Composite Structural Parts Research Articles

Increasing Cost and Eco Efficiency for Selective Tape Placement and Forming by Adaptive Process Design

The automated placement of continuous fiber-reinforced polymer prepregs (pre-impregnated) is a generative manufacturing technology for composites. Particularly laser-assisted tape placement of unidirectional continuous fiber-reinforced tapes provides potentials for highly flexible composite manufacturing. Whereas the single process of tape placement to generatively build up load carrying structures was already optimized in several research activities and projects, an integrated process chain approach promises further increases in cost and eco efficiency. An adaptive process design considering interdependencies between selective tape placement and a subsequent forming improves the entire process chain. Due to the knowledge of process interdependencies, the advantages of high speed placement on predetermined load carrying areas can be fully exploited. The system and process design for this adaptive manufacturing approach, the underlying assessment methodology as well as its application on a manufacturing process chain for structural composite parts are presented in this paper.

Fatigue Damage Modeling Techniques for Textile Composites: Review and Comparison With Unidirectional Composite Modeling Techniques

Composite structural parts have been successfully introduced in high performance industries. Nowadays, also lower performance, high volume production industries are looking for the application of composites in their products. Especially attractive are textile composites (woven, braided, etc.) because of their better drapability and higher resistance to out-of-plane and dynamic loads. Currently, however, extensive mechanical tests are needed to properly design a composite structure. This is a requirement the large volume industries typically do not have the resources nor the time for. Reducing the need for structural tests can only be done if reliable simulation techniques are available. Simulation techniques for fatigue loading are particularly interesting because products generally have to perform their function over a period of time. For the textile structural composites concerned in this paper, some notable modeling techniques have been developed over the past 15 years. These techniques are presented here and the state of the art is established together with insights for future development by comparing the state of the art with the modeling techniques for laminates from unidirectional (UD) laminae.

Simulating tape resin infiltration during thermoset pultrusion process

The thermoset tape pultrusion is a widely adopted manufacturing process to produce long, constant cross-section composite structural parts. For high volume production, low cost can be achieved by maximizing the production rate which is a function of the material and process parameters, more specifically the rate of resin infiltration and resin cure. During resin infiltration, the resin saturates the dry reinforcement either under positive pressure in the pressure chamber, or, by the action of capillary and surface forces, within the resin bath. In either case, the saturation must be completed as the tape is squeezed into the final cross-sectional form at the entrance of the heated mold where the resin will be cured to form the composite part.This paper models the resin infiltration process during pultrusion, by modifying the pre-existing simulation tool for liquid molding processes. The formulated capability can be used not only to optimize the impregnation dynamics within the pressure chamber, but can also be used to predict the required forces for the selected pulling rate. The proposed model does allow one to handle a variety of tape cross-sections, not just rectangular prisms.

A numerical methodology for optimizing the geometry of composite structural parts with regard to strength

The increased use of composite materials in lightweight structures has generated the need for optimizing the geometry of composite structural parts with regard to strength, weight and cost. Most existing optimization methodologies focus on weight and cost mainly due to the difficulties in predicting strength of composite materials. In this paper, a numerical methodology for optimizing the geometry of composite structural parts with regard to strength by maintaining the initial weight is proposed. The methodology is a combination of the optimization module of the ANSYS FE code and a progressive damage modeling module. Both modules and the interface between them were programmed using the ANSYS programming language, thus enabling the implementation of the methodology in a single step. The parametric design language involves two verifications tests: one of the progressive damage model against experiments and one of the global optimization methodology performed by comparing the strength of the initial and the optimum geometry. There were made two applications of the numerical optimization methodology, both on H-shaped adhesively bonded joints subjected to quasi-static load. In the first application, the H-shaped joining profile was made from non-crimp fabric composite material while in the second from a novel fully interlaced 3D woven composite material. In the optimization of the joint’s geometry, failure in the composite material as well as debonding between the assembled parts was considered. For both cases, the optimization led to a considerable increase in joint’s strength.

A detailed experimental study of the effects of pre-bond contamination with a hydraulic fluid, thermal degradation, and poor curing on fracture toughness of composite-bonded joints

Adhesive bonding is applied by the aircraft industry both for assembling composite structural parts and implementing composite patch repairs in damaged structural parts. In both applications, there exist several scenarios, related to surface contamination and processing, that could affect bonding quality and thus, degrade bond strength. In this paper, the detailed effects of pre-bond contamination with a hydraulic fluid, thermal degradation of the composite substrate, as well as poor curing (lower curing temperature) on strength of composite-bonded joints were studied experimentally by conducting mode I fracture toughness tests on double-cantilever beam specimens. These three application scenarios are possible to appear in the implementation of a composite patch repair in a damaged composite structural part. The experimental results showed a contradictory effect as the presence of the hydraulic fluid and poor curing degrades the fracture toughness whereas thermal degradation enhances fracture toughness of the composite-bonded joints. These findings are explained by means of extended non-destructive inspection, surface analysis, and evaluation of fracture surfaces.

Experimental Study on the Identification of the Saturation of a Porous Media through Thermal Analysis

Resin Transfer Molding (RTM) is among the most commonly used fabrication processes for producing high quality and complex composite structural parts. RTM process consists of placing a dry fibrous preform into a mold cavity. A liquid resin is subsequently injected into that cavity. The consolidation of the part is then obtained by crosslinking in case of a thermosetting resin or by crystallization in case of thermoplastic one. Voids can be created in the porous medium during the flow of the resin. Presence of residual voids in the composite part at the end of the filling drastically affect mechanical performances. Even if several authors have contributed to a better understanding and modeling of the mechanisms of formation and transport of voids during injection, few experimental approaches allowed a direct measurement of the saturation curve. The aim of this study is then to identify the saturation of a fibrous preform by a liquid through thermal analysis. To address this issue, an experimental bench that allows the injection of a fluid into a textile preform has been used. This apparatus combines the measurement of temperatures and wall heat flux densities at several locations. A simplified modeling of the filling front has been performed with FEM using Comsol Multiphysics™. The saturation curve is modeled using several geometric parameters. Saturation is taken into account through the evolution of thermophysical properties. Effective thermophysical properties of the dry and completely-saturated porous medium in transverse and longitudinal directions have been measured by several methods, and their results have been then cross-checked and compared with good accuracy. The evolution between these two states has been modeled. A particular attention has been paid for the modeling of the transverse thermal conductivity. This parameter has been modeled using a periodic homogenization method as a function of the micro- and macro-saturation. The saturation curve parameters are determined by minimizing the cost function defined as the square difference between the measured and computed heat flux. The obtained saturation curve is finally compared with the one measured by a conductometric sensor.

Adhesive bonding of composite aircraft structures: Challenges and recent developments

In this review paper, the challenges and some recent developments of adhesive bonding technology in composite aircraft structures are discussed. The durability of bonded joints is defined and presented for parameters that may influence bonding quality. Presented is also, a numerical design approach for composite joining profiles used to realize adhesive bonding. It is shown that environmental ageing and pre-bond contamination of bonding surfaces may degrade significantly fracture toughness of bonded joints. Moreover, it is obvious that additional research is needed in order to design joining profiles that will enable load transfer through shearing of the bondline. These findings, together with the limited capabilities of existing non-destructive testing techniques, can partially explain the confined use of adhesive bonding in primary composite aircraft structural parts.

Simulation Technique Application in Composite Material Structure Manufacture

Along with the wide range application of composite material structural parts in the field of aviation, the research of its manufacture technique, especially the research of composite material entirety structure parts with complex outline surface becomes more and more important. This article proceeds the simulation analysis of spring-back transformation caused in proceedings of composite material structure solidifying. It states the necessity of the application of composite material solidifying deformation simulation technology in airplane structures manufacture.

Recent advances in sharing standardized STEP composite structure design and manufacturing information

Composite structures have been developed and used in the aerospace, automobile, sports, and marine industries since the early 1940s. Compared to conventional metallic structures, newer high-performance composite structures provide benefits such as decreased weight and reduced energy consumption. An international standards subcommittee on industrial automation systems and integration has developed and implemented a standard, ISO 10303-209, for sharing the manufacturing information for these complex composite structures. This standard, part of the family of standards commonly known as the Standard for Exchange of Product model data (STEP), is considered essential for improving the design, analysis, and manufacturing productivity of composite structures. The ISO 10303-209 standard also enables the long-term data retention necessary to support the composite structures throughout the lifetime of the products that use them. This paper describes recent advances that led to the development of ISO 10303-209 data models for composite structural shape and composition. The paper also reports the status of ongoing implementation and testing efforts. Varied usage scenarios have motivated several areas for future improvement, such as full three-dimensional representation and the efficient cost-effective visualization of composite structural parts. Issues and their proposed solutions, along with their anticipated impacts on the design, analysis, manufacturing, and long-term support of composite structures are also discussed.

Micromechanical-based hybrid mesoscopic three-dimensional approach for non-linear progressive failure analysis of composite structures—Part B: Comparison with experimental data

This paper presents a comparison between the experimental results provided in the PART B of the second World Wide Failure Exercise and the predictions obtained from a Micromechanical-based hybrid mesoscopic 3D approach described in the PART A of this exercise. This hybrid damage and failure approach is based on physical principles and introduces micromechanical aspects (such as the effect of the local debonding on the non-linear behaviour and on the strengths) at the mesoscopic scale. The behaviour of the UD ply is described by a thermo-viscoelastic model. For the failure phenomena, a distinction is made between different modes of failure: failure in fibre mode, in-plane interfibre mode and through-the-thickness interfibre mode. A fine damage model, that describes the evolution of the crack density and of the associated local delamination, is used to take into account the degradation of the mechanical properties of a failed ply in in-plane interfibre mode until the final failure of the laminate. Finally, the final failure of the specimen is defined as a critical loss of rigidity of the laminate. The predictions are in quite good agreement with the experimental results.

Three-dimensional braiding for composites: A review

The aim of this study is to review three-dimensional (3D) braided fabrics and, in particular, to provide a critical review of the development of 3D braided preform structures and techniques. 3D braided preforms are classified based on various parameters depending on the yarn sets, yarn orientation and intertwining, micro-meso unit cells and macro geometry. Biaxial and triaxial two-dimensional (2D) braided fabrics have been widely used as simple- and complex-shaped structural composite parts in various technical areas. However, 2D braided fabric has size and thickness limitations. 3D braided fabrics have multiple layers and no delamination due to intertwine-type out-of-plane interlacement. However, the 3D braided fabrics have low transverse properties and they also have size and thickness limitations. On the other hand, various unit cell base models on 3D braiding were developed to analyze the properties of 3D braided structures. Most of the unit cell base models include micromechanics and numerical techniques. Multiaxis 3D braided fabrics have multiple layers and no delamination. The in-plane properties of multiaxis 3D braided fabrics may be enhanced due to the ±bias yarn layers. However, the multiaxis 3D braiding technique is at an early stage of development and needs to be fully automated.

Analyze of the Contact Behaviour between Two Layers of Dry Glass Plain Weave Fabric

The market demand for thicker complex shaped structural composite parts is increasing. Processes of the Liquid Composite Moulding (LCM) family, such as Resin Transfer Moulding (RTM) are considered to manufacture such parts. The first stage of the RTM process concerns the preforming of the part. During the preforming of multi-layered reinforcements, friction between the plies occurs and needs to be characterize and then to be taken into account for the forming simulation. An experimental device designed to analyze the ply/ply, ply/tool and yarn/yarn frictions has been built. Tests carried out on a glass plain weave highlight specific contact behaviour for dry reinforcement fabric in comparison to non-technical textiles. This behaviour exhibits a substantial variation of the contact tangential loads which is directly related to shocks between the yarns. It demonstrated that period and amplitude of the friction response is directly related to the relative positioning of the samples but also to fabric meso-strucrure. In addition, the sample relative orientation has a significant influence on the friction response. The meso-architecture is responsible for the high variations of the friction coefficient as a function of the ply orientations for different fabrics. In addition, the friction response appears to be very sensitive to tests parameters like the relative positioning, orientation of the samples and the cycling. A honing effect classically observed in dry fabric testing has also been pointed out through cyclic experiments. It can be attributed to both fibre material abrasion and fibre reorganisation inside the yarn.

Multiaxis three-dimensional weaving for composites: A review

The aim of this study is to review three-dimensional (3D) fabrics and a critical review is especially provided on the development of multiaxis 3D woven preform structures and techniques. 3D preforms are classified based on various parameters depending on the fiber sets, fiber orientation and interlacements, and micro–meso unit cells and macro geometry. Biaxial and triaxial two-dimensional (2D) fabrics have been widely used as structural composite parts in various technical areas. However, they suffer delamination between their layers due to the lack of fibers. 3D woven fabrics have multiple layers and no delamination due to the presence of Z-fibers. However, the 3D woven fabrics have low in-plane properties. Multiaxis 3D knitted fabrics have no delamination and their in-plane properties are enhanced due to the ±bias yarn layers. However, they have limitations regarding multiple layering and layer sequences. Multiaxis 3D woven fabrics have multiple layers and no delamination due to Z-fibers and in-plane properties enhanced due to the ±bias yarn layers. Also, the layer sequence can be arranged based on end-use requirements. However, the multiaxis 3D weaving technique is at an early stage of development and needs to be fully automated. This will be a future technological challenge in the area of multiaxis 3D weaving.

Design and Potentiality of an Apparatus for Measuring Yarn/Yarn and Fabric/Fabric Friction

The market demand for thicker complex shaped structural composite parts is increasing. Processes of the Liquid Composite Moulding (LCM) family, such as Resin Transfer Moulding (RTM) are considered to manufacture such parts. The first stage of the RTM process consists in the preforming of the part. During the pre-forming of multilayered reinforcements, frictions between the plies occur and need to be taken into account for the forming simulation. An experimental device designed to analyse the ply/ply and ply/tool frictions has been set up. The different set up steps of the device are described. First results are presented, which show the ply/ply friction behaviour for a glass plain weave fabric. A specific contact behaviour has been observed for dry reinforcement fabric in comparison to non-technical textiles. A honing effect classically observed in dry fabric testing has also been pointed out through cyclic experiments. It can be attributed to both fibre material abrasion and fibre reorganisation inside the yarn.

Analysis of Stud Connector of Steel-Concrete Composite Structure

The steel - concrete composite structure has many advantages in the field of reinforcement of bridge. But it is an important factor that whether the stud connector can make the components be firmly combined and make them work together. The research in this area has been not enough depth. The purpose of this study is to establish the design formula of stud in composite structure. Based on the conversion section theory, the strengthened part of composite structure is simplified into a kind of structure which is composed by only one kind of equivalent material and its physical property is similar to the original. In addition, the simplified model is gotten by mechanical analysis of the composite structures with steel plate and stud. Then through the application of elasticity theory method, the static equilibrium is carried out on the integrated structure and so the shear capacity in stud of connectors is gotten.

Use of numerical simulation of woven reinforcementforming at mesoscale: Influence of transversecompression on the global response

Among the possible forming processes for structural composite parts, the Liquid Composite Moulding ones are widely used. For such kind of forming process, a resin injection phase occurs after the forming of a dry fibrous reinforcement skeleton. Several parameters can affect the quality of the manufactured part. It has been experimentally proved that the deformation of the fibrous reinforcement has a significant influence on its permeability. In order to evaluate that parameter, it is necessary to have a realistic deformed solid skeleton. During the pre-forming stage, the fibrous reinforcement can be subjected to different kind of loading: yarn tension and in-plane shear to obtain the correct part shape, but also transverse compression. The aim of this paper is to analyze the influence of that last loading mode on the global state of the solid skeleton. For that purpose, two aspects are explored. First, numerical simulations are performed at the mesoscopic scale: a finite element model of the smallest pattern of the woven textile is realized in which each yarn is modelled used 3D elements. The constitutive behaviour of the yarn must exhibit the specificities of a fibrous material. Secondly, experimental characterization of the yarn material is realized. For that, a new experimental setup is used which allow to investigate the relation between longitudinal tension and transverse compression stiffness of the yarn. This allows determining the material parameters used in the yarn constitutive equation. The other material parameters are determined using a tensile test and an in-plane shear test. X-ray tomography gives geometrical validations of the model.

Innovative Tape Placement Robotic Cell: High Flexibility System to Manufacture Composite Structural Parts With Variable Thickness

Until today, there are only automated processes able to manufacture composite components with a constant thickness. This work focuses on the need to find a system able to manufacture composite structural parts characterized by a variable thickness. An innovative tape placement robotic cell composed of a deposition integrated system and an anthropomorphic robot with 6DOF is shown in this work. The main characteristics of the designed deposition integrated system are (i) alternate deposition movement, (ii) tape compaction system, and (iii) tape tension control system by proportional-integral-derivative (PID) controllers. With these systems, it is possible to obtain a high flexibility robotic cell that allows to manufacture variable thickness components with good mechanical volumetric properties. After the design phase, the system has been realized and afterwards it has been validated by analyzing the experimental tests with the quality of some benchmark manufactured by the innovative cell.

Optimal Injection Design for Resin Transfer Molding with In Situ Permeability Measurement and Process Simulation

Resin transfer molding (RTM) process has been gaining extensive attention because of its ability to produce complex structural composite parts. Researchers have made significant progress toward obtaining quality products. The preform permeability change during actual molding process brings up difficulty in achieving consistency in part quality. This article presents an adaptive RTM injection design approach in which process simulation and Hardware-In-the-Loop-Simulation (HILS) technique are used: the whole-field preform permeability profile is provided by an in situ gas-assisted permeability measurement system and then inputted to the process simulation right before each control step during molding; an open loop control method steering the resin flow is also proposed. It is found that the HILS can be used to realize optimal injection design and flow control with accurate online permeability estimation.

Multiobjective stacking sequence optimization for laminated composite structures

A Pareto-based multiobjective evolutionary algorithm is presented for stacking sequence optimization of composite structural parts. Special attention has been paid to engineering design guidelines for stacking sequence design. These guidelines are included into the formulation of the optimization problem as constraints or additional objectives. A new initialization strategy is proposed following mechanical considerations. The method is applied to the optimal design of a composite plate for weight minimization and maximization of the buckling margins under three hundred load cases that make also the originality of this work. It is shown that the introduction of new ply orientations compared to the classical 0°, ±45° and 90° plies can lead to significantly improved optimal designs.

Behavior of Steel Beam-to-Column Joints at Elevated Temperature: Experimental Investigation

Although beam-to-column joints are a critical part of steel and composite framed structures, very few tests have been conducted under fire conditions. Of the tests conducted, only a limited range of joint types has been studied. The main reason for this is the high cost associated with elevated-temperature tests. This paper presents the results of an experimental investigation of typical steel extended end-plate beam-to-column joints at elevated temperatures. Six beam-to-column joints were tested. These included three tests conducted at 400, 550, and 700°C, and another three tests on specimens at 700°C with different axial compression forces applied to the beams to simulate restraint effects. Moment-rotation-temperature characteristics are summarized in order to investigate the degradation of this type of steel joint at elevated temperatures.