Yoshiyasu Hirano

Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation

We have developed a method for the three-dimensional (3D) printing of continuous fiber-reinforced thermoplastics based on fused-deposition modeling. The technique enables direct 3D fabrication without the use of molds and may become the standard next-generation composite fabrication methodology. A thermoplastic filament and continuous fibers were separately supplied to the 3D printer and the fibers were impregnated with the filament within the heated nozzle of the printer immediately before printing. Polylactic acid was used as the matrix while carbon fibers, or twisted yarns of natural jute fibers, were used as the reinforcements. The thermoplastics reinforced with unidirectional jute fibers were examples of plant-sourced composites; those reinforced with unidirectional carbon fiber showed mechanical properties superior to those of both the jute-reinforced and unreinforced thermoplastics. Continuous fiber reinforcement improved the tensile strength of the printed composites relative to the values shown by conventional 3D-printed polymer-based composites.

Development of Variable Camber Morphing Airfoil Using Corrugated Structure

This paper describes the development and the wind tunnel test of a variable geometry morphing airfoil using corrugated structures. Proof-of-concept study of a morphing wing with corrugated flexible seamless flap-like structure is verified by finite element analysis, and a prototype is manufactured using carbon fiber reinforced plastics. For the actuation system, two servomotors are installed inside the prototype wing to control the airfoil shape by the chordwise tension of the connected wires. Successful actuation of the prototype wing is demonstrated under the air speed up to 30  m/s in the wind tunnel test. Basic aerodynamic properties are also evaluated in comparison to traditional airfoil with a hinged control surface. Lift increase of variable corrugated wing is recognized compared to the traditional wing when the aileron angle increases.

Damage Identification of Woven Graphite/Epoxy Composite Beams using the Electrical Resistance Change Method

This study examines the damage identification for woven graphite/epoxy composite beams by means of an electrical resistance change method. The method has been proposed by the authors and successfully applied to cross-ply and quasi-isotropic laminates; the method has yet to be applied to woven laminates. In many practical structures, woven plies are adopted to prevent peeling of the surface layer. Therefore, a woven graphite/epoxy composite is selected as the target material of the electrical resistance change method to identify the damage. Beam type specimens consisting of woven laminates are the focus of this article. For the purpose of identification, the response surface is adopted as a solving method for the inverse problem. As a result, the method shows an excellent performance for estimating delamination crack locations and sizes.

Development of variable camber wing with morphing leading and trailing sections using corrugated structures

This article describes the development of variable camber morphing wing, which is mainly composed of corrugated structures. The morphing wing with both leading edge and trailing edge morphing sections is proposed and the prototype model is designed by consideration of finite element structural analysis with actuation mechanisms and aerodynamic analysis. Through wind tunnel experiment with the manufactured prototype model, smooth actuation without harmful deformation under 20 m/s airflow is demonstrated. The observed deformation shape is well correlated with simulated shape by analysis. Thereby, the feasibility of the present morphing wing mechanism and design process are verified.

Monitoring of a CFRP-Stiffened Panel Manufactured by VaRTM Using Fiber-Optic Sensors

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures.

Development and Wind Tunnel Test of Variable Camber Morphing Wing

This paper describes the development and the wind tunnel test of a variable geometry morphing airfoil using corrugated structures. Proof-of-concept study of a morphing wing with flexible seamless flap-like structure is performed by the finite element analysis. For the actuation system, two servomotors are installed inside the prototype wing to control the airfoil shape by the chord-wise tension of the connected wires. Successful actuation of the prototype wing is demonstrated under the air speed up to 30 m/s in the wind tunnel test.

Elite-initial population for efficient topology optimization using multi-objective genetic algorithms

The purpose of this paper is to improve the efficiency of multi-objective topology optimization using a genetic algorithm (GA) with bar-system representation. We proposed a new GA using an elite initial population obtained from a Solid Isotropic Material with Penalization (SIMP) using a weighted sum method. SIMP with a weighted sum method is one of the most established methods using sensitivity analysis. Although the implementation of the SIMP method is straightforward and computationally effective, it may be difficult to find a complete Pareto-optimal set in a multi-objective optimization problem. In this study, to build a more convergent and diverse global Pareto-optimal set and reduce the GA computational cost, some individuals, with similar topology to the local optimum solution obtained from the SIMP using the weighted sum method, were introduced for the initial population of the GA. The proposed method was applied to a structural topology optimization example and the results of the proposed method were compared with those of the traditional method using standard random initialization for the initial population of the GA.

Visualization of lightning impulse current discharge on CFRP laminate

In this study, we performed optical visualization experiments on lightning impulse current discharge phenomena on carbon-fiber-reinforced plastic (CFRP) laminates. Lightning discharge is a phenomenon in which an extremely intense flash of light and heat is caused by a large electric current flow over a very short period of time; therefore, it is extremely difficult to observe. For this reason, we used a high-speed video camera to visualize the phenomenon at a frame rate of 1 Mfps. In addition, we used Schlieren photography to visualize shock waves propagating from the discharging electrodes. A lightning impulse current generator was used to replicate natural lightning strikes. We used two types of discharging electrodes: a conical electrode and a jet diverting electrode with an insulating sphere. The waveform of the applied lightning impulse current was T1/T2 = 18/55 [μs], and the maximum current was 40 kA.

Distributed strain and load monitoring of 6 m composite wing structure by FBG arrays and long-length FBGs

We equipped a composite wing structure fiber Bragg grating (FBG) arrays including 246 FBGs with 10 mm gauge length, eight and six long-length FBGs with 300 mm and 500 mm, respectively. The length of the wing was 6 m and it was made of carbon fiber reinforced plastics (CFRP). The sensing system based on optical frequency domain reflectometry (OFDR) was used in a series of load tests. The measured results by FBG arrays showed the overall deformation of the wing and good agreement with analysis results. Additionally, strain distributions of stress concentration zones were successfully measured by long-length FBGs.

DURABILITY AND DAMAGE TOLERANCE EVALUATION OF VARTM COMPOSITE WING STRUCTURE

Durability and damage tolerance of subcomponent and full-scale wing box structure fabricated by VaRTM are evaluated. Fatigue spectrum with load enhancement factor was applied to the test articles for 1 DSO of 40,000 flights. The Mini-TWIST fatigue spectrum is used for both tests. Then, impact damages are given to the skin stiffened by co-cured stringer and typical skin part by drop-weight to create the delamination. After that, impact damage growth is evaluated during 1 DSO fatigue spectrum and optimal inspection interval is examined. Finally, residual strength of structures is verified by ultimate load test with 150% design limit load. Applied strain level for Subcomponents are intentionally higher than original one in order to evaluate the structural performance in more critical condition. Non-destructive inspection is carried out by 3D ultrasonic scan system with multiple-array sensors to evaluate delamination growth. In Subcomponent test, stringer run-out shows local out-of-plane deformation and that causes disbonding of stringer termination. The disbonding area gradually increases during 1 DSO fatigue test. However, the structure did not show any degradation of structural performance. The damage tolerance tests verify that impact-induced delaminations have not grown throughout the 1 DSO. In the final ultimate load test, the load bearing-capabilities of present VaRTM wing structure have been verified and the structure could survive for 4 seconds without any detrimental deformation and damage growth.