Papers by George Jeronimidis
Morphological Aspects of Wood Fracture
Mechanical Behaviour of Materials, 1980
The challenges of an artist
What is the Architect Doing in the Jungle? Biornametics, 2013
Being part of the Biornametics project has been a very exciting opportunity. Working with colleag... more Being part of the Biornametics project has been a very exciting opportunity. Working with colleagues from different backgrounds and with a group of very able and dedicated students has prompted me to look again at aspects of Biomimetics I was less familiar with. Trying to abstract concepts from biology for a biornametic design which integrates functional, materials, geometrical, responsive and aesthetical aspects has been a very interesting and challenging exercise for the whole team.
eXPRESS Polymer Letters, 2009
The falling weight impact properties of composites obtained by introducing 16 wt% of phormium ten... more The falling weight impact properties of composites obtained by introducing 16 wt% of phormium tenax fibres extracted with two different methods i.e., either manually or by paddocking and scutching and in both cases chemically treated with a 1% solution of sodium hydroxide, have been investigated. The effect of the two extraction methods on fibre characteristics is compared by the tensile properties of the fibres and the flexural properties, fracture modes and hysteresis cycles parameters (impact energy partition, linear stiffness and normalised penetration energy) of final laminates. Laminates obtained using paddocked and scutched fibres are clearly superior to those manufactured using the manually extracted fibres: this is due to the more effective fibre impregnation in the former case than in the latter, which results in an improved dissipation of energy during the damping phase of the impact event. It is noteworthy, however, that the low volume of fibres introduced in the laminate with the manufacturing method adopted does not allow obtaining properties comparable with other semi-structural plant fibre composites, such as e.g., hemp fibre reinforced laminates.
Smart Materials and Structures, 2005
In this work, compliant actuators are developed by coupling braided structures and polymer gels, ... more In this work, compliant actuators are developed by coupling braided structures and polymer gels, able to produce work by controlled gel swelling in the presence of water. A number of aspects related to the engineering of gel actuators were studied, including gel selection, modelling and experimentation of constant force and constant displacement behaviour, and response time. The actuator was intended for use as vibration neutralizer: with this aim, generation of a force of 10 N in a time not exceeding a second was needed. Results were promising in terms of force generation, although response time was still longer than required. In addition, the easiest way to obtain the reversibility of the effect is still under discussion: possible routes for improvement are suggested and will be the object of future work.
Theoretical Analysis of Large Deformation Simultaneous Tearing and Peeling of Elastoplastic Materials
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1996
Simultaneous tearing and peeling of multiple strips is theoretically investigated using the large... more Simultaneous tearing and peeling of multiple strips is theoretically investigated using the large deflection theory of cantilevers made of elastoplastic material with linear strain hardening. The relationship between the fracture toughness and the curvature at the fracture propagation front is obtained for general cases. It is shown that for the moment loading case, the non-dimensional external moment, m1, during tearing and peeling along straight paths, is a constant and is independent of the initial beam length Lo. With concentrated force loading, the non-dimensional force f will reach a constant value f=fm during propagation. It is shown that fm is almost the same for both initially straight and pre-bent beams, and decreases with an increase in the external force loading angle φ. For initially straight beams, when the non-dimensional fracture toughness, D, is small, fm may be less than the initiation force f1 for fracture. Fm/H does not increase linearly with an increase in the b...
Biomechanics explained
Materials Today, 2004
Journal of Materials Science, 2004
A series of three-point bend tests using single edge notched testpieces of pure polycrystalline i... more A series of three-point bend tests using single edge notched testpieces of pure polycrystalline ice have been performed at three different temperatures (−20 • C, −30 • C and −40 • C). The displacement rate was varied from 1 mm/min to 100 mm/min, producing the crack tip strain rates from about 10 −3 to 10 −1 s −1. The results show that (a) the fracture toughness of pure polycrystalline ice given by the critical stress intensity factor (K IC) is much lower than that measured from the J-integral under identical conditions; (b) from the determination of K IC , the fracture toughness of pure polycrystalline ice decreases with increasing strain rate and there is good power law relationship between them; (c) from the measurement of the J-integral, a different tendency was appeared: when the crack tip strain rate exceeds a critical value of 6 × 10 −3 s −1 , the fracture toughness is almost constant but when the crack tip strain rate is less than this value, the fracture toughness increases with decreasing crack tip strain rate. Re-examination of the mechanisms of rate-dependent fracture toughness of pure polycrystalline ice shows that the effect of strain rate is related not only to the blunting of crack tips due to plasticity, creep and stress relaxation but also to the nucleation and growth of microcracks in the specimen.
Residual Stresses in Carbon Fibre-Thermoplastic Matrix Laminates
Journal of Composite Materials, 1988
Residual stresses in composite laminates depend on thermoelastic properties of the material and p... more Residual stresses in composite laminates depend on thermoelastic properties of the material and processing temperatures. Their distribution in the various laminae is a func tion of stacking sequence and ply orientation. In this work residual stresses in APC-2 cross-ply laminates have been investigated. Predictions based on classical laminate theory are compared to measured levels of residual stress obtained from a number of experimen tal techniques. The analysis of the results shows that accurate predictions can be made pro vided that the changes in thermoelastic properties of the materials with temperature are taken into account.
An EHT re-examination of Acetylcholine
Theoretica Chimica Acta, 1973
The results of EHT calculations on the most stable conformations of the neurotransmitter molecule... more The results of EHT calculations on the most stable conformations of the neurotransmitter molecule acetylcholine (ACh) are reported. These results are compared with those obtained with other semiempirical quantum mechanical methods CNDO/2, INDO and PCILO, and ...
Plant biomechanics
International audienc
Continuous hardness testing for the determination of mechanical and fracture-mechanical properties of laminated particleboards
Wood fibre cell walls: methods to study their formation structure and properties
Wood machining: problems, approaches and strategies
Stress generation in the tension wood of poplar is based on the lateral swelling power of the G-layer
The Plant Journal, 2008
The mechanism of active stress generation in tension wood is still not fully understood. To chara... more The mechanism of active stress generation in tension wood is still not fully understood. To characterize the functional interdependency between the G-layer and the secondary cell wall, nanostructural characterization and mechanical tests were performed on native tension wood tissues of poplar (Populus nigra x Populus deltoids) and on tissues in which the G-layer was removed by an enzymatic treatment. In addition to the well-known axial orientation of the cellulose fibrils in the G-layer, it was shown that the microfibril angle of the S2-layer was very large (about 36 degrees). The removal of the G-layer resulted in an axial extension and a tangential contraction of the tissues. The tensile stress-strain curves of native tension wood slices showed a jagged appearance after yield that could not be seen in the enzyme-treated samples. The behaviour of the native tissue was modelled by assuming that cells deform elastically up to a critical strain at which the G-layer slips, causing a drop in stress. The results suggest that tensile stresses in poplar are generated in the living plant by a lateral swelling of the G-layer which forces the surrounding secondary cell wall to contract in the axial direction.
Comparison of mechanical properties of tension and opposite wood in Populus
Wood Science and Technology, 2004
... technique has been used successfully by several authors to measure the energy associated with... more ... technique has been used successfully by several authors to measure the energy associated with cutting materials (Atkins and Vincent 1984; Huang et al. ... on the force-displacement curves, the zones corresponding to tension and normal wood (2nd year) and 1st year wood (Fig. ...
The fracture behaviour of wood and the relations between toughness and morphology
Proceedings of the Royal Society of London. Series B. Biological Sciences, 1980
Wood is a complex composite material that possesses an excellent combination of mechanical proper... more Wood is a complex composite material that possesses an excellent combination of mechanical properties. In particular the toughness, or work of fracture, is very high, reaching a value in excess of 1.0 x 10 4 J/m 2 , which, mass for mass, is roughly equal to the toughness of steel and higher than that of artificial composites. The high work of fracture of wood is shown to be due to the arrangement of the cellulose microfibrils in the secondary cell wall (S 2 ). The helically wound pattern of these fibrillae is such as to induce a novel form of buckling failure in tension, which produces an elastic behaviour analogous to the yield point of ductile metals. When glass-fibre composites were constructed with a similar morphology, a large increase in work of fracture was observed.
Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 1998
Previous studies have suggested that a controlled stiffness prosthesis is required to address the... more Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses. Both the conventional and controlled stiffness i...
Journal of Materials Science, 2005
Journal of Materials Science, 1998
Biaxial loading of pre-cracked cruciform testpieces has been preformed in a novel rig attached to... more Biaxial loading of pre-cracked cruciform testpieces has been preformed in a novel rig attached to a uniaxial testing machine. Fracture toughness R or c of the ductile acrylonitride butadiene styrene (ABS) and polyvinyl chloride (PVC) determined by the Cotterell-Mai method is dependent on remote biaxiality. Least toughness is shown for equibiaxial tension; greatest for uniaxial tension. These monotonic fracture results may be modelled using void growth mechanics. Fatigue crack growth rates also depend on remote biaxiality. Paris/Walker representation of the data shows that the slopes n of log (da/dN) versus log K do not change much, but the constant of proportionality C decreases as the tensile mean stress increases. There may be a connection between the biaxial-dependent C and R or c .
The Journal of Laryngology & Otology, 2009
Hypothesis:The aim of this study was to investigate the impact of cochlear implant electrode inse... more Hypothesis:The aim of this study was to investigate the impact of cochlear implant electrode insertion on middle-ear low frequency function in humans.Background:Preservation of residual low frequency hearing with addition of electrical speech processing can improve the speech perception abilities and hearing in noise of cochlear implant users. Preservation of low frequency hearing requires an intact middle-ear conductive mechanism in addition to intact inner-ear mechanisms. Little is known about the effect of a cochlear implant electrode on middle-ear function.Methods:Stapes displacement was measured in seven patients undergoing cochlear implantation. Measurements were carried out intra-operatively before and after electrode insertion. Each patient acted as his or her own control. Sound was delivered into the external auditory canal via a speaker and calibrated via a probe microphone. The speaker and probe microphone were integrated into an individually custom-made ear mould. Ossicu...
Uploads
Papers by George Jeronimidis