In the production of semi-finished metal products, hot forming is used to eliminate the pores and voids from the casting process under compressive stresses and to modify the microstructure for further processing. In the case of caliber and flat rolling processes, tensile stresses occur at certain roll gap ratios which promote pore formation on nonmetallic inclusion. The formation of new pores contributes to ductile damage and reduces the load carrying capacity of the material. In the literature, the damage nucleation and growth during the hot forming process are not comprehensively described. The aim of this study is to understand the damage initiation and growth mechanism during hot forming processes. Hot tensile tests are performed at different temperatures and strain rates for 16MnCrS5 steel. To investigate the influence of geometrical variations on the damage mechanism, specimens with different stress triaxiality ratios are used. Finite element simulations using the Gurson-Tvergaard-Needleman (GTN) damage model are performed to estimate the critical void fraction for the damage initiation and the evolution of the void volume fraction. The results showed that the GTN model underestimates the softening of the material due to the independence of the temperature and the strain rate.

1.
J.
Lin
,
A. D.
Foster
,
Y.
Liu
,
D. C. J
Farrugia
and
T. A.
Dean
, “
On micro-damage in hot metal working part 2: Constitutive modelling
”,
Engineering Transactions
55
,
43
60
(
2007
).
2.
S. L.
Semiatin
,
V.
Seetharaman
,
A. K.
Ghosh
,
E. B.
Shell
,
M. P.
Simon
and
P. N.
Fagin
, “
Cavitation during hot testing of Ti-6AL-4V
”,
Materials Science & Engineering A
256
,
92
110
(
1998
).
3.
J. C.
Gelin
, “
Modelling of damage in metal forming processes
”,
Journal of Material Processing Technology
80-81
,
24
32
(
1998
).
4.
O. D.
Sherby
,
J.
Wadsworth
, “
Superplasticity-Recent advances and future directions
”,
Progress in Material Science
33
(
3
),
169
221
(
1989
).
5.
J.
Lin
,
Y.
Liu
and
T. A.
Dean
, “
A review on damage mechanisms, models and calibration methods under various deformation conditions
”,
International Journal of Damage Mechanics, SAGE Publications
14
(
4
),
299
319
(
2005
).
6.
K.
Tanaka
and
T.
Mura
, “
A theory of fatigue crack initiation at inclusions
”,
Metallurgical Transactions A
13
(
1
),
117
123
(
1982
).
7.
A.
Piñol-Juez
,
A.
Iza-Mendia
and
I.
Gutiérrez
, “
Damage formation of A 2304 duplex stainless steel under hot working conditions
”, In
ECFl3
,
San Sebastian
(
2000
).
8.
S. T.
Mandziej
and
G.
Krallics
, “
Crack Appearance in Hot Rolled Billets
”,
Hot Cracking Phenomena in Welds
II
,
371
(
2008
).
9.
M. F.
Novella
,
A.
Ghiotti
,
S.
Bruschi
,
P. F.
Bariani
, “
Ductile damage modeling at elevated temperature applied to the cross wedge rolling of AA6082-T6 bars
”,
Journal of Materials Processing Technology
222
,
259
267
(
2015
).
10.
P.
Hu
,
D.
Shi
,
L.
Ying
,
G.
Shen
,
W.
Liu
, “
The finite element analysis of ductile damage during hot stamping of 22MnB5 steel
”,
Materials & Design
69
,
141
152
(
2015
).
11.
C.
Sommitsch
,
P.
Pölt
,
G.
Rüf
, and
S.
Mitsche
, “
On the modelling of the interaction of materials softening and ductile damage during hot working of Alloy 80A
”,
Journal of materials processing technology
177
(
1
),
282
286
(
2006
).
12.
J.
Lin
,
M.
Mohamed
,
D.
Balint
, and
T. A.
Dean
, “
The development of continuum damage mechanics-based theories for predicting forming limit diagrams for hot stamping applications
”,
International Journal of Damage Mechanics
23
(
5
),
684
701
(
2014
).
13.
V.
Tvergaard
, and
A.
Needleman
, “
Analysis of the cup-cone fracture in a round tensile bar
”,
Acta metallurgica
32
(
1
),
157
169
(
1984
).
14.
E.
Parteder
,
H.
Riedel
,
D.
Sun
, “
Simulation of hot forming processes of refractory metals using porous metal plasticity models
”,
International Journal of Refractory Metals and Hard Materials
20
(
4
),
287
293
(
2002
).
15.
V.
Brinnel
, “
Improved Limit State Definitions for Pressure Vessels by a Scale-bridging Application of Damage Mechanics
” Ph.D. thesis,
RWTH Aachen University
,
2017
.
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