Calculation Of Residual Stresses Research Articles

Measurement of scratch-induced residual stress within SiC grains in ZrB 2–SiC composite using micro-Raman spectroscopy

An analytical framework for determination of scratch-induced residual stress within SiC grains of ZrB 2–SiC composite is developed. Using a “secular equation” that relates strain to Raman-peak shift for zinc-blende structures and the concept of sliding blister field model for scratch-induced residual stress, explicit expressions are derived for residual stress calculation in terms of phonon deformation potentials and Raman peak shift. It is determined that, in the as-processed composite, thermal expansion coefficient mismatch between ZrB 2 and SiC induces compressive residual stress of 1.731 GPa within the SiC grains and a tensile tangential stress of 1.126 GPa at the ZrB 2–SiC interfaces. With increasing scratch loads, the residual stress within the SiC grains becomes tensile and increases in magnitude with scratch load. At a scratch load of 250 mN, the calculated residual stress in SiC was 2.6 GPa. Despite this high value, no fracture was observed in SiC grains, which has been rationalized based on fracture strength calculations from Griffith theory.

Numerical simulation of welding induced damage and residual stress of martensitic steel 15-5PH

This paper is about the modeling of damage and residual stresses induced by a complex history of thermo-elasto-plastic multiphase in welding heat affected zone (HAZ). A two-scale model for elasto-plastic damaged multiphase is developed. The constitutive equations of the model are coupling ductile damage, elasto-plastic strains, phase transformation and transformation plasticity. In this study, an equation of damage evolution is proposed based on the continuum damage mechanics. In order to validate the proposed damage evolution, a set of flat notched bars with various notches are to simulated and then compared to experimental results. An example of laser heated disk is simulated to elaborate the two-scale model and the simulated results of the two-scale model in CAST3M ® is compared the results calculated by a homogenized macroscopic model in SYSWELD ®. The study shows the two-scale model provides valuable freedom to choose the material or mechanical law for each phase. The proposed damage equation extends the application of existing ductile damage models. In the calculation of residual stresses, damage decreases the residual stresses in HAZ by a small amount.

Measurement and Calculation of Residual Stress in Axi-Symmetric Glass Sample Using Structural Relaxation Theory

Consistent model including structural relaxation is necessary for correct glass stress calculation in numerical computations of glass forming processes. Calculation of glass relaxation phenomena is often done by combining independent empirical formula on stress relaxation (for a simple temperature regime) and independent model of time-temperature dependence on Tool fictive temperature, Tf. Another approach was developed and verified here. Tool-Narayanaswamy and Moynihan/Mazurin relaxation model was adopted. Relaxation was obtained not from empirical model, but from calculated time-temperature dependence of Tool fictive temperature (Tf), dynamic viscosity, heat capacity and coefficient of thermal expansion. Heat conduction in a glass probe of known temperature history, structural relaxation and stress calculation were used in one computation scheme using Matlab. The stress of glass probe was measured using polarized light (Senarmont method). Rather high stress computation accuracy was obtained in comparison to stress experimental results. The applied model approach is being to be extended for application in commercial finite element codes for modeling of glass forming processes.

Role of thermal expansion matching in CdTe heteroepitaxy on highly lattice-mismatched substrates

We report on the significance of thermal expansion mismatch in the heteroepitaxial growth of CdTe on highly lattice-mismatched substrates. Such substrates including Si, Ge, or GaAs are desirable for CdTe buffer layer growth and subsequent deposition of HgCdTe infrared absorber layers. Besides lattice misfit, the thermal mismatch associated with these systems can produce additional strain and defects at low or elevated temperatures. However, little work has been done towards documenting and understanding these effects. Experimental evidence of thermal-expansion-dependent residual stress is presented for CdTe/Si(2 1 1), CdTe/Ge(2 1 1), and CdTe/GaAs(2 1 1) films based on X-ray diffraction studies. The experimental results are also compared with residual stress calculations based on known material properties. These results may play a vital role in the design and development of HgCdTe detectors for large-format, infrared focal plane arrays (FPA).

Residual stress and distortion calculation of laser beam welding for aluminum lap joints

Abstract A numerical simulation model of the laser beam welding (LBW) process is developed, aiming to a reliable prediction of the residual stress and distortion fields. As LBW is a thermo-mechanical process, a thermal analysis is conducted to analyze the spatial temperature distribution history, coupled to a mechanical analysis to calculate the residual stresses and distortions. An innovative and efficient keyhole model, independent of any empirical parameter, is introduced for the prediction of the keyhole size and shape required for the thermal analysis. All the major physical phenomena associated to the LBW process, such as, heat radiation, thermal conduction and convection heat losses are taken into account in the model development. The thermal and mechanical material properties are introduced as temperature dependent functions, due to the high temperature variations and the material phase changes occurring during the welding. The simulation algorithm is programmed as a macro routine within the ANSYS finite element code. The model is validated for the case of butt joint welding DH-36 steel plates and its efficiency is demonstrated for the lap-joint welding of two aluminum 6061-T6 plates. The main advantage of the developed model is its generality and flexibility, as it is independent of any empirical parameter, enabling its application in parametric studies of a wide range of LBW problems of different geometrical, material and joint type, requiring only the basic mechanical and thermal material properties.

Surface and bulk residual stresses in Li 2O · 2SiO 2 glass–ceramics

In the present work surface and bulk residual stresses generated in partially crystallized Li 2O · 2SiO 2 glass–ceramics are analyzed after different heat treatments. The phase specific residual stresses in the crystalline Li 2Si 2O 5-phase are evaluated for the first time in the near-surface zone and the bulk of the samples using both medium and high energy synchrotron radiation. The results reveal that in the crystals within the bulk of the samples micro residual stresses generated by the thermal anisotropy of the isolated individual crystallites depend on the crystallographic direction. In contrast, the residual stress state in the near-surface zone is isotropic due to the superposition of thermal residual stresses in and around the crystals of the near-surface area. Residual stress calculations using a modified Selsing’s model yield a good estimate of the anisotropic residual stresses in the bulk crystallites, whereas the isotropic residual stress state in the crystallized surface layer can be described by an elastic stress model for thin films.

Hole-Drilling Residual Stress Profiling With Automated Smoothing

An effective procedure is presented that allows stable hole-drilling residual stress calculations using strain data from measurements taken at many small increments of hole depth. This use of many strain measurements is desirable because it improves the data content of the calculation, and the statistical reliability of the residual stress results. The use of Tikhonov regularization to reduce the noise sensitivity that is characteristic of a fine-increment calculation is described. This mathematical procedure is combined with the Morozov criterion to identify the optimal amount of regularization that balances the competing tendencies of noise reduction and stress solution distortion. A simple method is described to estimate the standard error in the strain measurements so that the optimal regularization can be chosen automatically. The possible use of a priori information about the trend of the expected solution is also discussed as a further means of improving the stress solution. The application of the described method is demonstrated with some experimental measurements, and realistic results are obtained.

Nanoparticulate origin of intrinsic residual stress in thin films

The formation of grains in thin films generates intrinsic residual stress. In this work, we present a model of intrinsic residual stress calculation based on the size-dependent phase transitions of the nanograins. Evaporated thin films are produced by condensation from the vapor on the substrate. It is assumed that the starting nanograins grow from the liquid phase. It is well established that the melting temperature of nanoparticles is a function of their size. By assuming that the intrinsic stress originates from the volume change of the nanograins, and taking into account relaxation processes, the generated intrinsic residual stress in the films is evaluated. The results of the model are compared quantitatively with experimental data obtained from Ta, Mo, Pd and Al films deposited on Si. This model also gives a theoretical interpretation of Thornton and Hoffman’s modelling of the stress-temperature diagram of thin films.

FEM calculation of residual stresses induced by laser shock processing in stainless steels

Laser shock processing, also known as laser shock peening, generates through a laser-induced plasma, plastic deformation and compressive residual stresses in materials for improved fatigue or stress corrosion cracking resistances. The calculation of mechanical effects is rather complex, due to the severity of the pressure loading imparted in a very short time period (in the ns regime). This produces very high strain rates (106 s−1), which necessitate a precise determination of dynamic properties.Finite element techniques have been applied to predict the residual stress fields induced in two different stainless steels, combining shock wave hydrodynamics and strain rate dependent mechanical behaviour. The predicted residual stress fields for single or multiple laser processes were correlated with those from experimental data, with a specific focus on the influence of process parameters such as pressure pulse amplitude and duration, laser spot size or sacrificial overlay.Among other results, simulations confirmed that the affected depths increased with pulse duration, peak pressure and cyclic deformations, thus reaching much deeper layers (> 0.5 mm) than with any other conventional surface processing. To improve simulations, the use of experimental VISAR determinations to determine pressure loadings and elastic limits under shock conditions (revealing different strain-rate dependences for the two stainless steels considered) was shown to be a key point.Finally, the influence of protective coatings and, more precisely, the simulation of a thermo-mechanical uncoated laser shock processing were addressed and successfully compared with experiments, exhibiting a large tensile surface stress peak affecting a few tenths of micrometres and a compressive sub-surface stress field.

Calculation of residual stress and permanent deformation in wrought-wire gold and Co-Cr alloy clasps

Calculation of residual stress and permanent deformation in wrought-wire gold and Co-Cr alloy clasps

Fatigue life prediction of autofrettage tubes using actual material behaviour

There is a profound Bauschinger effect in the behaviour of high-strength steels used in autofrettaged tubes. This has led to development of methods capable of considering experimentally obtained (actual) material behaviour in residual stress calculations. The extension of these methods to life calculations is presented here. To estimate the life of autofrettaged tubes with a longitudinal surface crack emanating from the bore more accurately, instead of using idealized models, the experimental loading–unloading stress–strain behaviour is employed. The resulting stresses are then used to calculate stress intensity factors by the weight function method as input to fatigue life determination. Fatigue lives obtained using the actual material behaviour are then compared with the results of frequently used ideal models including those considering Bauschinger effect factors and strain hardening in unloading. Using standard fatigue crack growth relationships, life of the vessel is then calculated based on recommended initial and final crack length. It is shown that the life gain due to autofrettage above 70% overstrain is considerable.

The New Materials Science Diffractometer STRESS-SPEC at FRM-II

In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. Non-destructive analysis for phase specific residual stresses and textures is only possible by means of diffraction methods. In order to cater for the development of these analytical techniques the new Materials Science Diffractometer STRESS-SPEC at FRM-II is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The system compromises a highly flexible monochromator setup using three different monochromators: Ge (511), bent silicon (400) and pyrolitic graphite (PG). This range of monochromators and the possibility to vary the take-off angles from 2θM = 35º to 110º allows wavelength adjustment such that measurements can be performed around a scattering angle of 2θS ~ 90º. This is important in order to optimise neutron flux and resolution, especially for stress analysis on components, since the gauge volume element in that case is cubic and large vertical divergences due to focusing monochromators do not affect the spatial resolution. The instrument is now available for routine operation and here we will present details of recent experiments and instrument performance.

The new materials science diffractometer STRESS-SPEC at FRM-II

In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. In order to cater for the development of these analytical techniques the Materials Science Diffractometer STRESS-SPEC at FRM-II is designed to be equally applied to texture or residual stress analysis by virtue of its flexible configuration and the high neutron flux at the sample position. The instrument is now available for routine operation and here we present details of first experiments and instrument performance.

Calculation of residual stresses in multilayer helical surfacing of cylindrical components on the basis of the theory of growth of visco-plastic solids

(2006). Calculation of residual stresses in multilayer helical surfacing of cylindrical components on the basis of the theory of growth of visco-plastic solids. Welding International: Vol. 20, No. 2, pp. 150-156.

The effect of anisotropy on residual stress values and modification of Serruys approach to residual stress calculations for coatings such as TiN, ZrN and HfN

The residual stresses in literature on hard coatings (e.g., TiN, CrN, HfN and ZrN) are usually calculated using the mechanical elastic constants often determined by indentation technique by assuming isotropic behavior. The effect of anisotropy of the hard coatings on residual stress values such as TiN, ZrN and HfN has been documented using classical technique and Thin Film techniques (fixed incidence multiplane (FIM) Technique). Due to lack of the single crystal data, the anisotropy of coatings has been taken into account through XECs determined experimentally for ZrN, HfN and TiN films. Recently, single crystal elastic constants of the ZrN, HfN and NbN have been measured. In the light of single crystal elastic constant data, residual stresses reported in the literature were reevaluated according to Reuss, Voigt, Hill (or mixed) and Kröner models using the best fitting approach after modifying Serruys approach. The modified Serruys approach captures the anisotropic behavior of coatings such as ZrN and Zr(Hf)N. The residual stress calculations were improved and the residual stress values were significantly increased as high as 30% compared to the previously published data. The best fitting approach (modified Serruys approach) was compared to the procedure used by Perry using experimentally determined XECs.

Determination of residual stresses in multipass weldments of high strength steels with experimental and numerical techniques

This paper presents part of the work from the EU project ELIXIR on a series of welded geometries. Experimental and numerical techniques have been applied to determine residual stresses in buttwelded joints of high strength steel. Starting from simple weld geometries that served for validation of these tools, residual stresses were measured and calculated for an industrial component for offshore application. In spite of some simplifications in the numerical simulation of the welding process, satisfying agreement with experimental data has been achieved especially if relevant three-dimensional effects have been modelled. The validation of numerical techniques for residual stress calculations can help to enable cost effective fabrication and repair of steel components.

Theoretical and Experimental Studies on Residual Stresses in Laminated Polymer Composites

In this research, the residual stresses in thermoset polymer composites are studied. Generally, these stresses are studied from the macroscopic and microscopic points of view. The main factors responsible for the buildup of these stresses in composite materials are the curing process, moisture, and temperature. The stress-free temperature of various samples of a laminated composite is measured. The macroscopic residual stresses due to the curing process of orthotropic thermoset polymer composites are determined analytically by two methods in addition to an experimental one. The classical lamination theory (CLT) is used for the calculation of residual stresses in each layer of laminated composites. It is shown that the capability of the classical lamination theory in the calculation of the residual stresses without considering the temperature dependent properties is very good. However, the shape of the unsymmetrical laminated specimen at room temperature, calculated by the CLT, is not generally accurate. The energy method is used for the modification of the CLT in predicting the room-temperature shape of the unsymmetrical laminated composites. Experimentally, glass/epoxy and carbon/epoxy laminated composites are studied by the hole drilling method. This method is shown to be reliable for an accurate measurement of the residual stresses in the first layer of laminated composites.

Repair of Stress Corrosion Cracking in Overlaying of Inconel 182 by Laser Surface Melting

The final purpose of this study is to establish the technology repairing the stress corrosion cracking (SCC) of overlaying of Inconel 182, which has been used as the material of the nuclear power plants and chemical plants by laser surface melting (LSM). In this study, residual stress and corrosion resistance were analysed on the case of LSM in the material without SCC. The SCC susceptibility was evaluated by the Streicher test. The parameters of LSM were laser power, travelling speed, defocus length and lapping rate of the weld bead. By LSM procedure, the SCC resistance in the remelted area was remarkably improved in low heat input. LSM was considered to be a useful method for repairing SCC in overlaying of Inconel 182. The microstructure was observed and the residual stress was analysed in order to make clear the reason why SCC resistance in overlaying remarkably improved by LSM. The precipitates on the grain boundary did not exist in the area of LSM. According to the calculation of residual stress in the area of LSM, high tensile residual stress of about 500 MPa was applied in this area. It was considered that the metallographic factor strongly affected the improvement of SCC susceptibility comparing the residual stress in the area of LSM.

Determination of residual stress by use of phase shifting moiré interferometry and hole-drilling method

A phase-shifting moiré interferometry and hole-drilling combined system was developed to determine residual stresses. The relationship between the 2D displacement data of three points around the drilled hole and the residual stresses relieved by hole-drilling was established. The experimental setup consisted of a four-beam moiré interferometer and a computer-controlled hole-drilling system. Two phase shifters controlled by computer were fixed in two of the four optic paths to directly get the displacement data. With special residual stresses calculation software, the phase distributions of the u and v field obtained by moiré interferometry were quickly converted into values of residual stresses. To analyze the accuracy of this experimental system, an aluminum specimen with a blind hole in the center was real-time tensioned in this system. The displacement field obtained by phase shifting moiré interferometry was compared with the finite element method solution. Good agreement was found with respect to each other. As an application, the in-depth residual stresses of a shot-peened aluminum plate were measured by this method, and possible error sources were discussed.

Tribological contact analysis of a rigid ball sliding on a hard coated surface, Part III: Fracture toughness calculation and influence of residual stresses

The surface fracture mechanisms, that are the origin to wear, were analysed by three-dimensional finite element method (FEM) modelling on micro-level by stress and strain computer simulations and by experimental studies with a scratch tester. The studied tribological contact was a diamond ball sliding with increasing load on a thin titanium nitride (TiN) coating on a steel substrate. The ball was modelled as rigid, the coating linearly elastic and the steel substrate elastic–plastic taking into account strain hardening effects. In a sliding contact the first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The effect of initial residual stress fields on coating cracking was approached by carrying out stress simulations with a pre-stressed coating. The stress fields near the indenter were found to relax by plastic deformation to such extent that the remaining stresses had only a marginal effect to macroscopic behavior. Fracture mechanical evaluation of crack driving force and fracture toughness were performed by determining stress intensity factor (SIF) solutions using boundary element analysis. SIF solutions were evaluated for crack fields of different density, location, crack angle, type of loading and mode of loading. The results were utilized to evaluate fracture characteristics and compute fracture toughness for the TiN to high speed steel coating substrate system.