Preparation and incorporation of microcapsules in functional coatings for self‐healing of packaging board

The replacement of flexible polyolefin barrier layers with novel, thin, functional polymer coatings in the production of paperboard packaging involves the risk of deteriorated barrier and mechanical properties during the converting process. Local defects or cracks in the protective barrier layer can arise because of the stress induced in creasing and folding operations. In this study, the incorporation of microencapsulated self‐healing agents in coating formulations applied both by spot‐ and uniform‐coating techniques was studied. The preparation process of microcapsules with a hydrophobic core surrounded by a hydrophobically modified polysaccharide membrane in aqueous suspension was developed to obtain capsules fulfilling both the criteria of small capsule size and reasonably high solids content to match the requirements set on surface treatment of paperboard for enhancement of packaging functionality. The survival of the microcapsules during application and their effectiveness as self‐healing agents were investigated. The results showed a reduced tendency for deteriorated barrier properties and local termination of cracks formed upon creasing. The self‐healing mechanism involves the rupture of microcapsules local to the applied stress, with subsequent release of the core material. Crack propagation is hindered by plasticization of the underlying coating layer, while the increased hydrophobicity helps to maintain the barrier properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of submicron admixtures on mechanical and self‐healing properties of cement‐based composites

This study presents the development of novel submicron super absorbent polymers (SAPs) used as admixtures in cement‐based matrices with significant advantages over conventional products. The produced SAPs were characterized in respect of their morphology and composition, while their water absorption capacity was determined in different electrolyte solutions. The hybrid core‐shell spherical structure of the fabricated materials offered significant compatibility enhancement with cement while the workability of the mixture was maintained. The assessment of the cement‐based composites including SAPs revealed that their flexural strength increased by 78%. Self‐healing/sealing behavior was assessed by monitoring the crack sealing via SEM, elemental analysis of the healing products, and determination of the water absorbance coefficient for different times of treatment. The cement/SAPs composites with a concentration of SAPs 2% by weight of cement exhibited self‐healing/sealing responsive capability when an artificial crack was induced. According to the SEM characterization, the crack demonstrated complete healing for the better part of its length after 28 days of treatment.     

Effect of high‐pressure processing on the mechanical and barrier properties of selected packagings

This investigation focuses on the effect of high‐pressure processing (HPP) on possible changes of the mechanical properties and of the water vapour permeability of seven selected packaging materials. NOD 259 (PA‐PE), BB4L (Cryovac‐Grace packaging), PET/BOA/PE, PET/PVDC/PE, PA/SY, LDPE and EVA/PE were investigated (PET, polyester; PE, polyethylene; SY, surlyn; LDPE, low‐density polyethylene; EVA, polyethylene–vinyl acetate co‐polymer; BOA, biaxially oriented polyamide). These packaging materials were selected because of their interest to the food industry. All had an internal film of PE for food use. High‐pressure tests were realized at 10°C for 10 min at pressures of 200, 400 and 600 MPa, with water as a food‐simulating fluid. The depressurization rate was either rapid (pressure drop in <10s) or slow (20 MPa/min). Permeability to water vapour was realized using the NFF H 00 030–ASTM E96‐90 standard. Mechanical tests were carried out with a tensile testing machine (Lloyd LR5K), according to the NF 54‐102 standard. Maximal stress, rupture stress and strain at rupture were evaluated with non‐treated and treated samples. Obtained results showed that HPP minimally affects the mechanical strength of packaging material. The depressurization rate did not have any significant influence in our conditions. The barrier properties to water vapour were not significantly affected and were even slightly enhanced for LDPE, which is a packaging material commonly used for HPP applications and at least as a food contact material. Copyright © 2006 John Wiley & Sons, Ltd.     

A combined FIC‐TDG finite element approach for the numerical solution of coupled advection–diffusion–reaction equations with application to a bioregulatory model for bone fracture healing

Numerical schemes for the approximative solution of advection–diffusion–reaction equations are often flawed because of spurious oscillations, caused by steep gradients or dominant advection or reaction. In addition, for strong coupled nonlinear processes, which may be described by a set of hyperbolic PDEs, established time stepping schemes lack either accuracy or stability to provide a reliable solution. In this contribution, an advanced numerical scheme for this class of problems is suggested by combining sophisticated stabilization techniques, namely the finite calculus (FIC‐FEM) scheme introduced by Oñate et al. with time‐discontinuous Galerkin (TDG) methods. Whereas the former one provides a stabilization technique for the numerical treatment of steep gradients for advection‐dominated problems, the latter ensures reliable solutions with regard to the temporal evolution. A brief theoretical outline on the superior behavior of both approaches will be presented and underlined with related computational tests. The performance of the suggested FIC‐TDG finite element approach will be discussed exemplarily on a bioregulatory model for bone fracture healing proposed by Geris et al., which consists of at least 12 coupled hyperbolic evolution equations. Copyright © 2012 John Wiley & Sons, Ltd.     

A mixed‐enhanced finite‐element for the analysis of laminated composite plates

This paper presents a new 4‐node finite‐element for the analysis of laminated composite plates. The element is based on a first‐order shear deformation theory and is obtained through a mixed‐enhanced approach. In fact, the adopted variational formulation includes as variables the transverse shear as well as enhanced incompatible modes introduced to improve the in‐plane deformation. The problem is then discretized using bubble functions for the rotational degrees of freedom and functions linking the transverse displacement to the rotations. The proposed element is locking free, it does not have zero energy modes and provides accurate in‐plane/out‐of‐plane deformations. Furthermore, a procedure for the computation of the through‐the‐thickness shear stresses is discussed, together with an iterative algorithm for the evaluation of the shear correction factors. Several applications are investigated to assess the features and the performances of the proposed element. Results are compared with analytical solutions and with other finite‐element solutions. Copyright © 1999 John Wiley & Sons, Ltd.     

Solution strategies for the delamination analysis based on a combination of local‐control arc‐length and line searches

The paper describes a local‐control arc‐length method which can be combined with various forms of line‐search procedure. In particular, a new ‘double‐line‐search’ method is developed, which significantly improves the solution procedure and turns out to be efficient and robust. Although the potential range of applications is wide, the method is here limited to the finite element analysis of delamination in a laminated composite using a cohesive‐zone model combined with interface elements. Three problems have been analysed and comparisons have been made with experimental results. Copyright © 2003 John Wiley & Sons, Ltd.     

Numerical study on the effect of the thermo‐mechanical properties of alloys on the behaviour of super plastic forming tools

The paper describes a numerical study to investigate the effect of the thermo‐mechanical properties of heat resisting nickel and chromium alloys, used for super plastic forming (SPF) tools, on the tool service behaviour. The purpose of the paper is to rank the relative importance of each property studied for the heat resisting class of cast nickel and chromium alloys, subjected to repeated thermal cycles under typical industrial super plastic forming conditions. A finite element model of a tool block within an industrial press furnace was developed to simulate the typical thermal cycles of an super plastic forming tool, and predict the resulting mechanical performance. Important thermal and mechanical properties were identified for the cast nickel and chromium class of alloys studied in this paper and suitable ranges for the properties were determined for numerical simulations. The results include a quantitative analysis of the effect of the properties studied.     

Phases analysis and impact of phases on fracture mechanism of AZ61‐SiC composite

Phase composition of AZ61‐SiC composite with 5 wt.% of nanosized silicon carbide reinforcement was analysed and failure mechanism by in situ tensile test in scanning electron microscope was observed. Microstructure of the experimental materials was heterogeneous with grain size of 15 μm. Based on the quantitative analysis of composite, besides, silicon carbide strengthened particles added externally into the matrix magnesium silicide, magnesium oxide, and aluminium/manganese particles formed in situ were found in the matrix. In situ tensile test in scanning electron microscope has shown that reinforcing particles substantially influenced failure mechanism. Large, brittle magnesium silicide particles (size of 40 μm–50 μm) cracked during tensile deformation and at the same time, as a result of different physical properties, decohesion of the matrix and smaller aluminium/manganese, silicon carbide and magnesium oxide particles (size of 5 μm–10 μm, 10 μm and 50 nm respectively) occurred. Reinforcing particles and brittle secondary phases driven micro voids and their coalescence was found as a major cause of large cracks formation. Subsequently the increase of stress caused the cracks propagation by the coalescence of fractured particles and decohesively release smaller dispersed particles. The fracture propagated at approximately 90° angle to the direction of the tensile load direction. Fracture surface had feature of transcrystalline and intercrystalline failure.     

Variational approach to the analysis of steady‐state thermo‐elastic wear regimes

A transient wear process on frictional interface of two thermo‐elastic bodies in a relative steady sliding motion induces shape evolution of contact interface and tends to a steady state for which the wear process occurs at fixed contact stress and strain distribution. The temperature field generated by frictional and wear dissipation on the contact surface is assumed to reach a steady state. This state is assumed to correspond to minimum of the wear dissipation power and the temperature field corresponds to maximum of the heat entropy production. The stationarity conditions of the response functionals provide the contact pressure distribution and the corresponding temperature field. The present approach extends the authors previous analyses of optimal or steady‐state contact shapes by accounting for coupled wear and thermal distortion effects. The wear rule is assumed as a non‐linear relation of wear rate to shear stress and relative sliding velocity. The analysis of disk and drum brakes is presented with account for thermal distortion effect. It is shown that the contact shape in a steady thermo‐elastic state essentially differs from that specified for mechanical loading with neglect of thermal effects. The thermal instability regimes are not considered in the paper. Copyright © 2009 John Wiley & Sons, Ltd.     

A Thermodynamics Model for the Emergence of a Stripe‐like Binary SAM on a Nanoparticle Surface

It has been under debate if a self‐assembled monolayer (SAM) with two immiscible ligands of different chain lengths and/or bulkiness can form a stripe‐like pattern on a nanoparticle (NP) surface. The entropic gain upon such pattern formation due to difference in chain lengths and/or bulkiness has been proposed as the driving force in literature. Using atomistic discrete molecular dynamics simulations it is shown that stripe‐like pattern could indeed emerge, but only for a subset of binary SAM systems. In addition to entropic contributions, the formation of a striped pattern also strongly depends upon interligand interactions governed by the physicochemical properties of the ligand constituents. Due to the interplay between entropy and enthalpy, a binary SAM system can be categorized into three different types depending on whether and under what condition a striped pattern can emerge. The results help clarify the ongoing debate and our proposed principle can aid in the engineering of novel binary SAMs on a NP surface.     

The effect of ferrite phases on the micromechanical response and crack initiation in the intercritical heat‐affected zone of a welded 9Cr martensitic steel

This paper presents a crystal plasticity model to predict the tensile response and crack initiation in a mixed ferrite‐martensite material with a low volume fraction of pro‐eutectoid ferrite, representative of a welding‐induced intercritical heat‐affected zone. It is shown that small volume fractions of ferrite can have a significant effect on material strength and ductility depending on the ferrite grain orientation. For relatively “soft” ferrite grains, microcracks can grow across interferrite ligaments with damage accumulating in the ferrite, leading to a reduction in strength and strain hardening, but with little influence on ductility; in contrast, relatively “hard” ferrite grains act to accelerate microcrack initiation, leading to reduced ductility, with negligible influence on strain hardening up to the maximum load.     

Study of low‐temperature effect on the fracture locus of a 420‐MPa structural steel with the edge tracing method

Quasi‐static tensile tests with smooth round bar and axisymmetric notched tensile specimens have been performed to study the low‐temperature effect on the fracture locus of a 420‐MPa structural steel. Combined with a digital high‐speed camera and a 2‐plane mirror system, specimen deformation was recorded in 2 orthogonal planes. Pictures taken were then analysed with the edge tracing method to calculate the minimum cross‐section diameter reduction of the necked/notched specimen. Obvious temperature effect was observed on the load‐strain curves for smooth and notched specimens. Both the strength and strain hardening characterized by the strain at maximum load increase with temperature decrease down to ?60°C. Somewhat unexpected, the fracture strains (ductility) of both smooth and notched specimens at temperatures down to ?60°C do not deteriorate, compared with those at room temperature. Combined with numerical analyses, it shows that the effect of low temperatures (down to ?60°C) on fracture locus is insignificant. These findings shed new light on material selection for Arctic operation.     

High‐pressure processing effects on the mechanical,barrier and mass transfer properties of food packaging flexible structures: a critical review

Food products can be high‐pressure processed (HPP) either in bulk or prepackaged in flexible or semi‐rigid packaging materials. In the latter case the packaging material is subjected, together with the food, to high‐pressure treatment. A number of studies have been performed to quantify the effects of high‐pressure processing on the physical and barrier properties of the packaging material, since the integrity of the package during and after processing is of paramount importance to the safety and quality of the food product. This article reviews the results of published research concerning the effect of HPP on packaging materials. Copyright © 2004 John Wiley & Sons, Ltd.     

The effect of frequency on the giga‐cycle fatigue properties of a Ti–6Al–4V alloy

The effect of frequency on giga‐cycle fatigue properties was investigated in smooth and 0.3 mm‐hole‐notched specimens at three heats (Heats A, B, and C) for a 900 MPa‐class Ti‐6Al‐4V alloy. Fatigue tests were performed at frequencies of 120 Hz, 600 Hz, and 20 kHz using electromagnetic resonance, high‐speed servohydraulic, and ultrasonic fatigue testing machines, respectively. Heats A and B developed internal fractures, and in these cases, frequency effects were negligible. On the other hand, Heat C developed only surface fractures. In this case, high‐frequency tests showed a higher fatigue strength, indicating frequency effects were not negligible. The tests using the notched specimens showed almost no frequency effects regardless of the heat. The frequency effects observed in the cases of surface fracture were believed to be related to a delay in local plastic deformation in response to high‐frequency loading, since temperature increases in these specimens were successfully suppressed. The delay in the plastic deformation was observed to be reduced in the notched specimens because of stress concentration and limitation in the plastic deformation zone. In turn, the significant conclusion of this research is that high‐frequency tests can be applied not only to internal fractures but also to notch problems, but are not applicable to surface fractures of smooth specimens.     

Experimental and numerical investigation of the effect of temperature on mixed‐mode fracture behaviour of AM60 Mg alloy

The aim of present paper is to experimentally investigate mixed‐mode fracture behaviour of AM60 Mg alloy at low and elevated temperatures. For this purpose, mode I, 45° mixed‐mode, and mode II tests were conducted using a modified version of Arcan device at three different temperatures. An elastic‐plastic finite element model was used to extract necessary geometric parameters. Crack resistance curves (J‐R) and critical J‐integral of the material were extracted. The results indicated that, for all loading modes, maximum critical J‐integral value was observed at ambient temperature and decreased by either increasing or decreasing the temperature. It was observed that effect of temperature on fracture behaviour is much larger at temperatures above 0°C rather than sub‐zero temperatures. By changing the loading angle to go from mode I to mode II, a decreasing trend was observed in the values of critical fracture parameters at all temperatures. Finally, the surfaces were examined using scanning electron microscopy (SEM).     

A novel approach to investigate the effect of meso-scale yarn structure on the in-plane mechanical response of woven monofilament textiles by numerical modeling of experiments

The mechanical response of textiles depends upon various parameters including materials, yarn structure, and the architecture of the textile. These factors play an important role in the nonlinear mechanical response. In this work, a novel numerical modeling approach is proposed to better capture the effect of the meso-scale structure on the textile's mechanical response. Monofilament textiles exhibiting meso-scale irregularities due to the manufacturing are studied. A novel numerical method is developed to study these effects on the in-plane mechanical response. The in-plane experiments validated the proposed modeling approach. The results show the importance of the meso-scale structure induced by manufacturing.     

A cell‐based smoothed discrete shear gap method (CS‐FEM‐DSG3) based on the C0‐type higher‐order shear deformation theory for dynamic responses of Mindlin plates on viscoelastic foundations subjected to a moving sprung vehicle

A cell‐based smoothed discrete shear gap method (CS‐FEM‐DSG3) based on the first‐order shear deformation theory (FSDT) was recently proposed for static and dynamic analyses of Mindlin plates. In this paper, the CS‐FEM‐DSG3 is extended to the C⁰‐type higher‐order shear deformation plate theory (C⁰‐HSDT) and is incorporated with damping–spring systems for dynamic responses of Mindlin plates on viscoelastic foundations subjected to a moving sprung vehicle. At each time step of dynamic analysis, one four‐step procedure is performed including the following: (1) transformation of the weight of a four‐wheel vehicle into the sprung masses at wheels; (2) dynamic analysis of the sprung mass of wheels to determine the contact forces; (3) transformation of the contact forces into loads at nodes of plate elements; and (4) dynamic analysis of the plate elements on viscoelastic foundations. The accuracy and reliability of the proposed method are verified by comparing its numerical solutions with those of other available numerical results. Copyright © 2014 John Wiley & Sons, Ltd.     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.