A study to identify and correct friction-induced error of penetration measurement for agricultural materials

Penetration resistance (PR) has been regarded as a common measure for characterizing the density profile of soil and biological materials in agricultural engineering. Due to diversity of agricultural materials associated with different elastic–plastic properties, a prerequisite for a reasonable measurement is to preclude the effect of penetration friction component (PFC) between the penetration shaft and surrounding material during a penetration process, otherwise an additional error may be significantly induced relating to the cone penetration depth. In this study, a bi-directional penetration method was proposed to determine PFC using a specially designed cylinder with tests of two types of agricultural materials (silty–clay loam and chopped maize). No significant PFC was observed from the soil sample, whereas significant PFC was observed to be strongly dependent on penetration depth from the chopped maize. Thus, a mathematical filter was developed to correct the friction-induced error of the PR measurements.

► A novel method to identify friction-induced error from penetration measurement.
► No friction error was induced for measuring soil samples using ASABE-Standard cone.
► Significant friction error was observed in penetrating chopped maize samples.
► A filter is developed to eliminate the friction-induced error.