SU911129A1 - Method of measuring deformation in bending - Google Patents

Description

(METHOD OF MEASURING DEFORMATION DURING BENDING

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The invention relates to a measurement technique, in particular, to methods for measuring the deformation of solids.

A known method for determining deoormia in bending is that a strain gauge is installed on the sample surface, a bending moment is applied to the sample and, according to the strain gauge indications, the strain value l is determined.

The disadvantage of this method is its low accuracy, due to the fact that the measurement of the deformation is carried out over the surface and the deformation of the bend, recorded, according to the instructions of the strain gauge, corresponds only to the deformation of the surface layer.

The closest to the invention in technical essence and the achieved result is the method of measuring the deformation. The fact is that a strain gauge installed in the form of two clamps for clamping the sample, two strain gauges, two straps in the form of elastic plates, the planes of the lowest stiffness are parallel, and the planes of the greatest stiffness coincide, one ends of which are rigidly attached to the sample under test. zany with one of the clamps, and the second are installed with the possibility of sliding 10 or on the second clamp, apply a bending moment to the sample and, by an average sign. deformation sensors, judge the amount of deformation t2 .

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The disadvantages of this method are relatively low accuracy and reliability of measurements with alternating loads, due to the fact that the installation of clamps on the upper

Claims (2)

The most loaded layers of the sample cause the appearance of a parasitic focus of the nucleation of a fatigue crack due to the surface deformation of the 3 specimen by clamps. In addition, the dependence of the true deformation on the bend is non-linear, and there is also friction between the clamp, in which they are installed with the possibility of sliding. The aim of the invention is to improve the accuracy and reliability of strain measurement with alternating load., This goal is achieved so that the strain gauge is placed on the middle layer of the specimen located in the middle of the cross-sectional height of the specimen, alternating bending moment is applied, the location of the neutral layer with using the same strain gauge and rearranging the latter to the neutral layer, the magnitude of which is displaced relative to the average slips of the specimen Yedelev by the formula: L - f L LlIal 16 J .. fV where A - the amount of displacement of neutral layer of the sample relative to the middle layer; E is the base of the strain gauge G; deflection of the outer layer of the specimen upon the application of a bending moment of one sign; Г - deflection of the outer layer of the sample with the application of the bending moment of the opposite sign. , The drawing shows a scheme for measuring the strain and a device for carrying out a method for measuring the strain under bending. A device for measuring the deformation of a npw bend contains a U-shaped frame, made in the form of body 1 and two columns 2 and 3 with elastic hinges 4 and 5, supports 6 and 7, and an indicator of 8 hours. The device with the help of supports 6 and 7 is mounted on the sample 9. The method of determining the strain by bending is carried out as follows. If the cross section of the specimen to be taken is symmetrical, and the sample material equally resists stretching and compression, the strain gauge is immediately installed on the neutral layer of the sample 9 94 which coincides, in this case, with the middle layer (located at half the height, the cross section of the sample). 9). If the above conditions for the material and sample 9 are not feasible, then the strain gauge is installed on the middle layer of sample 9, a bending moment is applied, as a result of which sample 9 is propelled, for example by convex upwards | according to the drawing). In this case, the neutral layer is folded along the arc of a circle of radius R, the middle layer (with the strain gauge installed) is an arc of a circle of radius RH-D, and the indicator 8 shows the amount of deflection f. The radius of the middle layer is equal. (R-D) (2) By applying a moment of opposite sign, the neutral layer is bent along the arc of a circle of radius R. with a bulge down, the middle layer is along an arc of a circle of radius (G + L), and the indicator: 8 shows a deflection f. The radius of the middle layer in this case is equal to f (K.D.). 1 A joint solution of equations (2) and (3) makes it possible to obtain formula (1). After that, the strain gauge is rearranged by the obtained value D, reckoning it from the middle layer, the sample 9 is again loaded with a bending moment, and the indicator 8 is read, according to which the strain value is judged. The application of the invention allows to increase the accuracy and reliability of strain measurement with alternating loads by installing a strain gauge on the neutral layer of the sample. The invention of the method for measuring the strain under bending, which consists in the fact that a strain gauge is installed on a test specimen, a bending moment is applied to the specimen and, according to the indications of the strain gauge, a strain value is obtained, that is, In order to increase the accuracy and reliability of strain measurement with alternating load, the strain gauge is mounted on the middle layer s of the sample, located in the middle of the sample cross section height, and alternating bend is applied At the moment, the location of the neutral layer is determined using the same strain gauge and the latter is rearranged on the neutral layer, the displacement of which relative to the middle layer of the sample is determined by the formula L-e (16 × 12 D - the magnitude of the displacement of the neutral layer of the sample relative to the middle layer; the moment of one $ naka; f2 is the deflection of the outer layer of the sample upon application of the bending moment of opposite sign. Sources of information, ntye into account during the examination 1. Chern to N.I., Gavrilov D.A. Rotation of deformed Matel with repeated static pressure. K., Naukova Dumka; 1971 88. 2. USSR author's certificate in application number 2701092 / 25-28, G 01 B 5/30, 1978 (prototype).