M. J. L. van Tooren

Analysis and evaluation of bondline thickness effects on failure load in adhesively bonded structures

It is well known that adhesive joints have their optimum strength for thin bondline thicknesses (0.1-0.5 mm). The most common analytical methods used for adhesive joint analysis show an improved strength with increasing bondline thickness. This erroneous trend in prediction is investigated in this article. It is found that the through-the-thickness stress distribution in the adhesive is the main cause for the errors. The stresses, both peel and shear, at the interface between the adhesive and the adherend are found to increase, after an initial decrease in the low bondline thickness range, with increasing bondline thickness while the average stresses decrease. This trend explains the trends found in experiments. Further, as experimental results have shown, a theoretical optimum bondline thickness is found.

Enabling distributed multi-disciplinary design of complex products: a knowledge based engineering approach

In this paper, it is discussed how knowledge based engineering has been exploited to develop a flexible design system, able to integrate a heterogeneous set of distributed discipline-specific design and analysis tools into a modular design framework. This system, called Design and Engineering Engine (DEE), demonstrated its capability to support designers in performing what-if studies and accelerate Multi-disciplinary Design and Optimisation (MDO), through the automation of those lengthy and repetitive activities typically hampering the design process. Design quality and innovation are also supported by enabling the use of high fidelity analysis tools in the early design phase.

Implementation of bending-torsion coupling in the design of a wind-turbine rotor-blade

An investigation is performed on the implementation of bending-torsion coupling of a composite wind turbine rotor blade to provide passive pitch-control. Limited passive torsion deformation is realised with a structural coupling between flapwise bending and elastic twist of a constant speed rotor-blade. The blade and skin laminate configuration are analysed with a FEM program, in which a complete blade with spar webs is modelled. This conventional blade configuration has some disadvantages. Therefore alternative design concepts are reviewed, where the coupling plies are restricted to a load-bearing spar, while a softer skin provides for the aerodynamic shape. From additional analysis, it is found that, while for the two alternative design concepts the stress concentrations at the leading edge joint are bypassed, the bending-torsion coupling response is lower. An experiment was performed to validate the calculation methods. The experimental results show good correlation with theoretical predictions. It is recommended to investigate further the fatigue life properties of a glass/carbon hybrid FRP with off-axis fibre orientations.

Composite adhesive joints under cyclic loading

Abstract With the increasing use of adhesive bonding in structural joints in many applications, the interest in the behaviour of adhesive joints under cyclic loading has increased as well. Much work has already been performed on the analysis of adhesively bonded joints under static loading. Also the damage growth and failure mechanisms of adhesive joints under cyclic loading has been investigated, to a less extent for joints in composite structures. A major difficulty is the large amount of parameters that can be of influence on crack initiation and growth in adhesive joints. This makes it hard to characterise the debond behaviour of a joint. This article is intended to give an overview of studies performed on adhesive composite joints under cyclic loading on and to serve as a starting point for designers who need information on experimental and analytical methods of composite adhesive joints.

Knowledge-based engineering to support aircraft multidisciplinary design and optimization

Abstract This paper discusses structure and functionalities of a knowledge-based engineering (KBE) application, called multimodel generator (MMG), developed to support aircraft multidisciplinary design, analysis, and optimization. Designers can use the MMG as an advanced modelling tool to swiftly generate geometrical models of many and diverse aircraft configurations and variants, by combining and adjusting a limited number of parametric objects, called high-level primitives. Besides capturing the geometric aspects of the design, the MMG also has the capabilities to automate a large part of the lengthy and non-creative pre-processing activities involved in the design verification process. The proposed KBE application has demonstrated to be a valuable solution for some of the critical needs indicated by the multidisciplinary design and optimization community, namely a flexible and robust generative tool to increase the level of automation in aircraft design, including the development of novel configurations; the exploitation of high-fidelity analytical tools already in the early design phase; the management of the design activities across distributed networks of disciplines specialists.AbstractThis paper discusses structure and functionalities of a knowledge-based engineering (KBE) application, called multimodel generator (MMG), developed to support aircraft multidisciplinary design, analysis, and optimization. Designers can use the MMG as an advanced modelling tool to swiftly generate geometrical models of many and diverse aircraft configurations and variants, by combining and adjusting a limited number of parametric objects, called high-level primitives. Besides capturing the geometric aspects of the design, the MMG also has the capabilities to automate a large part of the lengthy and non-creative pre-processing activities involved in the design verification process. The proposed KBE application has demonstrated to be a valuable solution for some of the critical needs indicated by the multidisciplinary design and optimization community, namely a flexible and robust generative tool to increase the level of automation in aircraft design, including the development of novel configurations...

Concurrent Subspace Width Optimization Method for RBF Neural Network Modeling

Radial basis function neural networks (RBFNNs) are widely used in nonlinear function approximation. One of the challenges in RBFNN modeling is determining how to effectively optimize width parameters to improve approximation accuracy. To solve this problem, a width optimization method, concurrent subspace width optimization (CSWO), is proposed based on a decomposition and coordination strategy. This method decomposes the large-scale width optimization problem into several subspace optimization (SSO) problems, each of which has a single optimization variable and smaller training and validation data sets so as to greatly simplify optimization complexity. These SSOs can be solved concurrently, thus computational time can be effectively reduced. With top-level system coordination, the optimization of SSOs can converge to a consistent optimum, which is equivalent to the optimum of the original width optimization problem. The proposed method is tested with four mathematical examples and one practical engineering approximation problem. The results demonstrate the efficiency and robustness of CSWO in optimizing width parameters over the traditional width optimization methods.

Experimental verification of a stress singularity model to predict the effect of bondline thickness on joint strength

A stress singularity model is used to predict joint failures in single-lap joints with varying bondline thickness. The theoretical results are compared with experimental results for verification purposes. Essentially the experimental analysis is split into two parts. The first part determines the Youngs modulus and Poissons ratio of the adhesive selected for this verification study and the second part measures the failure loads versus bondline thickness of the single-lap joint specimens. Based on the experimental data on the adhesive properties, predictions are made of the joint strength (assuming failure is in the adhesive) for varying bondline thickness. It appears that the relation between the joint strength and bondline thickness can be described with a two-parameter Weibull function. The critical stress intensity factor, or bondline toughness, is derived from the test data using an approximation formula for the change in external loading with bondline thickness. The resulting critical stress intensity factor combined with the calculated stress intensity factors gives a good prediction of the joint strength over a practical range of bondline thickness.

A surrogate-based optimization method with RBF neural network enhanced by linear interpolation and hybrid infill strategy

In engineering, it is computationally prohibitive to directly employ costly models in optimization. Therefore, surrogate-based optimization is developed to replace the accurate models with cheap surrogates during optimization for efficiency. The two key issues of surrogate-based optimization are how to improve the surrogate accuracy by making the most of the available training samples, and how to sequentially augment the training set with certain infill strategy so as to gradually improve the surrogate accuracy and guarantee the convergence to the real global optimum of the accurate model. To address these two issues, a radial basis function neural network (RBFNN) based optimization method is proposed in this paper. First, a linear interpolation (LI) based RBFNN modelling method, LI-RBFNN, is developed, which can enhance the RBFNN accuracy by enforcing the gradient match between the surrogate and the trend observed from the training samples. Second, a hybrid infill strategy is proposed, which uses the surrogate prediction error based surrogate lower bound as the optimization objective to locate the promising region and meanwhile employs a linear interpolation-based sequential sampling approach to improve the surrogate accuracy globally. Finally, extensive tests are investigated and the effectiveness and efficiency of the proposed methods are demonstrated.

Quasi-Three-Dimensional Aerodynamic Solver for Multidisciplinary Design Optimization of Lifting Surfaces

This paper presents the development of a quasi-three-dimensional aerodynamic solver, which provides accurate results for wing drag comparable to the higher-fidelity aerodynamic solvers at significantly lower computational costs. The proposed solver calculates the viscous wing drag using the combination of a two-dimensional airfoil analysis tool with a vortex lattice code. Validation results show that the results of the quasi-three-dimensional solver are in good agreement with higher-fidelity computational fluid dynamics solvers. The quasi-three-dimensional solver is used for a wing shape multidisciplinary design optimization. A multidisciplinary design optimization problem is formulated to design the wing shape of a typical passenger aircraft. The aircraft maximum takeoff weight is considered as the objective function. Two optimization algorithms, a local and a global optimum finder, are implemented in the multidisciplinary design optimization system. The optimization results indicate that the global opti...

A stress singularity approach to failure initiation in a bonded joint with varying bondline thickness

The stress singularity at the theoretical point of maximum stress in an uncracked single lap joint is analysed by a finite element method. By treating the interface corner of a bonded joint (between adherend and adhesive) as a perfectly bonded wedge and using a fracture mechanics method, considerable advantages over other continuum mechanics approaches for investigating the bondline thickness effect on joint strength are shown. This study has essentially two aims: (i) determination of the strength of the singularity by finite element analysis and comparison with the analytical prediction of Bogy for varying bondline thickness; and (ii) determination of stress intensity factors for varying bondline thickness. Good agreement is shown between the numerically-calculated strength of the singularity with the analytical value obtained from Bogy. The calculated stress intensity, after an initial decrease in the low bondline thickness range, is found to increase with increasing bondline thickness. This agrees well with the trends predicted by experiments.