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10:00   Poster pitches day 3 Chair: Marcel Bos 10:00 0 mins Fatigue performance and cyclic deformation behaviour of titanium TI-6AL-4V additively manufactured by wire + ARC directed energy deposition Rob Plaskitt, Michelle Hill, Xiang Zhang, Abdul Khadar Syed Abstract: NEWAM (NEw Wire Additive Manufacturing) is a 5 year research programme focused on the process, material and structural integrity of wire based directed energy deposition AM (w-DEDAM) processes. Four universities (Cranfield, Manchester, Strathclyde and Coventry) are combined in a research programme with UK EPSRC funding and industry support from AM equipment supply chain, service providers and industry end users. Project partners include aerospace OEMs who are interested in the future potential of this manufacturing method for increased material buy-to-fly ratio, manufacturing lead time reduction and weight reduction. Coventry University are leading the “Material Performance and Structural Integrity” of NEWAM, determining structural integrity through fatigue initiation, fatigue fracture, and residual stress research. Hottinger Bruel & Kjaer are working with Coventry researchers and contributing strain-life fatigue testing and material characterization services at their Advanced Materials Characterization & Test (AMCT) Facility. This presentation will describe this fatigue initiation research and findings for as-deposited wire + arc additive manufactured high strength titanium Ti-6Al-4V alloy. Two walls were manufactured with an oscillatory torch and wire path. Cylindrical blanks were extracted from these walls in horizontal and vertical orientations with respect to the deposited layers. Fatigue test specimens were manufactured and tested according to ASTM E606 standard. Fully reversed strain-controlled fatigue testing were performed for 50 fatigue test specimens to investigate material deformation behaviour and fatigue performance from low cycle fatigue (LCF) through high cycle fatigue (HCF) regimes. X-ray computed tomography was used to detect defects in the test samples, and microstructure and fractography were performed to understand the role of microstructure on crack initiation and fracture. Fatigue testing and investigations revealed no porosity defects in the material, crack initiation was from microstructure features. Fatigue characterisation showed marginal difference in fatigue performance with build layer orientation (anisotropy) in LCF at high applied strain, with no significant difference (isotropy) in HCF at low applied strain. 10:00 0 mins Optimal design and static load testing of tow-steered aircraft fuselage frames Hitoshi Arizono, Yuichiro Aoki, Sunao Sugimoto, Ryosuke Yoshimura, Yuji Ikeda, Daisuke Nishida, Hiroharu Suzuki Abstract: Weight reduction is required as one of the measures to improve the fuel consumption rate of newly developed airframes but securing the strength of high-stress areas is an issue. One of the objectives of this research is to establish a design method that secures strength by a new method that achieves fiber orientation optimization and part thickness distribution optimization at the same time. In addition, as another purpose, it is shown that it is possible to reduce the manufacturing cost through the experience of full-scale structure manufacturing for Automated Fiber Placement (AFP) manufacturing, which is expected as a manufacturing method suitable for this design method. Regarding fiber orientation optimization, tow steering (curved tow) along the load flow using AFP improves strength and makes it possible to reduce weight. Regarding the optimization of sheet thickness distribution, in conventional manual layup, frequent use of part thickness variations leads to an increase in manufacturing costs (fabrication time), but by utilizing AFP, the fabrication time can be shortened and fine variations in part thickness can be provided. This makes it possible to reduce the weight of the structure. The fuselage frame around the emergency escape door of single-aisle aircraft was selected as a part where cost reduction effect by AFP manufacturing and weight reduction by application of optimization design method are expected. We examined and applied the optimization design method to the target part and confirmed its effectiveness by comparing it with the conventional design method. A test concept for evaluating the effect of the optimization design method on the actual structure was studied, and the basic design of the test article and the layup mandrel necessary for the fabrication of the test article was carried out. A test article is currently being manufactured, and the test is scheduled to be conducted in January next year. 10:00 0 mins Crack growth analysis of fiber metal laminates stiffened panels Pedro Felix, Mariano Arbelo, Marcelo Bertoni Abstract: The use of fiber metal laminates stiffened panels for aerospace application has been largely increasing due to its low crack propagation rate and excellent residual strength behavior. In order to compare the traditional built up aluminum constructed stiffened panels and fiber metal laminates materials under the context of damage tolerance, two stiffened panels are design, tested and compared against finite element models: (1) aluminum skin with riveted stringers and (2) fiber metal laminate skin with bonded stringers. The two panels exhibited significantly different results, with the fiber metal laminate stiffened panel having the best response in both crack propagation and residual stress. With the objective of obtaining an accurate analysis tools for these two panels, filling a gap of available commercial softwares, detailed Finite Element Models are built aiming the use of Virtual Crack Closure Technique to obtain Stress Intensity Factors, taking into account the delamination phenomenon during crack propagation on fiber metal laminates materials. Numerical results show that the proposed technique can reach good correlation and it is observed that the chosen delamination shape largely dictates crack growth behavior on the fiber metal laminates stiffened panel. 10:00 0 mins Assessment on fatigue behavior of AL7475 T7351 subjected to natural corrosion, accelerated corrosion and artificial damages Daniele Mezzanzanica, Giuseppe Ratti, Andrea Baldi, Ugo Mariani, Marco Giglio, Andrea Manes, Andrea Brenna, Marco Ormellese Abstract: The typical in-service corrosion of helicopter components is due to improper material coupling or degradation / damage of the protection coating; corroded items increase with the size of the fleet, the exposure to aggressive environment and the ageing of the aircrafts. Into the mainstream of Leonardo Helicopters plan, for European Plan for Aviation Safety 2020-2024 on ‘ageing of the fleet’, this research activity is focused on experimental activities devoted to evaluate the fatigue material behaviour in presence of several kind of corrosion pits, either from accelerated and natural corrosion, with the final objective to identify a correlation with artificial defects made by Electrical Discharge Machining (EDM), when subjected to fatigue loads. More specifically, in the context of damage tolerance assessment, the analysis focuses on the evaluation of threshold to propagation of small cracks emanating from either corrosion pits or EDM notch; the crack growth threshold and the fatigue endurance limit are combined through the Kitagawa-Takahashi diagram, defining the area of non-propagating cracks. Kitagawa-Takahashi is usually based on the crack length; the fatigue strength of metallic materials in the presence of small defects are well predicted applying the √area parameter model proposed by Murakami and Endo. Experimental activities have been performed on Aluminium Alloy 7475 T7351 in alternate bending, in presence of a defect with √area = 0.445 mm, equivalent to a semi-circular flaw of 0.35 mm radius. Evaluated defects are EDM notch, accelerated corrosion pits from galvanostatic and salt spray techniques, natural corrosion from exposition in urban and in marine environments. An ad-hoc galvanostatic procedure has been developed to promote a localized corrosive electrochemical attack. EDM notch, well-known for shape, size and technological process, are considered as a base case study and accelerated corrosion pits were generated to obtain the same value of √area. The results of the activity show a strong correlation among the threshold to propagation from accelerated corrosion, natural corrosion and the artificial flaws obtained by EDM technique confirming the applicability of Kitagawa diagrams derived from EDM notches to describe the damage tolerance behaviour in presence of corrosion pits with equivalent size. 10:00 0 mins Development of a numerical model of tire fragments for high-speed impact. Jean-Roch Augustin Abstract: On July 25, 2000 during the flight Air France 4590, the Concorde at takeoff on a runway of the airport of Paris Charles de Gaulle rolls at high speed on a metallic debris lost by a preceding plane, this incident causes immediately the explosion of the tire and the crash of the aircraft. Since then, the resistance to pneumatic impact has been a dimensional factor in the design of aircraft wings [1]. Impact tests to justify, evaluate or repair equipment are often complex to implement and therefore expensive. Developing a robust numerical model for the dynamic impact of tire fragments can limit the number of tests and better understand the mechanical phenomena of impact. Within the framework of a European TIOC wing project carried out with Dassault, SONACA and CENAERO, DGA TA has developed a tire behavior model. In order to build a robust numerical model, the characterization of the impactor's behavior under real test conditions is essential. In order to have the most global model possible, the geometric parameters, the Mullins effect, the viscoelasticity [2] and the hyper-elastic nonlinearity of the elastomer have been studied. The elastomers that make up aircraft tires are still little known materials, a methodology to characterize their behavior has been developed. Most of the models proposed for the characterization of elastomers are phenomenological models[4], because the internal mechanisms are not yet well identified. The complexity of the construction of a behavioral model lies first in the definition of the domain of use of the specimen and then in the construction of the model adapted to the conditions of use. The last step consists in implementing the model in a finite element software[3]. Phenomenological models being very sensitive to the material data and to the conditions of use, it is difficult to rely on a standard. The identification of the parameters will have to be based on three elements: tests, measurements and modelling. The challenge is to succeed in bringing these elements together to build the building blocks of a Virtual Testing approach, i.e. a robust model of the tire debris and material models validated under the specific impact conditions. This has been achieved by setting up a methodology including tests, measurements by innovative methods of stereo-correlation of digital images and modelling which allows the identification of digital models. 10:00 0 mins Combined mechanical and environmental ageing of FRPs - Hygrothermal fatigue case study Valentin Perruchoud, Yasmine Mosleh, René Alderliesten Abstract: FRP composites are used in aerospace, marine, and civil engineering structural applications where the materials constituting these structures are often exposed to outdoor environment or particular climate. Aircraft fuselage, wind-turbine blades, ship hulls, and bridge decks are examples of large-scale structures that must be designed considering both environmental and mechanical ageing to ensure structural safety. The mentioned structures are commonly made of FRP with carbon or glass fibre reinforcement. Decades of research and operation of those materials have shown that FRPs are suitable in terms of durability with, in most situations, limited assessment of environmental loading effects on the structural integrity during laboratory testing. However, with rising concerns on climate change and the significant impact of engineering structures on the global CO2 emissions, using traditional FRP composites does not meet the requirements of low embodied-energy and easily disposable or recyclable materials. Bio-based fibres or resins satisfy those requirements with one example of such being flax fibre reinforced polymer composites. Flax fibres are a sustainable alternative that could replace synthetic fibres in FRP composites thanks to their renewability, low embodied energy, ease of disposal, competitive mechanical and high damping properties. Example of this is the use of flax fibre composites in satellite for clean burn upon re-entry to the atmosphere (Natural fibre reinforced satellite panel by ESA and Bcomp). While carbon and glass fibres are relatively inert to water, bio-based material alternatives are usually hygroscopic and susceptible to environmental humidity. Since existing lifetime prediction models for FRPs often neglect hygrothermal effects, they cannot be directly and confidently applied to bio-based FRPs or to FRPs subjected to harsh climate conditions. In the last decade, research on flax FRPs mainly focused on the characterisation of mechanical properties, fatigue life and effect of environmental ageing on the residual properties. The literature shows that environmental ageing has an effect on the damage in flax FRP with strength and stiffness moderately affected. Literature also shows that damage due to cyclic mechanical loading (fatigue) is similar to damage due to environmental ageing. Although environmental and fatigue effects have been studied separately, to this day, no comprehensive investigation on the interaction of these two has been carried out. To ensure the competitive durability and service life of biobased FRPs compared to synthetic composites, the effect of environmental loadings such as moisture and temperature cycles concomitant to mechanical loading must be considered in the structural design. The aim of the current study is to identify the phenomenological commonalities between the damage due to environmental and cyclic mechanical loadings (fatigue) when they occur sequentially or simultaneously. Understanding the interaction between damage mechanisms originated from environmental and mechanical loadings and how this affects the residual material properties is pivotal for the adoption of biobased FRPs in structural applications in terms of durability of such structures. This study critically discusses current understanding of this interaction in existing literature and proposes an experimental methodology that aims to set the foundation for further development of reliable life prediction models for FRPs regarding environmental effects. This ultimately leads to safer and more durable design of large-scale engineering structures with bio-based materials as constituents having low environmental impact. 10:00 0 mins The integrated maintenance system (IMx+) Dallen Andrew, Josh Hodges, Robert Pilarczyk Abstract: The use of tools and methodologies for capturing the digital thread data generated through on-aircraft maintenance actions continues to be a key focus area for improved execution of aircraft structural integrity programs across the aerospace community. This includes tools to perform nondestructive inspection (NDI) and cold expansion (Cx) of holes, as implemented in the new Integrated Maintenance System+ (IMx+), an advanced maintenance technology integrating smart shop tools with automated data collection and spatial position tracking to improve aircraft quality assurance. The digital thread tools implemented within the IMx+ system helps to enable an effective ASIP to: • Establish digital thread with customized data fidelity level to better support fleet management and bridge the gap between maintenance tools and databases • Enable automatic maintenance data capture (Cx, NDI/NDE, geometric, photos, spatial position, etc.) and output to user-defined maintenance database • Establish quality assurance tools necessary for Cx full credit • Expand flexibility to interface with various maintenance tools and spatial tracking technologies • Complete cybersecurity requirements for approved use on secure networks While this type of technology is necessary to meet the growing needs for a sufficient digital thread, we must also be cognizant of their impacts on the maintenance community and find ways to meet structural integrity needs without overburdening the maintainer executing the work. This introduces the concept of data fidelity levels, which are determined based on the scope and criticality of each maintenance action. Have you ever asked what fidelity level of data is actually necessary to support your current and future structural integrity needs, as a one-size-fits-all approach is not practical? Current guidance does not exist to answer that question, leaving each entity in the community individually guessing on what fidelity of data is good enough for each scenario. Some initial guidance will be presented to facilitate that determination. The combination of defined methods and an array of tools as implemented in the IMx+ system is necessary to sew the digital thread together, ensuring the necessary quality assurance requirements are achieved for critical maintenance processes and supplying the structural integrity community with the necessary data to optimize fleet management. 10:00 0 mins The engineered residual stress implementation (ERSI) working group Dallen Andrew, Jacob Warner, TJ Spradlin Abstract: The Engineered Residual Stress Implementation (ERSI) working group was formed in 2016 with a mission to “develop a holistic paradigm for the implementation of engineered residual stresses into lifing of fatigue and fracture critical components”. ERSI emerged from within the United States Air Force (USAF) aircraft structural integrity community as a forum for individuals and organizations to collaborate constructively, transition technology and data to the public sphere, and consult on policy/best practices concerning the incorporation of residual stresses with other entities such as the FAA, DoD, ASTM, SAE, etc. ERSI members represent a broad diversity of interests and backgrounds, both domestic and international, from military, academia, and industry. The primary focus of ERSI so far has been the transition of a classic engineered residual stress technology, cold expansion of holes, into life extension for USAF weapon systems. Although hole cold expansion is known to provide significant structural fatigue life extension, the full potential improvement has not been included in certified airworthiness limits. With extensive support from ERSI, the USAF recently issued a Structures Bulletin which allows aircraft structural integrity managers to utilize cold expansion benefits for initial and recurring inspection intervals, a significant achievement for both platform availability and fleet-wide cost savings. This achievement is a holistic product from the six primary focus areas, or committees, within ERSI that represent different technical disciplines of aircraft structural integrity: 1) fatigue crack growth analysis, 2) validation testing, 3) residual stress measurement, 4) nondestructive inspection/evaluation and quality assurance, 5) residual stress process simulation, and 6) risk assessment and uncertainty quantification. While ERSI does not fund work directly, these six committees work together to identify and address technical gaps, define the requirements and guidelines for implementation, and collaboratively develop and accomplish new round robin activities that advance the state-of-the-art. An overview of the activities of the ERSI working group will be presented, including round robin efforts related to residual stress measurements, FE process simulations of cold expansion of holes, fatigue crack growth analyses incorporating residual stresses and/or interference fit fasteners, stress spectrum effects, and stress intensity factor comparisons. 10:00 0 mins Ultrasonic measurement of residual stresses in aluminium alloys Yuri Kudryavtsev, Lana Potapova Abstract: Residual stresses (RS) can significantly affect the engineering properties of materials, parts and welded elements and this factor should be taken into account during the design, manufacturing, maintenance and repair of different products and structures [1]. Although certain progress has been achieved in the development of different experimental techniques, a considerable effort is still required to develop efficient and cost-effective methods of RS measurement. The non-destructive ultrasonic method allows one to measure the RS in both cases: averaged through thickness or in surface/subsurface layers of material. The present version of the developed compact equipment allows measuring the averaged through thickness RS in plates 2 - 200 mm thick as well the RS in surface/subsurface layers of material to the depth of 1-4mm [2-4]. RESULTS AND CONCLUSIONS. The RS were measured in a number of welded AA5083 and AA6061- T6 aluminum alloys specimens. Distribution of both longitudinal and transverse components of RS was analyzed along the weld and in direction transverse to the weld. The relaxation of RS in one of the welded sample during fatigue loading was also analyzed [5]. The comparison of the results of ultrasonic measurements of RS with the results received by destructive crack compliance method of RS evaluation showed reasonable agreement. 10:00 0 mins Friction stir welds with enhanced fatigue strength and life via laser peening Joana Antunes Abstract: Friction Stir Welding (FSW) is being studied as a viable solid-state joining process for aircraft fuselage structures. As with any other high-temperature joining process, FSW will create variably distributed residual stress fields that adversely affects the dynamic performance of the joint. The FSW process may also introduce defects that would act as sites for fatigue crack initiation during dynamic testing. Laser Peening (LP) has been demonstrated as an effective tool to improve overall fatigue life in aerospace aluminium alloys due to the introduction of a through-thickness compressive residual stress state. This could also act as a deterrent for crack initiation from a pre-existing defect and potentially recover the fatigue life of a FSW joint. The objective of this study is to understand and quantify the influence of LoP defect depth and profile on the fatigue life of peened and unpeened FSW joints. To investigate this, controlled LoP defects of 400 µm depth have been introduced during FSW. Fatigue testing revealed significant reduction of fatigue life with considerable scatter in fatigue performance. This not only shows that 400 µm defects are providing a higher level of stress concentration, resulting in faster crack initiation but also that the defect geometry is critical. Scanning electron microscopy and optical microscopy were carried out to accurately characterize the impact of defect geometry on crack initiation. Preliminary results have shown that crack initiation does not seem to be influenced only by the defect length, as the crack initiation did not coincide with the sites where the LoP depth was the highest. The influence of defect geometry in the crack initiation behavior is currently being investigated using synchrotron X-ray tomography as an imaging technique to reconstruct the LoP defect profile in peened and unpeened samples. This could allow to investigate changes in the defect profile through the width, as well as to calculate the stress intensity factor along the weld, using finite element modelling. Understanding of the underpinning crack initiation and propagation mechanism would help in designing the peening process to ensure a compressive stress state to delay fatigue crack propagation from LoP defects or similar discontinuities. 10:00 0 mins Stacking sequence effect on the fatigue behavior of single lap shear bonded joints Francis Mariana Gonzalez Ramirez, Luiz Lise, Andreas Baumann, Fabian Nowacki, Ilona Kunzler, Joachim Hausmann Abstract: The stacking sequence of composite joints, especially the ply orientation at the substrate/adhesive interface, plays an important role on their fracture behaviour. However, few works are available in this subject, especially under fatigue loading conditions. In this study, the stacking sequence effect on the fracture and fatigue/fracture behaviour of glass-fibre reinforced polymers bonded joints is addressed. Two layups were considered: [0°, 90°, 90°, 0°]s and [0°, 45°, 90°, -45°]2s. Single-lap shear (SLS) specimens bonded with a two-component epoxy-based adhesive system (SikaPower® 1200) were subjected to quasi-static and fatigue testing. Quasi-static tensile tests were executed with the aim of obtaining the load-displacement curves and their respective average fracture ultimate load (Pu). Such tests were conducted at a velocity of 1 mm/min using a Zwick testing machine with a loading cell of 10 kN. Fatigue tests were performed considering a maximum load (Pmax) equal to 40% of Pu. The evolution of the specimens compliance (C=d/P) as a function of the number of cycles (N) was recorded during the SLS fatigue/fracture tests. Every fatigue tests considered a sinusoidal waveform with a load ratio, R of 0.1. Cyclic tests were conducted on a servo-hydraulic Instron machine equipped with a 10 kN load cell at a frequency of 4 Hz (Fig. 1). Fractographic analyses were conducted using a scanning electron microscope (SEM). The failure mechanisms of both stacking sequences were compared and correlated with the fracture strength, compliance and fatigue life results. This paper provides experimental data for composite joints considering different layups and gives important insights on the fracture mechanisms observed under fatigue loading. This information could be used as a guideline in the selection of the best composite joint configuration for high-performance engineering applications 10:00 0 mins Simulation of crack growth in adhesively bonded joints via cohesive zone models Nicola Zavatta, Maria Pia Falaschetti, Enrico Troiani Abstract: Adhesively bonded joints have shown great advantages in the aerospace industry when compared with traditional mechanical fastening methods. These types of joints allow to reduce the overall structural weight, improve the fatigue life characteristics due to reduction of stress concentrations (uniform stress distribution), smooth external finish, sealed surfaces, and many others. However, one of the main concerns with these joints is their characterization under fatigue loading, i.e., a comprehensive study of crack growth which will allow the development of standardized tests and certification in the aerospace sector. At the moment, their certification for primary structures requires that critical disbond be prevented by proper design. To this end, Disbond Arrest Features (DAFs) have been tested as a mean to improve the fatigue resistance of bonded joints. In this work, the authors developed a numerical model to assess fatigue disbonding under mixed-mode loading, a condition which is frequently encountered in adhesive joints. The model was based on a cohesive zone formulation, which was implemented via user-defined subroutines UMAT in the finite element software Abaqus. Mixed mode disbonding was modelled through the Bürger’s modification of Paris’ law. Two test cases were simulated: a double cantilever beam (DCB) specimen and a modified cracked-lap shear specimen with a bolted DAF. The results of the simulations were compared with experimental data from previous tests, showing that the model is able to reproduce the observed fatigue disbonding and capture the disbond arrest provided by the DAF. 10:00 0 mins Opmimization of hybrid composite-metal joints Ruopu Bian, Bin Wang, Hongying Yang, Jiazhi Ren, Lujun Cui, Oluwamayokun B. Adetoro Abstract: Better understanding of the methods of composite and metal joints in airline industry has significant role in reducing the operational costs. New joining methods between composites and metals are investigated involving additively manufactured rivet pins. This paper focuses on numerical analyses of the strength of the joint, as well as optimization of the pins. The joint morphologies of metal to metal, metal to composite materials were studied through the finite element analysis, involving individual and multiple pins and adhesive-bonding layer joint models. The model divides into three parts, top metal plate with a pin growing on the bottom surface, middle adhesive layer and the bottom composite plate. The mesh of model is shown in Figure 1 and the parameters of the model are detailed in Table 1. By setting certain boundary conditions(fixed the left side of the metal plate) and loads(along the X direction on the right side of the composite plate), results show that the largest bending stress in the pin occurs at the cross section between the bottom of the pin and the metal plate. In addition, bearing stresses around the composite hole for the pin increases with the external tensile loading. Besides, a plot of the shear stress along the loading direction can be obtained by modeling six pins uniformly distributed along the center line of the adhesive layer in the X direction(Figure2). The conclusion is that by optimizing the shape of the pins, the shear stress and axial stress are reduced. A parametric study is carried out for joint design optimization involving aluminum and titanium alloys and carbon fibre reinforced composites. Following the optimization, experimental study using additive manufactured pins are to be conducted. This study put forward optimization of joining configurations between composites and metals for improved strengths.

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