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Composite structures in aeroplanes are often thin-walled and lightweight, resulting in significant compliance, which presents a handling and assembly challenge due to the associated part deformations. In order to counteract these deformations, the parts are held in their specified geometry using stiff and correspondingly heavy fixtures or jigs. Mobile industrial robots are very versatile and widely used in industrial volume production, but they are limited in their payload capacity. High-rate production of large aerospace modules requires highly automated flexible assembly processes. The approach presented in this paper is to combine mobile units with lightweight assembly jigs that have the capability of deformation compensation. The subject of the study is a high-rate assembly process for flap modules using an Autonomous Industrial Mobile Manipulator (AIMM) and a lightweight end effector. The end effector has a shape compensation function, implemented by an integrated Stewart platform, which enables the compensation of manufacturing tolerances as well as gravity effects. The compensation function is used in a closed loop and counteracts shape deviations by appropriate fixture shape adjustments. The paper reports on the conceptual design of the assembly scenario, the design of the end effector, its realization and the successful experimental demonstration at 1:1 scale.

Composite frames in aerospace applications often show a lack of dimensional fidelity, which creates the necessity of costly shimming efforts within final assembly lines. A numerical study on C-profile frames has been performed to examine the mechanisms inducing these distortions. The paper shows that distortions are directly related to the composite’s material architecture, the part geometry and interestingly also to the state of the art zone-based frame design philosophy applied today. The paper shows that frame distortions arise from the 3D orthotropic nature of composite laminates , in-plane CTE inhomogeneity of laminate zones and coupling of different part areas. The main mechanisms inducing frame distortions are deduced from the numerical models. The paper also shows that trimming operations, which are necessary to bring frames from the manufactured to the engineered shape, significantly affect the frames’ final distortion state, the internal residual stress level as well as corresponding assembly forces during assembly.

Unavoidable deformations occur during part production due to the non-isotropic nature of carbon fibre reinforced plastics (CFRP). These deformations often lead to dissatisfaction of tolerances or result in cost and time intensive rework of the tooling. In a cost driven production environment, similar to the automotive industry, it is essential to predict the deformations early on in the part development process in order to compensate toolings accordingly. In future applications, Fast Curing Epoxy Resins (FCER), with curing times of less than 20 min, will play a key role in high rate CFRP-production at low cost. The present paper reports on a comprehensive experimental study on different FCER systems. It includes the thermo-chemical characterization of neat resin samples as well as the quantification of spring-in deformations of L-profiles. Essential part and processing parameters, as the lay-up, the curing temperature, the cooling rate and the fibre volume fraction are varied and their effect on process induced deformations is quantified. Results for FCER system are compared to slower curing systems to assess differences.

Curved structures made of fibre-reinforced plastics tend to show an out-of-plane failure type, when loaded under bending. One method to determine the related tensile strength in thickness direction, is the standardised unfolding test related to ASTM D6415 with L-profile specimens. However, the standard shall be used for unidirectional materials only, which is not the case for multidirectional laminates. Therefore, this publication presents methods to determine the layer-wise stress and strain state as well as occurring failure types of multidirectional laminates. An extension of the Lekhnitski formulae is presented and its results are validated by comparison with high resolution strain measurements by Digital Image Correlation. Based on the analytical solution, a failure analysis using Cuntze’s Failure Mode Concept is conducted. It was revealed, that the failure load and position can be predicted accurately, if a failure type related strength –in-plane or out-of-plane failure– is used. In the presence of [Formula: see text]-layers higher deviations occur between test and prediction and therefore limits the validity of the presented analytical failure analysis.

The present paper reports on an anomaly of laminates’ coefficients of thermal expansion (CTE), which has been observed for more-orthotropic laminates of a series-quality M21E/IMA prepreg-made composite frame. It was found that measured CTEs increasingly deviate from theoretical CTE values, derived from unidirectional ply data, when the degree of laminate orthotropy increases. The paper comprises experimental CTE measurements for the unidirectional M21E/IMA ply and six specific laminates of a full-scale frame. Analyses suggest that the observed discrepancy correlates with the laminates' degree of orthotropy, which is quantified by the in-plane Young's modulus ratio E x / E y in this paper. The observed effect is considered critical as inhomogeneous CTEs lead to process-induced distortions of curved composite structures. Thus, they play a key role when carbon-fiber-epoxy composite frames shall be made in tight dimensional tolerances. Wrong CTE calculation leads to erroneous shape predictions, inaccurate tool compensation and finally to assembly problems.

The use of fiber-metal laminates (FML) allows for substantial advantages over a fuselage skin made of monolithic aluminum materials. Glass fiber prepreg reinforced aluminium is characterized by high damage tolerance capabilities, supporting the structural strength capability in case of any kind of damage. For this reason, FML, and GLARE in particular, have been identified as superior materials for aerospace applications. More than 400m2 FML is applied on each A380, as skin panels and as D-noses for both, vertical and horizontal stabilizer. FML possess the potential to become the baseline material for next-generation single-aisle aircrafts [1, 2, 6]. The development of a new production chain that will allow automated fuselage production for future short-haul aircrafts is the focus of the studies that make up the joint project AUTOGLARE. As part of the fifth call-up for the German Aeronautical Research Programme (LuFo), the German Aerospace Center (DLR) is working with its project partners Airbus Operations, Premium Aerotech (PAG) and the Fraunhofer Gesellschaft (FhG). The development of a production chain for stiffened fuselage panels made of Fiber metal Laminates should support a production rate of 60 aircraft per month [3]. This study contains the research work of the DLR and FhG regarding the automated and quality assured process for chain stiffened FML fuselages. In addition to a detailed explanation of the systems that were set up, this paper covers the planned tests, the completed demonstration models and the findings derived from them.

In this paper, a smart cure cycle with an additional cooling step for co-cure bonded fiber metal laminates (FML) is developed to reduce process related thermal residual stresses . An online measuring technique with fiber Bragg grating (FBG) sensors is used to gain a clear understanding of the formation process of residual stresses during cure, as well as to determine the resulting residual stress level. Fiber optic sensors are integrated in carbon fiber reinforced plastic (CFRP) – steel laminates. The recorded processing strain curves enable the characterization of the mechanical interaction of the metal and CFRP-layers. By introducing an additional cooling-step, the moment of the connection between the individual components is being influenced. The conducted experiments show a significant reduction of the resulting stress-free temperature. A variety of temperature cycle modifications, like different cooling temperatures, as well as modified cooling and heating rates, are investigated. The impact of these parameters on the process-induced strains and stresses are detected by the fiber optic strain sensors. The thermal residual stresses are reduced by up to 23% for the specimens in focus, when the developed cure cycles with FBG sensors for a monitored cooling and reheating are used.

The determination of in-plane coefficients of thermal expansion (CTEs) of full-stack composite laminates by means of thermo-mechanical analysis (TMA) is affected by free-edge effects. A numerical study has been performed, which is focussed on the quantification of the effects of TMA sample size, laminate layup and the presence of discrete interleaf layers on the determined laminate CTEs. Fine finite-element (FE) meshes have been used to visualize and to examine free-edge effects. The study results call for carefulness when CTEs of full multi-angle laminates shall be determined by means of TMA. When the typical sample dimensions of a few millimeter are used CTEs will likely be overestimated.

Manufacturing of composite structures is inevitably impeded by process-induced distortions. In aerospace industries suppliers are often responsible for making parts according to requirements. Thus, the typical ‘supplier scenario’ is characterized by a strong demand for distortion predictions for sake of tool compensation, in order to make parts conform to given tolerances. However, suppliers simultaneously face a lack of relevant information to derive compensation measures, as neither process-simulation models nor corresponding parameters are accessible. A novel approach is presented within this paper which amalgamates latest experimental results on spring-in distortions in form of a ‘spring-in reference curve’ and an earlier presented phenomenological-numerical simulation concept. This combination leads to a zone-based prediction strategy, focusing on process-induced distortions, which is close to engineering practice and applicable within the typical ‘supplier scenario’.

A numerical study is performed which analyzes the effect of mesh parameter settings on the prediction accuracy of the P-approach, a simulation concept which has been proposed earlier by the author for predicting process-induced distortion of composite structures. A parameterized solid-element finite element (FE) ABAQUS model of a composite L-profile is used as the reference geometry, while numerically predicted distortions are compared with nominal values. This paper shows that significant, unacceptable mesh-related deviations occur for some mesh-parameter configurations. The paper also shows that the main drivers of these deviations are related to the effective geometry of the finite elements at the L-profile’s bend. Based on this finding, the P-approach has been extended with a novel model formulation, which helps to minimize mesh-related deviations, especially for coarse meshes. The validity of the proposed model is verified by a re-execution of the full study, which shows a remarkable reduction of mesh-related deviations. The paper provides general mesh-parameter guidelines for the P-approach application in ABAQUS as well as measures to apply coarser meshes without losing prediction accuracy.

Process-induced distortions (PID) of high-performance CFRP structures lead to problems with dimensional control if the distortions are not accounted for by compensating the process tool accordingly. There is a need to predict PID via simulation in industry rather than relying on less reliable information such as past experience or measurements on prototype structures. PID are caused by many phenomena, which can make detailed simulation complex and time consuming. This paper presents three simplified techniques for prediction of PID with sufficient accuracy but that are much faster and cheaper to run than traditional complex process models. The three techniques use solid or shell finite elements and use inputs based on measured spring-in of simple L-angles made of the same material and process conditions as the larger scale structures to be simulated. Application of the three techniques to example structures show that the predictions agree well with each other and that they give good predictions compared to experimentally measured distortions of a CFRP box. Given their speed and simplicity they have the potential to be useful for predicting PID for simpler composite structures, particularly early on in the design cycle where quick approximate calculations are of great value to evaluate different design concepts.

Counteracting undesired manufacturing distortions of carbon-composite structures is still a challenge for manufacturers. This paper presents a semi-numerical methodology to predict manufacturing-induced distortions of complex composite parts. The novel approach uses a combination of experimental, analytical and numerical procedures whereas standard shell elements are used for the FE calculations. The main innovation is the significant parameter reduction. Only one simulation parameter is necessary to predict the manufactured shape of a complex CFRP structure. For validation purposes, two CFRP box structures with dimensions of 798 mm × 206 mm × 55 mm ( l × w × h ) were manufactured and process-induced distortions are evaluated in detail using a high-precision 3D full-field measurement system. Measurements show that manufacturing distortions are mainly driven by the spring-in effect. However, a global curvature of the part is obtained which is likely due to forced-interaction induced by the aluminum male tool. The predicted process-induced deformations match precisely with the measurement results. Evaluation of the predicted distortions allow a clear distinction between spring-in induced and forced-interaction induced deformations. In consequence, obtained results show that effects due to forced-interaction need to be considered for suchlike structures fabricated on metallic tools when CTE tool is larger than CTE CFRP .

Autoclave processing of reproducible carbon fibre reinforced plastic (CFRP) structures with high dimensional fidelity is a main challenge for today’s composite manufacturing within the aerospace industry. An ex ante geometrical tool compensation as well as an appropriate process control to minimise dimensional variations requires a good understanding of the crucial parameters. In the present paper a wide range of experimental investigations affirm that warpage deformation of symmetric and initially flat laminates is mainly driven by mechanical tool–part interaction. Furthermore, tool surface roughness and interleaved neat resin areas are observed to influence the magnitude of these deformations significantly. For the description of the effective mechanism a new model, accounting for these findings, is proposed.

This paper reports on a comprehensive study on process-induced distortions (PID) of curved CFRP/foam-core sandwich panels. The study’s aim is to validate the prediction quality of two existing analytical models and a novel straightforward simulation technique, which utilizes measured spring-in distortions of representative monolithic samples as input. Sandwich specimens with a radius of approximately 350 mm are manufactured with three different core thicknesses and two different core run-out geometries. The manufactured parts show a significant radius reduction which declines for increasing core thickness which is satisfactorily predicted by both, the analytical models and the simulation. The effect of the run-out shape turned out to be of inferior relevance for the investigated specimen configurations. However, it is found to be essential to use plane-stress assumptions and to capture the stiffness ratio between the skins and the core. Therefore, an extension of the Fernlund model is proposed whose predictions match excellently with the measured distortion of the specimens. Given the simplicity of the simulation approach in combination with the limited number of inputs makes it a tool of great value, particularly early on in the design cycle.

After demolding, plane structures made of fibrous polymer-matrix composites often show a warpage and, owing to spring-in angles, do not reach the designed shape. Considerable effort has been put into the development of methods for simulating the distortions in order to avoid them by countermeasures. Besides the empirical trial-and-error-based procedure, there is a choice between simulation-based and semianalytical approaches. This paper focuses on the latter ones as being fast and sufficiently accurate for an initial design. Spring-in is observed in curved structures. A simple formula relates the amount of spring-in to the difference between their in-plane and transverse properties. Furthermore, it has been shown that an equivalent coefficient of thermal expansion can be determined with the use of L-shaped coupons. With the aid of this coefficient, the spring-in of more complex structures can be calculated with a sufficient accuracy. Experiments reveal a considerable warpage of plain structures, especially of slender plates. This happens in the cases of one-sided molds, obviously depends on the part/tool connectivity, and is caused by the difference in thermal expansion, as well as by the development of cross-linking in the thickness direction. Other parameters of influence may be gradients in the fiber volume fraction or resin-rich layers. A simple formula based on a model of two beams on top of each other was developed. It relates the artificial coefficients of thermal expansion to the curvature of the compound beam. Warpage measurements on simple test specimens allow one to determine these coefficients, which then can be used in detailed FEM analyses of more complex structures in order to anticipate their behavior on demolding.

Rehabilitation is a cornerstone in the treatment of chronic obstructive pulmonary disease. KOALA is a web-based database where information about patients' rehabilitation sessions in hospital or in municipalities can be registered. A retrospective study of the effect of rehabilitation in 63 patients at Frederiksberg Hospital showed results in accordance with earlier studies. The database could be improved by including more co-morbidities and pharmacological treatment. Not all hospitals or municipalities employ KOALA which we would recommend to ensure quality assurance and material for further research.

The aggregation of functionalities offers additional benefits to the customers such as reduced weight, reduced life cycle costs and an increased range of applications. For a compliant aggregation of functionalities according to given requirements clear instructions on how to conduct lightweight design are essential, but often not available today. High performance lightweight structures are made from carbon fiber reinforced plastics increasingly. Due to the specific composite manufacturing process four different levels of function-integration are conceivable. The pre-fabrics or components of the composite can include smart materials with enhanced functionalities. The structure design can better exploit the composite potentials of anisotropic material properties. Passive components integrated into the structure provide additional functionalities as for example de-icing and lighting protection. In adaptive systems active elements significantly improves the ability of the structure to adapt changing environmental conditions. The development of the potentials resulting from the compliant aggregation of functionalities is presented in this chapter.

A straightforward approach to predict spring-in deformations of angled composite parts is presented. Therefore, a proposal by Radford is extended in order to calculate the spring-in contribution due to chemical shrinkage. For this, the volumetric shrinkage of neat thermoset resin, which is in the range of 2–7%, is transferred to equivalent strains on ply level assuming no shrinkage in fiber direction. As the fiber volume fraction (FVF) affects mechanical and chemical properties significantly, the spring-in angle is affected as well. Therefore, the numerical investigation accounts for the spring-in angle and its thermal and chemical contributions depending on the FVF. Classical laminate theory (CLT) is utilized to homogenize layup expansion and shrinkage properties. For validation purposes, model predictions are compared with measurement results gained from one manufactured test specimen. Good agreement between analytical and experimental results is found. Furthermore, the chemical contribution of the total spring-in angle ∆φ turned out to be significantly larger than the thermal contribution.

The manufacturing of composite structures is accompanied by fabrication induced deformations. Those deformations are undesirable and lead to transgression of geometric tolerances in the finished parts. In order to get the part within aspired dimensional tolerances, geometrical compensation of the tool is necessary. This often iterative conducted tooling-rework is commonly time consuming and costly. This paper presents an shell element based. semi-analytical simulation approach focusing on warpage deformations due to tool part interaction, in order to account for manufacturing induced deformations within the tool design process. Deviation measurements on test specimen level serve as inputs for the calculation of equivalent coefficients of thermal expansion according to the proposed analytical model. Thus, ‘warpage properties’ of different prepreg – tool–material combinations are determined. The use and the practicability of the developed approach is demonstrated by means of the calculation of a warpage compensated tool surface.