CN1082192A - The measuring method of thin plate unrelieved stress - Google Patents

Abstract

The present invention relates to a kind of measuring method of light sheet unrelieved stress.This method is to go out a circular hole on tested sheet material fast, measures the rate of change of the relative punch diameter of this circular hole all directions diameter then.Because the rate of change of punching hole diameter has relation one to one with herein stress distribution, thus the mathematical model of setting up according to calibration experiment, can by draw the unrelieved stress of tested sheet material punching towards circular hole all directions diameter variation rate.This measuring method is quick, easy, can be used for the on-the-spot actual detected of supplying.

Description

The measuring method of thin plate unrelieved stress

The present invention relates to a kind of method for measuring stress, is a kind of method of measuring the thin plate unrelieved stress.

Along with science and technology development is more and more high to the requirement of some light sheet material angularity, particularly its robotization stamping line is higher to the requirement of thin plate angularity in electronics industry, thereby the user of thin plate band often proposes the unrelieved stress of delivery thin plate band is carried out Testing requirement to manufacturer, so that the angularity of control sheet material.As the thin plate band that is used for the integrated circuit framework requires must not have the angularity greater than a millimeter in one meter long, and this just requires strip can not have uneven stress distribution before punching press.At present, the method for sheet material measurement unrelieved stress has multiple, as X-ray diffraction method, moire method, strain gauge method, brittle with cut open bar observation method etc.What comparatively generally adopt for the measure field of thin plate unrelieved stress is to cut open the bar observation method.But the method can not be measured the concrete numerical value of plate face all directions stress, and measuring accuracy is not high yet, and cuts open the strictness of bar technological requirement, can not increase additional stress to sample in cuing open bar.Strain gauge method can be used for measuring the plane unrelieved stress of thin plate, and it is attached to foil gauge around prebored hole of plate surface, measures strain after the boring with foil gauge, calculates stress value according to the Elasticity formula again.But each measurement all needs to paste the operation of foil gauge in the time of in this way, and paster is demarcated and it is too loaded down with trivial details to calculate, and reaches 2～3 days measuring period, and cost is higher, be difficult to satisfy on-the-spot actual needs, therefore, this method does not obtain to use widely at present in production reality.

The purpose of this invention is to provide a kind of fast, accurately and the method for the measurement thin plate unrelieved stress of less expensive.

The inventor finds through a large amount of tests: when the stress distribution on the thin plate was inhomogeneous, perforate on thin plate made stress relief, and then the shape in this hole will change, and this variation is relevant with the stress distribution of thin plate.Draw after further study: if the mode of employing fast precise punching is at thin plate upper punch circular hole, then the stress distribution at the vary in diameter of these hole all directions and this place has relation one to one, its diameter variation even can reach 0.050mm, available present caliper is measured fully.Therefore can utilize this principle to measure the unrelieved stress of thin plate.

The measuring method of thin plate unrelieved stress provided by the present invention is

(1) mode that adopts the fast precise punching is at Board Under Test upper punch circular hole,

(2) measure above-mentioned the aperture D on the different directions of circular hole _n,

(3) calculate towards circular hole varying aperture rate λ in different directions,

$\mathrm{\lambda \; =}\frac{D_n{\mathrm{-\; D}}_O}{D_O}\mathrm{·\; 100\%}$

D in the formula _o-punch diameter, D _nDiameter on a certain direction of-punching,

(4) the corresponding regression relation that is calibrated according to stress value of measuring with existing physical measurement method and the punching hole diameter rate of change of measuring can draw the unrelieved stress of tested sheet material punching place all directions.

The above said existing physical measurement method that is adopted in demarcation can be the whole bag of tricks such as X-ray diffraction analysis method, moire method or strain gauge method, but because of in demarcation, also carrying out the rate of change that the aperture is measured in punching, so save trouble to adopt strain gauge method to demarcate comparatively.

Above said tested sheet material towards circular hole typically have a diameter from 1/10～1/3 of sheet material width, if punching hole diameter is too small, then measuring accuracy is lower; Punching hole diameter is excessive, then unnecessary distortion will take place.

Below in conjunction with concrete example content of the present invention is illustrated.

Fig. 1 is the synoptic diagram of calibration experiment.

Fig. 2 be in this example on light sheet towards the stress envelope at circular hole place.

The used tested sheet material of this example is iron bronze thin plate band, is divided into five kinds of specifications by its thickness and width.

1, calibration experiment

Get one group of tested strip, measure the thickness H and the width B of each strip, at its plate face midpoint circle that draws lightly, its diameter is identical with punch diameter then.The periphery of this circle is divided into eight equal portions, selects the identical foil gauge of resistance, on corresponding position, stick eight foil gauges 1～8, as shown in Figure 1.Can connect strainmeter after the operation such as drying, sealing wire base then.Then with quick punch press in drawn circle towards circular hole, make stress relief.With the strain value of each foil gauge of strain-ga(u)ge measurement, as one group, the Hooke's law under the substitution plane stress condition is obtained the stress value σ of this direction with the strain value of the foil gauge on the perpendicular direction of the strain value of each foil gauge _nAgain with the high-precision reading microscope measure the diameter D on the circular hole all directions _n, and with punch diameter D _oFor benchmark calculates vary in diameter rate on the punching all directions

${\mathrm{\λ}}_n=\frac{D_n\·D_O}{D_O}\·100\%=\frac{\mathrm{\Δ}{D}_n}{D_O}\·100\%$

Measurement result is as shown in the table:

Do many group tests as stated above, can set up equation with statistical method according to measured result:

σ _n＝f（△D _n/D _o，H，B）

According to this equation, as long as measure the vary in diameter rate △ D of punching _n/ D _o, sheet material width B and thickness H, can obtain the unrelieved stress of punching place.

For the iron bronze thin plate of this example, the concrete form of following formula is

σ _n＝2.6543+6189.5△D _n/D _o+64.364H-0.29977B

The coefficient R of this formula=0.866, residual standard deviation σ=2.8MP _a, the F test value is 18.34, as seen this equation is reliable.

2, test result analysis

The varying aperture and the stress value of above-mentioned No. 1 sample all directions are depicted as broken line graph shown in Figure 2, among the figure dotted line be towards the vary in diameter situation of circular hole all directions; Solid line is the stress distribution situation of each point; Dotted line is the distribution situation of all directions stress mean value.As can be seen from the figure: towards circular hole on all directions vary in diameter and the mean value of same direction upper stress be very identical.When varying aperture and stress distribution broken line graph all were octagon, then the stress distribution of sample all directions was even, i.e. the unrelieved stress minimum.Otherwise then stress distribution is inhomogeneous, and unrelieved stress is big.

The above-mentioned relationship input computing machine of in this example calibration experiment being set up carries out stress measurement to tested sheet material by this method then, and the time of measuring once is no more than 20 minutes.

From the above, residual stress measuring method provided by the present invention is easy, economical, measurement, time weak point, and can carry out residual stress measurement to the comprehensive of plate face, thus improved the work efficiency of measuring greatly.Just because of this, this measuring method can be used for the on-the-spot actual detected of supplying.

Claims (2)

1, a kind of measuring method of thin plate unrelieved stress is characterized in that

(1) mode that adopts the fast precise punching is at Board Under Test upper punch circular hole,

(2) measure above-mentioned the aperture D on the different directions of circular hole _n,

(3) calculate towards circular hole varying aperture rate λ in different directions,

$\mathrm{\lambda \; =}\frac{D_n{\mathrm{-\; D}}_O}{D_O}\mathrm{·\; 100\%}$

D in the formula _o-punch diameter, D _nDiameter on a certain direction of-punching,

(4) the corresponding regression relation that is calibrated according to stress value of measuring with existing physical measurement method and the punching hole diameter rate of change of measuring can draw the unrelieved stress of tested sheet material punching place all directions.

2, measuring method as claimed in claim 1, it is characterized in that tested sheet material be 1/10～1/3 of tested sheet material width towards the diameter of circular hole.