The effect of incorporation of montmorillonite layered silicate (MLS) on poly (ethylene terephthalate) (PET) matrix was investigated. MLS was added in varying concentration of 1 to 5 weight percent in the PET matrix. DSC and polarized optical microscopy were used to determine the crystallization effects of MLS addition. Non isothermal crystallization kinetics showed that the melting temperature and crystallization temperature decrease as the MLS percent increases. This delayed crystallization along with the irregular spherulitic shape indicates hindered crystallization in the presence of MLS platelets. The influence of this morphology was related with the fracture toughness of PET nanocomposites using essential work of fracture coupled with the infra red (IR) thermography. Both the essential as well as non essential work of fracture decreased on addition of MLS with nanocomposite showing reduced toughness.

The context of this thesis is a research project focused on the investigation of a renewable biopolymer-poly(lactic acid) (PLA) as a potential replacement of petroleum-based polymers in advanced nanocomposites reinforced with Microfibrillated cellulose (MFC). MFC is extracted from wood, which is a renewable, sustainable, carbon neutral and recyclable material. This advanced MFC-PLA bio- based composite material is expected to allow for the substitution of petroleum-based plastics in various markets and applications. The specific objectives of the thesis are: 1) to describe the morphological characterization of MFC used for prototype MFC-PLA composites, and 2) to determine the mechanical properties of the prototype MFC-PLA nanocomposites formulation generated in form of thin transparent films. In order to meet this objective it was necessary to: 2.1) develop a methodology for optical strain measurement in transparent thin films; and 2.2) develop an effective methodology for obtaining multiple mechanical properties from small number of specimens of prototype materials subjected to tensile tests. Two types of MFC, one obtained by courtesy of University of Maine and the other purchased from Innventia AB company, were investigated under a field emission scanning electron microscopy (FESEM). The micrographs obtained from FESEM showed that both types of MFC were of complex hierarchical structures, which did not allow qualitative characterization of the morphological features in terms of particulate composites nor cellular solids. Since prototype formulations of MFC-PLA composites were generated in small amounts (typically one Petri dish) in a form of thin transparent films, there was a need for quick and efficient assessment of their key mechanical properties that would provide feedback and guide further prototyping work. An optical measurement method based on digital image correlation (DIC) principle was developed to measure the deformation and strains of the tensile film samples. In our study, the accuracy and precision of the measurement of deformation were ±1.5 µm and 0.4 µm respectively. The corresponding accuracy and precision in terms of strains were ±30 µstrain and 75 µstrain respectively. This method can be successfully used to determine the critical mechanical properties, such as elastic modulus, toughness and Poisson's ratio, of transparent thin films by a single tensile test, all of which require precise strain measurement. In addition, this optical measurement method makes it possible to significantly simplify the testing for measuring essential work of fracture (EWF), an important material property of thin transparent films. In traditional method, measurement of EWF requires large amount of notched specimens. However, our study showed that only a small amount of notched specimens were needed to measure the EWF of a material. This method could not be successfully used to determine EWF from un-notched tensile specimens. / Graduation date: 2012 / Folder labeled "UMaine MFC aerogel" contains SEM micrographs of MFC from University of Maine (referred as type A MFC in the thesis). Two pieces of leaf-like flakes at different locations were cut by Focused Ion Beam (FIB) in order to observe the internal structure of the flakes. Folder "FIB_01 ": a series of SEM micrographs of FIB-cut flake at different magnification levels. Folder "FIB_02 ": another series of SEM micrographs of FIB-cut flake at various magnification levels. Folder labeled "Swedish MFC aerogel" contains SEM micrographs of MFC from Innventia AB company, Sweden (referred as type B MFC in the thesis). There is a series of SEM micrographs of type B MFC aerogel at various magnification levels in this folder.

O polietileno de média densidade (PEMD) é um polímero termoplástico parcialmente cristalino, cujo uso tem crescido bastante em aplicações de engenharia, como em tubos plásticos para sistemas de distribuição de água e de gás. Sob carga constante, entretanto, este material pode eventualmente apresentar fratura por fluência, por meio de um mecanismo de crescimento lento de trincas, provocando acentuadas perdas por vazamento nos sistemas. Os métodos atuais empregados pela indústria para estimar a durabilidade dos tubos são caros, demorados, pouco práticos e imprecisos. Busca-se o desenvolvimento de técnicas mais eficientes, sendo que os métodos da mecânica da fratura são promissores no sentido de descrever a etapa de propagação da trinca. Ensaios de mecânica da fratura, entretanto, requerem a introdução de pré-trincas nos corpos de prova. Sabe-se que as técnicas artificiais de introdução de pré-trincas causam algum tipo de dano na matriz polimérica, que pode ou não afetar os resultados dos ensaios, dependendo dos eventos que ocorrerem após o carregamento inicial. A principal propriedade requerida de um método de introdução de pré-trinca, portanto, é reprodutibilidade. Neste estudo foram aplicados três importantes métodos de mecânica da fratura ao PEMD e investigados os efeitos de diferentes técnicas de introdução de pré-trincas sobre os resultados dos ensaios e sobre as estruturas de deformação na matriz do material na ponta da trinca. Os ensaios de tenacidade à fratura no estado plano de deformação - KIc - foram realizados em condições criogênicas, em vista do comportamento dúctil do material à temperatura ambiente, sendo que a estratégia mostrou-se satisfatória. Os resultados dos ensaios de Integral-J sugerem que o método pode não ser aplicável ao PEMD, devido ao peculiar mecanismo de fratura do material. O método do trabalho essencial de fratura - EWF - se aplica bem ao PEMD. Os resultados dos ensaios de KIc e EWF demonstraram que diferentes técnicas de introdução de pré-trincas provocam diferentes estruturas de deformação no material na ponta da trinca e afetam os resultados de ensaios de fratura no PEMD. Os resultados de EWF demonstraram ainda que o processamento também afeta as propriedades de fratura do material. É proposta uma nova técnica para a introdução de pré-trincas, com características mais naturais, a qual requer estudos complementares para seu aperfeiçoamento. / Medium density polyethylene (MDPE) is a semicrystalline thermoplastic polymer that has been increasingly used in engineering applications, as plastic pipes for water and gas distribution systems. Under constant load, however, this material may occasionally present creep failure, by means of a mechanism of slow crack growth, leading to leakage losses in the systems. Current methods used by industry to estimate durability of pipes are expensive, time consuming, non practical and inaccurate. The development of more efficient methods is a common target and fracture mechanics methods are promising in describing the crack propagation stage. Fracture mechanics testing methods, however, require the introduction of pre-cracks into the specimens. It is known that artificial methods of introducing pre-cracks produce some damage on the polymeric matrix, which may or not affect the results of tests, depending on the events that occur after the initial loading. Main propriety required of a pre-crack introducing method, therefore, is reproducibility. In this study three important fracture mechanics methods were applied to MDPE and the effects of different methods of pre-cracking over test results and over deformation structures of material matrix at the crack tip were investigated. Plane-strain fracture toughness - KIc tests were performed under cryogenic conditions, in view of the ductile behavior of material at room temperature and this strategy was well succeed. Results of Integral-J tests suggest that this method may not be applicable to MDPE, due to the peculiar fracture mechanism of the material. The essential work of fracture method EWF is well suited to study MDPE. The results of KIc and EWF tests showed that different pre-cracking methods cause different deformation structures in the material at the crack tip and affect the fracture tests with MDPE. EWF results showed also that the processing affect the fracture properties of materials too. It is proposed a new method for introducing pre-cracks, with more natural characteristics that requires complementary studies for its improving.

No description available.

O polietileno de média densidade (PEMD) é um polímero termoplástico parcialmente cristalino, cujo uso tem crescido bastante em aplicações de engenharia, como em tubos plásticos para sistemas de distribuição de água e de gás. Sob carga constante, entretanto, este material pode eventualmente apresentar fratura por fluência, por meio de um mecanismo de crescimento lento de trincas, provocando acentuadas perdas por vazamento nos sistemas. Os métodos atuais empregados pela indústria para estimar a durabilidade dos tubos são caros, demorados, pouco práticos e imprecisos. Busca-se o desenvolvimento de técnicas mais eficientes, sendo que os métodos da mecânica da fratura são promissores no sentido de descrever a etapa de propagação da trinca. Ensaios de mecânica da fratura, entretanto, requerem a introdução de pré-trincas nos corpos de prova. Sabe-se que as técnicas artificiais de introdução de pré-trincas causam algum tipo de dano na matriz polimérica, que pode ou não afetar os resultados dos ensaios, dependendo dos eventos que ocorrerem após o carregamento inicial. A principal propriedade requerida de um método de introdução de pré-trinca, portanto, é reprodutibilidade. Neste estudo foram aplicados três importantes métodos de mecânica da fratura ao PEMD e investigados os efeitos de diferentes técnicas de introdução de pré-trincas sobre os resultados dos ensaios e sobre as estruturas de deformação na matriz do material na ponta da trinca. Os ensaios de tenacidade à fratura no estado plano de deformação - KIc - foram realizados em condições criogênicas, em vista do comportamento dúctil do material à temperatura ambiente, sendo que a estratégia mostrou-se satisfatória. Os resultados dos ensaios de Integral-J sugerem que o método pode não ser aplicável ao PEMD, devido ao peculiar mecanismo de fratura do material. O método do trabalho essencial de fratura - EWF - se aplica bem ao PEMD. Os resultados dos ensaios de KIc e EWF demonstraram que diferentes técnicas de introdução de pré-trincas provocam diferentes estruturas de deformação no material na ponta da trinca e afetam os resultados de ensaios de fratura no PEMD. Os resultados de EWF demonstraram ainda que o processamento também afeta as propriedades de fratura do material. É proposta uma nova técnica para a introdução de pré-trincas, com características mais naturais, a qual requer estudos complementares para seu aperfeiçoamento. / Medium density polyethylene (MDPE) is a semicrystalline thermoplastic polymer that has been increasingly used in engineering applications, as plastic pipes for water and gas distribution systems. Under constant load, however, this material may occasionally present creep failure, by means of a mechanism of slow crack growth, leading to leakage losses in the systems. Current methods used by industry to estimate durability of pipes are expensive, time consuming, non practical and inaccurate. The development of more efficient methods is a common target and fracture mechanics methods are promising in describing the crack propagation stage. Fracture mechanics testing methods, however, require the introduction of pre-cracks into the specimens. It is known that artificial methods of introducing pre-cracks produce some damage on the polymeric matrix, which may or not affect the results of tests, depending on the events that occur after the initial loading. Main propriety required of a pre-crack introducing method, therefore, is reproducibility. In this study three important fracture mechanics methods were applied to MDPE and the effects of different methods of pre-cracking over test results and over deformation structures of material matrix at the crack tip were investigated. Plane-strain fracture toughness - KIc tests were performed under cryogenic conditions, in view of the ductile behavior of material at room temperature and this strategy was well succeed. Results of Integral-J tests suggest that this method may not be applicable to MDPE, due to the peculiar fracture mechanism of the material. The essential work of fracture method EWF is well suited to study MDPE. The results of KIc and EWF tests showed that different pre-cracking methods cause different deformation structures in the material at the crack tip and affect the fracture tests with MDPE. EWF results showed also that the processing affect the fracture properties of materials too. It is proposed a new method for introducing pre-cracks, with more natural characteristics that requires complementary studies for its improving.

No description available.

Ziel der vorliegenden Arbeit war es, die Zusammenhänge zwischen der molekularen Architektur, Morphologie und den mechanischen bzw. bruchmechanischen Eigenschaften in S-SB-S-Triblockcopolymeren und deren Blends und in PI-PS-Multipfropfcopolymeren herauszuarbeiten und damit einerseits einen Beitrag für das Verständnis der Struktur-Eigenschaftsbeziehungen in Block- und Pfropfcopolymeren zu leisten und andererseits Möglichkeiten zur Entwicklung neuer Materialien aufzuzeigen, welche besondere Eigenschaftskombinationen aufweisen und damit ein bedeutendes Interesse für industrielle Anwendungen hervorrufen. Für die Untersuchungen wurde dabei der PS-Außenblockanteil und das S/B-Verhältnis im SB-Mittelblock in S-SB-S-Triblockcopolymeren, die Thermoplast/Thermoplastisches Elastomer (TP/TPE) -Zusammensetzung in S-SB-S-Triblockcopolymer-Blends sowie die Funktionalität und die Anzahl der Verknüpfungspunkte in PI-PS-Multipfropfcopolymeren variiert. Zur Charakterisierung der Phasenmischbarkeit und der Morphologie wurden die dynamisch mechanische Analyse (DMA), die Transmissionselektronenmikroskopie (TEM) und die Röntgenkleinwinkelstreuung (SAXS) angewandt. Die mechanischen Eigenschaften wurden mit dem einachsigen Zugversuch untersucht. Bruchmechanische Untersuchungen erfolgten unter Anwendung der „Essential Work of Fracture“- (EWF-) Methode, welche als Konzept der „Post-Yield“-Bruchmechanik innerhalb der Fließbruchmechanik für duktile nanostrukturierte polymere Materialien sehr gut anwendbar ist und Aussagen zur Bruchzähigkeit der Materialien liefert. Zur näheren Charakterisierung des zeitaufgelösten Deformationsverhaltens sowie der Rissausbreitungskinetik wurden die Dehnungsfeldanalyse, eine Bruchflächenanalyse mittels Rasterelektronenmikroskopie (REM) sowie das Risswiderstandskurven-Konzept angewandt. Die Untersuchungen der S-SB-S-Triblockcopolymersysteme und der PI-PS-Multipfropfcopolymere konnten den signifikanten Einfluss der molekularen Architektur, der Blockzusammensetzung und des PS-Gehaltes auf das Phasenverhalten, die Morphologie und die Eigenschaften klar herausstellen. Durch die Variation dieser Parameter kann das Eigenschaftsspektrum von thermoplastisch zu elastomer eingestellt und somit sowohl TPs oder TPEs mit hoher Steifigkeit und Zähigkeit als auch TPEs mit superelastischem Charakter erzeugt werden. Daraus eröffnet sich ein breiter Anwendungsbereich dieser Materialien, welche aufgrund ihrer Transparenz und physiologischen Verträglichkeit auch interessante optische und gesundheitliche Vorteile mitbringen. Es konnte gezeigt werden, dass durch die systematische Variation der Architektur die gezielte Einstellung gewünschter Eigenschaftsprofile möglich ist. Die Arbeit leistet somit einen Beitrag zur Entwicklung anwendungsorientierter Materialkonzepte, welche ingenieurwissenschaftlich interessant sind. / The aim of this thesis was to study the relation between molecular architecture, morphology and (fracture) mechanical properties of S-SB-S triblock copolymers and PI-PS multigraft copolymers. Hence, this work should contribute to the understanding of structure-property-relationship in block and multigraft copolymers and thus offer possibilities for the development of novel materials with special properties interesting for industrial application. Within this study in the case of S-SB-S triblock copolymers the PS outer block content and the S/B ratio of the middle block, in the case of S-SB-S triblock copolymer blends the thermoplast/thermoplastic elastomer (TP/TPE) composition and in case of PI-PS multigraft copolymers the functionality and number of branch points were varied. For the characterisation of morphology and phase miscibility dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) were applied. Uniaxial tensile tests were carried out to investigate the mechanical properties. The fracture mechanical behaviour was studied using essential work of fracture (EWF) concept based on the post yield fracture mechanic principles, which is suitable to characterise fracture toughness of ductile nanostructured materials. The time resolved analysis of deformation and fracture behaviour was characterised qualitatively by strain field analysis, scanning electron microscopy (SEM) of the fractured surfaces and quantitatively by evaluation of the crack propagation kinetics and construction of R-curves. This study clearly highlights the significant influence of molecular architecture block composition and PS content on the phase behaviour, morphology and properties of S-SB-S triblock copolymers and PI-PS multigraft copolymers. By varying these parameters the property profile can be adjusted diversifying from thermoplastic to elastomeric and both TP or TPE materials with high stiffness and toughness and TPEs with super-elastic characteristics can be designed. Hence, fundamentally it offers a broad scope of application of these materials, in which physiological compatibility and transparency are added advantages. Thus, conceptually it could be shown, that by systematic variation of the architecture desired property profiles can be adjusted. Therefore the present work contributes to the development of application-oriented material concepts, which are interesting in engineering terms.

Ziel der vorliegenden Arbeit war es, die Zusammenhänge zwischen der molekularen Architektur, Morphologie und den mechanischen bzw. bruchmechanischen Eigenschaften in S-SB-S-Triblockcopolymeren und deren Blends und in PI-PS-Multipfropfcopolymeren herauszuarbeiten und damit einerseits einen Beitrag für das Verständnis der Struktur-Eigenschaftsbeziehungen in Block- und Pfropfcopolymeren zu leisten und andererseits Möglichkeiten zur Entwicklung neuer Materialien aufzuzeigen, welche besondere Eigenschaftskombinationen aufweisen und damit ein bedeutendes Interesse für industrielle Anwendungen hervorrufen. Für die Untersuchungen wurde dabei der PS-Außenblockanteil und das S/B-Verhältnis im SB-Mittelblock in S-SB-S-Triblockcopolymeren, die Thermoplast/Thermoplastisches Elastomer (TP/TPE) -Zusammensetzung in S-SB-S-Triblockcopolymer-Blends sowie die Funktionalität und die Anzahl der Verknüpfungspunkte in PI-PS-Multipfropfcopolymeren variiert. Zur Charakterisierung der Phasenmischbarkeit und der Morphologie wurden die dynamisch mechanische Analyse (DMA), die Transmissionselektronenmikroskopie (TEM) und die Röntgenkleinwinkelstreuung (SAXS) angewandt. Die mechanischen Eigenschaften wurden mit dem einachsigen Zugversuch untersucht. Bruchmechanische Untersuchungen erfolgten unter Anwendung der „Essential Work of Fracture“- (EWF-) Methode, welche als Konzept der „Post-Yield“-Bruchmechanik innerhalb der Fließbruchmechanik für duktile nanostrukturierte polymere Materialien sehr gut anwendbar ist und Aussagen zur Bruchzähigkeit der Materialien liefert. Zur näheren Charakterisierung des zeitaufgelösten Deformationsverhaltens sowie der Rissausbreitungskinetik wurden die Dehnungsfeldanalyse, eine Bruchflächenanalyse mittels Rasterelektronenmikroskopie (REM) sowie das Risswiderstandskurven-Konzept angewandt. Die Untersuchungen der S-SB-S-Triblockcopolymersysteme und der PI-PS-Multipfropfcopolymere konnten den signifikanten Einfluss der molekularen Architektur, der Blockzusammensetzung und des PS-Gehaltes auf das Phasenverhalten, die Morphologie und die Eigenschaften klar herausstellen. Durch die Variation dieser Parameter kann das Eigenschaftsspektrum von thermoplastisch zu elastomer eingestellt und somit sowohl TPs oder TPEs mit hoher Steifigkeit und Zähigkeit als auch TPEs mit superelastischem Charakter erzeugt werden. Daraus eröffnet sich ein breiter Anwendungsbereich dieser Materialien, welche aufgrund ihrer Transparenz und physiologischen Verträglichkeit auch interessante optische und gesundheitliche Vorteile mitbringen. Es konnte gezeigt werden, dass durch die systematische Variation der Architektur die gezielte Einstellung gewünschter Eigenschaftsprofile möglich ist. Die Arbeit leistet somit einen Beitrag zur Entwicklung anwendungsorientierter Materialkonzepte, welche ingenieurwissenschaftlich interessant sind. / The aim of this thesis was to study the relation between molecular architecture, morphology and (fracture) mechanical properties of S-SB-S triblock copolymers and PI-PS multigraft copolymers. Hence, this work should contribute to the understanding of structure-property-relationship in block and multigraft copolymers and thus offer possibilities for the development of novel materials with special properties interesting for industrial application. Within this study in the case of S-SB-S triblock copolymers the PS outer block content and the S/B ratio of the middle block, in the case of S-SB-S triblock copolymer blends the thermoplast/thermoplastic elastomer (TP/TPE) composition and in case of PI-PS multigraft copolymers the functionality and number of branch points were varied. For the characterisation of morphology and phase miscibility dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) were applied. Uniaxial tensile tests were carried out to investigate the mechanical properties. The fracture mechanical behaviour was studied using essential work of fracture (EWF) concept based on the post yield fracture mechanic principles, which is suitable to characterise fracture toughness of ductile nanostructured materials. The time resolved analysis of deformation and fracture behaviour was characterised qualitatively by strain field analysis, scanning electron microscopy (SEM) of the fractured surfaces and quantitatively by evaluation of the crack propagation kinetics and construction of R-curves. This study clearly highlights the significant influence of molecular architecture block composition and PS content on the phase behaviour, morphology and properties of S-SB-S triblock copolymers and PI-PS multigraft copolymers. By varying these parameters the property profile can be adjusted diversifying from thermoplastic to elastomeric and both TP or TPE materials with high stiffness and toughness and TPEs with super-elastic characteristics can be designed. Hence, fundamentally it offers a broad scope of application of these materials, in which physiological compatibility and transparency are added advantages. Thus, conceptually it could be shown, that by systematic variation of the architecture desired property profiles can be adjusted. Therefore the present work contributes to the development of application-oriented material concepts, which are interesting in engineering terms.

Les aciers inoxydables austéno-ferritiques présentent une microstructure biphasée dans laquelle se mêlent austénite et ferrite. Leurs caractéristiques mécaniques élevées ainsi que leur bonne tenue en corrosion en font un candidat sérieux pour remplacer les aciers inoxydables austénitiques. Malheureusement, la faible forgeabilité de ces alliages rend la fabrication de tôles particulièrement critique. En effet, le phénomène de « crique de rive » est fréquemment rencontré au cours des étapes du laminage à chaud. Par conséquent, cela nécessite des opérations supplémentaires comme le découpage des rives, ce qui aboutit à une augmentation des coûts de production. Les différents facteurs influençant la ductilité à chaud de ces aciers sont passés en revue afin d'identifier quels sont les zones d'ombres. La synthèse bibliographique révèle deux zones d'ombres : d'une part, le manque d'un essai de ductilité à chaud permettant de discriminer différentes microstructures en terme de résistance à la propagation de fissure à haute température ; et d'autre part l'absence de données quantitative concernant la partition de la déformation entre la ferrite et l'austénite lors des étapes de mise en forme à chaud. Le concept de travail essentiel de rupture a été appliqué à hautes températures. Il a été démontré que cette méthode est fiable et discriminante pour quantifier la résistance à la propagation de fissure à haute température. Elle permet également de générer un paramètre physique pertinent pour optimiser les microstructures par rapport à un mode de mise en forme donné. La technique conventionnelle de micro-grilles a été adaptée de manière à cartographier à haute température les déformations à l'échelle de la microstructure. Cette technique fournit en plus des résultats qualitatifs concernant les mécanismes de déformations, des données quantitatives à propos de la partition de la déformation entre la ferrite et l'austénite. Ces données peuvent être utilisées afin de valider les modèles qui prédisent le comportement à chaud des aciers duplex pendant les premières étapes du laminage à chaud. Les deux outils developpés au cours de cette étude permettent de donner des solutions pour éviter le phénomène de « crique de rives ». / The Duplex Stainless Steels (DSS) are defined as a family of stainless steels consisting of a two-phase microstructure involving δ-ferrite and γ-austenite. Exceptional combinations of strength and toughness together with good corrosion resistance under critical working conditions designate DSS a suitable alternative to conventional austenitic stainless steels. Unfortunately, the relatively poor hot workability of these alloys makes the industrial processing of flat products particularly critical. Cracking of the coils during hot rolling along the edges is frequently reported. As a consequence, additional operations like grinding, discontinuous processing or scraping are often required, leading to increased manufacturing costs. The different parameters affecting the hot working of duplex stainless steels have been reviewed in order to identify which are the missing pieces of the puzzle. The bibliographical review reveals that two pieces are missing in the hot workability puzzle. On the one hand, it is necessary to develop a new hot ductility test which allows discriminating microstructures in terms of high temperature tearing resistance, and on the other hand, quantitative data about the strain partitioning between ferrite and austenite during the hot working operations are needed. The Essential Work of Fracture concept has been applied at high temperature. It has been demonstrated that this method is a reliable and discriminating tool for quantifying the high temperature tearing resistance and to generate a physically relevant index to guide the optimization of microstructures towards successful forming operations. A modified micro-grid technique has been developed to experimentally simulate the local state of deformation of different duplex microstructures at high temperature. This technique provides qualitative results about the deformation features as well as quantitative data about the strain partitioning between ferrite and austenite. The micro-strain distributions measured can be used to validate the models predicting the hot deformation of duplex stainless steels during the roughing-mill operations. The two tools developed in this investigation allow suggesting possible remedies for the edge cracking phenomenon.