Method For Determination Of Stresses Research Articles

In situ measurement of residual stresses and elastic moduli in thermal sprayed coatings: Part 1: apparatus and analysis

Mechanical properties, such as residual stress and Young’s modulus, play a critical role in the synthesis and performance of thermally sprayed coatings. Thus, it is important to understand their evolution, the influence of processing parameters, and to be able to determine them accurately. The first part of this two-part paper presents a novel in situ curvature method for determination of stresses and Young’s modulus of plasma sprayed coatings. The principle of the method is explained, details of the instrument are provided and the analytical procedure is described. The capabilities of the method are discussed in detail, namely the ability to observe the stress evolution during the entire spraying process, to separate the quenching and thermal stress contributions to final residual stress and to determine the Young’s modulus of the coating. Brief examples of application are also included, and the potential for use of this method for process control of coating quality is addressed. In the second part, a case study for plasma sprayed molybdenum will be presented, focusing on the influence of the key processing parameters.

Effective Stress Reduction in Diamond Films on Alumina byCarbon Ion Implantation

We show the effective stress reduction in diamond films by implantingcarbon ions into alumina substrates prior to the diamond deposition.Residual stresses in the films are evaluated by Raman spectroscopy anda more reliable method for stress determination is presented for thequantitative measurement of stress evolution. It is found thatcompressive stresses in the diamond films can be partly offset by thecompressive stresses in the alumina substrates, which are caused by theion pre-implantation. At the same time, the difference between theoffset by the pre-stressed substrates and the total stress reductionindicates that some other mechanisms are also active.

A review for cutting forces and stresses in circular saws

The stresses in circular saws together with classical theories and new methods of stress determination are reviewed. The use of the Finite Element Analysis package (ANSYS) for the determination of these stresses and their combined effects is discussed.

孔内載荷による大深度岩盤応力測定の現状と問題点

The hydraulic fracturing technique as a method for determination of in-situ stresses has the advantage over other stress measuring methods in that it can be used at considerably greater depths from a point of access. This is of great significance in earthquake regions where stresses at hundreds or thousands of meters are of interest. Despite of the increasing use of hydraulic fracturing, however, there are uncertainties associated with the interpretation of the resulting data. In particular, confidence in the calculated maximum principal stress is less than in the minimum principal stress, although the former is often of great moment. Furthermore, the equation established to calculate the maximum principal stress is unclear. More recently, dry fracturing techniques have been developed and examined as the new potential method for determination of in-situ stress at great depth, through studies both in the laboratory and in the filed. In dry fracturing, the borehole wall is subjected to shear load as well as normal load, which are induced by internal pressurization of the probe. The state of the art of rock stress measurement by hydraulic fracturing is reviewed and a comparative study is made of two kinds of dry fracturing techniques, which have been developed as the potential method for stress determination. The general review is followed by individual summaries of each method and the main characteristics of its validations and applications.

Stress analysis in Si membranes for open stencil masks and mini-reticles using double bulging and resonance methods

This paper presents two measurement methods for stress determination of Si-membranes. The first one is based on the bulging method. This method was modified by the deflecting of the membrane in both direction, the so-called double bulging technique. A novel improved least-square fitting technique to double bulging data allows to increase the accuracy of the method especially for the membranes with stresses lower than 2 MPa. Additionally it is possible to verify the set up alignment for the diffraction-image method. This method we have used for measurement of membrane deflection. The second method — resonance frequency method — is based on the classical theory of membrane vibration. It uses the dependency of the membrane resonance frequency on membrane residual stress. This novel technique applies a soft piezoresistive cantilever in contact mode for the detection of membrane vibration. The influence of the cantilever on the vibration of the membrane was studied. Initial results show the small lowering of the resonance frequency in measurements with the cantilever in comparison with the optical measurements.

Measurement of the Yield Stress of Gellike Protein Layers on Liquid Surfaces by Means of an Attached Particle

We propose a new method for determination of the yield stress of adsorbed protein layers on an air−water interface. A small spherical particle is attached to the surface, and the latter is deformed by pulling up a barrier attached to it. When the tangential projection of the gravity force exerted on the particle exceeds a certain threshold, then the layer starts to undergo significant elastic deformation. This is registered as a difference between the experimentally measured particle displacement and that calculated by solving the Laplace equation of capillarity for the liquid boundary. After the yield threshold, there is a linear dependence of the strain on the applied stress. We propose a modified Bingham model (two springs and a plastic element) to describe this particular rheological behavior. The elastic moduli found by a linear regression analysis of the stress (strain) relationship agree well with literature data for globular proteins. The corresponding yield stress turns out to be very sensitive to changes in the protein layer structure (caused either by the presence of surfactant molecules (Tween 20) or by differences in the bulk protein concentration). The threshold stress monotonically increases with rising protein content, which suggests a possible reinforcement of the adsorbed layer. The addition of Tween 20 brings about surface fluidization. Tween 20 can replace part of the adsorbed protein molecules and/or attach to them breaking the intermolecular linkages.

Comparison of numerical and experimental analyses for contact problems under normal and tangential loads

The methods of finite element (FE) analysis and stress frozen photoelasticity were used to investigate the stresses resulting from the contact of an infinite cylinder with an elastic half-space for comparison with the well-known theoretical solution. Two load cases were studied, that of a load normal to the plane and another where a normal and tangential load are applied to the cylinder. The coefficient of friction was controlled in the photoelastic experiment and the same value used in the finite element analysis. Plots of the Cartesian stresses in the plane of symmetry, the Cartesian shear stress along a line below the surface and the full field of the Cartesian shear stress were obtained and compared. As a result of these analyses, more complex tests were performed which involved using finite element methods and photoelasticity to investigate the stress distributions in the roots of two types of dovetail joint from the compressor of a gas turbine engine. It was found that the two methods yielded results that correlated very closely. The correlation between the experimental, numerical and theoretical results is very close and suggests that combining the experimental and numerical techniques provides a reliable method of stress determination in complex components and structures.

The wall shear stress produced by the normal impingement of a jet on a flat surface

A method for the theoretical determination of the wall shear stress under impinging jets of various configurations is presented. Axisymmetric and two-dimensional incompressible jets of a wide range of Reynolds numbers and jet heights are considered. Theoretical predictions from this approach are compared with available wall shear stress measurements. These data are critically evaluated based on the method of measurement and its applicability to the boundary layer under consideration. It was found that impingement-region wall shear stress measurements using the electrochemical method in submerged impinging liquid jets provide the greatest accuracy of any indirect method. A unique wall shear stress measurement technique, based on observing the removal of monosized spheres from well-characterized surfaces, was used to confirm the impinging jet analysis presented for gas jets. The technique was also used to determine an empirical relation describing the rise in wall shear stress due to compressibility effects in impinging high-velocity jets.

X-Ray Intergranular Stresses Analysis in a Cast Duplex Stainless Steel

Polycrystalline approaches are more and more used to characterise the mechanical behaviour of material with the interest to take into account the mechanical properties of the material constituants. In this case; for a better understanding of the polycrystalline material mechanical response, mesoscopic and microscopic parameters must be clearly identified. Our purpose is also to characterise the mechanical behaviour of a cast duplex stainless steel, containing 30% ferrite and 70% austenite, using X-ray diffraction. The mechanical state can be determined using X-ray diffraction technique which enables to measure strains in each phase separately. The measurements are performed at the grain scale because the studied material exhibits coarse grains of up to one millimeter. In this case, only few crystals are irradiated by the incident X-ray beam and the classical sin 2 ψ method for stress determination can not be applied to this material. An adaptation of the single crystal measurement method to large grains materials is used Stresses so determined correspond to second order stresses. The measurement in each phase has successfully been applied to follow the stress state evolution during an in-situ tensile test. Several grains, with different crystallographic orientations were studied. For each one, the stress tensor was determined in the two phases under different macroscopic loading in elastic and plastic domains, different A modelling of the mechanical single crystal behaviour is developed and our pourpose is to identify the parameters of the single crystal behaviour law using X-ray single crystal stress analysis during in situ tensile test.

Compatibility conditions of structural mechanics

The theory of elasticity has camouflaged a glitch in the compatibility formulation since 1860. In structures the ad hoc compatibility conditions through virtual ‘cuts’ and closing ‘gaps’ is not parallel to the strain formulation in elasticity. The deficiency in the compatibility condition has prevented the development of direct stress determination method in structures and in elasticity. We have addressed and attempted to unify the theory of compatibility. This has lead to the development of the Integrated Force Method for structures and the Completed Beltrami–Michell's Formulation in elasticity. The utilization of the compatibility conditions allows mapping of variables and facile movement among different structural analysis formulations. This paper reviews and illustrates the requirement of compatibility in structures and in elasticity. Addresses the generation of the conditions and quantifies the benefit of their use. The traditional analysis methods and available solutions should be verified for compliance of the compatibility conditions. Published in 2000 by John Wiley & Sons, Ltd.

Compatibility conditions of structural mechanics

The theory of elasticity has camouflaged a glitch in the compatibility formulation since 1860. In structures the ad hoc compatibility conditions through virtual ‘cuts’ and closing ‘gaps’ is not parallel to the strain formulation in elasticity. The deficiency in the compatibility condition has prevented the development of direct stress determination method in structures and in elasticity. We have addressed and attempted to unify the theory of compatibility. This has lead to the development of the Integrated Force Method for structures and the Completed Beltrami–Michell's Formulation in elasticity. The utilization of the compatibility conditions allows mapping of variables and facile movement among different structural analysis formulations. This paper reviews and illustrates the requirement of compatibility in structures and in elasticity. Addresses the generation of the conditions and quantifies the benefit of their use. The traditional analysis methods and available solutions should be verified for compliance of the compatibility conditions. Published in 2000 by John Wiley & Sons, Ltd.

Characterisation of CVD grown diamond and its residual stress state

Abstract One of the most important quality factors in the judgement of thin diamond layers is the adhesion between the substrate and the layer which is limited by the residual stress state. The main reason for residual stress in coatings is the misfit in various properties of the layer and also the substrate, e.g. thermal expansion and crystal lattice type. The most common method of residual stress determination, based on X-ray diffraction, has to date found little application in the study of diamond films. In this paper, the method is applied to determine the residual stress in a CVD diamond film grown on a polycrystalline Al substrate. The results are interpreted with regard to the crystal structure and orientation of the layer, determined by X-ray diffraction and scanning electron microscopy.

Anelastic Strain Recovery and The Kaiser Effect Retention Span in the Carnmenellis Granite, U.K.

Knowledge of in-situ stress in rock masses is essential for mining and civil engineering design and the Kaiser effect method of stress determination provides an economical alternative to currently applied investigation techniques. A practical problem associated with this method is the loss of the Kaiser effect over time during the process of anelastic strain recovery, but a direct relationship is observed between anelastic strain recovery and the number of acoustic emissions. The behaviour is modelled here using the Kelvin and Burger rheological models, for the stages of creep during uniaxial laboratory loading, anelastic strain recovery and the loss of the Kaiser effect, with constants being calculated and compared for samples loaded under geological and laboratory conditions. It is found that the loss of the KE at low stress levels compares directly with the process of anelastic strain recovery and fits the Burger model over the time scales of interest. A difference between primary and secondary (undercored samples) recovery is demonstrated with a slower recovery for primary relaxation and with samples taken from geological stress environments recovering more slowly than those loaded under laboratory conditions, for all stress levels tested.

On the feasibility of determining discrete photoelastic parameters using the multi-load method

An alternative method for the determination of three-dimensional stresses in photoelastic models is discussed. The model is sectioned into discrete, imaginary slices and a relationship is derived between the retardation and isoclinic angle of each slice and characteristic photoelastic parameters measured using a transmission polariscope. An illustration of the multi-load method is given and the practical application of the technique is discussed.

Analytical determination of the average Eshelby tensor for transversely isotropic fiber orientation distributions

The analytical expression for the average S tensor in Eshelby's equivalent inclusion method of internal stress determination in composite materials is derived for any transversely isotropic fiber orientation distribution function specified by a generic histogram. The analytical average provides a basis for direct application of experimentally measured fiber ODFs in the modelling of internal stresses and effective properties of thermomechanical fiber composites. Upper and lower bound estimates utilizing the analytical expression for the average S tensor are presented and discussed.

Numerical analysis of limit load and reference stress of defective pipelines under multi-loading systems

The concepts of limit load and reference stress have been widely used in structural engineering design and component integrity assessment, especially in Nuclear Electric's (formerly CEGB) R5 and R6 procedures. The reference stress method has been proven to be successful in problems pertaining to creep growth, rupture damage, creep buckling, and more recently, elastic–plastic fracture toughness. An approximate method of reference stress determination relies on prior knowledge of limit loads for various configurations and loadings. However, determination of the limit loads for the problems with complicated geometric forms and loading conditions is not a simple task. In the present paper, a numerical solution method for radial loading is presented, the mathematical programming formulation is derived for the kinematic limit analysis of 3D structures under multi-loading systems, and moreover, a direct iterative algorithm used to determine the reference stress is proposed which depends on the evaluation of limit load. The numerical procedure is applied to determine the limit load and reference stress of defective pipelines under multi-loading systems. The effects of four kinds of typical part-through slots on the collapse loads of pipelines are investigated and evaluated in detail. Some typical failure modes corresponding to different configurations of slots and loading forms are studied.

A Study of Wind Stress Determination Methods from a Ship and an Offshore Tower

Comparisons are made between surface wind stress measurements obtained by the inertial-dissipation and direct covariance methods on a stable offshore tower and by the inertial-dissipation and bulk methods on a ship. The shipboard inertial-dissipation friction velocity measurements agreed very well with both the tower inertialdissipation and direct covariance values, to within 62% in the mean and with a 10% or lower rms scatter. The inertial-dissipation determinations also exhibited less scatter than the tower direct covariance measurements. A detailed error analysis indicates that shipboard inertial-dissipation wind stress values can have an accuracy of better than 15% in near-neutral conditions, as compared to an accuracy of roughly 30% for the bulk method. The accuracy of shipboard inertial-dissipation values was shown to be equal to that of direct covariance measurements from a tower. Errors in inertial-dissipation wind stress values are most likely due primarily to deviations from the assumed balance between turbulent kinetic energy production and dissipation and to errors in determining the wind speed variance spectra. Errors in direct covariance measurements are most likely due primarily to finite time averaging and to flow distortion effects, unless great care is taken to minimize or correct for flow distortion. The high accuracy of inertial-dissipation wind stress values found in this study, combined with the well-known difficulties in shipboard direct covariance measurements due to platform motion and flow distortion, demonstrate that the inertial-dissipation method is the best option at present for determining the wind stress from a ship.

The holographic-hole drilling method for residual stress determination

Holographic-hole drilling is a method developed for the rapid determination of residual stresses from an optical interference fringe pattern. A small diameter blind hole is drilled into a part containing residual stresses, and the displacements caused by localized stress relief are registered by real-time holographic interferometry. The resulting fringe pattern is evaluated to calculate residual stresses, using a simple ‘fringe counting’ method described here. Results of applying the method in laboratory tests to a variety of uniform biaxial states-of-stress from equibiaxial compression to pure shear are shown. Two sample applications of the method, the evaluation of residual stresses at a cold-worked hole and at a weld bead, are also given. Extensions of the method to evaluate stresses non-uniform in depth and/or along the surface are discussed.

Stress distribution in heteroepitaxial chemical vapor deposited diamond films

The stress distribution in heteroepitaxial chemical vapor deposited diamond films has been investigated by Raman spectroscopy. A new method for stress determination based on polarized confocal micro-Raman is presented and used for the measurement of the stress evolution across the film thickness in the center of the sample. The presence of highly inhomogeneous stresses at a microscopic scale is first demonstrated. The interface appears to be under compressive stress which rapidly decreases and then stabilizes, but remains compressive. The strain tensor is also shown to vary. Near the interface, the common assumption of biaxial stress in the plane of the film has been confirmed. Near the growth surface, the stress tensor appears to be more complicated. Grain boundaries are suggested to be mainly responsible for the intrinsic stress generation when the grain boundary density is high. Inhomogeneous impurity distribution could be related to stress inhomogeneities near the growth surface, where the grain boundary density becomes small. Agreement has been obtained between micro- and macro-Raman stress measurements. The average stress (over film thickness) as determined by macro-Raman is shown to increase by 30%–40% from the sample center to the edge.

High-resolution x-ray diffraction measurements of residual stresses in polycrystalline thin films deposited on single crystalline substrates

A nondestructive method for stress determination in polycrystalline/amorphous thin films deposited on the nearly perfect crystals was developed. High-resolution x-ray diffraction rocking curves are taken from the substrate using a monochromatized and quasiparallel incident x-ray beam. Changes in the rocking curve shape, caused by stress-induced bending of the substrate, are compared with the newly derived analytical expression of the diffraction spectrum, and as a result the radius of curvature and hence the biaxial stress is obtained. For the (004) Si reflection and the Cu Kα1 radiation the radii of curvature within the interval, 3 m<R<500 m, can be resolved. The method was successfully applied to measure stresses in heat-treated Ni90Ti10 alloy films deposited on a Si (001) substrate. The stress behavior (as a function of the annealing temperature) was found to reflect the sequence of the formation of silicides and enabled the evaluation of their thermal expansion coefficients.