WEB-ресурс научно-практических конференций

Kustov А .I. , Scherbinin I.A., Migel I. А

Voronezh State Pedagogical University , Russia ; Voronezh Military Air Engineering Institute, Russia

ELABORATION AND APPLICATION OF INFORMATION TECHNOLOGIES FOR EXPOSURE the limit states OF materials in condense state

1. Introduction. At present the problem of nondestructive express control of physic-mechanical properties of materials in condenses state is one of the most important scientific problems. Objects of investigations of the most interest were the different metal materials, used in processing of fuel elements too. That is, dependences of such properties from structural parameters of material play very important role.

The paper deals with the perspectives of the application of acoustic microscopy methods for studying the changes of physical - mechanical properties of materials in a condensed state. The basic principles of the methods as well as the results of the experiments of studying the structure of materials in a condensed state and its transformation upon changing the composition and types of thermomechanical treatment are given in the article. The high sensitivity to non-heterogeneity and defects upon acoustic visualization and in the regime of determining physic-mechanical properties are demonstrated. The paper deals with the study of process modifications of the elastic-mechanical characteristics of materials, the damage accumulation, the output of the limit state criteria for them.

At present significance restrictions are in possibility of carrying out of experiments. Compute experiments are using for cutting of production costs on investigation wider and wider now.

In this paper the results of experimental work of investigation of physic-mechanical properties materials with the help of scanning acoustic microscope (SAM) [1; 2] are given. The essence of the subjected methods is first inlayer visualization of subsurface structures of the objects under investigation and second in the definition of velocity values of acoustic waves and calculate the elasticity constant of solid material. The nondestructive methods of investigation of structure and characteristics used have no limits by the nature of materials, including nanostructural materials. The state of the material when it is close to the loss of stability is called limit. It is necessary to reveal such states at the possibly initial stages. First the local structure changes inner stress, physical-mechanical parameters (e.g. the velocity of acoustic waves (AW)) can be used as the limit criteria. The problem of reveals the limit state of solid materials including the hydrogenous ones has become urgent recently. The paper deals with the study of process modifications of the elastic-mechanical characteristics of materials, the output of the limit state criteria for them. Different build functions of standard applications take into advantage for analyzes of experimental results.

2. Results and discussion

Base methods of acoustomicroscopy defectoscopy are the visualization and V (Z)-curve methods. The image analyses assignment us possibility to calculate grain dimensions, to observe their transformation from time or with external influences. V( Z)-method allow to determine some elastic-mechanical parameters ( u _R , E, G, D V/V% ) [3 ,4 ].

Example of the obtained by SAM image of microstructure of ВНС -2 М steel is represented on Fig.1.

Fig. 1. Acoustical image of subsurface Fig. 2. V( Z)-curve for investigation

layers ВНС -2 М steel ( Н ₂ О , region in 60 Г steel ( Н ₂ О , f = 407 М Hz,

f = 407 М Hz, scale: 28 m m /div., scale: horizontal - 6 ,2 m m /div.,

Z = -12 m m). vertical – 0,5 V/div.).

The comparative optical photo with the same magnification gives the image of a polished surface without revealing structure elements. Structure transformation has been observed after deformational and thermal influences. In figure 2 present V( Z)-curve for 60 Г steel. In according to principles as account earlier [5 ,6 ], obtained curve permit to determine the significance of velocities ( u _R ) of surface acoustic waves (SAW). For this calculation we use characteristic distance ( D Z _N ) between maximums, situated on the right of the main one.

In order to calculate the value of the elastic modules in the local area of the studied material one should use the tabular values r _S of density and of Poisson coefficient ( n ), or their quantity, determined by one of the certain standard methods. Then, with taking into account the definition u _R in material: (1)

and (2).

V( Z)-curve method allow to distinguish quantity properties of steel with different extent of deformation or to conduct texture characterization [6,7]. In figure 3 present the example of exposed the texture (anisotropy of elasticity modulus in 60 Г steel).

Fig 3 . Anisotropy of elasticity modulus E _eff after different type TMO in specimens of 60 Г steel: 1- trail deformation (57%); 2- patenting; 3 - nothing deformation (in left and middle columns measurements were carry out in direction, which is along to direction of rolling ; in right columns – across to it).

One of the important parameter of solid state sample is the grain dimension (d _З ). The dependences of conventional fluid point ( s _{0 ,2} ) from dimension d _З in one of low carbon steel type are present in fig.4. The results were obtained with standard definition. As follow from that diagram, linear dependence s _0,2 from grain dimension observes in 10-150 m m interval.

Received dependences s _0,2 from d _З are in good accordance with low Hall - Peach: s _0,2 = s ₀ + k d _з ^-1/2 , (3)

were k and s ₀ – the constant for that material.

Fig . 4 . The strength properties dependence from grain dimension ( d _З ) by 14 ХГС steel

Analogical dependence was obtained for 15 Х 2 НМФА steel too . If we estimated grain dimension from acoustic image , then we calculate critical significance s _0,2 for this material. That significance may be to determine with method V( Z)-curve. Since change of grain dimension transforms value of SAW velocity.

The limit state reveal at the initial stages can be carried out by sensitive to micro- and nanoinhomogeneous methods. The limit criteria are possible to be evaluated according to the quantity, form, and distribution in volume of such inhomogeneities . Acoustic microscope defectoscopy methods actively developing in the in the latest 10 - 15 years can be referred to such methods [ 3,7]. They allow both to get subsurface acoustic images of object microstructures and to define their physical – mechanical characteristics. In Fig. 5 the acoustic image of subsurface layers of the steel sample (06 Х 14 Н 6 МД 2 Т ), subjected to corrosion is presented. The pitting with the special dimensions of 3 – 15 m m are visualized with high resolution. Besides, the depth of demonstration of the defects, their dimensions and quantity in the raster allow to judge by the limit state. It was not possible to reveal such inhomogeneities both at the optical images and with the help of some other scientific methods.

Fig 5 . The pitting corrosion visualization by steel surface with

acoustomicroscopy method, (scale 24 m m/div., Z =-7 m m )

Visualization method allow to calculate the depth of penetration microdefects in specimen experimentally and carry out modeling of their form. For example , form of pitting surface in 06 Х 14 Н 6 МД 2 Т steel is defined by logarithmic curve (Fig.6).

Fig 6 . The change of pitting diameter dimension in steel

depend from thickness of taking down layer.

It is also possible to apply acoustic microscopy methods based on the use of V( Z) – curves for the study of the limit state of the materials in a solid state. It makes it possible to calculate the values of velocities SAW and to define the quantity of the coefficient changes of AW fading in the material at the relative modification D V/V% of height of the main maximum of the V(Z) – curves. The control technology of limit state with appliance of V(Z) – curves consists of the analysis of their form transformation. The values of velocities of surface acoustic waves (SAW) and the change of the level of their fading were calculated due to the special dependencies. The limit state of material conclusion was made according to the dimension of local fluctuations of physical – mechanical parameters.

The results of the experiments illustrating the possibility to define the thickness of the modified layer caused by hydrogen diffusion in the metal materials according to the value of velocity SAW or the ratio D V/V % were presented before. The difference between the initial and modified material according to these characteristics can reach 5–20%. The results of modeling experimental for nitrogen steel are presented in fig. 7 ( steel 08 Х 18 Н 10 Т ).

Fig.7 . The dependence of SAW velocity in steel (08 Х 18 Н 10 Т ) on the depth penetration

Obtained experimental curve u _R are approximated by parabolic dependence with coefficient 0,986. We can to ensure definition depth of transformed layer, if shell analyses that dependence.

It is possible to estimate the value and some other sample characteristics, for example the hydrogen concentration, according to the changes of the velocity SAW and the relative height D V/V% of the maximum V( Z) – curve.

The dependencies both between the hydrogen concentration and the number of the microcracks emerged, and the values of velocity SAW on depth of the hydrogen penetration into the sample, period of diffusion, etc. are received at that. The limit hydrogen concentration in this material can be evaluated concerning the value of velocity SAW from the received dependence for steel. In Fig. 8 presented curve of u _R - dependence from time exposure of steel (40 ХН ) specimens in hydrogen. The optimum time dimensions are in interval ~55-67 h.

Fig 8. Dependence of SAW velocity from time exposure ( t )

of steel specimens in hydrogen

As examples for a number of steels it is possible to consider dependencies of the number of originating defects of the flocken type [7], change of the velocity values of surface acoustic waves (SAW), characteristics of the absorption process ( D V/V), sizes of appearing hete-rogeneities upon concentration of the diffusion hydrogen. In Fig. 9 the dependence of relative height ( D V/ V% ) V( Z)-curves from hydrogen con- centration in steel (55 ХН ) are presented. This experimental curve was approximated by trend of polynomial of 2 degree. The trend permit to estimate a content of hydrogen at (5,2-5,8) ^. 10 ^-5 m ³ /kg meaning as dangerous.

Fig. 9. The dependence of of relative height ( D V/V%) on steel (55 ХН )

from content of hydrogen

3. Conclusion Acoustic microscopy methods have prospects for studying the materials on condensed state, their properties and dependences from structural parameters. The results obtained have proved the possibility of output of the limit state criteria of the hydrogenous materials by applying acoustic microscope defectoscopy methods.

The main criteria of the limit is the size of the grains of the structure, their orientation, the presence of the texture. The methods AMD used in this work give the opportunity to determine the solidity of steel ( s _0,2 ) safely and evaluate their changes because of the effects of deformation or concentration.

The essential advantage in AM experiments is the simultaneous use of different work time table SAM. It allows increasing the reliance of the results to a high degree. The methods of revealing the defects with the help of SAM systems have a great independent impotence. Their efficacy is confirmed with the results of the pitting corrosion in steel. The particular attention should be paid to further working out devoted to studying diffusive layers in steel with information technologies.

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