CN100359317C - Method and device for three-point bending mechanical property test of small-sized sheet sample - Google Patents

Abstract

The invention relates to a method for testing the curvature physical property at three points of small sheet sample, wherein said method comprises: arranging preformed sheet sample with micro cracked surface deposit on the sample table; using force control method, to contact the compress head with the upper surface of sample; entering into testing conditions, to avoid high load at contact moment; connecting two electrodes of said sheet sample with voltage collecting system, and increasing load stepped, recording the maximum load, and detecting the voltage change at the crack moment of said micro crack, and converting the voltage and time data into the relationship between speed and time. Said device is formed by three-point curvature sample table, sample table support system, cooling system, heating system, loading system, and testing system. The invention can directly mount small sheet sample on the tester, to process three-point curvature test and process critical stress strength factor test of preformed micro cracked sample.

Description

A kind of small-sized sheet sample three-point bending mechanical property method of testing

Technical field

The invention belongs to a kind of method and device thereof of small-sized sheet sample three-point bending mechanical property test, comprise that being applied to surface preparation has the Mechanics Performance Testing of membraneous material sheet sample and be shaped on micro-crack hard brittle material high speed crack velocity test experiments research field in advance.

Background technology

At present, emission behavior of the small-sized sheet sample brittle ductile transition of material at home and abroad, crack tip dislocation and the hard brittle material that is shaped on micro-crack in advance ftracture at a high speed in the research of behavior, the former generally adopt nano impress and block materials etc. method such as axle stretching etc., and usually sample is fixed on the hard elastic framework in latter's research, by the mechanical meaurement system framework loading realization large scale or block materials are realized that under the situation of little distortion crackle ftractures at a high speed again.But along with current science and technology development, each side is launched the related experiment of different materials, comprise macromolecular material, monocrystal material, polycrystalline material, membraneous material and non-crystalline material, small scale sample crack initiation behavioral study is proposed more and more higher requirement, require to avoid in the sample test process more extraneous interference simultaneously, because the subject matter of paying close attention in crack tip and crackle ftracture behavioral study at a high speed is the relation between material intrinsic structure and the energy dissipation, though a large amount of related works have been arranged at present to be carried out, comprise and adopt molecular dynamics simulation and finite element analogy method that the motion and the crack tip energy variation of crack tip are analyzed, but the dynamic mechanism that the control crackle ftractures at a high speed still is not the fine understanding of people, yardstick at research material, aspect such as temperature effect and control accuracy need be carried out in a deep going way down, and in the method for using at present, require sample bigger, can't realize the research of small scale sample high speed crack initiation, and method makes more the research in the temperature field carry out on the framework by being fixed on.Small and Medium Sized sample specification of the present invention is: (16～20) mm * (3～10) mm * (0.3～1) mm.

Summary of the invention

The object of the present invention is to provide a kind of method and device thereof of small-sized sheet sample three-point bending mechanical property test, comprise being applied to Mechanics Performance Testing and the sheet hard brittle material crackle high speed crack velocity test experiments research aspect that surface preparation has membraneous material, can well avoid loading frame that the influence of signals collecting be can be implemented in the related experiment that is lower than expansion small-sized sheet sample in the 1200 degree celsius temperature fields simultaneously.

Technical scheme of the present invention is:

A kind of small-sized sheet sample three-point bending mechanical property method of testing is characterized in that concrete steps are as follows:

1) at first sheet sample is installed on the sample stage strong point of sample stage, prefabricated micro-crack in the middle of the sheet sample is remained on the centre of two sample stage strong points, make its top corresponding with the power drive link of loading system, the loading that guarantees the power drive link is directly over crack tip;

2) adjust caging bolt, keep the vertical of sheet sample; Control the acting force between caging bolt and the sheet sample simultaneously, the caging bolt tip is contacted with flaky material;

3) the power drive link is adopted the power control mode, pressure head is contacted with the upper surface of sheet sample;

4) connect two prefabricated electrodes on lead and the sheet sample surface film, it is connected with the potential acquisition system;

5) changing control mode makes it to mate with test condition;

6) upper and lower surface of thermopair at sheet sample is installed, adjusts the height of resistance wire heating furnace simultaneously, guarantee that sheet sample is in the soaking zone of resistance wire heating furnace;

7) the resistance wire heating furnace is closed in the pass, the operation loading system, and until the sheet sample fracture, record fracture instantaneous load and the variation of electrode both end voltage.

Described sheet sample is non-standard sample, calculates critical stress intensity factors K in described step 7) _cThe time, adopt following formula:

$K_c=f\left(\frac{a}{w}\right)\frac{3\mathrm{PL}}{{\mathrm{Bw}}^2}\sqrt{\mathrm{\πa}}$

Wherein a is a crack length, and P is a ram load, and w is the height of sample, and B is a sample thickness, and L is a sample stage strong point span,

Be the shape corrections function.

A kind of small-sized sheet sample three-point bending mechanical property proving installation, have sample stage, sample stage support system, cooling system, heating system, loading system, test macro, described sample stage is the three-point bending sample stage, the three-point bending sample stage is processed by high temperature alloy, be processed with the spacing point of sample outside the narrow slit of placing sheet sample, two sample support points and the sample support point above, on corresponding of sample stage and the sheet sample of vertical placement caging bolt is housed, caging bolt is adjusted the upright position of sheet sample.

The invention has the beneficial effects as follows:

1, the present invention directly installs small-sized sheet sample on proving installation, carries out the three-point bending experiment of sheet sample, also can carry out the critical stress intensity factors test of prefabricated micro-crack sheet sample.

2, the parallel placement surface preparation of the present invention has the membraneous material sheet sample, directly carries out Mechanics Performance Testing, the bond strength of research membraneous material and matrix material.

3, the present invention is coated with the nano ceramics film on sample stage and loading pressure head, prevents to conduct electricity between sample stage and the sample, avoids interference acquisition signal in high speed crack initiation test process.

4, the present invention can carry out related experiment in being lower than 300 degrees centigrade temperature environment.

Description of drawings

Fig. 1 is a proving installation synoptic diagram of the present invention.

Fig. 2 is sample stage synoptic diagram among Fig. 1 of the present invention.

Fig. 3 is the side view of Fig. 2.

Description of symbols among the figure:

1-1-power drive link, 1-2-pressure head, 1-3-sheet sample, 14-recirculated cooling water, 1-5-sample stage the strong point, 1-6-pressure transducer, 1-7-thermopair, 1-8-resistance wire heating furnace, 1-9-temperature switch board, 1-10-potential difference meter, 1-11-sample stage support bar, 1-12-electrode, 1-13-sample stage; 2-1-sample support point, 2-2-caging bolt, the spacing point of 2-3-sample.

Fig. 4 is for to vary with temperature curve in different loading speed lower critical stress intensity factors.

Voltage starts the cracking time change curve with crackle to Fig. 5 on the micro-crack sample in order to be shaped in advance.

Embodiment

Below in conjunction with accompanying drawing the present invention is described further.

Shown in Fig. 1～3, small-sized sheet sample three-point bending mechanical property proving installation of the present invention, has sample stage, the sample stage support system, cooling system, heating system, loading system, test macro is formed, described sample stage is the three-point bending sample stage, the three-point bending sample stage is processed by high temperature alloy, be processed with the narrow slit of placing sheet sample 1-3 above, the spacing some 2-3 of sample in two the sample support point 2-1 and the sample support point 2-1 outside, on corresponding of the sheet sample 1-3 of sample stage 1-13 and vertical placement caging bolt 2-2 is housed, caging bolt 2-2 adjusts the upright position of sheet sample 1-3.Described sample stage support system comprise sample stage strong point 1-5 with and the sample stage support bar 1-11 that go up to be provided with, the three-point bending sample stage is installed on the sample stage support bar 1-11, is provided with pressure transducer 1-6 below the sample stage strong point 1-5; Described loading system comprise power drive link 1-1 with and the pressure head 1-2 that connects below, pressure head 1-2 contacts with sheet sample 1-3; Described cooling system is the recirculated cooling water 1-4 that is surrounded on the power drive link 1-1 and the sample stage strong point 1-5 outside; Described heating system comprises resistance wire heating furnace 1-8, thermopair 1-7 and the temperature switch board 1-9 that links to each other with resistance wire heating furnace 1-8, and heating system of the present invention adopts two galvanic couple monitor modes; Described test macro comprises potential difference meter 1-10, is installed on the electrode 1-12 on the sheet sample 1-3, and electrode 1-12 links to each other with potential difference meter 1-10 by the potential acquisition system.

Small-sized sheet sample three-point bending mechanical property method of testing of the present invention is specifically finished by following experimental procedure.In critical stress intensity factors test and the test of high speed crack initiation:

1.1 at first sheet sample 1-3 is installed on the sample stage strong point 1-5 of sample stage 1-13, the planarization that will keep sheet sample 1-3 simultaneously, prefabricated micro-crack in the middle of the sheet sample 1-3 is remained on the centre of two sample stage strong point 1-5, make its top corresponding with the power drive link 1-1 of loading system, the loading of assurance power drive link 1-1 guarantees the accuracy of test data directly over crack tip.

1.2 adjust caging bolt 2-2 subsequently, keep vertically putting of sheet sample; Acting force between appropriateness control caging bolt 2-2 and the sheet sample 1-3 makes the caging bolt tip contact gently with flaky material simultaneously, prevents acting force perturbed force drive link load that 1-1 adds therebetween, and then avoids influencing test result;

1.3 power drive link 1-1 is adopted the power control mode, pressure head 1-2 is contacted gently with the upper surface of sheet sample 1-3, avoid displacement control contact big load of moment to destroy sample and pressure transducer 1-6;

1.4 connect two prefabricated electrode 1-12 on lead and the sheet sample 1-3 surface film, it be connected with the potential acquisition system.

1.5 the change control mode adopts displacement control to make it to mate with test condition.

1.6 the upper and lower surface of thermopair 1-7 at sheet sample 1-3 is installed, adjust the height of resistance wire heating furnace 1-8 simultaneously, guarantee that sheet sample 1-3 is in the soaking zone of resistance wire heating furnace 1-8, temperature range can be 100～1200 ℃ in crisp toughness commentaries on classics of research and the development test of change crack velocity, but temperature need be lower than 300 ℃ in the strain measurement test, it is the effect of research temperature that heating arrangement is installed, and is important indicator in the mechanical property research.

Close resistance wire heating furnace 1-8 1.7 close, make resistance wire heating furnace 1-8 enter duty, the operation loading system, progressively increase load (gather way is 4 little meter per seconds, 8 little meter per seconds, 16 little meter per seconds) by displacement control, until loading sheet sample 1-3 fracture, maximum load in the record loading procedure, record fracture instantaneous load and electrode 1-12 both end voltage change, and conversion current potential and time data are speed and time relationship.

In above-mentioned 1.7, write down maximum load in the loading procedure, but can not react sheet sample crackle feature, because the criteria of right and wrong sample of Cai Yonging in the present invention need change according to formula, so calculating critical stress intensity factors K _cThe time, normalized form is handled, obtain following formula:

$K_c=f\left(\frac{a}{w}\right)\frac{3\mathrm{PL}}{{\mathrm{Bw}}^2}\sqrt{\mathrm{\πa}}$

Wherein a is a crack length, and P is a pressure head 1-2 load, and w is the height of sample, and B is a sample thickness, and L is a sample stage strong point 1-5 span,

Be the shape corrections function.

In Fig. 4, provided critical stress intensity factors (K at the situation lower mono-crystalline silicon sheet sample of different loading speeds (4 little meter per seconds, 8 little meter per seconds, 16 little meter per seconds) _c) with the change curve of temperature (T).As seen from Figure 4, be lower than the brittle ductile transition temperature stage, belonging to the brittle cracking stage, in this stage, raising critical stress intensity factors K along with temperature _cSubstantially constant, along with temperature continues to raise, become critical stress intensity factors K a less temperature range _cSignificantly raise, realize brittle ductile transition.

In Fig. 5, provided be shaped on micro-crack in advance sheet sample in high speed cracking process current potential with the change curve of cracking time.Can see by Fig. 5, effectively write down 10 by this method and device thereof ^-6The current potential dynamic changing process of time second internal fissure cracking is for the analysis of high speed crack velocity provides authentic data.

Claims (2)

1. small-sized sheet sample three-point bending mechanical property method of testing is characterized in that concrete steps are as follows:

1) at first sheet sample (1-3) is installed on the sample stage strong point (1-5) of sample stage (1-13), prefabricated micro-crack in the middle of the sheet sample (1-3) is remained on the centre of two sample stage strong points (1-5), make its top corresponding with the power drive link (1-1) of loading system, the loading that guarantees power drive link (1-1) is directly over crack tip;

2) adjust caging bolt (2-2), keep the vertical of sheet sample; Control the acting force between caging bolt (2-2) and the sheet sample (1-3) simultaneously, the caging bolt tip is contacted with flaky material;

3) power drive link (1-1) is adopted the power control mode, pressure head (1-2) is contacted with the upper surface of sheet sample (1-3);

4) connect prefabricated two electrodes (1-12) on lead and sheet sample (1-3) surface film, it is connected with the potential acquisition system;

5) changing control mode makes it to mate with test condition;

6) upper and lower surface of thermopair (1-7) at sheet sample (1-3) is installed, adjusts the height of resistance wire heating furnace (1-8) simultaneously, guarantee that sheet sample (1-3) is in the soaking zone of resistance wire heating furnace (1-8);

7) resistance wire heating furnace (1-8) is closed in the pass, the operation loading system, and until sheet sample (1-3) fracture, critical stress intensity factors K is calculated in record fracture instantaneous load and the variation of electrode (1-12) both end voltage _c

2, according to the described method of testing of claim 1, it is characterized in that sheet sample is non-standard sample, in described step 7), calculate critical stress intensity factors K _cThe time, adopt following formula:

$K_c=f\left(\frac{a}{w}\right)\frac{3\mathrm{PL}}{B{w}^2}\sqrt{\mathrm{\πa}}$

Wherein a is a crack length, and P is pressure head (1-2) load, and w is the height of sample, and B is a sample thickness, and L is the sample stage strong point (1-5) span,

Be the shape corrections function.

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