practical considerations in determining material properties susan i. hill structures and materials...
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Practical Considerations In Determining Material Properties
Susan I. HillStructures and Materials Evaluation Laboratory
University of Dayton Research Institute
(937) 229-4704 [email protected]
www.udri.udayton.edu
Future of Modeling in Composites Molding Processes Workshop
June 9-10, 2004
Defining Needs• Depends on application and model
– Impact can be compressive event but material failure is tensile event
– Localized delaminations, cracking, interfacial bonding in composites
• Necessary test data are defined by selected model– Tensile, compression, and shear data– Energy absorption– Temperature effect– Strain rate effect– Failure
Types of tests required
• Uniaxial compression• Confined compression (bulk
modulus)• Cyclic tension• Stress relaxation• Resonant Beam• ?
May need to go beyond the typical tensile strength, modulus, failure strength data, e.g.
Impact-related models
• Material models exist for structural polymers• Lacking for composites• FE codes may not incorporate correct
material models– Current models have poor handling of viscoelastic
effects, plastic flow, strain rate effects, and fracture
– Use of quasi-static data will underestimate material response at higher impact rates
Polyolefin
0 50 100 150 200 250 300 350
0.5/s5/s50/s250/s450/s
En
gin
eer
ing
str
ess
[MP
a]
Engineering strain [%]
Polyolefin
Polyolefin relationship with strain rate
0.1 1 10 100 1000
Polyolefin
Peak StressBreaking Stress
En
gin
eeri
ng
str
ess
[M
Pa
]
Engineering post-yield strain rate [1/s]
Polycarbonate
0 50 100 150 200
0.4/s40/s300/s
TE
NSI
LE
EN
GIN
EE
RIN
G S
TR
ES
S
ENGINEERING STRAIN [%]
Relationship with Strain Rate
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
0.01 0.1 1 10 100 1000
NO
RM
AL
IZE
D Y
IEL
D S
TR
EN
GT
H
STRAIN RATE [SEC-1]
Highly glass-filled polymer
0.001 0.01 0.1 1 10 100 1000
Highly glass-filled polymer
Failure stress
En
gin
eeri
ng
str
ess
[M
Pa
]
Engineering post-yield strain rate [1/s]
Failure stress relativelyconstant across strain rates
Defining Needs
• Strain rate defines test method– Quasi-static -- Screw-type test machines
• 0.0001 to 0.1/s
– Intermediate (“High”) -- Servo-hydraulic test machines
• 0.1 to 200-700/s
– Bar Impact -- Split Hopkinson Bar• 200 to 10,000/s
Types of high rate problems
Structural Dynamics Wave PropagationProblem Areas Vibration Impact, shockTime Duration Milliseconds — seconds Nano — millisecondsStrain Rates < 10 1 — 106
Frequency Content Low — moderate Moderate — highSolution Method Implicit ExplicitFEA Codes ABAQUS, ANSYS,
NASTRANAutoDyn, DYNA,
PAMCrash, RADIOSS