Herschel-Bulkley Model | Rheological Expertise

Many products do not follow simple Newtonian behavior. Their viscosity varies with shear rate, and some exhibit a yield stress before they begin to flow. In this context, rheological models make it possible to turn experimental measurements into behavior laws that can be used for process sizing, pumping, and mixing. The Herschel-Bulkley model is particularly well suited to materials that are pasty, structured, or filled, when the material requires a minimum stress to flow.

The Herschel-Bulkley model combines three useful dimensions for interpretation: a yield stress, a consistency index, and a flow index. This approach captures the behavior of products that resist the start of flow and then shear-thin under stress. It is therefore particularly relevant for greases, pastes, suspensions, concentrated formulations, or materials with a pronounced internal structure.

Flow tests are used to measure viscosity and stress as a function of shear rate. They make it possible to identify Newtonian, shear-thinning, shear-thickening, or yield-stress behavior. These measurements are essential for fitting a model such as Herschel-Bulkley and predicting behavior under industrial processing conditions such as transfer, dosing, coating, or stirring.

L’expertise laboratoire repose sur la mise en œuvre d’analyses rhéologiques adaptées au matériau, à son historique thermique et à ses conditions d’usage. Les mesures peuvent être intégrées à une démarche de caractérisation plus large en lien avec d’autres techniques physico-chimiques ou thermiques, par exemple pour corréler comportement d’écoulement, structure, transition thermique ou évolution de formulation. Cette approche permet de sécuriser l’interprétation des résultats et de fournir des données exploitables pour l’industrialisation.

A rheometer makes it possible to carry out several complementary test families. The flow test establishes a viscosity curve as a function of shear in order to reproduce conditions close to pumping or mixing. The oscillation test applies very small deformations to probe the internal structure and distinguish the elastic component from the viscous component. These data make it possible to assess texture, stability, storage behavior, and processability, then feed a robust mathematical model for your calculations and simulations.

The Oswald model, often used for power-law behavior, correctly describes fluids whose viscosity varies with shear but does not include a yield stress. It is therefore less representative when the material requires an initial force to start flowing. In that case, the Herschel-Bulkley model offers a more faithful description of the real behavior and improves the relevance of extrapolations for process calculations.

Oscillation tests explore the structure of the material at low deformation and distinguish the elastic response from the viscous response. They are useful for assessing the stability, cohesion, or mechanical integrity of a formulation. In addition, temperature sweeps make it possible to track changes in viscosity or thermal structure. For matrices such as greases, the use of successive temperature holds is preferable to a continuous ramp when the goal is to limit thermal inertia effects thermal and obtain more representative results.

Rheological characterization helps compare formulations, validate a raw material change, understand a process drift, or document product performance. It is also a decision-support tool in R&D for adjusting an additive, improving heat resistance, stabilizing a texture, or anticipating in-use behavior. The parameters derived from Rheological Models then become practical tools for design and industrial robustness.

FILAB supports manufacturers in the characterization of materials and formulations with a problem-solving, development, and validation-oriented approach. The value of specialized support lies in defining a relevant protocol, correctly interpreting the curves, selecting the most suitable model between the power law and Herschel-Buckley, and then delivering results that your technical teams can use directly. This expertise naturally fits into broader investigations in physico-chemistry, thermal analysis, or materials science when rheological behavior needs to be correlated with composition or structure.