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Cutting science in biology and engineering

Event

Location

Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire, MK16 9JJ

Overview

Theo Murphy international scientific meeting organised by Professor Gordon Williams FREng FRS, Professor Tony Atkins FREng, Professor Peter Lucas and Dr Maria Charalambides

Event details

Specific theories and applications of cutting are being reported in a bewildering number of journals. This is across materials, engineering, food, agriculture, health sciences, ecology, palaeontology, archaeology and more but they can be unified under the umbrella of fracture mechanics. Our aim is examine and disseminate this unified theory in discussion with investigators from many disciplines to advance research in these fields.

The draft programme is available to download and as are the biographies of the speakers. Recorded audio of the presentations will be available on this page after the event. Papers relating to this meeting will also be published in Interface Focus.

Call for posters - deadline 1 September 2015

A poster session will be held throughout the meeting alongside the schedule of presentations. To submit a poster please email a title, 200-word abstract and list of authors to the Royal Society events team at kavli.events@royalsociety.org no later than Tuesday 1 September 2015. The scientific organisers will make a selection based on the abstracts received. Please note spaces are limited.

Attending this event

This is a residential conference, which allows for increased discussion and networking. It is free to attend, however participants need to cover their accommodation and catering costs if required.

Enquiries: Contact the events team

Event organisers

Select an organiser for more information

Schedule of talks

26 October

09:00-12:30

Session 1

4 talks Show detail Hide detail

Chairs

Professor John A Nairn, Oregon State University, USA

09:05-09:40 Fundamentals of cutting

Professor Gordon WIlliams FREng FRS, Imperial College, UK

Abstract

Cutting is a process in which a tool is used to create a new surface in a solid. The creation of new surfaces is a fracture process so that cutting may be regarded as fracturing. However, fracture is usually driven by forces remote from the failure point while cutting involves forces being applied locally via the tool. The crucial factor in both processes is the energy per unit area required to create the new surfaces which is the notion introduced by A.A. Griffith. An understanding of the processes involved requires an energy balance to be drawn up to include the fracture energy, Gc, and other forms of energy dissipation. These include plastic deformation and friction and the latter is particularly important in cutting when the tool, or blade, rubs on the material being cut.

The analysis will be illustrated by considering the removal of a surface layer by a sharp wedge. If all the deformation is elastic, and hence there is no permanent deformation, and there is no friction then Gc is given simply by the cutting force divided by the cut width, This is similar to the splitting of wood though friction usually occurs and must be included. If the removed layer deforms plastically chip curling and shearing occurs and there is additional dissipation. For this rather simple system there are a series of transitions from elastic bending of the chip to firstly plastic bending and then to plastic shearing as the wedge angle of the tool increases.

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09:40-10:20 Cutting of soft solids

Dr Maria Charalambides, Imperial College London, UK

Abstract

The fracture toughness of soft solids such as foods is often needed for correlations to important parameters such as sensory attributes or release rates of contained substances (e.g. salt) and as input in model simulations of industrial food processes or mastication. Soft solids are more difficult to test and analyse due to their high compliance and strong non-linearity as well as their strong dependence on loading rate. This behaviour makes conventional fracture tests used for structural materials unsuitable for soft solids. Cutting tests in the form of wire or blade cutting offer an attractive alternative for such materials.

Cutting tests in the form of wire and blade cutting are presented for a range of food materials including cheese, gels and pet foods. The fracture toughness calculated from the cutting test data are compared to independent fracture tests for validation purposes. Methods enabling modelling of fracture initiation and propagation in such soft solids will be presented. Possible failure criteria based on critical maximum strain and cohesive zone models are employed and their accuracy is judged by comparing with experimental data. The studies enable the effect of strain rate on fracture toughness of this class of materials to be determined.

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10:45-11:25 What is sharpness?

Mr Roger Hamby, CATRA, UK

Abstract

This talk will discuss and define sharpness from a practical and scientific point of view, across all aspects of the use of sharp edge cutting technology from micro surgical cutting, to shaving, to food processing, to industrial processes. Methods of sharpness measurement, both human subjective assessment to scientific measurement and quantitative measurements will be described, including their drawbacks and implications.

The talk will explain in detail the physical and material requirements of a sharp edge, the implications on cutting performance in terms of energy consumption and quality of the resultant cut and condition of the cut item. Sharpening techniques will be described, illustrating how incorrect sharpening can lead to significantly inferior performance both in terms of how sharp a blade is, but also how long a cutting edge will last.

An overview of the instrumentation used to quantify sharpness, edge durability and cutting edge geometries will be given and how they can be used both within blade / knife manufacture and importantly in re-sharpening. The talk will describe a number of real life stories, indicating significant financial losses, some incurred by World class companies, through ignorance of the simple but essential application of sharpness technology.

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11:25-12:10 Scale effects and slice-push in cutting

Professor Tony Atkins FREng, University of Reading, UK

Abstract

Why it is easier to cut when there is motion along, as well as perpendicular to, a cutting blade is explained and the analysis is applied to optimisation of blade geometries to produce minimum damage in cut surfaces.

The formation of grooves by scratching is an example of cutting with more than one edge. The mechanics are investigated and applied to the topic of abrasive wear. It is shown that not only hardness and contact load is important, but also the fracture toughness of the surface material.

Cutting the same material at different depths of cut results in a spectrum of different forms of offcut, from ductile continuous ribbons at small depths to brittle ‘knocking lumps out’ at large. The associated forces vary from steady, through oscillating, to intermittent. Which behaviour occurs depends on the depth of cut relative to a material length parameter given by [ER/k2] = [KC/k]2 where E is Young’s modulus, R is fracture toughness, k is the shear yield strength and KC is the critical stress intensity factor. Glass has low KC/k and is normally brittle, but it can be machined with continuous chips at micrometre depths of cut; steel has high KC/k and normally machines in a ductile manner, but at metre depths of cut becomes brittle. This behaviour represents a ‘cube-square’ scale effect and supports the contention that analysis of cutting is a branch of elastoplastic fracture mechanics. Its connexion with allometry (scaling in biology) is discussed.

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12:30-13:30 Lunch

13:30-17:00

Session 2

4 talks Show detail Hide detail

Chairs

Professor Roland Ennos, University of Hull, UK

13:30-14:10 Cutting in dentistry

Professor Timothy Watson, King's College London, London

Abstract

Most dentists pay little heed to what is actually happening at the end of their turbine but as they proceed to prepare a cavity within a tooth for restoration. However, there are many surface preparation factors that will influence how well our adhesive and non-adhesive materials will work. Many of these will relate to the methods used to prepare the cavity in the first place such as diamond, tungsten carbide and steel burs.  Cutting of the root dentine is also needed in preparation prior to endodontic treatment, with significant commercial investment for the development of flexible cutting instruments based around nickel titanium alloys.

Tooth-cutting interactions have been examined microscopically for over twenty five years using a variety of microscopic techniques; in particular, video-rate confocal microscopy. This has given a unique insight into how many of the procedures that we take for granted are achieved in clinical practice, by showing microscopic video images of the cutting as it occurs within the tooth. Cutting techniques with high and low torque handpieces, dry and wet airbrasive applications and laser cutting have all been imaged microscopically. The influence of these preparation modalities on both sound and diseased (carious) enamel and dentine is profound: especially when the integrity of the remaining tooth surface has such a strong influence on success or failure for bonding adhesive materials. 

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14:10-14:50 Surgery and puncturing

Dr Ferdinando Rodriguez y Baena, Imperial College London, UK

Abstract

Surgical robotics is gaining in popularity due to the ever-increasing need for more complex, accurate, but less invasive surgery, which conventional instruments are holding back. Amongst the many embodiments at different stages of research and development, needle steering holds promise, but has yet to demonstrate real clinical impact. This minimally invasive procedure involves the insertion of a thin, flexible needle through the skin and into tissue, for application to a variety of clinical needs, including diagnostics, therapy and therapy monitoring. The ability to steer the needle enables the surgeon to avoid obstacles and counteract targeting inaccuracies due to tissue deformation (due to tool-tissue interactions) and organ motion (due to e.g. breathing and pulsatile forces), but these first need to be appropriately modelled and tracked, which remains an open challenge.

In this presentation, the complexity of tool-tissue interaction modelling will be reviewed in the context of exciting new research on a steerable needle, codenamed STING, which is inspired by the ovispotior (or egg laying channel) of parasitic wasps. The biomimetic foundations of this unique design will be discussed, followed by an overview of several unique approaches to the characterisation and modelling of the needle behaviour. These have been developed specifically for STING, with the aim of understanding and optimising its performance in surgery, but many of the results have broader implications. The talk will end with a summary of the current state of the field and an outlook of what is to come.

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15:15-15:55 Teeth as cutting tools

Professor Gordon Sanson, Monash University, Australia

Abstract

Insects and mammals, in general, consume each other or terrestrial plants; in other words they eat organisms with structures that resist gravity. Insects have a tough exoskeleton while mammals have an endoskeleton. The leaves and stems of vascular plants, in contrast, have tough structures around each cell. The scale, heterogeneity and temporal variability of food affect the adaptations for cutting and processing food. The requirements for processing insects as food therefore differ from those for processing relatively large animals. Herbivores face the added complication that the physical properties of plant food can vary with environmental factors.

Herbivores range from the smallest insects that can live and feed inside a single leaf to larger insects and the smallest mammals that consume individual leaves but are still small enough to be able to select parts of leaves. Cutting adaptations relate to the fine scale properties of the food. On the other hand the largest mammals process food in bulk and the implications of this are not well understood.

Grazing (grass eating) in large mammals has generally evolved from browsing (eating dicotyledonous plants). Browse is commonly assumed to be relatively easy to physically process, compared with a diet of grasses (a group of monocotyledonous plants) that are considered to be tough and fibrous. These assumptions are reviewed. Browsers are potentially faced with a highly heterogeneous diet, particularly when living in seasonal environments. Cutting adaptations appear to include clearance of fractured components of the diet away from the cutting edges. In grazers, the more complicated cutting patterns of the teeth may relate not so much to relative toughness, or even the pattern of the veins, but to the bulk processing of very long, thin and narrow leaves.

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15:55-16:35 Abrasive tooth wear as a cutting process

Professor Peter Lucas, Kuwait University, Kuwait

Abstract

Tooth wear in mammals gradually removes features of the working surfaces of teeth vital for breaking down food particles. This loss of tooth tissue is a major factor limiting the lifespans of individuals in the wild. The threat to enamel, the main contact tissue of tooth crowns, is mainly mechanical, stemming from contacts with hard objects including silica(tes) from soils, amorphous plant silica and also perhaps woody plant tissue such as seed coats. Shallow marks have been documented extensively on worn tooth enamel in microwear studies, forming the main indication of what has transpired during wear events. The circumstances of this mechanical wear qualify as a type of cutting process in which the foreign object (siliceous particle or seed shell) can be viewed as the ‘tool’ creating change in the enamel surface. During any one contact, there are two possibilities: either the enamel surface is re-arranged via plastic deformation (thus not losing material within that single event) or a chip or ribbon of enamel is created that results in immediate tissue loss (definitive of wear).  The factors affecting what transpires are well-known to include the relative hardness of the contacting materials, angulation of the contacting surfaces and friction. Less well-known is the effect that enamel toughness plays in protecting against wear, and the critical depth to which enamel is disturbed. In collaboration with a large group of collaborators that include A.G. Atkins, we have attempted displacement-controlled cutting tests on enamel designed to simulate wear conditions accurately and discover the effective value of the toughness of enamel at this scale. From this, we suggest that the standard ‘R-curve’ approach to biological mineralized tissues, which would have toughness values building from low values upwards with increasing scale, has to be revised for enamel. 

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27 October

09:00-10:00

Session 3

3 talks Show detail Hide detail

Chairs

Professor Peter Lucas, Kuwait University, Kuwait

08:30-08:55 Evolution and plasticity of leaf fracture toughness in species-rich tropical forests

Dr Robert Schofield, University of Oregon, USA

Abstract

Cutting and puncturing efficiency is likely to be especially important in small organisms (or small machines) with limited power output. This efficiency can be greatly reduced by fracture and wear of the cutting edge: we have found that leaf cutter ants with average levels of mandible wear cut roughly half as fast and likely spend twice as much energy on a cut as would their sisters with pristine mandibles. The ants with the most worn mandibles were found to be carrying but not cutting. This result suggests that cutting efficiency may play a more important role than previously recognized in the behaviour and ecology of small organisms. Leaf cutter ants, as well as a broad array of other small organisms, use materials containing up to 25% by mass of elements such as Zn, Mn, Fe, Cu and Br at the tips of their cutting, puncturing and grasping tools. These materials may play a role in preserving sharp tool.

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08:55-09:20 Wedging putative hominin foods revelas new insights on human evolution

Professor Nathaniel J Dominy, Dartmouth College, USA

Abstract

The dexterity of primate forelimbs is unique among vertebrates. Debate on the origins of this dexterity has focused the importance of insect capture or food acquisition amid fine terminal branches. The manual evaluation of fruit ripeness is seldom considered, and we suggest that the advantages of mechanosensory assessment favoured the evolution of enhanced manual dexterity among great apes. To explore this idea, a number of areas was studied including the foraging behaviour of chimpanzees in Kibale National Park, Uganda, and the spectral, chemical, and mechanical properties of fruit, with cutting tests revealing ease of fracture in the mouth. Seasonal fruits and figs were distinguished between, a critical “fallback food” that sustains chimpanzees when fruit is scarce. By integrating the ability of different sensory cues to predict fructose content in a Bayesian updating framework, the amount of information gained when a chimpanzee successively observes, handles, and bites figs was quantified. The cue eliciting fig ingestion was not colour or size, but fig mechanics (including toughness estimates from wedge tests), which alone predicted sugar concentration. This result accounts for observations of fig palpation and dental incision, tasks that require fine motor control of the digits. It is suggested that hominoid manual precision evolved in response to fruits without chromatic signals of ripeness

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09:20-10:00 Effect of mandibular wear on leaf-cutter ants

Professor Kaoru Kitajima, Kyoto University, Japan

Abstract

Leaves as the main photosynthetic organ of plants must be well protected against various hazards to achieve their optimal lifespans. Yet, within-species variations and the material bases of this ecologically important trait have not been explored for sufficiently many species. Here, a large dataset of leaf physical strength from a species-rich humid tropical forest on Barro Colorado Island, Panama is presented, reporting both among and within species variations in relation to light environments (sun-lit canopy vs. shaded understory) and ontogeny (seedlings vs. adults). In this data set encompassing 281 free-standing woody species and 428 species-light combinations, lamina fracture toughness varied ca. 10 times. A central objective of our study was to identify generalizable patterns on structural and material base for the interspecific variations in leaf lamina fracture toughness. The leaf lamina is a heterogeneous structure in which strong materials in cell wall, such as cellulose and lignin, contribute disproportionately to the mechanical strength. Significant increases in leaf fracture toughness from shade to sun, and from seedling leaves to adult leaves were found. Leaf fracture toughness variations within and across species showed positive correlation with tissue density (dry biomass per unit volume) and cellulose mass concentration, but showed negative correlation with mass concentrations of lignin and hemicelluose. These bivariate relationships shift between light environments, but the bulk abundance of cellulose (mass per unit volume) exhibits a common relationship between light environments and ontogeny. Hence, the bulk density of cellulose is likely a universal predictor of fracture toughness in humid tropical forests.

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10:45-12:40

Session 4

4 talks Show detail Hide detail

10:45-11:10 Cut marks on bone surfaces: Influences on variation in the form of traces of ancient behaviour

Professor David Braun, George Washington University, USA

Abstract

Although it is known that our lineage has been producing sharp edge tools for over 2.6 million years, our knowledge of what they were doing with these tools is far less complete. Studies of these sharp edged stone tools shows that they were most likely used as cutting implements. However, the only substantial evidence of this is the presence of cut marks on the bones of animals found in association with stone tools in ancient deposits. Numerous studies have aimed to quantify the frequency and placement of these marks. At present there is little consensus on the meaning of these marks and how the frequency relates to specific behaviours in the past. The possibility that mechanical properties associated with edges of stone tools as well as the properties of bones themselves may contribute to the overall morphology of these marks and ultimately their placement and frequency in the archaeological record will be investigated. Using standardized tests of rock mechanics (Young’s modulus and Vickers hardness) to effect of hardness of tool edges on cut mark morphology is identified. In addition how indentation hardness of bones may impact the overall morphology of cut marks is investigated. Using varied rock types and different bone portions the impact of is investigated mechanical properties of both bone surfaces and stone edges on the shape and prevalence of cut marks on animal bones.

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11:10-11:35 Toughness in arms and armour

Dr Eddie Cheshire, University of Reading, UK

Abstract

Reseach was carried out into the nature of cuir bouilli, a mediaeval  armour material believed to have been made from animal hide. Based on rawhide and leather, notional reproductions were produced which were subjected to mechanical  testing and arrow shooting trials. The most efficacious product was judged to be rawhide which had been  boiled for a limited time in water.

Depending on the raw material and the boiling time it was found that materials with a very wide range of toughnesses could be produced. Leather is tough but has limited ability to stop arrows whereas, at the other extreme, boiled leather is brittle and shatters under impact. Boiled rawhide can be made hard enough to firmly grip arrows as they penetrate but retain sufficient toughness to resist cracking. Work was also carried out to identify the most effective design of arrowheads. The addition of a hard impact face to the hide-based armour, as advocated in Arab literature contemporaneous with the Crusades, was found to significantly improve the resistance to penetration by arrows. Although dating from almost 1000 years ago, the overall principals of hardness and toughness of hide based cuir bouilli invite comparison with modern body armours.

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11:35-12:00 Point of impact: The influence of speed and tooth size on puncture mechanics

Dr Philip Anderson, Duke University, USA

Abstract

A diverse array of organisms utilize puncture to aid in prey-capture, from jellyfish injecting venom with single-cell nematocysts, to centimeter-scale shrimp harpooning fish, and human hunters shooting bows and arrows. Across seven orders of magnitude, these disparate examples are unified by a predator’s weapon (nematocyst, spine, arrow, etc.) delivering energy to prey in order to create fracture. The commonality of these systems offers an opportunity to explore how organisms at vastly different scales with distinct structures and kinematics perform puncture. Energy is a key variable linking kinematics to fracture mechanics in high-speed puncture systems. However, attempts to synthesize kinematics and fracture into a theoretical framework for puncture are complicated by factors such as weapon shape, material properties and impact dynamics. A review of the experimental literature reveals that as biological puncture systems get smaller, their speed tends to increase. A series of puncture tests were performed in order to examine this scaling relationship in terms of kinematics, fracture mechanics and impact. High-speed videography of arrows fired into ballistics gelatin at variable weight and speed revealed that the kinetic energy of the arrow in flight strongly influences fracture in the gelatin, more so than momentum or velocity alone. The fracture patterns seen during experiments give new insights into how organisms utilize speed and shape to successfully puncture biological tissues. By expanding the range of speed and size in future experimental analyses, a framework will begin to be established for comparing puncture mechanics across biological scales.

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12:00-12:25 Anisotroph: wood and veeners

Professor George Jeronimidis, University of Reading, UK

Abstract

Numerical simulation of orthogonal cutting is a complex, multi-physics problem involving large-deformation material modelling, contact with friction, and fracture mechanics for the propagating crack in the path of the cut. A previous paper has demonstrated that the material point method (MPM) can achieve robust numerical simulations of the entire cutting process including development of steady-state cutting conditions, crack tip touching, chip formation, and chip curling. This poster describes application of this new numerical tool to analysis of block planes used for wood planing. The simulations account for anisotropic and plastic behaviour of wood, allow for large rotation in the chip curling, and can explicitly model many features of block planes. Some key variables that will be presented are rake angle, honing angle on the blade, the use of a chip breaker, the role of mouth opening in the base plate of the plane, thickness of cut, tool sharpness, and the effect of friction. The cut material is based on fracture properties of Douglas-fir and accounts for fibre bridging affects observed in recent experiments. The simulations can also consider effect of the tool on fibre bridging process and effect of the orientation of growth rings in the wood with respect to the cutting plane.

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12:40-13:40 Lunch

13:40-17:00

Session 5

3 talks Show detail Hide detail

13:40-14:40 Discussion: Machining, weapons and armour

Paulo A. F. Martins, Universidae de Lisboa, Portugal

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14:40-15:40 Discussion: Soft solids and surgical cutting

Professor Ton van Vliet, University of Wageningen, Netherlands

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16:00-17:00 Discussion: Biology and ecology

Professor Roland Ennos, University of Hull, UK

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Cutting science in biology and engineering Theo Murphy international scientific meeting organised by Professor Gordon Williams FREng FRS, Professor Tony Atkins FREng, Professor Peter Lucas and Dr Maria Charalambides Kavli Royal Society Centre, Chicheley Hall Newport Pagnell Buckinghamshire MK16 9JJ
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