PostprintThis is the accepted version of a paper published in Structural and multidisciplinary optimization (Print). This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Kaufmann, M., Zenkert, D., Wennhage, P. (2010) Integrated cost/weight optimization of aircraft structures. July 2007A methodology for a combined cost/weight optimization of aircraft components is proposed. The objective function is formed by a simplified form of direct operating cost, i.e. by a weighted sum of the manufacturing cost and the component weight. Hence, the structural engineer can perform the evaluation of a design solution based on economical values rather than pure cost or weight targets. The parameter that governs the balance between manufacturing cost and weight is called weight penalty and incorporates the effect of fuel burn, environmental impact or contractual penalties due to overweight. Unlike previous work, the analytical cost and structural models are replaced by commercially available software packages. They allow for a more realistic model of the manufacturing cost, and for arbitrary constraints in the structural analysis. By means of parametric studies it is shown that the design solution strongly depends on the magnitude of the weight penalty.

decade, substantial efforts were devoted to the research and development of the nextgeneration composites. This new class of materials should not only possess higher strength-to-weight ratio than metals but also tailored with integrated intelligence, which is desirable as infrastructures for next generation of "internet of things." Carbon nanomaterials, such as carbon nanotubes and carbon nanofibers, have received dominant attention for the creation of intelligent composites. [3][4][5][6] They were dispersed in a polymer matrix to form conductive percolating networks as distributed sensors in situ to evaluate the strain, stress, damage, and temperature for self-sensing and on-line structural health monitoring applications. [3][4][5][6] However, these composites are restricted to (piezo) resistive effect based sensing capabilities from the included nanomaterials. Nextgeneration composites, however, should not only encompass sensing capabilities but also be equipped with other functionalities such as lighting, computation, and communication elements, as illustrated in Figure 1. One straightforward solution to achieve this goal is to integrate electronic circuits with off-the-shelf components in the composites. However, these functional composites usually have complex, 3D shapes, but conventional electronic circuits are rigid and planar. The shape mismatch between 3D composites and planar, rigid electronic circuits causes difficulties in integrating electronic circuit-based intelligences.Recent advancement of flexible and stretchable circuits has paved the way for integration of electronics in unusual shapes and forms. Through materials and structure innovation, [7] the circuits become stretchable, deformable, and conformable to curvilinear surfaces, [8][9][10] enabling a spectrum of applications such as stretchable sensors and actuators, [11][12][13][14] transparent conductors, [15,16] lighting, [17][18][19] and energy devices. [20][21][22] Various types of stretchable nanomaterials, such as carbon nanomaterials [23][24][25] and metal nanowires [26][27][28] have been synthesized and integrated to elastomeric polymer matrix for stretchable circuits. Despite their superior mechanical properties and potential to achieve transparent stretchable circuits, so far it has been a struggle to deliver high enough conductivities compared to structure engineered stretchable circuits.Fiber-reinforced polymer composites with integrated intelligence, such as sensors, actuators, and communication capabilities, are desirable as infrastructures for the next generation of "internet of things." However, the shape mismatch between the 3D composites and a planar electronic circuit causes difficulties in integrating electronic circuit-based intelligences. Here, an easily scalable approach, by incorporating a large-area stretchable circuit with thermoforming technology, to fabricate 3D multifunctional composites is reported. The stretchable circuit is first fabricated on a rigid and planar carrier board, then transferred and sandwiched bet...

Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of costeffective design strategies in which cost, weight and the desired laminate quality are taken into account. This paper proposes an optimization framework for composite aircraft structures that minimizes the direct operating cost on a part level. In addition to previous models, a nondestructive testing model is implemented that calculates design allowables of a laminate based on ultrasonic scan parameters. In a case study, the effect of the laminate quality on the direct operating cost is discussed. It is investigated how the permissible flaw size and therefore the scan pitch of a composite laminate can influence the optimal solution in terms of cost and weight; thus, the manufacturing cost, the non-destructive testing cost and the weight of a component can be balanced by optimizing the laminate quality in an early design phase.

The measurement of the internal deformations occurring in real-life composite components is a very challenging task, especially for those components that are rather difficult to access. Optical fiber sensors can overcome such a problem, since they can be embedded in the composite materials and serve as in situ sensors. In this article, embedded optical fiber Bragg grating (FBG) sensors are used to analyze the vibration characteristics of two real-life composite components. The first component is a carbon fiber-reinforced polymer automotive control arm; the second is a glass fiber-reinforced polymer aeronautic hinge arm. The modal parameters of both components were estimated by processing the FBG signals with two interrogation techniques: the maximum detection and fast phase correlation algorithms were employed for the demodulation of the FBG signals; the Peak-Picking and PolyMax techniques were instead used for the parameter estimation. To validate the FBG outcomes, reference measurements were performed by means of a laser Doppler vibrometer. The analysis of the results showed that the FBG sensing capabilities were enhanced when the recently-introduced fast phase correlation algorithm was combined with the state-of-the-art PolyMax estimator curve fitting method. In this case, the FBGs provided the most accurate results, i.e., it was possible to fully characterize the vibration behavior of both composite components. When using more traditional interrogation algorithms (maximum detection) and modal parameter estimation techniques (Peak-Picking), some of the modes were not successfully identified.

This is the published version of a paper published in Plastics, rubber and composites.Citation for the original published paper (version of record):Kaufmann, M., Czumanski, T., Zenkert, D. (2009) Manufacturing process adaptation for integrated cost/weight optimisation of aircraft structures. Plastics March 2009A methodology is developed that enables cost-efficient design of composite aircraft structures. In earlier work, a cost/weight optimisation framework was presented. This framework is here enhanced by a module that minimises the manufacturing cost in each iteration by adaptation of manufacturing parameters. The proposed framework is modular and applicable to a variety of parts and geometries. Commercially available software is used in all steps of the optimisation. The framework extension is added to an existing cost/weight optimisation implementation and tested on an airliner centre wing box rear spar. Three optimisation runs are performed, and a low cost, an intermediate and a low weight design solution are found. The difference between the two extreme solutions is 4.4% in manufacturing cost and 9.7% in weight. Based on these optimisation trials, the effect of the introduced parameter adaptation module is analysed.