New molecular sequences for two genera of marine planarians facilitate determination of their position in the phylogenetic tree, with new records for two species ( Platyhelminthes , Tricladida , Maricola )

Yang, Hee-Min,Sluys, Ronald,Kawakatsu, Masaharu,Min, Gi-Sik Pensoft Publishers 2018 ZooKeys Vol.781 No.-

<P>Abstract</P><P>For the first time, molecular sequences of the 18S ribosomal DNA were generated for representatives of the genera <I>Obrimoposthia</I> Sluys & Ball, 1989 and <I>Paucumara</I> Sluys, 1989 of the suborder of the marine triclads, or Maricola, by analyzing the species <I>Obrimoposthiawandeli</I> (Hallez, 1906) and <I>Paucumaratrigonocephala</I> (Ijima & Kaburaki, 1916). On the basis of this molecular data the phylogenetic position of these two genera in the phylogenetic tree of the Maricola was determined and compared with their position in the phylogeny based on the analysis of anatomical features. New records for these two species are documented and their taxonomic status is determined on the basis of histological studies.</P>

Remeshing techniques for r-adaptive and combined h/r-adaptive analysis with application to 2D/3D crack propagation

Askes, H.,Sluys, L.J.,de Jong, B.B.C. Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.12 No.5

Remeshing strategies are formulated for r-adaptive and h/r-adaptive analysis of crack propagation. The relocation of the nodes, which typifies r-adaptivity, is a very cheap method to optimise a given discretisation since the element connectivity remains unaltered. However, the applicability is limited. To further improve the finite element mesh, a combined h/r-adaptive method is proposed in which h-adaptivity is applied whenever r-adaptivity is not capable of further improving the discretisation. Two and three-dimensional examples are presented. It is shown that the r-adaptive approach can optimise a discretisation at minimal computational costs. Further, the combined h/r-adaptive approach improves the performance of a fully r-adaptive technique while the number of h-remeshings is reduced compared to a fully h-adaptive technique.

Theoretical prediction on thickness distribution of cement paste among neighboring aggregates in concrete

Huisu Chen,Lambertus Johannes Sluys,Piet Stroeven,Wei Sun 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.2

By virtue of chord-length density function from the field of statistical physics, this paper introduced a quantitative approach to estimate the distribution of cement paste thickness between aggregates in concrete. Dynamics mixing method based on molecular dynamics was employed to generate one model structure, then image analysis algorithm was used to obtain the distribution of thickness of cement paste in model structure for the purpose of verification. By comparison of probability density curves and cumulative probability curves of the cement paste thickness among neighboring aggregates, it is found that the theoretical results are consistent with the simulation. Furthermore, for the model mortar and concrete mixtures with practical volume fraction of Fuller-type aggregate, this analytical formula was employed to predict the influence of aggregate volume fraction and aggregate fineness. And evolution of its mean values were also investigated with the variation of volume fraction of aggregate as well as the fineness of aggregates in model mortars and concretes.

Computational modelling for description of rubber-like materials with permanent deformation under cyclic loading

Guo, Z.Q.,Sluys, L.J. Techno-Press 2008 Interaction and multiscale mechanics Vol.1 No.3

When carbon-filled rubber specimens are subjected to cyclic loading, they do not return to their initial state after loading and subsequent unloading, but exhibit a residual strain or permanent deformation. We propose a specific form of the pseudo-elastic energy function to represent cyclic loading for incompressible, isotropic materials with stress softening and residual strain. The essence of the pseudo-elasticity theory is that material behaviour in the primary loading path is described by a common elastic strain energy function, and in unloading, reloading or secondary unloading paths by a different strain energy function. The switch between strain energy functions is controlled by the incorporation of a damage variable into the strain energy function. An extra term is added to describe the permanent deformation. The finite element implementation of the proposed model is presented in this paper. All parameters in the proposed model and elastic law can be easily estimated based on experimental data. The numerical analyses show that the results are in good agreement with experimental data.

Gradient Viscoplastic Modelling of Material Instabilities in Metals

Wang, W . M .,Askes, H .,Sluys, L . J . 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.3

A gradient viscoplasticity model has been used to analyse stationary and propagative instabilities. It is demonstrated that the use of viscous regularisation is effective for both quasistatic and dynamic problems. Due to the influence of the length scales that are introduced in the model, the numerical simulation gives mesh-objective results with a finite width and unique orientation of the shear band. The numerical simulation of shear banding and propagative Portevin-Le Chatelier bands will be discussed. A 3D analysis of shear banding is shown to give significantly different results than the 2D plane strain analysis under similar conditions. Very fine meshes are needed to obtain accurate solutions for the shear hand. The Arbitrary Lagrangian Eulerian remeshing method will be used to relocate elements from outside to inside the shear band to minimise computer costs.

Influence of particle packing on fracture properties of concrete

Huan He,Piet Stroeven,Martijn Stroeven,Lambertus Johannes Sluys 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.6

Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physicalmechanical properties of the phases, whereby the ITZ takes up a major position.

An experimental-computational investigation of fracture in brittle materials

K. De Proft,G. N. Wells,L. J. Sluys,W. P. De Wilde 한국계산역학회 2004 Computers and Concrete, An International Journal Vol.1 No.3

A combined experimental-computational study of a double edge-notched stone specimen subjected to tensile loading is presented. In the experimental part, the load-deformation response and the displacement field around the crack tip are recorded. An Electronic Speckle Pattern Interferometer (ESPI) is used to obtain the local displacement field. The experimental results are used to validate a numerical model for the description of fracture using finite elements. The numerical model uses displacement discontinuities to model cracks. At the discontinuity, a plasticity-based cohesive zone model is applied for monotonic loading and a combined damage-plasticity cohesive zone model is used for cyclic loading. Both local and global results from the numerical simulations are compared with experimental data. It is shown that local measurements add important information for the validation of the numerical model. Consequently, the numerical models are enhanced in order to correctly capture the experimentally observed behaviour.

A coupled damage-viscoplasticity model for the analysis of localisation and size effects

J. M. Reynouard,J. F. Georgin,L. J. Sluys 한국계산역학회 2004 Computers and Concrete, An International Journal Vol.1 No.2

A coupled damage-viscoplasticity model is presented for the analysis of localisation and size effects. On one hand, viscosity helps to avoid mesh sensitivity because of the introduction of a length scale in the model and, on the other hand, enables to represent size effects. Size effects were analysed by means of three-point bending tests. Correlation between the fracture energy parameter measured experimentally and the density fracture energy modelling parameter is discussed. It has been shown that the dependence of nominal strength and fracture energy on size is determined by the ligament length in comparison with the width of the fracture process zone.

Optimization of particle packing by analytical and computer simulation approaches

Huan He,Piet Stroeven,Martijn Stroeven,Lambertus Johannes Sluys 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.9 No.2

Optimum packing of aggregate is an important aspect of mixture design, since porosity may be reduced and strength improved. It may also cause a reduction in paste content and is thus of economic relevance too. Several mathematic packing models have been developed in the literature for optimization of mixture design. However in this study, numerical simulation will be used as the main tool for this purpose. A basic, simple theoretical model is used for approximate assessment of mixture optimization. Calculation and simulation will start from a bimodal mixture that is based on the mono-sized packing experiences. Tri-modal and multi-sized particle packing will then be discussed to find the optimum mixture. This study will demonstrate that computer simulation is a good alternative for mixture design and optimization when appropriate particle shapes are selected. Although primarily focusing on aggregate, optimization of blends of Portland cement and mineral admixtures could basically be approached in a similar way.