Method to measure stresses in structure without removal of static loads

FIELD: instrumentation.

SUBSTANCE: measurements of surface deformations ε are carried out in controlled points on a structure, which is in stressed-deformed condition. Controlled points are selected so that they are capable of additional loading regardless of the structure. In controlled points they create with the help of the available external force P, additional stresses that match in direction with the measured ones, deformation is stepwise increased by Δε, change of the external force is measured ΔPi. Loading is increased until K = | Δ P i + 1 Δ P i 1 | * Δ ε increases to the value corresponding to the normalized deviation of mechanical characteristic of structure material from the Hooke's law. Structure deformation is determined, subtracting measured additional deformation from the available value of deformation for the previously known mechanical characteristic of structure material.

EFFECT: simplified process of measurement and no damage to integrity of the investigated structure.

3 cl, 3 dwg

 

The invention relates to the field of determining and controlling the stress-strain state of the structure (object), under load, and can be used to assess its strength and prediction of bearing capacity. Thus the design needs to be known about the material properties (modulus of elasticity E, the deformation of the limit of proportionality ε0.02and the elasticity ε0.2etc).

The method can be widely applied in monitoring the structural ability of industrial and civil buildings, special buildings (metro, bridges, nuclear plants, etc.).

The known method of non-destructive testing of materials [RF Patent №2146809], consisting in the fact that measure parameters of a magnetic field on the surface of the investigated object: to measure the absolute value of the maximum normal component of the magnetic field and calculate the value of stresses in the structure. Also known method [RF Patent №2146818], consisting in the fact that in the investigated object outraged ultrasonic normal waves take through the object vibrations, measure their parameters by which to judge the magnitude of the stress.

A disadvantage of the above analogs of determining the stresses in design is a significant scatter of experimental�social data the imperfection of methods of recalculation of the velocity of acoustic waves and magnetic parameters in the characteristics of the stress state of structures and, consequently, lower the accuracy and reliability of measurements.

As the prototype accepted method [RF Patent №2302610] closest to the proposed to the technical essence and the achieved effect. The method consists in that on the surface of the structure in the stress-strain state, fix the strain gauges and make measurements of surface deformations that take at the end. Then perform the cutting of the material around the strain gages to a depth corresponding to removal of the stress state of the structure at the points of deformation measurement, and measure the surface deformation of the structure, which one takes the initial. Based on these initial and final deformations determine the surface tension under load.

However, in the prototype there are drawbacks, namely:

- cutting material in the investigated structure around measuring resistance strain gage violates the integrity of the study design. The study of stress-strain state of the structure, as a rule, is carried out in the most loaded areas, it reduces the structural safety during the study;

The technical result of the invention consists in maintaining the integrity of the study design and the simplification of the measurement process.

The essence of the proposed method of measuring stress in a structure without removal of static loads is that in controlled points on the structure in the stress-strain state, make measurements of the surface strain ε. Moreover, the finer points chosen so that they have the possibility of additional loading, regardless of the design. In controlled locations create using a known external force P additional voltage, coincident in direction with the measured, stepwise increase strain Δε, measures the change in the external force ΔPi. The loading increases until such time asK=|ΔPi+1ΔPi1|*Δεdoes not increase more value corresponding to the normalized deviation from Hooke's law the mechanical characteristics of the structure material.

Step additional strain Δε select eno�but small, the measurement error ofK=|ΔPi+1ΔPi1|*Δεon the plot, corresponding to the Hooke's law, was less than the deviation in the plot above the limit of proportionality.

Then stop loading, and deformation and, consequently, stresses in the structure is determined by subtracting from the known values of the deformation for the early known mechanical characteristics of the material of construction of additional measured deformation.

For structures of low-alloy steels it is advisable to use as normalized deviations from Hooke's law the elastic limit, and for structures of high-strength steel, carbon fiber, iron - proof strength, as in this case, it is possible to reduce the accuracy requirements for measuring equipment.

The proposed method of determining the stress-strain state of structures without removal of static loads is illustrated by drawings, where

- figure 1 - chart changes additional external force P in some controlled point loaded structures from additional deformation ε;

- figure 2 - diagram of the metal box-shaped superstructure of the bridge and its cross-section;

- figure 3 - example of additional loading in a controlled point.

Figure 1 presents the diagram of loading of the structure material in the stress-strain state of its own weight. Point 1 corresponds to the initial measured amount of deformation εK. With the help of external forces P speed create additional strain on the value of Δε, coinciding in direction with the measured. The measure also the variations of the external power ΔPi. Step ∆ Ε is chosen small. For the case when the normalized deviations from Hooke's law the mechanical characteristics of the material of construction was adopted by the limit of proportionality ε0.02the measurement error ofK=|ΔPi+1ΔPi1|*Δεmust be at least an order of magnitude less than 2*10-4.

After reaching the material of construction of the limit of proportionality in point 2, on the next step in the point 3 the value ofK=|ΔP i+1ΔPi1|*Δεbecomes greater than 2*10-4. Loading of the construction is stopped. Thereafter, the deformation of the structure εKdetermined by subtracting from the known values of the deformation to the limit of proportionality ε0.02measured additional deformation εfromand stresses in the material of construction is calculated by the formula σ=E*(ε0.02from).

Figure 2 shows a drawing of a typical metal box-shaped superstructure 1 of the bridge and its cross-section. Controlled selected point on the bottom surface of the bottom plate at the edge of the side shelf 2. At the initial moment of tensile deformation in the controlled point is equal to the deformation of all points of the bottom plate section 1-1 from its own weight, but the lower surface side shelf 2 can be further stretched regardless of the point of the mid-section.

The method can be implemented, for example, the following device (figure 3). The Jack 3 oil pressure sensor 4 is installed between the flange 2 and beam 5 with hooks 6, geared to the lower surface of the shelf 2, on which is mounted a strain gauge 7. The outputs of both sensors are connected to the inputs of the transmitter 8, the control output of which seediness controlled pump station 9 (the transmitter station 8 and 9 schematically depicted). Under the action of force from the Jack 3 phase 2 shelves between the hooks 6 is bent, and on its lower surface tensile stresses occur, additional to the existing bend all of the superstructure 1 of the bridge.

Take measurements as follows. Pump station 11 by the command transmitter 8 delivers the oil in the Jack 3 to sample all gaps in the structure, which is determined by the change of the readings of the strain gauge 7. Then the pressure in the Jack 3 is increased until, until you reach the first level of strain increment Δε. After that, the evaluator determines the value of theK=|ΔPi+1ΔPi1|*Δεthe readings of the sensor 4 oil pressure in the Jack 3 and the strain gauge 7. The process is repeated until the material shelf 2 limit of proportionality.

Conducted by the authors numerical simulation (finite element method) showed that errors due to the biaxial stress state of the shelf 2 described above, when the nature of its additional loading does not exceed 1%.

The positive effect of the application of the proposed method definitions� stress-strain state of structures without removal of static loads is in the measurement process is not violated the integrity of the examined structure in controlled locations. This increases the safety of the measurement process. In comparison with the prototype, the measurement process is simplified, as it does not need to cut the material of construction in controlled locations, but just enough to set the device further loading.

1. Method for determining stresses in structures without removing the static loadings, consisting in the fact that in controlled points on the structure, which is deformed in a state of stress, produce measure the surface strain ε, characterized in that the controlled point is selected so that they have the possibility of additional loading, regardless of the design, in controlled locations create using a known external force P additional voltage, coincident in direction with the measured, stepwise increase strain Δε and measures the change in the external force ΔPias long as the valuedoes not increase more value corresponding to the normalized deviation from Hooke's law the mechanical characteristics of the material of construction, after which the deformation and, consequently, stresses in the structure is determined by subtracting from the known values of pre-strain for the Glo�Noah the mechanical characteristics of the material of construction of additional measured deformation.

2. Method of determining stress-strain state of structures without removing the static loads according to claim 1, characterized in that for the controlled points of the structure of low-alloy steels as normalized deviations from Hooke's law take the limit of proportionality.

3. Method of determining stress-strain state of structures without removing the static loads according to claim 1, characterized in that for the controlled points of the structure of high-strength steel, carbon fiber, iron as normalized deviations from Hooke's law take proof strength.



 

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FIELD: measurement equipment.

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2 cl, 1 dwg

FIELD: rescue equipment.

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8 cl, 3 dwg

FIELD: agriculture.

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1 dwg

Pressure regulator // 2526899

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2 cl, 5 dwg

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1 dwg, 1 tbl, 1 ex

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FIELD: measurement equipment.

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FIELD: instrumentation.

SUBSTANCE: in an output diagonal of a bridge circuit they install a heat-dependent process resistor Rαt, the par value of which is more than possible values of a compensation heat-dependent resistor Rα. In parallel to the resistor Rαt they install a link. Output resistance of the bridge circuit is measured Rout. The sensor is connected to a low-resistance load Rl=2·Rout. Initial unbalance is measured, as well as the output signal of the sensor at normal temperature t0, and also temperature t+, corresponding to the upper limit of working range of temperatures, and t-, corresponding to the lower limit of working range of temperatures. Measurements are repeated after connection of the sensor to the low-resistance load Rl'=Rout. On the basis of measured values of the initial unbalance and the output signal of the sensor, they calculate temperature coefficient of frequency αs meas+ and αs meas, and temperature coefficient of resistance for the output resistance at temperatures t+ and t- accordingly, and also non-linearity of temperature coefficient of frequency of the bridge circuit (Δαs meas=αs meas+αs meas). The link is removed from the resistor Rαt. They measure initial unbalance and output signal of the sensor at temperatures t0, t+ and t-. On the basis of measured values of initial unbalance and output signal of the sensor they calculate temperature coefficient of resistance for the heat-dependent resistor Rαt at temperatures t+ and t-. If temperature coefficient of frequency of the bridge circuit and its non-linearity belong to the area of method application, then they calculate par value of the heat-dependent resistor Rα and heat-independent resistor Rsh. The process heat-dependent resistor Rαt is replaced with the resistor Rα by partial engagement of the resistor Rαt. The output resistance of the bridge circuit is shunted by the heat-independent resistor Rsh.

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2 cl

FIELD: measurement equipment.

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2 cl

FIELD: measurement equipment.

SUBSTANCE: invention relates to measurement equipment. Essence of the invention is as follows: temperature-dependent technological resistor Rαm, the nominal value of which is higher than possible values of compensation temperature-dependent resistor Rα, is installed into an output diagonal of the bridge circuit. A bridge is installed parallel to resistor Rαm. Output resistance of bridge circuit Rout is measured. The sensor is connected to low-resistance load Rl=2·Rout. Initial imbalance and an output signal of the sensor is measured at normal temperature t0, as well as at temperature t+ corresponding to an upper limit of the working temperature range, and t- corresponding to a lower limit of the working temperature range. Measurements are repeated after the sensor is connected to low-resistance load RI'=Rout. Based on the measured values of the initial imbalance and the output signal of the sensor there calculated is temperature coefficient of frequency (TCF) of the bridge circuit αs meas+, and αs meas and TCF of output resistance at temperatures t+ and t- respectively, as well as non-linearity of TCF of the bridge circuit (Δαs meas=αs meas+αs meas). The bridge is removed from resistor Rαm. The initial imbalance and the output signal of the sensor is measured at temperatures t0, t+ and t-. Based on the measured values of the initial imbalance and the output signal of the sensor, TCF of temperature-dependent resistor Rαm is calculated at temperatures t+ and t-. If TCF of the bridge circuit and its non-linearity belong to the application field of the method, then, the nominal value of temperature-dependent resistor Rα and temperature-nondependent resistor R is calculated. Process temperature-dependent resistor Rαm is replaced with resistor Rα by partial activation of resistor Rαm. Resistor Rα is shunted with temperature-nondependent resistor R.

EFFECT: higher compensation accuracy.

2 cl

FIELD: measurement equipment.

SUBSTANCE: heat-dependent technological resistor Rαm is installed into a diagonal of bridge circuit power supply, the rating of which is higher than possible values of a compensating heat-dependent resistor Rα. In parallel to the resistor Rαm they install a link. They measure initial unbalance and output signal of the sensor under normal temperature t0, and also temperature t+, corresponding to upper limit of working range of temperatures, and t-, corresponding to lower limit of the working range of temperatures. On the basis of performed measurements they calculate temperature coefficient of frequency (TCF) of strain gauges of a bridge circuit α meas+ andα meas at temperatures t+ and t-, accordingly, and also non-linearity of TCF of strain gauges of the bridge circuit (Δα meas=α meas+α meas). They measure input resistance of a sensor bridge circuit. A heat-independent resistor Ri=0.5·Rinp is connected. They measure initial unbalance and output signal of the sensor at temperatures t0, t+ and t-. On the basis of completed measurements they calculate TCF of input resistance at t+ and t-. The resistor Ri is disconnected, and the link is removed off the resistor Rαm. They measure initial unbalance and output signal of the sensor at temperatures t0, t+ and t-. On the basis of completed measurements they calculate TCF of a process heat-dependent resistor Rαm at temperatures t+ and t-. If TCF of strain gauges of the bridge circuit and its non-linearity belong to the area of method application, they calculate the rating of the heat-dependent resistor Rα heat-independent resistor R with usage of produced values of TCF of strain gauges of a bridge circuit, TCF of input resistance and TCF of the technological heat-dependent resistor. The technological heat-dependent resistor Rαm is replaced with a resistor Rα by means of partial engagement. A resistor Rα is shunted with a heat-independent resistor R.

EFFECT: increased accuracy of compensation of multiplicative temperature error with account of negative non-linearity of temperature characteristic of an output signal of a sensor with usage of widely distributed measurement equipment.

2 cl

FIELD: measuring instrumentation.

SUBSTANCE: device for dynamic deformation measurement includes resistance strain gauges, reference resistors, amplifier, electronic computer with software, DC voltage source, standard resistor, switch, control unit, analogue programmed multifunctional board with software, connected to PC. Programmed board can be connected to PC via USB interface or by installation into PCI or PCIExpress expansion slot, and the device can include adaptor; connection of power source to the first analogue input of the board, second output of the amplifier to analogue output of the board, control unit input to digital output of the board, amplifier output to analogue input of the board is implemented via respective inputs and outputs of the adaptor connected by interface to compatible socket of the board.

EFFECT: extended range of measured values and linearity of output parameter, improved reliability of device operation.

3 cl, 2 dwg

FIELD: measurement equipment.

SUBSTANCE: on surfaces of upper and lower beam flanges at a point of maximum deflection Δ0 there bonded are strain gauges with similar characteristics directly onto the prepared surface of the upper and lower beam flanges. Operating and compensating strain gauges are bonded in the number of 3 to 5 pieces in each flange in a section 15 to 25 cm long with maximum deflection Δ0. The operating strain gauges are fixed along primary stresses σ along the beam, and compensating strain gauges are fixed between the operating strain gauges across the beam, protected against different actions with epoxy resin; bridge circuits are mounted for each pair of strain gauges (operating and compensating) and their wires are connected to a strain station; initial resistance R0 of the operating strain gauges is measured; with that, beam deflection Δ(t) at any point of time t is determined by the following formula: Δ(t)=Δ0+r·(|ΔR1(t)|+|ΔR2(t)|), where Δ0 - initial maximum beam deflection at point of time t=0, which is measured by means of a high-precision station rod and a level unit before bonding of the strain gauges; r - constant coefficient depending on design circuits and dimensions of the beam.

EFFECT: higher measurement accuracy.

4 dwg, 1 tbl

FIELD: measurement equipment.

SUBSTANCE: invention relates to measurement equipment and may be used to tune resistance strain gauge sensors with a bridge measurement circuit according to multiplicative temperature error. Substance: at load resistance Rl≥500 kOhm they determine temperature sensitivity coefficient (TSC) of the bridge circuit αdo+ and αdo at temperatures t+ and t-, which correspond to the upper and lower limit of the working range of temperatures, and non-linearity of the TSC of the bridge circuit (Δαdo=αdo+αdo). If the produced value ∆αdo is positive, then positive non-linearity of the bridge circuit TSC is converted into negative one. For this purpose they determine input resistance and its temperature resistance coefficient (TRC), as well as TSC of resistance strain gauges αd+ and αd at temperatures t+ and t- and calculate non-linearity of TSC of resistance strain gauges (Δαd=αd+αd). The rating of the thermally dependent resistor Rαinp, and the rating of thermally independent resistors Rdinp, and Ri are calculated. The resistor Ri is installed into the power supply diagonal of the bridge circuit, the input resistance of which is shunted by serially connected resistors Rαinp and Rdinp. The TSC of the bridge circuit is determined under temperatures t+ and t-, the non-linearity of TSC of the bridge circuit is calculated as ∆αdo. If non-linearity of the TSC takes a negative value that meets the inequality ∆αdo≤-2·10-6 1/°C, then multiplicative temperature error is compensated for by means of calculation and connection of a thermally dependent resistor Rαout, shunted with a thermally independent resistor Rdout, into the output diagonal of the bridge circuit in series with the load.

EFFECT: increased accuracy of tuning with positive non-linearity of bridge circuit TSC.

1 tbl, 2 dwg

FIELD: instrumentation.

SUBSTANCE: invention refers to instrumentation and can be used to measure deformations of nonmagnetic materials. Deformation measurement method for nonmagnetic items implies that on the surface of an item or inside it permanent dipole sources of magnetic field based on, for example, magnets from the alloy neodymium-iron-boron, are installed, at least two magnets not located in the same point are used to determine the parameters of linear (along the straight line) deformation, at least three magnets not located along the same straight line are required to determine the parameters of plane deformation, at least four magnets not located in the same plane are used to determine the parameters of volume deformation. At the surface of the examined item opposite each source a system of sensors is installed, the sensors allow for the measurement of 1, 2, 3 components of vector of magnetic field induction in several points concentrated in relatively small region of space if compared to the distance to the field sources, or one-, two- or three axial sensor with 3D-positioning system is used as the system of sensors, the signals from the sensors are amplified and converted into digital ones, numeric measurement data: coordinates of measurement points and values of components of magnetic field induction vectors in them in a laboratory coordinate system are processed by a computer programme, basing on the obtained data an inverse problem is solved for the system of weakly interacting magnets and their position in the laboratory coordinate system is determined as well as the vectors of magnetic moments in the laboratory coordinate system before and after the item deformation and by comparing the said solutions the deformation parameters are calculated. A plant for implementing the said method is also described.

EFFECT: possibility to measure linear (along the straight line), plane (in a plane) and volume (in space) deformation of items made from nonmagnetic materials.

5 cl, 1 dwg, 3 tbl

FIELD: measurement equipment.

SUBSTANCE: sticky foil from plastic metal is used, for instance, aluminium scotch tape. Foil is cut into fragments, stretched within the limits of elastic deformations, and in this condition, using a sticky foil layer, it is applied onto controlled surfaces of parts. Tail sections of fragments are rigidly fixed on the surface of the part with a mechanical or another available method. Afterwards in the transverse plane in the middle of the foil fragment length they make through slots and holes.

EFFECT: expanded arsenal of technical facilities to monitor cyclic deformations of machine parts that arise in process of their operation, higher efficiency of control due to increased sensitivity of sensors to low values of cyclic deformations.

3 dwg

FIELD: electric engineering.

SUBSTANCE: device has three identical distance sensors, connected to appropriate measuring converters and information processing block. Two distance sensors are mounted relatively to controlled object differentially, and third one is rigidly fixed at constant and known distance from controlled object surface. Information processing block has adder block, two subtracting blocks, three multiplication blocks, two division blocks and memory block. As information value, characterizing object movement, displacement of point is taken, which is placed on one of object sides. Value of deformation is determined on basis of integral deformation of object between its extreme points.

EFFECT: higher precision, broader functional capabilities.

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