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Abstract Autonomous long‐duration aerostats (LDA) are one of the most popular research directions of high‐altitude platforms (HAPS) in recent years. Solar photovoltaic (PV) array is the energy source of autonomous long‐duration aerostat, whose power generation predicting accuracy and speed affect the subsequent flight control strategy. Limited by incompleteness cognition of near space, current predicting results cannot meet the requirements of autonomous LDA. In this paper, a novel rapid prediction model of the PV array is proposed. Based on spatial position relation of PV cells, this model can predict the power of single PV cell in any state. The four influence factors including time difference, angle, efficiency loss and temperature are analyzed and optimized comprehensively and innovatively. The new model can be applied in both static state aerostat and dynamic state aerostat. Compared with the traditional model, the efficiency can be improved by 50% and the prediction accuracy can be improved by 10%.

In this work, a review of the theoretical aspects and an assessment to validate a Computational Fluid Dynamics (CFD) open- source code for applications in aerospace problems are discussed. The code uses a finite volume method, with cell-centered implementation, and it is suitable for simulations of inviscid, laminar, and turbulent flows. The code considers two-dimensional cases with unstructured meshes and employs the turbulence model known as Spalart-Allmaras. The implementation is detailed presenting the spatial discretization, including the upwind scheme, the linear reconstruction algorithm, and the calculation applying the method of gradients. The temporal discretization considers the application of a multistage explicit algorithm using a 5 stages Runge-Kutta method. The validation was done considering three cases of study: the inviscid shock tube, the laminar flat plate, and the flow over a rocket fairing. These cases are simulated using the software developed and the results are compared with analytical and experimental results. The rocket fairing case is related to the analysis of the Brazilian VLS launch during its transonic flight and it exemplifies the effect of the shock wave/boundary-layer interaction in its pressure distribution. The simulation results present a good agreement with the experimental results.

An efficient propulsion system holds the key to the smooth operation of any aerospace vehicle over different flight regimes. Apart from generating the necessary thrust, emphasis has also been laid on vectoring the direction of thrust. The primitive modes of thrust vectoring chiefly focused on mechanical means such as the use of gimbals or hinges. The current state-of-the-art technologies demand more efficient methods for thrust vectoring, which minimize the use of mechanical components. These methods termed fluidic thrust vector control methods, employ secondary jets for achieving the required attitude, and trajectory of the aerospace vehicles such as aircraft, rockets, and missiles. Such methods have greatly helped in reducing vehicle weight, vehicle maintenance requirements, and enhancement of stealth characteristics of such vehicles. This work presents a review of the various fluidic thrust vectoring systems, starting with a brief overview of traditional thrust vectoring systems, followed by a discussion on the various aspects of fluidic thrust vectoring systems. It also highlights the effect of the various geometrical and operating conditions on the performance parameters of the thrust vectoring system such as the thrust vector angle, system thrust ratio, and thrust vectoring efficiency among others. For ensuring the comprehensive character of this work, synthetic jet vectoring techniques have also been included due to their nonmechanical nature and similarities with purely fluidic thrust vectoring techniques. [ABSTRACT FROM AUTHOR]

Autonomous long‐duration aerostats (LDA) are one of the most popular research directions of high‐altitude platforms (HAPS) in recent years. Solar photovoltaic (PV) array is the energy source of autonomous long‐duration aerostat, whose power generation predicting accuracy and speed affect the subsequent flight control strategy. Limited by incompleteness cognition of near space, current predicting results cannot meet the requirements of autonomous LDA. In this paper, a novel rapid prediction model of the PV array is proposed. Based on spatial position relation of PV cells, this model can predict the power of single PV cell in any state. The four influence factors including time difference, angle, efficiency loss and temperature are analyzed and optimized comprehensively and innovatively. The new model can be applied in both static state aerostat and dynamic state aerostat. Compared with the traditional model, the efficiency can be improved by 50% and the prediction accuracy can be improved by 10%. [ABSTRACT FROM AUTHOR]

• This paper provides a comprehensive review of the fundamental principles, material development, coolant selection, and research methods of transpiration cooling technology, offering a solid foundation for further academic and engineering advancements. • Systematically examines the development and application of transpiration cooling technology in aerospace vehicles, highlighting its critical role in addressing thermal challenges in force-thermal concentrated environments. • Summarizes each research direction and outlines the path for further development, providing a clear roadmap for future innovations in the field of aerospace thermal protection. • Introduces the latest research progress, encompassing pivotal experimental outcomes, innovative modeling techniques, and advancements in porous materials development, catering to the needs of researchers and practitioners who are at the forefront of aerospace thermal protection solutions. With the continuous expansion of aerospace vehicles in military and civilian applications, their performance in complex environments is increasingly valued. In force-thermal concentrated environments, the extreme thermal load problems faced by the vehicles are particularly severe, necessitating urgent development of effective thermal protection technologies to overcome developmental bottlenecks. Among existing thermal protection methods, transpiration cooling technology has become one of the key technologies to solve these problems due to its excellent cooling capacity and environmental adaptability. This paper provides a comprehensive review of the current status and latest progress of transpiration cooling technology in the thermal protection system of aerospace vehicles, and elaborates in detail on the development of porous media materials, the selection of coolant, and the research methods of transpiration cooling technology. Lastly, potential directions for future research are suggested in light of the technology's existing challenges, aiming to provide references for the design and optimization of the thermal protection system of aerospace vehicles. [ABSTRACT FROM AUTHOR]

In this work, a review of the theoretical aspects and an assessment to validate a Computational Fluid Dynamics (CFD) opensource code for applications in aerospace problems are discussed. !e code uses a "nite volume method, with cell-centered implementation, and it is suitable for simulations of inviscid, laminar, and turbulent #ows. !e code considers two-dimensional cases with unstructured meshes and employs the turbulence model known as Spalart-Allmaras. !e implementation is detailed presenting the spatial discretization, including the upwind scheme, the linear reconstruction algorithm, and the calculation applying the method of gradients. !e temporal discretization considers the application of a multistage explicit algorithm using a 5 stages Runge-Kutta method. !e validation was done considering three cases of study: the inviscid shock tube, the laminar #at plate, and the #ow over a rocket fairing. !ese cases are simulated using the so$ware developed and the results are compared with analytical and experimental results. !e rocket fairing case is related to the analysis of the Brazilian VLS launch during its transonic #ight and it exempli"es the e%ect of the shock wave/boundary-layer interaction in its pressure distribution. !e simulation results present a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Three-port converter (TPC) with non-regulated bus cannot meet the voltage stability demands of high-altitude platforms (HAPs) during daytime operations. In contrast, full-regulated bus TPC is complex in topology and inferior in power density, although it can maintain voltage stability across whole day operations. Therefore, semi-regulated bus TPCs are more suitable for this scenario, which can not only maintain voltage stability during daytime operations, but also have simple topology. However, conventional semi-regulated bus structure converts the power twice, leading to lower efficiency and power density. In order to overcome this problem, the paper proposes a novel semi-regulated bus TPC that can be used on high-altitude platforms. The topology only has one conversion between the ports. It regulates the bus voltage during the day and prevents the loss of diode during the night by directly discharging through the MOSFET and achieving high efficiency. The paper adopts GaN devices to elevate the working frequency to further improve the power density, and conduct a theoretical analysis for all working modes and provide key equations. The closed-loop transfer function of the system is deduced for stability analysis. The results show that the proposed topology has high efficiency and power density.

Intelligent unmanned robotic systems have recently gained popularity due to their ability to potentially explore inaccessible and dynamically changing environments. In these environments, these vehicles might be subjected to unique types of disturbances that may lead to mission performance degradation. This paper describes the design, development and proof of concept of a novel adaptive control that combines concepts from model reference and feedback linearization and it is augmented via nonlinear bounded functions typical in immune system responses of living organisms. Proof of stability of the proposed control law using Circle Criterion is presented. Numerical hardware in the loop simulations along with actual implementation are performed using a gimbaled mini-free flyer vehicle that uses thrust vectoring control actuation. A set of performance index metrics are used to quantify and assess the performance of the adaptive control system which shows stabilizing capabilities in the presence of system disturbances and uncertainties. [ABSTRACT FROM AUTHOR]

This work presents a computational tool for preliminary analysis of hypersonic vehicles, based on local surface inclination methods: the HipeX. This program was developed for reading standard triangulation language (STL) geometry files and calculating pressure coefficient and temperature distributions over vehicle’s surface using the Newtonian, modified Newtonian or tangent-wedge methods. Validations were made with a cylinder and a sphere, where only the Newtonian method was applied, and with experimental data from Apollo capsule at Mach 10, where the Newtonian and the modified Newtonian methods were applied. These validations presented the code capability to read geometries as well as to estimate aerodynamic force coefficients. A preliminary application was to predict the aerodynamic force coefficients of a generic hypersonic vehicle over constant dynamic pressure trajectories of 23,940, 60,000 and 95,760 N/m2 with zero angle of attack. With a fixed dynamic pressure of 60,000 N/m2, this vehicle was tested over several Mach numbers and with angle of attack variation from –10 to 10 deg. Zero angle of attack investigation showed minor changes on the force coefficients with altitude, while the variation of angle of attack produced more pronounced variations on these parameters. Maximum flow temperatures over vehicle’s surface were estimated ranging from 850 to 5,315 K.

One of the most important features of an aerospace vehicle design is its shape, especially the forebody part, since it defines the main characteristics of the vehicle aerodynamic. In this context, the present work has the purpose of investigating the transonic aerodynamic regime in typical vehicle models, with different frontal geometry configurations, using the experimental techniques pressure sensitive paint (PSP) and Schlieren. The aim is to get more insights about the flow patterns over the selected models, regarding the transonic regime, in terms of qualitative density field evaluation, and the identification of important aerodynamic parameters, such as shock wave positioning and pressure gradients over the model, as well as the influence of the forebody configuration in the flow pattern. The test campaign was carried out in the Pilot Transonic Wind Tunnel of the Institute of Aeronautics and Space (IAE; in Portuguese, Instituto de Aeronáutica e Espaço), varying Mach numbers from subsonic to low supersonic. Five forebody configurations mounted in a cylindrical body having the standard cone–cylinder shape as baseline was considered. A description of the phenomena occurring around and on the models surface for all five models is presented, through analyses of the Schlieren images and PSP results.

Since the year 2000, several studies on bounding end-to-end delays in switched Ethernet topologies required in the design of distributed processing systems on board of aerospace vehicles were made public. These studies presented various approaches for dealing with the non-deterministic behavior of non-synchronized network traffic while striving to avoid overestimation. One of them described an effect observed in frame-based network transmissions and named it "serialization". This effect is used in this paper with the objective of constructing a new low-complexity method for estimating the worst case delay experienced by a frame crossing a switched Ethernet. This method results from the combination of two new propositions which inherit concepts originally formulated by schedulability analysis methods for multitask processing systems. Its implementation is shown on a case study using a step-by-step procedure and the results obtained are favorably compared with one previously published work. [ABSTRACT FROM AUTHOR]

The increase in air traffic and space flights, the rising cargo volumes and passenger numbers all set complex research and applied scientific tasks and therefore pose more complex requirements for obtaining up-to-date information on the system parameters and on the environment in which they function. After the advent of IoT platforms, their use in all areas of technology has been growing rapidly, as for instance in data collection and processing systems that are fully applicable to aviation needs. One of the major problems in the building of new systems or upgrading existing ones in line with current trends is the high cost of the innovations and the long time before their implementation. In line with the current trends in aviation, this paper proposes an approach for unified modules comprising a large set of possible sensors operating on a wireless standard for transmitting information and connected in a single and cost-effective network and with minimal time for construction, upgrading and renovation. [ABSTRACT FROM AUTHOR]

One of the most important features of an aerospace vehicle design is its shape, especially the forebody part, since it defines the main characteristics of the vehicle aerodynamic. In this context, the present work has the purpose of investigating the transonic aerodynamic regime in typical vehicle models, with different frontal geometry configurations, using the experimental techniques pressure sensitive paint (PSP) and Schlieren. The aim is to get more insights about the flow patterns over the selected models, regarding the transonic regime, in terms of qualitative density field evaluation, and the identification of important aerodynamic parameters, such as shock wave positioning and pressure gradients over the model, as well as the influence of the forebody configuration in the flow pattern. The test campaign was carried out in the Pilot Transonic Wind Tunnel of the Institute of Aeronautics and Space (IAE; in Portuguese, Instituto de Aeronáutica e Espaço), varying Mach numbers from subsonic to low supersonic. Five forebody configurations mounted in a cylindrical body having the standard cone-cylinder shape as baseline was considered. A description of the phenomena occurring around and on the models surface for all five models is presented, through analyses of the Schlieren images and PSP results. [ABSTRACT FROM AUTHOR]

The authors report a one‐piece flexible liquid level optical fibre sensing probe in this Letter, which is meant to measure the liquid level inside the cryogenic propellant tanks of spacecraft and rockets. The ultra‐lightweight sensing probe can be used in both aerospace vehicles and in any type of cryogenic fluid storage system. In contrast to current liquid gauging technologies such as Delta‐P pressure sensor, capacitance probe, ultrasonic sensor, and silicon diode liquid level sensing probe, the fibre optic continuous liquid level sensor has unique advantages in terms of gauging accuracy, reliability, simplicity, and maintenance. The sensor uses one single optical fibre probe to measure the liquid level and the liquid distribution of cryogenic propellant. Every point of the sensing fibre is a 'point sensor' that is able to distinguish liquid and vapour. The physical location of each 'point sensor' can be determined with 1 mm spatial resolution or better. The optical fibre probe can be installed in a propellant tank with the same manner as currently used silicon diode liquid level sensing probe via only one single feed‐through to connect to an optical signal interrogation unit located outside the tank. Experiments on measuring liquid nitrogen level are demonstrated. [ABSTRACT FROM AUTHOR]

The capsule SHARK (Sounding Hypersonic Atmospheric Re-entering “Kapsule”) was designed and realized for testing in real flight conditions a ZrB 2 -based Ultra High Temperature Ceramic (UHTC) Nose Tip. The capsule was instrumented with accelerometers, rate and pressure sensors, and thermocouples of which three were inserted inside the UHTC Nose Tip. The capsule was launched by the European Space Agency (ESA) rocket MAXUS-8 performing an atmospheric re-entry after a parabolic trajectory with an apogee at 700 km of altitude. The temperature profile recorded by the thermocouples inserted inside the Nose Tip reported a discontinuity at about 762 s after the release from the rocket, revealing the failure of the ceramic component during the flight. The capsule was recovered and the Nose Tip was found damaged: the fore half was missing while the inner part, fractured in three pieces, was recovered. The fractographic analysis of the three recovered fragments was carried out by optical microscopy techniques which allowed identifying the main fracture marks, such as fracture mirror, hackle lines, arrest lines, and Wallner lines. The fracture dynamic has been outwardly reconstructed and the stress at fracture was evaluated by means of the Orr's equation involving the measurement of the fracture mirror radius. Then applying the Griffith's relationship, the flaw size was estimated. The origin of the main fracture was identified on the edge of the hole manufactured by Electrical Discharge Machining (EDM) to lodge thermocouples inside the nose tip, causing the strength-limiting flaw. Thermal shock was recognized as the probable failure cause as already observed by on-ground tests performed in the Plasma Wind Tunnel (PWT) “Scirocco” by the Italian Aerospace Research Centre (CIRA) on a similar UHTC Nose Tips manufactured with the same machining technology. [ABSTRACT FROM AUTHOR]

The characterization of fracture toughness or critical energy release rate of adhesive joint in composite structures is a key parameter. In the present study, fracture toughness of adhesively bonded composite joints is experimentally investigated for the basic fracture modes. Experiments are conducted on the double cantilever beam, end notched flexure and edge crack torsion specimens to determine the fracture toughness of three modes, namely mode-I, mode-II and mode-III. Specimens are bonded with epoxy adherent and cured at room temperature. The fracture toughness values of mode-II and mode-III are 2.6 and 4.6 times respectively of mode-I. Acoustic emission (AE) technique is also employed to aid in determining the fracture toughness of bonded joints. The results indicate that AE signals have good correlation with load–displacement behavior to determine the fracture initiation stage especially in the mode-II loading. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) is restricted to non-safety–critical aerospace components because there is no reliable method for detecting kissing bonds (KB), which may have a significant effect on fatigue life. The effects of KB defects on the tensile and fatigue properties of 7475-T7351 friction stir welds were quantitatively evaluated with respect to a reference weld without any flaws and a base material. Various KB defects were investigated with the aim of determining the defect size that does not have a significant influence on the fatigue life of joined 6.35-mm-thick plates. A critical value for the KB geometry appears to be a depth of 0.3 mm considering the influence on fatigue life for the investigated configurations. This paper also presents results from micromorphological analyses of the fatigue crack initiation from the KB and from the analysis of the weld cross-section microstructure. [ABSTRACT FROM AUTHOR]

This work describes a mechanism for the initiation of delamination cracks in Al–Li alloys based on the soft/stiff character of adjacent grains. Small-scale-yielding, crystal plasticity simulations of divider grain configurations (L-T) reveal an elevated mean stress on grain boundaries. This mean stress increase drives a sharp localization of the Rice-Tracey parameter to the grain boundaries – elevation of the RT parameter indicates favorable conditions for void growth and triggering of delamination cracking, in agreement with the fractography of Ritchie and co-workers. Our simulation results and available experimental evidence indicate delamination initiates typically between soft/stiff grain pairs, often Bs (Bunge-convention Euler angles ϕ 1 = 131 ° , Φ = 83 ° , ϕ 2 = 307 ° ) or S ( ϕ 1 = 233 ° , Φ = 151 ° , ϕ 2 = 105 ° ) orientations. The crystal plasticity results and a simple model of a soft/stiff material interface show that mean stress accumulation is a consequence of the mechanics of such an interface, and not necessarily tied to material inhomogeneities near the GBs (such as precipitate free zones). [ABSTRACT FROM AUTHOR]

Purpose - T-sections of carbon fibre-reinforced composites are prone to delamination because they lack reinforcement through their thicknesses. The purpose of this paper is to present the structural response of cost-effective laminated T-sections when subjected to various types of loads and impacts. Design/methodology/approach - The core of the automated manufactured beams is analysed. Pull-off, flange tension, and flange bending were tested for specimens extracted from an I-beam. The failure processes for all of the specimens were investigated in detail, leading to the statistical evaluation of the failure modes. Findings - A correlation is apparent between the impact damage energy and certain fracture patterns. These results can be used to assess damage tolerance when designing stiffeners, beams, and various complex structures. The increase in strength by 25 per cent was measured for the advanced stitching located in the web section for the flange tension test. Originality/value - The resistance displayed by the T-sections toward impact damage was studied experimentally, as the literature describing this topic is limited. The prevalence of one fracture mode for higher impact energies shows a possible advantage of the cost-effective preforms for the damage tolerant philosophy. [ABSTRACT FROM AUTHOR]

Fatigue crack growth testing of 2024-T3 Aluminum plate was performed using compact tension (CT) specimens with chromate and non-chromate primer paint systems to evaluate the effects of the coatings on fatigue crack growth rates. The tests were conducted in lab air and sea water environments for each of the coating systems. Standard E399 CT specimens were tested to determine the influence level of environmentally assisted cracking (corrosion fatigue) on crack growth rates and cyclic count to prescribed pre-crack and final crack lengths. Increasing stress range (Δ K) tests were conducted at 10 Hz in the range of 6.5 to 26.5 MPa $$\sqrt m$$ . It was determined that the coated specimens exhibited a 12% shorter total life, on average, than the bare specimens for the lab air cases. In the case of salt water exposure, the coated specimens exhibited approximately 10% life increase over the bare specimens. The number of cycles to the 2.54 mm pre-crack length for the coated specimens was all less than the cycle count for the bare tests. In each case (coated or bare), there was an increased growth rate at the lower stress ranges in the salt water environment, with the chromate system case displaying the smallest change (increase). It can be concluded that the coated specimens initiate cracks and propagate faster than the bare specimens for short cracks at low stress range, but the environmental influence on the specimens is quickly overshadowed as the cracks elongate and the rate of growth increases. The coated specimens exhibited a higher total life cycle count to final crack length for this testing. [ABSTRACT FROM AUTHOR]

The short beam shear method is the most common test used to determine interlaminar shear strength (ILSS). However, different test standards provide a range of values and make this method unreliable. Carbon fiber-reinforced thermoplastic laminates were used for experiments with the boundary conditions specified under International Organization for Standardization and ASTM test standards. Additional factors, such as the matrix type, thermoforming, and carbon weave orientation, were chosen to build an experimental design. The work also demonstrates the unique visualization of the shear strain during three-point bending as determined via photogrammetric measurements. The specimen failure modes are described in detail. This paper highlights and evaluates the possible influences of the material and test factors that should be considered when ILSS tests are performed on woven fabric reinforced thermoplastics under different test standards and conditions. [ABSTRACT FROM AUTHOR]

• Low-velocity impacts were performed on single-sided, patch-repair CFRP panels. • Patch thickness, patch diameter and the inclusion of a plug were evaluated. • The damage area grows by ca. 50% when a pristine panel is impacted a second time. • Adding a plug to the patch-repair increased the structural performance. • A plug gave an interlaminar damage area that was smaller than the pristine panels. The present paper studies the low-velocity impact testing of carbon-fibre reinforced-plastic (CFRP) pristine and patch-repair CFRP panels. Firstly, the effect of repeated impacts on the pristine CFRP damage growth is considered at impact energies of 7.5, 10.5 and 30 J. Secondly, such tests lead to a single-sided, patch-repair panel being manufactured by removing a 40 mm diameter central hole, to act as the 'damaged area', from the parent CFRP panel and then adhesively-bonding a circular CFRP patch-repair over the hole so generated. Various diameters and thicknesses for the CFRP patch-repair are employed and, in some cases, a CFRP circular plug is also used to fill the hole created by removal of the parent composite. The measured load versus time, and load versus displacement, traces are compared. Further, the extent and location of any interlaminar damage, i.e. delaminations between the plies of the CFRP, caused by the impact event are mapped using an ultrasonic C-scan technique. It is shown that single-sided patch repairs can be very effective in restoring the impact performance of damaged CFRP panels. [ABSTRACT FROM AUTHOR]

Abstract: Fiber reinforced plastic composites are currently used in structures operating in a variety of environments where various forms of damage may occur. One form of possible damage in composite structures can be in the form of deep scratches causing a discontinuity in the load bearing plies. These scratches may occur accidentally by abrasion of the composite structure on a sharp object during normal operating conditions. Scenarios for these possibilities are discussed in the aerospace environment. Experimental and numerical studies performed show altered failure modes and J-Integral mode mixity affecting the tension behavior of the carbon/epoxy composites examined. [Copyright &y& Elsevier]

The effect of phosphorous on the integrity of the thermally grown aluminium oxide layer formed on a platinum-aluminide coated a single-crystal nickel-base superalloy (CMSX-4) was studied through oxidation tests for varying exposure times followed by analysis using scanning electron microscopy and microanalysis. The samples were oxidized for up to 72 hours in pure oxygen (0.2 atm) at 1150°C. Oxide spallation was shown on the surface even after short exposure (24 hour). The fraction of the spallation increased with time. Analysis revealed that phosphorous was associated with spalled areas in all conditions and is proposed to contribute to the failure by weakening to oxide/coating interface. A strong correlation was observed between phosphorous and chromium, as chromium was detected in phosphorous-rich areas. [ABSTRACT FROM AUTHOR]

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

study has been accomplished to characterize the fatigue crack growth rates and mechanisms in thick plate (16.51 cm) commercial grade 7050-T7451 aluminum plate in the L-S orientation. Examination of the effects of potential property gradients in the plate material was accomplished through hardness measurements along the short transverse direction and with compact tension tests. Tests exhibited a distinct trend of reduced center plane hardness in the plates. Compact tension specimens and the compliance method were used to determine crack growth rates for specimens machined from the t/4 and t/2 planar locations and oriented for L-S crack growth. Crack growth rate data (long crack) from the tests highlighted significant growth rate differences between the t/4 and t/2 locations. No significant effect of R-ratio was observed in the 0.05-0.3 range tested. Additionally, crack front splitting was noted in all specimens to differing degrees with data showing significant retardation of growth rate curves for the L-S orientation above 13 MPa √m in the center plane, and 10 MPa √m at quarter plane, where branching and splitting parallel to the load axis are dominant growth mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: The multi-site damage problem of aging aircraft has raised the issue of obtaining accurate stress intensity factors of interacting collinear cracks under external load. The simple approximate technique proposed by Kachanov (1987) is specialized in this work to arbitrary length collinear cracks with arbitrary spacing under far field tension. This approach yields simple formulas that can be used to quickly and accurately assess the mode I stress intensity factors of any number of collinear cracks in an infinite body under far field tension considering interactions between all cracks. The advantage of this approach over others is that it is simple, has good accuracy, and is very efficient. Kachanov''s method is further enhanced here such that a repeating subpanel of cracks of arbitrary number, size, and spacing can be modeled implicitly with resulting efficiency gains. The effect of interaction cracks can be used to build up stress intensity factor solutions for more complex geometries. Several numerical examples and timing studies are used to demonstrate the efficacy of this approach. [Copyright &y& Elsevier]

Abstract: A study has been accomplished to characterize the fatigue crack growth rates and mechanisms in thin and thick plate commercial 7050-T7451 aluminum plate in the L–S orientation. Crack growth and crack shielding with branching behavior of long, through thickness cracks is examined and compared to L–T and T–L oriented growth data. Compact tension specimens and the compliance method were used to determine crack growth rates. Constant ΔK data showed significant retardation of growth rate curves for the L–S orientation in the range of 10–13MPa√m where branching and splitting parallel to the load axis are dominant growth mechanisms. [Copyright &y& Elsevier]

Abstract: This paper proposes a new virtual crack closure-integral method (VCCM) for quadratic tetrahedral finite element to compute the energy release rates/stress intensity factors. The formulations, numerical implementations and some numerical results of proposed VCCM are presented in this paper. Proposed VCCM enables us to adopt the tetrahedral finite element in 3D crack problems and us to use automatic mesh generation programs. Therefore process time to perform 3D crack analysis drastically reduces compared with the case of hexahedral elements. [Copyright &y& Elsevier]

To enable the application of optical fiber sensors to aerospace vehicles, the sensor interrogation or data acquisition system has to meet small size and low weight requirements. This paper presents the developmental work of an echelle diffractive gratings (EDGs) demultiplexer-based optical fiber sensor interrogation system. The operation principle of this system and its application to fiber Bragg grating (FBG) sensor interrogation are presented. The experimental results have shown that the developed interrogator (not including the electronic controller) weighs less than 60 g and provides better than 1 pm measurement resolution and better than plusmn10 pm measurement accuracy. [ABSTRACT FROM PUBLISHER]

All aerospace vehicles have the common constraint of limited space for the electronic systems. The challenge has always been how to pack effective electronic systems into the space available. Higher levels of electronic integration can give a competitive advantage; for example, by providing extra channels in a communications satellite thereby increasing revenue to the operator. Today's deep sub-micron manufacturing processes for integrated electronics offer an opportunity for a step change for electronic functionality that can be packaged in a given space. This technology makes possible, for the first time, a true system-on-chip approach to electronic systems, which is already being exploited by the commercial sector in products such as the mobile telephone [ABSTRACT FROM PUBLISHER]

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