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ON THE CHALLENGING FEM APPLICATION FIELDS IN THE FRACTURE MECHANICS. Institute of Physics of Materials, AS of CR, Brno, Czech Republic. Vladislav Kozák. Outline. 1. Introduction 2. Local approach -Beremin 3. GTN model 4. Cohesive-zone modelling 5. Summary. 1.Introduction FTTD.

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on the challenging fem application fields in the fracture mechanics

ON THE CHALLENGING FEM APPLICATION FIELDS IN THE FRACTURE MECHANICS

Institute of Physics of Materials, AS of CR, Brno, Czech Republic

Vladislav Kozák

slide2

Outline

  • 1. Introduction
  • 2. Local approach -Beremin
  • 3. GTN model
  • 4. Cohesive-zone modelling
  • 5. Summary
slide3

1.Introduction FTTD

lower transition

upper

stress control

fracture

SSY

deformation

control

fracture

lower

bound

upper

bound

transition

three different approaches to the damage modelling
Three different approaches to the damage modelling
  • no damage evaluation, elasto-plastic constitutive equation, process zone is small, K, J, C*
  • separation of surfaces is admitted, material outside is described conventionally, the process zone is some surface region, fracture criterion is cohesive law
  • softening behaviour is introduced into the constitutive model, e.g. accumulation of damage, described by additional internal variables, GTN
slide5

Plastic zone ahead the crack tip

region:

condition SSY

large deformation

J-integral conception K faktor conception

non defined only by one parameter

condition

elasto-plastic

conditionLSY

slide6

2. Local approach - Beremin

  • ·    Beremin model
  • 1. averaging stresses over FPZ
  • 2. probability of fracture
  • ·    Extension to Fracture Mechanics
  • 1. direct toughness prediction for SSY
  • 2. TSM, Minami, Koppenhoefer, Ruggieri
slide9

f0

fC

GT

plast.

HMH

plasticity

D

3. Gurson-Tvergaard model(GT)

nucleation

fN = 0,004

eN = 0,3

SN = 0,1

f0 = 0,005

fC = 0,035

q1 = 1,5; q2 = 1

D = 0,2 mm

slide10

f *

fu*

fc

GT

GTN

fF

fc

f

GT x GTN model

q1, q2, q3 are used to adjust the model

sm is hydrostatic stress

sYS is yield stress

f* is void fraction, fc is the critical void fraction for coalescence

fF is the final value of f, fu*=1/q1.

dfnucl.=Adep

material parameters identification

f1=0.0073

f2=0.0073

f3=0.0083

f4=0.0126

f5=0.0131

f6=0.0349

500 mm

material parameters identification

void distribution in non-affected area

void distribution in the neck area

of the round tensile bar

varying values of f 0 and f n and determination of input data
varying values of f0 and fN and determination of input data

f0 = 0.005, fF (fC) = 0.035 q1 = 1.5, q2 = 1 (q3 = q12)

eN = 0.3, SN = 0.1

fN = 0.004

slide14

W

a

L/2

B/2

3PB SE(B)

L = 250 mm

l = 200 mm

W = 50 mm

B = 25 mm

a = 25,25 mm

slide16

J

J0.2BL

J0.2

JI SZW

JI

0.2 mm

Da

DaSZW

FEM J=1,39syDa

slide17

The influence of q2on the values of J-integrálu at stable crack initiation

The influence of the h parameter (triaxiality parameter)

5 summary
5. Summary
  • The coincidence of the results of the numerical modelling and the experiment is generally the basic criterion.