Aerospace Composites Research Articles

Impact properties of thermoplastic composites

The excellent properties exhibited by thermoplastic composites at much reduced weight have attracted attention in the development of products in different sectors. Thermoplastic (TP) composites, because of their distinctive properties as well as ease of manufacturing, have emerged as a competitor against the conventional thermoset resin-based composites. Depending on the application, these composites may undergo impact events at various velocities and often fail in many complex modes. Hence, the development of TP composites having high energy-dissipation at (the desired) much-reduced weight has become a challenging task, but it is a problem which may be alleviated through the appropriate selection of materials and fabrication processes. Furthermore, fibre surface modification has been shown to increase fibre-matrix interfacial adhesion, which can lead to improved impact resistance. Textile preforms are helpful in acting as a structural backbone in the composites since they offer a relatively free hand to the composite designer to tailor its properties to suit a specific application. Additionally, hybrid textile composite structures may help in achieving the desired properties at much lower weight.Simulation software can play a significant role in the evaluation of composites without damaging physical samples. Once the simulation result has been validated with actual experimental results, it should be possible to predict the test outcomes for different composites, with different characteristics, at different energy levels without conducting further physical tests. Various numerical models have been developed which have to be incorporated into these software tools for better prediction of the result.In the current issue of Textile Progress, the effects of various materials and test parameters on impact behaviour are critically analyzed. The effect of incorporating high-performance fibres and natural fibres or their hybrid combination on the impact properties of TP composites are also discussed and the essential properties of TP polymers are briefly explained. The effects of fibre and matrix hybridization, environmental factors, various textile preform structures and fibre surface modification treatments on the impact properties of thermoplastic composites are examined in detail. Various numerical models used for impact analysis are discussed and the potential applications of TP composites in automobile, aerospace and medical sectors are highlighted.

Delamination fatigue growth in polymer-matrix fibre composites: A methodology for determining the design and lifing allowables

The introduction, originally in 2009, by the FAA of a ‘slow growth’ approach to the certification of polymer-matrix fibre composites has focused attention on the experimental data and the analytical tools needed to assess the growth of delaminations under cyclic-fatigue loads. Of direct relevance is the fact that fatigue tests on aircraft composite components and structures reveal that no, or only little, retardation of the fatigue crack growth (FCG) rate occurs as delamination/impact damage grows. Therefore, of course, the FCG data that are ascertained in laboratory tests, and then employed as a material-allowable property to design and life the structure, as well as for the development, characterisation and comparison of composite materials, must also exhibit no, or only minimal, retardation. Now, in laboratory tests the double-cantilever beam (DCB) test, using a typical carbon-fibre reinforced-plastic (CFRP) aerospace composite, is usually employed to obtain fracture-mechanics data under cyclic-fatigue Mode I loading. However, it is extremely difficult to perform such DCB fatigue tests without extensive fibre-bridging developing across the crack faces. This fibre-bridging leads to significant retardation of the FCG rate. Such fibre-bridging, and hence retardation of the FCG, is seen to arise even for the smallest values of the pre-crack extension length, ap − a0, that are typically employed. The results from the DCB tests also invariably exhibit a relatively large degree of inherent scatter. Thus, a methodology is proposed for predicting an ‘upper-bound’ FCG curve from the laboratory test data which is representative of a composite laminate exhibiting no, or only very little, retardation of the FCG rate under fatigue loading and which takes into account the inherent scatter. To achieve this we have employed a novel methodology, based on using a variant of the Hartman-Schijve equation, to access this ‘upper-bound’ FCG rate curve, which may be thought of as a material-allowable property and which is obtained using an ‘A basis’ statistical approach. Therefore, a conservative ‘upper-bound’ FCG curve may now be calculated from the DCB laboratory test data for material development, characterisation and comparative studies, and for design and lifing studies.

Towards High Productivity in Precision Grinding

Over the last century, substantial advances have been made, based on improved understanding of the requirements of grinding processes, machines, control systems, materials, abrasives, wheel preparation, coolants, lubricants, and coolant delivery. This paper reviews a selection of areas in which the application of scientific principles and engineering ingenuity has led to the development of new grinding processes, abrasives, tools, machines, and systems. Topics feature a selection of areas where relationships between scientific principles and new techniques are yielding improved productivity and better quality. These examples point towards further advances that can fruitfully be pursued. Applications in modern grinding technology range from high-precision kinematics for grinding very large lenses and reflectors through to medium size grinding machine processes and further down to grinding very small components used in micro electro-mechanical systems (MEMS) devices. The importance of material issues is emphasized for the range of conventional engineering steels, through to aerospace materials, ceramics, and composites. It is suggested that future advances in productivity will include the wider application of artificial intelligence and robotics to improve precision, process efficiency, and features required to integrate grinding processes into wider manufacturing systems.

Recent Advances in Active Infrared Thermography for Non-Destructive Testing of Aerospace Components.

Active infrared thermography is a fast and accurate non-destructive evaluation technique that is of particular relevance to the aerospace industry for the inspection of aircraft and helicopters’ primary and secondary structures, aero-engine parts, spacecraft components and its subsystems. This review provides an exhaustive summary of most recent active thermographic methods used for aerospace applications according to their physical principle and thermal excitation sources. Besides traditional optically stimulated thermography, which uses external optical radiation such as flashes, heaters and laser systems, novel hybrid thermographic techniques are also investigated. These include ultrasonic stimulated thermography, which uses ultrasonic waves and the local damage resonance effect to enhance the reliability and sensitivity to micro-cracks, eddy current stimulated thermography, which uses cost-effective eddy current excitation to generate induction heating, and microwave thermography, which uses electromagnetic radiation at the microwave frequency bands to provide rapid detection of cracks and delamination. All these techniques are here analysed and numerous examples are provided for different damage scenarios and aerospace components in order to identify the strength and limitations of each thermographic technique. Moreover, alternative strategies to current external thermal excitation sources, here named as material-based thermography methods, are examined in this paper. These novel thermographic techniques rely on thermoresistive internal heating and offer a fast, low power, accurate and reliable assessment of damage in aerospace composites.

Numerical Modelling for Optimization of Fibres Winding Process of Manufacturing Technology for the Non-Circular Aerospaces Frames

This article deals with the issue of mathematical calculating the trajectory of the end-effector of an industrial robot in the manufacture of aerospace composites. Robots are used to define the winding orientation of the fibre strands on a non-bearing 3D core. The 3D core is attached to the robot-end-effector and is led through a fibre-processing head according to a suitably defined robot trajectory during winding of the fibre on the core. The quality of the composite depends greatly on the correct winding angles of the fibres on the frame and on the homogeneity of the individual winding layers. The implementation of these two conditions is related to determining the correct trajectory of the industrial robot, which is part of the composite production technology. The numerical modelling of a passage of the on-bearing 3D core through a fibre-processing head is described in the article. Differential evolution algorithm and matrix calculus are applied to the numerical calculation of optimized robot-end-effector trajectory to achieve optimal angles of windings of fibres on the frame. The numerical calculations of the trajectory of the robot-end-effector were used for verified for the calculated trajectory of the robot-end-effector in the real conditions of robotic laboratory of department of machinery construction.

On the fatigue response of a bonded repaired aerospace composite using thermography

Lock-in thermography was employed to investigate the repair efficiency of a bonded repaired aerospace composite subjected to step-wise cycling mechanical loading. The studied component (substrate) was artificially damaged with a 5 mm circular notch and subsequently repaired with a tapered bonded patch. Critical and sub-critical damage of the repaired component was monitored via thermography during 5 Hz tension–tension fatigue. The examination of the acquired thermographs enabled the identification of the patch debonding propagation as well as the quantification of the stress magnification at the patch ends and the locus of the circular notch. It was found that fatigue mechanical loading yields both thermoelastic and hysterestic phenomena with the latter being more prominent prior to the failure of the studied repaired component.

Low-Velocity Impact Localization on Composites Under Sensor Damage by Interpolation Reference Database and Fuzzy Evidence Theory

Composites are widely used in aeronautical manufacturing. Despite their excellent properties, composites suffer from barely visible impact damage caused by low-velocity objects. Random impacts need to be detected and located to alert pilots and engineers of the need for maintenance. Generally, fiber Bragg grating (FBG) sensors are installed in aerospace composites, and a reference database is established by recording the reference signals from different impact positions. The random impact is located by comparing its signal to the reference signals in the database. The performance of current localization algorithms mainly relies on the repeatability of FBG signals. However, the FBG sensors or their installation structures may be damaged by repeated impacts during the monitoring process, and the localization accuracy will decrease. In this paper, a new algorithm is proposed based on the interpolation reference database and fuzzy evidence theory to realize accurate impact localization under sensor damage. More correlation coefficients are obtained from the basic reference database by interpolation, and the influence of damaged sensors on localization results is reduced by fuzzy evidence theory. The proposed algorithm was tested on a carbon fiber reinforced polymer plate with four surface-attached FBG sensors. A parametric study was conducted to determine the coefficients of the algorithm. The localization performance was analyzed with both properly functioning sensors and damaged sensors. The results showed that the localization accuracy was better than the existing algorithms, especially in the case of sensor damage.

Machinability studies of aerospace steel using hot end milling

Hot Machining (HM), a hard part machining technology, has gained popularity due to its simplicity and economical solutions. It is possible to machine any material in the hardened state and can achieve the required surface finish without employing additional processes. Several HM systems have been emerged as most efficient machining processes and provided solutions for critical aerospace materials, super alloys, ceramics and composites. The aim of this paper is to investigate the effect of critical process parameters on the machinability of hardened EN24 steel using hot machining process. The material removal rate and surface finish are considered as responses as they are true measures of machinability of any material. Literature shows that little work has been carried out for EN24 steels using hot milling process. The experiments are conducted on 4-axis CNC Machining Centre, using Taguchi’s orthogonal arrays to select separate set of parameters for material removal as well as better surface finish. This report provides the details of experimentation, analysis of results and recommends the appropriate combination of process parameters to achieve better machinability in terms of surface finish and improved material removal.

Multifunctional graphene/POSS epoxy resin tailored for aircraft lightning strike protection

Abstract This paper presents a first successful attempt to obtain a conductivity mapping at nanoscale level of a new multifunctional fire retardant graphene/polyhedral oligomeric silsesquioxane (POSS) epoxy resin using Tunneling Atomic Force Microscopy (TUNA) that is a very sensitive mode by which ultra-low currents ranging from 80 fA to 120 pA can be measured. The multifunctional material, specifically designed to meet structural aeronautical requirements, such as suitable thermal stability, fire resistance, mechanical performance and electrical conductivity, has proven to be a promising candidate in the field of aeronautic and aerospace composites. The results also highlight the great potentiality of TUNA technique to analyze conductive networks at nanodomain level. Through simultaneous topographic and current images acquisition, this technique enables a direct correlation of local topography with electrical properties of the nanofiller based samples. The intrinsic electrical conductivity of the manufactured polymeric systems allows TUNA measurements without using electrical conductive paint, which is usually employed for polymeric systems to ensure effective electrical contacts to the ground.

Scheduling in aerospace composite manufacturing systems: a two-stage hybrid flow shop problem

This research investigates a real-world complex two-stage hybrid flow shop scheduling problem which is faced during the manufacturing of composite aerospace components. There are a number of new constraints to be taken into account in this special hybrid flow shop, in particular limited physical capacity of the intermediate buffer, limited waiting time between processing stages, and limited tools/molds used in both stages in each production cycle. We propose a discrete-time mixed integer linear programming model with an underlying branch and bound algorithm, to solve small- and medium-size problems (up to 100 jobs). To solve the large instances of the problem (up to 300 jobs), a genetic algorithm with a novel crossover operator is developed. A new heuristic method is introduced to generate the initial population of the genetic algorithm. The results show the high level of computational efficiency and accuracy of the proposed genetic algorithm when compared to the optimal solutions obtained from the mathematical model. The results also show that the proposed genetic algorithm outperforms the conventional dispatching rules (i.e., shortest processing time, earliest dues date and longest processing time) when applied to large-size problems. A real case study undertaken at one of the leading aerospace companies in Canada is used to formulate the model, collect data for the parameters of the model, and analyze the results.

Temperature driven failure of carbon epoxy composites – A quantitative full-field study

Aerospace composites are exposed to low temperatures that induce high levels of stress within the material. This is sufficient to induce fractures and eventually delaminations and failure. Thus, understanding how these temperature induced translaminar fractures can be reduced is an important area of research.This work investigates cross-ply unidirectional (UD) and woven (W) carbon fibre laminates with MTM46 epoxy to assess how the cure schedule (low temperature, LTC and high temperature, HTC) effect temperature driven fractures. A novel digital image correlation technique was applied to determine in-situ fracture progression versus temperature. Thermal techniques investigated the degree of cure, resin plasticity, thermal expansion and beta transition effects.The cure schedule for carbon epoxy laminates has a marked effect on quantity of manufacturing induced fractures and the temperature at which temperature induced internal fracture occurs. This work has demonstrated that a lower temperature cure is more robust against temperature driven fracture despite having a larger coefficient of thermal expansion (CTE) and similar levels of plasticity. Low temperatures induce high internal stresses but the residual stress resulting from high temperature cure is of greater concern.DIC is an excellent method to determine onset and progression of translaminar fracture as well as the behaviour of composite materials subject to temperature effects. This work is of great benefit when considering the design of CFRP structures subject to low temperature loading, furthermore the data can be used to more accurately model this phenomena in future.

Control of the through-thickness temperature distribution in carbon composite aerospace parts during induction welding

The increasing content of thermoplastic composites in the aerospace industry requires the application of new joining technologies. Their main assembly advantage is rivetless joining, which needs to be examined in greater detail in order to compensate the higher costs of these materials. Induction welding is already used in aerospace industry and shows a high potential for the application in helicopter manufacturing. In order to implement this technology in serial production, the main requirement is to determine and control the process temperature distribution. A wide range of literature describing various approaches that characterize the aforementioned temperature distribution exists. Although all approaches validate their findings by temperature measurement on the surfaces of their parts, their results seem inconsistent due to different results. In this article, a new approach is presented and validated by interlaminar temperature measurement. Based on this new approach, for induction welding, effects that are not yet described are discussed. Hereby, cooling of the surface by air jets is investigated as a mean to influence the thermal effects of the induction welding process.

Magnetostrictive Materials for aerospace applications

Structural health monitoring of composite structures to detect barely visible damage is vitally important for the aerospace industry. This research has investigated amorphous magnetostrictive wires (Fe77.5Si7.5B15 and Co72.5Si12.5B15), as a possible solution to monitoring aerospace composites. The different amorphous wires were either embedded into the composite or epoxied on to the surface. How the wires effected the structure of the composite along with ultimate tensile strength was studied. Inductance measurements were used to study the strain within the composite, which provided a non-intrusive method of monitoring the composite.

International Conference on Materials, Alloys and Experimental Mechanics (ICMAEM-2017)

International Conference on Materials, Alloys and Experimental Mechanics (ICMAEM) is an International Conferences intended to confer, share and innovation on recent developments and trends in Engineering for their research communities. Experts from the Material Science, Physics, Engineering sciences and Information Technology communities attended ICMAEM. This conference series provides an international forum to exchange experiences and the needs of a wide community, and to present and discuss recent, ongoing, and future activities. Although we are organizing first International Conference, we have taken every measure which keeps up the reputation of the college as well as Journal. Mainly, the latest developments in Material Science, Physics, Engineering Sciences and Information Technology were presented. The Mathematical models and computing for Material Science has been massively evolved since then, and along this inventions spread in to all parts of Engineering. A vibrant community of experts on a wide range of different Material Science and Engineering experiments, as well as technology explorer and industry contacts, attend and discuss the present and future challenges, and shape the future of an entire community. In such a rapidly evolving area, aiming to capture the state-of-the-art on Materials, software and computing through a collection of proceedings papers on a journal is a big challenge. Due to the large attendance, the success is enormous. Additionally, the contributions often report about studies at very heterogeneous statuses, namely studies that are completed, or are just started, or yet to be done. And by the time of conference, new ideas and explorations were discussed, suggested, and presumably have also followed previously unpredictable directions. The ICMAEM proceedings with IOP: Material Science and Engineering, in their variety and thanks to the condensed form of knowledge they offer, are what most likely will be more easily preserved for future generations, thanks to the outstanding Support of IOP for a collaboration of many Innovative ideas. The NREC (Narsimha Reddy Engineering College) centre hosted the event, and offered an outstanding location and efficient facilities for the event.

Analytical predictions of delamination threshold load of laminated composite plates subject to flexural loading

An analytical approach is proposed to determine delamination threshold loads of fiber-reinforced laminated composite plates with arbitrary stacking sequences under transverse loading conditions. Following the concept of cohesive zone modeling, a laminated plate is considered as an assembly of two sub-laminates connected by a virtual elastic-brittle layer with infinitesimal thickness. The problem is formulated and solved by the Rayleigh-Ritz method based on first-order shear deformation theory. The problem of quasi-static face-on (transverse) indentation test is analyzed as an example. The results, including elastic stiffness of flexural response, traction distributions over the potential crack interface, and threshold loads and initiating locations of delamination, are found to be in very good agreement with finite element simulations using cohesive elements. The modeling strategy, therefore, is useful for aerospace structural engineers at the preliminary design stage of laminated composite aerospace structures.

Design for manufacture: Cost-estimating model for randomly oriented strand advanced composite aerospace parts

This work aimed at developing a parametric cost-estimating model based on physical laws for making three categories of thermoplastic composites structural aerospace parts from discontinuous prepreg randomly oriented strands. The proposed cost model will use Microsoft Excel spreadsheet developed in house which imputes all industrial and academic data for calculating costs elements such as material, labour, energy, machinery, building costs and costs of working capital, overheads and then the total cost per part. This research study focused, on one hand, at estimating the heating costs for experimental and virtual parts by changing the volume and keeping the same process cycle times. The heating power was determined by simulating the process thermal diagram numerically using finite elements COMSOL software and validated by experimental data. On the other hand, the tooling costs were estimated by DFMA software for experimental and virtual moulds by changing the projected area. Then, the heating energy and tooling costs sizing scaling laws were established under linear equation forms limited to the size of platens areas. These linear equations were inputted in an Excel spreadsheet to calculate the cost of new parts, which have not been made yet. The variation of the total cost with the size and the complexity of the part were investigated. The results showed that the calculated heating energy costs of the three experimental randomly oriented strand parts were different due to different geometries of the heating platens and the moulds. For the mould cost, the more complex the form was the higher the cost. For total cost, it was also demonstrated that the manufacturing cost of L-bracket part was higher than that of flat plate and T-shape part due to higher process cycle time.

Aerospace looks to composites for solutions

New materials to reduce weight and speed manufacturing processes are being demanded by the aerospace industry and composites are rising to the challenge. Reinforced Plastics reports.

Influence of cutting parameters on tool wear and hole quality in composite aerospace components drilling

Composite Fiber Reinforced Plastics (CFRP) are characterized by their outstanding mechanical properties combined with reduced density and good resistance to corrosion and fatigue which make them suitable for aerospace components. During assembly procedures, one shoot drilling operations, usually including countersinking cycle, are required to minimize positional errors, enhance tight tolerances and reduce process time.Countersink drill bits were tested on CFRP test specimens, representative of aircraft components. Along testing, tool wear was monitored with an optical microscope to track its evolution and determine the dominant wear mechanism. On the other hand, hole quality was evaluated since tool life criterion is based on the assessment of machined surface quality.The influence of cutting speed and feed was analyzed with the objective of looking for extended tool life and more productive cutting parameters.The information gathered from monitoring tool wear and inspecting hole quality can be used for the enhancement of CFRP drilling and the improvement of the manufacturing process competitiveness, in terms of production cost and time.

Cross laminated timber properties including effects of non-glued edges and additional cracks

Cross laminated timber (CLT) is usually comprised of multiple timber layers having alternating grain directions. Because individual boards are glued on their faces between layers, but usually not glued on their edges within layers, those edges define “precracks” in the composite. When exposed to differential thermal and moisture expansion after installation, CLT, like all cross-laminated composites, is prone to formation of “additional cracks”. Confidant CLT design must be able to account for changes in CLT properties during life of a structure caused by such additional cracks. By extending variational mechanics methods for aerospace composites, this paper provides analytical solutions for all in-plane mechanical, thermal expansion, and moisture expansion properties of a three-layer CLT panel. By using the three-layer solution to evaluate effective layer properties as a function of the number of cracks, the analysis can be extended to in-plane mechanical, out-of-plane bending, and expansion properties for CLT panels with any number or arrangement of layers. Some sample calculations are provided along with comments on limitations of the approximations and needs for future work.

Composite Aerospace Structures Shape Distortion during All Stages of Vacuum Infusion Production

The main reason of the deformations of aggregate aerodynamic surfaces could be tool deformation under its own weight and thermoelastic deformations of the infusion tool system. Resin polymerization and form fixation take place in the thermal chamber at 200°C, with subsequent cooling. For modelling the stress–strain state of heated infusion tool that is made of materials with different coefficients of thermal expansion, the static structural module of the ANSYS system is used. Results of this analysis are displacement and stress fields, applied in mesh nodes. For the next cooling analysis the geometry of the infusion tool is used as an initial geometry, that was deformed in heating process. This is made by the means of APDL commands and Finite element modeler modules. Consequently, as the results of ANSYS analysis the module of impedance during full manufacturing process was received. The results were imported to MATLAB system for analysis. In the MATLAB system the component-wise addition of displacement fields of heating and cooling processes and an estimation of maximum displacement and visualization of the results are carried out. This method, used for the analysis of large scale aggregates of the production of aviation structures using vacuum infusion methods, helps to compare the accuracy of the theoretical contour of airfoils replication using different frame materials - steel and composite material during its full manufacturing process. Recommendations for the preferred infusion tool manufacturing, including frame, from composite materials, similar to the coefficient of thermal expansion of the material molded part was given. The received recommendations are considered in case of infusion tool production– its frame was made of composite material.