### Abstract

Normal stresses in complex fluids lead to new flow phenomena because they can be comparable to, or even larger than, the shear stress. In addition, they are of paramount importance for formulating and testing constitutive equations for predicting nonviscometric flow behavior. Very little attention has thus far been paid to the normal stresses of yield stress fluids, which are difficult to measure. We report the first systematic study of the first and second normal stress differences in both continuous and slow oscillatory shear of three model nonthixotropic yield stress fluids, with N
_{1}
> 0 and N
_{2}
< 0. We show that both normal stress differences are quadratic functions of the shear stress both above and below the shear yield stress, leading to the existence of a yield normal stress. However, the contribution of the normal stresses to the von Mises yield criterion for these materials is small.

Original language | English |
---|---|

Pages (from-to) | 285-290 |

Journal | Journal of Rheology |

Volume | 63 |

Issue number | 2 |

DOIs | |

Publication status | Published - 1 Mar 2019 |

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### Cite this

*Journal of Rheology*,

*63*(2), 285-290. https://doi.org/10.1122/1.5063796

}

*Journal of Rheology*, vol. 63, no. 2, pp. 285-290. https://doi.org/10.1122/1.5063796

**The yield normal stress.** / De Cagny, Henri; Fazilati, Mina; Habibi, Mehdi; Denn, Morton M.; Bonn, Daniel.

Research output: Contribution to journal › Article › Academic › peer-review

TY - JOUR

T1 - The yield normal stress

AU - De Cagny, Henri

AU - Fazilati, Mina

AU - Habibi, Mehdi

AU - Denn, Morton M.

AU - Bonn, Daniel

PY - 2019/3/1

Y1 - 2019/3/1

N2 - Normal stresses in complex fluids lead to new flow phenomena because they can be comparable to, or even larger than, the shear stress. In addition, they are of paramount importance for formulating and testing constitutive equations for predicting nonviscometric flow behavior. Very little attention has thus far been paid to the normal stresses of yield stress fluids, which are difficult to measure. We report the first systematic study of the first and second normal stress differences in both continuous and slow oscillatory shear of three model nonthixotropic yield stress fluids, with N 1 > 0 and N 2 < 0. We show that both normal stress differences are quadratic functions of the shear stress both above and below the shear yield stress, leading to the existence of a yield normal stress. However, the contribution of the normal stresses to the von Mises yield criterion for these materials is small.

AB - Normal stresses in complex fluids lead to new flow phenomena because they can be comparable to, or even larger than, the shear stress. In addition, they are of paramount importance for formulating and testing constitutive equations for predicting nonviscometric flow behavior. Very little attention has thus far been paid to the normal stresses of yield stress fluids, which are difficult to measure. We report the first systematic study of the first and second normal stress differences in both continuous and slow oscillatory shear of three model nonthixotropic yield stress fluids, with N 1 > 0 and N 2 < 0. We show that both normal stress differences are quadratic functions of the shear stress both above and below the shear yield stress, leading to the existence of a yield normal stress. However, the contribution of the normal stresses to the von Mises yield criterion for these materials is small.

U2 - 10.1122/1.5063796

DO - 10.1122/1.5063796

M3 - Article

VL - 63

SP - 285

EP - 290

JO - Journal of Rheology

JF - Journal of Rheology

SN - 0148-6055

IS - 2

ER -