1. Identification of mechanical properties from tensile and compression tests of unidirectional carbon composite
Jan Krystek
Tomáš Kroupa
Radek Kottner

2. Outline Introduction Tensile test Two compression tests
Identification of material properties
Summary

3. Introduction Aim: Unidirectional composite material
5 independence component of stiffness matrix (C11 , C12 , C22 , C23 , C66)
5 independence material constant (EL, ET , GLT , υLT , υTT´)
strength parameters (XT, XC, YT, YC, SL, α0)
Stiffness matrix of transverse isotropic material
Aim:
Identification of mechanical properties using numerical simulation of tensile and compression test in FE system MCS. Marc and optimization algorithm in optiSlang software
Material: carbon fibers Tenax HTS 5631 and epoxy resin

4. Tensile test Measured properties: EL, ET , νLT , XT, YT
Tensile specimens
Fracture of specimens

5. Fracture of specimen C-I_a → α0 = 57°
Compression test - type I
Measured properties:
YC, α0
Fracture of specimen C-I_a → α0 = 57°
Labelling
Length
Width
Thickness YC
[mm]
[MPa]
C-I_a
4.9
9.9
2.2
210
C-I_b
220
C-I_c
10.0
C-I_d
17.8
203
C-I_e
245*
C-I_f
272*
* incorrect fracture
Compressive strength

6. Compression test - type II
Measured properties:
Labelling
Length
Gage length
Width
Thickness
Fiber angle YC XC
Failure
[mm]
[ °]
[MPa]
identification code
C-II_a
165
5.0
25.0
1.1 90
185 -
HAM
C-II_b
170
10.0
2.2
175
AAT
C-II_c
9.8
987
TAM
C-II_d
853
XC, YC, α0
Fracture of specimens

7. Compression test specimen three-part identification codes
Failure identification codes
Compression test specimen three-part identification codes
First character
Failure mode
Code
Angled A
Brooming B
end-Crushing C
Delamination D
Euler buckling E
tHrough-thickness H
Kink bands K
Lateral L
Multi-mode
M(x,y,z)
long.-Splitting S
Transverse shear T
eXplosive X
Other O
Second character
Failure area
Code
Inside grip/tab I
At grip/tab A
Gage G
Multiple areas M
Tab adhesive T
Various V
Unkwnow U
Third character
Failure location
Code
Bottom B
Top T
Left L
Right R
Middle M
Various V
Unkwnow U
ASTM International: D 3410 Standard Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported Gage Section by Shear Loading. ASTM International, USA.

8. Comparison between linear and nonlinear models
Identification of material parameters
From experiment:
In case of specimens with fibre angles between 15° and 75°, the nonlinear dependence of tensile force on displacement is obvious
Nonlinear function with constant asymptote was used for shear modulus GLT in the process of identification:
Comparison between linear and nonlinear models
By means of otimization algorithms , the following function was minimized
Parameters of optimization
The strength criterion LaRC04 was used for identification of shear strength SL

9. Schema of identification process Identified material properties
Identification of material parameters
EL – elastic modulus in the longitudinal direction
ET – elastic modulus in the transverse direction
νLT – Poisson´s ratio
GLT – shear modulus
G0LT – initial shear modulus
τ0LT – asymptote value of shear
nLT – shape parameter
XT – tensile strength in the longitudinal direction
XC – compressive strength in the longitudinal direction
YT – tensile strength in the transverse direction
YC – compression strength in the transverse direction
SL – shear strength
α0 – angle of the fracture plane in pure transverse
compression
Schema of identification process
Linear model
Nonlinear model EL ET
υLT
GLT
G0LT
τ0LT
nLT XT XC YT YC SL α0
[GPa]
[ - ]
[MPa]
[ °]
120.0
8.0
0.337
4.0
4.6
115.0
1.2
1480
850 55
213 82 57
Identified material properties

10. Summary
Specimens with different geometric properties were tested in tensile test and two types of compression tests
The material parameters were identified with the use of numerical simulation of tests in finite element system MSC.Marc and optimization algorithms included in optiSlang software
Failure criterion LaRC04 was used for the identification of strength parameters
The nonlinear function with constant asymptote had to be used for description of material behavior up to fracture in the process identification
In case of small displacement, the linear relationship can be used with sufficient accuracy