CN1392400A - Non-destructive testing method and device for mechanical property of brittle material - Google Patents

Abstract

The non-destructive test method and device for mechanical property of brittle material is base don the rule of stress gradient on material cracking characteristics and equal strength criterion. The measurement includes determining the mechanical performance of material via contact between small balls with high elastic modules and the tested part in certain load;o determining local material strength via measuring the maximum average stress in transition area while producing critical contact crack; and complete warranty test and reliability test in contact stress lower than the local strength. The method is convenient, simple and low in cost and is especially suitable for in-situ measurement and monitoring of brittle member in use state.

Description

Mechanical property of brittle material non-destructive testing method and device thereof

Technical field

The present invention relates to a kind of method of testing and device thereof of material property, particularly about a kind of method and device thereof of mechanical property of brittle material non-destructive testing.

Background technology

Hard brittle materials such as glass, pottery, concrete in the development of the national economy and national defense construction extensive application and aspect reliability more and more stronger demand, caused the military service performance on-line testing of fragility member and pressing for of life prediction assessment technique.The surface and interface analysis of Residual Stress of hard brittle material and surface damage and Damage Evolution process are significant to the application and the structural design of hard brittle material, also are that hard brittle material enters the safety guarantee that engineering is used.Decline and the Forecasting Methodology thereof of grasping the surface property of hard brittle material under the chemical radiation environment are very important to preventing and treating catastrophic failure.Usually, the strength test of material all is to adopt the destructive test of sample being broken or fracture etc., can't test the performance of military service member.For a long time, the evaluation of material worker wishes always can be with simple, need not standard sample and specific lab environment carry out the non-destructive Mechanics Performance Testing, this also is a 21 century mechanics and material supplier author's an applied research direction.But except nondestructive testing technique, the non-destructive testing technology never breaks through up to the present.And in actual applications, the demand of non-destructive testing is very large, such as: glass or ceramic component have been used several years, does its strength character have great variation? how long can also use? also as: several parts are with different materials or same type of material but different technology making, is that performance best? is that the poorest? and for example: borrow Japanese pottery parts, want to understand very much its intensity, hardness, elastic modulus, but can not damage it, can can't harm online these mechanical properties that obtains? for another example: a certain important fragility member will enter use, for perfectly safe, how to carry out non-destructive testing, can do you satisfy essential safety requirements with the performance and the life-span that guarantee it? although above problem is very important, never have effective solution.

Summary of the invention

Problem set forth above, the problem to be solved in the present invention just, purpose of the present invention will provide a kind of mechanical property of brittle material non-destructive testing method and device thereof exactly.

For achieving the above object, the present invention takes following technical scheme: a kind of mechanical property of brittle material non-destructive testing method is characterized in that:

(1) by with the mechanical property that is in contact with one another to determine material under certain load between the bead of high elastic modulus and the test specimen;

(2) by produce critical contact crackle constantly the maximum mean stress in the materials process district determine the local strength of material;

(3) carry out warranty test and fail-test with the contact stress that is lower than local strength;

Concrete operations are as follows:

(a) polished in the part of test specimen or polish;

(b) with the vertical described test specimen surface that is pressed in of spherical indenter of a known radius and elastic constant, show load value, be loaded on the test specimen surface and just produce a small circumferential crack that load this moment is critical load by sensor;

(c) with described critical load and spherical indenter and the contact radius of circle of test specimen in the critical load moment, the following formula of substitution can be obtained the local strength of described test specimen, and described formula is: ${\mathrm{\σ}}_c=({\mathrm{ar}}_c^2+{\mathrm{br}}_c+c)\·{\left(\frac{E}{k}\right)}^{2/3}\·\frac{1}{\mathrm{\π}}\·{\left(\frac{F_c}{{R_s}^2}\right)}^{1/3}---\left(1\right)$

Wherein: σ _cBe local strength, r is a contact radius, and a, b, c are respectively the constants relevant with measured material, and E is the elastic modulus of sample, and k is the constant relevant with the performance of pressure ball and measured material, F _cBe the critical load value, R _sIt is the pressure ball radius

(4) for the Elastic Contact problem of subcritical load, normal pressure p and contact radius a and the following formula of pressure ball radius r substitution can be obtained the elastic modulus of described test specimen, described formula is: $E=(1-v^2)/[\frac{{4a}^3}{3\mathrm{pr}}-\frac{{1-v}^{\′2}}{E^{\′}}]$

Wherein: E, v are the elastic modulus and the Poisson ratios of measured material; E ', v ' be pressure ball elastic modulus and Poisson ratio.

A kind of mechanical property of brittle material non-destructive testing device is characterized in that: it comprises a plane test board; One has the door shaped stent of a top board and two vertical rods, and it is arranged on the described test board; One crossbeam that moves by drive unit, its two ends are arranged on two vertical rods of described door shaped stent; One sensor, it is arranged on the described crossbeam; One pressure head, it is arranged on described sensor bottom.

Described pressure head is a kind of in ball pressure head, Vickers pressure head, the three-point bending pressure head.

Described test board is provided with a through hole corresponding with described ram position, and a cover plate is set on described through hole.

Sensor is installed in the place ahead of described crossbeam.

Two vertical rods of described door shaped stent are two leading screws, the two ends of described two leading screws respectively by Bearing Installation on top board and test board, the drive unit of described crossbeam is the speed reduction unit of a driven by motor, the output terminal of described speed reduction unit drives two leading screws respectively and rotates, and described crossbeam two ends are by being threaded on the described leading screw.

Two vertical rods of described door shaped stent are two guide pillars, the two ends of described two guide pillars are separately fixed on described top board and the test board, the drive unit of described crossbeam is one to revolve the spiral jack unit that is located on the described top board by screw thread, the output terminal top of described spiral jack unit is located on the described crossbeam, between described top board and the crossbeam back-moving spring is set.

The present invention is owing to adopt above method, it has the following advantages: 1, the present invention establishes small circumferential crack owing to only pressing on test specimen, just the formula of the equal criterion of strength that can derive by the applicant, therefore calculate the strength of materials performance of test specimen, solved the problem of the insurmountable always for a long time non-destructive strength test to test specimen.2, the inventive method restriction of condition and equipment that can not be put to the test can use the mechanical test machine of any routine to realize, adopts equal criterion of strength, more nondestructively reproduces the strength character of material.3, the inventive method can directly be tested test specimen itself, and does not need standard sample, and its simple testing process, test data have stability preferably, and discreteness is less, more approaches actual conditions.4, proving installation provided by the invention possesses advantages such as simple in structure, convenient test, test result true and accurate equally, both has been fit to use in the laboratory, is suitable for the tester again to carry on-line testing occasions such as on-the-spot test.The inventive method and device are easy to operate, and be simple, can save the wide variety of materials expense, test fee and time, be particularly suitable for the fragility member under the service state is carried out on-line testing and monitoring, and it has boundless application prospect to the development of the national economy.

Description of drawings

Fig. 1 is a proving installation structural representation of the present invention

Fig. 2 is the schematic side view of Fig. 1

Fig. 3 is another embodiment of proving installation of the present invention

Embodiment

At first theoretical foundation of the present invention and result of study are carried out comparatively detailed introduction.

Contact in the engineering structure generally can be divided into following three kinds: 1) quiet contact, as supporting between bridge pier and the pontic, between ground and the house etc.; 2) circulation contact is as the engagement between the gear etc.; 3) impact contact, as the bump of flying dust particle in automobile and aircraft windscreen and the air etc. etc.These three kinds of ways of contact all can produce damage in various degree, i.e. contact damage to two objects that are touched.

Theory of contact stress is a theoretical system of setting up hertz eighties in 19th century, has experienced 100 years of development and perfect so far.Hertz contact theory is found the solution with analysis on Stress Field etc. two elastomeric Elastic Contact stress and has been done classical description, has established the basis of contact theory.Wherein ball and contacting of semi-infinite body are widely used in analyzing and characterize problems such as the hardness of the fracture of pottery, metal and other material and deformation behaviour and evaluating material and granule impact, are also referred to as the impression method.

Contact theory and ball pressure method more and more come into one's own with the characteristics with analytic solution owing to easy to operate, and are widely used in hard brittle material fracture sign and deformation characteristic analysis.Impression damage research and application thereof also receive publicity day by day, and have been used in many practical field.The beginning of opening of hertz circumferential crack is represented the beginning of impression damage and the upper limit that the linear elasticity contact theory is set up for hard brittle material.The important parameter that the critical impression stress that surperficial circumferential crack opens the beginning is the analysis of material strength character.So for a long time, material and mechanics scientist want to obtain by contact method the intensity of material always.Yet many problems that exist some to await further understanding in impression fracture field that studies show that: the intensity of (1) material should be a constant, but the critical impression stress in when cracking is not constant, and far above conventional intensity level.Theoretical analysis shows that critical impression stress reduces along with the increase of pressure ball radius.(2) maximum tension stress occurs on the surface contact circumference, but circumferential crack is always greater than the contact circle in the practice, and promptly crackle is not to be created in the maximum tension stress place.

The research of these problems is to the development of impression theory and use significant.In fact it has hinted that stress gradient is to critical impression stress influence.The applicant explains the above several problems and the inefficacy rule of hard brittle material by stress gradient along with the change of pressure ball size and specimen material changes, and sets up the method with the strength character of ball-pressure method test and appraisal hard brittle material first.

The ball living circumferential crack of cutting down output is by the radial stress σ in the hertz Elastic Contact district _RDue to.Radial position R in axisymmetric cylindrical coordinates, normal direction position z and radial stress σ _RConcern as follows: $\frac{{\mathrm{\σ}}_R}{{\mathrm{\σ}}_o}=\frac{1}{2}(1-2v){\left(\frac{r}{R}\right)}^2[1-{\left(\frac{z}{\sqrt{u}}\right)}^3]+\frac{3z}{2\sqrt{u}}[\frac{(1-v)u}{(r^2+u)}+(1+v)\frac{\sqrt{u}}{r}\arctan \left(\frac{r}{\sqrt{u}}\right)-2]---\left(2\right)$ In the formula $u=\frac{1}{2}\{(R^2+z^2-r^2)+[(R^2+z^2-r^2)+{4r}^2{z}^2{]}^{1/2}\}$

Wherein, v is the Poisson ratio of material.When spherical indenter is pressed on the test specimen surface, along with normal pressure increases, the contact radius of ball and test specimen also increases, and the contact circumferential edge produces tension, so reach certain critical value when load, fragility test specimen surface produces a circumferential crack.According to the hertz contact theory, maximum tension stress occur on the edge of surface contact circle (z=0, R=r). ${\mathrm{\σ}}_m=\frac{1}{2}{(1-2v)\mathrm{\σ}}_o---\left(3\right)$

Viewpoint will take place to ftracture or crack when maximum stress value is higher than the tensile strength of material herein routinely.But surface in contact generation circumferential crack maximum tension stress constantly that the problem that makes domestic and international many researchers all feel confused is a hard brittle material, it is always much higher than the intensity of material to press following formula calculating, and crackle always occurs in outside the position of maximum tension stress.

The applicant shows by the Stress calculation result: on the contact rounded edge, radial stress reduces and becomes pressurized rapidly at depth direction.Promptly the stress gradient along depth direction is very big herein, changes along with the variation of the radius of a ball and R/r value along the stress of specimen surface depth direction.

Spherical impression demonstrates two features: (a) stress gradient on the depth direction reduces along with the increase of contact radius (or pressure ball radius); (b) stress gradient on the depth direction reduces with the increase of radial position coordinate R/r, and maximum stress gradient occurs in the R/r=1 place.In fact, for a unequal stress field, the peak stress of any can not be controlled fracture and take place.Studies show that critical conditions that crackle in the hard brittle material opens the beginning depends on the mean stress in the specific zonule (process district), rather than depend on the peak stress of a bit.This is called equal criterion of strength.

Mean stress when the process district reaches a critical value σ _cThe time hard brittle material will rupture herein.Process sector width Δ be one depend on material behavior and with the irrelevant constant of sample size and shape.σ _cIt is the intrinsic strength of material.Like this, circumferential crack opens the condition of beginning and is under the effect of ball pressure: $\frac{1}{\mathrm{\Δ}}{\∫}_0^{\mathrm{\Δ}}{\mathrm{\σ}}_R\mathrm{dz}={\mathrm{\σ}}_c---\left(4\right)$

The value of Δ can be determined by the stress field that equal criterion of strength is used for crack tip $\mathrm{\Δ}=\frac{2}{\mathrm{\π}}{\left(\frac{K_{1c}}{{\mathrm{\σ}}_c}\right)}^2---\left(5\right)$

Usually Δ is an increasing function with the hard brittle material crystallite dimension, it reflected connect each other in the microstructure, the maximum region of mutual restriction, also represented crackle to open the limit of local energy accumulation before the beginning.All criterion of strength explanation cracking limit stress peak value constantly in the unequal stress field is not a constant but relevant with stress gradient.Stress gradient is big more, and accessible limit stress peak value is high more.Therefore, in the unequal stress field, peak stress substantially exceeds the strength of materials and material does not ftracture no wonder.

Because being the average tension in the process district, the condition of cracking reaches a critical value, so at first must calculate mean stress.The mean intensity σ of active region is the function of radial position R $\mathrm{\σ}\left(R\right)=\frac{1}{\mathrm{\Δ}}{\∫}_0^{\mathrm{\Δ}}{\mathrm{\σ}}_R(z,R)\mathrm{dz}---\left(6\right)$

With equation (1) substitution equation (5), and carry out numerical integration, obtain mean intensity as the function of R/r with computing machine.Result and radial surface stress are compared, can see that maximum radial stress occurs in the place of R=r, but mean stress minimum herein.Calculating shows that for the situation of Δ=0.03mm and r=0.5mm, the maximal value of mean stress occurs in the place of R/r=1.15.So the radius of the circumferential crack of situation should be 1.15r, rather than at the place of stress peak R=r cracking, this prediction conforms to actual.

The maximum mean stress σ of correspondence when crackle opens the beginning _mRepresented the local strength of sample.It also can regard the intensity of intrinsic strength or unit volume as.Circumferential crack radius and the ratio R that contacts the garden radius ₀The value of/r is to change along with pressure ball size and material, and always greater than 1, visible contact radius is more a little bit smaller than circumferential crack radius usually.

With the local strength that ball-pressure method can record material or member, this intensity level is subjected to the influence of sample edge defect hardly.So can think that it is the intrinsic strength of material.With the ball-pressure method surface residual stress of hard brittle material of also can testing and assessing easily, and can do the harmless assurance experiment of member.

According to above-mentioned research, the method that the applicant sets up first with ball-pressure method non-destructive testing hard brittle material performance, its concrete implementation step is as follows:

1, polished in the part of test specimen or polish;

2, with the ceramic bearing ball of a known diameter and elastic constant or tungsten-carbide ball as pressure head, the elastic constant of this pressure head is known;

3, pressure head vertically is pressed in polishing place, with the speed loading of per minute 0.1mm, by the online load value of sensor measurement.

4, be loaded on the test specimen surface and produce a small circumferential crack, load this moment is critical load.

5, measure the diameter of small circumferential crack, by formula derive spherical indenter and test specimen critical load constantly contact radius of circle, or directly measure spherical indenter and test specimen the radius of circle that contacts in the critical load moment with reading microscope.

6, critical load is brought into the local strength that formula (1) calculates described test specimen.

In the said method, can several measuring points be set on the test specimen surface, the local strength that draws each measuring point respectively by calculating, can obtain the average intensity value and the criterion numeral value difference of test specimen.

Said method also can be used for warranty test, promptly tests corresponding to the load of given requirement of strength, if under this rated load, small circumferential crack does not appear in test specimen, thinks that then the local strength of material is higher than desired intensity, is reliable.

Need to prove that non-destructive testing method of the present invention is meant that the one-piece construction to test specimen does not produce damage, such as, will vase destructive method of testing such as crushing sampling.

The inventive method can realize with the instrument of special use, also can realize with the mechanical test machine of any routine.

Be to introduce a kind of proving installation for realizing that the inventive method designs specially below.

As shown in Figure 1 and Figure 2, mechanical property of brittle material non-destructive testing device of the present invention comprises a plane test board 1, and its bottom surface is provided with feet, and end face is provided with one and has the door shaped stent that top board 2 and two leading screws 3 are formed.The two ends of two leading screws 3 are vertically mounted on top board 2 and the test board 1 by bearing 4 respectively, and the bottom of two leading screws 3 connects the speed reduction unit 6 that a motor 5 that is fixed on test board 1 bottom surface drives.The rotation of motor 5 can drive two leading screws 3 simultaneously by speed reduction unit 6 and rotate.One crossbeam 7, the two ends of crossbeam 7 are connected on two leading screws 3 by internal thread, and the rotation of two leading screws 3 can drive crossbeam 7 upper and lower moving.With a sensor 8, be arranged on the bottom surface of crossbeam 7, be that ceramic bearing ball or tungsten carbide, diameter are the bottom that 3-10mm spherical indenter 9 is arranged on sensor 8 again with a material, make to add the load value that is pressed on the spherical indenter 9 and can show by sensor 8.

In the foregoing description, can on test board 1, offer a through hole 10 corresponding, on through hole 10, place a cover plate 11 with spherical indenter 9 positions.When test one is difficult for mobile test specimen, can opens cover plate 11 through hole 10 that spherical indenter 9 leans out test board 1 is tested like this.

In the foregoing description, two vertical rods of door shaped stent also can be two guide pillars 12 (as shown in Figure 3), and 12 two ends of two guide pillars are separately fixed on top board 2 and the test board 1.The drive unit of crossbeam 7 is one to revolve the spiral jack unit 13 (such as a leading screw) that is located on the top board 2 by screw thread, and the output terminal top of spiral jack unit 13 is located on the crossbeam 7.Spiral jack unit 13 has one handle 14, and spiral jack unit 13 drives by manual rotary handle 14, is provided with back-moving spring 15 between top board 2 and crossbeam 7.Handle 14 also can be by drivings such as motor, speed reduction units.

As shown in Figure 2, the front portion of the top board 2 of door shaped stent can lean out two vertical rods, makes the sensor 8 that is installed on it be cantilever-shaped, and the test specimen volume just needn't be placed between two vertical rods of door shaped stent like this, helps bigger test specimen test.

The utility model can stand placement work in addition, also can be placed on work under the stereomicroscope by recumbency, and the sample local succeesion in the stand under load process is placed under the microscopical on-line monitoring.Stereomicroscope has digital camera and links to each other with computing machine, the photo of being taken directly can be passed to computing machine and handle.

In sum, the inventive method and device have simple and direct, rapid, need not prepare the advantages such as test sample of specific dimensions requirement to tested sample.Ball-pressure method is unique a kind of method with intensity analytic solution in the impression contact method, and in elastic range tested sample is not caused any damage.The present invention in brief introduction on the basis of hertz contact theory, provided the expression formula of utilizing the material local strength that ball-pressure method characterizes.By the contrast of unrelieved stress sample and no unrelieved stress sample intensity is arranged, can obtain the residual-stress value of material part easily.

Breakthrough of the present invention has been to find the influence rule of stress gradient to the hard brittle material cracking property, and the equal criterion of strength that utilizes doctor Bao Yiwang to propose has simultaneously been determined unequal stress cracking critical conditions after the match.

Claims (10)

1, a kind of mechanical property of brittle material non-destructive testing method is characterized in that:

(1) by with the mechanical property that is in contact with one another to determine material under certain load between the bead of high elastic modulus and the test specimen;

(2) by produce critical contact crackle constantly the maximum mean stress in the materials process district determine the local strength of material;

(3) carry out warranty test and fail-test with the contact stress that is lower than local strength;

Concrete operations are as follows:

(a) polished in the part of test specimen or polish;

(b) with the vertical described test specimen surface that is pressed in of spherical indenter of a known radius and elastic constant, show load value, be loaded on the test specimen surface and just produce a small circumferential crack that load this moment is critical load by sensor;

(c) with described critical load and spherical indenter and the contact radius of circle of test specimen in the critical load moment, the following formula of substitution can be obtained the local strength of described test specimen, and described formula is: ${\mathrm{\σ}}_c=({\mathrm{ar}}_c^2+{\mathrm{br}}_c+c)\·{\left(\frac{E}{k}\right)}^{2/3}\·\frac{1}{\mathrm{\π}}\·{\left(\frac{F_c}{{R_s}^2}\right)}^{1/3}$

Wherein: σ _cBe local strength, r is a contact radius, and a, b, c are respectively the constants relevant with measured material, and E is the elastic modulus of sample, and k is the constant relevant with the performance of pressure ball and measured material, F _cBe the critical load value, R _sIt is the pressure ball radius

(4) for the Elastic Contact problem of subcritical load, normal pressure p and contact radius a and the following formula of pressure ball radius r substitution can be obtained the elastic modulus of described test specimen, described formula is: $E=(1-v^2)/[\frac{{4a}^3}{3\mathrm{pr}}-\frac{{1-v}^{\′2}}{E^{\′}}]$

Wherein: E, v are the elastic modulus and the Poisson ratios of measured material; E ', v ' be pressure ball elastic modulus and Poisson ratio.

2, a kind of mechanical property of brittle material non-destructive testing device, it is characterized in that: it comprises a plane test board; One has the door shaped stent of a top board and two vertical rods, and it is arranged on the described test board; One crossbeam that moves by drive unit, its two ends are arranged on two vertical rods of described door shaped stent; One sensor, it is arranged on the described crossbeam; One pressure head, it is arranged on described sensor bottom.

3, mechanical property of brittle material non-destructive testing device as claimed in claim 2 is characterized in that: described pressure head is a kind of in ball pressure head, Vickers pressure head, the three-point bending pressure head.

4, mechanical property of brittle material non-destructive testing device as claimed in claim 2 is characterized in that: described test board is provided with a through hole corresponding with described ram position, and a cover plate is set on described through hole.

5, mechanical property of brittle material non-destructive testing device as claimed in claim 3 is characterized in that: described test board is provided with a through hole corresponding with described ram position, and a cover plate is set on described through hole.

6, as claim 2 or 3 or 4 or 5 described mechanical property of brittle material non-destructive testing devices, it is characterized in that: sensor is installed in the place ahead of described crossbeam.

7, as claim 2 or 3 or 4 or 5 described mechanical property of brittle material non-destructive testing devices, it is characterized in that: two vertical rods of described door shaped stent are two leading screws, the two ends of described two leading screws respectively by Bearing Installation on top board and test board, the drive unit of described crossbeam is the speed reduction unit of a driven by motor, the output terminal of described speed reduction unit drives two leading screws respectively and rotates, and described crossbeam two ends are by being threaded on the described leading screw.

8, mechanical property of brittle material non-destructive testing device as claimed in claim 6, it is characterized in that: two vertical rods of described door shaped stent are two leading screws, the two ends of described two leading screws respectively by Bearing Installation on top board and test board, the drive unit of described crossbeam is the speed reduction unit of a driven by motor, the output terminal of described speed reduction unit drives two leading screws respectively and rotates, and described crossbeam two ends are by being threaded on the described leading screw.

9, as claim 2 or 3 or 4 or 5 described mechanical property of brittle material non-destructive testing devices, it is characterized in that: two vertical rods of described door shaped stent are two guide pillars, the two ends of described two guide pillars are separately fixed on described top board and the test board, the drive unit of described crossbeam is one to revolve the spiral jack unit that is located on the described top board by screw thread, the output terminal top of described spiral jack unit is located on the described crossbeam, between described top board and the crossbeam back-moving spring is set.

10, mechanical property of brittle material non-destructive testing device as claimed in claim 6, it is characterized in that: two vertical rods of described door shaped stent are two guide pillars, the two ends of described two guide pillars are separately fixed on described top board and the test board, the drive unit of described crossbeam is one to revolve the spiral jack unit that is located on the described top board by screw thread, the output terminal top of described spiral jack unit is located on the described crossbeam, between described top board and the crossbeam back-moving spring is set.