RU2287775C2 - Method and device for measuring position of neutral layer of bending beam - Google Patents

Abstract

FIELD: test technique.

SUBSTANCE: method and device can be used as under laboratory conditions and when carrying calibration tests of materials for testifying correspondence to preset properties. Method of measuring position of bending beam is based upon measurement of beam's sag by means of brace mounted onto beam, which brace is provided with indicator. Elongation of outer layer of beam is measured additionally by means of ruler with indicator, which ruler has significant longitudinal and almost zero bend rigidity. Position of neutral layer of beam is found on the base of known distance between supports of brace, distance between point of fastening of ruler and indicator's needle at nominal position of beam as well as measured values of sag of beam and elongation of outer layer of beam. Device has ruler, brace with calibrated distance between support, mechanical shift indicator, mounted in center of brace, and additional indicator having case tightly fastened to ruler. Measuring tip of additional indicator has needle, which rests against surface of beam. Ruler is fixed at one end of beam. As ruler the ruler is used which has significant longitudinal and almost zero bed rigidity.

EFFECT: wider number of methods and aids for measurement.

2 cl, 3 dwg

Description

The invention relates to the field of testing structural elements for bending and can be used both in laboratory conditions and during verification tests of materials for compliance with specified properties.

There is a method of calculating the position of the neutral layer of a bent beam according to the textbook "Resistance of materials" Timoshenko SP M .: Nedra, 1965, v. 1, p. 87, based on a number of hypotheses about the properties of the beam material and load characteristics. The proposed technical solution considers only the geometry of the completed bend, regardless of the above factors.

The objective of the invention is to provide a method by which it is possible to determine the layered deformation of a bent beam, and a device for its implementation.

The method for measuring the position of the neutral layer of the beam, according to the invention, is carried out as follows: measure the deflection of the beam by means of a bracket with a mechanical indicator mounted on the beam, additionally measure the elongation of the outer layer of the beam using a ruler with a significant longitudinal and practically zero bending stiffness with an indicator , and based on the known distance between the supports of the bracket, the distance between the point of fastening of the ruler and the needle of the indicator in nominal beam position, and the measured values of the boom beam deflection and elongation for the outer layer of the beam is determined neutral position of the beam layer.

A device for measuring the position of the neutral layer of the beam, containing a ruler, according to the invention further comprises a bracket with a calibrated distance between the supports, a mechanical indicator of displacements installed in the middle of the bracket and an additional indicator rigidly fixed to the ruler with its body, with a needle fixed on the measuring tip resting on the surface of the beam, the ruler is fixed on one of the ends of the beam and a ruler is used as it, which has significant longitudinal and practical ki zero flexural rigidity.

The values of the beam deflection Δh and the beam elongation Δl obtained during bending make it possible to further calculate not only the location of the neutral layer of the beam during bending using well-known formulas, but also calculate the deformation of any layer. Supply of the device with a ruler fixed to the test sample with an indicator mounted on it allows one to obtain an elongation of the outer layer of the beam with bending Δl. The line has a thickness significantly less than the thickness of the bent beam, and therefore has a significant longitudinal and almost zero bending stiffness and thus does not affect the mode of bending of the beam. The indicator installed in the middle part of the bracket, which is located on the ruler, allows you to get the deflection of the beam Δh.

The above distinguishing features are new in comparison with the prototype, so the invention meets the criterion of "novelty."

Patent studies have shown that in the studied prior art there are no similar technical solutions, i.e. The claimed technical solution does not follow explicitly from the studied prior art and, thus, meets the criterion of "inventive step".

This technical solution can be reproduced industrially, therefore, it meets the criterion of "industrial applicability".

The invention is illustrated by drawings, where figure 1 schematically shows a device for measuring the position of the neutral layer of a bent beam (front view and top view), figure 2 - section aa in figure 1, figure 3 - section B- B in figure 1.

A device for measuring the position of the neutral layer of a bent beam consists of a bracket 1 with a calibrated distance between the supports 2 and a mechanical indicator of displacements 3, and an element in the form of a ruler 4.

The line 4 is fixed on one side to the beam 5 and has a thickness two orders of magnitude smaller than the beam 5 and therefore has almost zero bending stiffness, and due to its small thickness and width, significant longitudinal stiffness. An indicator 6 is rigidly fixed on the ruler 4, the measuring tip of which is equipped with a needle 7 resting on the surface of the beam 4. The bracket 1 is installed by means of supports 2 on the ruler 4, while the tip of the indicator 3 rests on the surface of the ruler 4.

The device operates as follows. Prior to testing the beam for bending on the beam 5, the ruler 4 is rigidly fixed. Indicator 6 is set to the zero position by means of the needle 7, and the nominal length of the layer adjacent to the ruler of the beam before bending is fixed. The bracket 1 is installed on the line 4 and the indicator of mechanical displacements 3, mounted on the bracket 1, touches the surface of the line 4 with its foot and is also set to zero. Beam 5 undergoes bending. In this case, the indicator of mechanical displacements 3 shows the amount of deflection of the beam Δh. Indicator 6 fixes the elongation of the beam 5 when bending Δl. Having received these data, the position of the neutral layer is calculated according to the formula H _n = ρε _p .

The radius of curvature of the neutral layer is calculated by the formula

,

,

where L is the distance between the supports 2 of the bracket 1.

The deformation of the upper layer of the test sample is calculated by the formula

,

,

where l ₀ is the distance between the point of attachment of the ruler and the needle of the indicator in the nominal position of the beam.

The proposed method of measurement and the device using the proposed method of measurement allows you to get the deformation when bending any layer of the beam. The reliability of the result is quite high. The design of the device is easy to manufacture and operate. This device was tested in laboratory tests at the Chelyabinsk Higher Military Aviation School of Navigators.

The measurement method can be extended both to single products used in laboratory conditions, and to products in operating conditions, i.e. technological capabilities of the proposed method are quite wide.

Claims (2)

1. A method of measuring the position of the neutral layer of the beam, characterized in that the deflection of the beam is measured by means of a bracket with a mechanical indicator mounted on the beam, the elongation of the outer layer of the beam is additionally measured using a rigidly mounted beam with significant longitudinal and practically zero bending stiffness of the ruler with indicator , and based on the known distance between the bracket supports, the distance between the point of fastening of the ruler and the needle of the indicator in the nominal position of the beam, as well as The values of the beam deflection of the beam and the elongation of the outer layer of the beam determine the position of the neutral layer of the beam. 2. A device for measuring the position of the neutral layer of the beam, containing a ruler, characterized in that it further comprises a bracket with a calibrated distance between the supports, a mechanical indicator of movement mounted in the middle of the bracket and an additional indicator rigidly fixed to the ruler with its body, with a needle fixed to the measuring tip, based on the surface of the beam, while the ruler is fixed at one of the ends of the beam and as it used a ruler with significant longitudinal and right almost zero bending stiffness.

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