1,720,983 research outputs found
Mass minimization approach for the optimal preliminary design of CMC inner liners in rocket thrust chambers
No full textIn the past decade, the world has witnessed a new space race, driven by a growing commitment to reducing the environmental impact of space missions. This has led to the widespread adoption of liquid-propellant rocket engines, which offer several advantages over their solid-propellant counterparts. One key advantage is their reusability, which not only helps to reduce the generation of space debris but also makes space exploration cheaper. To further enhance the performance of liquid rocket engines, researchers have been exploring innovative cooling techniques and advanced materials. Among these materials, Ceramic Matrix Composites (CMCs) have shown great potential in reducing the overall engine weight when used instead of high-tech metal alloys, resulting in lower fuel consumption and emissions during launches. This paper focuses on the mass minimization of inner liners made of CMCs in rocket thrust chambers. At this aim, a computationally efficient preliminary design approach, based on an analytical one-dimensional thermo-mechanical model, is proposed. A case study of mass minimization of an inner liner of rocket thrust chamber is also presented and discussed, by considering five different CMC materials
Experimental and Analytical Investigation of the Shear Fracture Behavior of Bonded Joints
No full textThe demand of adhesive bonding as technique for the strengthening of existing structures is currently increasing in many engineering fields. Therefore, the prediction of bonded joints fracture behavior is an open issue for the structural safety of repairs. With this aim, a cohesive zone approach is adopted to determine the shear fracture behavior of epoxy resin interface layer of end notched flexure (ENF) specimen. Experimental tangential slip displacements of adherends are evaluated by digital image correlation (DIC) analysis. The identified traction-separation law can be implemented in a finite element (FE) code to predict the decohesion of adhesively bonded joints
Effects of recycled PET fibres on the mechanical properties and seawater curing of Portland cement-based concretes
No full textThis paper deals with an experimental study on the mechanical properties of recycled polyethylene terephthalate fibre-reinforced concrete (RPETFRC) and its durability in an aggressive seawater environment. A Portland limestone cement-based concrete with a 0.38 water/cement ratio is used to cast cubic and prismatic specimens, in association with two different PET fibres obtained through extrusion of recycled PET flakes (R-PET). Some of these specimens were conditioned in the Salerno harbour seawater for a period of 6/12 months. Compressive strength and four-point bending tests are performed in order to investigate the mechanical properties of such RPETFRCs. Comparison of the present results and those in the literature for air-cured RPETRCs highlights the influence of the analysed R-PET fibres on the mechanical properties of concretes showing different water/cement ratios and binders. The given results for seawater-cured specimens demonstrate that such a curing condition slightly modifies the first-crack strength and markedly reduces the toughness of the RPETFRCs examined in the present work. © 2014 Elsevier Ltd. All rights reserved
Experimental analysis on the time-dependent bonding of FRP laminates under sustained loads
No full textFiber reinforced composite materials are frequently used in the rehabilitation or upgrading of existing structures. From a design point of view, current international guidelines on FRP strengthening applications do not give rules based on rigorous approaches to evaluate the reliability and durability of strengthening interventions with respect to long-term behavior. In order to give a contribution on this topic, the authors have carried out a creep experimental program on retrofitting systems, either of carbon or glass fibers and subject to different stress values in regime of constant temperature. The tests have been carried out by means of a dedicated test device that provided a pure bending stress state in the strengthened beam, being the external loads held constant over time. In this paper the results of their investigation and critical analysis are presented. © 2012 Elsevier Ltd. All rights reserved
Mode I Fracture Toughness Evaluation of Adhesively Bonded Joints via J-Integral and DIC
No full textAmorphous polymers, such as epoxy resins, are commonly used in the realization of adhesively bonded joints. In this paper an evaluation of mode I fracture toughness of bonded joints is presented. Moreover, an identification of cohesive zone model parameters via Rice's J-integral is described. Experimental tests are performed on double cantilever beam specimens and relative displacements between adherends are acquired by using the digital image correlation technique. The obtained interface law can be implemented in a finite element code for simulating the decohesion process of complex bonded structures
Pre-buckling imperfection sensitivity of pultruded FRP profiles
No full textThis paper presents a geometrically non-linear one-dimensional model suitable for analyzing thin-walled fiber-reinforced polymer profiles, which accounts for the effect of manufacturing imperfections. The kinematic model is developed under the hypotheses of small strains and moderately large rotations of the cross-sections, and is able to take into consideration the contribution of shear strains and the effects related to warping displacements. The aim of the study is to develop a proper tool to analyze the pre-buckling behavior of such beams, since current approaches based on two-dimensional finite element method analysis demand significant computational efforts to be applied to real structures. The numerical results underline the effectiveness of the proposed mechanical model in analyzing case studies of technical interest in Civil Engineering, and the relevant influence of geometrical imperfections on the structural performance of FRP components with regard to serviceability design requirements
HIGH-ALTITUDE CONSTRUCTIONS: SUSPENDED SCAFFOLDINGS AND INNOVATIVE PRESIDES
No full textIn the construction industry, temporary works, especially fixed metal scaffolding, represent the type of temporary structure necessary for the construction of the work and to ensure preventive actions aimed at guaranteeing the safety of workers in the workplace. All this requires a technical-organizational process able to guarantee careful planning, problem solving, content processing and an approach able to reduce the risks present in the construction process. In this context the following work is born with the intent of deepening the study of special high-altitude scaffolding which require particular requirements and great ingenuity for what concerns the design and organization. The goal is to define a valid design approach that aims to combine structural aspects with those of operator safety, which includes: on the one hand, the design of the scaffolding in operating conditions and in the assembly / dismantling phases; on the other hand to its correct use through the use of effective tools for the training of employees, monitoring and control in progress. The aim was first pursued through a preliminary investigation of the regulatory aspects, then an analysis of the knowledge and characteristics of the different types of scaffolding, an in-depth analysis of special applications for work with particular constraints, the design of a real scaffolding case suspended to high altitude through an FEM analysis, and finally, the identification of hypotheses of implementation and improvement of the control system for a correct assembly and use of the scaffolding through a new technological scenario
Buckling failure modes of FRP thin-walled beams
No full textA study on buckling phenomena in pultruded Fiber Reinforced Polymer (FRP) beams, based on two mechanical models recently formulated by the authors with regard to composite thin-walled beams, is presented in this paper. Global buckling behavior is analyzed by means of a one-dimensional model in which cross-section torsional rotation is divided into two parts: the first one, associated with Vlasov's axial warping, the second one, associated entirely with shear strains. The study of local behavior is based on the individual buckling analysis of the components of FRP profile, assumed as elastically restrained transversely isotropic plates. Both mechanical models take into account, within the field of small strains and moderate rotations, the contribution of shear deformation in the kinematic hypotheses. Design charts suitable to evaluate the buckling load of FRP "I" beams with either narrow or wide flanges are obtained and presented in this paper. © 2012 Elsevier Ltd. All rights reserved
Local buckling behavior of FRP thin-walled beams: A mechanical model
No full textA mechanical model able to predict the local buckling of pultruded FRP thin-walled beams and columns, taking into account the shear deformability of composite materials, is presented in this paper. The model is based on the individual analysis of the buckling of the components of the FRP profile, assumed as elastically restrained transversely isotropic plates. The analysis is developed within the hypotheses of small strains and moderate rotations. © 2012 Elsevier Ltd
Local buckling analysis of pultruded frpthin-walled beams and columns
No full textIn this paper a mechanical model capable to predict the local buckling of pultruded FRP thin-walled beams and columns, taking into account the shear deformability of composite materials, is presented. The model is based on the individual analysis of buckling of the components of FRP profile, assumed as elastically restrained transversely isotropic plates. The analysis is developed within the field of small strains and moderate rotations
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