Residual Stress Problems Research Articles

Large-scale non-linear analysis of residual stresses in multi-pass pipe welds by idealized explicit FEM

In this research, idealized explicit FEM (IEFEM), which can analyze residual stress of the practical structures in practical time, was applied to large-scale residual stress problem of X groove multi-pass pipe welding. The analysis model has 3,376,074 degrees of freedom and 108 welding passes. In the analysis, all the welding passes and welding pass grouping technique were considered to investigate the influence of welding pass grouping on residual stress distribution. As a result, it was found that the residual stress distribution can be different if pass grouping technique is used. In addition, to investigate the influence of the welding pass sequence on residual stress distribution, analyses which consider another in-layer welding sequence and build-up sequence were carried out. As a result, it was found that the influence of the welding sequence on residual stress distribution is small. The computing time was practical even though all the welding passes are modeled in a full pass model.

A study on drawbead restraining force effectiveness

Springback phenomenon is mainly a problem of residual stresses, which are released after die opening. The use of drawbeads in the blankholders of forming dies is a widely taken measure in order to influence the stress state through the thickness of the sheet material. Besides, blankholder closing force has implications in die design and energy consumption during production. This paper presents a methodology to evaluate the efficiency of different drawbead geometries regarding restraining capacity. An efficiency parameter was created which allows for a comparison between drawbead geometries. It is based on the measurement of the maximal in-plane strain in the test part which can be generated with a determined blankholder force. Finite element simulations using commercial software have been run on a test part, using different drawbead geometries and closing forces. The simulations were experimentally validated using a test die. With the methodology, it is possible to determine the most efficient drawbead geometry for a definite sheet metal part, allowing for reducing die investments and press energy consumption per part produced.

Development of idealized explicit FEM using GPU parallelization and its application to large-scale analysis of residual stress of multi-pass welded pipe joint

In this research, the authors developed the idealized explicit finite element method (IEFEM) to achieve shorter computing time and lower memory consumption in analyses of welding deformation and residual stress. IEFEM was parallelized by a graphics processing unit (GPU) to achieve even faster computation. To show its applicability to large-scale problems, the proposed method was applied to the analysis of the multi-pass welding of V-groove pipe joint that has 1 million elements, 13 layers, and 33 passes. In the analysis, isotropic hardening, kinematic hardening, and combined hardening were considered to investigate the influence of hardening rule on residual stress distribution. As a result, it is found that residual stress distributions were larger in the order of isotropic hardening, combined hardening, and kinematic hardening. In addition, the analyzed residual stress and experimental measurements showed good agreement. The computing time was approximately 70 h. From these results, it was shown that IEFEM can analyze a large-scale welding residual stress problem in realistic time with high accuracy.

A nonlinear Cosserat interphase model for residual stresses in an inclusion and the interphase that bonds it to an infinite matrix

Residual stresses in inclusions and interphases that are bonded to a matrix can significantly influence the response of composite materials to additional mechanical loads. These residual stresses are modeled by considering the nonlinear 2-phase problem of an inclusion that is bonded to a hollow spherical interphase with an internal unstressed radius that is different from the outer unstressed radius of the inclusion and with a traction-free outer deformed surface. The resulting macro-inclusion (i.e. the prestressed inclusion and interphase) is then embedded into a stress-free matrix. The linear equations for small deformations superimposed on this large deformation problem are developed and solved to study the influence of the residual stresses on the response of the 3-phase system of inclusion–interphase–matrix to external mechanical loads. The results of this solution indicate that this residual stress problem is essentially nonlinear and must be modeled directly by including the influence of coupled terms associated with products of the residual stresses and displacements.

Development of 3D Coupling Analysis Method for Spot Welding by Idealized Explicit FEM

In this study, the authors developed a three-dimensional coupling analysis method for spot welding by using Idealized Explicit FEM, which can analyze large-scale welding residual stress and deformation problems in practical computing time. This proposed method was applied to a spot welding problem to show its analysis accuracy. It was found that the nugget sizes obtained by experimental measurements and the method are in good agreement. In addition, to investigate the effect of shunt current on the nugget size in multiple-spot welding, the method was applied to three-dimensional spot welding with four points of welding. As a result, it was shown that the influence of shunt current in multiple-spot welding can be evaluated by using the proposed method in realistic computing time.

A composite insulation structure for silicon-based planar neuroprobes

Silicon-based planar neuroprobes are composed of silicon substrate, conducting layer, and insulation layers of SiO2 or SiN membrane. The insulation layer is very important because it affects many key parameters of neuprobes, like impedance, SNR (signal noise ratio), reliability, etc. Monolayer membrane of SiO2 or SiN are not good choices for insulation layer, since defects and residual stress in these layers can induce bad passivation. In this paper a composite insulation structure is studied, with thermal SiO2 as the lower insulation layer and with multilayer membrane composed of PECVD SiO2 and SiN as the upper insulation layer. This structure not only solves the problem of residual stress but also ensures a good probe passivation. So it’s a good choice for insulation layer of neuroprobes.

FINITE ELEMENT ANALYSIS OF WELDED JOINTS

Fusion welding is one of the most used methods for joining metals. This method has largely been developed by experiments, i.e. trial and error. The problem of distortion and residual stresses of a structure is due to welding is important to control. Industry where the components are expensive and safety and quality are highly important issues. The aim of the work presented in this paper is to develop an efficient and reliable method for simulation of the welding process using the Finite Element Method. The method may then be used when designing and planning the manufacturer of a component, so that introduction of new components can be made with as little disturbance as possible. When creating a numerical model, the aim is to implement the physical behavior of the process into the model. However, it may be necessary to compromise between accuracy of the model and the required computational time. Different types of simplifications of the problem and more efficient computation methods are discussed. Simulations have been carried out in order to validate the models. Moving heat source and element death & birth technique is used to simulate Welding Process.

Electromagnetic Field-Aided Magnetic Soft Mold Reverse Imprinting Technology Applied in Microstructure Replication

This paper proposes an advanced microstructure embossing replication technology that combines an electromagnetic-field-aided magnetic soft mold and a reverse imprinting technology to replicate microstructure. The main advantage of this technology is low pressure, low cost, and quick and easy forming. The entire imprinting process can be completed at room temperature using a ultraviolet (UV) curing technique. This study applied a compound casting technique to fabricate a magnetic poly(dimethylsiloxane) (PDMS) soft mold, with an electromagnetic chuck for even imprinting pressure, and reverse imprinting molding technology. Microstructure cavity of the mold was fully filled with photoresist before imprint replication, and improved microstructure transfer ratio. Examination of the results showed that, the magnetic PDMS soft mold integrated electromagnetic-field-aided reverse imprinting process developed by this study, can successfully replicate microstructure at room temperature, low pressure, and avoid deformation and residual stress problems due to heating and cooling.

Multilayer DLC coatings via alternating bias during magnetron sputtering

To combat the high residual stress problem in monolayer diamond-like carbon coatings, this paper fabricated multilayer diamond-like carbon coatings with alternate soft and hard layers via alternating bias during magnetron sputtering. The surface, cross sectional morphology, bonding structures and mechanical properties are investigated. The atomic force microscopy images indicate low bias results in rougher surface with large graphite clusters and voids suggesting low coating density. The multilayered coatings demonstrate relatively smooth surface stemming from higher bias. The cross sectional images from field emission scanning electron microscopy indicate coating thickness decreases as substrate bias increases and confirm that higher bias results in denser coating. Delamination is observed in monolayer coatings due to high residual stress. The trend of sp 3/sp 2 fraction estimated by X-ray photoelectron spectroscopy is consistent with that of I D/I G ratios from Raman spectra, indicating the change of bonding structure with change of substrate bias. Hardness of multilayer diamond-like carbon coating is comparable to the coatings deposited at low constant bias but the adhesion strength and toughness are significantly improved. Alternately biased sputtering deposition provides an alternative when combination of hardness, toughness and adhesion strength is needed in an all diamond-like carbon coating.

Low-temperature embossing technique for fabrication of large-area polymeric microlens array with supercritical carbon dioxide

This study reports an effective process for low temperature replication of polymeric microlens array using carbon dioxide (CO 2) as softening solvent and then as embossing pressure. Supercritical CO 2 is employed to soften the surface of polymer substrate and then apply pressure on it. Accordingly, microlens can be formed on the polymer substrate at low temperature. Using gas as embossing pressure can provide uniform pressure for large-area replication. During the embossing process, an array of convex microlenses is generated by partial protrusion of the substrate into the micro-holes of the mold under the action of embossing pressure and surface tension. The uniformity of large-area fabrication and optical property of the fabricated refractive microlens array on a 260 mm × 110 mm poly (methyl methacrylate) (PMMA) substrate have been verified. Little residual stress can be observed by polariscope. With the proposed method, the large-area embossing can be performed without heating and cooling. Moreover, the problems of non-uniform pressure and residual stress can be overcome.

Calculation and experimental determinations of the residual stress distribution in alumina/Ni/alumina and alumina/Ni/nickel alloy systems

Residual stress problems encountered in joining ceramics–ceramics or ceramics–metals systems for high-temperature applications >1000 °C have been studied. A solid-state bonding technique under hot-pressing via metallic foils sheet of Ni was used for joining alumina–alumina and alumina–nickel alloy (HAYNES® 214™). The residual stresses expected in the specimen were predicted by finite-element method (FEM) calculations using an elastic–plastic-creep model (EPC). Stress distributions in the specimen were characterized experimentally using X-ray diffraction (XRD) and Vickers Indentation Fracture (VIF) techniques. The tensile and shear stress profiles have been determined along selected lines perpendicular to the bonding interface. The results of the FEM calculation of residual stresses have been compared experimentally with the results of classical XRD and indentation methods. It was found that the tensile stress concentration showed higher values at the edge of the boundary. The residual stresses caused by the thermal expansion mismatch between alumina (Al2O3) and Ni-based super-alloy (HAYNES® 214™) severely deteriorated the joints compared to Al2O3–Al2O3 joint with the same solid-state bonding parameters. The correlations between the FEM calculations and experimental results obtained by XRD and VIF method were discussed.

Residual Stresses in Dried Bodies

The problem of residual stresses in porous materials as a result of drying and the presumable influence of these stresses on the swelling effect by rehydration are discussed. The drying model comprising the specific mechanisms suitable for the first and second periods of drying is applied, and the numerical algorithm enabling calculation of the drying-induced stresses is constructed. The numerical calculations exemplifying the history of stresses leading finally to the residual stresses are carried out. The outcome of these stresses on the swelling strains during rehydration is illustrated using an example of a finite dimensions kaolin cylinder dried convectively.

A Study on Damage Behavior and Strength of Smart Material under Low Temperature Using Acoustic Emission

Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite (MMC). TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress using shape memory effect in the matrix. A hot press method was used to create the optimal condition for the fabrication of shape memory alloy (SMA) composite. The bonding effect between the matrix and the reinforcement within the SMA composite was strengthened by the cold rolling. The fabricated composite by these processes can be applied as a part of the aircraft, and this part is operated under severe flying condition such as low temperature and high pressure. In this study, an acoustic emission technique was used to quantify the microscopic damage behavior of cold rolled TiNi/Al6061 SMA composite at low temperature condition. The results showed that the tensile strength of the TiNi/Al6061 SMA composite increased with the TiNi reinforcement at low temperature condition, but the strength for the specimen subjected to the cold rolling decreased. AE parameters of AE counts, amplitude and energy were useful to evaluate the microscopic damage behavior of the composite.

Residual Stress Reconstruction by Variational Eigenstrain Procedures

Residual stress can be found in engineering components as a result of non-uniform plastic strain introduced through a variety of manufacturing processes such as rolling, casting, hot forging, cold working, shot-peening, laser shock peening, welding, etc. The numerical simulation of the resulting residual stress field requires the use of sophisticated coupled microstructural and thermomechanical models that rely on profound understanding of the constitutive laws and detailed knowledge of material parameters. In practice this level of understanding is not generally available, leading to the use of simplified models that are unable to reproduce or predict reliably the real residual stress distributions. This leads to the necessity of using increased safety factors and utilising overly conservative designs. A rational approach to the description of residual stress states is proposed that relies on the use of eigenstrain distributions as sources of residual stress. The problem of residual stress evaluation can then be replaced by the problem of determining the underlying eigenstrain distribution. An approach to this problem is proposed based on a simple variational formulation. Some examples of its application are shown, and the difficulties and challenges that may arise are discussed.

Application of polyimide to bending-mode microactuators with Ni/Fe and Fe/Pt magnet

Out-of-plane polyimide (PI) electromagnetic microactuators with different geometries are designed, fabricated and tested. Fabrication of the electromagnetic microactuators consists of 10 μm thick Ni/Fe (80/20) permalloy deposition on PI diaphragm by electroplating process, electroplating of copper planar coil with 10 μm thick, bulk micromachining, and excimer laser selective ablation. They are fabricated by a novel concept to avoid the etching selectivity and residual stress problems during wafer etching. A simulation model is created by ANSYS software to analyze the microactuators. The external magnetic field intensity ( H ext) generated by the planar coil is simulated by this software. Besides, to provide bi-directional and large deflection angles of the microactuators, hard magnet Fe/Pt is deposited at low temperature of 300 °C by sputtering onto the PI diaphragm to produce a perpendicular magnetic anisotropic field. This magnetic field can enhance the interaction with H ext to induce attractive and repulsive bi-directional force to provide a larger displacement. The results of the magnetic microactuators with and without hard magnetic are compared and discussed, respectively. The preliminary result reveals that the electromagnetic microactuators with hard magnet exhibit a greater deflection angle than that without one.

Non-linear least-squares solution to the moiré hole method problem in orthotropic materials. Part 1: Residual stresses

The hole method problem relates to two inverse problems of interest: the first, most commonly addressed by practitioners, is to obtain residual stresses; the other, generally neglected, inverse problem can be posed as either a stress separation problem or a material elastic properties identification problem. In both this Paper I and Paper II, we pose and solve this dual hole method problem in an orthotropic plate, using computer generated moire isothetics, by means of a non-linear least-squares approach. In Paper I we address the residual stress problem. In Paper II we pose the use of moire isothetics as a means to achieve separation of stresses, but we deal with the determination of the five orthotropic elastic constants, four of which are independent.

Residual Stress Measurements in Australia: Present and Future

The Australian Nuclear Science and Technology Organisation, ANSTO, (http:\\www.ansto.gov.au) has initiated a “Neutrons for Engineering” project to provide an integrated residual stress service to Australian industry and academia. The service is based around measurements of residual stress using neutrons on a newly-refurbished instrument on the HIFAR research reactor. In addition to the neutron measurements there is a range of expertise available on the ANSTO site to solve residual stress problems using other techniques including hole-drilling, strain-gauging, and x-ray diffraction, as well as capabilities for finite element modeling and mechanical testing. In this paper we describe briefly the existing and future facilities at ANSTO for neutron strain scanning and present some benchmark results for the HIFAR strain scanner.

Three dimensional fracture analysis of FGM coatings under thermomechanical loading

The main objective of this study is to examine the three dimensional surface crack problems in functionally graded coatings subjected to mode I mechanical or transient thermal loading. The surface cracks are assumed to have a semi-elliptical crack front profile of arbitrary aspect ratio. The cracks are embedded in the functionally graded material (FGM) coating which is perfectly bonded to a homogeneous substrate. A three dimensional finite element method is used to solve the thermal and structural problems. Collapsed 20-node isoparametric elements are utilized to simulate the strain singularity around the crack front. The stress intensity factors are computed by using the displacement correlation technique. Four different coating types are considered in the analyses which have homogeneous, ceramic-rich (CR), metal-rich (MR) and linear variation (LN) material composition profiles. In the mechanical loading problems, the composite medium is assumed to be subjected to fixed-grip tension or three point bending. In the thermal analysis, a transient residual stress problem is considered. The stress intensity factors calculated for FGM plates are in good agreement with the previously published results on three dimensional surface cracks. The new results provided show that maximum stress intensity factors computed during transient thermal loading period for the FGM coatings are lower than those of the homogeneous ceramic ones.

Thermal Residual Stress Analysis of Ni–Al2O3, Ni–TiO2, and Ti–SiC Functionally Graded Composite Plates Subjected to Various Thermal Fields

This study investigates the thermal elastic residual stresses occurring in Ni–Al2O3, Ni–TiO2, and Ti–SiC functionally graded plates due to uniform, linear, and parabolic temperature fields through the plate thickness. A 3D eight-noded isoparametric layered (no limit layer number) finite element with three degrees of freedom at each node was implemented to the residual stress problem analogous to the shell elements proposed by Ahmad et al. (Ahmad, S., Irons, B.M. and Zienkiewicz, O.C. (1970). Analysis of Thick and Thin Shell Structures by Curved Finite Elements, Int. J. of Numerical Methods in Engineering, 2: 419–451.) and Yunus and Khonke (Yunus, S.M. and Khonke, P.C. (1989). An Efficient Through-Thickness Integration Scheme in an Unlimited Layer Doubly Curved Isoparametric Composite Shell Element, Int. J. of Numerical Methods in Engineering, 28: 2777– 2793.). The longitudinal stresses (11, 22) and transverse shear stresses (13, 23) were dominant. The shear stresses become important especially at the free edges of the plate. As the compositional gradient was increased the normal and shear stresses increased. Whereas the normal stresses become tensile in both ceramic-rich and metal-rich regions; the shear stresses, which are not severe in both the regions, change their directions and become a maximum inside the plate. The thermal and mechanical properties of constituents played an important role on the stress magnitudes rather than on the profiles of the through-thickness variations of normal and shear stresses. Thus, the difference of the coefficients of thermal expansion of the ceramic and metal phases affected the magnitudes of the normal and shear stresses. In addition, the continuous temperature fields through the plate thickness resulted in similar normal and shear stress variations.

Polymeric magnetic microactuator with efficient permalloy loop design

In the study, two types of polyimide (PI) magnetic microactuator with different geometries were designed, fabricated and tested. Mathematic model is created by ANSYS software to design the two microactuators, respectively. The magnetic field generated by the planar coil with permalloy circuit loop design was simulated by ANSYS software. The simulation result shows that the magnetic force can be up to 34.69 mN. Fabrication of the electromagnetic microactuator combines with 10 μm thick Ni/Fe (80/20) permalloy circuit loop deposition, 10 μm thick permalloy plate with 800 × 800 μm in area on PI diaphragm, high aspect ratio electroplating of copper planar coil with 10 μm in thickness, bulk micromachining, and excimer laser ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems during wafer etching. First, PI diaphragm with micro-electroplated Ni/Fe permalloy was released by anisotropic wet etching, followed by mask projection of 248 nm excimer laser ablation. The new concept of excimer laser ablation process demonstrates that microstructure can be post-ablated after bulk micromachining. By applying a current through planar coil, the PI diaphragm will be actuated. ANSYS software was used to predict the deflection angle of the two types of microactuators. The preliminary theoretical simulation shows a good agreement with experimental result.