Nobuo Takeda

• PhD
• Professor (Full) at The University of Tokyo

Carbon fibers and resin used in manufacturing carbon fiber-reinforced plastic composite structures flow before the resin solidifies, resulting in disrupted fiber orientation and non-uniform thickness. This process, known as consolidation, is critical for the quality of the composite structure, but no technology exists to measure the deformation in...

In recent automobile developments, the compatibility between a lighter vehicle body for lower fuel consumption and high clash safety performance has been an essential requirement. It is necessary to increase the energy absorption (EA) efficiency of car body frames, for which the continuous brittle destruction phenomenon of carbon fiber reinforced p...

Composite structures are generally considered to be difficult to apply to joining components. A T-joint is an important element in aircraft structures that transfers loads between vertical and horizontal panels. However, T-joints present cracks that occur in the deltoid during their manufacture because of process-induced cure and thermal stress. Su...

Moisture absorption and desorption by a matrix resin, and the resulting deformation, have a critical adverse effect on the shape stability of carbon fiber reinforced plastic space structures. This study evaluates the effect of the moisture content in prepreg sheets on the life-cycle behavior of the prepreg-based carbon fiber reinforced plastic. Aft...

Self-healing composites using microvascular channel networks have been intensively studied. Microvascular networks in composite in-plane directions are normally utilized to deliver healing agents to damaged areas. However, this channel configuration is not optimal to form robust networks and to infuse large damaged areas. This study proposes a self...

Moisture absorption and desorption by a matrix resin, and the resulting deformation, exert a critical adverse effect on the shape stability of carbon fiber reinforced plastic (CFRP) space structures. This study evaluates the effect of the moisture content of prepreg sheets on the life-cycle behavior of the prepreg-based CFRP. After evaluating the m...

One of the difficulties in composite structural application is joining components. A T-joint is a critical component in aircraft structures that transfers loads between vertical and horizontal panels. However, in T-joints, a critical concern is that cracks occur in the deltoid and immediately propagate along the flange-skin interface. Therefore, in...

Dimpling in the composite face sheets of honeycomb sandwich structures due to mismatch in the thermal expansion coefficients of the constituent materials was studied with emphasis on its monitoring and prediction. Strain distributions along optical fibers embedded in the face sheet were monitored during manufacturing. Dimple formation and in-plane...

Self-healing composites using microvascular channel networks have been intensively studied. Microvascular networks in composite in-plane directions are normally utilized to deliver healing agents to damaged areas. However, this channel configuration is not optimal to form robust networks and to infuse large damaged areas. This study proposes a self...

Composite tapered sections with ply drop-off are prone to delamination due to stress concentration at the edge of the terminated 0° plies. Currently quite gradual taper angle is used in aircraft composites to suppress delamination, which leads to weight increase. Structural modification that can suppress the stress concentration is necessary to rea...

We have been developing an Ultrasonic based structural health monitoring (SHM) system which can provide essential information on structural integrity of airframes. The information can contribute to create novel design philosophies, improve inspection activities in manufacturing processes, and optimization of aircraft operation with the condition-ba...

In thick thermoplastic composite laminates, nonuniform temperature distribution arises in the through-thickness direction during high-rate manufacturing processes. This causes the so-called thermal skin-core effect. The surface region solidified in advance constrains shrinking of the inside region, so nonuniform residual stress/strain distribution...

L-shaped composites are fundamental parts of complex-shaped structures and it is well-known that shape distortion (i.e., spring-in deformation) arises after curing due to the orthotropic nature of composites. This residual deformation significantly increases the manufacturing costs, attracting significant attention to the mechanisms of spring-in de...

L-shaped composites are fundamental parts of complex-shaped structures, and it is well-known that shape distortion (i.e., spring-in deformation) arises after curing due to the orthotropic nature of composites. This residual deformation increases the manufacturing costs, attracting significant attention to the mechanisms of spring-in deformation. Me...

A systematic study has been conducted to investigate the influence of silane treatment on the interfacial shear strength of glass fibre/epoxy composites by means of microbond tests, and to clarify the relationship between the interphase consisting of physisorbed and chemisorbed silanes on glass fibre surfaces and the corresponding interfacial shear...

In thick thermoplastic composite laminates, nonuniform temperature and cooling rate distribution arises in the through-thickness direction during cost-effective high-rate manufacturing processes. Annealing is often carried out after molding to homogenize degree of crystallinity (DOC) and to reduce residual stress. Even though the change in the resi...

One of the difficulties in composite structural application is joining components. A T-joint is one of the important elements in aircraft structures. T-joints often fail at low load in the curved region of the L-shaped parts or the deltoid area because of its low through thickness strength properties and cure-induced residual stress. Previous works...

Dimpling in the face sheets of honeycomb sandwich structures due to mismatch in the thermal expansion coefficient of the constituent materials, with emphasis on its monitoring and assessment, was studied by utilizing embedded distributed fiber optic sensors. Strain distributions along optical fibers embedded in the face sheet of the sandwich struct...

Fiber Bragg grating sensors (FBG) were embedded into the CF/PPS laminates to demonstrate the monitoring of the press forming of the L-shaped CFRTPs (Carbon Fiber Reinforced Thermoplastics). In-plane strain of the flexion represented a unique change from contact with the flat plate to position of bottom dead center. Residual strains along the FBG ar...

This study investigates the influence of macroscale skin-core residual stress and cooling rate on the impact response of aerospace grade carbon fibre/polyphenylenesulphide (CF/PPS). Numerical simulations are developed which analyse the thermal shrinkage and residual stress development of unidirectional (UD) lay-up configurations. Macroscale skin-co...

Process-induced shape distortion is generated in curved composite parts. In the accompanying paper, the authors developed a fiber-optic monitoring method and confirmed that chemical cure shrinkage induces through-thickness shear deformation, which is the key deformation affecting final shape. The present paper first investigated the effects of thic...

Process-induced shape distortion is generated in curved composite parts. Although the distortion mechanisms have been understood through considerable previous efforts, they were validated by indirect methods such as shape measurement, leaving some room for discussion. The present work developed a novel direct method using in-situ fiber-optic-based...

Development of new design features that stop cracks from growing above a critical size is one of the key steps to realization of boltless composite structures. The authors have proposed a fiber-reinforcement-based concept that introduces continuous fibers in the adhesive layer and suppresses the crack propagation using massive fiber bridging. Follo...

This paper reviews fiber optic sensor applications in the field of space engineering. Some of the R&D activities introduced are; (1) structural health monitoring of cryogenic liquid hydrogen tanks, (2) FBGbased hydrogen sensors, (3) thermal strain monitoring of sensing coils in fib

Vacuum-bag-only curing is an attractive out-of-autoclave method as an alternative to conventional autoclave curing. Previous extensive researches provided great insight into void formation during the vacuum-bag-only method and these findings are reflected in current vacuum-bag-only cure cycles to minimize void content. Cure process can be further i...

This study investigates the influence of cooling rate on the residual strain of the carbon fibre/polyphenylenesulfide unidirectional laminates. Three different cooling rates (−300℃/min, −100℃/min and −10℃/min) were applied to simulate a wide range of cooling conditions. The crystallisation behaviour which depends on the cooling rate was evaluated u...

This study proposes a new approach to determine key material parameters for stress/strain calculation of curing composite laminates and validate the simulation. Specifically, fiber Bragg grating (FBG) strain sensors are embedded in a composite laminate and the two key parameters for simulation, composite shrinkage strain and stiffness change during...

Indentation loading or low-velocity impacts on foam core sandwich structures can leave only barely visible damage on the face sheets while causing notable damage in the core due to the thin face sheets and relatively weak core. In practical applications, the measurement and damage detection can also be notably affected by environmental conditions a...

Prediction of the residual state of sandwich structures after impact or indentation loading is important for estimation of their residual properties and for damage detection purposes. An extended foam material model, that takes into account the degradation of elastic modulus during compression and the changed tensile response after compressive dama...

This study seeks to clarify the mechanism of strain development in curing a thick composite structure with a temperature distribution in the thickness direction. Strain developed during curing can be separated into two parts according to the causes. One is chemical cure shrinkage of the matrix; the other is thermal shrinkage (or expansion) of the c...

Our previous study proposed a hierarchical sensing-healing system combining a microvascular self-healing material and a fluid distribution system with local pressure monitoring. This study demonstrated the hierarchical system in a structural composite element. First, the overview of the system was given for the sake of the completeness and the tech...

Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber-reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG usin...

Foam core sandwich structures are rather vulnerable against transverse loading which can leave only barely visible damage in the structures. Environmental conditions can further affect the loading response and thus the formation of damage. To study this, uniaxial compression-tension loading tests were conducted at 30, 60 and 80℃ temperatures using...

Carbon fiber reinforced plastic (CFRP) pipes are key structural elements for observation satellites. Significant radial tensile stress, however, is induced in thick-walled CFRP pipes during curing, leading to premature delamination failure and performance degradation. This study proposes a residual stress-reduction method to develop a thick-walled,...

Stringent process control of bonding is one of the keys to realization of bonded joints in composite aircraft primary structures (i.e., realization of boltless structures). This study develops the first fiber-optic-based quality control technique. Bonding pressure and residual strain in the adhesive are monitored using a birefringence effect of emb...

This study demonstrated the first ultra-lightweight composite stiffened panel designed based on an SHM and rapid repair system. First, the feasibility and technical merit of the new design concept was discussed along the lines with the current damage tolerance philosophy. Next, the new design concept was validated using compression after indentatio...

Process-induced residual strain causes unexpected shape distortion, leading to premature failure and high manufacturing cost. Cure process simulation is an effective way to optimize the cure process in a reasonable manner. Accurate material properties (i.e., shrinkage strain and elastic modulus change during curing) are vital for high-fidelity simu...

Stress transfer efficiency for 60 walls multi-walled carbon nanotube (MWNT) was calculated by the shear-lag theory. The results indicated that stress transfer between walls is insufficient at several tens of nanometer from the end; however stress converged to the same value for adequate length. Effective young’s modulus was also calculated and indi...

This study combines our hierarchical fiber-optic-based delamination detection system with a microvascular self-healing material to develop the first autonomous sensing-healing system applicable to large-scale composite structures. In this combined system, embedded vascular modules are connected through check valves to a surface-mounted supply tube...

This paper presents effects of carbon nanotube (CNT) orientation angle distribution on elastic moduli of aligned CNT/epoxy composites that were fabricated with various volume fractions using hot-melt prepreg method. Tensile testing was conducted to evaluate the composites’ mechanical properties. The composites’ Young’s moduli increased with increas...

This study investigates the computer simulation of fracture process in compressive failure of cross-ply laminate of composite materials. The purpose of this study is to establish the numerical analysis method to understand the fracture mechanism and predict the mechanical response of composite materials through the computer simulation. The stacking...

This study investigates numerical analysis for effect of applied shear stress on longitudinal compressive strength of fiber reinforced composite materials. For this purpose, firstly numerical simulation of longitudinal compressive failure of composite materials is conducted. Simulated results show that when compressive failure initiates in the mate...

This study investigates the preparation for supercomputing of numerical simulation of fracture process of composite materials. The purpose of this study is to establish the numerical analysis method to understand the fracture mechanism and predict the mechanical response of composite materials through the supercomputing. The numerical model is cons...

This study investigates the numerical simulation and theoretical modeling of longitudinal and transverse compressive failure in fiber reinforced composite materials.Firstly the numerical simulation of longitudinal compressive failure is conducted.The simulated results show that at one moment of the loading,the localized deformation catastrophically...

This study investigates computational modeling of microscopic fracture process in compressive failure of quasi-isotropic laminate of composite materials. The purpose of this study is to establish the numerical analysis method to understand the failure mechanism and predict the mechanical response of quasi-isotropic laminate of composite materials t...

Airframe structures, especially composite structures, are prone to damage by tool drops, bird strikes, hailstones, etc. The authors have developed an optical fiber based impact damage detection system for composite airframe structure since 1998. In this method, impact locations are measured with the signals of multiple Fiber Bragg Grating (FBG) sen...

This study demonstrates the first autonomous sensing-healing system applicable to large-scale composite structures. The microvascular self-healing system is combined with our hierarchical fiber-optic-based sensing system. The hierarchical system is a fluid distribution system with a local pressure monitoring function, and the combined system offers...

To detect indentation or low-velocity impact induced damage in foam-core sandwich structures, a fiber-optic distributed strain monitoring system is applied to the structures. An optical fiber is embedded into the sandwich structures and the strains are measured using a Rayleigh scattering based monitoring system which offers high resolution. Indent...

Applying secondary bonding to places where carbon fiber reinforced plastic (CFRP) structures are conventionally bolted leads to significant cost and weight saving. However, it has yet to be utilized due to difficulties in quality control. Lack of local pressure in bonding process has detrimental influence on the quality of the cured adhesive layer....

This study investigates a numerical model for addressing strain localization appearing in fiber reinforced composite materials. Firstly numerical simulation of localization phenomenon in composite materials is conducted to understand how this deformation phenomenon appears in the material. Secondly mathematical equations expressing deformation of c...

A method of repairing an embedded optical fiber of a composite material structure including an embedded optical fiber embedded in a composite material, includes removing a portion of the composite material including a damaged portion of the embedded optical fiber to form an opening portion; polishing an end surface of the embedded optical fiber exp...

Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG usin...

This study investigates the numerical simulation and theoretical modeling of longitudinal compressive failure in fiber reinforced composite materials. Firstly the numerical simulation of longitudinal compressive failure is conducted. The simulated results show that at one moment of the loading, the localized deformation catastrophically appears in...

CFRP pipes are used in spacecraft to support heavy optical instruments. CFRPs’ low coefficients of thermal expansion and high stiffness improve the instrument performance. However, significant through-thickness strain arises in thick CFRP pipes in curing and operation at low temperature, resulting in delamination failure. In this study, we develope...

Pitch-based carbon fiber reinforced plastics (CFRP) have been widely utilized for observation satellites, improving their performance. Recently the size and stiffness required for the materials have been increased due to increased size of optical instruments. However, significant throughthickness tensile stress/strain arises during cure in thick hi...

In previous research, the authors studied detection of transverse cracks in CFRP laminates using small-diameter fiber Bragg grating (FBG) sensors. FBG sensors were embedded in cross-ply or quasi-isotropic laminates, and tensile tests were carried out. As transverse cracks occurred, a reflection spectrum of FBG sensors was deformed due to a non-unif...

A method is proposed to identify the various damage state in a composite laminate using an embedded fiber Bragg grating (FBG) sensor. Numerical analysis to calculate a reflection spectrum of an FBG sensor is directly linked to a damage analysis based on layer-wise finite element method. ill this damage analysis, cohesive elements are arranged at in...

Applying secondary bonding to places where carbon fiber reinforced plastic (CFRP) structures are conventionally bolted leads to significant cost and weight saving. However, it has yet to be utilized due to difficulties in quality control. Lack of local pressure in bonding process has detrimental influence on the quality of the cured adhesive layer....

Taking advantage of the sensitivity of ultrasonic waves to internal damages in composite laminates, the authors are constructing a new damage detection system. In this system, a piezo-ceramic actuator generates an ultrasonic wave at a surface of a CFRP laminate. After the wave propagates in the laminate, the transmitted wave is received by a fiber...

The objective of this study is evaluating the effect of stretching on the angular orientation of carbon nanotubes (CNT) and the mechanical properties of aligned CNT/epoxy composites. Stretching tests were conducted by tensile testing after fabricating prepregs with stretch ratios of 0%, 2%, 5%, 10% and 18%, respectively. Microscopic observations by...

Optical fiber sensors have attracted considerable attention in health monitoring of aerospace composite structures. This paper briefly reviews our recent advancement mainly in Brillouin-based distributed sensing. Damage detection, life cycle monitoring and shape reconstruction systems applicable to large-scale composite structures are presented, an...

This study examined the nanoscopic damage progression of aligned multi-walled carbon nanotubes (CNT)/epoxy composites under tensile loading using transmission electron microscopy (TEM). Aligned CNT/epoxy composite films (30 mu m thickness) were processed using a forest-drawn aligned CNT sheet and hot-melt prepreg method. Four film specimens, respec...

A surface layer formed of a composite material is stacked on the surface of a core layer formed of a foam synthetic resin material, and an arrester portion is provided in an interface region between the surface layer and the core layer to prevent the progression of delamination between the surface layer and the core layer. Optical fibers with grati...

Structural health monitoring refers to the process of making an assessment, based on nondestructive, in-situ, autonomous measurements, about the ability of a structure to perform its intended function. This paper presents work done on a bolted connection in carbon-fiber reinforced polymer composite materials. A composite specimen is bolted in a dou...

The authors proposed fiber-optic-based damage monitoring of carbon fiber reinforced plastic (CFRP) bolted joints. Optical fibers were embedded along bolt holes and strain change along the optical fiber induced by internal damage was measured by a Brillouin Optical Correlation Domain Analysis (BOCDA), which is a high spatial resolution distributed s...

A beamforming array technique with four sensors is applied to a cylindrical geometry for detecting point of impact. A linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. A beamforming technique in conjunction with an optimization scheme that incorporates...

L-shaped composite parts are structural key elements in complex-shaped aerospace composite structures, and life cycle cross-sectional strain change is their key. This study developed a fiber-optic-based life cycle monitoring system for L-shaped corner parts. A fiber Bragg grating (FBG) sensor was embedded in the through-thickness center of a corner...

Bearing damage in composite bolted connections (such as those commonly used in aerospace applications) is investigated through the application of ultrasonic guided waves. Specifically, identical macro-fiber composite sensor arrays were bonded to each of two identical composite plates. One plate was then inspected ultrasonically in the unloaded cond...

A residual facesheet dent on an indented or impacted foam-core sandwich structure significantly affects the residual mechanical properties and the detectability of the damage. However, previous studies have not sufficiently addressed residual dent formation during unloading and the subsequent relaxation. This study quantitatively clarifies the mech...

Sandwich structures may experience wide range of varying temperature and humidity conditions (e.g., in aerospace and marine applications). However, effect on especially the complex polymer-based foam core materials is still rather poorly known. Therefore, influence of the temperature and humidity on the mechanical behavior of polymethacrylimide (PM...

We have been developing a Structural Health Monitoring (SHM) System for Carbon Fiber Reinforced Plastic (CFRP) structure of an aircraft. This system consists of piezoelectric transducer (PZT) actuators, fiber Bragg grating (FBG) optical fiber sensors and a control device. This SHM system can monitor debonding in interface between a skin panel and s...

This paper presents outline of our structure health monitoring (SHM) project in Japan. We are developing four (4) SHM systems for composite structures of aircraft. This project is conducted by MHI (Mitsubishi Heavy Industries, Ltd.), KHI (Kawasaki Heavy Industries, Ltd.), FHI (Fuji Heavy Industries, Ltd.), MELCO (Mitsubishi Electric Corporation), Y...

Acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication is applied here to a carbon fiber composite laminate. Difficulties associated with this technique are investigated. It is noted that the accuracy of this technique depends strongly on the accuracy of the measurement of the time delays in...