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  • Open access
  • 67 Reads
Ab initio generation of binary alloy foams: the case of amorphous Cu64Zr36
Published: 26 April 2016 by MDPI in 2nd International Electronic Conference on Materials session Porous Materials

We report ab initio-based approaches to generate amorphous nanoporous Cu64Zr36 bulk metallic glass. Starting with two different initial configurations: an unstable crystalline sample (cCu64Zr36) and an amorphous sample (aCu64Zr36), the transferable expanding lattice method–previously used with semiconducting and pure metal systems– was applied in order to increase the volume of the cells (and atomic distances proportionally) so that the density was halved, thus obtaining 50% porosity. The initial samples were subjected to either constant room temperature ab initio molecular dynamics or geometry optimization only, which resulted in well-defined pores growing along specific spatial directions. Herewith we report partial and total pair distribution functions, as well as nearest neighbor distances and coordination numbers which let us discern discrepancies in backbone and pore topology. Also we report the bond-angle distribution which let us track the presence of icosahedral-like short-range order which is often related to the glass forming ability in amorphous alloys. The so-called depletion of the pair distribution function at mid range order reported in the literature, along with an estimation of pore sizes are also reported.

  • Open access
  • 57 Reads
Failure analysis of hydrophilic and hydrophobic aerogels under liquid nitrogen thermal shock

As the best thermal insulator, aerogels could be used for high-efficiency insulation under exoplanet environment. There is the high day-night temperature difference in the exoplanets, thus the failure analysis of the aerogels under thermal shock could be studied. In this paper, hydrophilic and hydrophobic fiber-reinforced silica aerogels were forced to undergo liquid nitrogen-room temperature thermal shocks. Thermal conductivity, mechanical property and the microstructure were characterized for understanding the failure mechanism. It was found that after multiple shocks, the thermal conductivity of hydrophilic aerogel increased 35.5% after the first shock and kept in a high value, while that of the hydrophobic aerogel increased 19.5% and kept in a relatively low value. Pore size distribution results showed that after the first shock the peak pore size of the hydrophilic aerogel increased from 18 nm to 25 nm due to the shrinkage of the skeleton, while the peak pore size of the hydrophobic aerogel kept at ~9 nm probably induced by the spring-back effect. The high-strain hardening and low-strain soften behaviors further demonstrated the skeleton shrinkage of the hydrophilic aerogel. The existence of the free water in the infrared spectra of both aerogels indicated the driving force of the skeleton shrinkage may be the volume change of the absorbed water during freezing process. For further demonstrating the mechanism, the aerogels were treated at 80 oC under vacuum environment before conducting shock experiments. After the first shock, the thermal conductivities of the hydrophilic and hydrophobic aerogels were increased only 14.0% and 0.4%, respectively. In addition, multiple shock experiments showed that the failure processes of the hydrophilic and hydrophobic aerogels are irreversible and reversible, respectively, revealing their different failure modes.

  • Open access
  • 63 Reads
Recent trends in development of self‐flowing mortar incorporating supplementary cementitious materials

Self‐flowing mortar (SFM) is being popular in recent time. Its’ easy‐placement nature makes it suitable for narrow or congested reinforced places. To comply with modern‐age needs, many supplementary cementitious materials (SCMs) are gaining importance nowadays. Using industrial and agricultural wastes as SCM, ensures proper management of many hazardous materials and saves cost as well. Incorporation of these two techniques can offer cost‐effective and environment‐friendly solutions to many construction problems. Many researchers studied the effect of different SCMs on mortar properties in recent years. The objective of this study is to summarize the findings of recent experiments. This will help the experts of this field to optimize their mix design easily, as well as, the researchers to find the research gap and determine the direction of their future studies.

  • Open access
  • 79 Reads
Wood filled plastics – machining and surface quality

Components made of wood plastic composites are used in exterior application, where in comparison with nature wood composite do not require further maintenance (predetermine to long-term usage for its physical and mechanical properties). Adding wood to plastic significantly increases mechanical properties (utmost stiffness), reduces thermal expansion of the plastic and decreases of cost. Design of product is not limited by material and technology and is possible to product different types of profile and shapes. Nowadays demand on wood plastic composites is with increasing character. For this reason, a better understanding of this composite material in regards to machining and texture of surface is necessary. The paper deals with a comparison of the surface roughness of Wood Plastic Composite with traditional wood (oak) after turning. Presented paper is focused on observation changes of average maximum height Rz with change of speed of feeds f and speed of rotations nc (simultaneously compare predicted and real values of surface roughness parameter Rz). Experiment was realized with monolithic cutting tool made of high speed steel (EN ISO HS6-5-2) with positive geometry. Machining of WPC was in direction parallel to extruding axe, and verification sample in parallel fiber direction. Graphical evaluation of experimental values was realized using software OriginLab. Detecting surface quality was made using microscopic camera DigiMicro 2.0

  • Open access
  • 90 Reads
Experimental testing of material Mosten GB 005 on various concertation of recycled material

Main objective of presented scientific article is to define mechanical properties of polypropylene Mosten GB 005 in dependence on prescribed precentral ratio of recycled regranulate. Polypropylene Mosten GB 005 is a general purpose homopolymer, intended for injection moulding and for production of thermoforming films. It can be also used for production of various compounds. Experimental verification of mechanical properties was realized by testing samples produced with various concentrations of the recycled material. Experimental samples were realized undergo tests to obtain mechanical properties of produced new material (on these tests were realized and evaluated rheological tests, tensile and flexural tests as well as hardness and Charpy impact toughness tests). Experimental samples were divided into 7 classes depend on percentage ratio of added recycled material into raw material concretely 0%,10%,20%,30%,50%,70% a 100 %. Mentioned mechanical tests were realized according to ISO standards valid for individual testing method. Each testing method was carried out using prescribed numbers of testing samples. The flexure test was realized on five experimental testing samples and subsequent tests were carried out on ten experimental samples from each class of produced material. Presented scientific article is also focused on changes in microstructures of testing materials in depends on percentage ratio of recycled regranulate. Recycled regranulate of thermoplastic was not necessity to additionally modify. Presented article also contain experimental verification of thermal properties using Differential Scanning Calorimetry (DSC).

  • Open access
  • 59 Reads
Mechanical Property Studies of Nanolayered Polymer Membranes
Published: 03 May 2016 by MDPI in 2nd International Electronic Conference on Materials session Membranes

Nanolayered polymer membranes, which have biomimicking layered structures, have been developed in recent years. The unique microstructures allow the membranes many potential applications. To facilitate the application of the membranes, the understandings of mechanical properties of the pristine and aged membranes are needed for the short and long-term applications. The current study focuses on the study of the relationship between the microstructure of the membrane and the mechanical properties including stiffness, strength, and ductility. The effect of the microstructure on the long-term application has been evaluated by thermal aging. The nanolayered polymer membranes have been subjected to thermal aging at various temperatures for different time frames. It has been found that the microstructure parameters, such as layer thickness, have great effect on the mechanical properties and thermal aging resistance. The thinner the layer of the membrane is, the better the strength and thermal aging resistance are.

  • Open access
  • 206 Reads
A comparative study of hyperelastic constitutive models to characterize the behavior of a polymer used in automotive engines

The global automotive industry faces the challenge of increasing engine efficiency, reducing fuel consumption and the size of them gradually. Not only the engine block must reduce its size, but also other components, requiring more compact and flexible designs using materials such as thermoplastic elastomers. These kinds of materials are used due to their characteristics, such as ability of deformation, durability, recyclability, and its cost/weight ratio. They are able to hold large deformations and they have very good damping characteristics, making them suitable for use in energy dissipation. Characterization of the dynamic mechanical properties of these materials is essential to make a correct analysis and modeling of the behavior of components. Although the constitutive models of these materials are complex due to high deformability, quasi-incompressibility, softening, and time dependent effects, typically, these materials have a mechanical behavior which can be represented by a phenomenological hyperelastic model. While it is easy to fit a model of elastic behavior, set a model for a hyperelastic material is a very complex task, so in practice simplified models are used. This paper proposes a comprehensive comparison of six hyperelastic models to simulate the behavior of Santoprene 101-73 material manufactured by ExxonMobil. The ability of these models to reproduce different types of loading conditions is analyzed through uniaxial tensile data obtained experimentally. The parameters of each of the hyperelastic models are determined by a least-squares fit and then a classification of these six models is established, highlighting those that are most suitable for characterizing the material.

  • Open access
  • 92 Reads
Mechanical behavior of human bones with different saturation levels

Human bone is one of the most common connective tissue of biological human structure. In  relation to the internal microstructure there are two main types of bone tissue: compact in the cortical zone and spongy or trabecular in the internal zone.  The porous structure in general is side for the marrow. Considering the relevant function of that tissue, the porosity is not uniform. Porous diameter increase from the cortical to the centre of bones, as the connections of porous increasing with the thickness of the bone tissue.

The presence of serum inside the porous structure of bone tissue produce a different behaviour in bones below loads, and related with the condition of the load is applied. The response of material is different in relation at the level of serum inside the tissue and in relation of the load action direction. In same stress condition the velocity of loading generate different response related with the dimensions of porous and permeability parameters.

In this work, three different type of bone tissue are investigated. From Calcaneus, from skull and form rib of human skeletal system. The specimens are subjected at compression test in, displacement control, until they reach the ultimate stress, in dry and wet condition. It is observed that level of serum.

A 3 groups (one for each tissue type) of 20 specimens each are tested in dry and wet condition. maximum stress, strain, elastic deformation Energy, total deformation energy, are measured. statistical analysis is conducted and qualitative relationship are deducted in reference to the density and specific mechanical characteristics.

The tests show compact tissue as skull are more appropriate to perform load action, instead calcaneus work as reticular structure with high deformation levels.

  • Open access
  • 35 Reads
Effects of polyol composition on physico-morphological and mechanical properties of polyurethane foams

In the last years, increasing interest has been paid to polyurethane (PU) foams with open porosity to be used as scaffold in numerous tissue engineering applications. In fact, they possess good cyto- and biocompatibility, and they can be synthesized with tunable chemico-physical and mechanical properties by varying the base reagents used for their synthesis (polyol, isocyanate, and expanding agent) and the stoichiometric ratio between them. The aim of this work was to design and develop novel PU foams with high open porosity and tunable physical and mechanical properties by varying the polyol composition and the stoichiometric ratio between the base reagents.

PU foams were synthesized by a one step gas foaming method (stoichiometric and not stoichiometric foams), by reacting a polyol mixture ad hoc set up with MDI prepolymer, using Fe-AA as catalyst, and water as expanding agent. Different polyol mixtures were prepared by varying the ratio between the main polyol components, e.g. a polyether-polyol (component A), a polyether-polyol containing styrene (component B), and an amine-based tetrafunctional polyether-polyol (component C). The PU foams were characterized by SEM, micro-CT, ATR-FTIR analysis, and evaluation of density, water uptake, and mechanical properties by uniaxial compressive tests in dry and wet conditions.

Polyol composition do not affect PU foam open porosity, while the pore size and water uptake increase with the increase of components B and C. All the foams show higher compressive properties in dry than in wet state, due to the plasticizing effect of water. PU foams synthesized with an excess of diisocyanate are significantly stiffer than the stoichiometric ones. In addition the compressive properties of the PU foams are mostly affected by the amine-based tetrafunctional component, that causes a higher level of cross-linking, stiffness and strenght. Preliminary tests show no cytotoxic effects for all the tested PU foams.

  • Open access
  • 63 Reads
Experimental Study on T-shaped Joints Composed of Plaster-Concrete Compound Panels

A hidden concrete column was built at the core of the T-shaped joints composed of plaster-concrete compound panels in order to study their earthquake resistant behavior. In this paper, earthquake resistance tests were performed on two types of composite T-shaped joints, six samples in total, in which the horizontal steel bars were embedded and not embedded in their core, to analyze the mechanical deformation, cracking, hysteretic behavior, ductility, and stiffness degeneration of the composite T-shaped joints as well as their energy dissipation properties such as damping coefficient, energy dissipation coefficient, and power ratio coefficient. The two types of composite joints composed of interior and exterior compound walls were found to have good mechanical properties. A comparison of the various indicators for the two types of T-shaped joints revealed that embedding the horizontal steel bars embedded in the web and flange of the T-shaped joints in their core can help improve the earthquake resistance and energy dissipation properties of the composite T-shaped joints.

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