On the sharpness of straight edge blades in cutting soft solids: Part I – indentation experiments

Abstract

The sharpness of a blade is a key parameter in cutting soft solids, such as biological tissues, foodstuffs or elastomeric materials. It has a first order effect on the effort, and hence energy needed to cut, the quality of the cut surface and the life of the cutting instrument. To date, there is no standard definition, measurement or protocol to quantify blade sharpness. This paper derives a quantitative index of blade sharpness via indentation experiments in which elastomeric materials are cut using both sharp and blunt straight edge blades. It is found that the depth of blade indentation required to initiate a cut or crack in the target material is a function of the condition or sharpness of the blade's tip, and this property is used to formulate a so-called "blade sharpness index" (BSI). It is shown theoretically that this index is zero for an infinitely sharp blade and increases in a quadratic manner for increasing bluntness. For the blades tested herein, the sharpness index was found to vary between 0.2 for sharp blades and 0.5 for blunt blades, respectively. To examine the suitability of the index in other cutting configurations, experiments are performed using different blade types and target materials and it is found that the index is independent of the target material and thus pertains to the blade only. In the companion Part II to this paper a finite element model is developed to examine the effect of blade geometry on the sharpness index derived herein.

The influence of composition and location on the toughness of human atherosclerotic femoral plaque tissue

“…It has been previously demonstrated that the majority of blades indent the target substrate prior to cut initiation [55]. Furthermore, the extent of indentation can be significant depending on the substrate material and the condition of the blade.…”

“…Several techniques are available to induce a controlled fracture during toughness testing, including tearing [53]; scissoring [54,55]; and cutting [56,57]. Considering the size and shape of the plaque samples obtained from endarterectomy, it was not feasible to perform tearing tests to evaluate toughness [58].…”

“…During testing, a sample is clamped across the slit to the flat surface using custom designed clamps that are tightened with four equispaced bolts, Figure 1. The clamps are lined with sand paper and designed to provide minimal clamping force that limits the movement of the sample in the p-direction during cutting without inducing noticeable compressive transverse stresses that may reduce the energy required to cut the section [55].…”

On the sharpness of straight edge blades in cutting soft solids: Part II – Analysis of blade geometry

“…In Part I of this companion paper [1] a quantitative metric for the sharpness of a straight edged blade was developed and critically assessed for different blade types and target or substrate materials (i.e. the material being cut).…”

A combined experimental and numerical study of stab-penetration forces

“…Previous authors have examined the effect of using various different blades and it is now well established that the blade tip-geometry has a significant effect on the penetration force [3,4,8,23,24]. [3], in particular, has even examined the effect of using blunted blades.…”