Fracture toughness of pea: Weibull analysis

The study focuses on evaluation of the fracture behavior of peas by examining the effect of moisture content upon seed fracture toughness and Weibull modulus. Individual pea seeds with varying water content between 4% and 20% (wet basis) were compressed using a universal testing machine, Zwick Z020. On the basis of recorded load–deformation curves, three different toughness indices were determined. They were based on energy inputs during compression and were calculated from varied areas under the force–displacement characteristic. A relation between the rate of energy increase for the pre-cracking phase and the seed cracking phase was employed to propose a new procedure for the fracture toughness determination. The data scatter for the toughness index was evaluated by Weibull statistics. The dimensionless toughness index computed according to the new procedure showed on increase with the rise in seed moisture from 0.9 to 2.7. It was shown that in the moisture range from 4% to 16% the Weibull modulus increased from 1.3 to 16.2. This may correspond to the transition in the fracture mechanism from being brittle in nature for dry seeds to more ductile for the wet ones. The applicability of Weibull statistics as a measure of mechanical properties of biological materials has been briefly discussed.