Now showing 1 - 4 of 4
  • Publication
    An Investigation into Scalpel Blade Sharpness Using Cutting Experiments and Finite Element Analysis
    (Trans Tech Publications, 2005-09-15) ; ;
    This paper presents an investigation into the sharpness of a surgical scalpel blade. An experiment was carried out in which a surgical scalpel blade was pushed through an elastomeric substrate at a constant velocity. The force-displacement characteristics were examined by plotting the stiffness as a function of blade displacement and it was found that this curve could clearly identify the point where the material separates to form a cut. A blade sharpness measurement was defined as the energy required to initiate an opening or cut in the substrate. A finite element model was developed to examine the stress state in the substrate at the point where the opening initiates. The development of this model is described. The model was validated against the experiment and close agreement was obtained. The von-Mises stress distribution under the blade tip was plotted and it was shown that the peak stress actually occurs away from the blade tip, suggesting that material separation would initiate away from the substrate surface.
      496
  • Publication
    Predicting Failure in Multi-Bolt Composite Joints Using Finite Element Analysis and Bearing-Bypass Diagrams
    (Trans Tech Publications, 2005-09-15) ; ;
    A three-dimensional finite element model of a three-bolt, single-lap composite joint is constructed using the non-linear finite element code MSC.Marc. The model is validated against an experiment where the load distribution in the joint is measured using instrumented bolts. Two different joint configurations are examined, one with neat-fit clearances at each bolt-hole and another with a 240 μm clearance at one hole with neat-fits at the others. Bearing and by-pass stresses are extracted from the model and used in conjunction with published bearing/by-pass diagrams to predict the failure load, mode and location for the joints. It is shown that the proposed model accurately predicts the failure behaviour of the joints, as determined from experiments on three-bolt joints loaded to failure. It is also shown that introducing a clearance into one hole significantly changes the failure sequence, but does not affect the ultimate failure load, mode orlocation. The proposed method demonstrates a simple approach to preg damage in complex multi-bolt composite joints.
      1109
  • Publication
    On the sharpness of straight edge blades in cutting soft solids: Part II – Analysis of blade geometry
    In Part I of this paper a new metric, titled the “blade sharpness index” or “BSI”, for quantifying the sharpness of a straight edge blade when cutting soft solids was derived from first principles and verified experimentally by carrying out indentation type cutting tests with different blade types cutting different target or substrate materials. In this Part II companion paper, a finite element model is constructed to examine the effect of different blade variables including tip radius, wedge angle and blade profile on the BSI developed in Part I. The finite element model is constructed using ABAQUS implicit and experiments are performed to characterise the non-linear material behaviour observed in the elastomeric substrate. The model is validated against the experiments performed in Part I and a suitable failure criterion is determined by carrying out experiments on blades with different tip radii. The paper finds that a simple maximum stress criterion is a good indicator for predicting the onset of cutting. The validated model is then used to examine blade geometry. It is shown that finite element analysis is an important tool in helping to understand the mechanics of indentation. Furthermore, the study finds that all the blade geometric variables have an influence on the sharpness of a blade, with the BSI being most sensitive to tip radius. Increasing the tip radius and wedge angle decreases the sharpness of the blade.
      1100Scopus© Citations 93
  • Publication
    On the sharpness of straight edge blades in cutting soft solids: Part I – indentation experiments
    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 cutting edge, 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, target materials and cutting rates and it is found that the index is independent of the target material and cutting rate 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.
      2372Scopus© Citations 128