Applied Composite Materials (v.25, #5)

Application of Bionic Design to FRP T-Joints by Guang-Min Luo; Chia-Hung Kuo (983-999).
We applied the concepts of bionics to enhance the mechanical strength of fiberglass reinforced plastic T-joints. The failure modes of the designed arthrosis-like and gum-like joints were determined using three-point bending tests and numerical simulations and compared with those of normal T-joints bonded using structural adhesives. In the simulation, we used cohesive elements to simulate the adhesive interface of the structural adhesive. The experimental and simulation results show that the arthrosis-like joint can effectively delay the failure progress and enhance the bonding strength of T-joints, thus confirming that an appropriate bionic design can effectively control the bonding properties of structural adhesives.
Keywords: Bionics; Numerical simulation; Structural adhesive

In this thesis, a double-scale model for 3 Dimension-4 directional(3D-4d) braided C/SiC composites(CMCs) has been proposed to investigate mechanical properties of it. The double-scale model involves micro-scale which takes fiber/matrix/porosity in fibers tows into consideration and the unit cell scale which considers the 3D-4d braiding structure. Basing on the Micro-optical photographs of composite, we can build a parameterized finite element model that reflects structure of 3D-4d braided composites. The mechanical properties of fiber tows in transverse direction are studied by combining the crack band theory for matrix cracking and cohesive zone model for interface debonding. Transverse tensile process of 3D-4d CMCs can be simulated by introducing mechanical properties of fiber tows into finite element of 3D-4d braided CMCs. Quasi-static tensile tests of 3D-4d braided CMCs have been performed with PWS-100 test system. The predicted tensile stress-strain curve by the double scale model finds good agreement with the experimental results.
Keywords: 3D-4d braided CMCs; Double-scale model; Crack band theory; Cohesive zone model; Transverse tensile

Damage evaluation of laminated composite material using a new acoustic emission Lamb-based and finite element techniques by Jalal Yousefi; Mehdi Ahmadi Najfabadi; Hossein Hosseini Toudeshky; Mehdi Akhlaghi (1021-1040).
In this paper, a very promising procedure is proposed to evaluate delamination using Acoustic Emission (AE) technique in composite laminates. First, a new procedure was developed to decompose the fundamental Lamb wave modes in small size specimens. The damage mechanisms in End Notched Flexure (ENF) in woven and unidirectional specimens were then discriminated using Fuzzy Clustering Method (FCM). Afterwards, the crack-arrest phenomenon was examined in each specimen. After that, experimental and Cohesive Zone Modeling (CZM) techniques were conducted to characterize the delamination using ENF specimens. The results showed how, it is possible to successfully decrease the effect of propagating media such as attenuation of AE signals using the new proposed methodology. As a final point, the results of this study could lead to efficiently distinguishing different damages in laminated composite using AE Lamb-based technique.
Keywords: Lamb Wave; Acoustic Emission; Damage Mechanisms; Composite Laminates; Delamination

Honeycomb structures are increasingly being used in many important fields. A novel combined embedded enhanced honeycomb (CEEH) in developed in this paper based on the two existing embedded enhanced honeycombs, the single rib embedded enhanced honeycomb (SREEH) and the rhombic grid embedded enhanced honeycomb (RGEEH). Analytical model related to the in-plane Young’s modulus and Poisson’s ratio is built and validated by using two different finite element (FE) models (3D beam model and 3D solid model). The in-plane elastic behavior of the honeycomb is also investigated against the geometrical parameters by using the numerically validated analytical solutions. The results show that the new CEEH can achieve a wide range value of Poisson’s ratio and Young’s modulus by tailoring geometric parameters. The results also show that the new CEEH exhibits higher x- directional specific stiffness than SREEH while higher y- directional specific stiffness than RGEEH. Moreover, the new CEEH can weaken even eliminate the difference between the two principal directions which can be hardly achieved by the SREEH and RGEEH. Given these advantages, this new design may be promising in some applications. This work provides a new insight into the designs of embedded enhanced honeycombs.
Keywords: Basic re-entrant hexagonal honeycomb (BRHH); Embedded enhanced honeycombs; Tunable mechanical properties; Negative Poisson’s ratio (NPR); Zero Poisson’s ratio (ZPR)

An approach to identify parameters of interface friction model for Ceramic Matrix composites based on stress-strain response was developed. The stress distribution of fibers in the interface slip region and intact region of the damaged composite was determined by adopting the interface friction model. The relation between maximum strain, secant moduli of hysteresis loop and interface shear stress, interface de-bonding stress was established respectively with the method of symbolic-graphic combination. By comparing the experimental strain, secant moduli of hysteresis loop with computation values, the interface shear stress and interface de-bonding stress corresponding to first cycle were identified. Substituting the identification of parameters into interface friction model, the stress-strain curves were predicted and the predicted results fit experiments well. Besides, the influence of number of data points on identifying the value of interface parameters was discussed. And the approach was compared with the method based on the area of hysteresis loop.
Keywords: Ceramic matrix composites; Identification of interface parameters; Symbolic-graphic combination; Stress-strain curve

A New Adaptive Response Surface Model for Reliability Analysis of 2.5D C/SiC Composite Turbine Blade by Yaning Chang; Zhigang Sun; Weiyi Sun; Yingdong Song (1075-1091).
In order to calculate the failure probability of complex structures such as a 2.5D/SiC composites turbine blade and improve the structure safety, a new adaptive model of Response Surface (RS) analysis has been developed in this paper, which can improve the computational efficiency of structural failure problem while ensure the accuracy. The Gaussian Process Regression (GPR) theory was used to establish the RS and reconstruct the performance function of structure. And, an Adaptive Latin hypercube Sampling (ALHS) strategy was adopted in the process of establishing and correcting the RS. Finally the Direct Simulation Monte Carlo(DSMC)was utilized to calculate the failure probability of the performance function replacing the complex structure. Two numerical examples were calculated to validate the accuracy and computational efficiency of the proposed method. Additionally the finite element stress analysis results of 2.5D C/SiC composite turbine blade were used to structural reliability analysis by the proposed method. The approach in this paper provides a new way to evaluate the risk of the complex structures.
Keywords: Reliability analysis; 2.5D C/SiC composites; Adaptive response surface approach; Gaussian regression; Latin hypercube sampling

Study on Mechanical Behavior of CVD-SiC Coated C/SiC Composites under Simulated Space Environments by Xiang Yang; Cao Feng; Wang Yi; Li Guang-de; Cao Jie (1093-1101).
SiC coating was prepared on the surface of C/SiC composites by chemical vapor deposition (CVD) method, and then mechanical behavior of CVD-SiC coated C/SiC composites under cold and thermal cycling had been investigated. Specimens were thermally cycled between the temperatures of −100 °C and 100 °C for up to 200 cycles, respectively. The coating was characterized by XRD, SEM and EDS. The results showed that there were no significant changes in the flexural property. CVD-SiC coated C/SiC composites had good mechanical stability in above simulated space environments. While great changes occurred on both elements and structure of the coating, from homogeneous single-phase of SiC into the inner layer of SiC and the outer of C, which caused the change of the bending strength.
Keywords: C/SiC composites; SiC; Coating; CVD; Thermal shock

Numerical Study on the Tensile Behavior of 3D Four Directional Cylindrical Braided Composite Shafts by Guoqi Zhao; Jiayi Wang; Wenfeng Hao; Yinghua Liu; Ying Luo (1103-1114).
The tensile behavior of 3D four directional cylindrical braided composite shafts was analyzed with the numerical method. The unit cell models for the 3D four directional cylindrical braided composite shafts with various braiding angles were constructed with ABAQUS. Hashin’s failure criterion was used to analyze the tensile strength and the damage evolution of the unit cells. The influence of the braiding angle on the tensile behavior of the 3D four directional cylindrical braided composite shafts was analyzed. The numerical results showed that the tensile strength along the braiding direction increased as the braiding angle decreased. These results should play an integral role in the design of braiding composites shafts.
Keywords: Braided composite shaft; Unit cell; Tensile behavior; Finite element model; Hashin’s failure criterion

Influence of the Hybrid Combination of Multiwalled Carbon Nanotubes and Graphene Oxide on Interlaminar Mechanical Properties of Carbon Fiber/Epoxy Laminates by J. A. Rodríguez-González; C. Rubio-González; M. Jiménez-Mora; L. Ramos-Galicia; C. Velasco-Santos (1115-1131).
An effective strategy to improve the mode I and mode II interlaminar fracture toughness (G IC and G IIC ) of unidirectional carbon fiber/epoxy (CF/E) laminates using a hybrid combination of multiwalled carbon nanotubes (MWCNTs) and graphene oxide (GO) is reported. Double cantilever beam (DCB) and end notched flexure (ENF) tests were conducted to evaluate the G IC and G IIC of the CF/E laminates fabricated with sprayed MWCNTs, GO and MWCNTs/GO hybrid. Scanning electron microscopy was employed to observe the fracture surfaces of tested DCB and ENF specimens. Experimental results showed the positive effect on the G IC and G IIC by 17% and 14% improvements on CF/E laminates with 0.25 wt.% MWCNTs/GO hybrid content compared to the neat CF/E. Also, the interlaminar shear strength value was increased for MWCNTs/GO-CF/E laminates. A synergetic effect between MWCNTs and GO resulted in improved interlaminar mechanical properties of CF/E laminates made by prepregs.
Keywords: Hybrid; Composite laminate; Multiwalled carbon nanotubes; Graphene oxide; Interlaminar fracture toughness

Numerical Identification of Meso Length-Effect and Full-Field Edge-Effect of 3D Braided Composites by Diantang Zhang; Song Yu; Guyu Feng; Xueliang Xiao; Qianru Ma; Kun Qian (1133-1154).
A study is conducted with the aim of developing two numerical models, meso-scale model and fiber embedded matrix model, for evaluating the length-effect and full-field edge-effect of 3D braided composites. Also, for the validation of fiber embedded matrix model, a series of digital image correlation measurements are conducted along the axial directions. The results show that the predicted mechanical behaviors of the tensile and compressive samples are essentially sensitive to the RVC number. Moreover, the proposed fiber embedded matrix method is capable of accurately predicting the cut-edge effect on the full-field mechanical behaviors of 3D braided composites when subjected to the axial tensile and compressive loading, validated by the comparison of the full-field displacement and strain fields.
Keywords: 3D braided composites; Mechanical properties; Finite element method; Length effect; Edge-effect

Curing of Thick Thermoset Composite Laminates: Multiphysics Modeling and Experiments by S. Anandan; G. S. Dhaliwal; Z. Huo; K. Chandrashekhara; N. Apetre; N. Iyyer (1155-1168).
Fiber reinforced polymer composites are used in high-performance aerospace applications as they are resistant to fatigue, corrosion free and possess high specific strength. The mechanical properties of these composite components depend on the degree of cure and residual stresses developed during the curing process. While these parameters are difficult to determine experimentally in large and complex parts, they can be simulated using numerical models in a cost-effective manner. These simulations can be used to develop cure cycles and change processing parameters to obtain high-quality parts. In the current work, a numerical model was built in Comsol MultiPhysics to simulate the cure behavior of a carbon/epoxy prepreg system (IM7/Cycom 5320–1). A thermal spike was observed in thick laminates when the recommended cure cycle was used. The cure cycle was modified to reduce the thermal spike and maintain the degree of cure at the laminate center. A parametric study was performed to evaluate the effect of air flow in the oven, post cure cycles and cure temperatures on the thermal spike and the resultant degree of cure in the laminate.
Keywords: Composite cure; Multiphysics model; Cure kinetics; Heat transfer

Efficient Permeability Measurement and Numerical Simulation of the Resin Flow in Low Permeability Preform Fabricated by Automated Dry Fiber Placement by Romain Agogue; Naziha Chebil; Mylène Deleglise-Lagardere; Pierre Beauchene; Chung Hae Park (1169-1182).
We propose a new experimental method using a Hassler cell and air injection to measure the permeability of fiber preform while avoiding a race tracking effect. This method was proven to be particularly efficient to measure very low through-thickness permeability of preform fabricated by automated dry fiber placement. To validate the reliability of the permeability measurement, the experiments of viscous liquid infusion into the preform with or without a distribution medium were performed. The experimental data of flow front advancement was compared with the numerical simulation result using the permeability values obtained by the Hassler cell permeability measurement set-up as well as by the liquid infusion experiments. To address the computational cost issue, the model for the equivalent permeability of distribution medium was employed in the numerical simulation of liquid flow. The new concept using air injection and Hassler cell for the fiber preform permeability measurement was shown to be reliable and efficient.
Keywords: Permeability measurement; Hassler cell; Automated dry fiber placement; Resin infusion

A multi-scale modeling approach is presented to simulate and validate thermo-oxidation shrinkage and cracking damage of a high temperature polymer composite. The multi-scale approach investigates coupled transient diffusion-reaction and static structural at macro- to micro-scale. The micro-scale shrinkage deformation and cracking damage are simulated and validated using 2D and 3D simulations. Localized shrinkage displacement boundary conditions for the micro-scale simulations are determined from the respective meso- and macro-scale simulations, conducted for a cross-ply laminate. The meso-scale geometrical domain and the micro-scale geometry and mesh are developed using the object oriented finite element (OOF). The macro-scale shrinkage and weight loss are measured using unidirectional coupons and used to build the macro-shrinkage model. The cross-ply coupons are used to validate the macro-shrinkage model by the shrinkage profiles acquired using scanning electron images at the cracked surface. The macro-shrinkage model deformation shows a discrepancy when the micro-scale image-based cracking is computed. The local maximum shrinkage strain is assumed to be 13 times the maximum macro-shrinkage strain of 2.5 × 10−5, upon which the discrepancy is minimized. The microcrack damage of the composite is modeled using a static elastic analysis with extended finite element and cohesive surfaces by considering the modulus spatial evolution. The 3D shrinkage displacements are fed to the model using node-wise boundary/domain conditions of the respective oxidized region. Microcrack simulation results: length, meander, and opening are closely matched to the crack in the area of interest for the scanning electron images.
Keywords: Thermo-oxidative damage; Object oriented finite element; Extended finite element; Traction-separation laws; High-temperature polymer matrix composites

Thermal and mechanical properties of 3D printed boron nitride – ABS composites by Tyler J. Quill; Matthew K. Smith; Tony Zhou; Mohamed Gamal Shafik Baioumy; Joao Paulo Berenguer; Baratunde A. Cola; Kyriaki Kalaitzidou; Thomas L. Bougher (1205-1217).
The current work investigates the thermal conductivity and mechanical properties of Boron Nitride (BN)-Acrylonitrile Butadiene Styrene (ABS) composites prepared using both 3D printing and injection molding. The thermally conductive, yet electrically insulating composite material provides a unique combination of properties that make it desirable for heat dissipation and packaging applications in electronics. Materials were fabricated via melt mixing on a twin-screw compounder, then injection molded or extruded into filament for fused deposition modeling (FDM) 3D printing. Compositions of up to 35 wt.% BN in ABS were prepared, and the infill orientation of the 3D printed composites was varied to investigate the effect on properties. Injection molding produced a maximum in-plane conductivity of 1.45 W/m-K at 35 wt.% BN, whereas 3D printed samples of 35 wt.% BN showed a value of 0.93 W/m-K, over 5 times the conductivity of pure ABS. The resulting thermal conductivity is anisotropic; with the through-plane thermal conductivity lower by a factor of ~3 for injection molding and ~4 for 3D printing. Adding BN flakes caused a modest increase in the flexural modulus, but resulted in a large decrease in the flexural strength and impact toughness. It is shown that although injection molding produces parts with superior thermal and mechanical properties, BN shows much potential as a filler material for rapid prototyping of thermally conductive composites.
Keywords: 3D–printing; thermal conductivity; composite; Boron Nitride; Fused Deposition Modeling

The tape winding technology is an effective way to fabricate rotationally composite materials. Nevertheless, some inevitable defects will seriously influence the performance of winding products. One of the crucial ways to identify the quality of fiber-reinforced composite material products is examining its void content. Significant improvement in products’ mechanical properties can be achieved by minimizing the void defect. Two methods were applied in this study, finite element analysis and experimental testing, respectively, to investigate the mechanism of how void forming in composite tape winding processing. Based on the theories of interlayer intimate contact and Domain Superposition Technique (DST), a three-dimensional model of prepreg tape void with SolidWorks has been modeled in this paper. Whereafter, ABAQUS simulation software was used to simulate the void content change with pressure and temperature. Finally, a series of experiments were performed to determine the accuracy of the model-based predictions. The results showed that the model is effective for predicting the void content in the composite tape winding process.
Keywords: Composite tape winding; Void content; Finite element analysis; Domain Superposition Technique

The layer nesting phenomenon of multilayer fabric has a great influence on the through-thickness permeability, which is a key parameter for the simulation of the through-thickness LCM (Liquid Composite Moldling) processes. In this paper, based on the analyses of the formation reason and characterization parameters of layer nesting, the geometry models of fabric unit-cells with nesting are established. The through-thickness flow in the unit-cell is analyzed to built the governing equations of the resin flow. The inter-yarn and intra-yarn regions of the unit-cell model are discretized uniformly, then the governing equations of the through-thickness flow are numerically solved based on Adams-Bashforth scheme and Chorin projection method, so the through-thickness flow parameters is obtained and the through-thickness permeability of the fabric with nesting can be predicted. The verification of the above method is implemented by comparisons with the available experimental results. A series of simulation experiments are carried out to investigate the nesting behaviors under different layer shifts, and the effects of nesting on the total thickness and through-thickness permeability of woven fabric are researched in detail.
Keywords: LCM; Nesting; Through-thickness permeability; Numerical simulation