A new two-stage method for the automated manufacture of high performance composites components is presented which aims to combine the capacity for forming complex shapes of Hand Layup with the speed of existing automated systems. In the first stage of the new process plies are formed into the approximate shape of the mould using a press mechanism. They are then passed onto a layup stage which uses multiple end effectors controlled by a six axis robot to stick the plies down onto the mould. This is the first time an automated process has been capable of forming sheets of woven prepreg onto truly complex moulds while maintaining a high level of fibre alignment. This work represents a condensed version of the second half of the thesis by the author entitled ‘The evolution and automation of sheet prepreg layup’.
The combination of additive manufacturing (AM) with advanced composites unlocks potentials in the design and development of highly integrated lightweight structures. This paper investigates two design potentials where the combination of AM and carbon fiber prepreg technology is applied to honeycomb sandwich structures: (i) Reduction of number of parts: The use of selective laser sintered cores allows the integration of various functions into one single part. These include structural as well as tooling, positioning and assembly functions. (ii) Tailored mechanical performance: With AM it is possible to adapt the mechanical properties of the core according to local load requirements. These potentials are demonstrated using the example of the development of an aircraft instrument panel. The approach of combining AM with advanced composites is evaluated by assessing the weight and the number of parts for the demonstrator panel compared to a state-of-the-art aluminum machined instrument panel. Weight savings of 40 % and parts reduction by 50 % indicate that the technology is competitive for complex low volume parts.
The objective of the present work is to investigate the compressive response of shallow curved composite plates with longitudinal-internal-ply-drop-off configurations. The Ritz method is used for the global buckling analysis considering uniaxial compressive load. Linear buckling analysis is carried out based on eight well-known classical shallow shell theories, namely Donnell's, Love's, Mushtari's, Timoshenko's, Viasov's, Sander's, Koiter's and Novozhilov's theory. The strength characteristics and load carrying capability of the tapered curved plates are investigated considering the first-ply failure analysis using ANSYS. Based on the failure and. buckling analyses, the critical sizes and parameters of the tapered curved plates that will not fail before global buckling are determined. A parametric study is conducted that encompasses the effects of boundary conditions, stacking sequence, taper configurations, radius, and geometric parameters of the plates.
In this research article, areca fiber composite laminates were prepared with randomly distributed fiber and different proportions of phenol formaldehyde (PF). The standard specimen of the areca PF composite was made at recommended temperature of 140 degrees C under pressure in a hot press. The thermal properties of areca reinforced phenol formaldehyde (PF) composite materials were studied experimentally. The thermal properties like thermal conductivity, specific heat, thermal diffusivity, thermal resistivity and co-efficient of thermal expansion have been determined for areca reinforced PF composites. The results were compared with other wood based thermal insulators, brick and asbestos cement sheets. Areca fiber reinforced PF composite shows lower thermal conductivity compared to other thermal insulating materials.
The effect of fiber preform consolidation on Mode-I fracture toughness of composite laminates was investigated. Woven roving E-glass/vinyl-ester composite plates were fabricated with a pliable:bag VARTM process using consolidation pressures and consolidation times commonly incorporated when fabricating marine grade polymer composite parts. This study investigated the range of 0.85 to 0.98 bar (25 to 29 in-Hg) for consolidation pressure, and a consolidation time range of 1 to 5 hours. The general trend at the lower consolidation pressures was that shorter consolidation times produced larger onset fracture toughness values and smaller propagation fracture toughness values, while longer consolidation times produced smaller onset fracture toughness values and larger propagation fracture toughness values. There was not a consistent effect at the higher pressure. There was no correlation found between the global fiber volume fraction of the specimens and the fracture toughness properties.
Curing process and phenomena description of thermoset - based carbon fiber reinforced matrices has been well achieved by successfully utilizing kinetic viscoelasticity modeling. Essentially, the change of fundamental material descriptors as a result of reaction kinetics is the main difference from classic viscoelasticity. Accordingly, the same concept can be applied for different kinetic phenomena with simultaneous curing and degradation. The application of this concept can easily be utilized in processing and manufacturing of carbon-carbon composites, where phenolic resin matrices are cured, degraded and rein fused in a carbon fiber bed. This work provides a major step towards understanding complex viscoelastic phenomena that go beyond simple thermomechanical descriptors.
This paper presents the results of an experimental investigation on the influence of long term hygrothermal exposure on the delamination growth in an aerospace grade carbon/epoxy composite (AS4/5276-1). Double cantilever beam specimens were immersed in water at 70 degrees C until saturation. De lamination growth tests were performed under quasi-static and fatigue loading conditions. Results showed that moisture decreases the delamination growth threshold and the delamination toughness and that it increases the delamination growth rate in the studied material. Scanning electron micrographs of the delaminated surfaces indicated that moisture causes a degradation of the interface between the fibers and the matrix.
Energy storage flywheel technology is attractive for various industrial applications. Traditionally, system mass has been of great importance in flywheel design. For stationary implementations, however, design optimization is considerably driven by cost considerations. A novel and promising optimization objective is energy-per-cost. For a multi-rim hybrid composite flywheel rotor an optimization problem was solved with a varying cost ratio of the rim materials. An analytical approach as well as a finite element analysis were employed in a multifidelity strategy. Global and local optimization methods were used. A multi-strategy was found to provide an efficient solution approach for the design problem.
Flexural stiffness effects in quasi-isotropic laminates are analytically evaluated and compared for potential composite fabrication materials for precision mirrors. Based on analytical results, radial variations of flexural stiffness in quasi-isotropic laminates are associated with stacking sequences within the laminates, and the inequality of the flexural stiffness will play one of the most significant factors for causing unfavorable surface waviness which could hinder fabricating precision composite optics using CFRP. For precision composite optics, distributed reinforced plastics (veils, chopped mat. or other short fiber materials) might be superior to conventional CFRP for uniform extensional and flexural stiffness that require in precision composite optics.
The scope of this study is to examine the development of an artificial neural network (ANN) method for the prediction of maximum failure loads of two serial pinned/bolted E-glass reinforced epoxy composite joints. The experimental data provided from the previous study with different geometrical parameters without preload moments and various applied preload moments were used for developing the ANN model. Comparisons of ANN results with desired values pointed out that there is an excellent agreement between input and output variables of the experimental data. Consequently, ANN was showed to be a suitable powerful tool for the prediction of maximum failure loads of two serial pinned/bolted composite joints.
Glass fiber reinforced polymer (GFRP) rebars have many advantages compared to traditional reinforcing steel such as higher strength to weight ratio, higher resistance to corrosion, as well as higher resistance to fatigue loads. One of the main disadvantages of GFRP rebars is their lack of ductility. The linear behavior of the GFRP bars up to failure makes their application difficult to compare with conventional steel bars. One solution to this difficulty is to provide ductility for FRP by using hybrid FRP reinforced bars. A pilot trial to manufacture locally hybrid FRP rebars using the pultrusion method produced rebars consisting of glass fiber combined with both carbon and aramid fibers with three different ratios for each. Tension test results showed that the locally produced hybrid FRP rebars had a semi-ductile behavior similar, to some extent, to that of conventional reinforcing steel.
Cured epoxy resins are strong, tough and inherently adhesive making them the material of choice for many composite applications. Their adhesive qualities allow them to stick to glass and carbon fiber surfaces as well as bond composites to each other and metals. Structure property relationships for epoxy resins are straight forward. In general, a lower number of epoxy groups per molecule and lower molecular weight lead to more liquid systems with lower temperature capability. A minimum of two epoxy groups per molecule are required to yield a crosslinked load-bearing material. Higher than two epoxy groups per molecule leads towards higher crosslinking and subsequent higher temperature capability. Almost limitless blending options of liquid and solid epoxy resins and lower and higher epoxy groups per molecule can balance process requirements with cured performance options such as operating temperature, toughness, and composite mechanical performance dominated by resin characteristics such as flexural, compressive and shear strengths as well as impact resistance.Epoxy resins must be reacted or cured to be converted from single molecules into a structural load-bearing material in a process called curing or crosslinking (and sometimes referred to as polymerization). In addition to structure property considerations in the cured resin, the curative chosen will determine the crosslinking reaction mechanism and reaction rate, thus controlling shelf life, pot life, cure cycle and general applicability to a fabrication method and raw material form. A wide adaptability to composite fabrication techniques has been made possible by a wide variety of curatives.This article will focus on curatives used for matrix resins used in composites. There are many ways to examine and discuss this subject such as by the nature of the curing reaction or by the chemical family of the curative. In this paper, the curatives will be discussed based upon the composite manufacturing method used for specific applications such as prepreg, filament winding, resin transfer molding, wet lay up and compression molding applications. The emphasis will be on why the chemical and physical attributes of certain types of curatives have found utility in a given application and less emphasis on specific chemical reaction mechanisms which have ;been covered in many excellent reviews(1,2). The examples shown in this paper are not exhaustive by any means: there are many additional materials used in the composites industry.Structures are shown to demonstrate similarities and differences in terms of physical form (liquid or solid), equivalent weight, viscosities where this is an important attribute and reactivity with a standard difunctional liquid bisphenol-A (bis-A) epoxy resin. Shorter gel times indicate faster reactions.Physical properties such as melting point, viscosity, amine content, epoxy content and particle size are shown as single values where in reality they are ranges.
In this paper, the damping characteristics of nanocomposite plates were studied via experimental methods. The nanocomposite plates with different weight percentages of carbon nano fibers (CNFs) in the polymer matrix were fabricated using the vacuum-assisted resin transfer molding (VARTM) process. The damping ratios of the nanocomposite plates were tested and the results show a significant increase of the damping ratio of the plates with a small amount of CNFs. Between a CNF-free plate and a 1.5 wt% CNF-modified plate, over a two-fold decrease in amplitude in the vibration response was observed. The damping factors obtained from dynamic mechanical analysis (DMA) are consistent with the results obtained using PZT. The CNF-modified polymer composites have potential applications in aerospace and wind turbine, where increased structural damping is preferred.
This paper presents a review of corrosion and corrosion protection practices so far practiced on oil and gas systems in corrosive environments. A review of corrosion monitoring techniques and measurement, integrity management and assessments on oil and gas pipeline transmission was done. Sensitization designs and approaches against the corrosion potential of the atmosphere and relative components were also included. Finally, the all important overview of the recent research development in the area of composite materials, especially in the 3-dimensional reinforcement of plastics, which has made a breakthrough in finding the solution against corrosion, in the form of Glass Reinforced Plastic (GRP) pipes was highlighted. It was observed that oil and gas systems are installations found within aqueous solutions that are electrochemical in nature constituting galvanic cells. The containing elements are either noble metal (active) or base metal that may be passive whose electrode potentials determine the corrosion pace. The electrode potentials of the surrounding environment (electrolyte) of gas and oil systems were also found to determine the rate of corrosion. Polymer matrix composites were found to be more cost advantageous and less corrosion prone than other competitive materials that could be selected to solve corrosion problems. The effect of corrosion was found to supersede a simple loss of mass of metal, while galvanic cell formation in oil and gas installations constitutes the major causative agent of corrosion.
The crashworthiness performance of a composite structure depends largely on its ability to absorb energy through controlled failure mechanisms during crushing. Crush testing of simple specimen geometries, including tubes, is often used to characterize these failure mechanisms. Research has shown that the energy absorption of composite tubes is a function of many variables including material type, fiber architecture, tube geometry, and loading rate. This review focuses on topics associated with composite tube testing for crashworthiness applications including measures of energy absorption, failure modes observed, and a discussion of variables affecting energy absorption during crush testing.
The hygrothermal and UV radiation influences on shear properties and moisture diffusion aging in polyetherimide (PEI) reinforced with continuous fibers were systematically studied in this research, by using ILSS and losipescu shear tests. The moisture weight gain curves of the PEI composites reinforced with glass fiber and carbon fiber were compared in order to determine the interface effect on moisture absorption. Both composites display similar anomalous diffusion behavior; the PEI reinforced with glass fiber presented higher diffusion and water absorption values. The mechanical results indicate that moisture associated with temperature and UV radiation degrades the shear properties by about 20%, giving evidences of plasticization of PEI matrix.
The air drawing model of polypropylene (PP) polymer in the spunbonding process is established. The influence of the density and the specific heat capacity of a polymer melt at constant pressure are examined. Also, the effect of changes in polymer temperature on the fiber diameter are also studied. The air drawing model of polypropylene (PP) polymer in spunbonding is confirmed by the experimental results obtained with our university's equipment. The predicted filament fiber diameter is in accord with the experimental data. The effects of the process parameters on the filament fiber are further investigated in this work. It is found that a lower polymer throughput rate, a higher polymer melt initial temperature, a higher air primary speed, a higher air primary temperature, a higher air suction speed, a higher quench pressure, and a smaller venturi gap can all yield finer fibers, whereas the effect of the web basis weight is not significant. The results show good prospects for this research in the field of computer-assisted design of spunbonding technology.
Tapered laminated structures have received significant attention from researchers for creating considerable weight savings in engineering applications. Due to the variety of tapered composite plates and the complexity of the analysis, no closed form analytical solution is available based on third-order theory regarding their response to compressive loading. Therefore in the present work, the Ritz method is used for the global buckling analysis considering uniaxial compressive load. The buckling loads obtained using Ritz method are also compared with the existing analytical results. The strength characteristics and load carrying ability of the tapered plates are investigated considering two types of (local) failure: first-ply failure and delamination failure. Based on the above mentioned analyses, the critical sizes and parameters of the tapered plates that will not fail before global buckling are determined. Finally, a parametric study is carried out.
This paper presents the static and dynamic analysis of systematically creased polymer membranes. First, static analysis was performed to study the non-linear material response of singly- and doubly-creased membranes. Then, numerical analysis of a creased membrane was performed with a modified wrinkle algorithm where the nonlinear material response was incorporated. Numerical results were validated with corresponding experiments. Finally, dynamic analysis of a four-corner loaded square membrane was performed under pristine and creased configurations. The pristine model was considered linear isotropic, and the creased model was analyzed with combined linear isotropic and nonlinear orthotropic material behavior. Numerical results of pristine, singly- and doubly-creased membranes were also validated with corresponding experiments. Physical explanations are provided addressing the numerical and experimental observations. The outcomes of the present work will have significance to large, lightly-tensioned gossamer spacecraft such as solar sails.
