modeling of serrated chip formation in high speed ...xinran/index_files/poster.pdf · simulation...
TRANSCRIPT
The proposed dynamic fracture based constitutive model
predicted the physical and morphological characteristics of
serrated chip formation in HSM of AISI steel 1045.
It is shown that the ductility of AISI steel 1045 as the work
material can be substantially reduced by applying a certain
combination of the strain rate and negative stress triaxiality. It
sets a foundation for the development of a methodology of
selecting the proper tool geometry and optimal machining
regime.
Reduction of friction at the tool-chip interface may result in:
Improved chip breakability
Up to 25% reduction of the overall energy consumed by
the process
This can be achieved by using tribological coating and/or
metal working fluids of high lubricity.
Abstract
For the first time, serrated chip formation is modeled based
on a novel definition of the metal cutting process as the
purposeful fracture of the layer being removed and the First
and Second Laws of metal cutting. The present work aims to
develop a fracture-based constitutive model of the work
material considering the special loading characteristics of the
orthogonal cutting regime and evaluating the equivalent
fracture strain to be used in the prediction of segmented chip
formation and energy partition in the cutting system. In this
model, both the equivalent strain rate and stress triaxiality
define the material fracture locus. The physical and
morphological characteristics of the chip formation were
analyzed. The anticipated fluctuation of the cutting force
caused by the chip segmentation was observed. The main
objective of the modeling has been formulated – reduction of
plastic deformation of the layer being removed that results in
higher process productivity and efficiency, longer tool life and
better integrity of the machined surface
Material Plasticity Model
General description of a
material plastic flow
Material Damage Model Results
Modeling of Serrated Chip Formation in High Speed Machining: The Fracture Locus Approach
Yalla Abushawashia, Xinran Xiaoa, Viktor Astakhovb a Department of Mechanical Engineering, Michigan State University, E. Lansing, MI, USA
b Production Service Management Inc. (PSMi), Saline, MI, USA
Stress State
Parameterization
Effective strain
Effective strain
Strain rate
σ=f ε g ε h T
σ
ε
T Tempera
ε
ture
n
o
Initial yield strength
Hardening modulus
Strain rate sensitivity
n
εσ= A+Bε 1+
Thermal s
Clnε
A
B
ofte
C
ningFig. 2 JC model optimization for AISI steel 1045
Strain Rate Dependency
Constructing the Plane Strain Fracture Locus with superposition of
hydrostatic stresses to predict damage initiation using flat-grooved
specimen (Bai et al. 2009)
22C η
f 1 1Rice and Tracey model . C and C are the material fracture parε a= sC e meter
Fig.3 Typical 3D fracture locus
(general loading conditions)
Fig.4 Typical 2D Fracture locus
(Specific loading conditions)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
Stre
ss t
riax
ialit
y
Equivalent plastic strain
R12.7-to1.62 R3.97-to1.55
Fig.5 1045 steel plane strain
flat specimens with different
notches (Bai et al. 2009)
Fig.6 Stress triaxiality evolution
diagram of AISI steel 1045
obtained from finite element
simulation for three selected
flat-grooved specimens
Fig. 7 AISI steel 1045 fracture locus based on
initial stress triaxiality, averaged using
displacement limit simulation model, averaged
using strain limit model, and the fracture locus
based on strain at fracture. Stress triaxiality
evolution curves are also shown
0.0
0.2
0.4
0.6
0.8
1.0
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Equiv
ale
nt s
train
at fr
actu
re
Stress triaxiality parameter
Initial [Wierzbicki, Teng, and Bai] Avg.-disp. limit [Wierzbicki, Teng, and Bai] Avg.-strain limit Strain at fracture
Flat grooved
Tubular specimen
(Tortion test)
0
f
stress state at fractureE d
( , , ) ( , ) ( )f f f f fS R
A modified version of the material
energy density criterion is suggested
to account “indirectly” for material
strain rate sensitivity. It states that
the material toughness in general is
a function of stress state
The general equivalent strain at
fracture is introduced in the following
form
where S is the fracture locus at the
reference equivalent strain rate.
Post Damage Contribution
Damage evolution is assumed to
grow exponentially according to:
The material is assumed to start the
strain softening and degradation
process when the damage indicator
Effe
ctive
str
ess
Effective strain
Dam
age
init
iati
on
Damage Evolution
11
pm
pjc
Conclusions
Fig.10 Serrated chip
simulation in HSM
(Vc=3000m/min, to=0.2mm)
Fig.11 Plastic effective strain
contours in both damaged
and undamaged elements
Fig.12 Stress triaxiality state
contours
Fig. 9 Comparison between the
experimental and modeled
segmented chip morphology. Ref.
(Duan et al. 2010) (cutting speed 432.6m/min, uncut chip thickness to=0.2mm, and rake angle 10o)
Fig. 8 Finite element simulation of the serrated chip formation
with: (a) contact friction, (b) no friction at the tool-chip interface,
and (c) the corresponding cutting force chart
Fig.1 Typical metal stress-strain response
in a uniaxial test
Material plasticity model is represented by a separable function
in terms of the loading condition and uncoupled with the
material degradation beyond damage initiation. This model is
considered as the undamaged hypothetical behavior of the
material.
Reduced form of the Johnson
and Cook model [1]
Predicted Measured Shear angle 27.2deg 31deg peak/valley ratio 1.46 1.41 Chip comp. ratio 1.4 1.43
pf
pc
εp
εf
h
p p
c f
f
1 D=1-exp Lσdε
G
σ= 1-D σ
ε and ε are the eff. plastic strains at the
initiation and fracture site respectively
G is the material fracture energy
L
h
is the element characteristic length
σ is the hypothetic undamaged eff .stress
500
600
700
800
900
0.00 0.10 0.20 0.30 0.40
Effe
ctive
str
ess
Effective plastic strain
Torsion test (Bai et al. 2009)
Johnson and Cook model