Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

3.6: Numerical and experimental buckling loads.
Buckling loads (kN)
Core type Debond diameter (mm)
Experiment Non-linear FE eigenbuckling FE
H130
100
200
106.5±4.5
27±1
100
26
94.5
26.9
300 15 12 12.9
H250
100
200
121±9
24±1
104
28
100
28
300 16 13 12.5
PMI
100
200
85.5±3.5
28.5±3.5
94
28
109
33.8
300 11.5±4.5 14 15.9
In order to estimate the crack propagation load of the panels, the energy release rate and phase
angle were determined along the debond front. The energy release rate (G) was determined from
relative nodal pair displacements along the crack flanks obtained from the finite element
analysis. The energy release rate and mode-mixity phase angle are given by Equation (1.18) and
(1.19) in the Introduction of this thesis. h, which is the characteristic length of the crack problem,
is chosen as the face sheet thickness. In Figure 3.18 the normalised energy release rate and phase
angle with respect to the maximum determined energy release rate and phase angle along the
debond front are plotted in polar diagrams for the H130 panels with 100 mm, 200 mm and 300
mm debond diameter in a load level close to the experimental debond propagation load.
Maximum energy release rate and minimum phase angle occur in the 0-degree debond front,
implying the onset of debond propagation in this location, which is similar to experimental
observations, see Figure 3.12. The same conclusion may be drawn for the panels with PMI and
H250 core.
90
1
120
135
0.8
150
0.6
0.4
165
0.2
180
0
105
195
210
225
240
255
75 60
15
0
345
330
315
300
285
120
1
90
75
60
45
30
135
150
0.5
45
30
105
(a) (b)
270
270
100 mm 200 mm 300 mm
100 mm 200 mm 300 mm
3.18:(a) Normalised energy release rate (G/Gmax) and (b) normalised phase angle (/max)
for H130 panels with debond diameters of 100 mm, 200 mm and 300 mm.
55
165
180
195
210
225
240
255
0
-0.5
15
0
345
330
315
300
285