 0 and 1, depending on relative modulus and relative thickness of film and substrate. Finally, using element birth and death technique, a finite element model was presented to verify the analytical multiple layer model. Good agreement was obtained between the analytical and FE results.

Numerical Methods to Predict Distortion in Welded Components

2008 ◽  
Author(s):  
N. A. Leggatt ◽  
R. J. Dennis ◽  
P. J. Bouchard ◽  
M. C. Smith
Keyword(s):  
Residual Stress ◽  
Numerical Methods ◽  
Structural Integrity ◽  
Large Strain ◽  
Stress Fields ◽  
Specimen Thickness ◽  
Single Bead ◽  
Stress Profiles ◽  
Welding Processes ◽  
Integrity Assessments

Numerical methods have been established to simulate welding processes. Of particular interest is the ability to predict residual stress fields. These fields are often used in support of structural integrity assessments where they have the potential, when accurately characterised, to offer significantly less conservative predictions of residual profiles compared to those found in assessment codes such as API 579, BS7910 and R6. However, accurate predictions of residual stress profiles that compare favourably with measurements do not necessarily suggest an accurate prediction of component distortions. This paper presents a series of results that compare predicted distortions for a variety of specimen mock-ups with measurements. A range of specimen thicknesses will be studied including, a 4mm thick DH-36 ferritic plate containing a single bead, a 4mm thick DH-36 ferritic plate containing fillet welds, a 25mm thick 316L austenitic plate containing a groove weld and a 35mm thick esshete 1250 austenitic disc containing a concentric ring weld. For each component, distortion measurements have been compared with the predicted distortions with a number of key features being investigated. These include the influence of ‘small’ vs ‘large’ strain deformation theory, the ability to predict distortions using simplified analysis methods such as simultaneous bead deposition and the influence of specimen thickness on the requirement for particular analysis features. The work provides an extremely useful insight into how existing numerical methods used to predict residual stress fields can be utilised to predict the distortions that occur as a result of the welding fabrication process.

Residual Stress Analysis Considering Phase Transformation and Transformation Plasticity for Heat-Treated Large Size Shaft

2016 ◽  
Vol 725 ◽  
pp. 647-652 ◽  
Author(s):  
Yusuke Yanagisawa ◽  
Yasuhiro Kishi ◽  
Katsuhiko Sasaki
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Phase Transformation ◽  
Air Cooling ◽  
Water Cooling ◽  
Stress Distributions ◽  
Transformation Plasticity ◽  
Large Size ◽  
Heat Treated ◽  
Good Agreement

The residual stress distributions of the forgings after both water-cooling and air-cooling were measured experimentally. The residual stress occurring during the heat-treatment was also simulated considering the phase transformation and the transformation plasticity. A comparison of the experiments with the simulations showed a good agreement. These results shows that the transformation plastic strain plays an important role in the heat treatment of large forged shafts.

Analysis on Secondary Effect of Corrugated Webs in Steel-Concrete Composite Beams

2011 ◽  
Vol 255-260 ◽  
pp. 596-601 ◽  
Author(s):  
Ke Bin Jiang ◽  
Yong Ding ◽  
Ya Wen Liu ◽  
Feng Zheng
Keyword(s):  
Local Buckling ◽  
Secondary Effect ◽  
Shape Parameters ◽  
Corrugated Webs ◽  
Analytical Work ◽  
Corrugated Web ◽  
Finite Element Package ◽  
First Time ◽  
Numerical And Analytical Methods ◽  
Good Agreement

Some secondary effect introduced by corrugated configuration of corrugated web was studied and formulas were proposed. The deduction for these formulas was resolved into two steps. Step I: to solve the behavior of whole corrugated web by considering it as an orthotropic plate; Step II: to solve the secondary effect according to the shape parameters of corrugation based on the result of Step I. Subsequently, a numerical experiment was designed to validate the analytical work with the help of finite element package ANSYS taking material nonlinearity into consideration. The results obtained from numerical and analytical methods show good agreement. It indicates that the formulas proposed in this paper are convenient and efficient. This research deals with this secondary effect for the first time; more studies are needed for the effect on local buckling of corrugated webs.

Optimal Cool-Down in Linear Viscoelasticity

1980 ◽  
Vol 47 (1) ◽  
pp. 35-39 ◽  
Author(s):  
Y. Weitsman
Keyword(s):  
Residual Stress ◽  
Optimal Path ◽  
Viscoelastic Plate ◽  
Geometric Constraints ◽  
Optimal Temperature ◽  
Cooling Process ◽  
Linear Viscoelastic ◽  
Stress Free State ◽  
Temperature Path ◽  
Optimal Cool

An optimal temperature path is derived for a thin viscoelastic plate which is cooled from a stress-free state against geometric constraints. The optimal path, which minimizes the final residual stress due to cool down, is shown to possess discontinuities at the initial and final times and to be smooth and continuous during all intermediate times. An iterative convergent scheme is provided for a wide class of linear viscoelastic responses and typical paths are determined for two specific cases. In addition, a time-temperature path which maintains constant stress values during cool-down is derived. The problem is motivated by the cooling process of composite materials.

Extensive Experimental Study on Diaphragm-Based Piezoelectric Microphone

1999 ◽  
Author(s):  
Meng-Nian Niu ◽  
Hong Zeng ◽  
Hai Yan ◽  
Eun Sok Kim
Keyword(s):  
Residual Stress ◽  
Experimental Study ◽  
Acoustic Pressure ◽  
Structural Integrity ◽  
Vertical Displacement ◽  
Active Area ◽  
Zno Film ◽  
Beam Laser ◽  
Acoustic Chamber ◽  
Focused Beam

Abstract This paper reports our extensive experimental study on diaphragm-based piezoelectric microphones fabricated on a silicon substrate. We have fabricated and carefully analyzed about 60 micromachined piezoelectric microphones (composed of piezoelectric ZnO film, insulating layers and electrodes) built on a low-stress silicon nitride diaphragm (with and without corrugation on the diaphragm and with five kinds of residual stress in the diaphragm). Microphone sensitivity is measured in an acoustic chamber with a B&K4135 microphone. Vertical displacement of a microphone diaphragm under an applied acoustic pressure is measured with a focused-beam laser Doppler displacement meter. Our results show that (1) corrugation releases both tensile stress and compressive stress effectively, and increases the center displacement greatly, (2) a good bending curvature in the active area is needed for a good microphone sensitivity, and (3) ZnO structural integrity is the major factor that affects the bending curvature in the active area.

CRITICAL BEHAVIOUR OF FERROELECTRIC THIN FILMS

2002 ◽  
Vol 16 (03) ◽  
pp. 473-480 ◽  
Author(s):  
JULIA M. WESSELINOWA ◽  
STEFFEN TRIMPER
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Scaling Laws ◽  
Transverse Field ◽  
Ferroelectric Thin Film ◽  
Ferroelectric Thin Films ◽  
Number Of Layers ◽  
Ising Systems ◽  
2D And 3D ◽  
Good Agreement

Based on an Ising model in a transverse field (TIM) and using a Green's function formalism the critical exponents of the polarization β and of the longitudinal susceptibility γ are calculated for a ferroelectric thin film consisting of N layers. The exponents depends on the number of layers in a significant manner. Whereas for N=3 layers the exponents are β=0.131 and γ=1.739 there is a change over to β=0.315 and γ=1.239 in case of N=30. The datas are in a good agreement with predictions for 2D and 3D Ising systems. Using scaling laws other exponents like α, δ, η and ν are obtained, too.

Structural Integrity of Penetration Nozzle of Reactor Pressure Vessel Head of PWR Plant

2008 ◽  
Author(s):  
Kiminobu Hojo ◽  
Naoki Ogawa ◽  
Yoichi Iwamoto ◽  
Kazutoshi Ohoto ◽  
Seiji Asada ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Field ◽  
Pressure Vessel ◽  
Structural Integrity ◽  
Complex Structure ◽  
Reactor Pressure Vessel ◽  
Reactor Pressure

A reactor pressure vessel (RPV) head of PWR has penetration holes for the CRDM nozzles, which are connected with the vessel head by J-shaped welds. It is well-known that there is high residual stress field in vicinity of the J-shaped weld and this has potentiality of PWSCC degradation. For assuring stress integrity of welding part of the penetration nozzle of the RPV, it is necessary to evaluate precise residual stress and stress intensity factor based on the stress field. To calculate stress intensity factor K, the most acceptable procedure is numerical analysis, but the penetration nozzle is very complex structure and such a direct procedure takes a lot of time. This paper describes applicability of simplified K calculation method from handbooks by comparing with K values from finite element analysis, especially mentioning crack modeling. According to the verified K values in this paper, fatigue crack extension analysis and brittle fracture evaluation by operation load were performed for initial crack due to PWSCC and finally structural integrity of the penetration nozzle of RPV head was confirmed.

Measurement and Modelling of Residual Stresses in Fracture Toughness Specimens Extracted From Large Components

2008 ◽  
Author(s):  
S. J. Lewis ◽  
S. Hossain ◽  
C. E. Truman ◽  
D. J. Smith ◽  
M. Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Mechanical Load ◽  
Crack Driving Force ◽  
Neutron Diffraction Technique ◽  
Fracture Specimens

A number of previously published works have shown that the presence of residual stresses can significantly affect measurements of fracture toughness, unless they are properly accounted for when calculating parameters such as the crack driving force. This in turn requires accurate, quantitative residual stress data for the fracture specimens prior to loading to failure. It is known that material mechanical properties may change while components are in service, for example due to thermo-mechanical load cycles or neutron embrittlement. Fracture specimens are often extracted from large scale components in order to more accurately determine the current fracture resistance of components. In testing these fracture specimens it is generally assumed that any residual stresses present are reduced to a negligible level by the creation of free surfaces during extraction. If this is not the case, the value of toughness obtained from testing the extracted specimen is likely to be affected by the residual stress present and will not represent the true material property. In terms of structural integrity assessments, this can lead to ‘double accounting’ — including the residual stresses in both the material toughness and the crack driving force, which in turn can lead to unnecessary conservatism. This work describes the numerical modelling and measurement of stresses in fracture specimens extracted from two different welded parent components: one component considerably larger than the extracted specimens, where considerable relaxation would be expected as well as a smaller component where appreciable stresses were expected to remain. The results of finite element modelling, along with residual stress measurements obtained using the neutron diffraction technique, are presented and the likely implications of the results in terms of measured fracture toughness are examined.

Residual Stress Prediction for Non-Axisymmetric Vessel Penetration Welds

2008 ◽  
Author(s):  
Kazuo Ogawa ◽  
Nobuyoshi Yanagida ◽  
Koichi Saito
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Three Dimensional ◽  
Measurement Data ◽  
Fe Model ◽  
Stress Distributions ◽  
Dimensional Finite Element ◽  
Stress Prediction ◽  
Three Dimensional Finite Element ◽  
Good Agreement

Residual stress distribution in an oblique nozzle jointed to a vessel with J-groove welds was analyzed using a three-dimensional finite element method. All welding passes were considered in a 180-degree finite element (FE) model with symmetry. Temperature and stress were modeled for simultaneous bead laying. To determine residual stress distributions at the welds experimentally, a mock-up specimen was manufactured. The analytical results show good agreement with the experimental measurement data, indicating that FE modeling is valid.

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