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Journal of Materials Science 04/2012; 45(14):3957-3960. · 2.02 Impact Factor
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ABSTRACT: The tensile strength of unidirectional carbon fiber-reinforced plastic (CFRP) composites was predicted by numerical simulation plus size scaling. The fiber strength distribution used in the numerical simulation was determined from the fragmentation process in a single fiber composite. Since the experimental data obviously did not fit the normal Weibull distribution, we fitted them with the Weibull of Weibull model, considering the statistical distribution of scale parameters of fiber strength in the normal Weibull model. Moreover, the constitutive law of the matrix was derived from the stress–strain curves of the angle ply laminates, utilizing the micromechanics approach proposed by Tohgo et al. [9]. Based on these parameters, we simulated the tensile fracture of unidirectional CFRP composites with the spring element model (SEM). The predicted tensile strength by numerical simulation plus size scaling agreed well with the experimental data. The results also confirmed that the Weibull of Weibull model is important to predict size-dependent composite strength.
Advanced Composite Materials - ADV COMPOS MATER. 01/2010; 19(3):229-241.
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ABSTRACT: Numerical simulation by finite element analysis was used to investigate the relationship between the strength of glass fiber reinforced plastic (GFRP) and fiber length. Load speed dependability was also investigated, since thermoplastic resin used for GFRP exhibits much nonlinear stress—strain behavior and strong dependency on load speed. For this purpose, we conducted a periodic-cell simulation to address the effect of composite microstructure, matrix viscoplasticity, and microscopic damage (fiber break and matrix crack). When the fiber length was varied, the damage pattern was divided into two patterns: fiber-avoiding propagation and fiber-breaking modes of the matrix crack from fiber ends. When the matrix crack easily propagated in a fiber-avoiding way for shorter fiber lengths, the rate-dependent effect of the matrix was significant. Moreover, we considered the length at which the fracture mode changed based on this analysis, and compared it with the conventional critical length given by Kelly. Since the conventional critical length does not ensure improved composite strength, the consideration of the damage mode transition is essential for selecting the appropriate fiber length for strength improvement.
International Journal of Damage Mechanics - INT J DAMAGE MECH. 01/2010; 19(3):339-360.
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ABSTRACT: This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in composites influences the formation and growth of the cluster of fiber-end damage, which causes the damage mode transition. Since the composite strength is significantly reduced below the critical fiber-length for the transition to fiber-avoiding crack mode, we should understand the damage mode transition appropriately with the analysis on the cluster growth of fiber-end damage.
Advanced Composite Materials - ADV COMPOS MATER. 01/2009; 18(1):77-93.
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ABSTRACT: The single-fiber composite (SFC) has been widely used to quantify fiber strength and fiber–matrix interfacial properties of fiber-reinforced composites. Here, a numerical model with an embedded-process-zone model to permit both interface debonding and matrix cracking is used to predict the fragmentation process and the microscopic damage around fiber breaks in SFC tests as a function of the interface strength and toughness. For low interface strengths, interface debonding occurs. For intermediate interface strengths, matrix cracks occur and delay debonding. For high interface strengths, debonding does not occur and deformation is controlled by a matrix shear, with strain hardening playing an important role. Interface toughness plays a secondary role in determining the transitions in damage modes. Well-established models assuming a constant interfacial shear strength can fit SFC data for low interface strengths, but the interface strength parameter is unrelated to the actual shear strength. In the high-strength regime, a strain-hardening shear-lag model can fit the SFC data quite well. Overall, the fiber strength distribution can be obtained from SFC tests by fitting to the fragment length versus applied strain, but estimation of interfacial properties is difficult due to the transition in dominant deformation and damage mechanisms, including matrix cracking.
Modelling and Simulation in Materials Science and Engineering 06/2008; 16(5):055009. · 2.30 Impact Factor
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ABSTRACT: This paper investigates the effect of transverse cracks on the S
0 mode velocity in GFRP and CFRP cross-ply laminates, and proposes a new AE source location method that considers the change in the S
0 mode velocity due to the transverse cracks. We found experimentally that the stiffness and the velocity decreased as the transverse crack density increased. Analytical predictions deduced from the combination of the complete parabolic shear-lag analysis, the classical plate theory and the laminated plate theory are in good agreement with the experimental results. Utilizing this relationship between the velocity and the mechanical damage, we located AE sources of transverse cracks in cross-ply laminates with the calculated in situ velocity. We were able to show that highly accurate source location requires the reduction of the in situ value of the velocity. The present method is simple but quantitative and useful in health-monitoring for detecting and localizing the damage in composite structures.
Journal of Materials Science 03/2003; 38(8):1765-1771. · 2.02 Impact Factor
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ABSTRACT: The failure process of unidirectional BN-coated HI-NICALONTM SiC fiber reinforced glass matrix composites was examined under tensile loading. In situ observation of the mean matrix crack interval was conducted by the replica observation during tensile testing. Axisymmetric cylindrical models extended to the system considering the strength distribution of fibers were proposed to predict the whole stress-strain curve for comparison with the experimental results.
Journal of Materials Science 06/1999; 34(14):3405-3412. · 2.02 Impact Factor
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Rinsho hoshasen. Clinical radiography 05/1978; 23(4):491-5.
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ABSTRACT: A new numerical model is proposed for simulating the mechanical behavior of unidirectional composites which is based on a three-dimensional (3D) shear-lag model. The 3D shear-lag model considers the micro-damage phenomena of interfacial debonding and interfacial yielding. In order to confirm the validity of the model, the calculated stress concentration is compared with the HVD model (Hedgepeth JM, Dyke P. Local stress concentrations in imperfect filamentary composite materials. J Comp Mater 1967;1:294–309) in the appropriate limit. Monte Carlo simulations with the present shear-lag model were then conducted to obtain the ultimate tensile strength (UTS) as a function of fiber strength and interfacial properties. The damage progression and formation of clusters versus the type of interfacial damage, and the size-scaling of the tensile strengths, are carefully examined. Coupled with a size-scaling analysis, model predictions for tensile strength show good agreement with experiment.
Composites Science and Technology.
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ABSTRACT: This study proposes a new approach to monitoring the damage process in holed CFRP laminates using an embedded chirped fiber Bragg grating (FBG) sensor. To this end, we experimentally and numerically investigated the damage process and the damage-induced changes in the spectrum shape. It was experimentally confirmed that multiple types of damage (e.g., splits, transverse cracks and delamination) appeared near a hole, and that the spectrum shape of the embedded chirped FBG sensor changed as the damage extended. Our proposed simulation for the reflection spectrum considering the damage agreed with the experiments. Furthermore, this study investigated the effect of each damage pattern on the changes in the spectrum shape. Finally, based on these discussions, we present simple damage identifications with the embedded chirped FBG for the holed CFRP laminates under completely unloaded conditions.
International Journal of Solids and Structures.
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ABSTRACT: This study proposes a numerical method for analyzing and simulating the failure of unidirectional fiber-reinforced composites using the spring-element model (SEM). We compare the stress distribution calculated by this method with that of the 3D finite-element method (FEM). A Monte Carlo simulation is performed to simulate failures by this method. The computational efficiency is discussed in comparison to our previous SLM. Additionally, we demonstrate a hybrid (SEM/FEM) analysis to show the compatibility for the structural analysis. We found this method accurate and efficient for simulating and analyzing the failure process in the damaged composite.
Composites Science and Technology.
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ABSTRACT: A new procedure is proposed to predict the strength of multi-fiber composite based on the single fiber composite test. First, the flaw distribution in an embedded fiber is estimated with the statistical simulation. The stress distribution in the simulation is obtained by the elastoplastic shear-lag analysis considering the linear strain hardening effect of matrix. The simulated results are found to fit well with the experimental data, which shows the validity of the present simulation to estimate the statistical strength parameters for the embedded fiber. Then, the multi-fiber composite strength is predicted based on the obtained statistical fiber strength parameters. The stress profile in the multi-fiber composite is calculated with the elastoplastic three-dimensional (3D) shear-lag-analysis. The predicted strength via the weakest size scaling technique has a good agreement with our previous experimental data.
Composites Part A: Applied Science and Manufacturing.
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ABSTRACT: We propose a new approach to predicting multiple damage states in composite laminates using embedded fiber Bragg grating (FBG) sensors. FBG sensors are sensitive to a non-uniform strain distribution along their longitudinal direction, and the effects appear in the power spectrum of the reflected light from the gage section. In this paper, we propose a numerical model to predict both the damage process of the laminate and the change of the reflection spectrum from the FBG sensor. The proposed approach is then applied to explain the results of a quasi-static tensile test for a notched CFRP cross-ply laminate with an embedded FBG sensor. The results demonstrate that the proposed approach is useful for predicting multiple damage states in composite laminates.
Composites Science and Technology.
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ABSTRACT: This study proposes damage identification for holed CFRP cross-ply laminates using an embedded chirped fiber Bragg grating (FBG) sensor. We investigated changes in the reflection spectrum of the chirped FBG sensor due to damage near the hole. The reflection spectrum of the chirped FBG sensor was further studied by estimating the strain distribution along the gage section as an inverse problem based on the spectrum shape. We experimentally confirmed that the reflection spectrum of the chirped FBG sensor changed distinctively within certain wavelengths when each type of damage (transverse cracks or delamination) occurred and extended. Local strain changes were estimated from the reflection spectrum of the chirped FBG sensor; their locations coincided with those for the observed transverse cracks. We also demonstrate damage identification for the holed specimen and conclude that this feature of the chirped FBG sensor provides successful identification of a damage pattern near the hole.
Composites Science and Technology.
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ABSTRACT: The present paper addresses the correlation between mechanical damage and the change in electrical resistance of CFRP under tensile loading. A linear relation between the strain and the electrical resistance of single carbon fibers was obtained experimentally, and the electrical behavior of CFRP under tensile loading was investigated. At stresses approaching the failure stress, the composite resistance rises non-linearly, which is attributed to damage in the form of broken fibers. These experiments lead to the concept of electrical ineffective length over which a broken fiber does not carry electric current, in analogy to the well-established mechanical ineffective length over which a broken fiber carries reduced stress. Based on this concept, a DC circuit model consisting of a serial array of discrete parallel cells of length equal to the electrical ineffective length is proposed to explain the resistance evolution in the composite. An analytical model for fiber damage evolution within the electrical ineffective length is constructed using the Global Load Sharing model and the Weibull fiber strength distribution. The model successfully explains the experimental results on the resistance change of CFRP under tensile loading with an electrical ineffective length of 5 mm.
Composites Part A: Applied Science and Manufacturing.
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ABSTRACT: This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as (TII,max, GIIc) = (75 MPa, 200 J/m2). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.
Materials Science and Engineering: A.
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ABSTRACT: This study proposes a new method to estimate the damage patterns of notched composite laminates as an inverse problem using the reflection spectrum of embedded Fiber Bragg Grating (FBG) sensors. The damage pattern near the notch is analyzed by a layer-wise finite element model with cohesive elements to represent various cracks. The reflection spectrum of the FBG sensor is then analyzed from the strain distribution obtained in the damage analysis. The damage pattern is optimized as an inverse problem based on the above analyses while the spectrum shape is adopted as the objective function. The damage pattern is expressed by the residual strength distribution of the cohesive elements in the estimation scheme. The applied strain is also estimated by the wavelength shift of the reflection spectrum. The damage pattern and the applied strain estimated from the measured spectrum are found to agree with the experimental results.
Composites Science and Technology.
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ABSTRACT: A numerical model of the progressive damage in cross-ply laminates (e.g., transverse cracks, interlaminar delaminations, and fiber breaks) is proposed. In this model, the embedded process zone (EPZ) model is used for the transverse cracks and interlaminar delaminations; the truss elements are used to express the fiber breaks. First, we describe the formulation and algorithm of this model. Second, we calculate the transverse cracking stress in CFRP [0/90]s laminates and compare it with the experiments by Boniface et al. The comparison validates that our model can appropriately simulate the onset and accumulation of transverse cracks for an arbitrary thickness of the 90° ply to the 0° ply with a set of parameters. Finally, this model is applied to our experiments for GFRP [90/0]s laminates. The simulated results reproduce the complicated progressive damage in GFRP [90/0]s laminates very well.
Composites Science and Technology 68:2282-2289. · 3.14 Impact Factor
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ABSTRACT: This paper investigates the tensile damage process and strength in glass fiber reinforced plastics (GFRP) cross-ply laminates experimentally and numerically. Detailed observations are conducted with a video microscope to comprehend the damage process in the 90° ply. Experimental results indicate that the strength can be approximately estimated from the strength of the 0° ply, independent of the thickness of the 90° ply. Based on these experimental results, we propose a new Monte-Carlo simulation for predicting the damage process and strength in cross-ply laminates. The transverse cracks are expressed by utilizing the cohesive elements, considering both local strength and fracture toughness of the 90° ply. Consequently, the stress–strain relationship, the crack progress, and some characteristic phenomena, such as the constrained effect and incomplete transverse cracks, observed in the experiments can be expressed with this simulation.
Materials Science and Engineering: A. 383(2):381-389.
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ABSTRACT: A new model is proposed for multiple matrix cracking in order to take into account the role of matrix-rich regions in the cross section in initiating crack growth. The model is used to predict the matrix cracking stress and the total number of matrix cracks. The model converts the matrix-rich regions into equivalent penny shape crack sizes and predicts the matrix cracking stress with a fracture mechanics crack-bridging model. The estimated distribution of matrix cracking stresses is used as statistical input to predict the number of matrix cracks. The results show good agreement with the experimental results by replica observations. Therefore, it is found that the matrix cracking behavior mainly depends on the distribution of matrix-rich regions in the composite.
Acta Materialia. 47(17):4299-4309.
