Pokusi delaminacije s grednim uzorcima se cesto koriste kod ispitivanja razlicitih suvremenih materijala sa slojevitom strukturom, i kod razlicitih vrsta ovih pokusa javljaju se i razliciti nacini loma (otvaranja pukotine). Kod pokusa s mjesovitim nacinom loma znacajno je s aspekta dizajna napraviti podjelu energije loma na udjele od razlicitih nacina loma, tj. odrediti mjesovitost nacina loma. Problematika podjele energije loma u pokusima delaminacije s grednim uzorcima je predmet velikog broja istraživanja u posljednjih tridesetak godina i kao rezultat toga predložena su razlicita rjesenja zasnovana na analitickim i numerickim metodama. Rezultati dobiveni primjenom ovih rjesenja pokazuju dobro slaganje kod primjene na pokuse sa simetricnom geometrijom uzoraka, međutim, kod primjene na pokuse s asimetricnom geometrijom uzorka pokazuju znacajno neslaganje. U ovom radu je dat osvrt na odabrana analiticka i numericka rjesenja koja se mogu primijeniti za podjelu energije loma. Razmatrane su dvije pionirske, suprotstavljene teorije, prema Williamsu i prema Hutchinsonu i Suou, te nedavno predložena, poluanaliticka, SACA metoda, koja je s novim pristupom problemu objedinila ove dvije teorije. Rezultati primjene spomenutih metoda su na primjeru pokusa delaminacije s dvostrukim grednim uzorkom, kome je jedan krak opterecen momentom savijanja, uspoređene s rezultatima odabranih numerickih istraživanja zasnovanih na primjeni modela kohezivne zone.

Publisher's statement This is the author's version of a work that was accepted for publication in Engineering Fracture Mechanics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Engineering Fracture Mechanics (78, 6, (2011)) DOI: http://dx.doi/org/10.1016/j.engfracmech.2010.11.014

Delamination (fracture) tests have been numerically investigated using various cohesive zone properties. The test utilises asymmetric and symmetric double cantilever beam specimens loaded with bending moment. Energy release rate contributions from mode I and mode II fracture are calculated using a global and local approach. Mode-mixities results are presented and analysed. The numerical partitioning results for different configurations are compared to two analytical partitioning theories, namely, after Williams and after Hutchinson and Suo. Opposite to these theories, partitioning is observed to be dependent on cohesive zone properties.

Adsorption-desorption processes of polydisperse mixtures on a triangular lattice are studied by numerical simulations. Mixtures are composed of the shapes of different numbers of segments and rotational symmetries. Numerical simulations are performed to determine the influence of the number of mixture components and the length of the shapes making the mixture on the kinetics of the deposition process. We find that, above the jamming limit, the time evolution of the total coverage of a mixture can be described by the Mittag-Leffler function θ(t)=θ∞-ΔθE[-(t/τ)β] for all the mixtures we have examined. Our results show that the equilibrium coverage decreases with the number of components making the mixture and also with the desorption probability, via corresponding stretched exponential laws. For the mixtures of equal-sized objects, we propose a simple formula for predicting the value of the steady-state coverage fraction of a mixture from the values of the steady-state coverage fractions of pure component shapes.

Forces generated in the muscles and tendons actuate the movement of the skeleton. Accurate estimation and application of these musculotendon forces in a continuum model is not a trivial matter. Frequently, musculotendon attachments are approximated as point forces; however, accurate estimation of local mechanics requires a more realistic application of musculotendon forces. This paper describes the development of mapped Hill‐type muscle models as boundary conditions for a finite volume model of the hip joint, where the calculated muscle fibres map continuously between attachment sites. The applied muscle forces are calculated using active Hill‐type models, where input electromyography signals are determined from gait analysis. Realistic muscle attachment sites are determined directly from tomography images. The mapped muscle boundary conditions, implemented in a finite volume structural OpenFOAM (ESI‐OpenCFD, Bracknell, UK) solver, are employed to simulate the mid‐stance phase of gait using a patient‐specific natural hip joint, and a comparison is performed with the standard point load muscle approach. It is concluded that physiological joint loading is not accurately represented by simplistic muscle point loading conditions; however, when contact pressures are of sole interest, simplifying assumptions with regard to muscular forces may be valid. Copyright © 2014 John Wiley & Sons, Ltd.

This paper establishes a procedure for numerical analysis of a hip joint using the finite volume method. Patient-specific hip joint geometry is segmented directly from computed tomography and magnetic resonance imaging datasets and the resulting bone surfaces are processed into a form suitable for volume meshing. A high resolution continuum tetrahedral mesh has been generated, where a sandwich model approach is adopted; the bones are represented as a stiffer cortical shells surrounding more flexible cancellous cores. Cartilage is included as a uniform thickness extruded layer and the effect of layer thickness is investigated. To realistically position the bones, gait analysis has been performed giving the 3D positions of the bones for the full gait cycle. Three phases of the gait cycle are examined using a finite volume based custom structural contact solver implemented in open-source software OpenFOAM.

Correct calculation of stresses at the interface of bonded or otherwise joined materials plays a significant role in many applications. It is therefore important that traction at the material interface is calculated as accurately as possible. This paper describes procedures that can be employed to achieve this goal by using centre‐based finite‐volume method. Total traction at the interface is calculated by decomposing it into normal and tangential components, both being calculated at each side of the interface, and applying the continuity assumption. The way in which the traction approximation is achieved depends on calculation of tangential gradient of displacement at the interface. To this end, three different methods are proposed and validated against problems with known solutions. It was shown that all methods can be successfully used to simulate problems with multi‐material domains, with the procedure based on finite area method being most accurate. Copyright © 2012 John Wiley & Sons, Ltd.

Original scientific paper This paper presents an analysis of the stress distribution on the outer surface of the riding ring of rotary cement kiln during working cycle using both the theory and finite element simulation. In the theoretical analysis, the total stress is obtained as a combination of bending, thermal and contact stresses. To obtain bending stress the kiln is considered as a simply supported, indeterminate beam subjected to static and symmetrical loads and Castigliano’s theorem is employed. Thermal stresses are obtained assuming both linear and non-linear temperature distribution over the ring thickness. Contact stress between ring and supporting rollers is obtained using Hertz contact theory. Bending, thermal and contact stresses are also obtained numerically in separate simulations, mimicking conditions assumed in the theoretical part. All results are in excellent agreement. In addition, a more realistic ring model subjected to all loads simultaneously is also simulated. These results showed slight disagreement with theory in the contact region, mainly due to sliding contact between the roller and the ring, but overall agreement was good.

Structural epoxy adhesives typically contain second phase particles to improve their resistance to crack growth. The presence of these particles can dramatically raise the toughness of the system to several times that of the neat epoxy. One of the most common tougheners are core shell rubber (CSR) particles which consist of a glassy shell surrounding a rubbery core. The bulk fracture properties of these systems have been studied by many authors. It is generally accepted that the improvement in toughness is derived from the plastic growth of voids that nucleate from the failure of CSR particles and the development of shear bands between these voids [1]. The development of these mechanisms within the joint are affected by the level of stress triaxiality which depends on many factors including the thickness of the adhesive layer, ha [2]. The aim of this work is to identify the primary toughening mechanisms that develop during fracture of metal joints that are bonded with these adhesives. This is completed with tapered double cantilever beam (TDCB) fracture tests combined with fracture surface analysis, numerical modelling of the adhesive joints and analytical modelling of the adhesive microstructure. Additionally, a novel test method, the bonded circumferentially deep notched tensile test (CDNT) is used to measure the traction separation behaviour of the adhesive as a function of constraint. The findings of this work also support another study which involves the development of a numerical micromechanical model of the adhesive microstructure. Ultimately, this will evolve into a design tool for the development of improved materials.

In-service adhesive joints and composite laminates are often subjected to a mixture of mode I (tensile opening) and mode II (in-plane shear) loads. It is generally accepted that the toughness of such joints can vary depending on the relative amounts of mode I and mode II loading present. From a design perspective, it is therefore of great importance to understand and measure joint toughness under a full range of mode-mixities, thus obtaining a failure locus ranging from pure mode I to pure mode II. The pure mode toughnesses (I, II) can be measured directly from experimental tests, the most common tests being the double cantilever beam (DCB) for mode I and end loaded split (ELS) for mode II. Unfortunately, the analysis of a mixed mode test is not straightforward. In any mixed mode test, one must apply a partition in order to estimate the contributions from each mode. The particular test under study in this work is the fixed ratio mixed mode test (FRMM) with a pure rotation applied to the top beam (fig. 1). In this test, a range of mode-mixities can be obtained by varying γ, where γ = h1/h2. This test is normally analysed using analytical or numerical methods, each of which suffers from a number of uncertainties. The present work attempts to shed some light on both analytical and numerical approaches and ultimately develop a testing protocol and recommendations for the accurate determination of mode-mixity in the FRMM test and other similar beam-like geometries.