Cutting Mechanism Of Claws Of The Mole-rat (Scaptochirus Moschatus)

The mole rats are good at digging and can dig through a 300-foot long tunnel in just one night. In addition, moles have a peculiar digging mechanism, humeral rotation digging. Their manus are the main tools for digging soils. The wide and shovel-like manus has five digits and grows outwards. All these above result from the long-term evolution in the soil environment. The claw of the manus is the bionic prototype for the soil cutting tools and excavation tools. Studies on them can provide the useful biologic information for the bionic cutting technology and the design of soil cutting tools and excavation tools.Coupled with the metal cutting theory, the cutting process used by the mole rats was studied from the claw and the relative movement between claws and tunnel wall, and the studies of claws included their morphology and material performance.1. Aspect of clawThe macro-geometry of claws for the mole rats was made the qualitative and quantitative analysis using the stereomicroscopy and the reverse engineering. The claws of manus are similar in shape. Among them the three middle claws are a little round and the two outer claws are a little tip. All the claws are obviously curved in the transverse and longitudinal direction. They are thin at the tip and thick at the root. In addition, the three middle claws have a larger value in length, width and thickness than the two outer claws. The dorsal surface of claws is smoother than the ventral surface. The lower edge of front section is smoother than the upper edge for the claw 1 and 2; they are approximately symmetrical for claw 3; on the contrary for the claw 4 and 5. The lower and upper edges of hind section can be considered as the straight line through the fitting for all claws.The data clouds of ventral and dorsal surface of the claw for the mole's manus were obtained with 3-D laser scanning system. The surface reconstruction was made using the point-line-surface method after they were reduced and made the smoothing processing. Moreover, the model precision of surface reconstruction was analyzed. The results showed that the precision was satisfactory and the surface reconstruction can be used for the quantitative analysis of geometric shape for the mole's claw.Based on the claw's model, the quantitative analysis of surface characteristic was made. The second derivative and curvature of contour curves were calculated, accordingly the surface characteristic of claws was concluded. The results showed that the dorsal and ventral surface have the smaller vertical bending and more lateral bending. The dorsal surface is smoother than ventral surface. The ventral surface characteristic influenced the cutting performances of the claw.The section structure of claw was examined by carrying out the stereomicroscopy and scanning electronic microscopy (SEM). It was found that the claw mainly comprises four layers: the dorsal layer (DL), the ventral layer (VL), the intermediate layer (IL) and strengthening layer (SL). The mechanical properties were studied in micro- and nano-indentation experiments, including the surface hardness, section hardness and elastic modulus. The results showed that the dorsal hardness (DH) of the claw is harder than the ventral hardness (VL), that the tip hardness is harder than the central hardness, and that the claw is consist of a hard core covered by the softer layers.2. Aspect of relative movement between claws and tunnel wallThe test results show that the movement trajectory of mole rats' foreleg has three vectors: vector X, in the direction of body width; vector Y, in the direction of body length; vector Z, in the direction of body hight. The cutting amount in the direction of body width is larger than that in the direction of body hight.By means of the metal cutting theory, the cutting theory of mole rat's claw was preliminary established. During the soil cutting process, the cutting movement of claws is composed of one main movement V_c, the rotation of humerus around the axis of humerus, and two feeding movements V_f1 and V_f2, the forward movement of body and the rotation of elbow respectively. The cutting amount and cutting structure parameters of claws were defined. Moreover, the applications of the cutting theory of mole rat's claw were discussed.By the help of the cutting theory of metal, the cutting mechanism of claws of the mole-rat was studied from the shape, material performance and cutting behavior of the claw, which has the significance for building the bionic excavating and cutting theory.