PSI - Issue 42

Monika Středulová et al. / Procedia Structural Integrity 42 (2022) 1537– 1544 M. Strˇedulova´ et al. / Structural Integrity Procedia 00 (2019) 000–000

1543 7

80

80

1.0 1.1 1.2 1.3 1.4 1.5 2.0 2.5

40

60

60

30

40

40

σ x [MPa]

20 σ x [MPa] σ x [MPa] 20

20

10

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0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 x [ − ] 0

0 . 00

0 . 05

0 . 10

0 . 15

0 . 20

x [ − ]

0

0 . 0000

0 . 0001

0 . 0002

x [ − ]

Fig. 5. Averaged stress–strain diagrams of the free (left) and the fixed (right) simulations for di ff erent slenderness ratios.

80

0.4 0.2 0.1 0.005 experiments area between fixed & free simulations

1 . 6

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1 . 2 P / P R2 . 5 1 . 4

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fixed µ = 0 . 4 µ = 0 . 2 µ = 0 . 1 µ = 0 . 005 free

σ x [MPa]

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0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 x [ − ] 0

1 . 0

1 . 0

1 . 5

2 . 0

2 . 5

slenderness ratio

Fig. 6. Left: peak forces obtained via simulations with di ff erent friction coe ffi cient and peak loads observed in experiments (Lisztwan et al., 2021); right: stress–strain diagrams obtained by simulations with the slenderness ratio 1.0.

specimens and also enhances further the ductility of the post-peak response. The largest friction coe ffi cient µ = 0 . 4 is already very close to the full friction case as the stress–strain diagram of these two scenarios almost coincide. Out of those which were tested, friction coe ffi cients µ = 0 . 2 matches best the experimental results for slenderness ratio from 2 until approximately 1.2. However, for the smallest slenderness ratios, 1.1 and 1.0, it diverges, predicting peak load greater by 20 % to the one which was experimentally obtained. For these slenderness ratio, the friction coe ffi cient of µ = 0 . 1 is closer to the experimental data. As discussed before, simulations with low slenderness ratios might produce artificially large strengths due to possibly incorrect formulation of the constitutive model in the state of the triaxial compression. Therefore friction coe ffi cient of µ = 0 . 2 shall be identified as the one that shows the best correspondence to the experimental measurements.

4. Conclusion

Discrete mesoscale model of concrete is employed to identify friction coe ffi cient between loading platens and concrete cylinder. The e ff ect of friction observed in the experiments is strongly a ff ected by the slenderness ratio of the cylinders. For ratios above 2, there is almost no friction e ff ect on the measured strength. For lower ratios, the strength rapidly increases with decreasing slenderness ratio. The same e ff ect was seen in simulations. The best correspondence between simulations and experimental results is seen for friction coe ffi cient around 0.2. The simulations showed unrealistic post-peak behavior in the case of high friction and low slenderness ratios. There is a clear need to update the constitutive formulation according to Refs. (Cusatis et al., 2011a,b), where simulations of uniaxial compression with prismatic specimens are performed. Unlike in the present models, the post-peak behavior of prisms with low slenderness ratio exhibit, in agreement with the experiments, softening.