SU1357830A1 - Method of determining strength of shell made of polymeric composite materials - Google Patents

Abstract

The invention relates to acoustic methods for continuous testing of the strength parameters of products. The aim of the invention is to improve the accuracy of strength determination by receiving and measuring the parameters of acoustic emission signals (AE), resulting in areas with maximum damage to the material. The controlled shell is subjected to pressure of the pressure bar and the AE signals are uniformly installed on the outer surface of the shell by the receiving transducers. AE parameters are measured, for example, the total emission, and the section with the maximum value of the measured parameter is selected. In the selected area, the elongation of the casing caused by pressure crimping is measured using a strain gauge and, based on the measured elongation taking into account the calibration dependence, the strength of the shells made of polymer composite materials is determined. 1 yl. i (L CO 01 oo with

Description

The invention relates to acoustic methods for non-destructive testing of the strength parameters of products and can be used in determining the strength of shells made of polymer composite materials, in particular, cylindrical structures made of glass organoplastic.

The purpose of the invention is to improve the accuracy of determining the strength due to the discovery in the shell of the areas with the greatest damage to the polymeric composite material.

The drawing shows the results of measurements of the parameters of acoustic emission sigols (AE) along the perimeter of two shells at two different pressures and crimps.

The method for determining the strength of polymer composite shells is as follows.

The controlled casing is pressurized. Signals Eoo AE are received at points evenly distributed over the shell. The parameters of the AE signals are measured and the control section of the shell is selected according to the maximum value of the measured parameters. The elongation of the control section, caused by the pressure action of the pressure test, is measured. Based on the measured elongation, the durability of the shell is determined using a calibration dependence.

The method for determining the strength of shells made of polymer composite materials is carried out as follows. On the outer surface of a controlled shell, for example, a cylindrical tank with spherical bottoms of glass organoplastic, receive piezoelectric transducers of AE signals and strain gauges of elongation are evenly arranged. the minimum number of observation points should be 10-20. To process the received AE signals, it is advisable to fully use the twenty-channel NPP-20 acoustic-emission system. When inspecting elongated objects, the receiving points are evenly distributed along the outer surface of the cylindrical part, preferably 4-7 normal to its

forming sections, in each at least three.

Controlled shell load

The internal pressure P of the polarizing, for example, by hydraulic loading, accepts AE signals by converters, and their parameters, in particular, the total emission, are measured. Based on the measurement, the shell section at which the total emission is maximum is selected (control plot). .

The drawing shows the measurement results of the relative total

Qf emission over the reduced length Hj, / H of the cylindrical part of the shell from the bottom side for two shells of the same type (curves with indices 1 and 2) at pressures of pressure: P, 0.4 P (curves 1a and 2a) j PO 0, 7 Р (curves 16 and 26), where РЗ is the failure pressure for the reference envelope.

From the measurement results it follows

that for the first shell, the control area lies on the normal cross section gauge at 0.1, and for the enclosure shell, at, 5.

The elongation Jl of the selected control area is measured by the readings of the strain gauge and the shell strength P is determined by the calibration dependence

p p

D

Al

+ P

Uh

five

Where

0

0

five

-determine the strength of the controlled shellJ

-pressure pressure of con-, controlled shellJ

- pressure at which the reference shell is destroyed; ,

-longation of the control area of the controlled shell under pressure crimping;

- extension of the site, similar to the control, of the reference shell under pressure molding;

- extension of the area, similar to the control, reference shell at a pressure close to the pressure of destruction.

The frequency f of receiving AE signals from the low-frequency side is limited by production noise. When hydrod,

I,

LU,

shell loading the lower boundary lies within 100 kHz. On the high frequency side, the frequency f of receiving AE signals is limited by the geometrical properties of the envelope surface, as a reflecting or scattering diffraction grating with a small periodicity, roughness. The frequency of the grille barrier is estimated with respect to C / A, where c is the velocity of propagation of longitudinal vibrations in the matrix material, A is the period of irregularities equal to the quotient from dividing the width of the tape by the number of threads in it.

For an epoxy resin matrix with 2600 m / s, tape width b, number of filaments 40, the frequency of the barrier is 33 MHz. Considering the spectrum of AE signals to be uniform, and the attenuation of AE signals at a frequency of an obstacle equal to their dynamic range of 80 gB and taking into account the fact that as the frequency decreases, the absorption coefficient of polymer composites decreases in proportion to the square of the frequency, we get an estimate of limitations from the high frequencies equal to 330 kHz. If we assume that the number N of points of reception of AE signals is unchanged, for shells of various area S, it is advisable to choose the reception frequency f from the expression

50

t5

20 0

five

five

where A is a parameter determined by the shell material, mainly the absorption coefficient of acoustic oscillations, equal to 0.1 for glass glass plastics.

When using this formula, the selected frequency lies within the above limitations for shells with an area of 3-40 m.

Improving the accuracy of determining the strength of the shells allows for a more accurate assignment of operating loads, as a result of which their service life increases, the number of accidents decreases, and so on

The Invention Method for Determining the Strength of a Cladding Made of Polymeric Composite Materials. The method consists in attaching a pressure to a casing, measuring the elongation of a section of the casing, and measuring the elongation using a calibration function to determine the strength of the casing. In order to increase accuracy, after the application of pressure, acoustic emission signals are taken at points evenly distributed over the shell, parameters of the received signals are measured by the maximum value at This parameter determines the area of the shell where the elongation is measured.

0.1 02 0.3 at 0-5 0.6 ol OV

- ™ 3acaz 5991/43 Circulation 776 Subscription Arbit-Polygr. pr-tie, Uzhgorod, st. Project, 4

Claims (1)

The claims of the invention A method for determining the strength of a shell made of polymer composite materials, which consists in applying pressure to the shell, measure the elongation of a portion of the shell and determine the strength of the shell using the calibration curve, which is characterized by the fact that, in order to increase accuracy , after applying pressure, acoustic emission signals are received at points uniformly distributed over the shell, the parameters of the received signals are measured, and the maximum value th parameters define the shell portion, which produce measuring elongation. ВНИИПИ Order 5991/43 Circulation 776 Subscription Custom polygon. ave, city of Uzhhorod, st. Project, 4