Materials Science Forum Vols. 730-732

Abstract: Nowadays, fibre reinforced plastics are used in a wide variety of applications. Apart from the most known reinforcement fibres, like glass or carbon, natural fibres can be seen as an economical alternative. However, some mistrust is yet limiting the use of such materials, being one of the main reasons the inconsistency normally found in their mechanical properties. It should be noticed that these materials are more used for their low density than for their high stiffness. In this work, two different types of reinforced plates were compared: glass reinforced epoxy plate and sisal reinforced epoxy plate. For material characterization purposes, tensile and flexural tests were carried out. Main properties of both materials, like elastic modulus, tensile strength or flexural modulus, are presented and compared with reference values. Afterwards, plates were drilled under two different feed rates: low and high, with two diverse tools: twist and brad type drill, while cutting speed was kept constant. Thrust forces during drilling were monitored. Then, delamination area around the hole was assessed by using digital images that were processed using a computational platform previously developed. Finally, drilled plates were mechanically tested for bearing and open-hole resistance. Results were compared and correlated with the measured delamination. Conclusions contribute to the understanding of natural fibres reinforced plastics as a substitute to glass fibres reinforced plastics, helping on cost reductions without compromising reliability, as well as the consequence of delamination on mechanical resistance of this type of composites.

Abstract: Mud acid attack of 14 lbm/gal Portland cement composites with 15 % of nonionic aqueous polyurethane was investigated. Plain Portland hardened cement slurries showed the loss of weight around 23 %. The addition of aqueous polyurethane resulted in longer durability, with reduction around 87 % on the loss of weight without influence on the compressive strength or fratographic. The mechanism is related with the decreased porosity and permeability due to the polymeric net formation on the bulk and minor quantities of Ca⁺², preferentially leached to the acidic solution. In this way, Portland-aqueous polyurethane composites are possible solutions to oil well cementing submitted to steam injection and mud acid acidizing operations.

Abstract: Mechanical properties of ferritic-marensitic steels can be improved through dispersion of fine particles with large industrial applications like nuclear, military and aeronautic areas. Steels used at nuclear reactors suffer some damage when exposure to various kinds of radiation such as gamma, plasma, neutrons among others. Special steels have been studied to resist these processes in which cause a significant degradation of these materials. Reduced activation ferritic/martensitic steels (RAFM) are used for fusion structural materials with the substitution of some alloying elements such as Mo, Nb and Ni present in the commercial martensitic steels by other elements which exhibit faster decay of induced radioactivity, such as Ta, W and V. This present work study the development of EUROFER97 steel reinforced with 3wt% of tantalum carbide (TaC).

Abstract: This paper discusses the behaviour of the granular soil reinforced with the random inclusion of the short and superficially treated curaua fibers with asphalt. These fibers are extracted from the leaves of Ananas erectifolius plants, which are a natural occurring bromeliacea from Amazon region, Brazil. The curaua treated fibers were mixed in the granular soil in order to evaluation their influence on the mechanical properties improvements of the soil. In order to characterize the performance of these fibers, scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) were employed. Also a series laboratory triaxial compression tests were performed to determine the static stress–strain response of the composites. Through the obtained results, it was observed that the addition of vegetal fibers randomly distributed presented significant improvements on the mechanical properties of this soil. The results show the potential of the curaua fibers used as soil reinforcement.

Abstract: This paper presents the results and main conclusions of a study made to analyze the cause of failure occurred with an austenitic 304 class stainless steel wire rope of a helicopter rescue hoist. The cable is made up of 19 strands, 12 outside and 7 inside. As each strand contains 7 wires, the whole cable is made up of 133 wires. The study includes the chemical and microstructural characterization of the material, as well as the determination of its hardness, mechanical properties and the fractographic analysis by scanning electron microscopy (SEM). Tensile tests were performed for three velocities simulating different work conditions: 250mm/min, 50mm/min and 5mm/min. The fractographic analysis shows that the cable suffered lateral loss of material due to friction and leading to the failure of the remaining material by ductile mode.

Abstract: The present investigation is concerned with the development of fibre reinforced thermoplastic composite rods using braiding process. An innovative technique has been developed to produce composite rods with outer braided layer of polyester fibres and axially reinforced with high performance glass fibres. Polypropylene filaments which were introduced in to the core along with the glass fibres during the braiding process formed the thermoplastic matrix upon melting. A special mould has been designed for uniform application of heat and pressure during the consolidation of the composite rods as well as for the alignment of core fibres. The cross-section of composite rods was characterized with help of optical microscopy in order to see the distribution of core fibres and matrix. The effect of amount of glass fibres on the mechanical properties (tensile and flexural) of composite rods has been investigated and discussed.

Abstract: One of the major disadvantages of laminated composites is their tendency to delaminate. Unidirectional glass/epoxy laminates have been tested under static conditions by the use of fracture mechanics. Mode I, mode II, mixed mode I-II, mode III and mixed mode II-III tests were performed. Double cantilever beam (DCB), end-notched flexure (ENF), mixed-mode bending (MMB) and edge crack torsion (ECT) specimens were used. Scanning electron microscopy technique was used to identify distinguishing fractographic features and to establish the differences between the various modes of fracture after specimens testing. The propagated orientation of the delamination could be specified from the patterns of fracture surface. Scanning electron micrographs of fractured surfaces showed that the most predominant fractographic features in mode I and mode II are the large amount of fibre pull-out and the cusps markings respectively. In the MMB specimen the fracture surfaces are characterized by fibre breakage under shearing with fractures localized in the resin with cusps having an orientation of 90º (mode II) and also fractures localized in the resin and along the resin/fibre interface (mode I). Mode III characterization concluded that some limited mixed mode II-III seems to be present for ECT specimen on delamination initiation and growth, but a large majority of mode III delamination is present.

Abstract: This paper reports the results of a series of experiments carried out to investigate the effectiveness of newly hybrid polyethylene/polypropylene (PP/PE) fibres inclusion in the mechanical performance of cement matrices, with regard to fibres properties and content. The results indicate that, compared with plain cement matrix, the PP/PE fibre-reinforced cement matrices (FRC) revealed improvements on their mechanical performance. Increases of 37 ± 1% on compressive (40.2 MPa) and flexural strengths (8.1 MPa) were obtained for 24 mm fibre length composites containing a rather low fibre’s content (1 wt.%). These mechanical improvements were achieved after optimisation of the mortar workability by the addition of a superplasticizer. FRC mechanical behaviours also evidenced that despite the compressive strengths increasing with fibre length, a flexural strength effect is only noticeable for a 24 mm length fibre-reinforced composite and for fibres volume higher than 2.9 %. Morphological observations showed a strong interaction between fibres and cement matrix, evidenced a crack arrest role (bridge effect) on fibre/cement interfacial zone and revealed a typical multiple fracture cracking mechanism.

Abstract: In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution. The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented.

Abstract: The inclusion of artificial fibers in the soil has been studied by many researchers during the last years and has shown efficient by improving the mechanical properties of the soil. This kind of association results in an interesting composite material for geotechnical engineering applications. In this context, the aim of this research is to analyze the behavior of a granular soil reinforced with random inclusion of short and curauá fibers superficially treated with recycled EPS (expanded polystyrene). The non-reinforced and reinforced soil samples were subjected to triaxial tests. Through the obtained results, it was observed that the addition of randomly distributed natural treated fibers presented significant improvements on the mechanical properties of this soil. The polymer used was shown quite applicable to the proposed analysis, promoting the decrease of the water absorption of the vegetal fibers.