Embedded discontinuity finite element method for modeling of localized failure in heterogeneous materials with structured mesh: an alternative to extended finite element method

In this work we discuss the finite element model using the embedded discontinuity of the strain and displacement field, for dealing with a problem of localized failure in heterogeneous materials by using a structured finite element mesh. On the chosen 1D model problem we develop all the pertinent details of such a finite element approximation. We demonstrate the presented model capabilities for representing not only failure states typical of a slender structure, with crack-induced failure in an elastic structure, but also the failure state of a massive structure, with combined diffuse (process zone) and localized cracking. A robust operator split solution procedure is developed for the present model taking into account the subtle difference between the types of discontinuities, where the strain discontinuity iteration is handled within global loop for computing the nodal displacement, while the displacement discontinuity iteration is carried out within a local, element-wise computation, carried out in parallel with the Gauss-point computations of the plastic strains and hardening variables. The robust performance of the proposed solution procedure is illustrated by a couple of numerical examples. Concluding remarks are stated regarding the class of problems where embedded discontinuity finite element method (ED-FEM) can be used as a favorite choice with respect to extended FEM (X-FEM).     

Phase-sensitive spatially-modulated surface plasmon resonance polarimetry for detection of biomolecular interactions

We here describe a scheme of spatially modulated surface plasmon resonance (SPR) polarimetry that enables to combine ultra-high phase sensitivity with good signal-to-noise background. The proposed approach uses spatial modulation of s-polarized component by birefringent elements and the extraction of phase-polarization information by Fourier-transform methods. This scheme was tested for monitoring the interactions between an antibody and its biological partner. Our experimental data, collected by amplitude-sensitive and phase-sensitive polarimetry demonstrate that the latter scheme provides at least one order of magnitude improvement in terms of detection limit.     

Breakage behaviour of spherical granulates by compression

This paper describes the deformation and breakage behaviour of granulates in single particle compression test. Three industrial spherical granulates—γ-Al₂O₃, the synthetic zeolite Köstrolith^® and sodium benzoate (C₆H₅COONa) were used as model materials to study the mechanical behaviour from elastic to plastic range. The elastic compression behaviour of granulates is described by means of force-displacement curves, by application of Hertz-Huber contact theory and continuum mechanics. An elastic-plastic contact model was proposed to describe the deformation behaviour of elastic-plastic granules. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic-plastic displacement are examined. It is shown that the zeolite granulates with elastic-plastic behaviour have viscous properties as well. Breakage mechanisms of granulates during elastic, elastic-plastic and plastic deformation are also explained. The breakage probability is approximated by Weibull distribution function. The behaviour of the granulate during compression under the repeated loading-unloading conditions was investigated.     

Effect of Loading History on Stress Corrosion Cracking of 7075-T651 Aluminum Alloy in Saline Aqueous Environment

An experimental study of stress corrosion cracking (SCC) was conducted on 7075-T651 aluminum alloy in a chromate-inhibited, acidic 3.5 pct sodium chloride aqueous solution using compact tension specimens with a thickness of 3.8 mm under permanent immersion conditions. The effects of loading magnitude, overload, underload, and two-step high-low sequence loading on incubation time and crack growth behavior were investigated. The results show that the SCC process consists of three stages: incubation, transient crack growth, and stable crack growth. The incubation time is highly dependent on the load level. Tensile overload or compressive underload applied prior to SCC significantly altered the initiation time of corrosion cracking. Transition from a high to a low loading magnitude resulted in a second incubation but much shorter or disappearing transient stage. The stable crack growth rate is independent of stress intensity factor in the range of 10 to 22 MPa ?{\textm} . \sqrt {\text{m}} .     

Einfluss der Feuchtebeladung bei der Druckbeanspruchung von Granulaten

The material behavior of γ‐Al₂O₃‐, zeolite 4A‐ und sodium benzoate granules at compression has been experimentally studied. The material behavior has been found to be dominant elastic, elastic‐plastic and dominant plastic. Additionally, the influence of moisture content on the material behavior has been investigated. The force‐displacement curves have been approximated using suitable mechanical models.     

Reconfigurable Anisotropic Coatings via Magnetic Field‐Directed Assembly and Translocation of Locking Magnetic Chains

A method for the generation of remotely reconfigurable anisotropic coatings is developed. To form these coatings, locking magnetic nanoparticles (LMNPs) made of a superparamagnetic core and a two‐component polymer shell are employed. Two different polymers form phase‐separated coaxial shells. The outer shell provides repulsive interactions between the LMNPs while the inner shell exerts attractive forces between the particles. Applying a non‐uniform magnetic field, one gathers the particles together, pushing them to come in contact when the internal shells could effectively hold the particles together. When the magnetic field is turned off, the particles remain locked due to these strong interactions between internal shells. The shells are thus made stimuli‐responsive, so this locking can be made reversible and the chains can be disintegrated on demand. In a non‐uniform magnetic field, the assembled chains translocate, bind to the solid substrate and form anisotropic coatings with a “locked” anisotropic structure. The coatings can be constructed, aligned, realigned, degraded, and generated again on demand by changing the magnetic field and particle environment. The mechanism of the coating formation is explained using experimental observations and a theoretical model.     

Formation of a Highly Protective Amorphous Aluminum Silicate Layer on Steel during Granite–Dry Steam Interaction

Formation of an amorphous Al₂Si₂O₅ layer on a steel pipe surface, after granite–dry steam interaction in the presence of copper, has been determined by XRD analysis and SEM (with energy dispersive X-ray microanalysis). Kinetic data indicate high-protective properties of the Al₂Si₂O₅ layer, which formed a three-dimension substrate ∼5 μm thick, after 100 h exposure.     

Hydrothermal corrosion of TiN PVD films on SUS-304

Hydrothermal corrosion of thin TiN PVD films (3 μm thickness) at 100 MPa water and 20-800 °C temperature range was studied. Noticeable oxidation starts above 200 °C and acceleration of oxidation processes takes place in hydrothermal conditions in comparison with airflow oxidation of corresponding PVD films and air oxidation of TiN powders. The formation of Ti_nO_2n−1 homological series phases and regular single crystals in oxide scale were observed. FeTiO₃ ilmenite layer secures high protective properties at 600 °C and practically does not contain chromium. Therefore, usual low alloy steel with TiN coating can be used instead superalloy for wet air oxidation system with working temperature up to 600 °C.     

Enhanced Osteoblast Adhesion to Epoxide‐Functionalized Surfaces

As an alternative to expensive extracellular matrix (ECM) proteins generally applied as coatings in Petri dishes used for cell binding, an innovative system based on epoxide‐functionalized monolayers capable of protein binding is proposed. Since cells bind to material surfaces through proteins, protein‐binding surfaces should also promote cell binding. Here we investigate how the cell‐binding properties of an epoxide‐functionalized surface compares with ECM protein gel coated surfaces and tissue culture polystyrene control surfaces. Glass surfaces are functionalized with glycidoxypropyltriethoxysilane (GOPS), which results in an epoxide‐functionalized surface capable of binding proteins through an epoxide–amine reaction. Advancing contact angle measurements and atomic force microscopy measurements confirm the formation of a homogeneous GOPS monolayer. This monolayer is micropatterned with fluorescein‐labeled ECM protein gel by microcontact printing (µCP). Confocal laser scanning microscopy (CLSM) shows accurately transferred ECM protein gel micropatterns. Osteoblasts that are seeded on these micropatterned substrates show a clear preference for adhering to the epoxide‐functionalized areas. The morphology of these cultured osteoblasts is needle‐like with high aspect ratios. As controls, osteoblasts are cultured on GOPS‐functionalized surfaces, unstructured ECM protein gel surfaces, and tissue culture polystyrene (TCPS). The GOPS surfaces demonstrate a drastic increase in cell adhesion after 2 h, whilst the other tests show no adverse effects of this surface on the osteoblasts as compared to ECM and TCPS. CLSM shows healthy cell morphologies on each surface. It is demonstrated for the first time that epoxide groups outperform ECM protein gel in cell adhesion, thereby providing new routes for cost‐effective coatings that improve biocompatibility as well as exciting, new methodologies to control and direct cell adhesion.     

Study of the filter cake formed due to the sedimentation of monodispersed and bidispersed particles using discrete element method–computational fluid dynamics simulations

This study aims to investigate the sedimentation and the consolidation of the packed bed/cake formed due to the monodispersed and bidispersed particles under different flow conditions. Mutual interactions between the bidispersed particles and the liquid are considered by using a polydispersed drag model. The attractive force is considered by using the JKR model. Sensitivity of the void fraction of a sedimented packed bed/cake due to particle–particle interaction parameters is studied. Furthermore, the effect of the fluid flow is analyzed by performing the simulations in two stages. In the first stage, packed bed/cake is formed by the sedimentation of the particles in the absence of the fluid forces and in the second stage flow through the packed bed/cake is simulated by using the CFD coupled with the discrete element method. Based on the simulations, correlations between the sedimented and the consolidated void fractions are developed. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1294–1303, 2019