Residual Stresses

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.

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.

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 existence of residual stresses locked-in prefabricated displacement piles is a well-known problem and has been addressed by a number of researchers in the last decades. This is not the case with cast in situ piles: as a consequence of concrete curing, pile-soil interaction starts soon after concrete casting, causing stress changes in terms of both normal and shear stresses. Such circumstance has been confirmed by few experimental evidences, reported in the paper, in saturated or dry soil conditions.

AISI310 is widely used in the manufacture of heat exchangers, radiant tubes, muffles, furnace parts, food processing equipments. Welding is widely used fabrication method in such type of industrial applications; but unfortunately welding induces few problems such as residual stresses and induced distortions. Residual stresses have significant effect on performance of the weld joint subjected to loading. The AISI310 is welded using matched filler material. Thus the weld joint consist of two different materials having different behavior under tensile loading. In this study residual stresses are estimated by using Labeas and Diamantakos formula and values are assigned as an initial stress in FEM of weld joint. The weldment specimen model is subjected to tensile loading and effect of residual stress on local yielding is investigated. The ANSYS is used for this purpose. The response of weld joint to monotonically increasing tensile load is determined experimentally by conducting the transverse and longitudinal tension tests on UTM. The stress-strain behavior of the weld joint is studied vis a vis virgin 310 stainless steel alloy.

In this paper, surface effects on the axial buckling and the transverse vibration of nanowires are examined by using the refined Timoshenko beam theory. The critical compression force of axial buckling and the natural frequency of nanowires are obtained analytically, in which the impacts of surface elasticity, residual surface stress, transverse shear deformation and rotary inertia have been included. The buckling and vibration behaviour of a nanowire is demonstrated to be size dependent, especially when its cross-sectional dimension reduces to nanometres. The surface effects with positive elastic constants tend to increase the critical compression force and the natural frequency, especially for slender nanowires, while the shear deformation lowers these values for stubby nanowires. This study may be helpful to accurately measure the mechanical properties of nanowires and to design nanowire-based devices and systems.

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.

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.

This study used finite element techniques to analyze the thermo-mechanical behaviour and residual stresses in butt-welded pipes. The residual stresses were also measured in some welds by using the Hole-Drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a finite element modelling procedure with reasonable accuracy was developed. The developed FE modelling was used to study the effects of weld groove shape and weld pass number on welding residual stresses in buttwelded pipes. The hoop and axial residual stresses in pipe joints of 6 and 10 mm thickness of different groove shapes and pass number were studied. It is shown that these two parameters may have significant effects on magnitude and distribution of residual stresses in welded pipes.

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. 

Based on piezoelectric constitutive equations and Bragg law, we proposed an extended model, in which the piezoelectric coupling factor determined by the elastic, dielectric and piezoelectric constants is introduced, to evaluate the residual stress in ferroelectric thin film with X-ray diffraction (XRD). Pb(Zr 0:52 Ti 0:48 )O 3 thin films with thickness 0.05, 0.5, and 1.0 lm were grown on Pt/Ti/ Si(0 0 1) by pulsed laser deposition (PLD) at the substrate temperature 650°C and oxygen pressure 40 Pa. D500 goniometer and sin 2 w method were used to measure the residual stress in PZT thin films. The origin of residual stress was theoretically discussed from the epitaxial stress, intrinsic stress, thermal stress, and transformation stress. The results show that the theoretical results are closer to the experimental results evaluated by the extended model, and the residual compressive stress evaluated by the extended model is larger than that evaluated by the conventional model due to the consideration of the piezoelectric coupling effects.

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

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.

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.

High residual stresses are developed on the surfaces of Electric Discharge Machined parts. In this study, Layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in Electric Discharge Machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function.

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.

Longitudinal and circumferential welds in transportable pressure vessels are produced by submerged-arc welding using a single vee preparation and multiple weld runs. Quenched and tempered (QT) steels, which are commonly used for transportable pressure vessels, require mandatory postweld heat treatment (PWHT), at temperatures between 540 and 590 8C, regardless of plate thickness. This paper reports on the weld procedure and cross-weld performance evaluation of weldments in 11 and 12 mm QT steel plate before and after PWHT. Root bend (1808) tests showed no evidence of cracking or tearing in any of the samples tested. After PWHT, tensile tests indicate a reduction in the ultimate tensile strength of all samples and a decrease in yield strength for the 12 mm sample only. The hardness results were consistent with the tensile test results because they revealed significant softening in the HAZ and WM as a result of PWHT. Additionally, residual stress measurements before and after PWHT showed that PWHT is effective in reducing surface residual stresses to levels low in the elastic range.

Silicone is a common dielectric elastomer material. Actuators made from it show excellent activation properties including large strains (up to 380%), high energy densities (up to 3.4 J g-1), high efficiency, high responsive speed, good reliability and durability, etc. When a voltage is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along the electric field and expands in the transverse plane. In this paper, a silicone dielectric elastomer is synthesized and the area strains are tested under different electric fields. Pre-strain and a certain driving electric field are applied to the film and the induced large strain by the Maxwell stress is measured. Barium titanate (BaTiO3) was incorporated into the silicone to fabricate a new dielectric elastomer: the experimental results show that the elastic modulus and dielectric constant were significantly improved. The experimental results coincide well with those of finite element analysis at a large deformation. Also, a theoretical analysis is performed on the coupling effects of the mechanical and electric fields. A nonlinear field theory of deformable dielectrics and hyperelastic theory are adopted to analyze the electromechanical field behavior of these actuators. Also the mechanical behavior of the dielectric elastomer undergoing large free deformation is studied. Finally, the constitutive model of a dielectric elastomer composite under free deformation and restrained deformation is derived. This article was originally submitted for the special section 'Smart Composite Materials: Selected Papers from the International Conference on Multifunctional Materials and Structures (MFMS 08) (Hong Kong, 28-31 July 2008)', Smart Materials and Structures, volume 18, issue 7.

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 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.

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.

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

In fusion welding, thermal cycle leads to undesirable metallurgical structure and causes residual stresses gets induced near the weld zone which plays an important role in determining the reliability of the weld joint. In this present work, the prediction of residual stresses in a welded joint has been done using Contour method. The measurements of the cross-sectional residual stress profile in a Duplex stainless steel 2205 welded with ER 2209 filler material are validated in the longitudinal direction. This method is simple in principle and easy in use. According to this method, the weld metal containing residual stresses is cut along the plane perpendicular to the weld line. The deformations occurring at the cut surfaces as a result of relaxation of the residual stresses are measured. The measured deformations are given as displacement boundary conditions to a finite element model to calculate the corresponding stresses normal to the cutting plane. This superposition principle assumes that the material behaves elastically during relaxation of residual stresses and that the cutting process does not introduce any new stresses to influence the measured displacements. It requires only one straight cut through a sample on the plane of interest, followed by measurement of the surface contour produced by relaxation of the internally stored stress field. This study indicates that the contour method is a powerful novel technique to obtain an accurate full three-dimensional map of residual stress field.

Application of shape memory alloy (SMA) actuators is limited to low frequencies due to slow cooling time especially in the embedded conditions where heat transfer rate is the controlling factor. In this study, we investigate various active cooling techniques and effect of pre-stress to improve the response time of two commercially available SMAs: Flexinol from Dynalloy Inc. and Biometal fiber from Toki Corporation. Flexinol and Biometal fiber of equal length and diameter were found to exhibit different actuation behavior under pre-stress. Time domain force response of SMA actuators was found to be dependent upon the applied prestress, heating rate, and amplitude of applied electrical stimulus. Compared to Biometal fibers, time domain response of Flexinol was found to decrease significantly with increasing pre-stress indicating the difference in transformation behavior. Fluid flow and heat sinking were found to be suitable methods for improving the response time by reducing the cooling cycle from 1.6 s to 0.300.45 s. This is a significant improvement in the actuation capability of SMAs.

& Procedures and results of experimental work to measure residual stresses and hardness depth in electric discharge machined surfaces are presented. Layer removal method is used to express the residual stress profile as a function of depth caused by a die sinking type EDM. Thin stressed layers are removed from machined samples by electrochemical machining. Corresponding deformations due to stress relaxation are recorded for each removal to determine the stress profile from elasticity theory. The relational dependence of the machining parameters with residual stresses is obtained and a semi-empirical model is proposed for plastic mold steel for de-ionized water as dielectric liquid. These stresses are found to be increasing rapidly with respect to depth, attaining to its maximum value, around the yield strength, and then fall rapidly to compressive residual stresses in the core of the material since the stresses within plastically deformed layers are equilibrated with elastic stresses.

The residual stress profile in a hardened layer of steel was measured and then compared with a finite element prediction. A thick ring made of low alloy gear steel was case hardened by carburization and quenching. The residual hoop stress variation in the 1 mm thick hardened layer was measured using the crack compliance method, in which surface strains are measured as an axial slot is incrementally extended from the outer surface inward using wire electric discharge machining (EDM). The surface residual stresses were also measured using x-ray diffraction. The results compared very well with finite element predictions using DANTE, a heat treatment simulation software package interfacing with the finite element code ABAQUS. The heat treatment cycle is simulated in an uncoupled serial analysis of carburization by diffusion, quenching by conduction and convection including phase transformation kinetics, and finally a structural analysis incorporating TRansformation-Induced Plasticity (TRIP). Accurate residual stress profiles require detailed knowledge of the heat transfer coefficients of the quench media as well as alloy-dependent descriptions for phase transformation kinetics and TRIP strains.

TIG welding is a popular joining method for stainless steel (SS) which contains 16-18% of Cr and is responsible for its corrosion resistance and good mechanical properties. The SS welding electrode is over alloyed with 18-22% of Cr. During TIG welding, fumes containing carcinogenic hexavalent Cr +6 are generated which are mainly from the electrode rather than the base metal and this affects the health of the welder. To mitigate these problem eight versions of nickel based Cr-free electrode materials were developed. After extensive literature survey and discussions with welding expert's chemical composition of filler rod (electrode) is decided such that the weld joint should have good mechanical properties. It is well known fact that structural components in addition to structural loads also experience welding induced residual stress. Presence of residual stresses may be favorable or harmful for the structural components depending on their nature and magnitude. Hence the main focus of the study is to perform Finite Element Analysis to understand the complete nature of residual stresses and distortions in butt welded joints using the eight novel Cr-free electrodes with base plates AISI SS304 and to determining the best weldment combination. Ansys 13, a finite element (FE) based commercial software, sequentially coupled transient thermal-mechanical, three dimensional finite element models were developed and the simulation was done using elemental birth and death technique. After the FE analysis it was seen that though the variation in distortions were not considerable by virtue of restraints, the stresses in each variety of the weld showed notable variations of about 30MPabetween the best and the least preferred composition.

The foreign object damage (FOD) on leading edge geometries from particles ingested into gas turbine engines found to be comprised of geometric discontinuities like a notch, the residual stresses in regions adjacent to the notch, and material degradation in the form of micro-cracks, plastic deformation, voids, etc. The extent of the damage is related to the geometry and characteristics of the impacting object as well as those of the leading edge in terms of the resultant high cycle fatigue (HCF) strength of a simulated airfoil geometry. Steel spheres having diameters ranging from 0.5 to 2.0 mm are used as the impacting objects at velocities over a range from 60 to 500 m/s. The role of residual stresses is identified through the use of samples subjected to stress relief annealing. Simple notch analysis is used to estimate the effect of the geometry on the fatigue strength.

Welding residual stresses have important consequences on the performance of engineering components. High residual stresses lead to loss of performance in corrosion, fatigue and fracture but as yet these consequences are poorly quantified. The major cause of this is that residual stress often remains the single largest unknown in industrial damage situations since they are difficult to measure or estimate theoretically.

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.

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.

The residual stress profile in a hardened layer of steel was measured and then compared with a finite element prediction. A thick ring made of low alloy gear steel was case hardened by carburization and quenching. The residual hoop stress variation in the 1 mm thick hardened layer was measured using the crack compliance method, in which surface strains are measured as an axial slot is incrementally extended from the outer surface inward using wire electric discharge machining (EDM). The surface residual stresses were also measured using x-ray diffraction. The results compared very well with finite element predictions using DANTE, a heat treatment simulation software package interfacing with the finite element code ABAQUS. The heat treatment cycle is simulated in an uncoupled serial analysis of carburization by diffusion, quenching by conduction and convection including phase transformation kinetics, and finally a structural analysis incorporating TRansformation-Induced Plasticity (TRIP). Accurate residual stress profiles require detailed knowledge of the heat transfer coefficients of the quench media as well as alloy-dependent descriptions for phase transformation kinetics and TRIP strains.

The present work focuses on the design and analysis of interlaminar fracture toughness tests for dissimilar (metal-composite) adhesive joints in the presence of residual thermal stresses. A generic joint configuration is studied; the thin metal and composite adherents have different thicknesses, while also two metallic stiffening beams of different thicknesses are applied in both sides of the joint to increase the strength of the joint and prevent undesirable failures during the tests. Also, residual thermal stresses are considered to account for high-temperature curing cases. Special attention was paid to the double cantilever beam (DCB) and end-notched flexure (ENF) tests. Firstly, a methodology was provided for the preliminary design of the specimens for these tests. Subsequently, an analytical model that is currently being extended by the authors was utilized to determine the mode I and II strain energy release rates (SERR) of the interface crack between the metal and composite components. It was shown that non-constant mode mixity is introduced during both pure mode fracture tests due to the dissimilar materials/geometries of the adherents in combination with the residual thermal stresses. Also, in DCB analyses, the SERR without considering residual thermal stresses are lower than those that take into account this effect. Finally, in ENF tests, specimen placement plays crucial role in the SERR results, something that is not the case with the DCB tests.

In the present paper the authors propose a portable and low-cost speckle interferometer for evaluating 3D deformation fields. The interferometer was designed and realized with the aim of carrying out measurements on small areas, hence it can be used to approach problems characterized by displacement field with highly localized gradients, such as the strain relief occurring in residual stress evaluation or the displacements which arise around notches or crack tips. The costs of the experimental equipment were reduced by employing laser diodes as light sources, a PZT actuator designed and calibrated by the authors and a control electronics realized on purpose. Moreover the configuration which was adopted allows further saving on optical components. The experimental results reported at the end of the paper, and obtained by a specimen subjected to 3D rigid body motions, show a high repeatability and accuracy. Furthermore the experimental results have shown that the geometry of the optical setup implies the variation of the sensitivity vectors on the inspected area, but this effect can be evaluated (analytically and/or experimentally) and taken into account in order to increase the accuracy of the measurements.

A finite element (FE) technique has been used to predict the residual and thermal stresses which occur during water quenching of solid stainless-steel (SS) spherical balls. The variations of residual stresses at different positions and cross-sections, e.g. the radial, axial and tangential directions, have been examined. Also, the influence of heat transfer coefficient, the initial temperature and the hardening assumption on residual stress results has been investigated. The results show that high compressive residual stresses occur along the cooling surface. Moving away from the surface, these residual stresses begin to decrease and reverse their sign, and near the centre are tensile. Preliminary quenching experiments have been carried out using spheres of type 316L stainless steel. The temperature during quenching was recorded and compared with finite element simulations. The surface residual stresses were determined using the incremental centre-hole measurement technique. Neutron diffraction (ND) was used to determine the residual stresses in the centre of the sphere. The paper compares these measurements with the finite element results as well as comparing the measured cooling temperature history with simulation. Overall there is good agreement between the predicted and measured stresses.

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

Superhard titanium diboride (TiB 2 ) coatings (H v 4 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB 2 target using an unbalanced direct current (d. c.) magnetron. Polished Si (0 0 1), stainless steel, high-speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, U s , and substrate temperature, T s , on mechanical properties of TiB 2 coatings was studied. X-ray diffraction (XRD) analysis showed hexagonal TiB 2 structure with (0 0 01) preferred orientation. The texture of TiB 2 coatings was dependent upon the ion bombardment (U s increased from 0 to À300 V) and the substrate heating (T s increased from room temperature (RT) to 700 1C). All TiB 2 coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness H v up to 34 GPa, effective Young's modulus E* ¼ E/(1-n) ranging from 450 to 600 GPa; here E and n are the Young's modulus and Poisson's ratio, respectively, and elastic recovery W e E80%. TiB 2 coating with a maximum hardness H v E73 GPa and E*E580 GPa was sputtered at U s ¼ À200 V and T s ¼ RT. Macrostresses of coatings s were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB 2 coatings exhibited compressive macrostresses. r

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.

The present work was aimed at evaluating the effects of shot peening on the fatigue performance of the well known age-hardening aircraft aluminium alloy Al 2024. Shot peening to full coverage was performed using spherically shot (SCCW14) with an average shot size of 0.36 mm and an Almen intensity of 0.20 mmA. After applying the various mechanical surface treatments, the changes in the surface and near-surface layer properties such as surface topography, micro-hardness and residual stress-depth profiles were determined. In addition to the mechanically surface treated specimens, electrolytically polished conditions were used to serve as reference. The fatigue results will be interpreted in terms of the process-induced changes in the resistances to crack nucleation and micro-crack growth.

Residual stress was measured on plasma sprayed crystalline Ni\Al, Al 2 O 3 and amorphous Al 2 O 3 \TiO 2 \ZrO 2-CeO 2 single splats, by using an incremental focused ion beam (FIB) micron-scale ring-core method (IμRCM). Tensile residual stress exists in polycrystalline Ni\Al splats, where the quenching stress is only partially relaxed by edge curling and through-thickness yielding. Significant compressive stress was observed for the amorphous Al 2 O 3 \TiO 2 \ZrO 2 \CeO 2 splats, where viscous flow above the glass transition temperature completely relaxed the quenching stresses without micro-cracking. Comparatively lower compressive stress was measured on crystalline Al 2 O 3 splats, where, in spite of extensive micro-cracking, not all of the tensile quenching stress was relaxed. Using stress data and micro-crack geometry, the intrinsic shear adhesion strength of Al 2 O 3 splats was calculated, giving insights into the role of (sub)micron-scale phenomena on adhesion/cohesion of thermally sprayed coatings. The proposed stress build-up mechanisms and relaxation phenomena are supported by a TEM microstructural analysis of the splats. The experimental methodology developed provided a unique way for the study of the residual stress buildup mechanisms in amorphous and crystalline single splats obtained by plasma spraying, and gave further insights into the actual micro-scale phenomena that give rise to adhesion and nano-mechanical behavior of thermally sprayed coatings. The proposed approach is also expected to find a wide range of applications in materials science and engineering, as it allows for the residual stress measurement even on amorphous materials with micrometer spatial resolution.