Design, fabrication and testing of a composite bracket for aerospace applications

In this paper the results of a programme, in which a composite bracket as a replacement for a metal forging was developed, will be presented. The finite-element method (FEM) in combination with an optimization module was used to design the bracket. Compared to its metal counterpart, the composite bracket demonstrated a weight reduction of 43%. Two composite brackets were fabricated by resin transfer moulding (RTM). One bracket was loaded statically to 1.38 × Design Ultimate Load. The bracket did not fail at this load level.     

Real-time ultrasonic monitoring of fiber-matrix debonding in ceramic-matrix composite

Real-time ultrasonic techniques were developed for monitoring damage in a unidirectional ceramic-matrix composite under longitudinal tensile loading. Specifically, shear-wave transducers producing waves polarized in the transverse to the fiber direction were used in contact with the specimen to detect the initiation and propagation of fiber—matrix debonding, and to determine the transverse shear modulus and its degradation. The ultrasonically measured transverse shear modulus and its degradation was in reasonably good agreement with a prediction based on a modified shear lag model and interpolation between available solutions for fully bonded and fully unbonded fibers.     

Design,fabrication and cryogenic testing of 0.6 MJ SMES coil

Our centre has taken up a project of development of superconducting magnetic energy storage (SMES) technology to have better power quality for its accelerator program. In the first phase, a prototype cryostable coil has been designed, fabricated and commissioned in a standard bath cryostat. The various parameters of the magnet coil have been determined in order to maximize stored energy taking into consideration the constraints like geometry, maximum current limit etc. Winding tension (Pre-stress) of 13.6 MPa is maintained to keep radial stress compressive in all possible scenarios (i.e. during cool-down, excitation, etc.). Mylar is used for turn to turn insulation while 1 mm thick glass epoxy based picket fences (G-10) are placed symmetrically azimuthally for layer to layer insulation as well as to ensure passage of liquid helium inside the winding.Cryostability of the conductor implies more copper to superconductor ratio and is desired as far as stability of the coil is concerned. Cryostability, however may degrade when helium vapor is trapped in between two layers. Therefore, quench behavior of the magnet along with protection system has also been studied and implemented. This paper describes issues related to design study, fabrication and also cryogenic test results of the coil.     

Design, testing, and FEM simulation of interlaced fiber composite structures

Design, testing, and FEM simulation of FRP structural parts manufactured using continuous fiber and light-curing resin are presented in this study. The structures can be described as formed by girders spaced by skew ribs. The study was limited to plane structures with two girders and 45° ribs between girders. Roving was positioned along the girders and the ribs so that fibers were interlaced at the joints between the ribs and girders. Several deposition paths were designed. They differ by interlacing, and proportions of fiber in the girders and ribs. Overall stiffness and strength of the structures were investigated in bending, and local deformations were measured with the strain gauges. Finite element modeling of four-point bending test for some test pieces were carried out using commercial code ANSYS to predict the deflection and the strains.     

Design optimization and fabrication of a hybrid composite flywheel rotor

This paper discusses three different rim design cases of a hybrid composite flywheel rotor using strength ratio optimization. The rotor is composed of four hybrid composite rims. These rims are made from carbon–glass/epoxy with varying volume fractions of hoop wound reinforcements. Optimization is performed to reduce the maximum strength ratio during two rotor states: stationary and the maximum allowable rotational speed. The input specifications for optimization are: maximum useable energy (35 kW h), rotational speed (15,000 rpm), height, and inner radius. In the first case, the rims are wound simultaneously by continuous winding. However, in the second case, the rims are wound separately, and interferences are incorporated for their assembly by press fit. In the third case, a hybrid version of the first two cases is used, whereby two pairs of rims are wound at the same time, and in a secondary operation, the first pair is press fitted to the second pair. Each case has different fabrication costs and different strength ratios. The third case rotor has been successfully manufactured by filament winding with in situ curing, followed by press fit assembly of machined rims.     

Design,fabrication, and testing of fiber Bragg grating sensors for cryogenic long-range displacement measurement

It is essential to measure the shrinkage/expansion and positioning/aligning of magnets and to control valve displacement which plays a vital role in experiments like the Karlsruhe tritium neutrino experiment beam tube and Cryo pumps. Hence, a displacement sensor which, over a long working range, can be operated under extreme environmental conditions needs to be developed. Fiber Bragg gratings (FBG) have been considered to be excellent sensor elements useful for a variety of applications. This paper will discuss a long range displacement sensors based on fiber Bragg gratings for cryogenic temperature applications. The cryo pump inlet valve control requirements have been taken as example specifications for sensor design. To achieve the development goal, a proper signal transducer and sensor package were designed. A study of the strain transmission of surface-bonded FBG was conducted. The influence of bonding thickness and bonding length was reported. The design, fabrication, and performance were tested at low temperature of around 77 K. The sensor performance was found to be satisfactory at both room temperature and 77 K and linearly for long-range displacement of 550 mm with 14 pm/mm sensitivity and 0.142 mm accuracy.     

Off-axis creep of a ceramic-matrix/continuous-ceramic-fiber composite: Experimental evaluation

The compression creep of a unidirectionally reinforced, SiC continuous fiber/calcium aluminosilicate (anorthite) glass-ceramic matrix composite was evaluated experimentally. Experiments covered the stress (–₁) and temperature (T) ranges of 20–40 MPa and 1300–1320°C, respectively. The experiments also emphasized characterization of the rheology as a function of the angle of misorientation () between the applied compressive load and the direction of reinforcement. For any given , T condition, the highest steady-state strain rate occurred for 50° (up to an order of magnitude faster than in the transverse, = 90°, case); overall composite strain in this case included a substantial contribution from displacement across the fiber-matrix interface. The data reveal that the interfacial rheology responsible for the displacement is distinctly temperature sensitive. Evaluation of the composite flow through its comparison to numerical/rheological models that scrutinize the interfacial effect implies that the interface is characterized by a non-Newtonian viscous rheology; this suggests that the interface response involves specifically the flow of the thin amorphous silica interphase that comprises a portion of the fiber-matrix interface in this material. The overall plastic response of the unidirectionally reinforced material is nevertheless rate-limited by plastic flow of the matrix and can be described by the superposition of three modes of strain, the magnitude of each being dependent specifically on .     

Design,manufacture, mechanical testing and numerical modelling of an asymmetric composite crossbow limb

This paper considers the design, manufacture, mechanical testing and numerical analysis of a crossbow beam (limb). The limb should be lightweight and permit a high deflection of the beam’s tip in order to achieve a good ballistic performance. Consequently, fibre-reinforced polymer matrix composites are suitable candidate materials. However, carbon fibres were considered too brittle for this application. Aramid fibres combine low density and high stiffness but are weak in compression. E-glass fibres are relatively flexible but are of high density. The optimised design developed here uses aramid fibres on the tension face with E-glass fibres on the compression side. This component was manufactured using resin infusion, modelled using a commercial finite element code (Abaqus^®) and the model was validated by mechanical testing. A good correlation was found between the experimentally measured deflections and the numerical results.     

Design of a fibrous composite preform for wind turbine rotor blades

The present work addresses the different factors and challenges one must cope with in the design process of a composite preform used for the load-carrying main laminate of a wind turbine rotor blade. The design process is split up into different key elements, each of which are presented and discussed separately. The key elements are all interconnected, which complicate the design process and involves an iterative procedure. The aim is to provide an overview of the process that governs the design of composite preforms for wind turbine blades. The survey can be used as an information source on composite preform manufacturing. Basic knowledge on wind turbine blade technology and composites is assumed.