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American Society for Testing and Materials

Computer and Robot Vision Vol. 1, by R.M. Haralick and Linda G. Shapiro, Addison-Wesley, 1992, ISBN 0-201-10887-1.

Computer and Robot Vision

Adhesion to wet and dynamic surfaces, including biological tissues, is important in many fields but has proven to be extremely challenging. Existing adhesives are cytotoxic, adhere weakly to tissues, or cannot be used in wet environments. We report a bioinspired design for adhesives consisting of two layers: an adhesive surface and a dissipative matrix. The former adheres to the substrate by electrostatic interactions, covalent bonds, and physical interpenetration. The latter amplifies energy dissipation through hysteresis. The two layers synergistically lead to higher adhesion energies on wet surfaces as compared with those of existing adhesives. Adhesion occurs within minutes, independent of blood exposure and compatible with in vivo dynamic movements. This family of adhesives may be useful in many areas of application, including tissue adhesives, wound dressings, and tissue repair.

Tough adhesives for diverse wet surfaces

Gait Analysis. An Introduction

A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

The strain rate sensitivity of two commercial aluminium alloys AA6082 and AA7108 in peak temper T6 and overaged T79 condition is analysed. These alloys are precipitation hardenable and as such, are expected to have a relatively low strain rate sensitivity. Their response to rapid loading has been tested over a wide range of strain rates, from 0.1 to 3000 s −1 at room temperature, 375 and 515°C for AA6082 and room temperature, 280 and 340°C for AA7108. Specimens were cut from planar extruded sections and tested in uniaxial compression with the deformation axis parallel to the extrusion direction. Intermediate strain rate testing was carried out using a computer controlled servo-hydraulic testing machine and high strain rate testing above 500 s −1 on a Split Hopkinson Pressure Bar (SHPB). Owing to inaccuracies of the conventional Kolsky solution of the SHPB, a numerical simulation was performed. The flow stress at a plastic strain of 5% was plotted as a function of strain rate and temperature. Up to 2000 s −1 , there is very little change of the activation volume with increasing temperature for both alloys, indicating that barriers to thermal activation are large and approximately the same. However, at higher strain rates, the rate controlling mechanism appears to change and at lower temperatures, a trend towards negative strain rate sensitivity was observed. Metallographic examination of AA7108 revealed strain localisation, seen as parallel deformation bands. The strain localisation could be the cause of the negative strain rate sensitivity.

High strain rate properties of selected aluminium alloys

Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer

Mechanical testing and modelling of a material for biomedical applications have to be based on conditions representative of the application of interest. In this work, an ether-based polyurethane elastomer is used to build mock arteries. The aim is to study the behaviour of arteries under pulsatile loading conditions and how that behaviour changes with the development and progression of atherosclerosis. Polyurethane elastomers are widely used as biomaterials, e.g. in tube form for bypasses and catheters. However, their mechanical behaviour has not been extensively characterised. This work establishes the variations in the behaviour of polyurethane elastomer with temperature, humidity and strain rate and also reports planar and equibiaxial tension, relaxation, creep and cyclic test results, providing a comprehensive characterisation of the material. Test results are used to determine the properties of the polyurethane elastomer and in the selection of a representative material model for future simulations of arterial behaviour and the development of atherosclerosis. The results show that the behaviour of the elastomer is significantly dependent on both humidity and temperature, with Young's modulus of 7.4 MPa, 5.3 MPa and 4.7 MPa under dry-room temperature, wet-room temperature and wet at 37 ( composite function)C conditions, respectively. The elastomer also exhibits rate-dependent viscoelastic behaviour. Yeoh's hyperelastic material model provided the best fit to the entire range of experimental data. The Neo-Hookean model provides a good fit at small strain but significantly diverges at large strains. Nevertheless, in applications where deformations are relatively small, i.e. below 15%, the Neo-Hookean model can be used.

https://researchrepository.ucd.ie/bitstream/10197/4615/2/Mechanical%20Characterisation%20of%20Polyurethane%20Elastomer%20for%20Biomedical%20Applications%20done.pdf

Mechanical characterisation of polyurethane elastomer for biomedical applications.

Enhancing mode-I and mode-II fracture toughness of epoxy and carbon fibre reinforced epoxy composites using multi-walled carbon nanotubes

The peel test is a popular test method for measuring the peeling energy between flexible laminates. However, when plastic deformation occurs in the peel arm(s) the determination of the true adhesive fracture energy, G c , from the measured peel load is far from straightforward. Two different methods of approaching this problem have been reported in recently published papers, namely: (a) a simple linear-elastic stiffness approach, and (b) a critical, limiting maximum stress,  max , approach. In the present article, these approaches will be explored and contrasted. Our aims include trying to identify the physical meaning, if any, of the parameter  max and deciding which is the better approach for defining fracture when suitable definitive experiments are undertaken. Cohesive zone models Fracture mechanics Laminates Peel tests Plastic deformation

/pdf/cohesive-zone-models-and-the-plastically-deforming-peel-test-39o4y81uh0.pdf

Alojz Ivankovic

Papers

High strain rate properties of selected aluminium alloys

Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer

Mechanical characterisation of polyurethane elastomer for biomedical applications.

Enhancing mode-I and mode-II fracture toughness of epoxy and carbon fibre reinforced epoxy composites using multi-walled carbon nanotubes

Cohesive zone models and the plastically deforming peel test