Nondestructive Stress Measurement Research Articles

A new ultrasonic method for stress determination in textured materials

Non-destructive measurement of stress using ultrasonics often fails because of texture in the analysed material: texture as well as stress influences the wave velocity and reliable methods are needed to separate the two effects. This contribution briefly reviews earlier approaches and presents a new method to separate texture and stress effects by measuring the velocity dispersion of polarized shear waves. The techniques is based upon recently published theoretical work on wave propagation in polycrystalline quasi-isotropic as well as textured materials. Experimental results are in general agreement with the theoretical data.

A comparison of two theories of acoustoelasticity

The presence of a plane stress field causes small changes in the phase velocities of orthogonally polarized SH waves. The (small) difference in phase velocities (birefringence) can be used for non-destructive stress measurement. However, material anisotropy can affect phase velocity to the same extent as stress. Two theories have been developed which account for the effect of both stress and anisotropy. The theory of Iwashimizu and Kubomura assumes isotropy in the third-order elastic moduli and anisotropy in second-order moduli. A different approach was taken by Okada, who assumed the existence of a matrix analogous to the index of the refraction matrix in optics. In this paper, we generalize the theory of Iwashimizu and Kubomura by retaining anisotropy in third-order moduli. We show how Okada's theory can be made to agree with this more general theory. We also compare the predictions of the various theories with birefringence data obtained from uniaxial tension tests on 2024-T351 aluminium specimens. Both the Okada theory and the theory of Iwashimizu and Kubomura gave good agreement with experiment.

Non-destructive Surface Stress Measurement of Chemically Tempered Glass Bottles by Using Optical Waveguide Effect

Non-destructive Surface Stress Measurement of Chemically Tempered Glass Bottles by Using Optical Waveguide Effect

Magnetomechanical acoustic emission — a new method for non-destructive stress measurement

This paper describes a newly found non-destructive testing technique for residual stress measurements, which is called magnetomechanical acoustic emission (MAE). It applies to ferromagnetic materials only, but has a greater depth of penetration than other common methods of residual stress analysis, such as X-ray diffraction and acoustic surface wave. Previous studies on MAE are reviewed, in which effects of metallurgical and magnetic parameters on MAE were evaluated. Our recent study has correlated magnetic properties of nickel and iron to MAE characteristics. Some of the observed features of MAe can be explained in terms of the domain theory, but many unresolved questions remain. Practical applications must await further developmental efforts, but some preliminary results of residual stress analysis for a welded steel plate and others are presented.

Non-destructive Surface Stress Measurement of Enameled Wares by Refractometry

Non-destructive Surface Stress Measurement of Enameled Wares by Refractometry

Non-destructive stress measurement using X-ray diffraction methods

The principles of stress measurement and analysis using X-ray methods is given, followed by a description of the two main techniques currently available. These are based on either a camera, which is readily portable and requires short testing times, or a diffractometer which although bulky and of higher initial cost, is more accurate.

Internal Plant-water-status and Its Control

The present paper deals with an experimental method for evaluating the plant water status. An apparatus which enables continuous and nondestructive measurement of internal plant water stress has been developed by making use of a strain-gauge. The apparatus shown in Fig. 1 was used to indicate the change in plant stem diameter.Experiments were carried out for two plants (Sunflower and Grapevine) to examine the relations between the change in stem diameter and other factors such as leaf water potential, water deficit and leaf temperature. The results show that the change in stem diameter has proved useful to indicate change in related factors.Stem diameter shows a linear relationships with water deficiency (Fig. 2) but when related to the water potential, it is represented by two straight lines which intersect at about -12 bars (Fig. 3). Under changing plant water condition stem diameter changes according to the change in the leaf temperature (Fig. 5, 6, 7). It is considered that this cyclic valiation was due to passive stomatal water movement. From these results it was concluded that the practical application of the present method has, therefore, been confirmed.

Measurement of Residual Surface Stress on Tempered Glass Plate

Following methods are usually adopted for measuring the residual surface compression present on tempered glass, (1) Observation of relative retardation of light passing through the cross-section of the plate parallel to its surface by photoelastic techniques. (2) Calculation of the stress by measuring the resultant curvature of the plane when a certain amount of thickness was etched-off by hydrofluoric acid from one side of the sample.However, these methods are inadequate for the non-destructive measurement of surface stress on commercial glass plates of large dimensions.The method described here is pertaing to the surface stress-induced birefringence of glass with the result that the angle of total reflection obtained by contacting an optical prism on the sample surface is different between two polarized components. Namely, the refractive indices of the compressed surface for the ordinary ray polarized in plane perpendicular to the surface is greater than that for the extraordinary ray polarized in plane parallel to the surface, thus the critical angle of total reflection of the ordinary ray is greater than that of the extraordinary ray. Since this difference is directly related to the magnitude of the surface stress and is detected in the field view of telescope as two regions of different brightness separated by a sharp boundary, it is possible to measure the surface stress in a rapid and non-destructive manner by calibrating the scale division of the eyepiece field. Calibration was done by giving a known degree of cancellation to the surface compression with the tension caused by bending the central portion of the sample supported freely at both ends.The constructed instrument provided very sharp boundary lines in the field of eyepiece and made it possible to determine the surface compressive stress on tempered glass with the accuracy of ±0.6kg/mm2.

Non-destructive surface stress measurements. Ultrasonic stress measurements for cast-wheel hub-cracks: Hiersch, F.A. Test Engineering Vol 22, No 2 (August 1969) p 15 (2281)

Non-destructive surface stress measurements. Ultrasonic stress measurements for cast-wheel hub-cracks: Hiersch, F.A. Test Engineering Vol 22, No 2 (August 1969) p 15 (2281)

X-Ray Investigation on the Strength of Inhomogeneous Metallic Materials

The X-ray method of stress measurement is taken as a unique method of non-destructive measurement of local surface stress. In the past few years, the experimental technique and theory of the stress measurement by X-rays have been remarkably improved, and the recent studies in this field have achieved the sufficiently accurate measurement of applied or residual stress for homogeneous metallic materials such as iron, steel, light metal, alloy and so on. However, the method of X-ray stress measurement is not established for inhomogeneous metallic materials such as cast iron, and there remain yet a few problems upon which there is much controversy.One of the most important problems is to find out the suitable elastic constant for the practical X-ray stress measurement of cast iron.In the previous papers, the authors discussed the effects of graphite on the deformation behavior of spheroidal and flake graphite cast iron from the lattice strain measured by X-rays. It was also suggested that the X-ray elastic constant obtained at after 3 to 10 stress cycles should be used for X-ray stress measurement of cast iron, and that its constant obtained by X-rays is different from the value obtained by the mechanical method. Besides, there is a wide difference in these values obtained by X-rays in cast iron from those obtained in wrought iron or steel.In the present investigation, further experiments were made of the application of X-ray stress measurement to cast iron. The elastic constant of spheroidal and flake graphite cast iron was measured by the mechanical method and by X-rays in detail. The X-ray measurement of applied stress and residual stress induced by grinding was carried out using the obtained X-ray elastic constant.The following conclusions were mainly obtained for these materials;(1) The macroscopic elastic modulus (EM) decreased with the increase of stress. For flake graphite cast iron it decreased having a straight line relation with stress. On the other hand, the elastic modulus pasted through two-stages for spheroidal graphite cast iron. It showed gradual decrease in a linear relation to stress to the stress of 25kg/mm2 and, after that, the rate of its decrease became larger until fracture occurred.(2) The macroscopic elastic modulus (EM) of flake graphite cast iron was markedly different from that of spheroidal graphite cast iron. It is believed that this wide difference is due to the effect of difference in the shape of the graphite on each deformation behavior.(3) On the other hand, the X-ray measurement yielded almost the same elastic constant for the two materials. It is considered that the value of the X-ray elastic constant of cast iron is controlled not so much by the shape of graphite as by the volume ratio of graphite to matrix. Therefore, it may be said in conclusion that the elastic constant measured by X-rays should be used in the X-ray stress measurement of cast iron.(4) If the X-ray elastic constant was used for stress calculation, the applied stress could be measured by the X-rays having a good correlation with mechanically applied stress.(5) A good correlation between the value measured by the X-ray method and by the mechanical method was found for the residual stress induced by grinding.

On the X-Ray Stress Analysis of Metals by the Oscillating Crystal Method

The principle of stress measurement by X-rays is based on the Hooks law which consists in the relation between the peak shift of the X-ray diffraction line and the magnitude of the stress, applied or internal. It has been noted as a unique method of nondestructive stress measurement of local stress. The X-ray stress measurement is applied in very wide fields of material engineering studies.The stress measured by X-rays, however, depends on the local value of the lattice strain observed in the certain diffracted crystal plane satisfying the Bragg's condition. In this connection, there are some problems regarding the character of X-ray stress measurement, for example, the generation of the lattice strain obtained from the peak shift of certain diffraction line is closely related to the crystal grain size, the deformation mechanism, the crystal anisotropy and other complicated factors. As mentioned above, the X-ray stress measurement of coarse grained materials is inadequate sometimes for the ordinary way as offered by Glocker and Macherauch etc. In other words, the stress measurement of coarse grained specimens is essential from the standpoint of the practical application of the X-ray method.For these reasons, the authors attempted to measure the lattice strain and analyse the stress with coarse grained crystal of aluminum, using the oscillating crystal method, and discussed the errors in the measured value. In this paper, the practical significance of the oscillating crystal method is made clear, and besides, it is concluded that the method is more useful than the divergent X-ray method for the stress measurement with coarse grained materials in the engineering sense. Moreover, when the micro-beam technique is introduced to this method, it is possible to measure the extremely localized stress such as tip of crack or one grain in industrial material.The results are as follows.(1) This camera can be applied to any size of grain under suitable geometrical conditions.(2) To correct systematic errors, it is necessary to use the standard specimens which have two or more diffraction lines on a film.(3) The errors of lattice strain were less than 6×10-5 for undeformed Aluminum.(4) The principal residual stress of a coarse grain in the specimen of 7% deformed Aluminum is σ1=2.5kg/mm2, σ2=0.1kg/mm2 and σ3=-1.7kg/mm2, and their directions agree respectively with that of the tensile axis, of the thickness and of the width.

X-Ray Investigation on the Residual Stress of Metallic Materials

The X-ray method of stress measurement is taken as a unique method of non-destructive measurement of local stress. Recently the experimental technique and the theory of stress measurement by X-rays have been greatly improved. From the results of recent study, it is understood that the mechanically applied stress with in the elastic limit can be measured by X-rays with sufficient accuracy.In the case of measurement of residual stress by means of X-rays, however, there remains a question whether the stress measured by X-rays represents the macroscopic residual stress itself. Since the lattice spacing is taken as the gauge length for measurement of strain, it is plausible that the microscopic nature as well as the macroscopic nature are included in the value of the stress obtained. In the present study, experiments were carried out to find the influence of microscopic nature on the valuation of residual stress by X-rays using stretched plate specimens of carbon steels.Eight sorts of carbon steels with carbon content ranging between 0.14 and 1.00 percent were used as the material of the specimens. All the specimens were annealed after the forming. The plastic tensile strain of a quarter and a half of the strain at the maximum load in tensile test was given for every material, and residual stress measurement was made by X-rays and mechanical methods for the stretched specimens. It was intended to compare the distributions of residual stress determined by both these methods.As the X-ray diffraction apparatus, an automitic X-ray stress analyzer of the parallel beam type with the Geiger-Müller counter tube was used. The Cr-Kα radiation was employed, which gave diffraction from the (211) crystal planes of carbon steel. For the purpose of determining the distribution of residual stress by X-rays, a thin layer was successively removed on both the surfaces of the plate specimen, and the stress on the revealed surface was measured. On the other hand, the macroscopic residual stress was measured by the conventional mechanical method of successively removing of thin layers only on one side of the specimen.The obtained results are summarized as follows: -1) Compressive residual stress is observed in the surface layers of the stretched specimens, and its value seems to be independent of the stretched strains.2) The accuracy of the stress value by X-rays measured by the sin2ψ method is sufficiently reliable.3) The residual stress on the surface of the stretched specimens by X-rays shows non-uniformity from place to place of the surface. It is considered that the non-uniformity of stress value by X-rays must be taken into consideration in the comparison of the stress measured by X-rays with that measured by mechanical means.4) The compressive residual stress measured by the X-ray method increases with the increase of carbon contents both on the surface layers and at the core of the specimen. If the stress value by X-rays represents only the macroscopic residual stress, it must converge to zero at an infinitely small thickness after the successive removal of layers from both the surfaces. However, the experimental result shows the existence of compressive residual stress in such a case. Therefore, it is considered that the residual stress measured by X-rays in the stretched carbon steel includes the macroscopic residual stress caused by the surface effect and also the microscopic nature due to the plastic deformation, and the cause of the discrepancy between the X-rays and the macroscopic residual stress in the stretched carbon streel cannot be explained by the criterion of the phase stress (Gefügespannung) alone.