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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.19, #3-4)

Methodology for Evaluating Manufacturability of Composite Materials by Jingjie Cong; Boming Zhang (pp. 189-201).

It is widely acknowledged that decisions made in the early design stages have a greater influence on the final product than those made in the later stages. In a conventional design process, composite products are designed without sufficient consideration being given to limitations of composite manufacturing process. Quite often some of composite designs cannot be produced with special performance requirement or cannot be produced at a reasonable cost. To resolve this drawback and achieve the competitive designs for composite product, an integrated knowledge framework that supports the quantitative manufacturability evaluation of composite design proposals was introduced. The essential concept of the composite manufacturability was defined through an in-depth analysis of composite manufacturing process. The evaluation flow was acquired according to the hierarchical indices. A stage-based quality assessment model for the composite multistage process was mainly studies. It relies on the consideration that the final quality of a composite product is mainly determined by some critical stages during a production cycle. Finally, the method is illustrated through a case focusing on the quality issue of void formation in autoclave process.

Keywords: Design for manufacturing; Polymer composites; Quantitative analysis; Manufacturability; Void formation

The Secondary Buckling and Design Criterion of Composite Laminated Cylindrical Shells by Tong Zhang; Wei Gu (pp. 203-217).

Even a weak disturbance caused by an asymmetric mesh is enough to break structural symmetry, which triggers the bifurcation buckling and post-buckling behavior of composite laminated cylindrical shells under compression loading by ABAQUS. The mesh perturbation is more objective and authentic; it will not destroy the original model structure in Finite Element Analysis, comparing with the traditional perturbation method by introducing the initial imperfections into the model. A series of numerical experiments are performed to investigate the influence of different types of asymmetric mesh on the predicted secondary buckling load. The predicted secondary buckling load agrees better with analytical solution than predicted primary buckling load and the results from the traditional perturbation method respectively. Therefore, secondary buckling load provides the key design criterion for composite laminated cylindrical shells. Primary and secondary post-buckling patterns of different complexity are explored, which agrees well with experimental buckling modes. Our major conclusions can be summarized briefly: different types of asymmetric mesh have little influence on the predicted secondary buckling load; Care must be exercised regarding the mesh density in order to produce the secondary buckling mode as well as the reliable secondary buckling load.

Keywords: Composite laminated cylindrical shells; Post-secondary-buckling; Numerical experiments; Asymmetric meshing technique

Post Buckling Progressive Failure Analysis of Composite Laminated Stiffened Panels by Konstantinos N. Anyfantis; Nicholas G. Tsouvalis (pp. 219-236).

The present work deals with the numerical prediction of the post buckling progressive and final failure response of stiffened composite panels based on structural nonlinear finite element methods. For this purpose, a progressive failure model (PFM) is developed and applied to predict the behaviour of an experimentally tested blade-stiffened panel found in the literature. Failure initiation and propagation is calculated, owing to the accumulation of the intralaminar failure modes induced in fibre reinforced composite materials. Hashin failure criteria have been employed in order to address the fiber and matrix failure modes in compression and tension. On the other hand, the Tsai-Wu failure criterion has been utilized for addressing shear failure. Failure detection is followed with the introduction of corresponding material degradation rules depending on the individual failure mechanisms. Failure initiation and failure propagation as well as the post buckling ultimate attained load have been numerically evaluated. Final failure behaviour of the simulated stiffened panel is due to sudden global failure, as concluded from comparisons between numerical and experimental results being in good agreement.

Keywords: Finite element analysis; Progressive failure; Damage mechanics; Buckling

Ablation Performance of Carbon/Carbon Composite Throat after a Solid Rocket Motor Ground Ignition Test by Jian Yin; Hongbo B. Zhang; Xiang Xiong; Jinlv L. Zuo; Baiyun Y. Huang (pp. 237-245).

The ablation performances of a fine-woven, pierced carbon/carbon (C/C) composite throats for solid rocket motor were investigated by a ground ignition test. The ablation surface morphologies of three regions (entrance, throat and exit) of the throats were examined in detail by scanning electron microscopy. The results show that the C/C composite throats retain smooth inner surface, experiencing ablation rates of 0.142–0.146 mm/s under a pressure of about 6.0 MPa. But ablation morphologies of the three regions are different, due to the continuously changing of temperatures, velocities, and oxidant concentrations of combustion gas plume.

Keywords: Carbon/Carbon composite; Throat; SEM; Ablation

Structural Analysis and Design of the Composite Wind Turbine Blade by Wen-Hsiang Wu; Wen-Bin Young (pp. 247-257).

The wind turbine blade sustains various kinds of loadings during the operation and parking state. Due to the increasing size of the wind turbine blade, it is important to arrange the composite materials in a sufficient way to reach the optimal utilization of the material strength. Most of the composite blades are made of glass fibers composites while carbon fibers are also employed in recent years. Composite materials have the advantages of high specific strength and stress. This study develops a GUI interface to construct the blade model for the stress analysis using ANSYS. With the aid of visualization interface, the geometric model of the blade can be constructed by only a few data inputs. Based on the numerical stress analysis of the turbine blade, a simple iterative method was proposed to design the structure of the composite blade.

Keywords: Wind turbine blade; Stress analysis; Structural design; Composite blade

Characterization of Biaxial and Triaxial Braids: Fiber Architecture and Mechanical Properties by Karin Birkefeld; Mirko Röder; Tjark von Reden; Martina Bulat; Klaus Drechsler (pp. 259-273).

Biaxial and triaxial carbon fiber braids with off-axis braiding angles of 30°, 45° and 55° are characterized with respect to their fiber architecture. All braids are produced on a round mandrel with constant cross section. Detailed geometric information on the different braids, like roving dimensions, roving shapes and the degree of nesting is given. The findings from measurements in photomicrographs are used to construct meso-model yarn architectures at the unit cell level which are then analyzed with the WiseTex software (Lomov et al. Compos. Sci. Technol. 60:2083–2095, 2000). The results of the models’ analysis with TexComp and comparison of mechanical properties with tests are consistent and essential for further steps in predictive modeling. Predictive modeling was also performed for biaxial braids based on the packing density in the material and parameters of the braiding process. The good conformance of the predictive models gives a validated starting point for development of braided structures concerning stiffness behavior. In addition, the information about the fiber architecture can be used for failure analysis on unit cell level.

Keywords: Braiding; Wisetex; Fiber architecture; Mechanical properties

Rubber Impact on 3D Textile Composites by Sebastian Heimbs; Björn Van Den Broucke; Yann Duplessis Kergomard; Frederic Dau; Benoit Malherbe (pp. 275-295).

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools.

Keywords: 3D textile composite; Rubber impact; Damage mechanisms; Numerical simulation

A Strategy to Support Design Processes for Fibre Reinforced Thermoset Composite Materials by Marc Gascons; Norbert Blanco; Joan Andreu Mayugo; Koen Matthys (pp. 297-314).

The concept stage in the design for a new composite part is a time when several fundamental decisions must be taken and a considerable amount of the budget is spent. Specialized commercial software packages can be used to support the decision making process in particular aspects of the project (e.g. material selection, numerical analysis, cost prediction,...). However, a complete and integrated virtual environment that covers all the steps in the process is not yet available for the composite design and manufacturing industry. This paper does not target the creation of such an overarching virtual tool, but instead presents a strategy that handles the information generated in each step of the design process, independently of the commercial packages used. Having identified a suitable design parameter shared in common with all design steps, the proposed strategy is able to evaluate the effects of design variations throughout all the design steps in parallel. A case study illustrating the strategy on an industrial part is presented.

Keywords: Functional composites (PMC); Finite element analysis (FEA); Production process; Cost analysis

Optimum Design of Composite Sandwich Structures Subjected to Combined Torsion and Bending Loads by Xiang Li; Gangyan Li; Chun H. Wang; Min You (pp. 315-331).

This research is motivated by the increase use of composite sandwich structures in a wide range of industries such as automotive, aerospace and civil infrastructure. To maximise stiffness at minimum weight, the paper develops a minimum weight optimization method for sandwich structure under combined torsion and bending loads. We first extend the minimum-weight design of sandwich structures under bending load to the case of torsional deformation and then present optimum solutions for the combined requirements of both bending and torsional stiffness. Three design cases are identified for a sandwich structure required to meet multiple design constraints of torsion and bending stiffness. The optimum solutions for all three cases are derived. To illustrate the newly developed optimum design solutions, numerical examples are presented for sandwich structures made of either isotropic face skins or orthotropic composite face skins.

Keywords: Optimum design; Sandwich structure; Bending; Torsion; Lightweight

Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis by Cuong Ha-Minh; François Boussu; Toufik Kanit; David Crépin; Abdellatif Imad (pp. 333-347).

3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2® fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.

Keywords: 3D warp interlock fabric; Numerical tool for geometrical representation; Ballistic impact; Finite element methode; Effet of friction; Dammage mechanisms

Hybrid S2/Carbon Epoxy Composite Armours Under Blast Loads by F. Dolce; Michele Meo; A. Wright; M. French; M. Bernabei (pp. 349-362).

Civil and military structures, such as helicopters, aircrafts, naval ships, tanks or buildings are susceptible to blast loads as terroristic attacks increases, therefore there is the need to design blast resistant structures. During an explosion the peak pressure produced by shock wave is much greater than the static collapse pressure. Metallic structures usually undergo large plastic deformations absorbing blast energy before reaching equilibrium. Due to their high specific properties, fibre-reinforced polymers are being considered for energy absorption applications in blast resistant armours. A deep insight into the relationship between explosion loads, composite architecture and deformation/fracture behaviour will offer the possibility to design structures with significantly enhanced energy absorption and blast resistance performance. This study presents the results of a numerical investigation aimed at understanding the performance of a hybrid composite (glass/carbon fibre) plate subjected to blast loads using commercial LS-DYNA software. In particular, the paper deals with numerical 3D simulations of damages caused by air blast waves generated by C4 charges on two fully clamped rectangular plates made of steel and hybrid (S2/Carbon) composite, respectively. A Multi Materials Arbitrary Lagrangian Eulerian (MMALE) formulation was used to simulate the shock phenomenon. For the steel plates, the Johnson-Cook material model was employed. For the composite plates both in-plane and out-of-plane failure criteria were employed. In particular, a contact tiebreak formulation with a mixed mode failure criteria was employed to simulate delamination failure. As for the steel plates the results showed that excellent correlation with the experimental data for the two blast load conditions in terms of dynamic and residual deflection for two different C4 charges. For the composite plates the numerical results showed that, as expected, a wider delamination damage was observed for the higher blast loads case. Widespread tensile matrix damage was experienced for both blast load cases, while only for 875 g blast load fiber failure damage was observed. This agrees well with the experimental data showing that the composite panel was not able to resist to the 875 g blast load.

Keywords: Blast; Delamination; Composite armours; Cohesive model

PLLA/Flax Mat/Balsa Bio-Sandwich—Environmental Impact and Simplified Life Cycle Analysis by Antoine Le Duigou; Jean-Marc Deux; Peter Davies; Christophe Baley (pp. 363-378).

In the present paper the environmental impact of biocomposites and bio-sandwich materials production are evaluated, using simplified Life Cycle Analysis (LCA) following the procedure recommended in the ISO 14044 standard. The materials are dimensioned and evaluated by comparing with reference materials, glass mat reinforced unsatured polyester and glass mat/unsatured polyester/balsa sandwich. The results indicate that bio-sandwich materials are very attractive in terms environmental impact. However further improvements in biocomposite and bio-sandwich mechanical strength are necessary if they are to be used in transport application compared to glass/polyester and glass/polyester/balsa sandwich.

Keywords: Sandwich; Natural fibre; Biopolymer; Balsa; Simplified Life Cycle Analysis (SLCA)

Mechanical Characterization of an Alternative Technique to Embed Sensors in Composite Structures: The Monitoring Patch by Mauricio Torres Arellano; Laurent Crouzeix; Francis Collombet; Bernard Douchin; Yves-Henri Grunevald (pp. 379-391).

Sensor embedding is one of the main operations in dealing with composites in-core instrumentation. In this work, an alternative encapsulation technique called “monitoring patch” is proposed to achieve correct sensor embedding, to facilitate the industrialised instrumentation procedure and to adapt the sensors according to the geometry and material heterogeneities required of the composite structures. The monitoring patch is mainly developed with the aim to reduce the variability effects produced if the sensor alone is placed. In this initial study, a first patch’s configuration is manufactured with CTMI pre-impregnate epoxy–woven glass, hosting two kinds of silicon prism sensors. The monitoring patch is then placed in the thick middle plane of an epoxy-carbon M21 T700GC quasi-isotropic plate. The plates are instrumented with strain gauges and tested using digital image correlation (DIC). The strain field maps are calculated to analyse the over-strain zones and to infer fracture paths. At the same time, a FEM model is developed to compare the numerical and the experimental observations. The results show that the mechanical strength of the instrumented plates is not significantly affected by the presence of the patch. The failure path of the instrumented plates with monitoring patch is found along the patch perimeter; therefore, the sensors can be recovered without damage even after the failure of the instrumented structure. The feasibility of the monitoring patch is discussed with other embedding techniques. In further studies, the monitoring patch will host a streaming sensor with an aim to carry out in-core strain measurements.

Keywords: Monitoring patch; Silicon sensor; Embedding; Strain field; Digital image correlation

A Comparison of Laser Shearography and C-Scan for Assessing a Glass/Epoxy Laminate Impact Damage by Martin Kadlec; Roman Růžek (pp. 393-407).

Impact damage is a serious damage mechanism in composite materials, which limits their performance and reliability. Impact damage can occur during in-service applications or as a result of handling during manufacturing. Methods used currently for damage detection are based on different principles, and for that reason, they give a range of results no matter what the real damage is. Therefore, a comparison of the internal real damage with the flaw indications of a glass fibre–reinforced polymer (GFRP) laminate made with two non-destructive technique (NDT) methods has been investigated. Laser shearography measurements and C-scan ultrasonic detection were compared. Metallographic examination and surface indentation measurements provided information about the character of the real damage. Such a comparison has not yet been published because laser shearography is considered a qualitative technique. Each NDT method was able to visualise a different type of damage. The knowledge of the applicability of these methods is the key to taking advantage of both methods by combining their respective strengths. In terms of the reliability, simplicity and rapidity of all of the mentioned techniques, laser shearography turned out to be the most suitable method for the detection of barely visible flaws. The C-scan was more appropriate for precisely defining the inner damage. The tested material was a laminate typically used for ultralight aircraft. Information about the extent of damage is very important for airplane certification and maintenance.

Keywords: Polymer matrix composite; Impact damage; Laser shearography; C-scan; Aerospace vehicles

Effect of Silane Coupling Agents on Rice Straw Fiber/Polymer Composites by M. R. Ismail; Ali A. M. Yassene; Hassan M. H. Abd El Bary (pp. 409-425).

The effect of coupling agents and electron beam (EB) irradiation dose on the mechanical properties of composites made from rice straw fibers and polymers have been studied. Samples were made by hot pressing of mix composition at 130°C. The pressed samples were subjected to electron beam irradiation dose ranged from 10 to 50 kGy. Increasing the electron beam irradiation dose increased the value of flexural strength, modulus of elasticity and impact strength. It was also observed that, the properties of composites containing γ-aminopropyltrimethoxy silane (A-1100) are lower than those of composites containing N-(2aminoethyl)-3-amino propyltrimethoxy silane (A-700) coupling agents. These are attributed to a hydrogen bonding formation between the amine or protonated amine and the hydroxyl groups of rice straw fibers. The presence of coupling agents in the composites during the EB irradiation process produce a more free radicals which are enough to form a chemical bonding between the rice straw fiber and polymer. The thickness swelling and water absorption values decrease with increasing the EB irradiation dose with presence of coupling agents in the composite.

Keywords: Coupling agent; EB irradiation; Fiber/polymer composite and mechanical properties

A Study of Strength Transfer from tow to Textile Composite Using Different Reinforcement Architectures by Irina Cristian; Saad Nauman; Francois Boussu; Vladan Koncar (pp. 427-442).

The paper proposes an experimental and analytical approach of designing composites with the predetermined ultimate strength, reinforced with warp interlock fabrics. In order to better understand the phenomena of transfer of tensile properties from a tow to the composite, intermediate phases of composite manufacturing have also been taken into account and tensile properties of tows taken from the loom and the woven reinforcements have also been tested. Process of transfer of mechanical properties of raw materials to the final product (composite) depends on various structural factors. Here the influence of weave structure, which ultimately influences crimp has been studied. A strength transfer coefficient has been proposed which helps in estimating the influence of architectural parameters on 3D woven composites. 3 woven interlock reinforcements were woven to form composites. The coefficients of strength transfer were calculated for these three variants. The structural parameters were kept the same for these three reinforcements except for the weave structure. In was found that the phenomenon of strength transfer from tow to composite is negatively influenced by the crimp. In general the strength transfer coefficients have higher values for dry reinforcements and afterwards due to resin impregnation the values drop.

Keywords: 3D weaving; Interlock reinforcement; Carbon composite; Tensile strength; Carbon tow; Mechanical properties

Compaction Behavior and Part Thickness Variation in Vacuum Infusion Molding Process by Jinshui Yang; Jiayu Xiao; Jingcheng Zeng; Dazhi Jiang; Chaoyi Peng (pp. 443-458).

In vacuum infusion molding process (VIMP), it is difficult to manufacture a composite part with small dimensional tolerance, since the upper mold for the process is flexible. In this study, the static and cyclic compaction responses of five kinds of fabrics were experimentally studied under real VIMP conditions, with the effects of compaction pressure, compaction time, compaction cycle and number of the fabric layers. The static and cyclic compaction responses of the all fabrics follow different power law models and the resulting fiber volume fraction and relaxation factor increase with the number of layers. Although the resulting fiber volume fraction increases with the layer numbers, change of the fiber volume fraction of the composite parts with 10 layers to 100 layers of the all fabrics is less than 2.5%. The thickness of the composite part was monitored and measured using micrometer gauges, and the effects of processing parameters on the final thickness of part was investigated. The part thickness varies as a function of spatial coordinates and time during pre-filling, filling and post-filling stages in VIMP. The variation and the final value of the part thickness would be significantly affected by the processing parameters. Statistical results show that the final part thickness is equivalent to the thickness of the dry preform under the 0.08 MPa vacuum compaction pressure in VIMP. The difference between the fiber volume fraction of the final part and that of the dry preform is 2% ~ 5.7%.

Keywords: Vacuum infusion molding process (VIMP); Compaction behavior; Composite materials; Fiber volume fraction; Thickness; Fabric preform

Sea Water Ageing of Composites for Ocean Energy Conversion Systems: Influence of Glass Fibre Type on Static Behaviour by Amélie Boisseau; Peter Davies; Frédéric Thiebaud (pp. 459-473).

Composite material components will be an essential part of ocean energy recovery devices, and their long term durability in sea water must be guaranteed. Despite extensive experience for boat structures and wind turbines few data exist to design structures subjected to a combination of mechanical loads and sea water immersion. This paper presents the first results from an experimental study, performed jointly with fibre manufacturers, and a resin supplier, to fill this gap. The experimental study is completed by numerical modelling to simulate the coupling between water absorption and mechanical behaviour. Sea water ageing is shown to result in a drop in quasi–static mechanical properties and a change in flexural mode from compression to tension at longer ageing times, which is consistent with results from the numerical simulations.

Keywords: Composite material; Sea water ageing; Failure mechanism; Flexure; Tidal turbine

Post-Impact Mechanical Characterisation of Glass and Basalt Woven Fabric Laminates by Igor M. De Rosa; Francesco Marra; Giovanni Pulci; Carlo Santulli; Fabrizio Sarasini; Jacopo Tirillò; Marco Valente (pp. 475-490).

Two woven fabric laminates, one based on basalt fibres, the other on E-glass fibres, as a reinforcement for vinylester matrix, were compared in terms of their post-impact performance. With this aim, first the non-impacted specimens were subjected to interlaminar shear stress and flexural tests, then flexural tests were repeated on laminates impacted using a falling weight tower at three impact energies (7.5, 15 and 22.5J). Tests were monitored using acoustic emission analysis of signal distribution with load and with distance from the impact point. The results show that the materials have a similar damage tolerance to impact and also their post-impact residual properties after impact do not differ much, with a slight superiority for basalt fibre reinforced laminates. The principal difference is represented by the presence of a more extended delamination area on E-glass fibre reinforced laminates than on basalt fibre reinforced ones.

Keywords: Basalt; E-glass; Acoustic emission; Residual properties; Impact

Modeling Smart Structure of Wind Turbine Blade by Yin-hu Qiao; Jiang Han; Chun-yan Zhang; Jie-ping Chen (pp. 491-498).

With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced the interest for aerodynamic control systems with build-in intelligence on the blades. The paper aims to provide a way for modeling the adaptive wind turbine blades and analyze its ability for vibration suppress. It consists of the modeling of the adaptive wind turbine blades with the wire of piezoelectric material embedded in blade matrix, and smart sandwich structure of wind turbine blade. By using this model, an active vibration method which effectively suppresses the vibrations of the smart blade is designed.

Keywords: Wind turbine blade; Smart composites material; Modeling; Active vibration control

Wear Behavior of Basalt Filled Low Density Polyethylene Composites by Akin Akinci; Senol Yilmaz; Ugur Sen (pp. 499-511).

The friction and wear performance of pure LDPE and 10%, 30%, 50% and 70% basalt filled (by wt) LDPE composite were comparatively evaluated under dry sliding conditions. Wear tests were carried out at room temperature under 5, 10 and 20N loads and at 0.5, 1.0 and 1.5 m/s sliding speeds. The coefficients of friction of the composites were significantly influenced with increase in basalt content. Friction coefficient of the LDPE was getting decreased from 0.51 to 0.13 with increase in basalt content, depending on applied loads and sliding speeds. The results show that the wear rates for pure LDPE and basalt filled composites increase with increasing loads and sliding speeds. The wear rates of the basalt filled composites were significantly affected from the basalt content. Wear rates of the LDPE was decreased from 2.596 × 10⁻³ to 6.8 × 10⁻⁵ mm³/m with increase in basalt content, depending on applied loads and sliding speeds.

Keywords: Low density polyethylene; Basalt; Friction; Wears

Analyses of the Deformation Mechanisms of Non-Crimp Fabric Composite Reinforcements during Preforming by Sylvain Bel; Philippe Boisse; François Dumont (pp. 513-528).

Two experimental devices are used for the analysis of the deformation mechanisms of biaxial non-crimp fabric composite reinforcements during preforming. The bias extension test, commonly use for the shear behaviour characterisation of woven fabrics, allows to highlight the sliding between the two plies of the reinforcement. This sliding is localized in areas of high gradient of shearing. This questions the use of bias extension test in determining the shear stiffness of the studied reinforcement. Then a hemispherical stamping experiment, representative of a preforming process, allows to quantify this sliding. The slippage is defined as the distance, projected onto the middle surface, of two points initially opposed on both sides of the reinforcement. For both experiments, the characteristic behavior of the non-crimp fabric reinforcement is highlighted by comparison with a woven textile reinforcement. This woven fabric presents only a very little sliding between warp and weft yarns during preforming. This aspect of the deformation kinematics of the non-crimp fabric reinforcement must be considered when simulating the preforming.

Keywords: Fabrics/textiles; Non Crimp Fabric (NCF); Preforming; Mechanical testing

Failure Locus of 3D Four-Directional Braided Composites Under Biaxial Loading by Baolai Wang; Guodong Fang; Jun Liang; Zhenqing Wang (pp. 529-544).

The failure locus of 3D braided four-directional composites under complex loadings, such as tension-shear, compression-shear and tension-tension, can be obtained by micromechanical computation model. A finite element model of representative volume cell (RVC) of the braided composites, explicitly taking into account the braid yarn and matrix, is chosen to analyze the mechanical response. The failure mechanisms of the braided composites observed in experiment can be reproduced by the numerical computation in which the mesoscopic damage models of the braid yarn and matrix are developed. Several failure points of the braided composites under the biaxial loadings can be obtained when different stress ratios are imposed upon the RVC. In comparison with the Tsai-Wu and Tsai-Hahn criteria, the numerical failure loci of the braided composites except the tension-tension results are in good agreement with those results. It can be pointed out that the failure loci of the braided composites can be obtained by the numerical fitting of a large number of the failure points which are calculated by the numerical model.

Keywords: Braided composites; Mechanical properties; Damage model; Failure criterion

Experimental and Numerical Investigation of Metal Type and Thickness Effects on the Impact Resistance of Fiber Metal Laminates by M. Sadighi; T. Pärnänen; R. C. Alderliesten; M. Sayeaftabi; R. Benedictus (pp. 545-559).

The impact response of fiber metal laminates (FMLs), has been investigated with experiments and numerical simulations, which is reported in this article. Low-velocity impacts were carried out to study the effects of metal type and thickness within FMLs. Glare5-3/2 laminates with two aluminum layer thicknesses and a similar FML containing magnesium sheets were impacted by drop weight tests. Also, a major part of this study was to accomplish a dynamic non-linear transient analysis to study the impact response of FMLs using the commercial finite element (FE) analysis code ABAQUS. By reviewing different approaches of modeling constituents of an FML, it is shown that the appropriate selection of elements has more significant role than failure criterion to predict acceptable results for this type of laminate and loading. The good agreement obtained between experimental and numerical results verifies the possibility of relatively simpler simulation by FE-analysis to predict overall response of FMLs under impact loading.

Keywords: Fiber metal laminates; Magnesium; Low velocity impact; Numerical modeling; Abaqus

Finite Element Analysis of Interlaminar Stresses for Composite Laminates Stitched Around a Circular Hole by Zhangxin Guo; Xiaoping Han; Xiping Zhu (pp. 561-571).

An approach is proposed to numerically study the composite laminates stitched around a circular hole. The local structure of stitching region is simplified and the finite element analysis (FEA) is carried out. With this approach, the interlaminar stresses are calculated, and the effects of stitching parameters such as edge distance, stitching needle span and row spacing of yarn are discussed on the interlaminar stresses. The effect of the reinforcement can be enhanced by properly reducing the edge distance or needle span when stitching at the hole edge. Compared with unstitching, there is an evident decrease for interlaminar stresses at the hole after stitching enforcement. The distribution of the interlaminar stresses around the hole is related with layers.

Keywords: Composites laminates with holes; Interlaminar stresses; Stitching reinforcement; FEA

An Empirical Model for Resin Viscosity During Cure in Vacuum Infusion Molding Process by Jinshui Yang; Jiayu Xiao; Jingcheng Zeng; Chaoyi Peng; Xuebin Feng; Binbin Hou (pp. 573-582).

The rheological behaviors of a low viscosity epoxy resin system (RIMR135/RIMH137) for vacuum infusion molding process (VIMP) were studied with viscosity experiments. And an empirical model has been developed to predict the viscosity of the resin system during curing at low extents of cure, which is of significance during the mould filling stage in VIMP. Good agreement is observed between the experimental data and the model predicted viscosity. The processing windows of the resin system for VIMP can be predicted by the proposed models. The results show that the optimum processing temperature range of RIMR135/RIMH137 epoxy resin system for VIMP is from 25°C to 45°C, at which the resin system can maintain the viscosity less than 500 mPa·s for 75 min at least.

Keywords: Vacuum infusion molding process (VIMP); Rheological behavior; Epoxy resin system

Role of Tool-Part Interaction in Consolidation of L-Shaped Laminates during Autoclave Process by Jing Sun; Yizhuo Gu; Yanxia Li; Min Li; Zuoguang Zhang (pp. 583-597).

The role of tool-part interaction in the consolidation process of the L-shaped laminate was studied using a finite element model. The tool-part shear actions during processing were modeled by introducing shear layers. The predicted data demonstrate the necessity of considering the slippage between the tools and the laminate in simulations. A parametric study examining the effects of the shear layer properties on the compacting behavior was performed and the results show that improving the slippage ability of the male mold upon the composite part is of advantage to apply the pressure on the corner section of the L-shaped laminate. Moreover, the mechanical properties and the thickness of the shear layer have a significant influence on the modeling of the consolidation process.

Keywords: Finite element analysis (FEA); Consolidation; Autoclave; Tool-part interaction

Design of a Motorcycle Composite Swing-Arm by Means of Multi-objective Optimisation by Alessandro Airoldi; Simone Bertoli; Luca Lanzi; Marco Sirna; Giuseppe Sala (pp. 599-618).

A study for the replacement of a metallic swing-arm of a high performance motorcycle with a composite part is presented. Considering the high structural effectiveness of the original metallic component, the case study evaluates the potential of composites in a challenging application. The FE model of the original component is developed to evaluate the structural performance in the most significant load conditions. A manufacturing process, based on a RTM technique, is proposed and analysed in order to develop realistic design hypotheses. The design approach is based on an optimisation process with 60 design variables. A constrained multi-objective genetic algorithm is applied to identify the solutions representing the best trade-off between mass reduction and improvement of torsional stiffness. Results show that composite materials can enhance the structural efficiency of the original metallic part, even considering technological limitations and damage tolerance requirements.

Keywords: Composite; Automotive; Optimisation; Genetic algorithms

Blast Resistance and Damage Modelling of Fibre Metal Laminates to Blast Loads by Galal F. A. Mohamed; Costas Soutis; Alma Hodzic (pp. 619-636).

A robust and efficient computational model has been developed which is capable of modelling the dynamic non-linear behaviour of GLARE panels subjected to blast loadings. Numerical model validation have been performed considering case studies of GLARE panels subjected to a blast-type pressure pulse for which experimental data on the back-face deflection and post-damage observations were available. Excellent agreement of mid-point deflections and evidence of severe yield line deformation were shown and discussed against the performed blast tests. A further parametric study identified GLARE as a potential blast attenuating structure, exhibiting superior blast potential against monolithic aluminium plates. It was concluded that further work needed to be carried out to take into account the influence of geometry (cylindrical structures), pre-pressurisation effects and boundary conditions

Keywords: Fibre metal laminates; Blast resistance; Damage; Finite element analysis

Finite Element Analysis of Drilling of Carbon Fibre Reinforced Composites by Ozden Isbilir; Elaheh Ghassemieh (pp. 637-656).

Despite the increased applications of the composite materials in aerospace due to their exceptional physical and mechanical properties, the machining of composites remains a challenge. Fibre reinforced laminated composites are prone to different damages during machining process such as delamination, fibre pull-out, microcracks, thermal damages. Optimization of the drilling process parameters can reduces the probability of these damages. In the current research, a 3D finite element (FE) model is developed of the process of drilling in the carbon fibre reinforced composite (CFC). The FE model is used to investigate the effects of cutting speed and feed rate on thrust force, torque and delamination in the drilling of carbon fiber reinforced laminated composite. A mesoscale FE model taking into account of the different oriented plies and interfaces has been proposed to predict different damage modes in the plies and delamination. For validation purposes, experimental drilling tests have been performed and compared to the results of the finite element analysis. Using Matlab a digital image analysis code has been developed to assess the delamination factor produced in CFC as a result of drilling.

Keywords: Carbon fibres reinforced composites; Polymer matrix composites; Delamination; Finite element analysis; Drilling; Cohesive zone

Progressive Failure Analysis of Composite Structures Using a Constitutive Material Model (USERMAT) Developed and Implemented in ANSYS © by Elisa Pietropaoli (pp. 657-668).

Composites are materials characterized by complex failure phenomena that onset and interact. Several approaches are available in literature to predict the behaviour of composite structures taking into account failure modes. However, most of them require the knowledge of experimental parameters, which generally are not provided by composite suppliers. Progressive failure techniques represent a valuable alternative to these methodologies because they rely on failure criteria and ply-discount techniques often based on the choice of a single degradation factor whose value is chosen by the analyst as small enough to prevent convergence problems in finite element analyses. The aim of this work is to analyze the behaviour of a composite structure taking into account the damage onset and evolution. The analysis is performed by using a constitutive material model (USERMAT) developed and implemented in the Finite element software ANSYS©. The accuracy of the procedure proposed is assessed by comparing numerical results and experimental data taken from literature.

Keywords: Composites; Finite element analysis; Damage; Progressive failure

Impact of the Fibre Bed on Resin Viscosity in Liquid Composite Moulding Simulations by Marc Gascons; Norbert Blanco; Pavel Simacek; Joaquim Peiro; Suresh Advani; Koen Matthys (pp. 669-688).

In the past, simulation of liquid composite moulding processes was often based on the assumption that resin viscosity could be implemented as a constant value. However, viscosity can be subject to changes during the infusion process and now, non-constant and process parameter dependent expressions have become more common in simulation practice. Nevertheless, even with the inclusion of more advanced resin viscosity models, the prediction of flow front propagation in large, thick composite parts or in slow infusion processes is often still inaccurate when compared to the real application. Discrepancies are found to be most pronounced in the final stages of the infusion process, exactly where high accuracy predictions are most valued. A new simulation method based on an infusion time-dependent resin viscosity expression is proposed in this work. The method not only incorporates non-linear viscosity behaviour, but also takes into account the impact of reinforcement fibre sizing and fibre bed architecture on resin viscosity characteristics. Such fibre bed effects are not identifiable in neat resin viscosity characterization tests but are thought to have substantial impact on in-situ viscosity values during infusion, especially for large, thick composite part applications and slow infusion processes. An application case study has been included to demonstrate the prediction capability of the proposed simulation method. The design of an infusion process for a composite pressure vessel was selected for this purpose. Results show high predictive power throughout the infusion process, with most pronounced benefit in the final infusion stages.

Keywords: Fibre bed; Viscosity; Resin infusion; Injection moulding; Composites

Optimisation of Composite Sandwich Structures Subjected to Combined Torsion and Bending Stiffness Requirements by Xiang Li; Gangyan Li; Chun H. Wang (pp. 689-704).

This research is motivated by the rapidly increasing use of composite sandwich structures to reduce weight and improve energy efficiency in a wide range of industries such as automotive, aerospace and civil infrastructure. The paper presents a minimum-weight optimization method for sandwich structures to meet both torsion and bending rigidity requirements. This multiple inequality-constrained optimisation problem is formulated using the Lagrange multiplier method. Solving the resulting equations reveals the optimum solution that can satisfy both flexural and torsion stiffness requirements depend on the stiffness ratio relative to elastic modulus ratio. To illustrate the newly developed optimum design solutions, numerical examples are presented for sandwich structures made of either isotropic face skins or orthotropic composite face skins.

Keywords: Laminates; Mechanical properties; Analytical modelling; Sandwich structures

Numerical and Experimental Investigations on Mechanical Behavior of Composite Corrugated Core by Iman Dayyani; Saeed Ziaei-Rad; Hamid Salehi (pp. 705-721).

Tensile and flexural characteristics of corrugated laminate panels were studied using numerical and analytical methods and compared with experimental data. Prepreg laminates of glass fiber plain woven cloth were hand-laid by use of a heat gun to ease the creation of the panel. The corrugated panels were then manufactured by using a trapezoidal machined aluminium mould. First, a series of simple tension tests were performed on standard samples to evaluate the material characteristics. Next, the corrugated panels were subjected to tensile and three-point bending tests. The force-displacement graphs were recorded. Numerical and analytical solutions were proposed to simulate the mechanical behavior of the panels. In order to model the energy dissipation due to delamination phenomenon observed in tensile tests in all members of corrugated core, plastic behavior was assigned to the whole geometry, not only to the corner regions. Contrary to the literature, it is shown that the three-stage mechanical behavior of composite corrugated core is not confined to aramid reinforced corrugated laminates and can be observed in other types such as fiber glass. The results reveal that the mechanical behavior of the core in tension is sensitive to the variation of core height. In addition, for the first time, the behavior of composite corrugated core was studied and verified in bending. Finally, the analytical and numerical results were validated by comparing them with experimental data. A good degree of correlation was observed which showed the suitability of the finite element model for predicting the mechanical behavior of corrugated laminate panels.

Keywords: Composite corrugated core; Finite element analysis; Glass fiber; Three-point bending test; Tensile test

Enhancing Ultimate Compressive Strength of Notch Embedded Steel Cylinders Using Overwrap CFRP Patch by Mohammad Z. Kabir; Alireza Nazari (pp. 723-738).

In this study, the application of Fiber Reinforced Polymer (FRP) patch for strengthening of the damaged area in thin walled steel cylinders under compression loading was investigated. In this direction, some experimental tests were carried out on the selected notch induced specimens with unique diameter-to-thickness ratio (D/t). The obtained results were compared to the intact cylinder in order to find out the reduction effect of notch on the buckling load of cylinders. Following that, the notched specimens were treated using externally FRP by wrapping around the notched area and the stability strength of the retrofitted specimens was measured experimentally. The investigation was also carried out in numerical analysis using FEM in order to develop the proposed technique for determination of optimum FRP configurations and also better understanding of the experimental observations considering the nonlinear behavior and failure modes for composite member.

Keywords: Repair; Notched cylinder; Nonlinear behavior; FRP patch; Compression

Preliminary Design and Investigation of Integrated Compressor with Composite Material Wheel by Jifeng Wang; Norbert Müller (pp. 739-746).

An integrated water vapor compressor with composite material wheel is developed and strength analysis using FEM is presented. The design of wound composite material allows for integrating all rotating parts of the drive that may simply reduce to only the rotor of the electrical motor, since no drive shaft is required anymore. This design can reduce the number of parts and mass, which is convenient for engineers to maintain the compressor. The electrical motors are brushless DC motors operating through a frequency drive and apply a torque on the wheels through the materials bonded in the wheel shrouds. This system allows a large amount of compression to be produced in a multi-stage compression setup. To determine the stress and vibration characteristics of this integrated compressor, numerical analysis is carried out using FEM. The simulation result shows that the integrated compressor with composite material wheel can be used in a chiller system where water as a refrigerant.

Keywords: Composite material; Integrated compressor; FEM; Design

Finite Element Analysis and Vibration Suppression Control of Smart Wind Turbine Blade by Yin-hu Qiao; Jiang Han; Chun-yan Zhang; Jie-ping Chen; Ke-chuan Yi (pp. 747-754).

With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced the interest for aerodynamic control systems with build-in intelligence on the blades. New structural concepts have emerged where multifunctional materials, exhibiting a strong coupling between its mechanical response and its electrical behaviour, which work as sensors and actuators, are embedded or bonded to composite laminates for high-performance structural applications. The paper aims to provide a way for modeling the adaptive wind turbine blades and analyze its ability for vibration suppress. This study provides a finite element model of the smart blade for wind turbines. Numerical analysis is performed using finite element method, which is used to calculate the time response of the model. The displacement response from the piezoelectric actuator and piezoelectric sensors is obtained to control the vibration. By using this model, an active vibration method which effectively suppresses the vibrations of the smart blade is designed.

Keywords: Wind turbine blade; Smart composites material; Active vibration control; Finite element analysis; independentmodal space control (IMSC)

The Behaviour of Naturally Debonded Composites Due to Bending Using a Meso-Level Model by C. E. Lord; J. A. Rongong; A. Hodzic (pp. 755-766).

Numerical simulations and analytical models are increasingly being sought for the design and behaviour prediction of composite materials. The use of high-performance composite materials is growing in both civilian and defence related applications. With this growth comes the necessity to understand and predict how these new materials will behave under their exposed environments. In this study, the displacement behaviour of naturally debonded composites under out-of-plane bending conditions has been investigated. An analytical approach has been developed to predict the displacement response behaviour. The analytical model supports multi-layered composites with full and partial delaminations. The model can be used to extract bulk effective material properties in which can be represented, later, as an ESL (Equivalent Single Layer). The friction between each of the layers is included in the analytical model and is shown to have distinct behaviour for these types of composites. Acceptable agreement was observed between the model predictions, the ANSYS finite element model, and the experiments.

Keywords: Interfacial friction; ESL theories; Layered composite; Debonded interface

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.19, #3-4)

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.19, #3-4)