Residual Stresses

This paper presents a fast and interesting chaining method for ultrasonic shot peening that allows a quick prediction of the deformed shot peened part from the ultrasonic shot peening process parameters. A simulation of the shot dynamics is done using the exact process parameters, in order to obtain the impact velocity field on the peened surface. This field is then used as an input data for an analytical residual stresses model to predict the induced residual stress field in the sample. The latter is then fed to a Finite Element Method model as an initial condition for an elastic equilibrium calculation to predict the deformation of the part. This allows a complete and fast chaining from the process parameters to the deformed shot peened component. This approach has been applied to an Almen strip. Experimental and numerical data of the strip curvature have been compared and show very promising results.

In this study, elastic and residual stresses around ball indentations on soda-lime silicate and silica glasses were measured using a micro-photoelastic imaging system and diamond indenters with different tip radii. Elastic stresses during ball indentation can be compared with classical Hertzian analytical solutions. As a result, it is found that the elastic stresses obtained from birefringence data are in good agreement with the analytical solutions calculated only from elastic moduli and Poisson's ratio of glass and of diamond. The residual stresses have been estimated assuming that the residual stresses satisfy the linear elastic constitutive law. These residual stresses around the indentation imprint without any cracks are compared with the estimated stresses using Yoffe's model and the morphology of subsequent cracks.

Significant progress has been made in the application of low plasticity burnishing (LPB) technology to military engine components, leading to orders of magnitude improvement in damage tolerance. Improved damage tolerance can facilitate inspection, reduce inspection frequency, and improve engine operating margins, all leading to improved military readiness at significantly reduced total costs. Basic understanding of the effects of the different LPB process parameters has evolved, and finite element based compressive residual stress distribution design methodologies have been developed. By incorporating accurate measurement of residual stresses to verify and validate processing, this combined technology leads to a total solutions approach to solve damage problems in engine components. An example of the total solution approach

The objective of this work is to develop models and techniques for predicting the temperature field and distortions induced in ship plates by the welding process. Finite Element models representative of real ship structures and components have been developed to simulate the transient thermal analysis with moving heat source model. Results have been compared to numerical and experimental results obtained by other researchers. The time variant temperature distributions obtained have been applied as thermal loads in mechanical analyses to predict the plate distortions. The study of the effects of different parameters on the welding response, including the torch speeds, heat inputs, thicknesses of plates has also been included. NOMENCLATURE ) r ( q Heat flux max q Maximum heat flux r Distance from heat source center Q Heat input R Radius of heating spot 1.

Sputter deposited molybdenum (Mo) thin films are used as back contact layer for Cu (In 1 À x Ga x )(Se 1 À y S y ) 2 based thin film solar cells. Desirable properties of Mo films include chemical and mechanical inertness during the deposition process, high conductivity, appropriate thermal expansion coefficient with contact layers and a low contact resistance with the absorber layer. Mo films were deposited over soda-lime glass substrates using DC-plasma magnetron sputtering technique. A 2 3 full factorial design was made to investigate the effect of applied power, chamber pressure, and substrate temperature on structural, morphological, and electrical properties of the films. All the films were of submicron thickness with growth rates in the range of 34-82 nm/min and either voided columnar or dense growth morphology. Atomic force microscope studies revealed very smooth surface topography with average surface roughness values of upto 17 nm. X-ray diffraction studies indicated, all the films to be monocrystalline with (001) orientation and crystallite size in the range of 4.6-21 nm. The films exhibited varying degrees of compressive or tensile residual stresses when produced at low or high chamber pressure. Low pressure synthesis resulted in film buckling and cracking due to poor interfacial strength as characterized by failure during the tape test. Measurement of electrical resistivity for all the films yielded a minimum v alue of 42 μΩ cm for Mo films deposited at 200 W DC power.

A partially embedded long fibre-Bragg grating (FBG) into an epoxy cylindrical specimen is used to monitor the strain distribution evolution along its axis when subjected to subsequent cycles of thermal ageing at 70°and 110°C. Assuming a total volume reduction of 2.5% at full cure, the epoxy conversion at the end of the thermal cycles was found $85%. Using strain data from the FBG, the coefficient of thermal expansion was evaluated as $11.5 Â 10 À5 C À1. Based on the strain data from the FBG, numerical simulations of an equivalent thermo-elastic matrix were performed to obtain the residual stresses in the specimen at the end of the thermal cycles. The results demonstrate the capability of FBG sensors in providing important information on the degree of cure and evolution of fabrication induced strains inside the epoxy.

This paper consid,ers the influence of _composite pulse eleclToplated nickel/tin WVS"j iayering: o" lft" mitigation of Sn whiskei growttr. The performance of ih".o-porit. p"ulsed plating-method in the mitigation of Sn whisker growth is also .o*pu".d with t'wo otf,er plating procedures. The results indicate that, uit.r a period of 6 months, the compoiite pulsed ptating-technique demonstrates much better resistance to Sn whisker growth than other plating t..ftttiq"es such as pure Sn plating and Sn plating \^Tth a Ni.underlayer onto a brass substrate subjected to various envirbnmental conditions. The primalY conclusions are based on the analysis of microstructural characteristics, the u"""ugu residual stress distribution in the film over different time periods .o*p,it"a by x-ray diffraction, the formation of intermetallic compounds, and the amounf of Sn whisker growth in each case.

Residual compressive stresses developed in layered ceramics may improve the crack resistance of the material during crack growth by reducing the crack driving force at the crack tip. i.e. R-curve behaviour occurs. Elastic contrast of layers often plays an important role by inducing an additional crack driving force term which can promote (anti-shield) or retard (shield) the crack propagation. Since the toughening effect of the residual stress state is often predicted by means of the weight function method, it is matter of interest to find limits for the application of weight function concept in elastically inhomogeneous laminates. Another objective of the paper is to investigate in detail the very process of crack transition across thermo-elastically mismatched layer interfaces. Due to the discontinuity in the elastic properties, finite crack extensions are to be considered instead of infinitesimal one. The concept of Finite Fracture Mechanics (FFM) is applied to tackle this problem.

The aim of this work is the numerical study of a crack path in a residual stress field resulting from a manufacturing process such as quenching. An XFEM technique is proposed to that end and the example illustrating the quenching of a large thick plate is considered so as to demonstrate the capability of the method proposed. Indeed, during the quenching of steels, metallurgical transformations can occur, leading to high residual stresses at room temperature. From the practical point of view, the thick plate must be sawn after quenching. But it is experimentally observed that, under certain quenching conditions, the crack initiated by the sawing, suddenly propagates through the thickness of the plate and then rotates through an angle of about 901. The numerical simulation of quenching is detailed and the results obtained under two operating conditions are given. Then the XFEM technique applied to the crack propagation in a residual stress field is presented and the cracking path obtained on the quenched plate is compared to that obtained using the FEM coupled with a remeshing technique. It is shown that the computed crack path justifies experimental observations.

In this paper the pulsed eddy current (PEC) response of a range of heat treatable and non-heat treatable aluminium alloys (AA-1050, 2024, 5083 and 7075) to applied stress well below the elastic limit is studied. The effect of prior heat treatment and prior plastic deformation on the stress dependency of the pulsed eddy current response is quantified using the peak value of the PEC difference signal. In certain cases non-linear stress responses are measured. Because it is well known that the effect of stress on conductivity is anisotropic both isotropic (circular) probes and directional (rectangular) probes are compared. It is found that both prior plastic work and heat treatment condition can have a strong effect on the stress coefficients, even changing the sign of the stress dependence. The implications of these effects for the future characterisation of residual stress state by PEC are discussed. 44 0 191 222 563; fax: + 44 0 191 222 8180. E-mail addresses: [email protected] (M. Morozov), [email protected] (P.J. Withers). NDT&E International 43 (2010) 493-500

In this work, the mode I fracture toughness behavior of dissimilar metal-composite adhesive joints is experimentally investigated utilizing the double cantilever beam (DCB) test. The under-study joint is envisioned to be applied in the hybrid laminar flow control system of future aircraft and it consists of a thin titanium sheet and a thin carbon fiber reinforced plastic (CFRP) laminate. Four different industrial technologies for the joining of the titanium and CFRP adherents are evaluated; co-bonding with and without adhesive and secondary bonding using either a thermoset or a thermoplastic composite. First, the vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the titanium-CFRP joint. After manufacturing, the joint is stiffened from both titanium and composite sides with two aluminum backing beams to ensure the non-yielding of the titanium during the subsequent DCB tests. Towards the fracture toughness determination from the experimental data, an analytical model recently developed by the authors, that considers the bending-extension coupling of each sub-laminate of the joint as well as the manufacturing-induced residual thermal stresses effect, is applied. The load-displacement behaviors, failure patterns, and fracture toughness performances for each of the four manufacturing options (MO) investigated are presented and compared.

Subsurface microstructural alterations and residual stresses caused by machining significantly affect component lifetime and performance by influencing fatigue, creep, and stress corrosion cracking resistance. Assessing the surface quality of a machined part by characterizing subsurface microstructural alterations and residual stresses is essential for ensuring part performance and lifetime in aero-engines and power generators. This comparative study characterizes and analyzes subsurface microstructural alterations and residual stresses in Inconel 718 subjected to high-speed machining with PCBN and whisker-reinforced ceramic cutting tools. Effects of cutting tool materials and microgeometry on subsurface deformation, microstructural alterations, and residual stresses were investigated. Surface and subsurface regions of machined specimens were investigated using X-ray diffraction, electron channeling contrast imaging, and electron back-scatter diffraction to characterize microstructural alterations and measure deformation intensity and depth.

This work analyses the influence of geometry, residual welding stresses and secondary bending effects on the fatigue strength of fillet welded joints made of structural steels. Joints with main plate thicknesses ranging from 10 to 100 mm subjected both to axial and to bending load with load ratios between Ϫ1 and 0.1 were considered. The experimental results were taken from the literature and then re-analysed in terms of local stress field intensity instead of nominal stress. This approach led to the definition of a new unified scatter band valid for structural steels, similar to that defined in the past for welded joints but with new characteristic parameters. The application of the scatter band to local strain fields evaluated by numerical analyses or measured by strain gauges is also discussed. 

The residual stresses in different welding methods are fundemental problems to consider. Friction stir welding is one of a solid state joining process, it is economical in that it permits joining together different materials, the specimens in this method (FSW) have excellent properties of mechanical as proven by tensile, flextural and fatigue tests, also it is environmentally friendly process minimizes consumption of energy and generate no gasses or smoke. In friction stir welding , there are two kinds of generated residual stresses: tensile stress and compressive stress. So, this study measuring the residual stresses by using a new method for measuring residual stresses depends on tensile testing and stress concentration factor, this method is a simple, fast and low cost, also it is not need special device. Design/methodology/approach: In previous studies, several techniques were used to predict the value of residual stress and its location, such as destructive, semi-destructive, and non-destructive methods. In this study, a simple, new, and inexpensive way was used based on the tensile test and stress concentration of the friction stir welding (FSW). Findings: By comparing the results obtained with the previous studies using the X-ray method, with the current research, it was found that the results are good in detecting the location and value of the residual stress of friction stir welding. The value of discrepancy of the residual stress in the results between those obtained by the previous method and the current method was about 3 MPa. Research limitations/implications: There are many rotational and linear feeding speeds used in this type of welding. This research used two plates from 6061 AA with 3mm thickness, 100 mm width, and 200 mm length. The rotational speed used in friction stir welding was 1400 rpm, and the feeding speed was 40 mm/min. Practical implications: The residual stress obtained with the new method is 6.2 MPa, and this result approximates other known methods such as the X-ray method in previus studies. Originality/value: Using a new simple method for measuring residual stresses of friction stir welding depends on stress concentration factor and tensile testing. This method is fast and low cost , also it is not need specialized device, compared to other methods such as x-ray or hole drilling methods.

This paper presents a fast and interesting chaining method for ultrasonic shot peening that allows a quick prediction of the deformed shot peened part from the ultrasonic shot peening process parameters. A simulation of the shot dynamics is done using the exact process parameters, in order to obtain the impact velocity field on the peened surface. This field is then used as an input data for an analytical residual stresses model to predict the induced residual stress field in the sample. The latter is then fed to a Finite Element Method model as an initial condition for an elastic equilibrium calculation to predict the deformation of the part. This allows a complete and fast chaining from the process parameters to the deformed shot peened component. This approach has been applied to an Almen strip. Experimental and numerical data of the strip curvature have been compared and show very promising results.

In this paper, Manual Metal Arc Welding of carbon steel plates was studied. The finite element analysis of residual stresses in butt welding of two similar plates is performed with the ANSYS software. This analysis includes a finite element model for the thermal and mechanical welding simulation. It also includes a moving heat source, material deposit, temperature dependant material properties, metal plasticity and elasticity, transient heat transfer and mechanical analysis. The welding simulation was considered as a sequential coupled thermo-mechanical analysis and the element birth and death technique was employed for the simulation of filler metal deposition. The residual stress distribution and magnitude in the axial direction was obtained. A good agreement between the computation and experimental results is obtained.

Authentication of coins is frequently presenting complicated problem in numismatics practice. Metal composition only may not be enough to identify forgeries, notably when one deals with noble metals-silver, gold or electron. Isotopic ratios, providing in certain cases information regarding metallic ore source (geographical provenance), require a sample to be extracted for MS-analysis while sampling is not permissible for numismatic material in principle. To solve the problem it becomes crucial, in addition to metal's composition, to establish the method used for a coin's manufacturing, as forgers are rarely realizing or following the method that was used in the original historical production. Conventional visual studying under microscope is not always being enough to understand how the coin was produced while metallographic examination of polished and etched metal samples, which might provide necessary information, is not applicable here for its destructive character. Necessary information regarding manufacturing could have been extracted from residual stress analysis, but, in general, there were very few published works regarding this kind of analysis for coins, and those few did not consider any connection between manufacturing process and residual stress in metal. The expected types of residual elastic stress arisen under historically known methods of coins production (casting in hot or cold mold, striking hot or cold metal) are considered in this work. On this base, non-destructive X-rays diffraction method (Sin 2 Ψ-method) is offered to distinguish between various methods of manufacturing. The results may be applied in museum's laboratory as useful criterion for authentication of coins and medals.

The bonding is one of the common processes performed during MEMS fabrication. It allows creating advanced microstructures and specific encapsulation. However, this process induces a residual stress into the structure as the annealing process is required. In this paper the bonding of silicon and pyrex glass is taken into account as these materials have different coefficients of thermal expansion. We analyze the bonding process performed in optimal temperature that induces residual stress as small as possible. The simulations show the influence of residual stress on membrane deflection in typical temperature range of operation.

The stability of plates stiffened with tee-shape stiffeners was investigated using a finite element model. Four series of stiffened plate panels were modeled using a finite strain fournode shell element. The model was validated using the results of tests on full-size stiffened plate specimens and was subsequently used to perform the study of various parameters presented in this paper. The parameters investigated are: the shape and magnitude of initial imperfections in the plate; residual stress magnitude and direction of applied uniform bending; plate slenderness ratio; plate aspect ratio; and plate to stiffener cross-sectional area ratio. The effect of the investigated parameters on the axial load carrying capacity and the mode of failure of stiffened plates is investigated both in the elastic and inelastic ranges. A comparison of these results with design guidelines formulated by Det norske Veritas and the American Petroleum Institute indicates that the guidelines are generally conservative for cases where initial imperfection magnitudes do not exceed the guidelines' prescribed maximum.

The present work presents results from an analysis of the mode I and II interfacial fracture behavior of a new adhesive joint between thin titanium and CFRP adherents, that is destined for application in the future aircraft’s leading edge. The joint is stiffened with two aluminum beams to prevent large deformations during testing. An engineering approach for the design of fracture toughness tests for the present joint is followed. The vacuum-assisted resin transfer molding technique is employed for the manufacturing of specimens subsequently tested using the double cantilever beam (DCB) and the end-notched flexure (ENF) configurations. Towards the fracture toughness determination from the experimental data, a new analytical model that considers the bending-extension coupling induced by the presence of the aluminum beams and the manufacturing-induced residual thermal stresses is applied. The analytical fracture toughness predictions are validated by two-dimensional finite element analyses. Crack propagation analyses based on the virtual crack closure technique and the cohesive zone modeling are performed to capture the experimental behavior and extract useful fracture toughness properties of the joint. A comparison of various literature’s data reduction schemes reveals the level of error if factors such as the bending-extension coupling and/or the residual thermal stresses are ignored.

Pour des composants mécaniques assurant le guidage ou la transmission de puissance (roulements, engrenages…) la tenue mécanique est particulièrement importante, mais les cycles de chargement comprenant de fortes contraintes de contact variables sont ...

This paper presents the results of a residual stress analysis that is part of a wider study of Cypriot Bronze Age knife and other weapon blades from a corpus of artefacts held by a number of institutions in Australia. The current focus is on knives from Early/Middle Bronze Age burial sites at Bellapais Vounous, Cyprus; a significant number of the blades were found on excavation to be bent. The aim of the study was to provide, by means of non-destructive neutron residual stress analysis, likely insights into fabrication methodologies of the knives and determine the stage in the life of each knife blade at which bending occurred. Two Vounous knives from the Australian Institute of Archaeology collection, one measurably bent and the other severely bent and broken, were studied using neutron diffractometer KOWARI to establish the residual stress profiles through the thickness of the knives at several locations. Since the knives were 1 - 2 mm thick at their thinnest sections, a very high...

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"A 3D model of the shot dynamics has been created based on models usually used in granular gases. A triangular mesh, representing the geometry of the entire setup (sonotrode, peening chamber and peened sample), is used in the calculations and define the space in which the spheres are able to move. In doing so, we are able to simulate thousands of impacts on the peened surface, from which statistical studies can be made to obtain direct information on the physical parameters. An experimental setup has been developed to access the shot trajectories and velocities during a peening operation, the surface coverage, as well as material related data used in the model. Preliminary studies show a good correlation with the numerical results.
An important contribution of the model to the various residual stresses prediction models (finite element models, analytical models, etc.) is that it allows them to benefit from more realistic data regarding the impact frequency and distribution on the sample, the energy dissipation, the impact velocities, etc. Such data is not available or very difficult to access experimentally at the present time.
"""""

Migration to low-k dielectric materials in wafer-fab backend-of-line (BEOL) interconnect schemes is necessary for improved electrical performance of smaller and tighter geometries enabled by advanced silicon technology nodes. Unfortunately, low-k dielectrics are mechanically weaker compared to previous generation materials. Concurrent technology and market driven changes such as tighter bump pitch and replacing SnPb with Pb-free solder bump composition are leading to increased stress and risk to damage of the inherently weaker dielectrics in flip-chip packages. It is, hence, critical to characterize the structural integrity of the BEOL interconnect schemes containing low-k dielectrics. Traditional environmental reliability stress testing, while effective, is time-consuming and expensive, and not conducive for fast learning cycles required during early development phases.

An analysis model has been developed to model the nonlinear strain rate dependent deformation of rolling bearing steel stressed in the elastic-plastic domain. The model is developed in the frame of the incremental theory of plasticity by using the von Mises yield criterion and Prandtl-Reuss equations. By considering the isotropic and non-linear kinematic hardening laws of Lemaitre-Caboche, the model accounts for the cyclic hardening phenomena.
To attain the final load of each loading cycle, the two bodies are brought into contact incrementally. For each new load increment new increments for the components of stress and strain tensors, but also increments of residual stresses, are computed for each point of the 3D mesh. Both, the new contact geometry and residual stresses distributions, are further considered as initial values for the next loading cycle, the incremental technique being reiterated. The cyclic evaluation process of both, plastic strains and residual stresses is performed until the material shakedowns.
Comparisons of the computed deformed profiles, as well as of the computed residual stresses distributions with those obtained by measurements or numerically, by using the finite element method or another semi-analytical method, reveal a very good agreement and validate the incremental analysis model

The generation of residual stresses in orthogonal machining is analysed by using an Arbitrary Lagrangian Eulerian (ALE) finite element approach. It is shown that a substantial level of tensile residual stresses can be obtained in the vicinity of the machined surface without any contribution of thermal effects. This motivates the development of a parametric study to analyse the effects of the thermomechanical coupling parameters on residual stresses. The roles of thermal expansion, of thermal softening and of the Taylor-Quinney coefficient (controlling the heat generated by plastic flow) are considered separately. The influence of friction is also analysed by assuming dry cutting conditions and a Coulomb friction law. The friction coefficient has a complex effect by controlling heat generation (frictional heating) along the tool rake and clearance faces and the propensity for the chip to stick to the tool. Geometrical effects such as the tool rake angle and the tool edge radius are also discussed.

Thick Ni electrodeposits, with thicknesses ranging from 18 to 90 μm, have been produced from sulfamate baths using very low current densities (1.5-5 mA cm −2 ). Increasing grain sizes, with a corresponding decrease in the hardness values, and more columnar grain morphologies were observed with increasing current densities in the deposits. The anisotropy in the mechanical properties of the deposits were found to correlate strongly with the deposit texture, where the change from a b101N dominated orientation at 1.5 mA cm −2 to a b 001N orientation at the higher (5 mA cm −2 ) current density led to a corresponding decrease in the indentation modulus values for the respective Ni films. The residual stress values measured in the deposits (75-136 MPa) were found to be comparable to literature values of deposits plated at higher current densities, which rules out any potential advantage from the use of such low current densities for producing lower residual stresses.

The porcelain tile is a ceramic product with high technical and aesthetic performance, whose composition is formulated from a mixture of clay or kaolin, quartz and feldspar. This paper is the first part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Seven compositions were prepared according to a simplex-centroid mixture design for a triaxial mixture, comprised of kaolinite, quartz and albite. The mixtures were processed reproducing industrial conditions: wet mixing followed by spray-drying, forming by pressing and fast firing with maximum temperatures ranged from 1210 to 1260 • C. The presence of kaolinite increases the dry apparent density in a significant way up to 30 wt%. Because of the fast firing, the microstructure is directly influenced by particle packing after forming. The internal porosity presented little change as a function of starting composition in the tested intervals. The surface porosity of the polished product increased with higher amounts of quartz. The results obtained in this first part of the study showed how the starting and end composition could generate the microstructure and suggest its influence on the mechanical properties of the porcelain tile, which will be later analysed in the second part of this paper.

CrN/AlN superlattice coatings with different CrN layer thicknesses were prepared using a pulsed closed field unbalanced magnetron sputtering system. A decrease in the bilayer period from 12.4 to 3.0 nm and simultaneously an increase in the Al/(Cr + Al) ratio from 19.1 to 68.7 at.% were obtained in the CrN/AlN coatings when the Cr target power was decreased from 1200 to 200 W. The bilayer period and the structure of the coatings were characterized by means of low angle and high angle X-ray diffraction and transmission electron microscopy. The mechanical and tribological properties of the coatings were studied using the nanoindentation and ball-on-disc wear tests. It was found that CrN/AlN superlattice coatings synthesized in the current study exhibited a single phase face-centered cubic structure with well defined interfaces between CrN and AlN nanolayers. Decreases in the residual stress and the lattice parameter were identified with a decrease in the CrN layer thickness. The hardness of the coatings increased with a decrease in the bilayer period and the CrN layer thickness, and reached the highest value of 42 GPa at a bilayer period of 4.1 nm (CrN layer thickness of 1.5 nm, AlN layer thickness of 2.5 nm) and an Al/(Cr + Al) ratio of 59.3 at.% in the coatings. A low coefficient of friction of 0.35 and correspondingly low wear rate of 7 × 10 − 7 mm 3 N − 1 m − 1 were also identified in this optimized CrN/AlN coating when sliding against a WC-6%Co ball.

Friction stir welding (FSW) between 3 mm thick AA 5052-O aluminum alloy plates was investigated in the present study. Different welded specimens were produced by employing a constant tool traverse speed of 120 mm/min and by varying rotating speeds from 800 to 3000 rpm. The welded joints were characterized by its appearances, microstructural and mechanical properties at room temperature. The measurement of different forces acted on the tool during the FSW of AA 5052-O plates provided a significant insight to determine the quality of the welded joints. From the appearances of the welded joints it was evident that, except the tool rotational speed of 3000 rpm all other rotational speeds produced sound welded joints with smooth surface. The joint produced at 1000 rpm yielded a maximum tensile strength of 132 MPa which was 74% of the base material strength. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) analyses on the stir zone suggested that, beta-Mg2Al3 intermetallic phases of the base material were mechanically fractured, smeared and mixed to different geometries due to tool stirring. The dissolution and redistribution of beta-Mg2Al3 second phase particles in the stir zone had a considerable effect on the reduction of the tensile strength of the welded joints. The reduction in hardness at the nugget zone (NZ) of the welded joints under different tool rotational speeds could be attributed to the dislocation of Mg-rich phases and segregation of Mg solute atoms at grain boundaries, which drew solute Mg atoms away from the alpha-aluminum matrix. (C) 2014 Elsevier Ltd. All rights reserved.

http://www.sciencedirect.com/science/article/pii/S0261306914008310 
http://eprints.um.edu.my/11621/ 
http://repository.um.edu.my/94959/1/FSW.pdf

The buckling problem of a circular cylindrical shell has long been widely investigated due to its great importance in the design of aerospace and marine structures. But very little attention has been paid until now on the influence of residual stresses on the critical and often unstable response of such structures. In this paper, a shell finite element is designed within the total Lagrangian formulation framework to deal with the elastoplastic buckling and postbuckling of thin cylindrical tubes under external pressure and axial compression. A specific experimental process will be introduced in order to measure residual stresses in the shell very accurately, so as to include them in the numerical calculations. The present formulation will enable us to describe the complete non-linear solution, namely the critical load, the bifurcation mode and the bifurcated equilibrium branch up to an advanced post-critical state corresponding to collapse. Comparisons will be made between numerical results and the experimental critical value and deformation patterns of a new generation profiler. Furthermore, the combined effects of geometric imperfections, residual stresses and plasticity will be analyzed.

The porcelain tile is a ceramic product with high technical and aesthetic performance, whose composition is formulated from a mixture of clay or kaolin, quartz and feldspar. This paper is the first part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Seven compositions were prepared according to a simplex-centroid mixture design for a triaxial mixture, comprised of kaolinite, quartz and albite. The mixtures were processed reproducing industrial conditions: wet mixing followed by spray-drying, forming by pressing and fast firing with maximum temperatures ranged from 1210 to 1260 • C. The presence of kaolinite increases the dry apparent density in a significant way up to 30 wt%. Because of the fast firing, the microstructure is directly influenced by particle packing after forming. The internal porosity presented little change as a function of starting composition in the tested intervals. The surface porosity of the polished product increased with higher amounts of quartz. The results obtained in this first part of the study showed how the starting and end composition could generate the microstructure and suggest its influence on the mechanical properties of the porcelain tile, which will be later analysed in the second part of this paper.

2G HTS coated conductor (CC) tapes are now used for electric device applications. The residual stress/strain induced in HTS coating films in CC tapes during cool down influences the critical current, I c , and should be investigated. In this study, the thermal residual stress/strain induced in the REBCO coating film was calculated from deposition temperature (1073 K) to 77 K by thermo-mechanical analysis and numerical simulation. Additionally, the improvement in irreversible strain limit, ε irr. , with copper electroplating has been investigated.

This paper illustrates the effect of thermal treatment and alloy composition on the microstructures of gold-silver films and subsequently dealloyed nanoporous gold films. Even though thermal treatment of alloys increases tensile stress in gold-silver films, it mitigates the formation of microscale voids during dealloying. The voids in the dealloyed film are too large to be rationalized by relaxation of the residual stress. The interplay between volume shrinkage during dealloying, residual stress and thermally induced deformation is discussed to explain void formation.

In bulk ferroelectric ceramics, extrinsic contributions associated with motion of domain walls and phase boundaries are a significant component of the measured dielectric and piezoelectric response. In thin films, the small grain sizes, substantial residual stresses, and the high concentration of point and line defects change the relative mobility of these boundaries. One of the consequences of this is that thin films typically act as hard piezoelectrics. This paper reviews the literature in this field, emphasizing the difference between the nonlinearities observed in the dielectric and piezoelectric properties of films. The effect of ac field excitation levels, dc bias fields, temperature, and applied mechanical stress are discussed.

A técnica de difração de neutrões é usada neste artigo para estudar amostras ferríticas, revestidas com aços inoxidáveis austeníticos através de soldadura por arco submerso. Este procedimento é frequentemente usado no fabrico de equipamentos de processo para as indústrias química e nuclear, por facilidade de execução e razões económicas. A principal desvantagem deste processo de revestimento é a fissuração que frequentemente ocorre na interface material base/soldadura, potenciada pela presença de tensões residuais resultantes da operação de soldadura, a qual pode ser minimizada com a realização de tratamentos térmicos de relaxação de tensões. As amostras foram produzidas a partir de placas em aço ao carbono, tendo uma das superfícies sido revestida com dois tipos de aço inoxidável. Para a primeira camada foi usado um elétrodo EN 12072 -S 23 12 2 L e para a segunda e a terceira camadas foi usado um elétrodo EN 12072 -S 19 12 3 L. Após a soldadura, as amostras foram submetidas a um tratamento térmico de relaxação de tensões, durante 1 hora, à temperatura de 620°C. Os perfis de tensões residuais obtidos por difração de neutrões evidenciam a relaxação de tensões residuais após o tratamento térmico realizado. A técnica de difração de neutrões revelou-se muito adequada na avaliação de tensões residuais neste tipo de ligações.

Measurements of residual stresses in textured thin films have always been problematic. In this article, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin c method. 2 Instead of using the Bragg-Brentano (B-B) or Seemann-Bohlin geometry, the proposed method utilizes an asymmetrical diffraction geometry for which the X-ray beam is incident at a grazing angle g to the sample surface, while the angle c is the tilt angle of the sample surface as defined by the conventional sin c method. Basic equations involved in the X-ray residual 2 stress analysis are described, along with exemplified experimental data. Analysis shows that, for an isotropic medium, strain measured using this grazing-incidence geometry assumes a linear relationship with the geometrical parameter cos a sin c, where 2 2 the angle a is a constant and is defined as the Bragg angle at cs08, u , minus the grazing incidence angle g, i.e. asu yg. o o The grazing-incidence diffraction geometry effectively increases the irradiation volume from a thin-film specimen, thereby giving rise to higher intensity for high-angle Bragg peaks than the conventional B-B geometry. The proposed analysis has another advantage, in that the inhomogeneous sample casts little effect on the residual stress results when compared to the traditional sin c method.

An analytical framework is presented to calculate the mode I and II components of the strain energy release rate (SERR) of a delamination between two generally layered sub-laminates, considering the residual hygrothermal stresses effect. First, the sub-laminates are modeled as Timoshenko beams, the crack tip is assumed rotationally flexible and the mode partitioning is based on the global method. Next, SERR and mode mixity are obtained for an arbitrarily loaded delaminated beam and reduced for some typical delamination fracture tests. An asymmetrically delaminated fiber metal laminate (FML) is analyzed under double cantilever beam (DCB) and end-notched flexure (ENF) configurations. For the ENF configuration, the inherent contact problem was analytically approached. We demonstrate that the thermal effect on the SERR and mode mixity of the FML, rather ignored so far in the literature, can be non-negligible. Finally, the analytical results are validated against numerical predictions using the finite element method.

This paper presents a portable device to measure residual stresses using the hole drilling technique combined with digital speckle pattern interferometry. This device, which is based on only one dual-beam illumination system, allows the determination of the three components of the residual stress from the measured displacement field generated by the hole when specimens are placed outside of the optical bench. The description of the portable device and its principal characteristics is followed by the presentation of some preliminary experimental results obtained in thin aluminium plates subjected to a uniform uniaxial stress. An error analysis of the uncertainty sources introduced during the evaluation of the residual stresses, namely the error generated by the automatic data processing, the error produced by an incorrect location of the hole centre and the introduction of rigid body displacements, is also presented. r

The porcelain tile is a ceramic product with high technical and aesthetic performance, whose composition is formulated from a mixture of clay or kaolin, quartz and feldspar. This paper is the first part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Seven compositions were prepared according to a simplex-centroid mixture design for a triaxial mixture, comprised of kaolinite, quartz and albite. The mixtures were processed reproducing industrial conditions: wet mixing followed by spray-drying, forming by pressing and fast firing with maximum temperatures ranged from 1210 to 1260 • C. The presence of kaolinite increases the dry apparent density in a significant way up to 30 wt%. Because of the fast firing, the microstructure is directly influenced by particle packing after forming. The internal porosity presented little change as a function of starting composition in the tested intervals. The surface porosity of the polished product increased with higher amounts of quartz. The results obtained in this first part of the study showed how the starting and end composition could generate the microstructure and suggest its influence on the mechanical properties of the porcelain tile, which will be later analysed in the second part of this paper.