Carbon Fiber Core Research Articles

SU‐F‐T‐430: Validation of IBEAM Evo Couch Top for Different Relative Electron Density (RED) Combination During Photon Beam Dose Calculation in Monaco− Treatment Planning System

Purpose:Validation of iBEAM™ evo couch‐top for different relative electron density (RED) combination during photon beam dose calculation in Monaco− TPS.Methods:The iBEAM™ evo couch‐top has two layers:outer carbon fiber (CF) and inner foam core (FC). To study the beam intensity attenuation of couch‐top, measured doses were compared with doses calculated for different REDs. Measurements were performed in solid water phantom with PTW‐0.125cc ion‐chamber positioned at center of the phantom with 5.3cm thickness slabs placed above and below the chamber. Similarly, in TPS, iBEAM™ evo couch‐top was simulated and doses were calculated for different RED combinations (0.2CF‐0.2FC, 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC) by using Monte Carlo dose calculation algorithm in Monaco TPS (V5.1). Doses were measured for every 10 degree gantry angle separation, 10×10cm2 field size and 6MV photons. Then, attenuation is defined as the ratio of output at posterior gantry angle to output of its opposed anterior gantry angle (e.g.225°/45°). output fluctuation with different gantry angle was within ±0.21%. To confirm above results, dose‐planes were measured for five pelvic VMAT plans (360°arc) in PTW two‐dimensional array and compared with different calculated dose‐planes of above‐mentioned couch REDs. Gamma pass rates<1.00) were analyzed for 3%/2mm criteria.Results:Measured and calculated attenuation was in good agreement for the RED combination of 0.2CF‐0.2FC and difference was within ±0.515%. However, other density combination showed difference of ±0.9841%, ±1.667%, ±2.9241% and ±2.8832% for 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC, respectively. Maximum couch‐top attenuation was observed at 110°–120° and 240°–250° and decreases linearly as the gantry angle approaches 180°. Moreover, gamma pass rate confirmed the above results and showed maximum pass rate of 96.23% for 0.2CF‐0.2FC, whereas others were 95.72%, 95.12%, 94.31% and 93.24%.Conclusion:RED value of 0.2CF‐0.2FC was found to be suitable for accurate couch‐top modeling for 6MV photon beam Monte Carlo calculations in Monaco TPS.

A Low Mass On-Chip Readout Scheme for Double-Sided Silicon Strip Detectors

B-factories like the KEKB in Tsukuba, Japan, operate at relatively low energies and thus require detectors with very low material budget in order to minimize multiple scattering. On the other hand, front-end chips with short shaping time like the APV25 have to be placed as close to the sensor strips as possible to reduce the capacitive load, which mainly determines the noise figure.In order to achieve both – minimal material budget and low noise – we developed a readout scheme for double-sided silicon detectors, where the APV25 chips are placed on a flexible circuit, which is glued onto the top side of the sensor. The bottom-side strips are connected by two flexible circuits, which are bent around the edge of the sensor.This so-called “Origami” design will be utilized to build the Silicon Vertex Detector of the Belle II experiment, which will consist of four layers made from ladders with up to five double-sided silicon strip sensors in a row. Each ladder will be supported by two ribs made of a carbon fiber and Airex foam core sandwich. The heat dissipated by the front-end chips will be removed by a highly efficient two-phase CO2 system. Thanks to the Origami concept, all APV25 chips are aligned in a row and thus can be cooled by a single thin cooling pipe per ladder.We present the concept and the assembly procedure of the Origami chip-on-sensor modules.

A self-deploying and self-stabilizing helical antenna for small satellites

Space antennas with a helical geometry are an advantageous choice for many applications, for instance if the transmission of electromagnetic waves with a circular polarization is intended, or if signals from terrestrial objects shall be received with a high angular resolution. In all these cases the desired electromagnetic properties of a helical geometry can be combined with the mechanical advantage that the antenna acts as a compression spring, provided that its core structure has the necessary high spring stiffness but can nevertheless easily be compressed. Such an antenna has been developed by DLR Institutes in Bremen and Braunschweig together with some industrial partners for a small satellite named AISat, which shall be able to pursue the position of individual ships in critical sea areas in order to improve the security of seafare trade. The development was very challenging since the antenna must expand from a stowed stack length of only 10cm to a total length of 4m. Only a special carbonfiber core under the conductive coating and a system of stabilizing cords led to a satisfying solution. Both the self-deployment and the self-stabilization function of this innovative antenna concept have been successfully tested and verified under zero-g-conditions in the course of a parabolic flight campaign. It could be convincingly demonstrated that the helical antenna can really achieve its desired contour in weightlessness within some seconds and maintain the required stability. Beyond the current application for the AISat satellite it is therefore quite a promising concept for future satellites.

Tension–tension fatigue of hybrid composite rods

The tension–tension fatigue behavior was investigated for a hybrid composite rod comprised of a unidirectional carbon fiber core and a glass fiber shell. Fatigue tests were performed at three R-ratios and four maximum applied stress levels (MAS) while recording the secant modulus at each cycle, and acoustic emission (AE) sensors were employed to monitor the activation of fatigue mechanisms. Fatigue failure occurred when the composite rod was no longer able to support the applied cyclic load. For a MAS level of 70% of the ultimate tensile stress (UTS), composite rods tested at higher R-ratios showed AE activity through a larger percentage of fatigue life, but exhibited a greater resistance to fatigue failure, whereas samples cycled at lower R-ratios displayed AE activity only near the end of fatigue life, and showed a lower resistance to fatigue failure. The hybrid composite showed modes of progressive fatigue damage at high R-ratios and low strain amplitudes in the form of longitudinal splitting of the GF shell. In contrast, failure of the CF core was catastrophic and non-progressive. The fatigue resistance and damage mechanisms of the composite rod were dependent on the MAS level and R-ratio. Fatigue cracks initiated because of fretting between the GF shell and grip surface, which led to the observed longitudinal splitting of the GF shell. Fatigue damage occurred along the GF/CF interface where non-uniform strains developed because of the clamping force of the grip on the GF surface. At an R-ratio of 0.85, a fatigue stress of 70% UTS caused catastrophic fatigue failure, while at lower stresses, composite rods did not fail and withstood cyclic loads up to 1 million cycles. The research conducted is the first to investigate the degradation in fatigue performance arising from grip/composite rod interactions and suggests that the results from the study provide new information for composite materials in industries that utilize unidirectional composites in cylindrical form.

All-carbon electrode-based fiber-shaped dye-sensitized solar cells

A novel fiber-shaped dye-sensitized solar cell (DSSC) based on an all-carbon electrode is presented, where low-cost, highly-stable, and biocompatible carbon materials are applied to both the photoanode and the counter electrode. The fibrous carbon-based photoanode has a core-shell structure, with carbon fiber core used as conductive substrate to collect carriers and sensitized porous TiO(2) film as shell to harvest light effectively. The highly catalytic all-carbon counter electrode is made from ink carbon coatings and carbon fiber substrate. Results show that the open circuit voltage can be largely improved through engineering at the carbon fiber/TiO(2) interface. An optimized diameter of the photoanode results in an efficiency of 1.9%. It is the first demonstration of efficient DSSCs based on all-carbon electrodes, and the devices are totally free from TCOs or any other expensive electrode materials. Also, this type of solar cell is significant in obtaining bio-friendly all-carbon photovoltaics suitable for large-scale production.

Manufacturing Technique of High Modulus Complex Ply Yarn and Stiffening Geogrids

In this study, carbon fiber/ polypropylene (PP) complex braiding yarn, with its different breaking strength, was prepared. It was designed by braiding polypropylene (PP) wrapped yarn and carbon fiber core yarn using eight and sixteen spindles braiding machines, with change of take-up gear number. Environmental factors, such as pH, temperature and time, were also changed to produce geo-grids with high strength, high modulus and better weather resistance. In order to make stable structure for complex braiding yarn, the heat treatment was also considered. Finally, geo-grids braiding by optimal treatment parameters were cut into single rib and junction specimens for tensile test.

Effect of filler on thermal aging of composites for next-generation power lines

The thermal aging of pultruded composite rods was investigated to determine the effects of filler on oxidation kinetics and degradation mechanisms. The unidirectional hybrid composite rods were comprised of a carbon-fiber core, a glass-fiber shell, and an epoxy matrix filled with clay particles. A reaction-diffusion model was implemented for each of the two hybrid sections to calculate the oxygen-concentration profile and the thickness of the oxidized layer (TOL) within the composite rods, and results were compared with measured oxidation kinetics. The TOL was measured for samples exposed isothermally in air and in vacuum at 200 °C for up to 13,104 h (1.5 year), and the measured values were similar to modeling predictions (within 10%). The domain validity for the reaction-diffusion model was determined from gravimetric experiments (weight-loss measurement), which showed that after prolonged thermal exposure, the degradation mechanism changed from thermal oxidation to thermal degradation. Thermogravimetric analysis (TGA) was performed to determine the thermal degradation and stability of the aged composite. In addition, the effect of thermal aging on glass transition temperature ( T g ) and short beam shear (SBS) strength was determined for isothermal exposures at 180 °C and 200 °C.

Thermal aging of fiberglass/carbon-fiber hybrid composites

Thermal oxidation of a unidirectional carbon-fiber/glass-fiber hybrid composite was investigated to determine oxidation kinetics and degradation mechanisms. The epoxy composite rods were comprised of a carbon-fiber core and a glass-fiber shell. A reaction–diffusion model was developed for each of the two hybrid sections to obtain the oxygen-concentration profile and the thickness of the oxidized layer (TOL) within the composite rods. The TOL was measured experimentally for samples exposed at 180 °C and 200 °C for up to 8736 h, and measured values were similar to the modeling predictions. The glass-fiber shell functioned as a protective layer, limiting the oxidation of carbon-fiber core. A relationship was derived relating TOL to tensile strength of the hybrid composite. The tensile strength remained essentially unchanged by thermal oxidation after 52 weeks of exposure. Inspection of thermally aged capped rods showed no cracking after long-term exposures.

Ductility of nonmetallic hybrid fiber composite reinforcement for concrete

Reinforcing units, FRP, of unidirectional fiber composites for concrete have elastic behavior up to tensile failure. For safety reasons an elongation of 3% at maximum load is usually required for the reinforcement. Ductile behavior with the necessary elongation and stress hardening could be obtained with braided fiber strands around a core of foam plastic, thin glass fiber cylindrical shell, or unidirectional carbon fibers. Braids around a porous core reveal the ductility when epoxy resin breaks up and collapse of core enables the braids to rotate. The same seems to happen at that cross section, where carbon fiber core breaks in tension. The best result is obtained using a cylindrical glass fiber reinforced core shell surrounded with aramid fiber braid.

The use of a surface acoustic wave technique to study the growth behaviour of small cracks in a high-strength steel alloy. (Dissertation): Yuce, H. H. Diss. Abstr. Int. May 1988 48, (11), Pp 189

The tension–tension fatigue behavior was investigated for a hybrid composite rod comprised of a unidirectional carbon fiber core and a glass fiber shell. Fatigue tests were performed at three R-ratios and four maximum applied stress levels (MAS) while recording the secant modulus at each cycle, and acoustic emission (AE) sensors were employed to monitor the activation of fatigue mechanisms. Fatigue failure occurred when the composite rod was no longer able to support the applied cyclic load. For a MAS level of 70% of the ultimate tensile stress (UTS), composite rods tested at higher R-ratios showed AE activity through a larger percentage of fatigue life, but exhibited a greater resistance to fatigue failure, whereas samples cycled at lower R-ratios displayed AE activity only near the end of fatigue life, and showed a lower resistance to fatigue failure. The hybrid composite showed modes of progressive fatigue damage at high R-ratios and low strain amplitudes in the form of longitudinal splitting of the GF shell. In contrast, failure of the CF core was catastrophic and non-progressive. The fatigue resistance and damage mechanisms of the composite rod were dependent on the MAS level and R-ratio. Fatigue cracks initiated because of fretting between the GF shell and grip surface, which led to the observed longitudinal splitting of the GF shell. Fatigue damage occurred along the GF/CF interface where non-uniform strains developed because of the clamping force of the grip on the GF surface. At an R-ratio of 0.85, a fatigue stress of 70% UTS caused catastrophic fatigue failure, while at lower stresses, composite rods did not fail and withstood cyclic loads up to 1 million cycles. The research conducted is the first to investigate the degradation in fatigue performance arising from grip/composite rod interactions and suggests that the results from the study provide new information for composite materials in industries that utilize unidirectional composites in cylindrical form.