RU2645430C1 - Testing method of flat specimens for bending - Google Patents

Abstract

FIELD: testing equipment.

SUBSTANCE: ends of the samples are fixed on the support, bent and the amount of deflection is determined under conditions of complex bending. The support is made in the form of a closed frame with two movable spacers, and loading is carried out by means of a loading hydraulic cylinder that transfers pressure to the compressing or expanding hydraulic cylinder, which deforms the support in the horizontal plane. The nominal stress level is created in the sample and spacer design, which is proportional to the transverse load on the sample.

EFFECT: possibility of testing the samples under conditions of complex bending with the variable in the process of loading the level of nominal stresses and the thrust ratio, depending on the magnitude of the lateral load, applied to the sample.

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Description

The invention relates to a testing technique, and in particular to methods for bending flat samples.

A device is known for testing plate samples for stress corrosion (Copyright certificate No. 355546, IPC G01N 17/00, G01N 3/22, G01N 3/20, publ. 10/16/1972) by the method of constant deformation during bending, containing the body in the form staples with supporting planes for the ends of the sample and a pressure screw located in the center of the bracket, equipped with devices for pressing the ends of the sample to the supporting planes, which, in order to twist the sample, are turned in opposite directions around the mounting axis of the bracket with respect to the plane perpendicular axis of the pressure screw.

The disadvantage of this device is the low productivity, as well as the fact that the device does not allow the study of bending with simultaneous axial load (complex bending).

A device for corrosion testing of samples under voltage (Copyright certificate No. 340931, IPC G01N 3/08, G01N 17/00, publ. 06/05/1972), containing a housing on which supports are installed with inserts for securing the ends of the samples and the loading mechanism specimens with a longitudinal bend, moreover, the body is made in the form of a rod with threaded ends, and the loading mechanism is in the form of nuts.

The disadvantage of this device is that the loading is carried out only by longitudinal force, while it is impossible to conduct tests in difficult bending conditions.

A known method of testing flat samples for bending (Copyright certificate No. 1128143, IPC G01N 3/20, publ. 12/07/1984), which consists in the fact that the ends of the samples are fixed on a support made in the form of a U-shaped bracket, bent and determined the magnitude of the deflection, and in order to expand capabilities by testing under complex bending, the ends of the samples are rigidly fixed on the flat surfaces of the branches of the bracket at different distances from its crossbeams perpendicular to the axis of symmetry of the bracket and change the distance between the branches of the latter.

This method has the disadvantage that in the process of testing the sample, its expansion coefficient remains constant, depending on the location of the sample on the bracket before the test. In this case, due to the rotation of the screw, it is only possible to set some fixed shortening of the spacer structure, which allows modeling the displacement of the edges of the support contour of the plate due to the bending of the ship floor. However, in the practice of operating ship structures, one has to deal with problems when the plate expansion coefficient continuously changes during operation, and the displacement of the support contour is proportional to the acting transverse load. Such a situation arises, for example, when researching the operation of ship plates in the bottom overlap, when the supporting edges of the plate come together in the process of bending the bottom overlap as a whole as a result of the action of a pressure pulse during hydrodynamic shock during slaming, and, at the same time, the same pressure pulse is lateral load acting on the plate.

As the closest analogue, a method for bending flat samples was adopted (RU 2533999, IPC G01N 3/20, publ. 11/27/2014), which consists in the fact that the ends of the samples are fixed on a support, bent and the magnitude of the deflection is determined under conditions of complex bending, the support is made in the form of a closed frame with two movable spacers and the expansion ratio is variable during loading.

This method has a significant drawback, namely, that it does not allow simulating a number of problems encountered in the practice of operation of ships. In particular, a ship plate operating as part of an overlap may be under the influence of a transverse load, and the entire overlap under the action of tensile or compressive forces proportional to this load, causing a displacement of the support contour of the plate and the occurrence of rated stresses proportional to the transverse load on the plate. An experimental study of such phenomena requires a method of testing samples for complex bending, which allows one to take into account the change in the nominal stresses during loading.

The invention solves the problem of expanding the capabilities of testing specimens for complex bending, making it possible to simulate loads during experimental studies of the deformation of the hull plates of ships' hulls acting on them under real operating conditions, due to the possibility of taking into account changes in nominal stresses during loading.

To solve the problem in the method of testing flat samples for bending, which consists in the fact that the ends of the samples are fixed on a support made in the form of a closed frame with two movable spacers, they are bent with a variable expansion coefficient during loading and the amount of deflection is determined under conditions of complex bending, It is proposed to additionally load the sample by deforming the support in the horizontal plane by an amount that varies in proportion to the transverse load applied to the sample.

In the proposed technical solution, tensile and compressing hydraulic cylinders act on a support made in the form of a closed frame in the horizontal direction, creating nominal stresses in the structure, the level of which is proportional to the transverse load on the test sample.

The attached graphic materials show:

in FIG. 1 - installation for implementing the proposed method;

in FIG. 2 is a diagram of the transmission of forces from hydraulic cylinders to a support.

The following notations are used on graphic materials:

1 - base;

2 - support, made in the form of a closed frame;

3 - dial indicator;

4 - loading hydraulic cylinder;

5 - sample;

6 - movable strut;

7 - switch;

8 - a hydraulic hose;

9 - an axis of levers;

10 - lever;

11 - compressive hydraulic cylinder;

12 - tensile hydraulic cylinder;

13 - axis support;

14 - strain gauge;

P is the external load applied to the sample through the loading hydraulic cylinder, N;

L is the shoulder of the force acting from the side of the lever on a support made in the form of a closed frame, together with the sample, relative to the axis of the levers, m;

- плечо силы, приложенной к рычагу сжимающим гидроцилиндром, относительно оси рычагов, м;

- shoulder forces applied to the lever by a compressing hydraulic cylinder, relative to the axis of the levers, m;

- плечо силы, приложенной к рычагу растягивающим гидроцилиндром, относительно оси рычагов, м;

- the shoulder of the force applied to the lever by a tensile hydraulic cylinder relative to the axis of the levers, m;

Nco - compressive force acting in a horizontal plane on a support from the side of the lever, N;

Npo - tensile force acting in a horizontal plane on a support from the side of the lever, N;

Nc is the force acting on the lever from the side of the compressing hydraulic cylinder, N;

Np is the force acting on the lever from the side of the tensile hydraulic cylinder, N.

Installation for implementing the proposed method for testing flat samples in bending comprises a base 1 with a support 2 mounted on it for fastening samples 5, made in the form of a closed frame. The samples are loaded with a loading hydraulic cylinder 4, to which an external load P is applied, the deflection of the sample is measured by indicator 3, the mechanical stresses in the sample are measured by strain gauges 14. Using horizontal movement of the movable struts 6, the compliance in the horizontal plane of the long sides of the support 2, made in the form of a frame, changes to which relies on the sample 5, while changing the coefficient of expansion of the sample 5. The loading hydraulic cylinder 4 is connected via hydraulic hoses 8 through a switch 7 with about a compressing hydraulic cylinder 11 or a tensile hydraulic cylinder 12, which act on the levers 10 mounted on the axis of the levers 9, mounted on the bearings of the axis 13.

The method of testing flat samples for bending is as follows. The ends of the sample 5 are rigidly fixed, for example, by spot welding, on the flat surfaces of the long sides of the support 2, made in the form of a closed frame. By moving the movable struts 6, it is possible to change the stiffness in the horizontal plane of the long sides of the frame on which the specimen rests. The specified stiffness is characterized by a coefficient of spread

Where

КР - spread coefficient;

- фиктивная площадь сечения «жестких связей», создающих распор, м²;

- fictitious cross-sectional area of “rigid bonds” creating a spacer, m ² ;

Fpl - the cross-sectional area of the sample, m ² .

The fictitious cross-sectional area of the “rigid bonds” that create the spacer, when testing samples according to the proposed method, is also determined as in the construction of the closest analog

Where

- рабочая длина образца, м;

- working length of the sample, m;

C is the distance from the sample to the movable strut, m;

- расстояние от образца до боковой стороны опоры, выполненной в виде замкнутой рамы, м;

- the distance from the sample to the side of the support, made in the form of a closed frame, m;

I is the moment of inertia of the cross section relative to the neutral axis when bending in the horizontal plane of the long side of the support 2, made in the form of a closed frame, m ⁴ .

может регулироваться за счет изменения параметра с, т.е. перемещения подвижных распорок 6 в горизонтальной плоскости. После установки образца 5 и выбора начального положения подвижных распорок 6 осуществляется нагружение при помощи нагружающего гидроцилиндра 4, к которому прикладывается внешняя нагрузка, в результате чего поршень нагружающего гидроцилиндра 4 перемещается, создавая давление в системе. Давление от нагружающего гидроцилиндра 4 по гидравлическим шлангам 8 передается на сжимающий гидроцилиндр 11 или растягивающий гидроцилиндр 12 в зависимости от положения переключателя 7. Сжимающий гидроцилиндр 11 или растягивающий гидроцилиндр 12 действует на рычаги 10, вращающиеся относительно оси 9 рычагов 10, установленной на опорах 13 оси 9. При этом рычаги 10 воздействуют на опору 2, выполненную в виде замкнутой рамы, вызывая ее деформации в горизонтальной плоскости и создавая в конструкции некоторый уровень номинальных напряжений σн, которые пропорциональны поперечной нагрузке Р, действующей на образец 5. Замер полного прогиба осуществляется при помощи индикатора 3, напряжения в испытуемом образце σг определяются при помощи тензорезисторов 14. После разгрузки производится замер остаточного прогиба при помощи индикатора 3.Value

can be adjusted by changing the parameter c, i.e. moving the movable struts 6 in the horizontal plane. After installing the sample 5 and selecting the initial position of the movable struts 6, loading is carried out using a loading hydraulic cylinder 4, to which an external load is applied, as a result of which the piston of the loading hydraulic cylinder 4 moves, creating pressure in the system. The pressure from the loading hydraulic cylinder 4 via hydraulic hoses 8 is transmitted to the compressing hydraulic cylinder 11 or the stretching hydraulic cylinder 12 depending on the position of the switch 7. The compressing hydraulic cylinder 11 or the stretching hydraulic cylinder 12 acts on the levers 10, rotating relative to the axis 9 of the levers 10 mounted on the bearings 13 of the axis 9 . in this case the arms 10 act on the support 2, designed as a closed frame, causing its deformation in a horizontal plane and providing some level design rated voltage σn, Kotor e proportional to the transverse load F acting on the sample 5. The measurement of full deflection is carried out by means of the indicator 3, the voltage in the test sample σg determined by means of strain gauges 14. After discharging residual deflection measurement is performed by means of the indicator 3.

Together with the rated stresses σ _n , the spread coefficient of sample 5, which can be determined in accordance with [Burakovsky EP Improving the regulation of operational defects in hulls. - Kaliningrad, KSTU, 2005. - 339 p.]:

Where

σg - tensile stresses in sample 5, determined using tensor resistors 14, Pa;

σн - nominal stress in the structure, proportional to the transverse load on the sample 5, Pa;

КР - spread coefficient at a zero level of rated stresses in the structure;

- коэффициент распора при некотором уровне номинальных напряжений в конструкции.

- expansion ratio at a certain level of nominal stresses in the structure.

и L, а также от соотношения площадей поршней нагружающего гидроцилиндра 4 и сжимающего гидроцилиндра 11 или растягивающего гидроцилиндра 12, в зависимости от положения переключателя 7. При действии на образец поперечной нагрузки Р давление р в системе будет равноThe level of rated stresses in the construction σn will depend on the geometric characteristics of the installation

and L , as well as the ratio of the piston areas of the loading hydraulic cylinder 4 and the compressing hydraulic cylinder 11 or the tensile hydraulic cylinder 12, depending on the position of the switch 7. When the transverse load P is applied to the sample, the pressure p in the system will be

where Sн is the piston area of the loading hydraulic cylinder 4, m ² .

In this case, the forces transferred to the levers 10 from the side of the compressing hydraulic cylinder 11 or the tensile hydraulic cylinder 12 ( Nc and Np, respectively) can be determined from the equalities

Where

Sc is the piston area of the compressing hydraulic cylinder 11, m ² ;

Sp is the piston area of the tensile hydraulic cylinder 12, m ² .

The force that acts in the horizontal plane on the support 2, made in the form of a closed frame, is determined from the condition

Where

Nco is the compressive force acting in the horizontal plane on the support 2 from the side of the lever 10, N;

Npo - tensile force acting in the horizontal plane on the support 2 from the side of the lever 10, N.

The rated stresses in the design, taking into account the sign, can be determined for compression and tension, respectively (depending on the position of the switch 7) from the equations

в каждый момент нагружения по представленной выше формуле. Изменять величину коэффициента распора образца

можно как за счет соотношений площадей гидроцилиндров, так и за счет регулировки положения сжимающего гидроцилиндра 11 и растягивающего гидроцилиндра 12 по высоте рычагов 10, т.е. корректируя величины

и

.Having determined the magnitude of the nominal stresses σn using these formulas and measured the tensile stresses σg in the specimen using strain gauges 14, one can find the current values of the specimen spread coefficient

at each moment of loading according to the above formula. Change the magnitude of the ratio of the sample

it is possible both due to the ratio of the area of the hydraulic cylinders, and by adjusting the position of the compressing hydraulic cylinder 11 and the tensile hydraulic cylinder 12 along the height of the levers 10, i.e. adjusting values

and

.

The proposed method for testing flat specimens for bending allows one to obtain important experimental results necessary for the design of ship hull structures, in particular bottom floors. The working conditions of the ship plates included in these structures are characterized by the fact that, along with transverse loads, they are subject to longitudinal forces arising from the bending of the floor as a whole, for example, when slaming. Consideration of this circumstance becomes possible when implementing the proposed method for testing flat specimens for bending.

Thus, the invention allows testing under difficult bending conditions with a variable level of nominal stresses in the structure and, correspondingly, a thrust coefficient that varies proportionally to the transverse load on the specimen, which makes it possible to carry out experimental studies of the deformation of the sheathing plates working as part of the overlapping bodies vessels with the perception of real operational loads.

Claims (1)

The method of testing flat samples for bending, which consists in the fact that the ends of the samples are fixed on a support made in the form of a closed frame with two movable spacers, bent with a variable expansion ratio during loading and determine the amount of deflection under conditions of complex bending, characterized in that load the sample by deforming the support in the horizontal plane by an amount that varies in proportion to the transverse load applied to the sample.

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