The influence of two lubricating and cleaning agents and diesel fuel on environmental stress cracking of polyamide reinforced by glass fibers and polycarbonate was studied in this master thesis. Testing of environmental stress cracking was performed by the method of critical bending deformation. Bergen elliptical strain jig was used for testing. The test liquids caused varying levels of environmental stress cracking of amorphous polycarbonate, but they did not cause environmental stress cracking of glass fiber reinforced polyamide. The test method used allows testing the resistance of both materials against environmental stress cracking of any liquid. The results can be used to design products that are expected to be exposed to corrosive liquids. Quantification of the influence of stress free corrosion on the static and impact properties of polycarbonate and glass fiber reinforced polyamide was performed by accelerated test. Specimens were exposed to test liquid and an elevated temperature of 70 °C. The mechanical properties of the tested materials were significantly affected by elevated temperature exposure. The yield strength of the polycarbonate has increased and the toughness has decreased due to physical aging. The tensile strength of glass fiber reinforced polyamide has increased due to a decrease of the moisture content of the material.

Hybrid systems with two or more fiber materials were used to combine the benefits of each fiber into a single composite product. Strength and toughness optimization of hybrid thin sheet composites has been studied extensively using combination of different fiber types with low and high modulus of elasticity. Hybrid reinforcement is more significant when the reinforcing structure is in fabric geometry. Fabric structure provides full control on the exact location of each yarn and its orientation in the composite during production, thus maximizes the reinforcing efficiency. A high-strength, high-modulus fiber primarily tends to increase the composite strength with nominal improvements in toughness. A low-modulus fiber expected to mainly improve toughness and ductility. Combination of two or more types of fiber can produce a composite that is both strong and tough as compared to a mono fiber composite. The purpose of the current work was to study hybrid warp knitted fabrics as reinforcement for cementbased composite, having AR (Alkali Resistance) glass and Polypropylene (PP) as the reinforcing yarns. The examined ratios between the two different yarns were 0:100, 25:75, 50:50, 75:25, 100:0 (glass: PP, by percentage). It was found that in the hybrid system, the fracture mechanism is a superposition of the mono systems, and the tensile behavior is a combination between the two materials.

No description available.

Tensile strength modelling is usually done to predict the mechanical properties of lamellargraphite iron considering microstructural features. This work attempts to create a simplifiedmodel incorporating cooling rate and solidification time without considering themicrostructural features. This model will save time and cost in industry with the presence of acommercially available software such as Magmasoft which simulates solidification time andcooling rate. A plate model was designed for this purpose as the test geometry to createvariation in solidification time and cooling rate. By altering fraction solid, thermalconductivity, specific heat capacity in Magmasoft, a good fit was created between simulatedcooling curve and experimental cooling curves. The experimental UTS data of samples fromthree moulds were investigated and a regression model was created using statistics toolMinitab. The effect of solidification time and alloying on the graphite length Lmax was studiedfor twelve samples from each mould. Quantification of the effect of cooling rate and alloyingon the pearlitic properties of grey iron like matrix microhardness, pearlite inter-lamellarspacing was also investigated in this work.The developed model has sixty three percent correlation and explains UTS well in terms ofsolidification time and cooling rate. Microhardness measurements show that there is an almostlinear relationship between the cooling rate and microhardness of the matrix structure.Microhardness data also provides an overview of the pearlite fineness/interlamellar spacing.Analysis of the outliers showed that the presence of free ferrite on a fully pearlitic structurereduces the UTS significantly. Comparison of the regression model obtained from this workwith previous work showed that, there is a reduction in the predicted strength with this model.The effort to identify the reason for this reduction was not successful and needs furtherinvestigation. Pearlite inter-lamellar spacing measurement was not accurate. The relationshipbetween pearlite interlamellar spacing and matrix microhardness needs to be investigated inthe future using a better technique for pearlite spacing measurement. This will be useful tounderstand the effect of cooling rate on pearlite spacing and consequently on the UTS of greycast iron. / Draghållfasthetsmodellering görs vanligtvis för att förutsäga de mekaniska egenskaperna av lamellärt grafitjärn. Detta arbete har försökt att skapa en förenklad modell som innehåller kylhastighet och stelningstid utan att överväga mikrostrukturella egenskaper. Modellen kommer att spara tid och kostnad i industrin tillsammans med kommersiellt tillgänglig mjukvara som Magmasoft som simulerar stelningstiden och kylningshastighet. En plattformig modell utformades för detta ändamål som testgeometrin för att skapa variation i stelningstid och kylningshastighet. Genom att ändra fraktion fast fas, termisk konduktivitet och specifik värmekapacitet i Magmasoft skapades en bra anpassning mellan simulerade och experimentella kylkurvor. Experimentella draghållfasthetsdata (UTS) för prover från tre gjutningar undersöktes och en regressionsmodell skapades med hjälp av statistikverktyg Minitab. Effekten av stelningstid och legeringshalt på grafitlängden Lmax studerades för tolv prover från varje form. Effekten av kylhastighet och legering på de perlitiska egenskaperna hos grått järn som matrismikrohårdhet och perlitlamellavstånd undersöktes också i detta arbete.  Den utvecklade modellen har sextiotre procent korrelation och förklarar UTS väl med avseende på stelningstid och kylningshastighet. Mikrohårdhetsmätningar visar att det finns ett nästan linjärt förhållande mellan kylhastigheten och mikrohårdheten hos matrisstrukturen. Mikrohårdhetsdata ger också en översikt över perlitens finhet/interlamellära avstånd. Analys av outliers visade att närvaron av fri ferrit på en fullständigt perlitisk struktur minskar UTS betydligt. Jämförelse av regressionsmodellen erhållen från detta arbete med tidigare arbete visade det att det finns en minskning av den förutsagda styrkan med denna modell. Ansträngningen att identifiera orsaken till denna minskning var inte framgångsrik och behöver ytterligare undersökas. Perlit mellan lamellär avståndsmätning var inte korrekt. Förhållandet mellan perlitens interlamellära avstånd och matrismikrohet måste undersökas i framtiden med hjälp av en bättre teknik för perlit-avståndsmätning. Detta kommer att vara användbart att förstå effekten av kylhastighet på perlitavståndet och följaktligen på UTS av grå gjutjärn

Thermoplastic composites that have been reinforced by thermotropic liquid crystalline (TLCP) fibrils in the microscale and by nanoparticles in the nanoscale are defined as multi-scale wholly thermoplastic composites (WTCs). Multi-scale WTCs have been proposed as lightweight replacements with high performance for some traditional glass fiber (GF) and carbon fiber (CF) reinforced composites materials in various applications. TLCPs are known for performing mechanical properties similar to those of the lower end of CF but significantly better than those of GF. To enhance the mechanical properties of TLPC reinforced WTCs, carbon nanotubes (CNTs) are considered being used as a secondary enhancement in WTCs. CNTs have gathered significant interest in the last 30 years because of their high aspect ratio, high mechanical properties, and other high-performance properties. The focus of this work is on investigating the processing conditions of generating in situ injection-molded multi-scale WTCs, then extending the technology to dual-extrusion and fused filament fabrication (FFF) and obtain high-performance multi-scale WTC products. This dissertation initially focused on investigating the processing conditions, in particular mixing histories and processing temperature profiles, of generating in situ injection-molded multi-scale WTCs, which consist of a representative TLCP, scCO2 aided exfoliated CNTs, and the thermoplastic matrix polyamide 6 (PA 6). The supercooling behavior of the TLCP and thermal stability of PA 6 are studied by applying the rheological methods of small amplitude oscillatory shear (SAOS). Multiple mixing histories with CNTs and processing temperature profiles are analyzed based on the criterion of maximizing tensile properties of multi-scale WTCs and minimizing thermal degradation of the matrix. Under the optimum processing conditions, the in situ injection-molded multi-scale WTCs exhibit a 26% and 34% tensile modulus and strength enhancement, compared to the in situ injection-molded WTCs with no CNTs. Scanning electron micrograph (SEM) images were used to understand the enhancement. The second part of this work is to extend the scCO2 aided in situ multi-scale WTCs processing technology to dual-extrusion and FFF. Multi-scale WTC filaments, which consists of TLCP, CNTs, and polyamide copolymer (PAc), are generated by dual-extrusion, and 3D printed into rectangular specimens in FFF. The 1 wt% CNTs reinforced multi-scale WTC filaments generated by the means of dual-extrusion exhibit 225% and 80% improvement in tensile modulus and strength, respectively, compared to the WTC filaments with no CNTs. In FFF, 40 wt% TLCP/1 wt% CNT/PAc 3D printed specimens with filament laid in longitudinal direction exhibited excellent tensile modulus and strength of 38.92 GPa and 127.16 MPa, respectively. The well-dispersed exfoliated CNTs show high alignment with TLCP microfibrils in the multi-scale WTC filaments and their laid-down specimens, which causes the significant tensile modulus enhancement. Bridging elements are discovered between TLCP fibrils and PAc matrix to improve interfacial adhesion, which is attributed to the well-dispersed exfoliated CNTs. Finally, the significant improvements in tensile properties attributed to scCO2 aided exfoliated CNTs in WTCs are verified on the multi-scale WTCs based on polypropylene (PP). Moreover, additional tensile properties improvements for exfoliated CNTs reinforced multi-scale WTCs are obtained with the use of maleic anhydride grafted polypropylene (MAPP). With 1 wt% CNTs and 16 wt% MAPP dual reinforcement, 20 wt% TLCP reinforced WTCs based on polypropylene (PP) exhibit 265%, 274%, and 182% improvement in the tensile modulus of the filaments, laid up specimens in the concentric pattern and laid up specimens in ±45° rectilinear pattern, respectively. The dual reinforcement also improves the tensile strength of 20 wt% TLCP reinforced WTC filaments by up to 73%. The high alignment between TLCP fibrils and CNTs are confirmed in the multi-scale WTCs based on PP. Besides the bridging elements attributed to CNTs found in the second part of this work, SEM images show that CNTs are partially trapped in TLCP fibrils. / Doctor of Philosophy / Considering the need for environmentally friendly materials, novel thermoplastic composites with high mechanical performance, lightweight, and potentially high recyclability properties were generated in this work. Two types of thermoplastic matrices, polyamide (PA or nylon) and polypropylene (PP) were reinforced with carbon nanotubes (CNTs) and rigid chain polymers known as thermotropic liquid crystalline polymers (TLCPs). CNTs are known for their high mechanical properties and high aspect ratio, which are helpful to reinforce thermoplastic composite materials. During injection molding and the dual-extrusion processes, TLCPs deform into almost continuous microfibrils and reinforce the thermoplastic matrices. Instead of using traditional glass fibers or carbon fibers to reinforce thermoplastics, TLCP reinforced thermoplastic composites, which are defined as wholly thermoplastic composites (WTCs), can retain their mechanical properties during the recycling process such as in injection molding and have better performance during the lay-down process in fused filament fabrication. The goal of this work was to generate CNTs reinforced WTCs for use in injection molding and fused filament fabrication with high mechanical performance. In the injection molding process for generating CNTs reinforced WTC end-gated plaques, it was determined that the optimum thermal mixing histories for the CNTs could be identified by the inspections of the tensile property measurements and scanning electron microscopy (SEM). With the obtained optimum thermal mixing histories with CNTs, CNTs reinforced WTC filaments were generated by dual extrusion technology and used in fused filament fabrication. With 1 wt% addition of CNTs, the tensile properties of WTCs were significantly enhanced in both the filament materials and the laid-down parts. Especially, the CNT reinforced WTC filaments based on nylon matrices exhibited competitive tensile moduli to long carbon fiber reinforced nylon composite filaments, which was also competitive to the properties of aluminum alloys. In addition, the laid-down parts of CNTs reinforced WTC based on PP presented further tensile strength improvement due to the improved interfacial adhesion between the laid-down filaments and between layers, which was attributed to the addition of maleic anhydride grafted polypropylene.

Selective laser melting (SLM) has been shown to be an attractive manufacturing route for the production of ??/?? titanium alloys, and in particular Ti-6Al-4V. A thorough understanding of the relationship between the process, microstructure and mechanical properties of the components produced by this technology is however crucial for the establishment of SLM as an alternative manufacturing route. The purpose of the present study is thus to determine the microstructure evolution, crystallographic texture and the mechanical properties of SLM Ti-6Al-4V. The effect of several processing parameters on the density and the microstructure of the SLM samples were initially investigated. It was found that different sets of process parameters can be used to fabricate near fully dense components. It was found that the samples built using the optimised process window consist exclusively of ????? martensitic phase precipitated from prior ?? columnar grains. It was observed that the ?? grain solidification is influenced by the laser scan strategy and that the ?? phase has a strong <001> texture along its grain growth direction. The ????? martensitic laths that originate from the parent ?? grains precipitate according to the Burgers orientation relationship. It was found that ????? laths clusters from the same ?? grain have a specific misorientation that minimise the local shape strain. Texture inheritance across successive deposited layers was also observed and discussed in relation to various variant selection mechanisms. The mechanical properties of as-built and stress relieved SLM Ti-6Al-4V built using the same optimised process parameters were then investigated. It was found that the build orientation affects the tensile properties, and in particular the ductility of the samples. Samples built perpendicularly to the building direction showed higher ductility than those built in the vertical orientation. It was also observed that a stress relief heat treatment was beneficial to the mechanical properties of SLM Ti-6Al-4V. The ductility of the stress relieved samples was indeed higher than those found in the as-built condition. It was found that the predominant fracture mode during tensile testing is inter-granular. In terms of high-cycle fatigue, it was found that SLM Ti-6Al-4V is comparable to HIPed cast Ti-6Al-4V but it has a significantly lower fatigue resistance than that of wrought and annealed alloys. It was observed that porosity and the elongated prior ?? grain boundaries decrease substantially the fatigue life of the components. Cracks propagate either by fatigue striation or ductile tearing mechanisms. Using alternative laser scan strategies it was possible to control the microstructure of the as-built samples. It was observed that the laser scan vector length influences several microstructural features, such as the width of the prior ?? grains and the thickness of the ????? laths. It was found that re-melting the same layer has instead little effect on the microstructure. A novel laser scan strategy characterised by much lower laser power and scan speed than those typically used in SLM enabled finally to fabricate SLM Ti-6Al-4V with a microstructure close to that of conventionally manufactured Ti-6Al-4V. This study investigates for the first time the crystallographic texture evolution in Ti-6Al-4V manufactured by SLM. Further, this research presents for the first time the effect of the characteristic microstructure and crystallographic texture on the mechanical properties and fracture of SLM Ti-6Al-4V. Lastly, for the first time this research shows examples of microstructural control during the SLM fabrication of the same alloy using long laser dwell times.

Aços microligados pertencem à classe dos aços ARBL contendo baixa ou média quantidade de carbono e pequena adição de elementos de liga tais como Mn, Nb, Mo, V e Ti. A variedade microestrutural desses aços pode ser obtida dependendo da temperatura de conformação, taxa de resfriamento e composição química. Os tratamentos intercríticos e isotérmicos produzem microestruturas multifásicas com diferentes quantidades de ferrita, martensita, bainita e austenita retida. A presença de diferentes fases nestes materiais, com morfologias distintas, pode afetar de modo significativo seu comportamento mecânico, afetando, por exemplo, o fechamento da trinca e resultando em mudanças na taxa de crescimento da mesma. O objetivo deste trabalho é avaliar as propriedades de tração e a resistência ao crescimento da trinca por fadiga de um aço microligado RD 480 com 0.08%C-1, 5%Mn (p), correlacionando-as com suas características microestruturais. Esse aço, desenvolvido recentemente pela CSN (Companhia Siderúrgica Nacional), é considerado promissor como alternativa para substituir o aço de baixo carbono utilizado em componentes de rodas na indústria automotiva. Distintas condições microestruturais foram obtidas por meio de tratamentos térmicos seguidos de resfriamento em água. As condições de tratamento intercrítico e têmpera simples foram escolhidas para se avaliar a resistência à propagação da trinca por fadiga. Os resultados dos ensaios foram sintetizados em termos da taxa de crescimento da trinca (da/dN) versus a variação do Fator Intensidade de Tensão (_K) no ciclo de carregamento. Para descrever o comportamento das trincas foram utilizados dois modelos: a equação convencional de Paris e um novo modelo exponencial que mostra o comportamento não linear das curvas de fadiga. Os resultados mostraram que uma microestrutura combinando ferrita de aspecto acicular e fases duras (martensita/bainita) resultou em menores taxas de crescimento da trinca. No entanto, a melhor combinação entre as propriedades de tração (limite de escoamento, resistência e ductilidade) e fadiga foi obtida com uma microestrura bifásica contendo martensita dispersa em uma matriz ferrítica. Observou-se uma transição nas curvas de crescimento da trinca para todas as condições tratadas termicamente e, por conta disto, as curvas das condições microestruturais bifásicas e multifásicas foram melhores modeladas quando divididas em duas regiões. As superfícies de fratura dessas amostras, bem como o caminho percorrido pela trinca, foram analisados via MEV e MO. / Microalloyed steels are a class of HSLA steels with low or medium carbon content and small additions of alloy elements such as Mn, Nb, Mo, V and Ti. A variety of microstructures in microalloyed steels can be obtained depending on the deformation temperature, cooling rate and chemical composition. Heat treatments and isothermal transformation on these materials, with various temperatures and holding times, produce multiphase microstructures with different amounts of ferrite, martensite, bainite and retained austenite. These different phases, with distinct morphologies, are determinant of the mechanical behavior of the steel and can, for instance, affect crack closure or promote crack shielding, thus resulting in changes on its propagation rate under cyclic loading. The aim of this study is to evaluate the tensile properties and resistance to fatigue crack growth in a microalloyed steel RD 480 with 0.08%C-1, 5% Mn (wt), correlating with their microstructural characteristics. This steel, recently developed by CSN (Companhia Siderurgica Nacional), is being considered as a promising alternative to replace low carbon steel in wheel components for the automotive industry. Distinct microstructural conditions were obtained by means of heat treatments followed by water quench. The intercritical treatment and quenching conditions were chosen to evaluate the strength to crack propagation. The crack propagation test results were summarized in terms of FCG rate (da/dN) versus stress intensity factor range (?K) curves. In order to describe the FCG behavior, two models were tested: the conventional Paris equation and a new exponential equation developed for materials showing non-linear FCG behavior. The results showed that a microstructure combining aspect acicular ferrite and hard phases (martensite / bainite) resulted in lower rates of crack growth. However, the best combination between the tensile properties (yield stress, tensile strength and ductility) and fatigue was obtained with a dual phase steel microstructure containing martensite dispersed in a ferrite matrix. It was observed a transition in the crack growth curves for all heat treated conditions, so the curves of the dual and multiphase microstructural conditions were better modeled by dividing them in two regions. The fracture planes of the fatigued specimens, as well as the crack path, were examined using a scanning electron microscope (SEM) and optical micrography (OM).

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 1983" Fei Tang. 12/19/2004. Report is also available in paper and microfiche from NTIS.

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Polyethylene terephthalate (PET) is the most used fibre in the textile industry. PET is also used in other products, e.g. soft-drink bottles and food packaging. Approximately 60% of the globally produced PET is intended for production of textile fibres and the demand for polyester fibres have steadily increased over the last decade. Yet, most of the recycled PET fibres are produced from discarded bottles and not discarded textiles even though the generation of textile waste is increasing year by year. The importance of finding efficient recycling routes for discarded PET textiles is obvious. In thermo-mechanical recycling the thermoplastic characteristic of PET is utilized to re-melt and re-form PET waste into new valuable products. Today, this is used for bottle-to-fibre recycling but not for fibre-to-fibre recycling. The main research question asked in this Master thesis is if the process of exhaust dyeing compromise the possibility to recycle PET textiles through remelt spinning. It is believed that PET degradation through hydrolysis may occur during dyeing. The degradation behaviour of PET has been widely studied. However, degradation during exhaust dyeing has not been investigated.   The process parameters temperature, time and number of dyeing cycles have been investigated. Also, possible effects of different auxiliary chemicals have been studied. Dyeing and characterisation of two PET fabrics with filaments of different titer was performed in order to investigate if the filament titer is also a parameter to consider.   Tensile testing and surface characterisation through demand absorbency test showed that the filament titer seems to affect how the tensile and moisture related properties change due to dyeing. Differential scanning calorimetry showed that the crystallisation rate is affected by the dyeing process. This can be an effect of formation of shorter PET chains during dyeing. The auxiliary chemicals have been shown to be the most critical factor in changes of the crystallisation behaviour. Fourier-Transform infrared spectroscopy indicated that chain scission has occurred during dyeing.   The results have shown that the exhaust dyeing process causes changes in tensile properties, moisture related properties, degree of crystallinity as well as crystallisation behaviour. DSC and FTIR results indicate chain scission. Based on the results it cannot be concluded if the changes are large enough to compromise the possibility to recycle PET textiles thermo-mechanically. Further research is required in order to correlate the observed changes with possible problems in thermomechanical recycling of dyed PET textiles.