Fracture toughness is an important mechanical property of materials that describes the failure of material by cracking. Yet, characterizing fracture toughness in soft tissue cutting is still a challenging task as the behavior of the soft tissue may vary under different tissue, cutting and pre-crack conditions [1]. Predicting cutting force has been important to needle biopsy design, surgical planning/training, and other surgical operations. However, in order to obtain accurate predictions, understanding the fracture toughness is crucial. In this study, we present an approach to characterize the fracture toughness directly from cutting experiments of hollow needle cutting soft tissue mimicking materials. Cutting tests are carried out to obtain the dynamic force response of gelatin samples when being cut by non-rotational and rotational hollow needles. The data is used to establish a mixed-mode fracture behavior which is then used to implement a cohesive surface based finite element model. Nearly 1% difference of the axial cutting force between the simulation and experimental results showed that the approach is capable of predicting accurate cutting force in rotational needle biopsy. The approach also has the potential to be used to predict the cutting force in various types of needle biopsy.

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