Autoclave Moulding Research Articles

EFFECT OF ELEVATED TEMPERATURES AND PRE-IMPACT ON RESIDUAL INTERLAYER STRENGTH OF CARBON FIBER REINFORCED PLASTIC

A series of experimental studies have been carried out to determine the effect of elevated temperatures and preliminary impact on the residual interlayer strength of structural carbon fibre reinforced plastics made on the basis of prepreg technology and autoclave moulding. Interlayer shear tests were carried out at room and elevated temperatures on specimens cut in the form of a short beam, which were subjected to preliminary dynamic impacts with different impact energies (from 1 to 6 J). Loading and energy absorption diagrams of specimens in impact tests were obtained and conclusions about material failure under dynamic loads were drawn. Loading diagrams under the influence of elevated temperatures and preliminary impact have been constructed, on the basis of which the most dangerous factors of external impact on structures have been analysed. During interlayer shear tests the stress and strain fields were recorded using a non-contact optical video system and acoustic emission signals were recorded. Based on the analysis of the data obtained using the digital image correlation method, it was possible to evaluate the mechanical behaviour of the test specimens depending on the impact of different intensity and the influence of elevated temperatures. When analysing acoustic emission data, parametric analysis based on cumulative energy and peak frequencies of signals was carried out, and material failure mechanisms at different pre-impact energies were evaluated. According to the results of complex studies of structural material, the process of damage accumulation, change of composite fracture mechanisms and the influence of external factors on the load-bearing capacity of structures made of the investigated material were qualitatively evaluated.

Effect of CFRP surface topography on the adhesion and strength of composite-composite and composite-metal joints

Manufacturing carbon-fibre reinforced polymer (CFRP) composites via different techniques often leads to contrasting surface topographies. Such differences can affect any subsequent surface pre-treatments that are performed and these can ultimately affect joint strength. In the present work, CFRP adherends made using compression moulding or autoclaving were investigated. Pre-treatment techniques of acetone cleaning, plasma treatment, and grit blasting were studied. It was found that the patterned surfaces which had resulted from the vacuum autoclave moulding resulted in improved joint performance when CFRP substrates were bonded together (homogeneous bonding) compared to joints formed with flatter surfaces following compression moulding. However, when CFRP substrates were bonded to flat aluminium alloy substrates (hybrid bonding) the patterned surfaces resulted in inferior joint performance compared to the flatter CFRP substrates. It is proposed that the dissimilarity of surface topographies on the metal and composite substrates negatively influences the strength of the joint.

Folding behaviour of a deployable composite cabin for space habitats - part 1: Experimental and numerical investigation

Recently, demands for space habitats have increased significantly with the growth of space applications for micro-gravity investigation and space travel. Therefore, there is an urgent need for feasible and practical space habitats to satisfy humanity's growing demands for deep space exploration. This paper and its companion paper propose a deployable composite cabin (DCC) and present a comprehensive study on the folding behaviour of the DCC. Part 1 provides the conceptual design of the DCC and verifies the effectiveness and feasibility of the DCC through the experimental method and numerical simulation. The DCC can achieve folding and deployment functions through elastic deformation in the large deformation process. Using T300/epoxy unidirectional reinforced prepreg as raw material, DCC specimens were prepared by the autoclave moulding process. The experimental fixture was designed and the large deformation folding function of the DCC was successfully verified. The load–displacement curves with typical three stages were obtained. In addition, based on the Riks method and the static method, a finite element analysis (FEA) model was established to predict the folding behaviour of the DCC. The geometric nonlinearity and initial imperfection were considered in the FEA model. The numerical simulation results were in good agreement with the experimental results.

Mechanical Properties of Banana/Bamboo/Coconut Fibre Based Phenolic Hybrid Composites Made by Using Autoclave Moulding Technique

Mechanical Properties of Banana/Bamboo/Coconut Fibre Based Phenolic Hybrid Composites Made by Using Autoclave Moulding Technique

Influence of manufacturing-induced defects on the fatigue performances of autoclave moulded laminates

In the present work, cross-ply and multidirectional laminates were produced by autoclave moulding. Changes in the process parameters led to different microstructural features in terms of fibre volume fraction, global void content, and void size. Fatigue tests revealed a strong influence of the microstructure on the long-term performances of the laminates, in terms of life to crack initiation, crack propagation, crack density evolution and associated stiffness drop. A criterion recently proposed by the authors to predict the formation of the first fatigue cracks accounting for the actual material microstructure, including voids, was then validated on the new experimental data. The results show the need to properly account for the manufacturing induced defects for a more efficient and safer design of composite parts, and remark the necessity of developing models that link manufacturing process parameters, micro-scale morphology, and mechanical performances to enable a cost-effective production that maximizes the performance/cost ratio.

Composite Laminates with Recycled Carbon Fibres and Carbon Nanotubes

Carbon fibre reinforced composites were manufactured by using recycled carbon fibres (CF) and carbon nanotubes (CNT). Dry fabrics were impregnated by hot melting with 1 wt% CNT filled epoxy resin to produce prepregs. Subsequently, composite laminates were manufactured by vacuum bagging and autoclave moulding. Only materials and industrial equipment were used for the laminate production. Laminates with unfilled resin and virgin CFs were also manufactured for comparison. Samples were extracted for physical and mechanical measurements. Dynamic mechanical analyses and bending tests were carried out to evaluate the interaction between CNTs, resin matrix and recycled CFs.

Study on the Effect of Fabric Parameters on the properties of Wave-Transparent Composites

Novel fabric structures of wave-transparent composites having excellent dielectric property were successfully prepared using autoclave moulding. The influence of fabric parameters (such as weaving patterns, hollow ratio, mix structure) on the properties of quartz fiber-reinforced modified cyanate ester composite were systematically investigated. The results show that satin weave fabric-reinforced composites have better mechanical performance than plain weave fabric--reinforced composites. With hollow ratio of fabric increasing the dielectric properties of composites becomes better, except for the mechanical performance. The prepared hollow/solid quartz fabric-reinforced composites in this study display lower dielectric constant and better mechanical properties than quartz/Aramid III and quartz/Poly-p-phenylene benzobisoxazole(PBO).

Evaluation of the Variability of Glass Transition Temperature of Carbon-Fiber-Reinforced Plastic Fabricated by Autoclave Molding

In this work, temperature fields have been modeled during autoclave molding of VKU-46 carbon-fiber-reinforced plastic. It has been shown that a degree of conversion of 97.2–98.4% is achieved in the center of plate upon curing according to the chosen temperature–time mode, while the material is cured completely near the ends. In this case, the glass transition temperature of the material is in the range of 193.2–205.7°C upon preliminary heating. On the contrary, it decreases to 182.5–197.6°C at repeated heating due to the conformational change of macromolecules.

Effect of Autoclave Molding Conditions on Joining Utilizing Thermal Expansion of Carbon-Fiber-Reinforced Thermoplastics

The purpose of this study was to clarify the relationship between the molding pressure of the autoclave when molding carbon-fiber-reinforced thermoplastics (CFRTP) and the bonding strength between CFRTP and aluminum alloy on the basis of the thermal expansion of CFRTP. A CFRTP plate was molded under arbitrary temperature and pressure conditions using an autoclave, and the CFRTP plate was inserted into a heated aluminum piece and joined. A tensile test was conducted on the joined sample, and the joining strength between CFRTP and the aluminum alloy was evaluated. When the molding pressure of the autoclave was varied from 0.2 to 0.8 MPa and the thickness of the CFRTP plate at each molding pressure was confirmed, it was found that a large drop in the plate thickness was observed at the molding pressures of 0.4 and 0.6 MPa. In addition, cross-sectional observation of CFRTP after autoclave molding and heating was conducted, and the unjoined portion was confirmed. Furthermore, from the observation of the cross section, the aspect ratio of the carbon fiber bundle was calculated. As a result, it was found that there is a relationship between the molding pressure of the autoclave and the joining strength between the heat-expanded CFRTP and the aluminum alloy.

Influence of Autoclave Molding Modes and Stack Structure on Porosity of Composite Materials

Influence of stack structure on porosity of composite materials at different modes of autoclave molding was studied. To reduce porosity of composite materials, specific stack structure and molding mode are recommended.

A review on the manufacturing defects of complex-shaped laminate in aircraft composite structures

Current development in the manufacturing of aircraft composite parts has greatly utilized the prepreg materials in the autoclave moulding process in producing exceptional quality of laminates. Nevertheless, several issues related to the manufacturing quality of the complex-shaped laminates are still found unresolved, where the thickness uniformity, resin distribution and fiber wrinkling have been mostly regarded as the critical issues that contribute to the reduced mechanical properties and life span of the structure. A review on the contribution of the processing parameters towards the manufacturing defects of the aircraft complex-shaped laminate is critically presented. The discussion included the effects of the parameters on the defect formation during the sub-processes involved. It was found that the defects occurring were substantially affected by various factors, including mould selection, material characteristics, bagging configuration, etc. Subsequently, the correlation between the processing parameters and the related defects was thoroughly investigated, in which several findings are decisively proposed.

Manufacturing procedure to make flat thermoplastic composite laminates by automated fibre placement and their mechanical properties

Automated fibre placement (AFP) is a relatively new process for the manufacturing of composite structures. Among many attractive features, it provides high-speed of material deposition, more repeatability in terms of quality of the part, less labour intensive (as compared with traditional methods of manufacturing such as Hand Lay-Up), less waste and the ability to transition more seamlessly from design to manufacturing. AFP can be used to process both thermoset composites and thermoplastic composites. Thermoplastic composites processing holds many potential benefits. This is because if the process is done right in producing parts with good quality, it is fast since it does not require a second process such as curing in an autoclave or oven. For the purpose of comparison of performance and for design, it is necessary to determine the mechanical properties of laminates made using this process. However, there are challenges in making flat coupons for the purpose of testing for mechanical properties. This article presents these challenges and the procedure developed to make flat laminates using a simple AFP machine. Mechanical properties of these laminates are also determined and compared with those obtained from laminates made using conventional autoclave moulding.

The Stacking Action in Autoclave Molding and a Process Judgment Analysis of the Worker

Three-dimensional components which incorporate CFRP are molded by skilled workers manually; this makes quality control difficult. This study discusses how workers’ skill influences the mechanical performance of molded products. This study aims to establish qualification criteria and standardize the manufacturing process. Carbon cloth prepreg was stacked in six layers in a mold in a fiber orientation pattern of 0°, 45°, 0°, 0°, 45°, and 0°. The hand lay-up process was applied and subjects chose their own process and tools. Subject A had 13 years of experience and subject B had 1 year of experience. The process was recorded with a video camera and results compared in an interview format, inspecting footage of the process together with the subject. Subject A's movements were very smooth, his body and face close to the mold, whilst subject B's movements were very awkward. Subjects’ use of tools and hands were analyzed. In the judgment analysis, subjects were interviewed and their responses analyzed. The subjects’ decision-making processes were given numeric values and studied, identifying the critical path. There was a noticeable difference in the subjects’ process and a significant difference in the mechanical properties of the molds. This study will be repeated with more subjects in order to identify the various factors.

Study on Scheduling Method for Reentrant Autoclave Moulding Operation of Composite Materials

The autoclave moulding process of composites is characterized by reentrance, capacity and time constraints. Its scheduling directly affects productivity and production cycle of composites. Scheduling methods in the existing literature can't meet the requirements of its scheduling optimization. Aiming at improving utilization and reducing energy consumption of autoclave, based on the Theory of Constraints, a heuristic algorithm considering the capacity and time constraints is proposed to solve the scheduling problem, and priority scheduling rules are established. The studying of a case shows the effectiveness of the algorithm.

A computer-aided design system for framed-mould in autoclave processing

The general computer-aided design (CAD) software cannot meet the mould design requirement of the autoclave process for composites, because many parameters such as temperature and pressure should be considered in the mould design process, in addition to the material and geometry of the part. A framed-mould computer-aided design system (FMCAD) used in the autoclave moulding process is proposed in this paper. A function model of the software is presented, in which influence factors such as part structure, mould structure, and process parameters are considered; a design model of the software is established using object oriented (O-O) technology to integrate the stiffness calculation, temperature field calculation, and deformation field calculation of mould in the design, and in the design model, a hybrid model of mould based on calculation feature and form feature is presented to support those calculations. A prototype system is developed, in which a mould design process wizard is built to integrate the input information, calculation, analysis, data storage, display, and design results of mould design. Finally, three design examples are used to verify the prototype.

Fiber optic sensors for monitoring flow in vacuum enhanced resin infusion technology (VERITy) process

Today, with cost becoming a very important factor, alternate processes for manufacturing composite structures, wherein the cost can be reduced but having similar properties to prepreg systems are being explored. National Aerospace Laboratories, India is developing the VERITy process, which is essentially a hybridization of the VARTM and the autoclave moulding process. One of the concerns in this process, especially when making large integrated co-cured structures with varying thickness, is the knowledge of the resin flow front location at all times. A network of flow-sensors, which could provide information on the flow front location, would be very useful. This paper discusses the experimental studies carried out towards the development of a flow-sensor in the optical domain to determine the presence of resin qualitatively. Three different approaches have been attempted to detect the arrival of the resin flow front and these results are presented.

Correlated Rules between Complex Structure of Composite Components and Manufacturing Defects in Autoclave Molding Technology

Based on statistical analysis, considerable defect information obtained by nondestructive identification (NDI) techniques for composite components, different type defects which often form in autoclave molding of composites were summarized, and the effect rules of complex structure in composite components on manufacturing defects were also revealed. Combined with statistical results and defect micrographs, the strong correlation between geometric characteristics (for instance, thickness, gradient of thickness variation, curvature radius) in composite components and controllability of manufacturing defects was discussed in detail. It was found that delamination, pore, void, and rich resin were the four main defects in autoclave molding, and that the ratio of defect appearance was remarkably influenced by complex structure of composite components. Especially, geometric characteristics of composite components had a significant influence on the defect type and defect ratio. For example, too thin or too thick components, too small radius and abrupt change of thickness in components would obviously increase the ratio of defect production. Thickness, curvature radius, and gradient of thickness variation would probably lead to the defects of delamination and void, and gradient of thickness variation would also result in rich resin around the overlap region of long fiber and short fiber in the thickness transition zone.

Beyond the pin-jointed net: maximising the deformability of aligned continuous fibre reinforcements

The ease with which reinforcements can be formed to the shape of the tool has a major influence on the labour required to make composite parts by manual lay-up and autoclave moulding, and thus on the cost of those parts. Woven cloth has been seen as the standard against which the drape and formability of other materials are judged. The emergence of alternative materials and manufacturing approaches, particularly, mechanical rather than manual forming, makes a reappraisal of the benefits and limitations of the deformation of woven cloths, a timely issue. This paper seeks to set out such a reappraisal. It compares the manual and mechanical forming processes and considers how the deformation properties of the reinforcement must be made to suit the process. Experimental data is presented to demonstrate that under some circumstances cross-plied unidirectional prepreg gives superior forming characteristics to woven cloth prepreg.

117 Cure Monitoring of FRP Laminates by Using FBG Fiber Optic Strain and Temperature Sensors during Autoclave Molding

117 Cure Monitoring of FRP Laminates by Using FBG Fiber Optic Strain and Temperature Sensors during Autoclave Molding

A study of the feasibility of a monoblock racing motorcycle rim

After having created inflatable silicone rubber tools that are adapted for the pressing of prepreg plies during the moulding of hollow complex forms made of composite materials, their production has not only been stabilised but also performed according to current industrial processes. Such a device is to be considered as an alternative to autoclave moulding (for which the hourly cost is too high) or to moulding on a solid foam core (limited to simple hollow shapes). Furthermore it is to be applied to a tool involved in manufacturing the monoblock of a racing motorcycle. The tool is made by vulcanising and inflating uncurred sheets of silicone rubber inside a forming mould. Thereby do we get a hollow core which is then coated by the prepreg plies? The coated core is then put inside a rigid mould which will shape the external side of the mould. During curing, done in a conventional oven, these tools are regulated under a controlled pressure in order to obtain an optimal pressing. Curing in an oven is not only cheap but also allows us to achieve a competitive cost for lines including more than five parts.