Macroscopic Residual Stresses Research Articles

The effect of crucible bottom deformation on the quality of Nd:GGG crystals grown by Czochralski method

AbstractIn this paper, we report the growth of neodymium doped Gadolinium Gallium Garnet (Nd: GGG) crystal using Czochralski (CZ) method, and study the effects of crucible bottom deformation and thermal insulator thickness on the growth process and crystal quality. Garnet structure and <111> crystallography orientation of the crystal were confirmed by the X‐Ray diffraction (XRD) analysis. Macroscopic defects, residual stresses, quality, and homogeneity of the crystals were investigated by means of parallel plane polariscope and laser fizeau interferometer respectively and the results compared together. Experimental observations show that the crucible bottom deformation from flat to convex, and decreasing the thickness of zirconia insulator under the crucible result in the formation of lateral cores and increasing the crystal inhomogeneity and tensions, leading to the decrease of the crystal quality. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Residual Stress in Ductile Iron Component on its Natural Frequency

In the paper four components of ductile iron cast in different stress status, including the cast status, the status of vibratory stress relief and the status of thermal stress relief with 3 months of the natural stress relief and 10 years of the natural stress relief, are selected.X-ray diffraction method is used to measure residual stress and experimental modal analysis is for measuring natural frequency. A quantitative relation between residual stress in ductile iron cast component and its natural frequency variation is obtained. Thus we provide a reference for using natural frequency to evaluate the macroscopic residual stress of ductile iron material component. The results show that the peak value variation of macro residual stress in ductile iron component have a logarithmic relation to its natural frequency variation, and same as the mean value variation in macro-residual stress and its natural frequency variation.

XRD characterisation of composite Ni-based coatings prepared by electrodeposition

The present work is aimed at XRD investigation of structural parameters that influence the functional properties of Ni–W/Al2O3 electrodeposit coatings. The relationship between electrodeposition parameters and structural properties of the coatings deposited on steel substrates has been determined. XRD investigations were performed on a Bruker D8 Discover diffractometer equipped with a position-sensitive linear detector. The modified sin2ψ X-ray diffraction method was used to determine the macroscopic residual stresses of deposits. The crystallite size and lattice strain of the coatings were evaluated by analysis of X-ray diffraction patterns (Rietveld analysis). The crystallographic texture was analysed using the orientation distribution function (ODF) calculated from the incomplete pole figures. It was shown that the structural properties of the deposits were strongly correlated with chemical composition. X-ray diffraction patterns of all Ni–W coatings exhibit mainly the fcc phase structure of the Ni–W solid solution with a lattice parameter intermediate between those of Ni and W, which rises when the tungsten content increases. At the same time the crystallite dimension (the size of the coherent domains) was gradually reduced. It was found that Ni–W coatings containing about 40wt.% W revealed the tensile residual stresses (2300–1200MPa), depending on deposition conditions.

Residual Stresses in Locally Long Fiber Reinforced Aluminum Parts

In locally long fiber reinforced aluminum parts two types residual stresses exist. They are the microscopic residual stress between fiber and matrix and the macroscopic residual stress between reinforced and unreinforced zones. The residual stresses between fiber and matrix in γ-Al2O3 long fiber reinforced aluminum alloy Al-6-1-1 were measured with X-ray Diffraction process as well as simulated with FEM method. The results indicated that the residual stresses in both fiber and matrix were distributed very unequally. The maximum tensile residual stress occurred at the boundary in the matrix and the maximum compressive residual stresses occurred near the boundary in the fiber. The macroscopic residual stresses between the reinforced and unreinforced zones were also measured with borehole method as well as simulated with FEM. It was found that the macroscopic residual stresses at most locations in both the reinforced and unreinforced zones were not harmfully high. However in both reinforced and unreinforced zones there were small sub-zones of very large tensile residual stresses.

Structure and Mechanical Properties of AlCrN Thin Films Deposited by Magnetron Sputtering

A magnetron sputtering system was used to deposit AlCrN thin films. Chemical compositions of the films were determined by both EDXS and RBS, while structures analyses were conducted by XRD in a Seifert XRD3000 diffractometer. Macroscopic residual stresses of films were determined by curvature measurements using DEKTAK IIA profilometer, while in-grain stresses were extracted by the “sin²Y method” from XRD measurements. A nanoindenter from CSM (Switzerland) was used to determine the hardness of the films. A CrN type FCC structure was obtained with a strong (200) fiber texture for the range of compositions Al1-xCrxNy(0.56 < x< 0.89) of interest here. The global stresses were compressive for all FCC films resulting from the high energetic deposition conditions used. In-grain compressive stresses were determined for the films with thickness < 500nm, while thicker films (> 500nm) showed tensile in-grain stresses. Stress-free lattice parameter a0strongly decreased from 4.13 to 3.97 A°. Hardness values were obtained in a range extending from 17 to 27 GPa with an increase obtained as Cr content increases and correlated to the residual-stress level.

Influence of composition on mechanical behaviour of porcelain tile. Part III: Effect of the cooling rate of the firing cycle

This paper is the third part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Tile compositions were prepared according to a simplex-centroid mixture design set out in Part I of this research, in which the microstructural characterisation of sintered specimens was carried out. In Part II the influence of the starting composition on the mechanical properties of sintered porcelain tile was evaluated on the basis of the linear elastic fracture mechanics. Finally, in this last Part, ceramic bodies from seven compositions were subjected to fast cooling after firing, in order to reproduce the industrial cooling rates. The main objective was to analyze the influence of the mineralogical composition of the starting mixture on the development of macroscopic residual stress and growth of flaw size. When the pieces were subjected to fast cooling, flaw size was the main factor determining the variation of the mechanical strength. This increase in flaw size can be interpreted from the Weibull modulus, from 6 to 8 in those mixtures, with high deterioration of mechanical properties. The mullite hypothesis as a strengthening mechanism in triaxial porcelains was clearly manifested when the samples are fast cooled. This mechanism was the main responsible for the strengthening, what contrasts with the increase in flaw size. The microscopic residual stress caused by the thermal expansion mismatch of the phases also acted as a reinforcement mechanism.

Vibration Stress Relief Treatment of welded high-strength martensitic steel

The influence of a vibration stress relief (VSR) treatment on the residual stresses for welded specimens of ultra high-strength steel (ARMOX 500T®) was investigated. For the residual stress measurements X-ray diffraction and magnetic Barkhausen noise analysis (BNA) were utilized. Before and after VSR treatment, a 3D measurement technique was used to control possible deformations. Only small changes in macroscopic residual stresses could be found at the surface of the specimens close to the weld. The BNA measurements showed changes in macroscopic residual stresses; however, no clear tendencies could be seen. Nevertheless, fatigue damage due to the VSR treatment could be found. The changes in residual stresses did not cause macroscopic deformations of the specimens.

STRESS–STRAIN EVOLUTION IN CAST IN-738 SUPERALLOY SINGLE FUSION WELDS

A three-dimensional finite element elastic–plastic model was developed to study localized plastic strains and residual stresses that exist in a body that has previously been subjected to nonuniform temperature changes. The mechanical model was used to compute the evolution of plastic strains and residual stresses of welded material. The thermal gradient histories calculated during the GTA welding of cast IN-738LC alloys were imposed as load conditions on structural calculations. It can be clearly seen that at constant heat input, the level of plastic strains and the level of residual (Mises) stresses increase with welding speed. The model predicts highest residual stresses in regions of highest elastic strains, in agreement with conventional phenomenological material models where the macroscopic residual stress is always directly related to the macroscopic elastic strain. The highest residual stresses are located at the fusion line (where coarser dendrite secondary arm spacing exist); and the highest plastic strains are located at centerline (where finer dendrite secondary arm spacing exist). The calculations were performed using ABAQUS®FE code on the basis of a time-increment Lagrangian formulation.

Infrared birefringence imaging of residual stress and bulk defects in multicrystalline silicon

This manuscript concerns the application of infrared birefringence imaging (IBI) to quantify macroscopic and microscopic internal stresses in multicrystalline silicon (mc-Si) solar cell materials. We review progress to date, and advance four closely related topics. (1) We present a method to decouple macroscopic thermally-induced residual stresses and microscopic bulk defect related stresses. In contrast to previous reports, thermally-induced residual stresses in wafer-sized samples are generally found to be less than 5 MPa, while defect-related stresses can be several times larger. (2) We describe the unique IR birefringence signatures, including stress magnitudes and directions, of common microdefects in mc-Si solar cell materials including: β-SiC and β-Si3N4 microdefects, twin bands, nontwin grain boundaries, and dislocation bands. In certain defects, local stresses up to 40 MPa can be present. (3) We relate observed stresses to other topics of interest in solar cell manufacturing, including transition metal precipitation, wafer mechanical strength, and minority carrier lifetime. (4) We discuss the potential of IBI as a quality-control technique in industrial solar cell manufacturing.

Finite element modelling of coverage effects during shot peening of IN718

AbstractCurrent 3D shot peening simulation models proposed in literature do not take into account coverage as a process parameter influencing the residual state after shot peening. In this study a classic approach, using an ordered dimple pattern, and a new approach, using a stochastic dimple pattern were tested to describe the correlation between coverage, the surface topography and the residual stress state. Model verification was conducted based on X-ray and confocal white light microscopy measurements on shot peened test specimens. The test material was age hardened IN718. Simulations showed that the dimple pattern and the impact order of the shots can have a strong influence on the calculated macroscopic residual stress state. The stochastic approach enabled a realistic prediction of the surface topography and the residual stress state for arbitrary values of coverage while the classic approach strongly underestimated the number of shot impacts needed to achieve a certain value of coverage.

Determination of the macroscopic residual stress in thin film with fiber texture on the basis of local grain-interaction models

Two local grain-interaction models (local Voigt and local Reuss models) were proposed to evaluate the macroscopic residual stress in thin film with fiber texture. The difference between the proposed models and traditional models was systematically discussed in theory and calculation. The X-ray stress factors of the two local models were deduced. The corresponding expressions of the macroscopic residual stress in thin film with fiber texture were obtained. As an example for experimental verification, X-ray diffraction measurements were performed on a sputtered platinum film. To demonstrate the dependability of the proposed local models, three reflections (3 1 1, 2 2 2 and 3 3 1) were considered in evaluating the macroscopic residual stress in the Pt film, and then consistent residual-stress values for these reflections were obtained based on the two proposed local models. This result indicates that both the proposed local models can be employed to evaluate the macroscopic residual stress in thin film with fiber texture.

Surface Layers' Real Structure of Metals Exposed to Inhomogeneous Thermal Fields and Plastic Deformation

Inhomogeneous thermal fields and plastic deformation are two basic phenomena present during surface creation and substantially determine future real structure of the surface layers. In the following, a closer look will be taken at some aspects connected with real structure of milled and ground steels. Impact of end-mill speed and thickness of removed layer on grain size, macroscopic and microscopic residual stress is discussed. Possibility of prestrained surface layer in ground steel has been examined on a set of five types of steels.

Aspects of the determination of residual stresses in ceramics by ultrasounds hole-drilling

The paper presents a method of drilling in ceramics materials, applied for the determination of macroscopic residual stresses. To this end, high frequency vibrations of the ultrasound waves exercised on a drilling device are utilized. The shape and dimensions of the resulting hole depend on the shape and dimensions of the drilling device. The advantages of this method are: no additional stresses result from the application of this drilling procedure, the resulting hole has a satisfactory precision and the experiment may be repeated, macrostresses' variation in the studied material's depth may be determined.

Neutron diffraction measurements of time-dependent residual stresses generated by severe thermomechanical deformation

Residual stresses were generated by severe thermomechanical deformation in an aluminum alloy plate. The evolution of the residual stresses during natural aging was investigated by neutron diffraction up to 10,000 h. A data reduction method was developed to eliminate microstructure influences (solute variations) on the lattice spacing changes, thereby allowing the determination of the long-range macroscopic residual stresses. The residual stress decreased (∼25 MPa) with time due to the microstructural modification within the deformed region during natural aging.

X-ray diffraction study of anisotropic state of residual stress after down-cut and up-cut face grinding

Differences between up-cut and down-cut grinding are usually not considered since both modes are alternating during conventional face grinding. Nevertheless, there is a pronounced distinction in the fashion of material removal which could lead to unequal states of surface residual stress. By means of X-ray diffraction analysis, ground plates made from three types of steel were investigated in order to compute and compare both macroscopic and microscopic residual stress and domains of coherent scattering. With respect to the main sources of residual stress generation, i.e., plastic and thermal deformation, machining process was carried out in two types of cooling environment. The results indicate significant influence of heat removal since differences between the two grinding modes are virtually nonexistent for liquid cooling, whereas dry grinding results in higher compressive normal residual stresses for down-cut mode in comparison to the up cut.

Charpy V-Notch Impact Behaviour of Structural Steels Subjected to Specific Manufacturing Conditions

Abstract The influence on the Charpy V-notch impact behaviour in the transition region is investigated taking into consideration the residual stresses, work hardening and the surface topology at the notch root caused by manufacturing. Three materials were made available for the investigation, an unalloyed structural steel in the normalised and in the partially austenitised microstructural state, a water quenched hardened and tempered high strength, fine grained structural steel, and a heat treated steel. Initially, the effects of the major geometric parameters are identified with constant manufacturing conditions at the notch root (part I). As shown in the present contribution, the required almost constant notch root manufacturing conditions are obtained by means of a defined notch grinding process. Following notch machining of two steels, a stress relieving heat treatment was carried out. This heat treatment relieves virtually all the macroscopic residual stresses and the work hardening in the surface layer. For constant notch manufacturing conditions, the notch root radius is the most effective geometrically influencing factor at low temperature. The specimen width has the least influence. Increasing level of notch impact energy reduce the effect of the geometric parameters. This is the case for increasing test temperature just as for tougher material states following partial austenitising of the unalloyed structural steel as well as for the heat treated steel with the finest microstructure. The present results provide a solid basis for further investigations (part II) which are to detect specifically varied notch manufacturing conditions on the Charpy V-notch impact behaviour.

Plastic incompatibility stresses and stored elastic energy in plastically deformed copper

The X-ray diffraction method and theoretical model of elastoplastic deformation were used to examine the residual stresses in polycrystalline copper. To this end, the {2 2 0} strain pole figures were determined for samples subjected to different magnitudes of tensile deformation. Using diffraction data and the self-consistent model, the tensor of plastic incompatibility stress was found for each orientation of a polycrystalline grain. Crystallographic textures, macroscopic and second-order residual stresses were considered in the analysis. As a result, the distributions of elastic stored energy and von Mises equivalent stress were presented in Euler space and correlated with the preferred orientations of grains. Moreover, using the model prediction, the variation of the critical resolved shear stress with grain orientation was determined.

Effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to different cooling rates

Porcelain tile is a high-performance ceramic tile, in which quartz is a major compositional component. After the firing cycle, macroscopic residual stresses develop in the product as a result of rapid cooling. Further, during cooling, the presence of quartz particles also increases natural flaw size. Both phenomena significantly affect the product's mechanical behaviour. This study examines the effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to two very different cooling rates: a rapid or a slow cooling rate. A series of porcelain tile compositions were designed for this purpose, in which quartz particle size was varied. The mechanical behaviour of the sintered pieces was evaluated on the basis of linear elastic fracture mechanics. It was verified that, in the slowly cooled material, the modulus of elasticity and fracture energy increased, and natural flaw size decreased as quartz particle size decreased. However, fracture energy also diminished in pieces that contained excessively small particles, with an advanced state of dissolution. For the rapidly cooled material, though the larger sized quartz particles debonded at higher temperatures owing to thermal stress, their presence, even in small quantities, contributed to natural flaw growth. The lower fracture energy associated with this last type of piece also favours this phenomenon.

On the ductility of a surface severely plastically deformed nickel alloy

The tensile ductility of a Ni-base, single-phase, face-centered-cubic alloy decreases after surface severe plastic deformation (S 2PD). The mechanism responsible for the reduced tensile ductility has been investigated via systematic experiments in conjunction with finite element modeling. The measured ductility parameters (i.e., the elongation, uniform true strain, and reduction of area), strain-hardening coefficient of the true stress–strain relation, and fracture surface observation have been elucidated based on the alternation of the microstructure and stress states induced by S 2PD. It is found that the reduced ductility is not due to the increased surface roughness and the presence of macroscopic residual stresses. Instead, it is induced by the presence of the work-hardened surface region and the formation of a nanocrystalline surface layer in S 2PD-processed samples.

The impact of various cooling environments on the distribution of macroscopic residual stresses in near-surface layers of ground steels

Grinding often plays the role of final machining, and, therefore, its parameters significantly affect the properties of the treated surface. In this study, the state of surface residual stresses (RSs) and their depth distribution into the bulk is investigated with respect to various cooling environments during grinding. In order to acquire complete stress tensors, the sample surfaces were analysed using the X-ray diffraction technique. Since ɛ φψ(sin 2 ψ) dependences in grinding direction are non-linear and exhibit psi-splitting, the method proposed by Dölle and Hauk was used to evaluate the tensors of anisotropic triaxial state of RS. The effective penetration depth of Cr Kα X-ray radiation into ferrous materials is approximately 4 μm, and, therefore, removal of surface layers is necessary in order to pinpoint the distribution of RSs beneath the surface. The process of electro-chemical polishing ensures that the impact of material removal causes minimal or negligible mechanical and thermal distortions of the investigated state of stress.