PSI - Issue 16

Volume 16 • 201 9

ISSN 2452-3216

ELSEVIER

6th International Conference “ Fracture Mechanics of Materials and Structural Integrity ” , FMSI 2019, 3 – 6 June, 2019, Lviv, Ukraine

Guest Editors: H r y hori y Ny k y forch y n I hor D m y trakh O lha Zvirko

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Procedia Structural Integrity 16 (2019) 1–2 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” FMSI 2019, 03 – 06 June, Lviv, Ukraine Editorial Hryhoriy Nykyforchyn*, Ihor Dmytrakh, Olha Zvirko Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv 79060, Ukraine 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” FMSI 2019, 03 – 06 June, Lviv, Ukraine Editorial Hryhoriy Nykyforchyn*, Ihor Dmytrakh, Olha Zvirko Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv 79060, Ukraine 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” FMSI 2019, 03 – 06 June, Lviv, Ukraine Editorial Hryhoriy Nykyforchyn*, Ihor Dmytrakh, Olha Zvirko Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv 79060, Ukraine © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers The problems of strength and fracture of the structural materials, as well as the related problems of structural integrity have always been and remain the objects of theoretical and applied studies by a wide range of scientists and practicing engineers. In particular, nowadays the problem of technological and environmental safety of the critical objects of industrial infrastructure becomes more and more important. In order to analyze the fundamental and applied results in this field of science, the European Structural Integrity Society (ESIS) regularly organizes and supports the international scientific conferences on the European, regional and national level. At these conferences, the new approaches and ideas on the problems of the strength of materials and structures and also the results of their practical applications to the evaluation of the durability and safe operation of the critical industrial objects are discussed, analyzed and synthesized. The 6 th International Conference on Fracture Mechanics of Materials and Structural Integrity (FMSI 2019), which is organized under the ESIS auspices, has a certain history. Previous conferences of this series were also held in Lviv in 1987, 1999, 2004, 2009 and 2014 years. The Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine (NASU) and the Ukrainian Society on Fracture Mechanics (USFM) were the main organizers of these conferences. © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers The problems of strength and fracture of the structural materials, as well as the related problems of structural integrity have always been and remai the objects of theoretical and applied studies by a wide range f scientists and practicing engin ers. In particular, owadays the problem of technological and environmental afety of the critical objects of industrial infrastructure becomes more and more important. © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers The problems of strength and fracture of the structural materials, as well as the related problems of structural integrity have always been and remain the objects of theoretical and applied studies by a wide range of scientists and practicing engineers. In particular, nowadays the problem of technological and environmental safety of the critical objects of industrial infrastructure becomes more and more important. In order to analyze the fundamental and applied results in this field of science, the European Structural Integrity Society (ESIS) regularly organizes and supports the international scientific conferences on the European, regional and national level. At these conferences, the new approaches and ideas on the problems of the strength of materials and structures and also the results of their practical applications to the evaluation of the durability and safe operation of the critical industrial objects are discussed, analyzed and synthesized. The 6 th International Conference on Fracture Mechanics of Materials and Structural Integrity (FMSI 2019), which is organized under the ESIS auspices, has a certain history. Previous conferences of this series were also held in Lviv in 1987, 1999, 2004, 2009 and 2014 years. The Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine (NASU) and the Ukrainian Society on Fracture Mechanics (USFM) were the main organizers of these conferences. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. The USFM was founded in Kyiv in 1992 and has been registered as the juridical person in the Ministry of Justice of Ukraine in 1993. USFM unites the Ukrainian scientists, engineers and other citizens of Ukraine, who deal with fracture mechanics of materials as well as with structural integrity. The Society co-operates with scientists and The USFM was founded in Kyiv in 1992 and has been registered as the juridical person in the Ministry of Justice of Ukraine in 1993. USFM unites the Ukrainian scientists, engineers and other citizens of Ukraine, who deal with fracture mechanics of materials as well as with structural integrity. The Society co-operates with scientists and In order to analyze the fundamental and applied results in this fiel of science, the European Structural Integrity Society (ESIS) regularly rganizes a d supports the i ternation l scientific conferences on the European, regional and national level. At these conferences, the new pproaches and ideas on the problems of the strength of materials and structures and also the results of their practic l applications to the evaluation of the durability and safe operation of the critical industrial objects are discussed, analyzed a d synthesized. The 6 th International Co f rence on Fracture Mechanics of Materials and Structural Integrity (FMSI 2019), which is organized under the ESIS auspices, has a certain history. Previou confe en es of this series were also held in Lviv in 1987, 1 99, 2004, 2009 and 2014 years. The Karpe ko Physico-Mechanical Institute of the N tional Academy of Sciences of Uk aine (NASU) and t e Ukrainian Societ on Fracture Mechanics (USF ) were the main organizers of these conferences. The USFM was founded in Kyiv in 1992 and has been registered as the juridical person in the Ministry of Justice of Ukraine in 1993. USFM unites the Ukrainian scientists, engineers and other citizens of Ukraine, who deal with fractu mechanics of materials as well as with structural integrity. The Society co-operates with scientists and 2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers * Corresponding author. Tel.: +38-032-263-2133. E mail address : nykyfor@ipm.lviv.ua * Corresponding author. Tel.: +38-032-263-2133. E-mail address : nykyfor@ipm.lviv.ua * Corresponding author. Tel.: +38-032-263-2133. E-mail address : nykyfor@ipm.lviv.ua

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. 10.1016/j.prostr.2019.07.014

Hryhoriy Nykyforchyn et al. / Procedia Structural Integrity 16 (2019) 1–2 Hryhoriy Nykyforchyn, Ihor Dmytrakh, Olha Zvirko / StructuralIntegrity Procedia 00 (2019) 000 – 000

2

2

engineers of the National Academy of Sciences of Ukraine, higher education institutions and industrial enterprises maintain scientific contacts with other related scientific societies of Ukraine and international organizations, in particular with the European Structural Integrity Society (ESIS). The Society presents Ukraine in the ESIS and participates actively in the three ESIS Technical Committees: TC10 Environmentally Assisted Cracking, TC13 Education and Training, and TC17 Non-Destructive Evaluation. The FMSI 2019 brought together leading scientists, researchers and research scholars to share their experience, research results and scientific ideas regarding key areas of fracture and damage mechanics, structural integrity assessment and maintenance. It has become an interactive platform for discussion of recent advances, trends and practical challenges in the field of fracture mechanics and structural integrity. Over 60 participants from Italy, Spain, Greek, France, USA, Canada, Poland, Hungary, Portugal, China, India, Mexico, Argentina and Ukraine attended the FMSI 2019 Conference. The programme consisted of four main sections:  Fracture and Strength of Materials (four sessions);  Environmentally Assisted Cracking (two sessions);  Non-Destructive Evaluation (two sessions);  Workshop on Applied Mechanics. Accepted extended abstracts were published as Book of Abstracts and were available during the Conference. This special issue contains the full-text conference’s papers accepted for publishing after the review. The efforts of the authors and of the colleagues that volunteered for the review process are kindly acknowledged. We hope that this issue will be interesting for scientists and researches in the field of the fracture mechanics, materials science and structural integrity as well for the lecturers of high schools, and post-graduate students of the corresponding specialties. We also hope that it will be useful for experts and engineers in the industrial sectors, such as the energy generation, machinery, transport, chemical industry, civil engineering, etc.

Hryhoriy Nykyforchyn Ihor Dmytrakh Olha Zvirko

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Procedia Structural Integrity 16 (2019) 169–175

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. © 2019 The Author(s). Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers In the long-term load (static, cyclic, shunting, etc.) much smaller than the destroyed one, as well as during the influence of physical and chemical factors in the material of the structural element, there is the emergence of new and diffusion of existing physical microdefects (vacancies, dislocations), their unification and formation mechanical defects (pores, microcracks). Further development of the last ones leads to the emergence of macrocracks and their subcritical growth. The result of such process is the loss of structural element integrity. All these processes together form the basis of the delayed fracture mechanics of structural materials. An energy approach was used for mathematical models construction of the structural materials delayed fracture under the mechanical loading and physicochemical factors influence. On this basis, the residual life of the structural elements could be determined. The application of this approach is demonstrated on the example of the high-temperature creep crack propagation. At the same time it should be noted that elementary acts in the delayed fracture mechanics are accompanied by the elastic waves emission (acoustic emission) and the new small size surfaces formation that could not be registered by the existing non-destructive testing. Therefore, in our opinion, the acoustic emission (AE) method is the only one that makes it possible to effectively investigate the structural materials delayed fracture kinetics. Nowadays devices are well fitted to capture the AE events parameters (amplitude and total impulses count), but their connection with the delayed fracture acts characteristics (mechanism and size of the new formed surface) are not known. In the previous studies, the authors theoretically found that the newly formed surface size for one AE event is proportional to its amplitude. This made it possible to determine the crack nucleation period as the sum of the AE events amplitudes multiplied by the corresponding constants. On the basis of this and the aforementioned energy approach, mathematical models were created here through the averaged values of the acoustic emission events parameters for the determination of the precritical periods of the delayed cracks growth during the long-term loads and high temperature influence. © 2019 The Author(s). Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” Acoustic emission method in the delayed fracture mechanics of structural materials Zinovij Nazarchuk a , Olexandr Andreykiv b , Valentyn Skalskyi a , Denys Rudavskyi a a Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., 79060 Lviv, Ukraine b Ivan Franko National University, 1, Universytetska St., 79000 Lviv, Ukraine In the long-term load (static, cyclic, shunting, etc.) much smaller than the destroyed one, as well as during the influence of physical and chemical factors in the material of the structural element, there is the emergence of new and diffusion of existing physical microdefects (vacancies, dislocations), their unification and formation mechanical defects (pores, microcracks). Further development of the last ones leads to the emergence of macrocracks and their subcritical growth. The result of such process is the loss of structural element integrity. All these processes together form the basis of the delayed fracture mechanics of structural materials. An energy approach was used for mathematical models construction of the structural materials delayed fracture under the mechanical loading and physicochemical factors influence. On this basis, the residual life of the structural elements could be determined. The application of this approach is demonstrated on the example of the high-temperature creep crack propagation. At the same time it should be noted that elementary acts in the delayed fracture mechanics are accompanied by the elastic waves emission (acoustic emission) and the new small size surfaces formation that could not be registered by the existing non-destructive testing. Therefore, in our opinion, the acoustic emission (AE) method is the only one that makes it possible to effectively investigate the structural materials delayed fracture kinetics. Nowadays devices are well fitted to capture the AE events parameters (amplitude and total impulses count), but their connection with the delayed fracture acts characteristics (mechanism and size of the new formed surface) are not known. In the previous studies, the authors theoretically found that the newly formed surface size for one AE event is proportional to its amplitude. This made it possible to determine the crack nucleation period as the sum of the AE events amplitudes multiplied by the corresponding constants. On the basis of this and the aforementioned energy approach, mathematical models were created here through the averaged values of the acoustic emission events parameters for the determination of the precritical periods of the delayed cracks growth during the long-term loads and high temperature influence. 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” Acoustic emission method in the delayed fracture mechanics of structural materials Zinovij Nazarchuk a , Olexandr Andreykiv b , Valentyn Skalskyi a , Denys Rudavskyi a a Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., 79060 Lviv, Ukraine b Ivan Franko National University, 1, Universytetska St., 79000 Lviv, Ukraine Abstract Abstract

* Corresponding author. Tel.: +38-032-229-65-46. E-mail address: rudavskyy@gmail.com * Corresponding author. Tel.: +38-032-229-65-46. E-mail address: rudavskyy@gmail.com

2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. 10.1016/j.prostr.2019.07.037

Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175

170

2 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000

Keywords: delayed fracture; macromechanisms of material delayed fracture; acoustic emission signals; residual life of structure elements.

1. Introduction

Delayed fracture of structural materials is dangerous due to difficulties in their prediction and diagnostics. Since such fracture is caused by the defects formation or association (vacancies, dislocations, pores, microcracks, macrocracks) during which the elastic waves are irradiated, AE method is the most effective to reveal delayed fracture of structural elements under a long-term static loading. To detect such fracture of structural elements, AE method has been used by Andreykiv et al. (2001), Nazarchuk et al. (2017), Skalskyi et al. (2018). However, it was only a qualitative diagnostics of the process and its initiation. To quantify the material delayed fracture, it is necessary to determine the AE parameters dependences on the parameters of this process. First of all, it concerns the acoustic signals generation theory creation during the elementary fracture acts, in particular the micro and macro defects formation, their growth and association. In this paper we give an example of creating such theory for the case of the high-temperature creep cracks propagation in structural materials. On this basis, an example of quantitative diagnostics of this process is given. This allows determining the parameters based on which it is possible to estimate the residual life of the structure element under long static load and, thus to prevent its unexpected fracture. In the studies of Andreykiv et al. (2009, 2011, 2015a, 2015b, 2017a) the energy approach for creating mathematical models of structural materials delayed fracture under the influence of mechanical, physical and chemical factors is developed. It is based on the first law of thermodynamics: the energy components balance in the loaded engineering system, as well as on their change rates balance. A number of mathematical models (Andreykiv et al. (2009, 2011, 2015a, 2015b, 2017a)) have been created and on this basis the methods for determining the structural elements residual life under mechanical loading (long-term static, cyclic and shunting) and other factors (high temperatures, hydrogen-containing and corrosive-aggressive environments, neutron irradiation) have been developed. Based on these methods the residual life of bimetal structural elements of oil reactor, gas pipelines, etc. was calculated (Andreykiv et al. (2015c, 2016, 2017b)). As an example, here is described the mathematical model of a high-temperature creep flat crack propagation in an infinite body and the period of subcritical crack growth is determined. The model essence is the following. Let us consider a metal body with a crack area S 0 , under long-term loading and high temperature (Fig. 1, a). We assumed that the crack is macroscopic, and the external tension stresses are applied in the way that the stress-strain state is symmetrical relative to the crack plane, and in the vicinity of the crack tip it is described only by the stress intensity factor K I . The problem is to determine the time t = t  when the high-temperature creep crack reaches the critical size and the body fractures. To solve the problem, we apply the energy approach (Andreykiv et al. (2017a)) and based on it we obtain the dependence for determining the subcritical growth period of the high-temperature creep crack 2. Energy approach in delayed fracture mechanics of structural materials

1



   

                        t L c m c t t d A t A    / } 0, ,0 {2 1 1 0 1  

         t t d  0, ,0

(1)

1 1 L

 

dt dS

.

c

L

The initial and final conditions should be added to the equation (1) to complete the mathematical model   0 0, 0 t S S   ;   * * * , t t S t S   ; . ( ) * c t S    (2)

Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175 171 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000 3

Here (0, )   t – a current crack tip opening for the average stress t  in the process zone;  c – critical crack tip opening (0, ,0)   t ;  – current coordinate along the crack front length L ; A 1 , m ,  0 – the high-temperature creep characteristics of the material (Andreykiv et al. (2009)).

3. Determination of creep crack growth subcritical period using the acoustic emission parameters

During the research of the structural elements residual life under long-term static loading it is important to determine the size of the initial defects, the kinetic diagrams parameters for the high-temperature creep cracks growth (values  0 , m , A 2 t ,  c ) and then on the basis of the mathematical model (1), (2) to estimate the residual life (the period of the high-temperature creep crack subcritical growth) t = t  . However, determination of the defects initial sizes and the parameters  0 , m , A 2 t ,  c , which must be found for the already exploited structural element material, is associated with significant technical difficulties (Nazarchuk et al. (2017)). Therefore, we will create a calculation model for estimating the residual life (the period of high-temperature creep crack subcritical growth) of structural elements under long-term static load using the parameters of the signals of AE (SAE), which are measured directly on the loaded element surface. The model essence is the next. Let us consider a three-dimensional body that is weakened by a flat macrocrack S 0 with a smooth convex contour L , which is tensioned at infinitely distant points by equally distributed long-term stresses of intensity p directed perpendicularly to the crack plane (see Fig. 1, a). We have assumed that such body is influenced by a homogeneous high-temperature field, which causes the high temperature creep in the process zone near the crack edge, which in turn causes the crack propagation. The task is to determine the crack growth kinetics and to estimate the subcritical crack growth period t  . As known (Andreykiv et al. (2017a)), the new formed defects area S (the crack growth area) can be determined by the sum of acoustic emission signals amplitudes A i :     n i i S A 1 (3) Here  – is the material AE constant, which is empirical (Andreykiv et al. (2017a)); n – the number of AE signals registered during the crack propagation. Is shown in the study (Andreykiv et al. (2017a)) that under the pure tension the planar creep crack area S change slightly depends on the crack contour geometry, and the crack contour during its propagation approaches to the circular form. Therefore, in this case, the crack area critical size S  is determined by taking into account the Irwin criterion – the stress factor K I critical value K CC in case of high-temperature creep: Hence, based on the formulas (3) and (4) we can write the equation for the SAE amount n determining that the crack radiates during its subcritical growth       n i T CC i A p K S 1 4 4 2 . (5) As follows from the foregoing, the growth jumps of the crack along its contour for high-temperature creep for a microisotropic material can be considered approximately the same for different incubation periods of their propagation. Therefore, the microfracture areas i s that generates each SAE are suppose to be on average the same (here we consider them as microcircles s i  const = s a (Fig. 1, b)). For real materials where the structure local parameters, the microfracture areas and, accordingly, the AE signals amplitude vary considerably, such an assumption would seem to 4 4 2 CC S p K    . (4)

172 Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175 4 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000

be incorrect. However, the material science justifies the grain size notion (the average grain size value on a certain material surface area). Therefore, in order to simplify the technical diagnostics problems solution, we introduce the microfracture area averaged size s a and the SAE amplitude A a that follows it, that is

n

1   i

a i const A A   ,

S t

s n t a

( ) A A n t

( )

( )



   

.

(6)

i

a

a

b

Fig. 1. (a) scheme of a loaded body with crack; (b) scheme of the body section on the crack plane of the initial a 0 and final a  radii.

On the basis of relations (4) – (6) we find SAE number critical value that corresponds to the spontaneous crack propagation start

T CC a n A p K S        4 4 1 1 2 .

(7)

4. Sack's problem analogue

As mentioned in Andreykiv et al. (2017a), in case of the body pure tension the plane creep crack area change slightly depends on the crack contour configuration and this dependence can be approximated by the rate of the penny-shaped crack area change. Then, let us consider the problem of the creep crack growth subcritical period determination in case of crack with a circle contour L of current radius ( ) a a t  , that is the Sack ’s problem analogue for a high-temperature creep crack (see Fig. 1, a). In this case, the mathematical problem (1) – (2) for the macrocrack is reduced to   2 2 1 2 2 2 2 ) (1 /       I CC m thc m I m t CC dt A K K K K K da , . ; ( ) , ( ) ; 0, (0) 0 CC I t a a t t a t a K a K          (8)

2

p S 2

( ) S S t  is written by the formula

K I

0,72 

Here

and the rate of the circular crack area change

0,28 0,5  

dt da /

dt S dS /

.

(9)

On this basis the mathematical problem (8) is reduced to form

 

   

2  S A S S S S m m m thc t cc

m

m S S

  m

1



,

/ dt dS

2  

1 (1

)



thc

cc

Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175 173 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000 5

t

, ( ) S S t t S t   ;

; ( ) S K S K  

0, (0)

.



(10)

I

CC

0









Here S 0 is the initial crack area size; S thc is the least size of the creep crack to start growth at the given external load value; S  is the crack critical size. Using the relation (6) the mathematical model (10) can also be written as follows

 

   

t

n 0, (0) 0;

     t t n t , ( )

n



2 1 1 A nA n n n n  m m m thc    t a

m

m m

1



)   

,

.

(11)

/ dt dn

n n

2  

1 (1





thc

Here n  is the SAE pulses critical number before spontaneous fracture which is determined by the formula (7); n thc – the number of the SAE events to form crack area S thc , which does not growth under the given value of external load p ( thc a thc A S n 1 1     ). Integrating the differential equation (11) for given initial and final conditions we obtain the formula (12) to determine the crack subcritical growth period t = t 

n

  

1



 

 

A A n n n m m 1   

n n n n m m m ) 

m



t

dn

0,28

(1

1





.

(12)

t

a

thc

thc

2







0

Thus, since the characteristics m , A 2 t ,  , n thc , A a have been found from the experiment the subcritical period of high-temperature creep crack growth t = t  is given by the formula (12). Along with this the important, for the technical diagnostics of the engineering structures materials, approximate formulas for the current cracks sizes S determination by the SAE parameters (Andreykiv et al. (2017a)) are shown as follows

m

m 0,5(3 1)

m

1 2

t A K 2    1 2 CC

2  

B

A

 

2 m B p n

 ,

.

(13)

0,5( 1)  m

S



a

0

0

Thus, if the material characteristics B 0 , m are known and the SAE intensity n  for a homogeneous load p has been experimentally found, then the crack size in the structural element are approximated by formula (13) in the case when any other SAE sources are not present. 5. Methodology of kinetic diagrams construction of the high-temperature creep cracks growth using the acoustic emission method During the experimental studies of the high-temperature creep cracks growth, in particular for the kinetic diagrams V ~ K I construction, the long-term pure bending load scheme for a beam specimen (cross section h 0 × h 1 ) with a lateral crack (initial length l 0 ) (see Fig. 2, a) is used. For this case, based on the results (Andreykiv et al. (2017a)) the following calculation model with acoustic emission parameters is created   1 2 2 2 1 2 2 2 1 ( )] [1 ( ) ) ( /         dt h K A A K n K K K n dn CC In m thc m In t a m CC ; . , ( ) 0, (0) 0;        t t n t n t n (14)

0 1 / ( ) A n h h S h h a      , ( )) 24,81 23,17 16 4 3    o 1 0 1

dS

dt

A dn a

dt

( ) ( ( ) K S K A n K n In a I I    , )

/

/

 

,

Here

1,5

2    

( ) (6 /  K S M h h I 1

) (1,99 2,47 12,97    

(15)

After integrating equation (14) under given conditions, to determine the high-temperature creep crack period of subcritical growth t = t  in the beam specimen, we obtain the formula

Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175

174

6 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000   K K n K n K dn t A K A h n m thc m In CC In t m a CC           0 2 1 2 2 2 1 2 1 2 ( ) ( )] ) [1 ( . (16) In order to determine the t  value from formula (16), it is necessary to have the values of the parameters m , A 2 t ,  , A a , n  , K thc , K CC . We determine the n  value by a formula similar to (7). Other values are found as follows. Let us write the relation (14) as   1 2 2 2 2 3 ( )] [1 ( )      n B K n K K K n CC In m thc m In  , (17)

m

2



t a B A A h K 2 1 3  

. Then with the help of the above mentioned loading scheme (Fig. 2, a), we carry out

where

CC

In n K ~  . In this case, using formula (15), changing the

experimental studies and construct a graphical dependence

specimen load parameters M and the crack length l , we set the stress intensity factor ( ) i ( ) i In K , using the experimental method described in (Andreykiv et al. (2017a)), we determine the SAE intensity n  . Such measurements are made at least four times for different values ( ) i In K and at least three values of t n  should to be got for each value ( ) i In K (Fig. 2, b). In K value within the CC i In thc K K K   ( ) limits. For these values

a

b

In n K ~  scheme.

Fig. 2. (a) beam with a lateral crack load scheme; (b) dependence

The obtained values of ( ) i In K , t n  and formula (17) are entered into the least squares method database to find the characteristics B 3 , K thc , K CC . These characteristics are finally substituted into the formula (17) and the kinetic diagram In n K ~  is obtained that is analytical dependence of the SAE intensity on stress intensity factor for the high-temperature creep crack growth. Such a kinetic diagram constructing scheme is shown at the Fig. 2, b. Along with the kinetic diagrams In n K ~  for determining the high-temperature creep cracks subcritical growth period t = t  , the kinetic diagrams V ~ K I that were used earlier are important. The method for constructing these diagrams is described in (Andreykiv et al. (2017a)). However, the kinetic diagrams V ~ K I direct construction without the AE method use is labor-intensive, due to large time of the experimental research. Therefore, we propose to construct first less time-consuming kinetic diagrams In n K ~  and then, with the help of the according analytical decoder convert them to the kinetic diagrams V ~ K I . The essence of this analytical decoder is as follows. With the help of relations (6) and (15) we can obtain the formula that connects V and n  values

V B h n  1 4 1  

.

(18)

Zinovij Nazarchuk et al. / Procedia Structural Integrity 16 (2019) 169–175 175 Zinovij Nazarchuk, Olexandr Andreykiv, Valentyn Skalskyi, Denys Rudavskyi / Structural Integrity Procedia 00 (2019) 000 – 000 7

The constant B 4 in formula (18) is defined as follows. For some high values , the high-temperature creep crack growth rate V will be significant, so that its visible growth will take place at short time intervals t i  . For these values of ( ) i In K we find i n  . Then we determine the constant B 4 by the formula         k i i i i l t B k h n 1 1 1 1 1 4 ( ) ( )  . (19) CC i In K K  ( )

3  k . In other words, at least three length changes of low-temperature creep

In formula (19) the value k must be

crack have to be fixed when measuring the values of l i  , t i  , i n  . Thus, using the formulas (18) and (19), relatively easily accessible kinetic diagram

In n K ~  can be translated into

an experimentally hard-to-reach diagram V ~ K I .

6. Conclusions

A new method for the investigation of the materials delayed fracture and determination of the structural elements residual life under the influence of the mechanical and physico-chemical factors is proposed. This method is based on the author's previously developed energy approach to the investigation of cracks subcritical growth in materials and on the known from the literature correlation between the new-formed defects area and acoustic emission parameters. The method application is demonstrated on the example of the residual life determination of the structural elements operating under long-term static load and high temperature. With the help of this method an effective methodology was developed for kinetic diagrams constructing of high-temperature creep cracks growth in metallic materials.

Acknowledgements

The investigation has been supported by the budget Program “ Support of development of scientific research priority directions ” ( KPKVK-6541230).

References

Andreikiv, O. E., Skal's'kyi, V. R., Serhienko, O. M., 2001. Acoustic-emission criteria for rapid analysis of internal defects in composite materials. Materials Science 1, 106 – 117. Andreikiv, O. E., Lesiv, R. M., Dolins’ka , I. Ya., 2009. Dependence of the period of subcritical growth of a creep fatigue crack on the duration of loading cycles. Materials Science 4, 494 – 503. Andreikiv, O . E., Dolins’ka , I. Ya., Yavors’ka , N.V., 2011. Estimation of the periods of initiation and propagation of creep-fatigue cracks in thin walled structural elements. Materials Science 3, 273 – 283. Andreikiv, O.E., Dobrovol’s’ka , L.N. , Yavors’ka , N.V., 2015a. Computational Model of Crack Propagation in Bimetallic Materials for High Concentrations of Hydrogen and High Temperatures. Materials Science 1, 76−87. Andreikiv, O.E.. Kukhar, V.Z,. Dolinska, I.Ya., 2015b. Propagation of High-Temperature Creep Cracks in Metals Subjected to Neutron Irradiation (A Survey). Materials Science 3, 299 – 310. Andreikiv, O. Ye., Skal’s’kyi , V. R., Dolinska, I. Ya., Opanasovych, V. K. , Dubyts’kyi , O. S., 2015c. Fatigue crack propagation kinetics in bimetallic plates. Strength of Materials 5, 662 – 669. Andreikiv, O. E., Dolinska, I.Ya, Kukhar, V.Z., Shtoiko, I.P., 2016. Influence of Hydrogen on the Residual Service Life of a Gas Pipeline in the Maneuvering Mode of Operation. Materials Science 4, 500 – 508. Andreykiv, O. Ye., Skalskyi, V. R., Dolinska, I. Ya., 2017a. Slow fracture of materials under local creep. Lviv, Ivan Franko National University of Lviv, 400. (In Ukrainian) Andreikiv, O. Ye., Skal’s’kyi , V. R., Opanasovych, V.К. , Dolins’ka , I. Ya., Shtoiko, I. P., 2017b. Determination of the Period of Subcritical Growth of Creep-Fatigue Cracks Under Block Loading. Journal of Mathematical Sciences 2, 103 – 113. Nazarchuk, Z., Skalskyi, V., Serhiyenko, O., 2017. Acoustic Emission: Methodology and Application. Foundations of Engineering Mechanics. Springer, pp. 283. Skalskyi, V., Andreikiv, O., Dolinska, I., 2018. Assessment of subcritical crack growth in hydrogen-containing environment by the parameters of acoustic emission signals. International Journal of Hydrogen Energy 43, 5217 – 5224.

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Procedia Structural Integrity 16 (2019) 176–183

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers The paper deals with the issues of an application of acoustic emission (AE) method of continuous monitoring, with prediction of breaking load. System of continuous AE monitoring of pipelines of hot industrial steam overheating in power unit #1 at Kiev TPP-6 has been developed and put into trial operation. Preliminary the acoustic properties of steam pipeline materials were studied; high-temperature AE studies of steam pipeline material were conducted. Developed procedure allows determination of structure material breaking load, based on AE data, under actual operating conditions of the structure at any mo ent of time, irrespective of operating time volume or temperature variations. Breaking load predicted by continuous AE onitoring system is determined with accuracy sufficient for practical purposes. To ensure the time margin when taking the decision on the monitored facility state, safety factors were established for the predicted breaking load, which are automatically determined by the monitoring system, depending on the degree of danger of the destructive processes developing in the material. Monitoring schematic and features of practical application of monitoring system are presented. Applied procedure and technology allow determination of the coordinates of monitored facility section with minimum breaking load magnitude. Remote access allows performance of author’s supervision of system operation through the Internet. © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” AE technology in continuous monitoring of high-temperature pipelines at heating power plants Borys Paton a , Leonid Lobanov a , Anatoly Nedoseka a , Stanislav Nedoseka a *, Mihail Yaremenko a , Janos Gereb b , Yuri Gladyshev c , Vadim Beshun c , Alexandr Bychkov c , Alexandr Gaidukevich c a E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine, 11, Kazymyr Malevich St., Kyiv, 03150, Ukraine b Geréb és Társa Kft, 28, Honfoglalás St., Budapest, 1029, Hungary c SVP “Kievskii TPP” PJSC “Kievenergo”, 57, Lva Tolstogo St., Kyiv, 01032, Ukraine The paper deals with the issues of an application of acoustic emission (AE) method of continuous monitoring, with prediction of breaking load. System of continuous AE monitoring of pipelines of hot industrial steam overheating in power unit #1 at Kiev TPP-6 has been developed and put into trial operation. Preliminary the acoustic properties of steam pipeline materials were studied; high-temperature AE studies of steam pipeline material were conducted. Developed procedure allows determination of structure material breaking load, based on AE data, under actual operating conditions of the structure at any moment of time, irrespective of operating time volume or temperature variations. Breaking load predicted by continuous AE monitoring system is determined with accuracy sufficient for practical purposes. To ensure the time margin when taking the decision on the monitored facility state, safety factors were established for the predicted breaking load, which are automatically determined by the monitoring system, depending on the degree of danger of the destructive processes developing in the material. Monitoring schematic and features of practical application of monitoring system are presented. Applied procedure and technology allow determination of the coordinates of monitored facility section with minimum breaking load magnitude. Remote access allows performance of author’s supervision of system operation through the Internet. 6th International Conference “Fracture Mechanics f Materials and Structural Integrity” AE technology in continuous monitoring of high-temperature pipelines at heating power plants Borys Paton a , Leonid Lobanov a , Anatoly Nedoseka a , Stanislav Nedoseka a *, Mihail Yaremenko a , Janos Gereb b , Yuri Gladyshev c , Vadim Beshun c , Alexandr Bychkov c , Alexandr Gaidukevich c a E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine, 11, Kazymyr Malevich St., Kyiv, 03150, Ukraine b Geréb és Társa Kft, 28, Honfoglalás St., Budapest, 1029, Hungary c SVP “Kievskii TPP” PJSC “Kievenergo”, 57, Lva Tolstogo St., Kyiv, 01032, Ukraine Abstract Abstract

* Corresponding author. Tel.: +38-050-351-3472. E-mail address: st_private@hotmail.com

2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers 2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers * Corresponding author. Tel.: +38-050-351-3472. E-mail address: st_private@hotmail.com

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers. 10.1016/j.prostr.2019.07.038

Borys Paton et al. / Procedia Structural Integrity 16 (2019) 176–183

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Borys Paton et al. / Structural Integrity Procedia 00 (2019) 000 – 000

2

Keywords: Acoustic emission; continuous monitoring; pipeline; high temperatures; prediction; power plant; breaking load.

1. Introduction

Pipelines exposed to high temperatures in operation, are high-risk industrial facilities. During operation, the metal of which they are made accumulates damage, caused, in particular, by violation of operating conditions, varying loads, corrosion and chemical processes and a number of other factors. As a rule, there is no direct dependence between pipeline operating period and degree of its damage, and it is also quite difficult to separate damage caused by the impact of each of the determinant factors. In this connection, comprehensive assessment of material damage, without detailing the factors, causing the damage, appears to be the most promising. Its main objective is accident prevention. Irrespective of the causes for accident occurrence, their consequences can be quite grave. Therefore, continuous monitoring of structure serviceability and its prediction for a period of time required to prevent the danger, becomes urgent to ensure safe operation of structures. This is largely due to the fact that calculations of load-bearing capacity of structures and structural elements, providing their sufficient operational reliability, are difficult for a number of reasons, the most important of which are:  insufficient study, incompleteness or unreliability of initial data for calculation performance  complexity, and more often impossibility of prompt acquisition of data in service on current state of structures, particularly, at their complex loading  danger, and sometime, impossibility of conducting experiments, in order to determine the load-bearing capacity  inaccessibility of facilities in some cases for conducting reliable nondestructive testing. As a result, any structure, even after passing current testing, has problem areas, substantiation of operating reliability of which is quite complicated, and sometimes even impossible, particularly after extended operating period. An effective tool for solving the problem of ensuring operating reliability of structures is creation of information measurement systems, allowing its assessment to be performed already at the testing stage under the conditions of forthcoming operation, as well as monitoring this structure serviceability directly in operation. Modern development of computer technology, radio electronics, applied mathematics, test equipment, materials strength and continuum mechanics science, allow solving the problem of continuous monitoring of structure performance in service at a quite high level. Functioning of information-measuring systems requires regular acquisition of on-line data, primarily about the state of structure components and various kinds of defects, which accumulate during operation. With availability of data about the structure and respective processing of this information, its load-bearing capacity can be promptly evaluated in real-time. This, in particular, provides large engineering and economic benefits in those engineering fields, where lack of knowledge about the actual service loads, true state of structure material, changing during its operation, may lead to essential errors, when assigning the working parameters. At present, automatic monitoring systems are rather widely applied which are based on checking the running of technological processes, associated with processing, producing or application of various products in energy cycles. At the same time, much less attention is given to monitoring the state of structures applied for implementation of these processes. As a rule, structure performance is assessed at scheduled stopping of the production process, when conducting number of technological operations on ensuring the technical possibility of inspection. Most often it is impossible to perform 100% inspection of the structure because of extremely large scope and cost of the work, involved in its performance. As a rule, just individual sections are selected for inspection, which do not always correspond to the most damaged areas of the structure. The problem of structure monitoring can be solved with success with application of the method of AE, which emerges in materials at critical combination of certain impact factors, leading to emergence or development of defects. A feature of this method is the ability to check material state at large distances from the site of transducer 2. Results of experimental studies and their discussion