Indentation of lipid-based particle gels: An experimental, theoretical and numerical study

The rheological properties of lipid-based particle gels are critical in defining end-use properties. Although indentation is commonly utilized to investigate the end-use properties of these materials, a comprehensive methodology for acquiring and characterizing fundamental rheological properties via indentation is lacking. This study sought to develop the indentation method for obtaining the large-strain viscoplastic characteristics of three lipid systems that vary in composition and structure: shortening, margarine and butter. Uniaxial compression and conical indentation tests were performed at various rates. Constitutive behaviour was fitted with a viscoplastic model, with the rate-dependent plasticity defined by the overstress power law equation. The static stress–strain curve was defined by a linear elastic region, a strain hardening plastic deformation region, and a subsequent region of perfect plasticity. Forward predictions of the indentation load–displacement response were obtained via finite element analysis using compression test data. Good reverse predictions of the stress–strain properties from the indentation response were obtained through a novel method developed in this study.