PSI - Issue 2_B

M. J. Mirzaali et al. / Procedia Structural Integrity 2 (2016) 1285–1294

1291

M. J. Mirzaali et al. / Structural Integrity Procedia 00 (2016) 000–000

7

Strength

Elastic Modulus

Yield Stress

2.44 1.7 0.92 0

1.93 1.06 -0.11

Group B Group D

Group B Group D

Group B Group D

Σ y0.2 [MPa]

Σ ult [MPa]

Ϲ [GPa]

R 2 = 0.36 n = 1.23

R 2 = 0.50 n = 3.43

R 2 = 0.09 n = 1.24

-0.69 -0.11 0.41

-2.3

-2.3

-2.3

-1.2 -0.36

-1.2 -0.36

-1.2 -0.36

ρ s

ρ s

ρ s

Fig. 2. Linear regression model in logarithmic scale for mechanical properties of closed-cell aluminum foams in groups B and D. Model is fitted to follow the power law presented in Eq. 1, to obtain the parameter n . Linear model is fitted on the pooled data (groups B and D. The parameter n for elastic sti ff ness and strength in open cell foam are reported as 2 and 1.5 (Gibson et al., 2010).

Fig. 3. Left: Monotonic stress-strain curve of monotonic compressive mechanical testing of closed-cell aluminum foam. Mechanical testing of 4 groups are compared to each other. Samples with skin in groups A and C show higher strength. There is no significant di ff erence between mechanical behavior of samples in groups B and D. Right: Normalized stress-strain curves; stresses were normalized to ρ n s , where n = 1 . 33 is calculated by fitting a power law relation between compressive strength and relative density in Eq. 1 and Fig 2. Average strength of 40 MPa was used as initial guess for the perfectly plastic behavior in FE-model.

Fig 2. These results give an estimation of solid constituent of foam material without artificial voids. Mean ± standard devision for specific strength, ( Σ ult ρ n s ), were 58 . 24 ± 6 . 57 MPa for samples in group B and 45 . 29 ± 6 . 81 MPa for samples in group D. Mean of specific strength was taken as an initial guess for the elastoplastic finite element simulation of each group (Fig. 4). Specific elastic modulus, ( C ρ n s ), for samples in group B and D were 7 . 19 ± 3 . 25 GPa and 4 . 79 ± 0 . 91 GPa, respectively. Samples in groups A and C (with skin) show higher mechanical properties than samples in groups B and D. It is because of approximately 1.5 mm aluminum shells that covers those samples and produces a circumferential rigidity which leads to increase of the mechanical properties. From the rule of mixtures, we can assume that foam samples