Abstract
This paper investigates the failure strain as a dependence of the stress triaxiality and the Lode angle parameter for polyurethane rigid foams (PUR) of two densities (100 and \(300\,\hbox {kg/m}^{3})\). Tests were carried out in tension for various configurations, resulting in different states of stress triaxiality at various Lode angles in the critical areas. The failure strain was determined for each setup using finite element analysis, as the tests were replicated with numerical models. The displacement at failure recorded in the experiments was imposed for the models, determining the failure strain as a function of stress triaxiality and the Lode angle parameter. The results were validated through the analysis of the failure of sandwich structures with aluminium faces and PUR cores.
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Abbreviations
- d :
-
Plastic displacement
- D :
-
Damage evolution parameter
- \(e^{\mathrm{c}}\) :
-
Logarithmic compressive strain
- \(e^{\mathrm{t}}\) :
-
Logarithmic tensile strain
- \(I_{1}\) :
-
First invariant of the stress tensor
- \(J_{2}\) :
-
Second invariant of the deviatoric stress tensor
- \(J_{3}\) :
-
Third invariant of the deviatoric stress tensor
- p :
-
Hydrostatic pressure
- \(p^{\mathrm{c}}\) :
-
Yield stress in hydrostatic compression
- \(p^{\mathrm{t}}\) :
-
Yield stress in hydrostatic tension
- q :
-
von Mises equivalent stress
- r :
-
Normalized third invariant
- \(s^{\mathrm{c}}\) :
-
True compressive stress
- \(s^{\mathrm{t}}\) :
-
True tensile stress
- \(\gamma \) :
-
Bai–Wierzbicki Lode angle-dependent parameter
- \(\varepsilon ^{\mathrm{c}}\) :
-
Engineering compressive strain
- \(\varepsilon ^{\mathrm{t}}\) :
-
Engineering tensile strain
- \(\bar{\varepsilon }_{\mathrm{D}}^{\mathrm{pl}}\) :
-
Critical plastic strain
- \(\bar{\varepsilon }^{\mathrm{pl}}\) :
-
Equivalent plastic strain
- \(\dot{\bar{\varepsilon }}^{\mathrm{pl}}\) :
-
Equivalent plastic strain rate
- \(\eta \) :
-
Stress triaxiality
- \(\bar{\theta }\) :
-
Lode angle
- \(\nu \) :
-
Poisson’s ratio
- \(\xi \) :
-
Lode angle parameter
- \({{\varvec{\sigma }}}\) :
-
Stress tensor
- \(\bar{{\varvec{\sigma }}}\) :
-
Effective stress tensor
- \(\sigma ^{\mathrm{c}}\) :
-
Engineering compressive stress
- \(\sigma ^{\mathrm{t}}\) :
-
Engineering tensile stress
- \(\sigma _{ij}\) :
-
Stress tensor components
- \(\sigma _{i}\) :
-
Principal stresses
- \({{\varvec{\sigma }}}^{\prime }\) :
-
Deviatoric stress tensor
- \(\sigma _{ij}^{\prime }\) :
-
Deviatoric stress tensor components
- \(\sigma _{\mathrm{y}}\) :
-
Equivalent yield stress
- \(\Phi \) :
-
Yield function
- \(\psi \) :
-
Dissipated plastic energy
- \(\omega \) :
-
Damage initiation parameter
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Acknowledgements
This work was supported by the Romanian National Authority for Scientific Research and Innovation, CCCDI—UEFISCDI, projects number PD 13/2018 and CCCDI—UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0391/CIA_CLIM.
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Communicated by Luca Placidi and Emilio Barchiesi.
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Şerban, DA., Negru, R., Filipescu, H. et al. Investigations on the influence of the triaxial state of stress on the failure of polyurethane rigid foams. Continuum Mech. Thermodyn. 35, 905–918 (2023). https://doi.org/10.1007/s00161-020-00924-x
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DOI: https://doi.org/10.1007/s00161-020-00924-x