High Performance Aerospace Applications Research Articles

Enhancing mechanical properties and defects elimination in 2024 aluminum alloy through interlayer friction stir processing in wire arc additive manufacturing

In this study, a hybrid wire arc additive manufacturing (WAAM) and interlayer friction stir processing (IFSP) approach was utilized to enhance the quality of 2024 aluminum alloy components. The defects characteristic, microstructure evolution, and mechanical properties of the fabricated components and after T6 heat treatment were analyzed systematically. Our analysis reveals that IFSP can break and dissolve the eutectic phases, significantly reduce porosity defects and refine the grain size of the as-deposited materials, thus improving the overall mechanical properties. Notably, compared to the WAAM as-deposited component, the yield strength (YS) and ultimate tensile strength (UTS) in the top-layer stir zone (SZ) of IFSP component increased from 154 ± 3 to 267 ± 2 MPa, and from 258 ± 12 to 360 ± 3 MPa, respectively. However, in the middle-layer SZ, S-phase precipitation and coarsening induced by thermal cycling during additive manufacturing slightly reduced the tensile properties. Post-T6 heat treatment led to uniformly distributed properties in the IFSP component along both horizontal and vertical directions, with the YS, UTS, and elongation (EL) averaging 353 ± 9 MPa, 470 ± 4 MPa, and 10.5 ± 1.6%, closely matching those of wrought counterparts. The significant improvements in mechanical properties are primarily attributed to the elimination of porosity and precipitation of fine needle-like S-phase. This research not only demonstrates the potential of IFSP in enhancing the mechanical properties of WAAM-fabricated 2024 aluminum alloy but also offers a promising technique for producing high-quality components suitable for high-performance aerospace applications.

Multifunctional composite structures with embedded conductive yarns for shock load monitoring and failure detection

This study evaluates the performance of composite structures with embedded conductive yarns during shock loads to create a multifunctional system for immediate failure detection. The scalable sensing yarns were made by braiding Kevlar fibers with Nitinol fibers and then integrating them into a carbon/epoxy prepreg. The multifunctional structure was subjected to a Mach 2 air blast load using a shock tube apparatus. The embedded sensor yarns were used to record their electrical performance, while Digital Image Correlation captured full-field displacements, velocities, and strains. In addition, pressure transducers measured shock event pressures. The results revealed that through-thickness failure of the laminated composite occurred at approximately 2.5% strain, which was visually observable. However, the embedded sensor exhibited out-of-range electrical measurements at around 1.5% strain, even though no visible structural damage was present. This demonstrates the embedded sensing yarns’ ability to detect delamination-type failures by responding to interlaminate damage, highlighting their advantages over conventional external sensors. Similarly, the gauge factor for the fiber system was determined to be 1.89 ± 0.07. This multifunctional system shows great potential for enhancing composite structure safety and performance in high-performance aerospace applications and offering real-time structural health assessment.

The Pressure and Temperature Dependency of Relative Volume, Low Shear Viscosity, and Non-Newtonian High Shear Viscosity in SAE AS5780 HPC, MIL-PRF-23699 HTS, and DOD-PRF-85734 Lubricants

This work quantifies the high-pressure rheological performance of two jet engine turbine oils and three helicopter transmission oils. The jet engine oils are qualified for both the MIL-PRF-23699 high thermal stability and AS5780 high performance classifications, and the helicopter oils are classified against DOD-PRF-85734. Rheological properties include relative volume, low shear, and high shear viscosity. Relative volume measurements are presented for temperatures ranging from 20 to 100 °C and up to 300 MPa. Low shear viscosity measurements range from 20 to 100 °C and up to 1 GPa. Apparent shear or high shear viscosity measurements varied pressure up to 550 MPa and shear stresses up to 5 MPa. The non-Newtonian limit for each lubricant was observed. Rheological models obtained from the measurements include the Tait and Murnaghan relative volume models, the Williams-Landel-Ferry (WLF) modified Yasutomi low shear viscosity model, and both the modified Carreau-Yasuda and double modified Carreau-Yasuda shear viscosity models. The regressed models highlight shortcomings of classical elastohydrodynamic lubrication (EHL) expressions in describing the measured lubricants’ rheological response. These property models support the development of modern EHL calculations as they relate to high-performance aerospace applications.

Numerical and Experimental Studies of Multi-ply Woven Carbon Fibre Prepreg Forming Process

Woven carbon fibre prepreg is being increasingly used in high-performance aerospace and automotive applications, primarily because of its superior mechanical properties and formability. A wide range of forming simulation options are available for predicting material deformation during the prepreg forming process, particularly change in fibre orientation. Development of a robust validated simulation model requires comprehensive material characterisation and reliable experimental validation techniques.This paper presents experimental and numerical methods for studying the fibre orientation in multi-ply woven carbon fibre prepreg forming process, using a double-dome geometry. The numerical study is performed using the commercial forming simulation software PAM-FORM and the material input data are generated from a comprehensive experimental material characterisation. Two experimental validation methods are adopted for fibre shear angle measurement: an optical method for measuring only the surface plies, and a novel CT scan method for measuring both the surface plies and the internal plies. The simulation results are compared against the experimental results in terms of fibre shear angle and the formation of wrinkles to assess the validity of the model.

SERIES PARTS MANUFACTURING BY INFRARED SUPERPLASTIC FORMING WITH NUMERICAL TECHNIQUES FOR THERMAL REGULATION

Materials used for Superplastic forming (SPF) are mainly titanium alloys which are good candidates to produce lightweight complex-shaped components for high performance aerospace applications. SPF process has limitations because it involves a high-temperature furnace with poor heat efficiency and expensive tooling with low management flexibility. Enhancing this manufacturing process is a major challenge for the aerospace industry which is facing to important production ramp-up and cost reductions. Direct heating combined with tool heat management result in significant savings of SPF process: production time savings by drastically reduce the heating time, reduction of maintenance costs and energy savings by significant heat efficiency improvement. Aurock developed direct heating by Infrared emitters and succeed in forming series 1.5x1m² Ti6Al-4V blanks. A key point with this new technology is to ensure a homogeneous blank temperature all along the forming. This point is achieved thanks to lamp power modulations and numerical techniques to secure the blank thermal regulation with a full radiative flux control at different forming stages. Results obtained are stable and repeatable regarding to dimensional criteria, post-forming thicknesses distribution and microstructure. Numerical predictions are in very good agreement with the experimental results, enabling robust machine setup for series Infrared SPF parts production.

Flexible low-cost tooling solutions for a one-shot resin infusion of a 3D woven and multi-textile preform

3D woven materials are extremely capable for high-performance aerospace applications. Traditionally, components comprised of 3D wovens are manufactured using Resin Transfer Moulding, requiring matched tooling that can result in high costs. Increasingly this is not feasible for mid-to-large structures, therefore flexible tooling strategies are necessary to facilitate low-cost one-shot vacuum mouldings of multi-textile composites. Towards this need, the authors investigated tooling materials and infusion strategies for an as-designed 3D woven pi-section incorporating a Non-Crimp Fabric (NCF) skin. Engaging with stakeholders presented two infusion strategies (flow ‘up’ or ‘down’ pi-NCF geometry) and three inserts (Polyetherimide, Silicone, and Aluminium) for the pi internal channel. Six infusions were completed with manufacturing data recorded followed by X-ray CT analysis to evaluate geometry and infusion quality; and manufacturing costs estimated. In combination, results suggest that coupling flexible tooling materials is most effective in both reducing costs and maximising injection quality, ensuring geometrical performance.

Determining effective interface fracture properties of 3D fiber reinforced foam core sandwich structures

Foam core sandwich composites are finding a wider use in aerospace, automotive, and construction applications. These structures present unique challenges in terms of material failure and interaction and are sensitive to damage and imperfections introduced during manufacturing. An emerging class of 3D fiber reinforced foam core aims to replace monolithic foams used in sandwich structure cores particularly in demanding high-performance aerospace applications. This research is focused on investigating the development of testing methods capable of measuring the effective interface fracture properties between the facesheet and the core in 3D fiber reinforced foam cores. Double cantilever beam and end-notched flexure specimens are developed to evaluate the mode I and mode II fracture properties of a 3D fiber reinforced foam core. The design, development, and initial failure of a mode I interface fracture test for 3D fiber reinforced foam cores are presented. The digital image correlation results on the failed tests allowed for a different approach to be utilized in designing a new bonded double cantilever beam specimen for testing the mode I fracture of a 3D fiber reinforced foam core sandwich structure that resulted in a successful interface fracture test. The bonded DCB specimens exhibited relatively smooth crack propagation and produced GIc values similar to honeycomb sandwich structures and significantly higher than comparable foam structures.

Curing of Thick Thermoset Composite Laminates: Multiphysics Modeling and Experiments

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

Low velocity impact resistance and energy absorption of environmentally friendly expanded cork core-carbon fiber sandwich composites

This study investigates the use of expanded cork (a 100% natural lightweight agglomerate material) as a core material in composite sandwich structures with carbon fiber face sheets. The characterization performed focused particularly on energy absorption capability. Rohacell® 110 IG, a synthetic foam commonly used as a core material in high performance aerospace applications, was also used and characterized to compare the energy absorbing characteristics of the sandwich composites. Bending tests were done to examine the stiffness of the sandwich beams. Wavenumber and damping tests were performed to characterize the acoustic and vibrational damping properties of the composites. Both full penetration and partial penetration low velocity impact tests were completed to determine the damage resistance of the composites. It was seen that when compared to the synthetic foam, expanded cork showed a decrease in bending stiffness, but a large improvement in acoustic, damping, and impact damage resistance characteristics. It seems that expanded cork could be an attractive lightweight sandwich core material that will allow for increased energy absorption and will also reduce the carbon footprint of the structures.

Environmental effects on viscoelastic behavior of carbon fiber/PEKK thermoplastic composites

In the last years, thermoplastic composites have been introduced as structural materials for high performance aerospace applications. However, these materials can present problems when exposed to moisture, temperature, and UV radiation, and besides it may occur as the synergy among the main degradation mechanisms. Among the thermoplastic composite materials, carbon fiber reinforced poly(ether-ketone-ketone) (PEKK) laminates have shown excellent balance of properties, including high glass transition temperature, high strength, stiffness and fracture toughness values, low moisture absorption, and good environmental resistance. The aim of the present work was to evaluate the influence of the environmental effect on the viscoelastic behavior and glass transition temperature of carbon fiber reinforced PEKK thermoplastic composites. In this work, the effects of environmental degradation on the viscoelastic properties of this composite material were studied by dynamic mechanical analyses. The most significant change was observed for the UV radiation accelerated weathering conditioning effects. A decrease of the storage modulus from 40 to 10 GPa and the Tg from 147 to 105℃ is observed, which decreases consequently the composite stiffness and the service temperature after exposed environmental effects. A synergetic degradation mechanism between UV radiation accelerated weathering test and hygrothermal conditioning is clearly verified.

Thermal expansion behaviors of yttrium tungstates in the WO3–Y2O3 system

Fully-dense, polycrystalline yttria (Y2O3) exhibits high infrared (ER) transmittance in the full mid range (3-5 mu m) with low emittance, but lacks thermal-shock resistance for high-performance aerospace applications due to its low strength and high coefficient of thermal expansion (Cm). An attempt was made to develop a low CTE and high strength composite of Y2O3 by dispersing the phase, Y2W3O12, known to exhibit a high negative CTE. The sintered mixture of Y2O3 and Y2W3O12, however, does not form a stable, two-phase composite. The sintered mixture forms new Y2O3-rich phases, such as Y2WO6 and Y6WO12, depending on the relative amounts of Y2O3 and WO3. Investigation of the thermal-expansion behaviors of these yttrium tungstates revealed that they have high CTEs comparable to pure Y2O3. The goal of obtaining a near-zero CTE composite with Y2O3 as the matrix and a yttrium tungstate with a negative CTE as the dispersed phase cannot be realized in this system. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Moisture Sorption Effects on Carbon Fiber-Reinforced Pheny L Ethnyl-Terminated UltemTM Composites

High-performance aerospace applications require materials that are able to withstand exposure to extreme temperatures, high relative humidities, solvents, and other chemicals. Due to their high-performance thermal and mechanical characteristics, poly(etherimide)s are being implemented in such applications. Prior to such use, environmental effects on material performance must be understood. In this study, the effects of moisture sorption on the mechanical properties of carbon-fiber-reinforced phenylethynyl-terminated poly(etherimide) matrix composites were investigated. The through-the-thickness moisture diffusion coefficient and the maximum moisture equilibrium content were determined for the unidirectional composites for exposure to 90'C and 85% relative humidity. In addition, the composites were tested for retention of transverse flexural strength and apparent interlaminar shear strength at maximum moisture equilibrium content. The same properties were tested for property retention following desorption of moisture to a 90'C, 2% relative humidity moisture content. The composite showed high mechanical property retention with recoverable matrix plasticization being the source of property reductions.

Adhesive Properties of Cured Phenylethynyl-Containing Imides

As part of a program to develop structural adhesives for high-performance aerospace applications, work has continued on phenylethynyl-containing imides. Initial work on linear phenylethynyl-terminated imides (PETI), led to a material called LaRC™ PETI-5, which is now commercially available and was selected as the composite matrix resin and adhesive on the High Speed Research Program. In this report, the preparation and evaluation of a series of modified phenylethynyl-containing imides, which are being developed as secondary bonding adhesives, will be discussed. The modification of these materials compared with the linear material involves the use of a small amount of trifunctional monomer to introduce branching. These adhesives exhibit excellent processability at pressures as low as 15 psi and temperatures as low as 288°C. The cured polymers exhibit excellent solvent resistance and high mechanical properties. Polymer properties can be controlled by varying the molecular weight, the amount of branching, and the phenylethynyl content. This research involves changing the flexibility in the copolyimide backbone of the branched, phenylethynyl-terminated adhesives and determining the effect on properties.

Synthesis and Characterization of Modified Phenylethynyl Imides

As an ongoing effort to develop structural adhesives for high-performance aerospace applications, recent work has focused on phenylethynyl terminated imide (PETI) oligomers. The work reported herein involves the synthesis and characterization of a series of phenylethynyl containing oligomers designated LARC™ MPEI (modified phenylethynyl imide). These oligomers presumably contain mixtures of linear, branched and star-shaped molecules. The fully imidized polymers exhibited minimum melt viscosities as low as 600 poise at 335 °C, significantly lower than equivalent molecular weight linear materials. Ti/Ti lap shear specimens processed at 288 °C under 15 psi showed tensile shear strengths as high as ∼6000 psi and ∼5200 psi at ambient temperature and 177 °C respectively. The chemistry and properties of these new MPEIs are presented and compared with an optimized linear PETI, LARC™ PETI-5.

A comparative study of permanent magnet and switched reluctance motors for high-performance fault-tolerant applications

Switched reluctance machines (SRMs) have been extensively researched for high performance aerospace applications because of their inherent fault tolerance. Recent work by the authors suggests that with careful design a similar degree of fault tolerance may be achieved with a permanent magnet machine (PM) at a significantly higher torque density than its SRM counterpart. This latter suggestion is of crucial importance in high performance applications, such as aerospace, where a low mass is essential. This paper is concerned with reporting measured results from a fault tolerant PM machine, and using these results to examine the relative merits of SR and PM technology for this application.

Adhesive Properties of Cured Phenylethynyl-Terminated Imide Oligomers

Abstract As part of a program to develop structural adhesives for high performance aerospace applications, phenylethynyl-terminated imide oligomers are under evaluation. Imide oligomers with different molecular weights and compositions endcapped with either 4-(3-aminophenoxy)-4′-phenylethynylbenzophenone (3-APEB) or 4-phenylethynylphthalic anhydride (PEPA) have been prepared and characterized. These oligomers exhibit excellent processability. After heating to 350°C for 1 hour, the terminal phenylethynyl groups have reacted to provide chain extension, branching and crosslinking. The cured polymers exhibit excellent solvent resistance and high mechanical properties as neat resins and in various adhesive forms (tensile shear, sandwich flatwise tension and climbing drum peel specimens). The chemistry and properties of these phenylethynyl-terminated imide oligomers are discussed.

Superplasticity in a powder metallurgy magnesium composite

Metal-matrix composites (MMC) have great potential to be used in high-performance aerospace and automobile applications. It is important, therefore, to develop secondary processing for MMCs which can effectively produce complex engineering components directly from wrought products. Many studies now have been performed that demonstrate superplasticity can be developed in MMCs. Superplasticity has been reported in some Mg alloys, including ZK60, AZ31, AZ61, and Mg-Li alloys. But, none of these alloys showed superplasticity at high strain rates. Although HSRS has been extensively demonstrated in Al-base MMCs, both in PM and IM products, neither conventional superplasticity nor HSRS has yet been shown in any Mg-base composite. The purpose of this paper is to present, for the first time, the observation of HSRS in a 17 vol% SiC particulate-reinforced ZK60A magnesium composite (ZK60/SiC/17p).

Adhesive and composite properties of LARCTM-8515 polyimide

LARCTM-8515 (Langley Research Center-8515) is an aromatic polyimide based on 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and an 85:15 molar ratio of 3,4'-oxydianiline (3,4'-ODA) and 1,3-bis(3-amnophenoxy)benzene (APB). This material is currently under evaluation as an adhesive and composite matrix resin for use in high-performance aerospace applications. The synthesis and development of the copolymer as well as studies of the effect of molecular weight on properties will be discussed. LARCTM-8515 has been evaluated as an adhesive, and titanium to titanium tensile shear strengths will be presented. Unidirectional prepreg was' made utilizing the Langley multipurpose tape machine. and the thermal and rheological properties and the solvent/volatile depletion rates of the poly(amide acid)/NMP resin system were determined. This information was used to successfully design a moulding cycle for composite preparation. Composite laminates were moulded under 200 psi, which consistently yielded good consolidation quality as measured by C-scan, acid digestion and optical photomicrography. Composite mechanical properties measured included short-beam shear strength and flexural strength and modulus at RT, 93, 150 and 177C. and compression strength (ITRI) and open hole compression (OHC) strength at RT and 177 C (wet).

Advanced Metal Matrix Composites

ABSTRACTAdvanced metal matrix composites are emerging as materials of construction for high performance aerospace applications. The thrust is to develop high specific strength and high specific modulus ultra-lightweight composites using Al or Mg as matrix materials for space structure applications, and for higher temperature applications, to develop materials using various aluminides as matrix materials. This paper presents an overview of the methodology used to develop advanced MMC's and discusses the problems and limitations faced in achieving the composite materials development goals.

Multicomponent Polymeric Engineering Materials

The great advances made in polymeric structural materials over the past decade have led to their replacement of conventional materials in a wide range of uses including high-performance aerospace applications. This shift in choice of materials is based on economic advantages, simplified fabrication, freedom from corrosion, and lower weight. The trend toward use of polymeric materials will grow as the materials science of this new technology is developed. Better insight into such fundamental problems as the mechanisms by which forces are transferred to the polymer molecule, the surface interactions between polymer phases or polymer and fiber, and the molecular processes by which energy is absorbed during fracture will greatly stimulate the development of this field.