Essential and Non-essential Work of Fracture of PI/SiO<Subscript>2</Subscript> Hybrid Thin Films

Essential work of fracture (EWF) analysis is used to study the effect of the silica doping level on fracture toughness of polyimide/silica (PI/SiO₂) hybrid films. By using double-edge-notched-tension (DENT) specimens with different ligament lengths, it seems that the introduction of silica additive can improve the specific essential work of fracture (w _e ) of PI thin films, but the specific non-essential work of fracture (βw _p ) will decease significantly as the silica doping level increasing from 1 to 5 wt.%, and even lower than that of neat PI. The failure process of the fracture is investigated with online scanning electron microscope (SEM) observation and the parameters of non-essential work of fracture, β and w _p , are calculated based on finite element (FE) method.     

In-plane and Out-of-plane Fracture Toughness of Physically Aged Polyesters as Assessed by the Essential Work of Fracture (EWF) Method

The in-plane (mode I) and out-of-plane (mode III) fracture behavior of amorphous (co)polyester sheets are studied as a function of physical aging using the essential work of fracture (EWF) concept. Physical aging was followed by measuring the yield stress and enthalpy relaxation of the (co)polyesters. The specific essential work of fracture term did not reflect the physical aging either in mode I or III loading. On the other hand, the corresponding values were closely matched indicating the mode III type loading turns into mode I for thin films. Aging was best manifested in the mode I – related EWF parameters, viz. specific yielding-related essential work and non-essential necking/tearing related work.     

Evaluation of fracture toughness of ABS polymers via the essential work of fracture (EWF) method

The essential work of fracture (EWF) method was employed to determine the fracture toughness of SAN/PB-g-SAN blends with the compositions of 65/35–0/100. It was found that the plane stress EWF approach is applicable for different SAN/PB-g-SAN blends. During EWF tests, three different types of load–displacement curves were recorded, depending on the blend composition. For the samples containing rubbery phase of 35–65 wt% crack growth occurred immediately after full ligament yielding. Further increase in rubber content and for the samples with 75 and 85 wt% of rubbery phase, the onset of crack growth was preceded by the formation of necking zone in the form of a sharp load drop after full ligament yielding. For the sample with the composition of 0/100, strain hardening behavior was observed without any sign of neck formation. The specific essential work of fracture (EWF) w _e increased at first with the increase of PB-g-SAN wt% and then decreased with further increasing amount of rubbery phase. The maximum value of w _e was observed for the blend with 75 wt% of PB-g-SAN. The specific non-essential work of fracture βW _p increased with increasing of rubbery phase concentration. The analyzing of yielding and necking/tearing components of essential and non-essential parameters showed that for the samples containing 55 wt% and higher of rubbery phase, w_\texte,nt \succ w_\texte,y w_{\text{e,nt}} \succ w_{\text{e,y}} and b_\textnt w_\textp,nt \succ b_\texty w_\textp,y \beta_{\text{nt}} w_{\text{p,nt}} \succ \beta_{\text{y}} w_{\text{p,y}} , indicating that a majority of fracture energy was dissipated in the necking and tearing stages of fracture process. Finally, it is shown that w _e values can be predicted via COD values.     

Influence of femtolaser notch sharpening technique in the determination of essential work of fracture (EWF) parameters

The fracture behaviour of a 0.5 mm thick ethylene-propylene block copolymer is analyzed using the essential work of fracture method, using DENT-type specimens. The influence of three experimental parameters in the technique is evaluated: the effect of the notch sharpening technique, the use of a videoextensometer for monitoring the deformations and the measurement of ligament lengths before or after fracture tests were carried on.The results showed that the femtosecond pulsed laser ablation technique (femtolaser) produced sharp notches with no plastic deformation ahead of the notch tip, which yield smaller specific essential work of fracture (w_e) values than in the cases where the notches were sharpened with razor blades. The use of a videoextensometer has allowed removing the viscoelastic energy from the plastic work, with lower values of βw_p. The measurement of the ligament lengths before or after the test did not affect the results.     

The enriched space–time finite element method (EST) for simultaneous solution of fluid–structure interaction

The paper introduces a weighted residual‐based approach for the numerical investigation of the interaction of fluid flow and thin flexible structures. The presented method enables one to treat strongly coupled systems involving large structural motion and deformation of multiple‐flow‐immersed solid objects. The fluid flow is described by the incompressible Navier–Stokes equations. The current configuration of the thin structure of linear elastic material with non‐linear kinematics is mapped to the flow using the zero iso‐contour of an updated level set function. The formulation of fluid, structure and coupling conditions uniformly uses velocities as unknowns. The integration of the weak form is performed on a space–time finite element discretization of the domain. Interfacial constraints of the multi‐field problem are ensured by distributed Lagrange multipliers. The proposed formulation and discretization techniques lead to a monolithic algebraic system, well suited for strongly coupled fluid–structure systems. Embedding a thin structure into a flow results in non‐smooth fields for the fluid. Based on the concept of the extended finite element method, the space–time approximations of fluid pressure and velocity are properly enriched to capture weakly and strongly discontinuous solutions. This leads to the present enriched space–time (EST) method. Numerical examples of fluid–structure interaction show the eligibility of the developed numerical approach in order to describe the behavior of such coupled systems. The test cases demonstrate the application of the proposed technique to problems where mesh moving strategies often fail. Copyright © 2007 John Wiley & Sons, Ltd.     

The resistance of metakaolin (MK)–Portland cement (PC) concrete to the thaumasite-type of sulfate attack (TSA)––Programme of research and preliminary results

The thaumasite form of sulfate attack (TSA), is a deleterious physico-chemical attack of the calcium silicate hydrate (C–S–H), binding phase of concrete. Water:binder ratios (w:b), are known to control ingress of potentially deleterious ions by pore structure refinement at low (0.40) values. Equally, a physical–chemical barrier exists at about w:b ratio of 0.45 regardless of the binder type. The inclusion of ultra-fine pozzalans (e.g. metakaolin) in the binder has been shown to impart such properties through densification of the matrix and removal of calcium hydroxide.

A small-scale experimental design programme to establish the potential resistance of metakaolin–Portland cement (MK–PC), blended concrete to the thaumasite-type of attack is ongoing. Results are presented for concrete incorporating dolomitic limestone aggregate and with 0% and 7% metakaolin replacement of a high-C₃A PC binder at w:b ratios to 0.40 and 0.46. Exposure to three environments containing a sulfatic clay, sulfate solution and water has produced evidence of deleterious reactions within these samples. Visual data are quantified by a wear rating and supported by compressive strength and expansion values for up to 280 days of exposure. These results confirm the importance of low water binder ratios in the resistance of ion ingress and give an early indication of the desirable durability-enhancing properties of MK replacement of PC. Finally, the results also show that the two sulfatic environments of exposure produce marked differences in the degradation modes, which may be important in the methodologies used to determine TSA in the laboratory with reference to field observations.     

Fracture behavior and environmental stress cracking resistance (ESCR) of HIPS/PE blends and the effect of compatibilization on their properties

Attempts have been made to study the fracture behavior and environmental stress cracking resistance (ESCR) of HIPS/PE blends. The effect of compatibilization on their properties was also studied. EWF tests were conducted to measure the essential specific work of fracture (w_e) and non-essential specific work of fracture (βw_p). The ESCR of the samples was investigated using a special modified tensile creep test under an aggressive environment (sunflower oil). It was found that EWF methodology could be applied to uncompatibilized and compatibilized HIPS/PE blends as well as HIPS. The essential specific work of fracture of compatibilized HIPS/PE blends was higher than uncompatibilized HIPS/PE blends and pure HIPS, while its non-essential work of fracture was higher than uncompatibilized blends and lower than pure HIPS. The results also showed that the ESCR of HIPS decreases with incorporation of PE, but an effective compatibilization of this blend increases its ESCR even higher than pure HIPS. The different properties of compatibilized and uncompatibilized blends and HIPS, in EWF and ESCR tests, were attributed to the different mechanisms of fracture in these materials. The different mechanisms of fracture were justified using morphological studies performed on fracture surfaces of each sample. SEM images showed that there is a reasonable correlation between mechanisms of fracture and microstructure of the samples.     

Equilibrium on line method (ELM) for imposition of Neumann boundary conditions in the finite point method (FPM)

Equilibrium on line method (ELM) for imposition of Neumann boundary conditions in the finite point method (FPM) is presented. In contrary to weak‐form‐based methods, strong‐form‐based methods such as the FPM are often unstable and less accurate, especially for problems governed by partial differential equations with Neumann (derivative) boundary conditions. In this paper, a truly meshless approach for imposition of Neumann boundary conditions in the FPM is proposed and adopted for 2D elasticity analyses. In the proposed method, equilibrium on lines on the Neumann boundary conditions is satisfied as Neumann boundary condition equations. Numerical studies show that this method for imposition of Neumann boundary is simple to implement and computationally efficient and also leads to more stable and accurate results. Copyright © 2006 John Wiley & Sons, Ltd.     

The weak substitution method – an application of the mortar method for patch coupling in NURBS‐based isogeometric analysis

In this contribution, a mortar‐type method for the coupling of non‐conforming NURBS (Non‐Uniform Rational B‐spline) surface patches is proposed. The connection of non‐conforming patches with shared degrees of freedom requires mutual refinement, which propagates throughout the whole patch due to the tensor‐product structure of NURBS surfaces. Thus, methods to handle non‐conforming meshes are essential in NURBS‐based isogeometric analysis. The main objective of this work is to provide a simple and efficient way to couple the individual patches of complex geometrical models without altering the variational formulation. The deformations of the interface control points of adjacent patches are interrelated with a master‐slave relation. This relation is established numerically using the weak form of the equality of mutual deformations along the interface. With the help of this relation, the interface degrees of freedom of the slave patch can be condensated out of the system. A natural connection of the patches is attained without additional terms in the weak form. The proposed method is also applicable for nonlinear computations without further measures. Linear and geometrical nonlinear examples show the high accuracy and robustness of the new method. A comparison to reference results and to computations with the Lagrange multiplier method is given. Copyright © 2015 John Wiley & Sons, Ltd.     

On the preconditioned conjugate gradient method for solving (A – λB)X =0

Classical iterative methods when applied to the partial solution of the generalized eigenvalue problem Ax =λ Bx , may yield very poor convergence rates particularly when ill-conditioned problems are considered. In this paper the preconditioned conjugate gradient (CG) method via the minimization of the Rayleigh quotient and the reverse power method is employed for the partial eigenproblem. The triangular splitting preconditioners employed are obtained from an incomplete Choleski factorization and a partial Evans preconditioner. This approach can dramatically improve the convergence rate of the basic CG method and is applicable to any symmetric eigenproblem in which one of the matrices A , B is positive definite. Because of the renewed interest in CG techniques for FE work on microprocessors and parallel computers, it is believed that this improved approach to the generalized eigenvalue problem is likely to be very promising.     

A discrete splitting finite element method for numerical simulations of incompressible Navier–Stokes flows

The presence of the pressure and the convection terms in incompressible Navier–Stokes equations makes their numerical simulation a challenging task. The indefinite system as a consequence of the absence of the pressure in continuity equation is ill‐conditioned. This difficulty has been overcome by various splitting techniques, but these techniques incur the ambiguity of numerical boundary conditions for the pressure as well as for the intermediate velocity (whenever introduced). We present a new and straightforward discrete splitting technique which never resorts to numerical boundary conditions. The non‐linear convection term can be treated by four different approaches, and here we present a new linear implicit time scheme. These two new techniques are implemented with a finite element method and numerical verifications are made. Copyright © 2005 John Wiley & Sons, Ltd.     

The M1 Energy‐efficiency building Plus – Conclusion of monitoring / Das M1 Energieeffizienzhaus Plus – Abschluss des Monitorings

The M1 energy‐efficiency building Plus was to render practical proof that the advantages of solid construction such as carrying capacity, fire protection and sound protection could be connected to state‐of‐the‐art and future energy efficiency standards in the scope of a pilot project. With simple and thought‐through planning details and a coordinated system technology, energy plus solid houses are no longer merely visions. The M1 project mostly focuses on the claim to economic efficiency and saleability of the product, points out new possibilities for implementation to consumers, planners and executing companies. The house is to document, that the means available now are sufficient to construct a solid building that produces more energy than it consumes. In the technical term of construction physics, the building is targeted at a negative final energy and primary energy consumption. The data presented in this article from the monitoring of the last two years show that a plus energy target can be achieved by “nearly” conventionally built solid buildings. For both years, the M1 pus energy house reached an excess of final and primary energy.     

Modeling and optimizing of factors affecting erosion–corrosion of AA6063–(TiC/Al2O3) hybrid composites by experimental design method

In this article, modeling and optimizing of factors affecting erosion–corrosion wear of aluminum alloy A6063 reinforced with (Al₂O₃/TiC) particles have been determined by experimental design method. The erosion–corrosion wear characteristics and mechanism of AA6063–(TiC/Al₂O₃) with experimental parameters namely; type and concentration of corrosive media in the slurry, erosion speed and time have been investigated. Two models for reinforced and unreinforced alloys were applied to describe the influences of these factors on the erosion behavior of alloys. The erosion–corrosion mechanisms of the AA6063–(TiC/Al₂O₃) were dominated by particles erosion wear in alkaline slurry, and by the interaction of particle erosion wear and medium corrosion in acidic slurry. The results of experimental work are coinciding with that of calculated ones confirming the successful modelization.     

Preparation of gold nanosheets using poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers via photoreduction

Gold nanosheets having single crystalline structure were successfully synthesized using the bulk phase mixture of HAuCl₄ and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers through the irradiation of a glow lamp for 5 days. When the molar ratio of propylene oxide to ethylene oxide block units in the block copolymer is about 1.75, mostly gold nanosheets were obtained. Gold nanosheets with an average width of 8 and 5 μm were obtained from the when the molar ratio of gold salt to the ethylene oxide units in the block copolymer were 1/80 and 1/160, respectively.     

Effect of hydrophilic–hydrophobic balance on biocompatibility of poly(methyl methacrylate) (PMMA)–hydroxyapatite (HA) composites

The purpose of this study is to put in evidence the correlation between hydrophilic/hydrophobic balance and biocompatibility of PMMA–HA composites, in order to select the best composites for futures clinical applications. For this purpose, PMMA–HA cements with different compositions were prepared and static contact angle measurements, water absorption and gingival fibroblasts cell culture were performed and discussed.