Search

The fundamental aeroelastic effect of the corrugation of an insect-sized simple flapping wing is numerically investigated. A baseline model for a corrugated flapping wing is constructed such that the balance among the aerodynamic, elastic, and inertial forces acting on the wing matches that acting on insect wings in accordance with the measured material properties of insect wings. The thickness of the corrugated airfoil and the amplitude of corrugation are systematically varied around the baseline to modulate both the natural frequencies and mode shapes. Unsteady aeroelastic simulation based on three-dimensional Naiver–Stokes equations is conducted for the corrugated flapping wings. The numerical simulation is validated by measuring the natural frequency and mean lift of corrugated flapping wings. The results indicate that the corrugation of insect flapping wings is aeroelastically effective in providing both an appropriate passive deformation and a light-weight wing. To maximize the hovering efficiency, the optimal amplitude of corrugation is 1.7 to 2.6% of the chord length, the wing mass ratio is 0.7 to 1.5, and the natural frequency is 2.1 to 2.6 times as large as the input flapping frequency. These optimal design parameters are close to (but slightly smaller than) those of insect wings., AIAA Journal, 60(5), pp. 3180-3193; 2022

High-velocity impact of foreign objects such as small stones will produce complex damage in composite laminates, which will severely degrade residual strength. This chapter first describes high-velocity impact tests for carbon fiber-reinforced plastic (CFRP) laminates and then observes damage states caused by near-perforation impacts. Extensive delamination and fiber breaks as well as matrix cracks appeared regardless of the stacking sequence. This study also quantitatively evaluates the influence of the stacking sequence and the material system (i.e., the presence or absence of toughened interlayers) on the damage area. Finally, the mechanisms of high-velocity impact damage in CFRP laminates are discussed, based on the observations.

Lamb wave propagation must be understood comprehensively for simply evaluating delamination during ultrasonic testing. However, the difference between wave propagation, visualized using laser Doppler vibrometer and pulsed-laser scanners, has not been sufficiently investigated, and knowledge of optimal conditions for evaluating delamination is limited. Thus, in this study, the mode conversion and multiple reflections of Lamb waves propagating in a delaminated cross-ply laminate were visualized using different laser scanners, delamination depths, and wave incident angles. Delamination was characterized using maximum-amplitude map postprocessing under specific conditions. Further numerical analysis revealed that owing to multiple reflections of the antisymmetric mode in incident and mode-converted waves, standing waves were generated in the delaminated sublaminate. Dispersion curve and flexural stiffness calculations confirmed the conditions required for high-amplitude standing waves, thereby providing guidelines for simply and reliably evaluating delamination during inspections.

In industrial processes, piercing and trimming are essential because composite structures are usually manufactured in a near-net shape to reduce machining operations. Punching and shear cutting using out-of-plane shear loading are expected to increase productivity. Nevertheless, little is known about the effects of such operations on polymer-matrix composites. This study presents on the characterization of piercing damage in typical carbon fiber reinforced plastic (CFRP) cross-ply laminates [0°2/90°2]s after punching using quasi-static (QS) and drop-weight impact (DWI) loadings. During QS punching, the upper and lower ply interfaces delaminate due to the high shear stress to cut fibers and gradual shear deformation in the middle ply; however, during DWI punching at a low impact velocity, delamination of the lower ply interface can be reduced due to the localization of shear deformation, as compared to that in QS punching. Finally, the damage accumulation process during DWI punching is discussed.

Fast machining is essential for mass production of composite structures, and out-of-plane shearing, also known as die cutting, is appropriate for trimming. Nevertheless, little is known about shearing of polymer-matrix composites. This study was done to investigate the damaging impact of shearing conditions on carbon fiber reinforced plastic (CFRP) laminates. The clearance and temperature affected the damage progress, while the cutting speed in the tested range had negligible effect. In cross-ply laminates, delamination and matrix cracks first appeared in a narrow shearing zone, and with further loading longitudinal plies broke at the dies’ edges. Although delamination occurred only in a narrow shear-stress concentrated zone in the case of a small clearance, it was significant for a large clearance, owing to the local bending deformation. A temperature slightly lower than the glass transition temperature narrowed the delamination area, owing to the increase in the interlaminar fracture toughness as well as insignificant strength degradation of the matrix.

Modeling the inhomogeneous microstructures of fibrous tows is important for analyzing the process of resin transfer molding because dual-scale pores in a preform can lead to void formation. This study focused on the development of a microscopic flow analysis method to predict the impregnation of fiber bundles. The moving particle semi-implicit method was adopted to model the microstructure of a fiber bundle explicitly and inter-particle potential force was introduced into the numerical model to take account for the capillary effect. The predicted process of impregnation and void formation agreed with empirical observations. The developed approach was applied to predict the relationship between the modified capillary number and void content to identify the optimal molding conditions to reduce microvoids. The obtained relationship reproduced the trends of a reported experiment, which indicates that the proposed approach will provide information about optimal conditions for minimizing void content.

Although techniques to visualize ultrasonic wave propagation help to detect defects, quantitative evaluation using these techniques remains a significant challenge. In this study, a topology-optimization-based damage identification method combined with an ultrasonic wave visualization technique is applied to the experimental results, and its performance is evaluated. This method estimates the target crack as the distribution of ‘damage parameters’ that reproduces the experimentally visualized ultrasonic wave propagation in an inverse analysis model. The objective function of the optimization was the sum of the squared error between the maximum amplitude distribution obtained in the experiment and finite element analysis. Our results suggest that the crack identification results depend on the incidence angle of the ultrasonic wave to the target crack. This is because the low amplitude in the downstream region of the ultrasonic wave to the crack causes low sensitivity of the objective function. Crack identification was performed using the dataset of ultrasonic wave propagation incident from two directions. The crack could be identified with high accuracy provided the sensitivity of the objective function was high in the entire design domain. Based on this mechanism of crack identification, this study proposes two indices to evaluate the validity of crack identification results in actual inspections.

This paper presents a stiffness and permeability multi-objective optimization method for carbon-fiber-reinforced plastic mesostructures based on a homogenization method. To reduce the computational cost of dealing with multiple design variables for complicated fiber mesostructures, we generate and extract effective design variables from optimization results derived from a smaller number of design variables. We applied the proposed method to optimization of the in-plane and out-of-plane stiffness and permeability of non-crimp fabrics. The optimization results showed that the application of effective design variables enabled attainment of an improved elastic modulus and permeability. From investigations of the obtained optimized design, we clarified the trade-off relationship between the elastic modulus and permeability, and elucidated the effects of dimensions of non-crimp fabric mesostructures on the elastic modulus and permeability.

Understanding the shear behavior and resulting fiber failure of fiber-reinforced plastics is required for better prediction of their behavior during the machining process, but knowledge regarding the shear strength of fiber failure is limited. In this study, out-of-plane shear tests were conducted to observe the shear behavior of carbon fiber-reinforced plastic laminates subjected to high shear stress exceeding the shear strength of matrix failure. The longitudinal fibers in carbon fiber-reinforced plastic unidirectional laminates were cut by shear loading without severe internal damage and the maximum shear stress causing progressive fiber breaks was much higher than the shear strength of matrix failure. This result suggested the possibility of out-of-plane shearing as a machining method for fiber-reinforced plastics and shear tests were subsequently performed for carbon fiber-reinforced plastic cross-ply laminates. Delamination was generated by high shear stress to cut the reinforcing fibers, but the size of the remaining damage was small even in the thermoset carbon fiber-reinforced plastic laminates in which delamination likely occurs, without any optimization of the trimming conditions.

In mode II interlaminar fracture toughness tests of composite laminates, the fracture toughness evaluated based on linear elastic fracture mechanics deviates from the true toughness due to the material nonlinearity of the matrix. In this study, an elastoplastic finite-element analysis was performed on a new quasi-static mode II interlaminar fracture toughness test, i.e., the doubly end-notched tension (DENT) test, to investigate the difference between the perceived energy release rate and the J-integral. The effect of material nonlinearity was compared with other quasi-static mode II interlaminar fracture toughness tests: three- and four-point bend end-notched flexure tests. Analysis of the DENT showed that for a given J-integral loading, the size of the plastic zone at the delamination crack tip was the same regardless of the crack length. The difference between the perceived energy release rate and J-integral in the DENT test with respect to the plastic zone size was independent of the crack length, and was smaller compared with that of flexure-type tests. Furthermore, the compliance calibration method was applied to the elastoplastic analysis results of the DENT test to reduce the evaluation difference of the energy release rate.

This paper quantitatively clarifies the effect of the fiber cut angle on the shearing strength of carbon-fiber-reinforced thermoplastic laminates. First, the shearing strength of the unidirectional and cross-ply laminates was measured at various cut angles. Next, two mechanics models, a rule-of-mixture-based model and a failure criterion model, were established to predict the shearing strength of the unidirectional and cross-ply laminates. The rule-of-mixture model explains the effect of the cut angle on the shearing strength of the unidirectional laminate. The failure criterion model predicts the dependence of the cut angle on the shearing strength for both laminates. Finally, finite element analysis was performed to semi-quantitatively evaluate the assistance effect of bending stress. It was revealed that the effective bending stress is almost equivalent to the stress averaged over approximately the one-layer thickness from the surface.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2017-08-27, 資料番号: PA1820040000

A multi-objective optimization (MOO) approach for multi-point injection of resin-transfer molding (RTM) is proposed to investigate the trade-off relationship between productivity and quality for composite structures. With this approach, the optimum gate positions for their molding properties are evaluated using finite-element analysis (FEA) with a multiple-objective genetic algorithm (MOGA), and the trade-offs are visualized with the combination of a self-organizing map (SOM) and a scatter plot matrix (SPM). We applied this approach to RTM for flat-plate and rib models. For the flat-plate model, we found a negative correlation between fill time and weld line contents, and between fill time and dry spot contents. These results imply difficulty for simultaneous reduction of cycle time and void contents. For the rib model, some tendencies agree with those of the flat-plate model, and others do not. This difference comes from complexity of structure. We also found Pareto solutions that satisfy both productivity and quality for the flat-plate and rib models (i.e., gate positions such as a combination of diagonal and quadrangle positions for the flat-plate model, and aggregation of gate positions at a beam part for the rib model). Furthermore, we conducted simple experiments for the flat-plate model to validate the simulation result. The trends acquired from MOO qualitatively agree with the experiments.

This study evaluated fatigue-induced disbond areas in carbon fiber–reinforced polymer double-lap joints using embedded fiber Bragg grating sensors. When the disbond grew by cyclic loading, the embedded fiber Bragg grating sensors yielded reflection spectra having two peaks representing a step-like strain distribution generated by the disbond; the peak at the shorter wavelength corresponded to the unloaded disbond region. The ratio of the peak intensity at the shorter wavelength to that at the longer wavelength increased gradually with increasing disbond length. The relationship between the peak intensity ratio and the disbond length was analyzed by coupled structural–optical analysis and was validated by comparing analytical peak intensity ratio with the experiment results. The disbond length was then estimated from the measured spectra based on this analytical calibration relationship, but the estimated disbond area exceeded that observed using the ultrasonic C-scan technique. Additional experiments including destructive observation of the adhesive suggested that an embedded fiber Bragg grating sensor could detect a moving disbond tip earlier than conventional nondestructive techniques.

Particle simulation methods represent deformation of an object by motion of particles, and their Lagrangian and discrete nature is suitable for explicit modeling of the microstructure of composite materials. They also facilitate handling of large deformation, separation, contact and coalescence. Mesh-free particle methods will thus be appropriate for a part of issues throughout the lifecycle of composite materials despite their high calculation cost. This study focuses on three particle simulation methods, namely, smoothed particle hydrodynamics, moving particle semi-implicit method, and discrete element method, and reviews approaches for modeling composite materials through these methods. Applicability of each method as well as advantages and drawbacks will be discussed from the viewpoint of engineering of composite materials. This reviewing study suggests capability of particle simulation methods to handle multiphysics and to predict various complex phenomena that necessitate explicit modeling of the material’s microstructure consisting of reinforcements (inclusions), matrix, and voids.

This study investigated the stress recovery of aligned multi-walled carbon nanotubes (MWCNTs) embedded in epoxy using Raman spectroscopy, and evaluated interfacial shear stress between MWCNTs and epoxy using shear-lag analysis. To this end, ultralong aligned MWCNTs (3.8 mm long) were embedded in epoxy to obtain Raman spectra at multiple points along the MWCNTs. Downshift of the G′-band due to tensile strain was measured from the nanotube end to the center, and the strain distribution of embedded MWCNTs was evaluated successfully. Interfacial shear stress was then estimated by minimizing the error between the shear-lag analysis and measured strain distribution. The maximum interfacial shear stress between the embedded MWCNTs and epoxy was 10.3–24.1 MPa at the failure strain of aligned MWCNT-reinforced epoxy composites (0.46% strain). Furthermore, the interfacial shear stress between an individual MWCNT and epoxy was investigated.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2019-11-28, 資料番号: PA2020013000

This study proposes a new damage identification method based on topology optimization, combined with visualized ultrasonic wave propagation. Although a moving diagram of traveling waves aids in damage detection, it is difficult to acquire quantitative information about the damage, for which topology optimization is suitable. In this approach, a damage parameter, varying Young&rsquo, s modulus, represents the state of the damage in a finite element model. The feature of ultrasonic wave propagation (e.g., the maximum amplitude map in this study) is inversely reproduced in the model by optimizing the distribution of the damage parameters. The actual state of the damage was successfully estimated with high accuracy in numerical examples. The sensitivity of the objective function, as well as the appropriate penalization exponent for Young&rsquo, s modulus, was discussed. Moreover, the proposed method was applied to experimentally measured wave propagation in an aluminum plate with an artificial crack, and the estimated damage state and the sensitivity of the objective function had the same tendency as the numerical example. These results demonstrate the feasibility of the proposed method.

This study presents a simple approach to model unidirectionally arrayed chopped strand (UACS) laminates via the extended finite-element method to represent slits (i.e., fiber cutting lines). This enables the introduction of slits independent of the finite-element mesh and reduces the effort to represent a complex discontinuity pattern when compared to standard modeling using double nodes. The laminated structure was represented by stacking two-dimensional layers, and cohesive elements were inserted into the layer interfaces to predict the extension of delamination. Damage progress in CFRP quasi-isotropic laminates with diagonal continuous slits were analyzed via the present approach, and the effect of the angle between the slit line and fiber direction on the tensile strength was investigated. The predicted strength was in agreement with the reported experiment results within the examined slit angle range. A numerical study revealed that the strength of the UACS laminates was enhanced by a low inclined slit angle.

SUMMARY This study proposes smoothed particle hydrodynamics (SPH) in a generalized coordinate system. The present approach allocates particles inhomogeneously in the Cartesian coordinate system and arranges them via mapping in a generalized coordinate system in which the particles are aligned at a uniform spacing. This characteristic enables us to employ fine division only in the direction required, for example, in the through-thickness direction for a thin-plate problem and thus to reduce computation cost. This study provides the formulation of SPH in a generalized coordinate system with a finite-deformation constitutive model and then verifies it by analyzing quasi-static and dynamic problems of solids. High-velocity impact test was also performed with an aluminum target and a steel sphere, and the predicted crater shape agreed well with the experiment. Furthermore, the numerical study demonstrated that the present approach successfully reduced the computation cost with marginal degradation of accuracy. Copyright © 2015 John Wiley & Sons, Ltd.

A chromiummolybdenum steel composed of 0.20 mass% carbon was used as a starting material. Three kinds of specimens having different case depths were made by carburizing and quenching. Using the scanning electron microscope, the crystallographic information was measured on the cross-sectional hardened layer by EBSD (electron backscattering diffraction) technique. The KAM (kernel average misorientation, Θ) maps were calculated from the carburized surface to the interior below the case depth of each specimen. The area-average, Θmean, of the KAM map was compared to the case depth and the cross-sectional residual stress distribution measured by x-ray. As a result, the area-average of the hardened layer was larger than that of the interior of specimen after quenching. The estimated depth of the increment in the Θmean was found to accord to the case depth and be proportional to the depth in which large compressive residual stress was distributed on the gradually polished surface. Therefore, both the case depth and eigen strain distribution that induce the compressive residual stress are indirectly estimable by electron backscattering diffraction method.

This study experimentally and numerically investigated the damage extension of a brittle monolithic silicon carbide plate in response to the high speed impact of a projectile. An out-of-plane impact of a silicon nitride sphere with a velocity of 50 to 600 m/s induced multiple ring cracks on the contact surface. A crater, a cone crack, and a median crack were observed in the cross section under the contact point. The generation and extension of the damage were numerically studied based on linear fracture mechanics. A dynamic stress analysis using the finite element method demonstrated that the distribution of the principal axis corresponding to the maximum principal stress aligned radically from the contact point to induce a circular crack on the surface.

High-velocity impact damage in CFRP laminates was studied experimentally and numerically. Part I of this study observed and evaluated near-perforation damage in the laminates and characterized the damage pattern experimentally. Part II predicts the extension of high-velocity impact damage based on smoothed particle hydrodynamics (SPH), which facilitates the analysis of large deformations, contact, and separation of objects. A cross-ply laminate was divided into 0 degree and 90 degree layers, and virtual interlayer particles were inserted to express delamination. The damage patterns predicted on the surfaces and cross-sections agreed well with the experiments. The analyzed delamination shape was similar to that resulting from a low-velocity impact, consisting of pairs of fan-shaped delaminations symmetric about the impact point. Finally, the mechanisms of high-velocity impact damage in CFRP laminates are discussed based on the observations and numerical analyses., 資料番号: PA1420009000

A hollow cylinder specimen of Cr-Mo steel with 0.20 mass% C was used as a model which simplified a motor cycle transmission gear. The specimen was carburized in carrier gas and quenched in oil bath. After quenching, the internal residual strain distributions in the radial, axial and hoop directions were mapped nondestructively by neutron strain scanning, and were compared with results of elastoplastic finite element analysis. The carbon content and hardness gradients were also measured to determine the case depth. Residual strain was calculated from lattice spacing change. In this study, unstressed lattice spacing was determined experimentally by measuring diffraction angle of coupons that were cut from the interior of the same carburized cylinder specimen. As a result, the carbon content and hardness distributions were almost accorded with finite element analysis results. On the other hand, the measured strains in some measuring points discorded with the analyzed weighted average strains. The peak widths in the interior of specimen equaled to that of unstressed coupons. Internal residual strain distributions were complicated and found to be elastic strains that were balanced with equivalent plastic strains due to transformation plasticity of case layer.

800x600 The short and long Japanese swords “WAKIZASHI” (back up sword of the main sword, “KATANA”) were made by one sword craftsman. The short and long swords “WAKIZASHI” were machined by rough grinding and final hand polishing, respectively. The microstructure, carbon content and hardness of short sword were measured experimentally on the cross section of sword blade. The 2θ-sin2ψ diagrams from Fe-211 plane using Cr-Kα radiation on the ground and polished blade were measured. An influence of final hand polishing process on the surface residual stress field of sword blade was examined. As a result, biaxial principal compressive residual stresses were generated and had constant stress gradients in depth on the ground and polished surfaces because the ψ-splitting was not observed and the measured 2θ vs. sin2ψ relations could be approximated as a parabolic curve. Large compressive residual stresses more than −1.0 GPa were distributed on the ground surface from “HASAKI” to “HAMON” of short sword. The surface compressive residual stress and its gradient were diminished gradually from “HAMON” to “MUNE” (the ridge of sword). On the other hand, compressive residual stresses more than −650MPa were distributed on the pol­ished surface from “HASAKI” to “HAMON” of long sword. The surface compressive residual stress and its gradient were also diminished gradually from “HAMON” to “MUNE”, and the residual stress gradient in the transverse direction were greatly degraded in comparison to the short sword. Additional compressive residual stress field induced by rough grinding was superimposed on the residual stress field after tempering process. The residual stress field near the blade surface after rough grinding was released partly by final hand polishing. Normal 0 21 false false false DE X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Century","serif";}

This study investigated mechanisms of the extension of high-velocity impact damage in CFRP laminates. To this end, damage states due to near-perforation impact were studied in detail. This study consists of two parts. Part I presents the experiment results of high-velocity impact tests for CFRPs with specified stacking sequences. A crater and splits were observed on the impacted surface, while multiple splits with fiber breaks extended on the back surface. The cross-section beneath the impact point included catastrophic ply failure with extensive fiber breaks. Impacted specimens also exhibited a particular delamination pattern consisting of pairs of symmetric fan-shaped delaminations emanating from to the impact point and elongated delamination along the cracks in the bottom ply. These damage patterns were common to all of the stacking sequences. Part II of this study presents a numerical analysis of high-velocity impact based on smoothed-particle hydrodynamics and discusses damage extension mechanisms.

This paper simulated the microscopic flow in a fiber bundle using the moving particle semi-implicit (MPS) method. Two phases (resin and air) were directly modeled to clarify the detailed mechanism of air entrapments in a fiber bundle. An external force was then introduced into the Navier–Stokes equation using a quasi-potential term to express the wettability between fiber and resin. To validate the MPS method for application to resin flow, we simulated a droplet of resin and the capillary flow of resin between the fibers. To validate the present approach, we simulated water-and-air two-phase flow and compared the simulation results with experiment results. The simulated results for water flow agreed well with the experiment results. Based on these validations, resin-and-air two-phase flow in a fiber bundle was simulated to analyze void formation in a fiber bundle. The simulation indicates that void formation depends on fiber arrangement as well as wettability.

This study investigates characteristics of foreign-object damage in plain-woven SiC/SiC composites after thermal loading. High-speed impact tests were conducted on virgin specimens, thermally exposed specimens, and thermally shocked specimens, in which the maximum temperature during thermal loading was 600 °C or 1000 °C. An oxide layer was generated on the specimen surface by thermal loading at 1000 °C. Damaged areas on the front and back surfaces induced by particle impact were independent of thermal loading. However, in specimens thermally loaded at 1000 °C, brittle failure, i.e. cone cracking without fiber pull-out, occurred due to oxidation of the fiber/matrix interfaces, and the ballistic limit velocity significantly decreased. Finally, the ballistic limit is predicted using static strength properties, and the effect of thermal loading on impact resistance is discussed.

This study investigated damage identification in holed CFRP laminates under cyclic loading by using an embedded fiber Bragg grating (FBG) sensor. Ply cracks and delamination extended near the hole with an increasing number of cycles, and the reflection spectrum from the FBG sensor was distorted. Moreover, debonding growth of the FBG sensor was observed. This study then estimated laminate damage pattern from reflection spectra and investigated the influence of the sensor debonding on damage identification. The debonding length was estimated from the spectrum simulated with a given debonding length and was successfully identified only when an appropriate damage pattern was assumed. Moreover, greater debonding induced invalid damage-pattern estimates, even if the debonding length was given in the estimation. The damage identification for simulations and for experiments required half of the intact gage section. These estimates indicated that information on the damage pattern disappeared from the spectrum shape because of debonding.

This paper presents empirical models for predicting matrix crack density in a carbon fiber reinforced plastic (CFRP) cross-ply laminate under static-fatigue and cyclic-fatigue loadings. First, a modified slow crack growth (SCG) law, that covers the whole range of stress ratio R of tension-tension fatigue (0 ≤ R ≤ 1), was proposed. The modified SCG law and three conventional SCG laws were then combined with Weibull's probabilistic failure concept for predicting fatigue matrix crack density in a cross-ply laminate. Matrix crack density was expressed as a function of R, the maximum stress in the transverse ply and the number of cycles. Next, fatigue tests were performed for R of 0, 0.2, 0.4, 0.6, and 1 to determine the applicability of these four models. Finally, constant fatigue life (CFL) diagrams were investigated based on the modified model. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers