FI75053B - X-ray diffraction method and device for measuring the state of tension - Google Patents

Abstract

X-ray diffraction method and device for measuring the state of tension in metals, especially in steel or similar. One directs the primary x-ray beams (X1p, X2p) to the sample (14) that is to be investigated in at least two directions in relation to the norm (N) of their surfaces. Through the use of a detector (15), one observes the diffracted x-ray beams (X1d, X2d) that are diffracted from the studied point (P) in the sample (14). The X-ray source used to generate the primary x-ray beams (X1p, X2p) is a radioisotope source (10, 11). The detector (15), with which the above mentioned diffracted X-ray beams (X1d, X2d) are observed, is comprised of a location sensing detector surface (15'), for example a semiconductor, whose photo- and/or electrical signal is transmitted to the measuring signal processing system (20), with which the tensions that shall be measured are calculated on the basis of the location sensing detector surface's (15') location observations (R1, R2) and the detector position in the plane (Xj-Xj) where the primary beams (X1p,X2p) are being transmitted. The radioisotope source is an advantageous Fe55 radiation source.<IMAGE>

Description

The invention relates to an X-ray diffraction method for measuring the stress state of metals, in particular steels or the like, in which at least two , which detects X-ray beams diffracted from the test site of the sample by the action of said primary X-ray beams 15.

The invention further relates to a device for carrying out the method according to any one of claims 1 to 6, comprising a body part 20 to which an X-ray source and a detector arrangement are attached, further comprising means for processing signals from the detector arrangement and calculating and displaying and / or recording voltage measurement results.

25 The need for non-destructive stress measurement has grown strongly in recent years. The only non-destructive stress measurement method in wider use is based on X-ray diffraction in a crystalline material. The main disadvantages of known measuring devices are their large size and slowness, which makes it difficult to work, especially in field conditions.

30 X-ray diffraction stress measurement methods measure the surface stresses of a crystalline material. The penetration depth of X-rays is in the order of about 5-25 μm. Surface stresses are significant for the durability of structures because damage usually originates from 35 surface layers; for example, stress corrosion, brittle fracture, fatigue, etc.

2 75053 1 In order to eliminate the above-mentioned disadvantages, the applicant has submitted (FI pat. No. 61 268) the so-called an improved camera method with a smaller equipment size and a simple structure compared to previously used diffractometer equipment in general use.

5 There are basically two types of voltage measuring devices based on X-ray diffraction: camera devices and diffractometer devices. The camera design achieved the simplest and smallest device design in the past, but its disadvantage is the relatively long time required to expose and develop the film. Diffractometers measure X-ray intensity as a function of 29-angle with either a proportionality and scintillation counter. The counter has to be swept over a certain 29-angle range, which requires an accurate goniometer device, which makes the diffractometers too large, complicated, and expensive devices for field work. The size of the diffract-15 meters has been somewhat reduced and the measurement speed has been increased. with location-aware detectors.

Em. The camera method and apparatus according to FI patent 61 268 have been further developed by the applicant in the method and apparatus disclosed in FI patent 67 956, in which scintillation coatings or a detector surface made by integrated circuit manufacturing techniques are used as the detector surface, by which the X-rays reflected from the sample are either transmitted by optical fibers to the detector or directly or indirectly as an electrical signal. Em. The apparatus according to F1 patent 67 956 is mainly characterized in that said detector surface is located symmetrically on both sides of the collimator and the detector surface has parts made of scintillator coatings or integrated circuits further a unit or units for deriving the voltages to be measured on the basis of the photographic signal and / or the electrical signal.

Em. The methods and devices according to FI patents 61,268 and 67,956 constituted a significant advance in the technology for measuring the stress state of metals, especially austenitic steels. It is an object of the present invention to further develop the methods and apparatus disclosed in said patents.

Il 3 75053 1 It is a particular object of the present invention to provide a method and apparatus having an order of magnitude or several orders of magnitude smaller than the above-mentioned known devices.

It is an object of the present invention to further develop said known devices based on X-ray diffraction so as to provide an even faster measuring device, which is intended to achieve a considerable extension of the field of application of the measuring device. A further object of the invention in this respect is to make possible a portable measuring device which can be used in difficult field conditions and in confined spaces, such as inside structures and machines, e.g. inside pipes for measuring stresses.

The object of the present invention is to provide an even faster measuring device with which even large amounts of stress observations can be collected and stored in memory, e.g. for statistical processing.

In order to achieve the above and later objects, the method according to the invention is mainly characterized in that a suitable radioisotope source is used as the X-ray source with which said primary radiation beams are obtained, that said diffused the photographic signal and / or the electrical signal is fed to a measurement signal processing system, and that said system calculates the voltages to be measured on the basis of the location observations of the locating detector surface 30 and the position of the detector in the plane where the primary beam clocks are transmitted.

The device according to the invention, on the other hand, is mainly characterized in that the radiation source is a radioisotope source which can be aligned with a primary beam or beams to the object to be examined. data logger or the like and that the measurement data, if necessary converted to digital format, can be transferred to a data-5 machine or microprocessor for further processing.

The use of easily movable small radioisotope sources in measurement technology to control production processes and to study and inspect materials has been known in the past. As an example of this, 10 can be mentioned e.g. radiation weight meters and various densitometers based on, for example, moving paper webs based on radiation attenuation or scattering, as well as elemental analyzers based on characteristic X-ray excitation. X-ray diffraction equipment based on a radioisotope source for determining the internal stresses, texture, phase ratios or grain size of crystalline materials has not been shown to our knowledge.

In the implementation of the method and apparatus according to the invention, when the aim is above all to reduce the measurement time and the size of the apparatus, the following essential factors must be taken into account:

In the invention, the energy emitted by the isotope radiation source must be chosen so that its level falls below the X-ray absorption thresholds of the test substance so that the fluorescence does not compete with the diffraction.

In the invention, it is advantageous to take advantage of parallel measurements so that several inverse lattice vectors are measured simultaneously, which can be accomplished by illuminating the test site with radiation from several different sources and observing diffracted radiation with several different detectors, while ensuring that different measurements do not interfere.

The invention uses a position-differential detector as efficiently as possible, which registers the quantifiers diffracted at different angles simultaneously, preferably a CCD detector or a linear LED series.

The invention uses an isotope source or sources with the highest possible surface brightness.

The invention preferably uses an annular isotope source and places incoming radiation-limiting gaps between the ring source and the surface to be examined, by means of which the apparent radiation sources located at the gaps can be given the position and position required by the focusing conditions.

Once the resolution required for the measurement according to the invention has been fixed, all the factors affecting the geometric efficiency are selected, i. the source-sample-detector distances, the size and shape of the source, and the size and shape of the illuminated sample area as advantageous in intensity as the required resolution allows. In this case, it is also possible to utilize the focusing possibilities of the focus-15 so that the quantums belonging to the same crystal reflection diffracted from different points of the sample hit the same point on the X-ray sensitive detector surface.

The minimization of the measurement time in the invention can be taken further the more precisely the measurement problem based on X-ray diffraction using an isotope source is defined.

An X-ray generator with high voltage sources typically weighs 50-100 kg. When a suitable radioisotope-25 source weighing only on the order of 10 g and pay-as-you-know semiconductor detectors are used in combination to provide a direct photovoltaic or, more preferably, an electrical signal containing measurement data, the weight and size of the device can be reduced by several decades compared to known devices. case very dramatically. Furthermore, in the invention, the measurement time required for a private measurement or a multi-level measurement series is only in the order of seconds or fractions of seconds, so that a small measuring device can collect a large number of measurement results from objects for which X-ray stress measurement was not previously possible. The measurement results 35 can be stored in the memory of a computer or the like for later processing. The simultaneous realization of all these advantages represents a significant advance in the field of stress measurement technology.

6 75053 1 The physical background of the invention and some preferred application examples thereof will now be described with reference to the figures of the accompanying drawing.

Figure A schematically shows the distance between the atomic levels of a given substance in the unstressed state and Figure B shows the corresponding distance in the stressed state.

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

Figure D illustrates the various parameters used in the stress measurement X-ray method.

Figure 1 schematically shows in vertical section the apparatus according to the invention and its geometry. Fig. 1 is at the same time a section at the line I-I marked in Fig. 2.

Figure 2 is a section A-A in Figure 1.

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Figure 3 is a section B-B in Figure 1.

Figure 4 schematically shows the principle and measuring geometry of the measuring method according to the invention.

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Fig. 5 shows, in a manner similar to Fig. 4, essential geometrical quantities in the measuring method according to the invention.

Figure 6 shows a block diagram of a measuring method according to the invention with measuring-30 data collection, processing and printing devices.

In the X-ray method underlying the present invention, the distance d between the atomic planes is used as a measuring length (Fig. A). X-rays having a wavelength λ are reflected from the atomic plane when they hit planes at an angle of 35 Θ, which is obtained from Braggl's law 1 d sin θ - λ (1) 7 75053 1 as shown in Fig. C.

In the case shown in Figures A and B, the normal stress σ perpendicular to the atomic planes increases the interval between the atomic planes from dQ to dQ.

5 Using Bragg's law (1), both distances dQ and dg can be calculated using the Bragg angle Θ in question, which is measured by X-ray diffraction, and thus the normal deformation can be calculated from the formula d - d Exx -2-2 1 10 do

The corresponding stress σ, which causes the deformation e, is now

XX XX

can be determined by Hooke's law 15 ϊχ - E · χχ · (3), where E is the modulus of elasticity.

More generally, the X-ray method produces a normal stress component σχχ in the selected direction x when at least two deformations e (ψ) in the xz plane are measured (Fig. D). The general Hooke's law gives „- E e (♦„> - e (* 1> (4) 1 + v sin »l ^ -sin 25 where v is the Poisson's ratio.

It follows from the equilibrium conditions of elastic theory that the stress state of a body is determined when the stress state of its surface is known. When no tensile or compressive stress perpendicular to the surface can be encountered on the surface, the elongation ellipsoid associated with the stress state is determined when at least three correctly selected relative elongations are measured, i.e., some distance d between the atomic planes in four correctly selected directions.

Figure 1 shows a preferred stress measuring device for ferritic steels according to the invention, comprising an annular radioactive isotope source 10, preferably Fe 2. The ring source 8 75053 1 10 is positioned so that its axis of rotation coincides with the normal of the test surface passing through the test point P. In the immediate vicinity of the radiating surface 11 of the ring source 10 there is a first blind plate 12 having a pair of aperture pairs 12a ^, 12b ^; 12β2 * 1202 and \ 2a ^ narrower apertures 120 ^, 120 ^ and 12b ^ and their diffraction images with the detector Xbld, Xb2d ^ bSd s * Divide in pairs at the same time by a circle adjacent to the surface to be examined at point P. The radially wider openings 12a 2, 12a 2 10 and 12a 2 may be so wide that the visibility of the isotope source is not at least substantially limited. Between the sample 14 to be examined and the first blind plate 12 there is a second blind plate 13 parallel to the first blind plate 12. The second blind plate has circumferentially arranged openings 12a and 12b at points 15 but with a smaller radius. .lSb ^.

Said blind plates 12 and 13 apply to the sample 14 to be examined at its point P in three different planes the radiation beams of X-rays from the isotope source χ ^ -χ ^, X2-X2 * x3-x3 and the apparent source surfaces of ^ p 'J ° ^ are located in narrow at the openings 12b ^, 12b2 · 12b ^, 13a ^, 20 13a2 »13a2. The planes χ ^ -χ ^, x2-x2 and x ^ -x ^ are perpendicular to the surface of the sample 14 or to the tangent plane set at P, and said planes are at an angle of 60 ° to each other.

The fact that ferritic iron has few diffraction peaks when generated by Fe-55 radiation from a radioisotope source in the invention leads to the finding that the same sample area can be illuminated from several different directions and viewed with several different detectors simultaneously without different measurements interfering with each other.

As shown in Figures 1, 2 and 3, the collimator plates 12 and 13 have wider (12a, 13a) and narrower (12b, 13b) collimator openings in their radial direction. Said apertures of the collimator plates and their locations are selected according to the SEEMANN-BOHLIN focusing principle so that the inaccuracy of both diffracted beams Xjj and X2 ^ on the X-ray sensitive surface 15 'of the detector 15 is equal. To this end, the first collimator plate 12 has a wider aperture 12a and a corresponding aperture 13b 11, 75053 Ί at the corresponding point in the path of the radiation beam X 1 at the primary beam opposite to the detector 15 and vice versa at the first beam X_ on the detector 15 side.

ZP

the collimator plate 12 has a smaller opening 12b and the second collimator plate 13 has a wider opening 13a.

5

In the following, with reference to Figures 4 and 5, the essential quantities of the measuring geometry of the method and device according to the invention will be described, from which the voltage measurement results can be derived by means of a position-separated detector 15.

10 In Fig. 4, ψ1 and ψ 2 show the tilt angles of the reflective lattice planes and and N'2 the corresponding normal planes of the reflective lattice planes.

The normal plane of the tangent plane set at the surface of the sample 14 or at the point P to be examined is denoted by N. and X2 show the primary X-ray beams centered on the collimator plates 12 and 13 from the radioisotope source 10, and X1 and X2J, respectively, show the radiation beams diffracted from the sample P at the point 14 to be examined.

In Fig. 5, the perpendicular distance of the X-ray sensitive surface 20 of the detector 15 from the point P and 14 of the sample 14 to be examined is denoted by the normal plane passing through the point P under the points where the maximum of the diffracted beam beams coincide.

25 The following representation shows the meanings of the other variables shown in Figures 4 and 5.

The stress can be calculated using the following formulas: 30 Ψ1 “®“ Ψ o (5) Ψ2 = Θ +% (6) whereby based on the above equations ^. E Δ d2n- Δ d1 (7) (1 + V) d x sin »sin29 35 10 75053 1 The measured quantities are R 1 / D and R 2 / D (Figure 5). From Bragg 's law (1) we get Δ d Δ 20 (8) 5 Δ 20 = 20 - 20Q, (9) where. = E Δ 2Θ. Δ 20. (10) υ 1 + V x 2tg0 (sin Ψ 0sin29) on the detector surface 15 'the displacements of the observed line Δ20 are solved as follows ^ Δ2Θ = + cos% q ^ (11)

D

where Ar * R - Rq

Rp = radius of unstressed material (12) 20 + sign for Debye line 2 - sign for Debye line 1

The above equations are used to solve the stresses in one or more measuring planes xj-xj on the basis of the distance 25 and the maxima of the diffracted radiation beams X1 and X2J on the X-ray sensitive, locating surface 15 'of the detector 15.

Figure 6 is a schematic block diagram of the equipment for processing and displaying the measurement results. According to Fig. 6, there are N detectors 15j, so that the voltages can be measured in N different levels x ^ -x ^ ... x ^ -x ^ with the apparatus according to Fig. 6.

According to the invention, e.g. commercially available optical and at the same time X-ray sensitive locating detectors, e.g. semiconductor detectors such as Philips CCD NXA1010 or Hamamatsu's linear photodiode array S2304-512F are used as detectors 15

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π 75053 "I or S2304-104F with 512 or 1024 discrete light emitting diodes in a linear series. For these" selfscanning photodiode arrays "used in the invention, reference is made to Adv. in X-ray Anal., Vol. 19, pp. 587-596; Louis N. Koppel, “Direct X-ray 5 Response of Self-Scanning Photodiode Arrays.” Said series is aligned with the measured quantities R 1 and R 2, and the light emitting diode at which the diffracted rays X 1 and / or their the maxima hit, conduct and give an impulse from which the data si »s2, s3 *, sn J ° ^ are fed to a data logger 21 which reads the detector and the detectors 15 ^ alternately. the measurement results are displayed or printed to a printer 23. The computer 22 can be programmed to process the measurement results, e.g., statistically.

15

According to Figure 6, the detectors 15 ^ -15 ^ are cooled. The cooling equipment is indicated by reference numeral 16 and the cooling medium flow by reference F. This cooling is necessary in order to make the dark current (thermal noise) of the optical detectors sufficiently small. If necessary, the detector 15 can be cooled down to -100 ° C.

In the invention, position detectors manufactured by integrated circuit technology can also be used as location detectors, in the structure of which more or less also sig-25 signal processing and memory (RAM) are integrated.

As stated above, in the invention, the level of energy emitted by the isotope source 10,11 is preferably selected so that said level falls below the X-ray absorption thresholds of the test substance so that the fluorescence 30 does not compete with the diffraction.

Other previously known or future-developed linear or matrix-like locating detectors can be used within the scope of the invention, which are also sensitive to electromagnetic radiation, i.e. also 315 X-rays, and which provide either a photovoltaic signal or, most preferably, a direct electrical signal containing information on the above and X2J hit points. When using matrix-like detectors, a larger part of the Debye ring can be registered, if necessary, for which additional information is available if desired.

Various non-ring-5 radioisotope sources can also be used within the scope of the invention. The most preferred radioisotope source suitable for measuring ferritic steels is the above-mentioned Fe 2+ source for several reasons.

In the following, the claims are defined, within the scope of the inventive idea defined by them, the various details of the invention may vary and differ from those set forth above by way of example only.

15 20 25 30 35

Claims (10)

1 Patent Claim 1. X-ray diffraction procedure for measuring the voltage state of metals, especially the like or the like, in the procedure of primary method X-ray radiation cones (Χ ^, ρ2ρ) of the sample (14) to be examined aminetone 1 in two directions 1 to the standard surface and at the choice of method a detector (IS) is used, with the observed X-ray radiation cones having been diffracted from the site under the influence of said primary rate radiation cones (X., Xp). thereof, providing the X-ray radiation source, whichever of the said sample radiation cones (X,, X), is made up of an appropriate radioisotope source (10, 11), said detector (15), with said diffracted radiation cone ( »X2d ^ ° beaver, is comprised of a sensing detector surface (15 '), suitably a semiconductor detector, the photocurrent and / or electrical signal obtained from the semiconductor detector is measured. The processing system (20) of the beam, and the 8 voltages to be measured are calculated with the said system p1 the base of the location sensing detector surface (15 ') location observations (R 1 R 2) and the position p1 of the detector 1 of the path (x-x). where the primer flow cones (X. , X «) j j lp ^ P 25 is dispatched. 2. A process according to claim 1, characterized in that in the process, the radiol isotope source is made up of an Fe 2 radiation source. Method according to claim 1 or 2, characterized in that the method uses an isotope source (10,11) which, during the measurement, states statonary 1 relating to the sample (14) to be investigated, from which source a pair of primary x-rays is directed. - Radiation cones (X,, X,) plotted sides of the normal (N) of the sample to be investigated, each cone being selected with aperture (12,13) and the area of the specimen (14) to be investigated and out of the sector (2 mail) mailing said pair of preamplifier cones (X., X,) to a location-distinctive detector surface (15 '), by means of which the hit points (R,, R) are observed. the diffracted rays (Χ ,,, Χ ,,,) formed in Fig. 2d due to the primary x-rays (X,, X.). 4. A method according to any one of claims 1-3, characterized in that the method uses a stationary, most preferably annular radioisotope source (10) with which several (N) pairs of primary X-ray radiation (ΧΧ) are obtained. ) ^), Which are simultaneously directed at the object (P) to be investigated and that in the process 10 ((st)) localistinctive detectors (15 ^ ... 15 ^) are applied, the voltages to be measured with the detectors being observed in several different pian ((χΓχΓ ·· χΝ-χΝ) * Method according to any one of claims 1-4, characterized in that the factors acting on the geometric efficiency of the method, such as the source-sample-detector distance, the size and shape of the apparent sources, the apertures, the openings and the brightness the sample range (P) is chosen from the intensity point of view as advantageous as the required resolving ability permits and that the pair or pairs of primary X-ray cones (χ ^ ρ »Χ2ρ) are focused in such a way that the quantifiers diffracted from different places of the sample -type reflection hits the same spot on the sensing detector surface (15 '). Method according to any one of claims 1-5, characterized in that the level of radiation energy emitted by the isotope radiation cold (10,11) is chosen below the X-ray absorption threshold of the substance to be examined so that the fluorescence does not disturb the X-ray diffraction observed in the process. (Χ ^, Χ2 +). Apparatus for carrying out the method according to any of claims 1-6, which comprises a body part, to which an X-ray source (10) is attached and a detector arrangement (15) and which apparatus further comprises an apparatus (20) for treatment. of signals (s) received from the detector arrangement (15) of the plant and for calculation and detection and / or recording of the voltage measurement results, characterized in that the radiation source is a radio source (10,11) with which a pr radiation cones or cones (X., X_) may be detected on the object (P) to be investigated, that the device-lp detector of the device is a circuit-inductive semiconductor detector, such as a CCD detector or a low-light diode series detector, obtained from this Act arranged can be read out with a data log ¢ 21) or the corresponding and ate measurement data if necessary, transmitted in 1 digital form, can be transmitted to a computer (22) or micropr ocessor for further processing. 8. Apparatus according to claim 7, characterized in that the method uses a statonary isotope irradiation system (10, 11), most preferably a Fe 2 radiation source, that between the radiation source (10, 11) and the object (P) which to be examined, an aperture arrangement (12,13) has been provided, by which preliminary X-ray cones (Χ ^^, Χ ^^) have been directed at the object to be examined on both sides of the normal (N) of the surface of the object (P) to be examined most conveniently on the same angle (Ψ), and that an out-of-plane detector has been arranged outside the sector between said primary beams, the arrangement of the detector's orthodontic signal being directed in accordance with the plane of said primer X-rays (X, X) and Rectified 1 ratio to the ratio of the lp Zp diffracted rays (Χ ^, Χ2 ^). 9. Device according to claim 7 or 8, characterized in that the radiation source consists of a continuous or continuous continuous source source, in contact with which a first mixer (12) is provided, whereby openings (12a, 12b) are provided with 1 extending to it. the center is essentially the same radius, which is in pairs towards each other and that the gap between said first mixer (12) and the object (P) to be examined is substantially parallel to that of the first mixer (12) and concentric second mixer (13). has openings on the same line with the opener and the first aperture (12) and the object (P) to be examined, which opening pairs control and limit the pair of preliminary X-ray radiation sources (Χ ^, Χ ^^) to the object to be examined. 35 Device according to any of claims 7-9, characterized in that the device comprises a plurality of (N) detectors (15j), II