Universal Correlation to Reconcile Yielding Characterizations of Waxy Oil Gels

Adhesive and cohesive fractures are the two possible modes of fracture during yield stress measurement of materials such as waxy oil gel. In this study, yield stress measurements were performed with a number of waxy crude and model oils using three geometries, including a smooth cylinder, a grooved cylinder, and a six-bladed vane. Experimental conditions were varied to obtain a wide range of gel strength. It is shown that the yield stresses observed with the smooth or grooved cylinder are close to each other while both are significantly lower than that obtained with the vane geometry. The difference between the yield stresses measured by vane geometry and the cylinder geometry was observed to correlate well with the intrinsic yield stress of the waxy oil gel, and this correlation is independent of the compositions of the waxy oil and the conditions under which the gels form. This correlation implies physically that it is the balance of cohesive strength versus adhesive strength that determines the fracture mechanism of gel in the yield stress measurement, while other factors of oil composition and test conditions may influence one or two of these strengths. Given that inconsistence of cohesive and adhesive strength would be a common occurrence, the understanding from the present work may also be applicable to other materials.

Automated summary

In this study, adhesive and cohesive fractures were identified as two possible modes of fracture during yield stress measurement of materials such as waxy oil gel. The balance between cohesive strength versus adhesive strength was found to determine the fracture mechanism of gel in the yield stress measurement, while oil composition and test conditions may influence one or both of these strengths.