Strain analysis near the cutting edge in orthogonal cutting of hinoki (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) using a digital image correlation method

A digital image correlation (DIC) method was utilized to measure strain distributed within approximately 0.5 mm of the cutting edge during slow-speed orthogonal cutting of air-dried hinoki (Chamaecyparis obtusa), to clarify the relationships of the strain distribution and cutting conditions, including cutting angle (\(\theta\)) and depth of cut (\(d\)). The strain was measured in 0.04 mm steps, and the measurable minimum strain was approximately 0.08%. Tensile strain of 3% or larger normal to the cutting direction, \({\varepsilon _y}\), tended to extend 0.2 mm or further ahead of the tool when \(\theta \leq 60^\circ\) and \(d \geq 0.1{\text{ mm}}\). This tensile \({\varepsilon _y}\) corresponded to the occurrence of the fore-split in Chip Type I. The tensile \({\varepsilon _y}\) detected along the path of the cutting edge decreased as \(\theta\) and/or \(d\) decreased. Positive shear strain, \({\gamma _{xy}}\), tended to be detected ahead of the tool in Type I. Negative \({\gamma _{xy}}\) tended to be detected ahead of the tool in Type II and III \(\left( {\theta \geq 70^\circ ,\,\,d \geq 0.05{\text{ mm}}} \right)\). These \({\gamma _{xy}}\) values were considered to be related to the elongation and shrinkage of the chip. The study confirmed the usability of the DIC method for the evaluation of cutting conditions and also to classify chip formation into chip types.