Studying the literature, drafts of papers, and proposals of test projects, some ideas on new tasks emerge. Not all thougths may be progressive to the experts. There may exist further problems to be solved in the future. Not mentioning them does not mean they are unimportant, but it is hoped the following may stimulate new methods, new tests, new results, new assessment of residual stresses (RS) to the benefit of this scientific branch.

There exists a tremendous volume of literature /\/. In referring to previous papers and results, the procedure of a great old physicist should be followed: mention both the first idea and a comprehensive treatment of the topic.

A method has heen developed to determine the dislocation configuration in a polycrystalline specimen from the direction dependence of line broadening. The method is based on an analytical expression for the integral breadth due to microstrain from sets of parallel edge and/or screw dislocations on the specific slip systems. Analysis of the x-ray-diffraction measurements obtained from poly crystalline aluminium layers, deposited onto silicon wafers and subsequently annealed and cooled to room temperature, shows unequal densities and unequal changes of densities of dislocations with the Burgers vector parallel and with the Burgers vector inclined with respect to the surface of the layer. Stress relaxation and dislocation annihilation occur at room temperature. A model was developed to describe the dependency of the decrease of macrostress on the decrease of the dislocation density.

The single crystal measuring and evaluation technique allows the analysis of stress states in large grained and single crystalline materials. The technique is based on the analysis of the orientation of crystallites under study. Using a fouf-circle-diffractometer, the knowledge of the orientation matrix allows the calculation of the diffractometer setting for every given reflection (hkl). After experimental determination of the precise diffraction angles 20 for at least six reflections of an individual crystallite, its strain tensor components can be obtained by applying least-squares methods. The stress tensor referred to the crystal axes system is calculated using the single crystal elastic constants.

The practical use of this measuring and evaluation technique is demonstrated on coarse grained and single crystal nickel-base superalloys and monocrystalline materials.

The present study concerns residual stresses analysis in porycrystalhtie solar silicon material, which is continuously cast in a cold crucible. The observation of cracks and a modeling of thermal stresses suggest us that stresses in the center region are tensile and the ones in the peripheral region are compressive. X-ray measurement of stresses would be an experimental proof of the observations and an evaluation of the stresses levels. Unfortunately, the obtained material exhibits coarse grains with the size of up to one millimeter. In this case, where only a few crystals are irradiated by the incident X-ray beam, the classical sin2Ψ method is no longer valid. A specific analysis must be carried out. The results are of good accuracy comparing the low stress levels observed. The measured stress distribution on a radius of the billet is not always in good agreement with the analytical calculus.

The nature of residual stress was determined in single crystal gallium arsenide (GaAs) bare wafers, silicon nitride-passivated GaAs wafers, and fully processed die. A methodology to determine strain in single crystals using X-ray diffraction was developed and applied to the specific case of gallium arsenide. The data show an increase in residual stress associated with the application of the Si3N4 passivation layer to approximately 60% of the fracture stress of the material. Further device processing only slightly increased residual stress values.

The microstructures and mechanical properties of Ni-Al system intermetallic compounds used as heat resisting materials have been investigated by many researchers[l,2], but there are few studies applying X-ray stress measurement to these materials[3]. Two problems make it difficult: One is the comparatively coarse grain size, the other is the strong preferred orientation along the direction of the solidification. Therefore, it become possible to evaluate mechanical behavior in these materials, if we can measure the residual stresses correctlv by X-rays.

In this paper, Ni-25mol%AI(Ni3Al) made by the arc-melting method was employed. It consists of comparatively coarse grains and has strong preferred orientation along the direction of the solidification.

A new method of X-ray measurements of triaxial residual stresses was proposed for hexagonal polycrystals with the [001] fiber texture. The relation between the strain and sin2ψ is linear for the cases of the fiber axis perpendicular or parallel to the specimen surface, provided that there is no shear stress acting on the specimen surface. The in-plane stresses, σ11, σ22, and σ12, and the normal stress perpendicular to the specimen surface, σ33, are determined from the slope and the intercept of the linear regression line for the relation between the X-ray strain and sin2ψ obtained for three different directions.

Production electrolytic chromium coatings suffer from cracks, which result from high internal stresses generated during the electrolytic crystallization process. This paper characterizes the anisotropy, texture and residual stress state in high contraction chromium coatings on steel-Strong <111> fiber texture, almost perfect in-plane azimuthal symmetry, and high surface residual stresses were observed. Anisotropy factor and aggregate elastic moduli were calculated from single crystal elastic constants. A matrix inversion method was developed to solve for biaxial residual stress and unstrained lattice parameter in textured chromium coatings. Assuming an isotropic elastic Hill-Neerfeld model, residual stress was also evaluated using the sin2ψ method adapted to multiple families of reflections.

A new method of the X-ray stress measurement was proposed for measuring the residual stress in Al thin films having the [111] fiber texture with the fiber axis perpendicular to the film surface. The strain was measured from Al 222 and 311 diffractions obtained by Cr-Kα radiation. The values of in-plane residual stresses σ11, σ22 and σ12, and out-of-plane normal residual stress, σ33 were determined from the measured strains by using the fundamental formulae derived on the basis of Reuss and Voigt models. The measured residual stress in the thin films was nearly equi-biaxial tension. The magnitude of the tensile residual stress decreased with increasing film thickness.

According to the standard model, strain in polycrystalline materials transforms like a tensor when measured with diffraction in different directions. This model predicts linear variation of d-spacing with sin2ѱ if the stresses σ13 and σ23 are absent or predicts ѱ-splitting if they are present. In diffraction stress measurements, d vs. sin2ѱ plots often exhibit behavior that cannot be predicted from this model. When such discrepancies are observed, stresses calculated from the data will not always be valid. Current practice is to determine the validity of data by visually inspecting d vs. sin2ѱ plots and subjectively assessing the goodness-of-fit. This paper proposes the χ2 statistic as a tool for quantitatively determining goodness-of-fit, and it presents experimental results from the application of the statistic.

This paper corrects assumptions made by previous authors regarding the magnitude of the error in d-versus-sin2ѱ plots resulting from deviations of the sample surface from the focusing circle. The results show that the effect is not significant for ordinary residual stress measurements. This investigation has also shown that shapes in d-versus- sin2ѱ plots, similar to the sample curvature effect, may exist in samples with large residual stresses. Interpretation of the data should consider the magnitude of the apparent stress, which allows one to distinguish between apparent sample curvature effects and other causes.

Neutron and x-ray scattering methods of residual stress measurement were applied to plasma arc welds made in aluminum-lithium alloy test panels as part of an evaluation of materials for use in welded structures. In the course of these studies discrepancies between x-ray and neutron results from the heat affected zone (HAZ) of the weld were found. Texture changes and recovery from the cold work, indicated in peak widths, were found in the HAZ as well. The consideration of x-ray and neutron results leads to the conclusion that there is a change in solute composition which modifies the d-spacings in the HAZ which affects the neutron diffraction determination of residual stresses. The composition changes give the appearance of significant compressive strains in the HAZ. This effect and sharp gradients in the texture give severe anomalies in the neutron measurement of residual stress. The use of combined x-ray and neutron techniques and the solution to the minimizing of the neutron diffraction anomalies are discussed.

Although it is widely known that small errors in d0 produce large errors in calculated components of the triaxial stress tensor, the magnitude and sign of errors in the elastic constants and do has not, thus tar, been visualized. In this study, the combined and isolated effects of errors on the resultant stress calculation is shown via three-dimensional, topographical, and onedimensional graphics. It has been found that stress is most sensitive to errors in d0, and least sensitive to S1. In most cases, errors lead to calculated stresses that differ from the true values by more than 20%, and in the worst cases change the magnitude by more than 200% and may even change the sign.

The X-ray diffraction method was applied to the measurement of residual stresses on the ground or polished surfaces of WC-Co alloys with various Co contents. The X-ray diffractions of WC 211 by Cu K α radiation were used for the stress measurement. The residual stresses on the ground or polished surfaces were all compression. For the same Co content, the compressive value increased with increasing surface roughness. The maximum residua) stress, which was -2.13 GPa, was observed in WC-5.5wt%Co ground with a #140 diamond wheel.

The bending strengths of each alloys were obtained by three point bending tests. The bending strengths were influenced by grinding conditions and Co contents. The maximum value of 3.6 GPa was obtained in WC-16.0wt%Co ground with a #140 diamond wheel.

For the same Co addition, the bending strengths were closely related to the residual stresses, These relations were approximated by straight lines.

Rietveld refinement of X-ray diffraction patterns has been used to provide microstructural information complementary to conventional X-ray residual stress measurements through a carburized layer containing a maximum vol. 25 % of retained austenite. Layers in a simple specimen were removed incrementally by electropolishing and, at each depth in addition to conventional residual stress measurements in both the martensite and retained austenite, data were collected at ѱ = 0 for Rietveld refinement. The refinements provide accurate values for the lattice parameters in the respective phases that can be related to carbon content and micro-structure. Besides to providing qualitative information concerning the microstructure and possible surface decarburization, the c/a ratio of the martensite potentially offers an independent technique for determining carbon content profiles

A new method of X-ray stress measurement was proposed to estimate non-destructively the steep residual stress distribution in the surface layer of ground Si3N4. We assumed an exponential decrement of the residual stress near the ground surface, and derived a formula for the lattice strain as a function of sin2Ψ. In the experiments, the diffraction angles were measured on the ground surface for a widest possible range of sin2ѱ using an Ω-goniometer. In order to measure the diffraction angle at very high sin η values, a scintillation counter was located on the -η side and an incident X-ray beam impinged on the ground surface with a very low angle from the +η side using the glancing incidence X-ray diffraction technique. A strong non-linearity was found in the 20-sin2ѱ diagrams especially at very high ѱ -angles. From the analysis of non-linearity, the stress distribution in the surface layer was determined. Tine residual stress took the maximum compression of 2 GPa at a depth of about 0.5 μm from the surface, and then diminished to zero at about 25 μm in depth. In the close vicinity of the ground surface, the compressive residual stress was relieved because of both the surface roughness and microcracking induced during the grinding process.

A method to obtain the triaxial depth profiles of strains and stresses as a function of the depth below the surface is described. Instead of using inverse Laplace transforms to extract the z-profiles from the measured τ-profiles, a numerically stable inverse formalism with trigonometric basis functions is used. The formalism has already been applied with great success to the hole-drilling method for the determination of residual stresses. It requires no prior knowledge of the stress state and is suitable even for strongly non-linear stress fields. This is demonstrated by experimental data sets for the conventional Ω-, ѱ- and modified ѱ goniometers. Furthermore this method enables in situ determination of Poisson's ratio as well as the stress free lattice spacing using a selfconsistency criterion for isotropic materials. It is now possible to find a proper normalization of the residual strains and residual stresses. Because of the formulation as an inverse problem, analytical expressions for the beam path integrals could be derived even for curved surfaces. Inverse problems are often extremely ill-conditioned. Therefore the uniqueness of the solution is discussed in terms of a spectral shift of the corresponding eigenvalues.

We have investigated the stresses existing before and during fatigue crack growth in a 1080 spheroidized steel. The total stress state, which consists of triaxial macro- and microstress components, has been measured around the fatigue crack tip using x-ray microbeam diffraction. A tapered glass capillary of 210μm diameter has been developed to provide increased intensity, smooth diffraction peaks and good spatial resolution. Findings indicate that stresses generated by the growing crack are mainly macro stresses, and dominate over pre-existing residual stresses around the tip.

Depth profiles of intrinsic in-plane, biaxial stresses were obtained as a function of τ, the 1/e penetration depth, in a 1.0 um thick planar d. c. magentron sputter deposited molybdenum film using asymmetric grazing incidence x-ray diffraction (GIXD). τ was varied between 20 and 276 Å. The stresses σ11 and σ22 were characterized in the directions parallel and perpendicular to the long axis of the cathode respectively using a cos2φ method. The results show that starting from τ=17Å, σ11 and σ22 are compressive and become rapidly more compressive with a minimum at τ ∼ 20 - 40 Å thereafter increasing gradually toward tensile values. The reasons for the shape of the stress gradient are not well understood but may be related to the relaxation of the stresses at the tops of the columnar Zone T-type microstructure and to the oxygen gradient in the film.

This study uses the asymmetric grazing incidence x-ray diffraction (GIXD) method and related z-profile retrieval techniques to study the near surface residual stress depth proflles on ground and on polished surfaces of hot-pressed Al2O2SiC(w) composite specimen. The z-profiles of stress components σ11, σ22 and σ33 of the Al2O3 matrix were obtained by using the numerical inversion method as well as the inverse Laplace method. Both τ- and z-profiles of residual stresses are presented.