Relação entre resistência ao cisalhamento no plano e parâmetros processuais de co-cura de juntas em compósitos auto-reforçados de polietileno de matriz reprocessada

Este estudo investiga a otimização da resistência ao cisalhamento no plano de juntas de sobreposição co-curadas de fitas de compósito termoplástico unidirecionais autoreforçadas feitas com polietileno de baixa densidade (PEBD) reciclado e reforçadas por fibras de polietileno de ultra alto peso molecular (PEUAPM) através da relação desta resistência com os parâmetros processuais de prensagem a quente para a conformação da junta (pressão, temperatura, tempo e comprimento). A matriz teve sua estrutura química analisada para verificar potenciais degradações devidas à sua origem de reciclagem. Matriz e reforço foram caracterizados termicamente para definir a janela de temperatura de processamento de junta a ser estudada, condizente com o intervalo entre as temperaturas de fusão dos materiais (Tf). Com base nestes experimentos, em uma extensa revisão da literatura e em conformações preliminares, os espectros dos parâmetros processuais a serem estudados de temperatura (90, 100, 110, 120 e 130ºC), pressão (1, 2, 3, 4 e 5 bar), tempo (1, 2, 3, 4 e 5 min) e comprimento de junta (12, 24, 36, 48 e 60 mm) foram definidos reunindo condições de cura intermediárias aos extremos nos quais as juntas podiam se formar sem que fossem degradadas estruturalmente durante sua cura. A elaboração das condições de cura dos corpos de prova foi feita de acordo com a metodologia de Projeto de Experimento de Superfície de Resposta de modo a gerar resultados estatisticamente significativos através de um número viável de experimentos, e a relação entre a resistência ao cisalhamento das juntas e os respectivos parâmetros de cura foi obtida através de equação de regressão gerada pelo método dos Mínimos Quadrados Ordinários, e otimizada através do método estatístico de Previsão de Múltiplas Respostas. Os mecanismos de fratura das juntas foram investigados. Devido ao caráter inovador do compósito estudado, a caracterização mecânica em tração do material também foi analisada, tanto micro quanto macromecanicamente. Devido às respectivas ineficiência e inexistência de normas técnicas para os ensaios de tração e de cisalhamento no plano de juntas co-curadas, metodologias de ensaio foram desenvolvidas. A análise química da matriz não demonstrou a presença de grupos carboxílicos que evidenciassem degradação por ramificações de cadeia e reticulação advindos da reciclagem do material, o que foi correspondido por sua caracterização mecânica revelando propriedades em tração iguais às do material virgem. As metodologias de ensaio propostas demonstraram ser eficazes, podendo servir futuramente como base para a constituição de novas normas de técnicas. Foi demonstrado que é possível obter juntas com resistência ótima ao cisalhamento de 6,88 MPa quando processadas a 1 bar, 115°C, 5 min e com 12 mm. A análise da fratura revelou que a ruptura por cisalhamento das juntas foi precedida por múltiplas fissuras longitudinais induzidas por sucessivos debondings, tanto dentro quanto fora da junta, devido à tensão transversal acumulada na mesma, proporcional a seu comprimento. A temperatura demonstrou ser o parâmetro de processamento mais relevante para a performance da junta, a qual é pouco afetada por variações na pressão e tempo de cura. O compósito de PEUAPM/PEBD se mostrou um material estrutural interessante a ser amplamente aplicado na indústria, com propriedades mecânicas específicas elevadas (em casos, maiores que as de carbono/epóxi), possibilidade de dano progressivo de juntas co-curadas (evitando falhas catastróficas repentinas) que podem ter uma resistência ao cisalhamento tão alta quanto aproximadamente 70% da resistência à tração da matriz, e reciclabilidade final.This study investigates the optimization of in-plane shear strength of co-cured overlap joints of unidirectional self-reinforced thermoplastic composite tapes made with recycled low density polyethylene (LDPE) and reinforced by ultra-high molecular weight polyethylene (UHMWPE) through the relationship of this resistance with the hot-press processing parameters for the conformation of the joint (pressure, temperature, time and length). The matrix had its chemical structure analyzed to check for potential degradation due to its recycled origin. Matrix and reinforcement were thermally characterized to define the joint processing temperature window to be studied, consistent with the interval between the melting temperatures of the materials. Based on these experiments, on an extensive literature review and on preliminary conformations, the spectra of the process parameters to be studied for temperature (90, 100, 110, 120 and 130ºC), pressure (1, 2, 3, 4 and 5 bar ), time (1, 2, 3, 4 and 5 min) and joint length (12, 24, 36, 48 and 60 mm) were defined considering intermediate curing conditions between the extremes at which the joints were able to be formed but without being structurally degraded during curing. The elaboration of the curing conditions of the specimens was done according to the Design of Experiment approach of Response Surface methodology in order to generate statistically significant results through a viable number of experiments, and the relationship between the shear strength of the joints and the respective cure parameters was obtained through a regression equation generated by the method of Ordinary Least Squares, and optimized through the statistical method of Multiple Response Prediction. The fracture mechanisms of the joints were investigated. Due to the respective inefficiency and inexistence of technical standards for tensile and in-plane shear tests for co-cured joints, new test methodologies were developed. The chemical analysis of the matrix did not demonstrate the presence of carboxylic groups that could account for degradation by chain-scission and cross-linking resultant from the recycling of the material, which was matched by its mechanical characterization showing tensile properties equal to those of the virgin material. The proposed test methodologies have proven to be effective and may serve in the future as a basis for the constitution of new technical standards. It has been shown that it is possible to obtain joints with optimum in-plane shear strength of 6.88 MPa when processed at 1 bar, 115 ° C, 5 min and 12 mm. The fracture analysis revealed that the shear rupture of the joints was preceded by multiple longitudinal cracks induced by successive debondings, both inside and outside the joint, due to the accumulated transverse tension, proportional to its length. Temperature proved to be the most relevant processing parameter for the performance of the joint, which is little affected by variations in pressure and curing time. The UHMWPE/LDPE composite proved to be an interesting structural material to be widely applied in industry, with high specific mechanical properties (in cases, greater than those of carbon/epoxy), possibility of progressive damage of co-cured joints (avoiding catastrophic failures) that can have a shear strength as high as approximately 70% of the matrix tensile strength, and ultimate final recyclability

Relationship between in-plane shear resistance and co-cure processing parameters of joints in self-reinforced polyethylene composite with reprocessed matrix

Este estudo investiga a otimização da resistência ao cisalhamento no plano de juntas de sobreposição co-curadas do compósito termoplástico unidirecional auto-reforçado de polietileno de baixa densidade reciclado reforçado por fibras de polietileno de ultra alto peso molecular através da relação desta resistência com os parâmetros processuais de prensagem a quente para a conformação da junta (pressão, temperatura, tempo e comprimento). A matriz teve sua estrutura química analisada para verificar potenciais degradações devidas à sua origem de reciclagem. Matriz e reforço foram caracterizados termicamente para definir a janela de temperatura de processamento de junta a ser estudada. A elaboração das condições de cura dos corpos de prova foi feita de acordo com a metodologia de Projeto de Experimento de Superfície de Resposta e a relação entre a resistência ao cisalhamento das juntas e os respectivos parâmetros de cura foi obtida através de equação de regressão gerada pelo método dos Mínimos Quadrados Ordinários. A caracterização mecânica em tração do material foi analisada micro e macromecanicamente. A análise química da matriz não demonstrou a presença de grupos carboxílicos que evidenciassem degradação por ramificações de cadeia e reticulação advindos da reciclagem do material. As metodologias de ensaio propostas demonstraram ser eficazes, podendo servir como base para a constituição de normas técnicas. Demonstrou-se que é possível obter juntas com resistência ótima ao cisalhamento de 6,88 MPa quando processadas a 1 bar, 115°C, 5 min e com 12 mm. A análise da fratura revelou que a ruptura por cisalhamento das juntas foi precedida por múltiplas fissuras longitudinais induzidas por sucessivos debondings, tanto dentro quanto fora da junta, devido à tensão transversal acumulada na mesma, proporcional a seu comprimento. A temperatura demonstrou ser o parâmetro de processamento mais relevante para a performance da junta, a qual é pouco afetada por variações na pressão e tempo de cura.This study investigates the optimization of in-plane shear strength of co-cured overlap joints of unidirectional self-reinforced thermoplastic composite tapes made with recycled low-density polyethylene and reinforced by ultra-high molecular weight polyethylene through the relationship of this resistance with the hot-press processing parameters for the conformation of the joint (pressure, temperature, time and length). The matrix had its chemical structure analyzed to check for potential degradation due to its recycled origin. Matrix and reinforcement were thermally characterized to define the joint processing temperature window to be studied. The elaboration of the curing conditions of the specimens was done according to the Design of Experiment approach of Response Surface methodology, and the relationship between the shear strength of the joints and the respective cure parameters was obtained through a regression equation generated by the method of Ordinary Least Squares. The tensile characterization of the material was also conducted both micro and macromechanically. The chemical analysis of the matrix did not demonstrate the presence of carboxylic groups that could account for degradation by chain-scission and cross-linking resultant from the recycling of the material. The proposed test methodologies have proven to be effective and may serve in the future as a basis for the constitution of new technical standards. It has been shown that it is possible to obtain joints with optimum in-plane shear strength of 6.88 MPa when processed at 1 bar, 115°C, 5 min and 12 mm. The fracture analysis revealed that the shear rupture of the joints was preceded by multiple longitudinal cracks induced by successive debondings, both inside and outside the joint, due to the accumulated transverse tension, proportional to its length. Temperature proved to be the most relevant processing parameter for the performance of the joint, which is little affected by variations in pressure and curing time

In-plane shear strength of single-lap co-cured joints of self-reinforced polyethylene composites

The present study introduces the analysis of single-lap co-cured joints of thermoplastic selfreinforced composites made with reprocessed low-density polyethylene (LDPE) and reinforced by ultra-high-molecular-weight polyethylene (UHMWPE) fibers, along with a micromechanical analysis of its constituents. A set of optimal processing conditions for manufacturing these joints by hot-press is proposed through a design of experiment using the response surface method to maximize their in-plane shear strength by carrying tensile tests on co-cured tapes. Optimal processing conditions were found at 1 bar, 115 ◦C, and 300 s, yielding joints with 6.88 MPa of shear strength. The shear failure is generally preceded by multiple debonding-induced longitudinal cracks both inside and outside the joint due to accumulated transversal stress. This composite demonstrated to be an interesting structural material to be more widely applied in industry, possessing extremely elevated specific mechanical properties, progressive damage of co-cured joints (thus avoiding unannounced catastrophic failures) and ultimate recyclability

Biomimetics and composite materials toward efficient mobility: a review

The development of new materials has always been strictly related to the rise of new technologies and progressively efficient systems. However, cutting-edge materials might not be enough to ensure the effectiveness of a given product if the design guidelines used do not favor the specific advantages of this material. Polymeric composites are known for their excellent mechanical properties, but current manufacturing techniques and the relatively narrow expertise in the field amongst engineers impose the challenge to provide the most suitable designs to certain applications. Bio-inspired designs, supported by thousands of years of evolution of nature, have shown to be extremely profitable tools for the design of optimized yet structurally complex shapes in which the tailoring aspect of polymeric composites perfectly fit. Bearing in mind the current but old-fashioned designs of auto-parts and vehicles built with metals with little or no topological optimization, the present work addresses how biomimicry is being applied in the mobility industry nowadays to provide lightweight structures and efficient designs. A general overview of biomimicry is made regarding vehicles, approaching how the use of composite materials has already contributed to successful cases

Survey on Experimental and Numerical Approaches to Model Underwater Explosions

The ability of predicting material failure is essential for adequate structural dimensioning in every mechanical design. For ships, and particularly for military vessels, the challenge of optimizing the toughness-to-weight ratio at the highest possible value is essential to provide agile structures that can safely withstand external forces. Exploring the case of underwater explosions, the present paper summarizes some of the fundamental mathematical relations for foreseeing the behavior of naval panels to such solicitation. A broad state-of-the-art survey links the mechanical stress-strain response of materials and the influence of local reinforcements in flexural and lateral-torsional buckling to the hydrodynamic relations that govern the propagation of pressure waves prevenient from blasts. Numerical simulation approaches used in computational modeling of underwater explosions are reviewed, focusing on Eulerian and Lagrangian fluid descriptions, Johnson-Cook and Gurson constitutive materials for naval panels, and the solving methods FEM (Finite Element Method), FVM (Finite Volume Method), BEM (Boundary Element Method), and SPH (Smooth Particle Hydrodynamics). The confrontation of experimental tests for evaluating different hull materials and constructions with formulae and virtual reproduction practices allow a wide perception of the subject from different yet interrelated points of view

Fracture Evaluation of the Falling Weight Impact Behaviour of a Basalt/Vinylester Composite Plate through a Multiphase Finite Element Model

Several investigations regarding the mechanical behaviour of composites reinforced by natural fibers under impact have been realized recently, aiming at achieve a low-weight and resistant design. At the same time, progressively accurate results on numerical simulations have been reached powered by modern Finite Element Method (FEM) approaches for composites; however, demonstrating a faithful indentation pattern is still a challenge. The present work aims at building an impact numerical simulation that exhibits a fracture mechanism exactly like the one seen in experimental tests, also carried in this work, on a Basalt Reinforced Composite Polymer (BRFP) plate subjected to low-velocity falling weight impact (IFW). The FEM simulation describes a multiphase model considering each ply and their inter-layer interactions

An overview of mooring systems: from small boats to offshore oil platforms

Anchoring perennially or intermittently is a need of all marine vessels, by reasons that range from maintenance stops to operational activities such as loading/offloading. Although an unexceptional procedure, designing a mooring system suitable to each application embraces many variables such as the vessel characteristics, the seabed mineral composition and whether the mechanical efforts on the anchor are predominantly horizontal, vertical or both

Green composites and safety: an impact study case

The development of new technologies and processes has been a permanent challenge in our society from its beginnings, being vital for the evolution of the way we live and how we treat the environment around us as a reflect; whereas the advancement of material sciences plays a deeply relevant role. Targeting both performance and sustainability, the so-called green materials have demonstrated to constitute a rising industry sector, often providing renewable feedstock and still offering enhanced economic compensation. Given the recent and prominent usage of green composites in vehicles, the present article discusses the potential application of those in a recreational vessel structure; focusing on an impact study case of vinylester plastic composites reinforced with basalt fiber

Increasing the Energy Efficiency in Solar Vehicles by Using Composite Materials in the Front Suspension

The pursuance of energy efficiency is a constant endeavour in modern mobility. Accordingly, several institutions worldwide have been investing time and resources in developing solar powered vehicles, directing their efforts towards a continual search of technical solutions aiming at attaining the highest energy efficiency levels. This work investigates and compares the mechanical behaviour of a front suspension wheel hub, subjected to its operational forces, when made by three different materials: aluminium, carbon or basalt fiber reinforced composites. Despite of investigating the sole mechanical response of materials, the comparison focuses on the feasibility of applying light and stiff composites in structural parts in order to improve the energy efficiency in vehicles due to weight reduction whilst granting safety