1

New On-line Monitoring Methodology for Improving

Performance of Ageing Critical Structures, Systems and

Components

Technical Meeting on Fatigue Assessment in Light Water Reactors for Long Term

Operation: Good Practices and Lessons Learned

6-8 July, Areva, Erlangen Germany

Dr. Bakirov M.

2

General approaches to calculation of load of equipment in Russian and ASME codes

are very similar. But, there are some differences

.

0,2 0,2min ,T T

m m pR n R n

For pressure-loaded elements , the following values of nominal allowable stresses :

Russian norms (PNAE G-7-002-86): ASME code:

Comparison of Russian and ASME codes

0.22,6; 1,5mn n

.

;10

9;

5.1;

3;

3min

2.0

20

2.020

00 T

ppT

mmm

RRRRS

ASME: events are grouped (PNAE G-7-002-86 very similar)

Condition I – normal operation

Condition II –faults that occur with moderate frequency

Condition III – infrequent faults that may accure

Condition IV –limiting faults postulated but not expected.

3

, МПаaF

0N

, МПаaF

0N

, МПаaF 0N- permissible amplitude of conditional elastic stress

- permissible number of cycles

Including influence of the environment Excluding influence of the environment

Fatigue curve

Determination of acceptable number of cycles or allowable stress amplitude for a

given number of cycles is carried out through the estimated fatigue curves or

according to formulae (adjusted calculation).

Calculated fatigue curves are determined by taking into account of dominancy of

average cycle stress and safety factors nσ =2 и nN = 10 (In

ASME nN = 20)

maxF aF

4

Fatigue cracks

Strength, Life time, Environment,

Structures, Surface condition,

Manufacturing defects have significant

influence on born and growing of fatigue

cracks.

One solution is in the extrapolation of

formulas of linear elastic fracture

mechanics for stress intensity factor

(SIF) on essentially nonlinear stage of

deformation using functions of plasticity

amendments.

Conditions of cyclic loading under given initial crack sizes are determined

by the magnitude of SIF (∆K) , stress ratio (R) and number of cycles (N).

💔

5

Fatigue crack growth

Diagram of cyclic crack growth is represented

with a broken line, the segments of which are

approximated by the Paris-law equation:

where the characteristics of the material Co, m

depending on loading conditions (class and

condition of the metal, temperature, working

environment, frequency of cycles.

0

m

eff

daC K

dN

4 1eff

KK

R

Material Co m

Alloy steels of the type Cr-Mo-V, Cr-Ni-Mo-V and welds

2,7 2,810-11

Carbon steels and their welded joints 3,1 1,5 10-

11

Chromium-Nickel corrosion-resistant austenitic steel and welds

3,3 5,210-12

6

Probability of Failure and Microstructure Changing on LTO

Slip

Slip

Slip

Brittle Fracture

(unstable cracks)

Visible growth and

connection of cracks

Fine cracks visible with

naked eye

Cracks visible with

dyes penetrants

Very fine microscopic cracks that

may or may not propagate

Str

ess

levels

Time of operation

Level A

Beginning of defect

formation

Level B

Formation of

acceptable operational

defects

Level C

Formation of

unacceptable

operational defects.

! LTM is required !

Level D

Further operation is

impossible

Ultra

Low

Risk

Low

Risk

Medium

Risk

High

Risk

Ultra

High Risk

Catastr

ophe

P(t)

6

7

mo

nit

ori

ng o

f in

tegri

ty

time of operation

design-experimental analysis

of the accumulated damage

T0 +1 +2 +3 +4 +5

P, MPa T, 0С

σ, MPa T, 0С

L, mm Alloy of abilities of:

Monitoring integrity&loads

and FAM Stress analysis

ai

ai→ [a]

Philosophy of the on-line monitoring

8

Examples of practical application of the on-line

monitoring philosophy

Example № 1. Design-experimental on-line monitoring of

operational damageability of steam generator’s critical zones on

WWER-1000 Units.

Example № 2. Design-experimental on-line monitoring of thermal

stratification of surge line on WWER-1000 Units.

9

Object of investigation: nozzle of the collector the vessel of PGV-1000M steam

generator (weld joint № 111).

Weld joint №111

Headache

During 10 years born and growing of cracks in

welding zone №111 (non-compensated damage) !

Opera

tional

cra

cks

Example № 1. History

Statistics of WJ №111 cracking from 1998-2013

Primary circuit

of WWER-1000

Critical nozzle

10

Main stages of New Failure Analysis 1. Development of the on-line monitoring procedure.

2. Development of technology of on-line monitoring of metal integrity based

on ultrasonic (US) and acoustic emission (AE) methods and strain –

displacement-temperature.

3. Design of the monitoring system architecture.

4. Manufacturing of the monitoring system components.

5. Manufacturing and testing of the system components on a full-scale test-

bench.

6. Mounting of the monitoring system on steam generators of the

Novovoronezh NPP, Unit 5.

7. Development of FEM model of the primary circuit.

8. Analysis of on-line monitoring results.

9. Teaching and calibration of FEM model.

10.Design- FEM of life time stress-strain analysis.

11.Real-time investigation of causes of failure.

12.Development of compensation procedure and checking its effectiveness.

11

Monitoring of the technical state of the inspected object

Non-destructive inspection of

the metal condition during

scheduled maintenance

Ultrasonic inspection of the

metal integrity by the

phased-array techniques

On-line monitoring of the metal condition and

of the actual thermo-force loading during NPP unit operation

Measuring of the actual

mechanical properties

Assessment of residual

stresses using magnetic

methods

Ultrasonic on-line monitoring

of the metal integrity

Acoustic-emission

on-line monitoring of the

propagating defects

Design-experimental modeling of the operational damageability and

justification of strength and survivability of the inspected object

Preliminary strength

analysis

Selection of places for mounting

of sensors of the on-line

monitoring system

Calibration of the finite-element

modulus using experimental data

Monitoring of the thermo-force loading:

- deformations in the most loaded zones,

- relative displacements,

- local temperature fields,

- work parameters (pressure, temperature, etc.)

Development of

compensating

measures

Stage 1. Development of the on-line monitoring procedure

12

Stage 2. Development of technology of on-line monitoring of metal

integrity based on ultrasonic (US) and acoustic emission (AE) methods

Acoustic waveguide with US sensors

AE antenna with high-temperature AE sensors Experimental data

+

US monitoring

AE monitoring

Problem issues:

Long time of monitoring (1 year).

Surface temperature 320 0С.

High level of radiation.

Unavailable access for service.

13

Stage 3. Development of the monitoring system architecture

ARCHITECTURE

On-line monitoring of growth of

hazardous defects by US method

On-line monitoring of origination and growth of

defects in WJ №111 (100 % along a perimeter)

by AE method Expert US inspection of the WJ №111 (1-3

critical zone of a perimeter) during unit

planned outage

Monitoring of metal integrity

Monitoring of leakage

Monitoring of actual thermo-force

operational loading

+

+

BASE FUNCTIONS

14

Stage 4. Designing of the monitoring system components

Fastening of AS sensors Fastening of US sensors

Control of displacements of equipment supports Electronic module

15

Stage 5. Manufacturing and testing of the system

components on a full-scale test-bench

Full-scale test-bench with mounted components

Server

Electronic module

16

Stage 6. Mounting of the monitoring system on steam

generators of the Novovoronezh NPP, Unit 5

Components of the AE subsystem Components of the US subsystem

Electronic module Strain gauges+thermocouple Displacement sensors

17

+0.0

+4.0

+8.0

+12.0

+16.0

+20.0

+24.0

+28.0

+32.0

+36.0

+40.0

+44.0

+48.0

+60

+120

+180

+240

+300

+360

+420

+480

+540

+600

+660

+720

+780SX [MPa]

SY [MPa]

SZ [MPa]

SI [MPa]

STEP=1

Distance from first point on the line

Y-v

alu

es

Hydro-tests of the secondary circuit

Critical zone

Distribution of stresses in the crack front

The maximum level of

relative-elastic stresses

(720 MPa) in the zone of

the defect are fixed in the

mode of hydro-tests of the

secondary circuit.

Stage 7. Development of FEM model of the primary circuit

18

23.08 Осевые деформации на СС 111 5ПГ-4 при

прохождении температурной аномалии № 8

-60,00

-50,00

-40,00

-30,00

-20,00

-10,00

0,00

10,00

6:00 6:30 7:00 7:30 8:00 8:30 9:00

Время, ч

Деф

ор

мац

ия

, 0.5

*10

-5

А (СС111, 0º, ос.) Б (СС111, 90º, ос.) В (СС111, 180º, ос.)

Г (СС111, 225º, ос.) Е (СС111, 315º, ос.)

Stage 8. Analysis of on-line monitoring results

New defect

Conclusion. Non-design thermo-force loads lead to born and growing of

operational cracks.

Revealed thermal shocks! High non-design loads

AE monitoring Expert US inspection

19

Comparison of calculation and experimental data

in the control nozzles of FEM-model in different

operational modes and at different levels of work

loading parameters

Comparison of calculation and

experimental data in such operating modes

and time periods when only one loading

parameter changes, and the other

parameters do not change

Adjustment of the calculative

modulus: improvement of the

software, refinement of the

monitored object’s geometry,

changing of the finite-element mesh

in definite zones, correction of the

boundary condition, etc.

The calculative modulus is calibrated

The

cal

cula

tive

mod

ulus

mus

t be

adju

sted

- data do not coincide

2

1

2

Comparison of calculation and

experimental data in cases when

simultaneous changing of two or more

loading parameters is observed

1

FEM-modulus works efficiently,

the loading processes in different

operational modes are modeled reliably

2

1

- data coincide

Stage 9. Teaching leeds calibration of FEM model

20

Stage 10. Design-experimental stress analysis

0

6

12

18

24

30

36

42

48

54

60

66

72

0 5 10 15 20

Число циклов нагружения

То

лщ

ин

а с

тен

ки

, м

м

ΔTCC №111 = 30 C ΔTCC №111 = 60 C ΔTCC №111 = 90 C

Conclusion. Thermal shocks cause stresses exceeding the yield strength value . Growth of

initial defects to a through wall crack can occur at small number of cyclic loads initiated by

thermal shocks.

σ, MPa

а→[a]

dL/dN

21

Stage 11. Real-time investigation of thermal shocks causes

This program was made specially for express analysis of technical needs of NPP staffs

23.08 Расход периодической продувки

0

5

10

15

20

25

30

35

23.08.12

0:00

23.08.12

2:00

23.08.12

4:00

23.08.12

6:00

23.08.12

8:00

23.08.12

10:00

23.08.12

12:00

Дата, время

Расхо

д,

м3/ч

Расход воды периодической продувки ПГ-4

23.08 Давление в 2 контуре

0

10

20

30

40

50

60

70

80

90

100

23.08.12

0:00

23.08.12

2:00

23.08.12

4:00

23.08.12

6:00

23.08.12

8:00

23.08.12

10:00

23.08.12

12:00

Дата, время

Да

вл

ен

ие

, кгс

/см

2

Давление пара в ПГ-4 Давление питательной воды в коллекторе №2

Conclusion. Absence of water discharge in the SG blowdown system causes cooling

down of water in blowdown pipelines, pressure jumps in secondary circuit lead to

back streaming of cold water to SG and to formation of a thermal shock.

SG blowdown is switched off Pressure jumps in secondary circuit

+

22

~ ~ ~ ~

~

~

~

~

~

~

~

~

~ в расширитель продувки

ПГ-1 ПГ-2 ПГ-3 ПГ-4

1 2

3

Conclusions.

1. Compensating measures on modification of SG blowdown regalement

had been applied.

2. Effectiveness of compensating measures was confirmed – the subsequent

on-line monitoring of SG on Novovoronezh NPP, Unit 5 during 2 years show

shat thermal shocks do not occur, dominating thermo-force factor of

operational damaging was successfully eliminated.

Stage 12. Development of compensation procedure and

checking its effectiveness

Scheme of cut-off of SG blowdown pipelines

23

Example № 2. History of stratification influence

Object of investigation: surge line of the primary circuit pressurizer system of

WWER-1000 Unit.

Recommendations of the audit

RE.NNPP.NSO.11.13

It is necessary to carry out analysis

of international experience on

thermal stratification study as

regards to the primary circuit

pipelines, and also to provide

assessments of thermal fatigue

effects on WWER-1000 NPPs.

Objective

Estimate real level of stratification for substantiation of long time extension

for additional 30 years.

Surge line

24 24 24

The effect of thermal stratification

(physics)

Stratification occurs at horizontal sections of pipelines when coolant having different temperatures flows with low rates and causes stratification of the whater on «cold» (lower) and «hot» (upper) layers.

25

1. Development of the monitoring system architecture .

2. Laboratory tests of strain gauges at temperatures up to 400 0С.

3. Mounting of the monitoring system on surge line

of the Novovoronezh NPP, Unit 5 during all fuel company (1

year).

4. Analysis of on-line monitoring results.

5. Development of FEM model of the surge line.

6. Teaching and modernization FEM model and calculation by

using of experimental data.Recommendation to NDT control.

7. Analysis of results of surge line’s weld joints non-destructive

inspection in recommended zones.

8. Development of compensating procedures and check of their

effectiveness.

Main stages of work

26

Stage 1. Development of the monitoring system architecture

Monitoring of temperatures and

deformations in control sections

of the surge line

26 26

Scheme of thermocouples and strain gauges location

ARCHITECTURE BASE FUNCTIONS

27

Def

orm

atio

n

Time, sec

Def

orm

atio

n

Time, sec

Stage 2. Laboratory tests of strain gauges at temperatures

up to 400 0С

28

Mounting of thermocouples

Electronic module

Mounting of strain gauges

Mounting of protective covers

Stage 3. Mounting of the monitoring system on surge line

of the Novovoronezh NPP, Unit 5

29 29

Stage 4. Analysis of on-line monitoring results

22-23.02 Распределение температур в сечении IV

20

70

120

170

220

270

320

370

22.02.14

0:00

22.02.14

6:00

22.02.14

12:00

22.02.14

18:00

23.02.14

0:00

23.02.14

6:00

23.02.14

12:00

23.02.14

18:00

24.02.14

0:00

Дата, время

Тем

пер

ату

ра,

0С

IV-T1 IV-T2 IV-T3 IV-T4 IV-T5

21.02-23.02 Тепловая мощность средневзвешенная

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

21.02.14 0:00 22.02.14 0:00 23.02.14 0:00 24.02.14 0:00

Дата, время

Мо

щн

ость

, М

Вт

Тепловая мощность средневзвешенная

22-23.02 Распределение температур в сечении I

20

70

120

170

220

270

320

370

22.02.14

0:00

22.02.14

6:00

22.02.14

12:00

22.02.14

18:00

23.02.14

0:00

23.02.14

6:00

23.02.14

12:00

23.02.14

18:00

24.02.14

0:00

Дата, время

Тем

пер

ату

ра,

0С

I-T1 I-T2 I-T3 I-T4 I-T5 TГЦТ1 TГЦТ2

22-23.02 Распределение температур в сечении II

20

70

120

170

220

270

320

370

22.02.14

0:00

22.02.14

3:00

22.02.14

6:00

22.02.14

9:00

22.02.14

12:00

22.02.14

15:00

22.02.14

18:00

22.02.14

21:00

23.02.14

0:00

Дата, время

Тем

пер

ату

ра,

0С

II-T1 II-T2 II-T3 II-T4 II-T5

22-23.02 Распределение температур в сечении III

20

70

120

170

220

270

320

370

22.02.14

0:00

22.02.14

3:00

22.02.14

6:00

22.02.14

9:00

22.02.14

12:00

22.02.14

15:00

22.02.14

18:00

22.02.14

21:00

23.02.14

0:00

Дата, времяТ

ем

пер

ату

ра,

0С

III-T1 III-T2 III-T3 III-T4 III-T5

In sections I, II, III stratification is absent

!!!Big thermal stratification in section IV!!!

Conclusion. Temperature

difference at control section IV

due to thermal stratification

reached 160°С, high thermal-

force stresses were revealed.

30

Stage 5. Development of FEM model of the surge line

ДТ

31

Stage 6. Design-experimental stress analysis

Conclusion. Zones of maximum accumulated cyclic damage locate at

outer surface of the dissimilar weld joint №7.

Weld №7

T, C σ, MPa

a→[a]

32

Conclusion. It is necessary to develop effective compensating procedure to solve the

problem of stratification cracking of dissimilar weld of surge line.

Thermal stratification

Stage 7. Analysis of results of surge line’s weld joints

non-destructive inspection in recommended zones

Cracks visible with dyes penetrants

33 33

Input parameters: roller size, force of rolling, number of loading cycles, velocity of rolling. Output parameters: surface roughness, loads on roller, distribution of residual stresses, new mechanical properties of surface

FEM modeling of the hardening process Surface rolling

hammering

Conclusions.

1. It is not possible to change operational modes of the pressurizer system and

additional cyclic loads caused by thermal stratification will influence in future.

2. Simple and original solution: change strength properties of metal in surface layer

where operational cracks had been found, i.e. increase yield and ultimate strength

by use of the hardening method (surface rolling hammering)

Stage 8. Development of compensating procedure and

check of their effectiveness

34 FEM model of the test-bench 3-D model of the test-bench

Calculation of reaction of the support

Stage 8.1. Design of the laboratory test-bench

35 35

Stage 8.2. Manufacturing of the laboratory test-bench,

testing of the technology and rolling modes

36

37

38 38

Video of the rolling process on the laboratory test bench

39

Using the technology of continuous registration of load

/indentation depth diagram in agreement with ISO 14577 it

is possible to solve a problem of reconstruction of

conventional stress – strain diagram.

t

P

P

t

Indentation diagram

d D

t

P

Stages of convertation of indentation diagram

f(∆t/D)

P

2 4

d P σ ×

× p

σp σm

f(∆l/l0)

S

The method is based on the phenomenon of the similarity of

indentation diagram with plastic hardening part of stress – strain

diagram. It was taken as a basis of new Russian standard GOST

56232 -2014 Determination of «stress – strain» diagram in the

course of ball instrumental indentation.

FEM - distribution of plastic strain

Stage 8.3. Selection of the method for measurement of

metal mechanical properties after hardening

Hardness tester Mubatec-HU1

Different zones of dissimilar welded joint were tested by

hardnes stester Mubatec-HU1 using ball instrumental

indentation technique.

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80

Depth, mkm

Fo

rce,

N

Base Metal

HAZ

Welding 2

Welding 1

Welded seam

0

100

200

300

400

500

600

700

800

900

1000

0 2 4 6 8 10 12

Strain, %

Str

es

s,

MP

a Base Metal

HAZ

Welding 2

Welding 1

Welded seam

1 2 3 4 5

Stress – strain diagrams for all tested materials were derived

which will be used while constructing of numerical model Material HB

Rp0,2,

MРa Rm,

MРa

1 Base Metal 198 456 581

2 Heat Affected Zone 274 693 814

3 Welding 1 197 412 617

4 Welding 2 211 456 647

5 Welded seam 233 534 679

Stage 8.4. Selection of control zones for measurement

of metal mechanical properties

41

Hardness tester Mubatec-

HU1 - Testing of sample tube

Inspection of surge line on

NPP Kozlodui

(Bulgaria 2015)

0

200

400

600

800

1000

1200

1400

1600

0 50 100 150

Depth, mkm

Fo

rce, N

Initial

Rolled

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10

Strain, %

Str

ess, M

Pa

Initial

Rolled

The results of rolling of sample 10GN2MFA tube were

tested by ball indentation method.

Stage 8.5. Analysis of results of measurement of metal

mechanical properties before and after hardening

Conclusion. Hardness of rolled surface increases

approximately 1.5 times and Yield strength – 2 times

more then those of initial material and + Bonus –

condition the surface!

Изменеие микротвердости по глубине

205

210

215

220

225

230

235

240

0 100 200 300 400 500 600 700

Глубина от поверхности, мкм

Ми

кр

отв

ер

до

сть

42 42

Stage 8.6. Measurement of residual stresses by the drill-hole method using strain gauges

43 43

Stage 8.7. Execution of cyclic loading tests (pure bending) of prism-type samples

F

F

incision

Fatigue crack

44

М incision

Stage 8.8. Execution of cyclic loading tests (pure bending) of corset-type samples

Fatigue crack

45 45

Results of tests of corset-type samples

Conclusion. The results demonstrated high effectiveness of the metal

hardening procedure, considerable rise of cyclic durability of hardened

samples was confirmed.

Results of tests of prism-type samples

Stage 8.9. Analysis of the results of cyclic loading tests

46 46

Stage 8.10. Manufacturing and testing of the full-scale facility for surface hardening

47 47

Video of the rolling process by the full-scale facility

48

Conclusion

1. Using of multipara metrical on-line monitoring of

survervalence (Patent RU№2014104752/07 (007605),

12.02.2014) showed high effectivenes for precise assessment

of residual lifetime (damageability) in critical zones

considering the PLiM issues.

2. Rolling hammering procedure were designed. Its

procedure decrease cycling damage in 3 times.

3. Designed method of instrumental indentation for non-

destructive testing of mechanical properties, showed its

effectiveness for control different zones of joint wield before

and after hammering.

4. Based on this monitoring we designed labor-educational

stand for fast learning of multipara metrical on-line

monitoring of survervalence for explaining to engineers

from NPPs.

• Specialized labor-educational training stand

49

50

NEW METHODOLOGY OF ON-LINE EXPERIMENTAL-CALCULATED MONITORING (AGEING MANAGEMENT) FOR IMPROVING PERFORMANCE OF

A SYSTEM, STRUCTURES OF COMPONENT - MUBATEC RESOURCE-EXPERT – BASIC PRINCIPLES

Analysis of initial design

documentation

Analysis of operation history, including fail by loss of strength

Analysis of inspection, monitoring,

maintenance history

Analysis of materials and

material properties and environment

condition

Development of monitoring programe

Implementation of 3D laser scanning in order

to restore the actual geometry of the structure

and thermal survey to determine the

temperature fields

Carrying out finite element

calculation. Load stress

can come arise from the

design.

Expert analysis critical areas (zone) and installation

of expert sensors - temperature, strain,

displacement, vibration, acoustic emission,

ultrasonic testing – for training and verification 3D

finite element model and receiving real data from

operation loads

Improvement of calculation

program (correction of the

boundary conditions, changes in

the finite element partition,

geometry change, fixing and

loading conditions)

Calculation of the factual

accumulated operational

defectiveness

(variations of stress σ – strain ε)

Initial examination of the objectRecovery of deficit information and verify the

information about real condition

Step 1

Step2

Finite element simulation of operation loading

by use design data

Step3

Determination of the most

loaded zones

Finite element training and stress-strain calculations by use intelligent finite element model. Managing

ageing, evaluating critical zones and estimation residual service life timeStep

5

Calculation code teaching

Evaluation of stress and strain state

in critical areas

Comparison of the calculated values with

the experimental data of deformations and

displacements

NO YES

Clarification of the factual survivability of critical areas of the structure as a result of laboratory

tests of scale models – BENEFITS and CHALLENGE of on-line monitoring

Step6*

critical areas

* Schematic illustration of the different regimes of stable fating crack propagation

Particular qualities :

• The unified electronic monitoring system based on modules National

Instruments

• Very fast communication of experimental data from slow channels

and fast channels in on-line mode

Assembling and installation of a unified electronic self-

contained monitoring system of acquisition and

transmission data. Collection and performance data.

Design and installation of control systems for

collecting, processing and transmission

monitoring

Step4

Slow channels

Fast channels

According to the factual data

obtained geometry design

finite element 3Dimentional

finite element model for the

calculation of stress-strain state

Overview of traditional performance test

Critical zone

Time, τ

Tota

l str

ess,

σ

σ max

σ min

F

A

B

C

D

E

A’

F’ F”

A”

FEM stress-strain variations

10-2

10-4

10-6

10-8

one lattice spacing per cycle

regime I regime II

regime IIIm

1

K1c

1 mm/week

1 mm/min

1 mm/hour

1 mm/day Cra

ck g

row

th r

ate

at 5

0 H

z

Stress intensity range ∆K (log ∆K)

Cra

ck p

rop

agat

ion

rat

e da

/dN

(mm

/cyc

le)

Kth

Finite element model on-line

teaching (improving software)

Static and dynamic failure

analysis by use on-line

monitoring data

Real critical zone discovery

Risk management of safety and

dependability

Cycles to failure, N

∆σStre

ss a

mp

litu

de,

∆σ

Nc

Step 6*

Probability of failure P

A scale model

of the critical

zone

Additional

control sensors

PROCESS COMPUTER

Generation of load sequence

Measurement of ∆ε, ∆σ

Evaluation storage

Damage parameter = ∆ σ ∙ ∆ε

Performance stress-strain variation

Plastic zone

Low-cycle fatigue test

Tensile Test

Strain concentration crack initiation and

growth

Schematic diagram illustrating the various stages of damage critical zone in an engineering component and the approaches used to estimate the residual life

Design testing programs by use data of on-line experimental-calculated monitoring

Damage parameter = ∆σ∙∆ε

Recourse correction

Critical zone marginal state assessment

Additional

control sensorsTest specimen

P

P

P

σ

ε

ε

P

P

P

u

P

v

Test specimen manufacture and testing formechanical properties estimation

51

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