FI61248C - PAO ROENTGENDIFRAKTION SIG GRUNDADE KAMERAFOERFARANDE FOER MAETNING AV SPAENNINGSTILLSTAONDET I METALLER I SYNNERHET AUSTENITISKA STAOL SAMT KAMERAANORDNING FOER TILLAEMPNING AV FOERFARANDET - Google Patents

Description

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C Patent granted 10 05 1932 • SäS (- »s) Patent tneddelat ^ T ^ (51) Kv.lk.3 / lnt.CI.3 G 01 N 23/205 FINLAND —FINLAND (21) P« * nttlh »k «Mui —P» t * nt * n »eknlng 801823 (22) H» k * ml «pUvi - An * eknlng» d * g 06.06.80 ^ ^ (23) AlkupUvi - Glltlgh «t * dig 06.06.80 ( 41) Tullut Julkliuk ·! - Bllvlt offuntilg 07.12.8l

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Patent- och reglsterityrelaen 'An * ttk »n« tltgd eeh utl. »Krift * n publicand 26.02.Ö2 (32) (33) (31) Requested privilege — Begird priori» t (71) Insinööritoimisto Mexpert Oy, Länsituulentie 10, 02100 Espoo 10,

Suomi-Finland (FI) (72) Matti Korhonen, Espoo, Veikko Lindroos, Espoo, Suomi-Finland (Fl) (7M Forssan & Salomaa Oy (5 * 0 X-ray diffraction camera system for measuring the stress state of metals, especially austenitic steels, and camera device applying the method - A X-ray diffraction pattern based on the refractive index of the spanning screen in the metal, and the synergistic austenitic st & l samt camaanordning för tillämpning av förfarandet

The invention relates to a camera method for measuring the stress state of austenitic steels or the like based on X-ray diffraction, in which method the Röugten film cassette is tilted through an axis running on the surface of the sample to be examined which is substantially perpendicular to the direction of detectable stresses. Horizontal diameters of debye tires or equivalent.

The invention further relates to a camera device for carrying out the method according to the invention, comprising a reticle tube, a camera tripod attached thereto and a film cassette in which the reticle film is placed.

The basis for the correct design and dimensioning of machines and structures is the need for information on the stress states that really affect them, both during manufacture and subsequent use. The stress measurement method must therefore be non-destructive.

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If a metal structure is improperly dimensioned — or if it is used in conditions for which it was not designed — it often results in the metal breaking at a point where the stress state can become too high. Often, such a local fracture will, over time, lead to damage or even destruction of the entire structure, as is the case with pressure vessel explosions. However, if damage has occurred, the reasons for the future must be determined, for which stress analysis is again required: it must be determined where and why the stress state has become greater than estimated at the design stage.

Recently, there has been a further increase in the need to obtain information on the stresses of metal structures to support the design, as the aim is to make the structures as light and thin-walled as possible, often for economic but also technical reasons. In this way, the "margin" used in the dimensioning becomes smaller and smaller, which requires more detailed information about the stresses that actually affect the structures. This need is further emphasized by the fact that manufacturing technologies, such as cold forming and welding, create considerable stresses in structures already during manufacturing. Thus, structures often have residual stresses that can cause them to break even before they have been used; in use, they can rupture at significantly lower loads than they are designed to withstand.

There are two basic ways to determine permanent or internal stresses, namely 1) non-destructive methods based on stress release by cutting the specimen, where the elastic deformation is measured e.g. with strain gauge strips, and 2) non-destructive methods which are also based on cutting.

X-ray diffraction reveals variations in the distance between the atomic levels of the metal as changes in the diffraction angle and thus offers the possibility to measure the stress state of the metal without breaking the substance. The X-ray diffraction method is, in fact, the only sufficiently accurate non-destructive stress measurement method of technical significance.

For stress measurement, either the camera or diffraction method is used. The camera method is more suitable for stress measurement when it is necessary to measure local stresses, when it is necessary to find out the course of stress distributions or when the surface of the object to be examined is not planar.

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When one of the above points usually applies to stress tests in practice, and because the camera equipment is also light and compact and easy to move and install, the camera method is suitable for practical stress tests, often "on-site", if it can achieve sufficient accuracy.

The object of the present invention is to further develop the so-called an improved camera method, which will be described in more detail later. A particular object of the invention is to provide a method and a camera device with which it is possible to measure the stress states of austenitic steels with an accuracy substantially as good as that obtained by studying the stress states of ferritic steels by previously known camera methods.

In order to achieve the above and later objects, the method according to the invention is mainly characterized in that the registration of said diameters of Debye rings at different tilt angles is performed by a film cassette and a supported film cassette perpendicular to said tilt axis the areas of the ends are sufficiently close to the tilt axis for measuring the stress state of austenitic steels and that the method uses an arcuate film cassette elongate and narrow enough in the direction of said tilt axis so that a sufficiently large tilt angle of the cassette is possible for carrying out the method.

The camera device according to the invention, on the other hand, is mainly characterized in that the tube and other devices are arranged to rotate about said tilt axis passing through the point to be examined and that the camera cassette is curved, preferably circular, seen perpendicular to the axis.

In the following, the invention will be described in detail with reference to the diagrams of the accompanying drawing, as well as examples of camera devices.

Figure 1A schematically shows the distance between the atomic levels of a given substance in the unstressed state and Figure 1B shows the corresponding distance in the state under stress σ, xx

Figure 2 illustrates the principle of reflection of X-rays from the object under study.

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Figure 3 illustrates the various parameters used in the X-ray method.

Figure 4 shows the so-called Debye ring registration for the film.

Figure 5 shows a cylindrical film cassette used in the invention.

Figure 6 shows an overview of a camera apparatus according to the invention seen from the side.

Figure 7 shows a more detailed view of the camera device and its film cassette seen from the side.

Figure 8 shows the same as Figure 7 seen from the sample side.

Figure 9 shows an assembled axonometric view of a particular invented film cassette used in a camera apparatus according to the invention.

Fig. 10 shows the different parts of the film cassette according to Fig. 9 separately.

In the X-ray method, the distance d between atomic planes is used as the measuring length (Fig. 1). X-rays having a wavelength λ are reflected from atomic planes when they hit planes at an angle Θ obtained from Bragg's law (1) 2 d sin θ = λ as shown in Fig. 2.

Let us now consider the case shown in Fig. 1, where a normal stress perpendicular to the atomic planes increases the interval between the atomic planes from d ^ to do.

Using Bragg's law, both distances dQ and d ^ can be calculated using the Bragg angle Θ, which is measured by X-ray diffraction, and thus the normal deformation can be calculated from the formula d - d (2) e = -2_ £ xx d o

The corresponding stress o causing the deformation e can now be determined

XX XX

Hooke law (3) o * E e,

XX XX

where E is the modulus of elasticity.

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More generally, the X-ray method produces a normal stress component in the selected direction x when at least two deformations e (* f) in the xz plane are measured (Figure 3). The general Hooke's law gives E e (* 2) - e (Ψχ) ^ ° xx 1 + v .2. 2 ψ sm ^^ - sin Ψ where v is the Poisson's ratio.

According to the general Kimmo doctrine, the whole stress state is defined when three stress components in different directions are known.

Verticals are measured in previously known standard camera methods

Debye rays S, Fig. 4. From the rays measured at two different inclination angles, the vert stress is solved as follows E cos22e S (ψ) -S (Ψ) (5) σ (φ) = ----- γ- 1 + v 2Dtg6 sin ^

It can be seen from the equation that the accuracy of the measured stress is better the - the larger the angle 2Θ - the greater the difference between the tilt angles ^^ and Ψ ^.

Of the commercially available X-ray tubes suitable for steel examination, the chromium tube gives the reflections of austenitic steels in the highest 2Θ range: (i) Cr-K a radiation: ^ ®220 s ^ - ^ 8 ° (strong reflection) (ii) Cr-K 8 - radiation: ^ ®3io ö 150 ° (low reflection) These are too small angles for good accuracy. In addition, the registration of these reflections requires that the cassette be brought so close to the sample (or the cassette size must be increased accordingly) that it can no longer be tilted sufficiently to achieve the angular difference required for good accuracy. the registered lines become different due to different focusing and absorption conditions, which further reduces the 6 61248 accuracy achievable. Thus, the determination of the stress state of austenitic steels by conventional camera methods with practically sufficient accuracy has proved impossible.

The following describes in more detail the improved camera method on which the invention is based, which the present invention is intended to further develop in order to achieve the previously stated objects.

When recording intensities with the camera, the axial diameters2S of the imaged Debye rings are measured, e.g., by photometry of the film. From these diameters, the tangent of the reflection angle 180 ° to 2Θ = 2Θ is obtained from formula (6) tg 2Θ =, where D is the distance between the test piece and the film. The deformations are thus obtained from the formula (7) e (O = | 2 |! 2 | (tg 2Θ ψ -tg20o), the placement of which in Equation (4) gives the working equation (8) σ xx = ^ 2 (S ψ 2 "S ψ i), where the stress coefficient is (g) v = E cos228 -2-1-T- 2 2D (l + v) tg8 s in ψ2-δ ^ η

The accuracy achieved by the described improved camera technique is very comparable to diffractometer methods due to the fact that focusing of the ideal Schultz type reduces focusing and absorption errors to a minimum and that measuring diameters instead of radii reduces random errors and many equipment errors; these same features are not available with conventional camera methods.

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In the improved camera method based on the present invention, axial diameters 2S are measured, Fig. 4. In addition, according to the invention, the radii of reflections are recorded by a cylindrical or similar cassette parallel to the measured diameter A-A (Fig. 5). (220) and (310) can be registered using sufficiently different heeling angles and so that sufficient stress determination accuracy can be achieved.

However, since the 20-angle is slightly too small, the Debye diameters must be measured correspondingly more accurately in order to achieve the accuracy characteristic of conventional camera methods known in the art for determining the stress state of ferritic steels. This is possible in the improved camera method on which the invention is based, because images taken at different inclinations are focused, the absorption factor does not depend on the inclination, several technical factors do not cause an error when measuring diameters, and 20-angle random errors are smaller than vertical-radial. .

Thus, with the improved camera method of the invention using a special film cassette suitable for examining austenitic steels, it is possible to measure the stress states of austenitic steels with the accuracy typical of examining ferritic steel stress conditions.

In the following, the structure and operation of the camera device implementing the method according to the invention and the special film cassette used therein in the execution of the method will be described in particular with reference to Figs.

The device shown in Figures 6, 7 and 8 comprises an X-ray tube 10 adapted to be rotated about a horizontal axis of rotation A-A in the figures. The axis A-A in Fig. 4 corresponds to the Ψ axis, which is perpendicular to the direction of action of the stress a to be measured. According to Figure 6, the axis A-A passes through or in the vicinity of the test point P of the present sample 15. To pivot the device about the axis A-A, the base of the device comprises a circular cross-sectional axis of rotation 11, around which a ring 16 is fastened and locked, which is fixed to the frame structures of the X-ray tube 10.

The camera device itself comprises a tripod 12 to which an X-ray film cassette 13 is attached, which is new and special in design. The X-ray collimator 14 8 61248 is directed from the center of the cassette 13 towards the test area P of the sample 15. In addition, according to Fig. 6, the device comprises a camera oscillating device 17 known per se, the more detailed structure of which can be seen in Fig. 7. The camera oscillating device 17 comprises a synchronous motor 18 with a non-Kesko 19 mounted on its shaft. Oscillating the camera during exposure results in a smoother and more accurate blackening of the film. The camera device also includes cooling devices 21 known per se. Within the scope of the invention, the support of the camera device for pivoting about the axis AA can be realized in many other ways than the shaft 11 and the ring 16 shown in Fig. 6. The camera device can be supported e.g. from above. a portion having a support groove in the shape of an arc of a circle centered on the axis AA, by means of which the X-ray tube 10 with its other devices can be locked in different positions.

In Fig. 7, the film cassette 13 according to the invention, viewed in a direction perpendicular to the tilt axis A-A, is arcuate in the shape of a circle with an angle α of about 140 ° and a radius R of about 70 mm. The width of the cassette in a direction perpendicular to the plane of Fig. 7 is about 40 mm.

Figures 1 and 10 show the structure of a film cassette according to the invention. The film cassette 13 comprises a cover plate 22, a film holder 23 and a body portion 24. These parts are fixed to each other by a fixing screw 25. In Fig. 9, the film is indicated by reference numeral 26 and the film cover by reference numeral 27. The cover plate 22 is a cassette-shaped curved body with fixing projections 28 the cover plate is optionally attachable to either side of the cassette so that only a certain half of the film is "exposed" at a time. The fixing screw 25 has a thread which engages the thread of the hole 30 in the body part. The screw 25 passes through a hole 31 in the film holder 23. The L-shaped edge portions 32 of the film holder press the film 26 with its covers 27 into a well-defined position and shape against the cylindrical inner surface of the body portion 24.

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

Claims (9)

1. On x-ray diffraction, basic camera method is used to measure the stress state of austenitic steel or the like, wherein an X-ray film cassette (13) is inclined around such a surface of the sample (15) to be examined the shaft axis (AA) which substantially disturbs perpendicular to the direction of the stresses (σ) to be recorded and in which method horizontal diameters (2S) or the like of so-called ax Debyeings are recorded in the X-ray film (26) at TVS or several inclination angles (Ψ), characterized in that the recording of the mentioned diameters (2S) at different inclination angles (Ψ) is carried out with the dX film cassette and the one inside it. the supported film, the cassette seen in a perpendicular to said inclination axis (AA) perpendicular (BB) is bag shaped in such a way that the end regions of the cassette and film are sufficiently close to the inclination axis (AA) given the measurement of the stress state in austenitic state and that the method utilizes a side in the direction of said inclination shaft (AA) elongated and sufficiently narrow bag-shaped film cassette that a sufficient cassette inclination angle (Ψ) is possible for the purpose of carrying out the process. Method according to claim 1, characterized in that the curvature of the film cassette (13) and the curvature of the film (26) supported by it is arranged so that it is essentially circular (radius R). Method according to Claim 1, characterized in that an axially aligned axis (BB) arranged through the film cassette (13) and the curvature point (BB) of the curvature of the film (26) is arranged to cut said inclination axis (AA) in the surface area of the sample to be examined. . A camera device for carrying out the method according to claim 1, 2 or 3, comprising a X-ray tube (10), a camera frame (12) attached thereto (12) and a film cassette (13) within which an X-ray film (26) is placed, characterized in that the x-ray tube (10) with other devices is pivotally arranged about the inclined axis (AA), which axis (AA) passes through the place (P) to be examined on the sample (15) to be examined and that the camera cassette (13) is curved, preferably circularly bifurcated in a direction perpendicular to the axis (AA) perpendicular (Fig. 7).