A Numerical Approach for Developing a Bearing-Bypass Design Criterion for Sizing Bolted Joints

A decision support system for assessing landfill performance

Efficient progressive damage modeling of hybrid composite/titanium bolted joints

BOJCAS: bolted joints in composite aircraft structures

The finite element method (FEM) is established as one of the most popular and powerful tools in analysis and design of engineering systems. However, the method can only be used at an advanced (or detail) design stage when a designer has developed sufficient confidence in the design scheme. In the early (or conceptual/ preliminary) design phase, the method can not be used directly due to the existence of uncertainties of various types. In this work, a procedure is proposed for the FEM to handle engineering systems in the presence of hybrid uncertainties that are characterized by randomness (or stochastic uncertainty) and fuzziness (or design imprecision). The proposed scheme utilizes the techniques of stochastic and fuzzy FEMs in a unified manner to investigate the effects of both input random and fuzzy uncertainties on the output system response. Interpretations of the generated solution space and guidelines in selection of an appropriate solution, according to specific design requirements, are discussed. Two numerical examples are presented to illustrate the computational aspects of the proposed scheme. The current procedure is expected to enhance the understanding of designers regarding the effects of uncertainties in an evolutionary design process, especially in the conceptual or preliminary design phase.

In the preliminary design phase of aircraft design, estimating the production cost accurately is a challenging task. At this stage, many design parameters that affect the overall cost are still undefined. This paper establishes cost-estimation models for civil, commercial aircraft using a parametric cost analysis (PCA) approach. Aircraft are characterised based on their size, ranging from a wide body to executive jets, into four categories. Key design parameters, such as maximum take-off weight, number of passengers, range, wing area, span, fuselage length, to name a few, are likely to be available in the preliminary design stage and significantly impact the aircraft design. These variables either directly or indirectly affect the overall production cost or performance. The PCA approach includes both correlation and multiple linear regression techniques. The empirical models thus developed were able to predict the aircraft cost with an error of less than ±4% for all aircraft categories considered. Two aircraft in each defined category were not part of the PCA models and were used to verify the models. The proposed models provide the ability to estimate the aircraft cost quickly in the early stages of the preliminary design phase and provide the possibility of performing parametric studies involving the key variables to determine the cost sensitivity to the main design parameters.

The use of composite materials is widely spread across the Aerospace sector. Scarf and step lap joints are amongst the most commonly used methods for flush joint repairs; they restore original stiffness and nearly original strength. Prior investigations conducted by the authors have shown that bonded and hybrid step lap joints have superior static strength capabilities than bolted joints. Hybrid step lap joints have shown the highest fatigue resistance than its bolted and bonded counterparts. This investigation aims at optimising the previous step lap joint design containing five steps with a 90 mm long overlap length in order to improve joint efficiency. Four new step lap joint configurations are considered based on a parametric study conducted using Abaqus; two of which contain seven steps and a 130 mm long overlap (bonded and hybrid) whilst the other two contain six steps and a 105 mm long overlap (bonded and hybrid) with a tapered outer step region. Experimental tests right through to numerical modelling using three-dimensional (3D) finite element (FE) models have been investigated. Adhesive non-linear material properties, fastener contacts and friction forces were all included in the 3D FE models. The Multicontinuum Theory (MCT) is used to simulate the progressive failure process and determine the stress states in the four configurations. Overall the FE models are able to accurately predict the bonded and hybrid joint strengths and highlights the importance of not only optimising the number of steps and their lengths but also the individual step heights. This is a parameter which has often been overlooked by fellow researchers. Experimental results showed that all four step lap joint configurations have significant improvement under static and fatigue load cases; the greatest improvement is seen in the two bonded step lap joint configurations. Overall the hybrid joint configuration consistently outperformed the bonded joint configurations. The presence of fasteners supress crack propagation, minimise peak peeling stresses at the ends of the overlap and increase the durability of the joint. This enables early crack detection which can assist composite joint repair certification.

Mechanical joints such as bolted or riveted joints are widely used in mechanical components. The reliable determination of the stress intensity factors for cracks in bolted joints is needed to evaluate the safety and fatigue life of them. The weight function method is an efficient technique to calculate the stress intensity factors for various loading conditions because only the stress analysis of an uncracked model is required. In this paper the mixed-mode stress intensity factors for cracks in bolted joints are obtained by weight function method, in which the coefficients of weight function are determined by finite element analyses for reference loadings. Critical inclined angle that mode I stress intensity factor becomes maximum is determined and the effects of crack length and the magnitude of clearance on critical inclined angle are investigated.

The circular economy, emphasizing resource efficiency and sustainability, highlights remanufacturing as a key aspect. However, ensuring the quality and reliability of remanufactured products is challenging due to uncertainties from prior product usage, especially for bolted joints affected by corrosion. Current methodologies, including analytical, numerical, and empirical models, often fail to meet accuracy and computation time criteria. Addressing this research gap, this paper presents a data-driven framework that couples empirical methods with artificial intelligence techniques to develop a predictive functional model. This model aims to accurately predict key variables such as load-bearing capacity and thread friction coefficient for the remanufactured bolted joints. The proposed framework comprises three main components: development of a test rig and experimental analysis, identification of key variables, and development of a predictive model. The model is based on empirical data from various Design of Experiments (DoE) tests and is refined using machine learning techniques. By embracing a data-driven approach, this research seeks to fill the gaps left by existing modeling techniques, enhancing the reliability of modeling techniques for corroded bolted joints. This framework contributes to the circular economy, product quality, reliability, and sustainability and can eventually be applied beyond bolted joints, addressing uncertainty across various products.

A proposal of a unique formula for computing compliance in bolted joints

This paper deals with knowledge integration during product design. An integrated design approach is presented based on two phases: The initial design and the detailed design phase. Those two phases must be as concurrent as possible. Nevertheless, minimal structural definition of the product is necessary prior to manufacturing process planning as part of the detailed design phase. During the initial design phase, the structural technology is chosen according to the product main functions. This phase aims at defining minimal functional data that are used as a starting point for other knowledge integration in the detailed design phase. During the detailed design, other people that are actively involved in the product development process evaluate the product with their own point of view and their own tools. This paper presents the use and the limits of two features-based tools for process planning knowledge integration: a What-if system and a CAPP system. Both tools make an analysis of the product. As a result of these analyses, designers add new data to the product definition. Thus, the design solution is progressively defined. A Cooperative Design Modeller supports this knowledge integration and gathers the data provided by the What-if and the CAPP systems.

A parametric study is performed to eliminate some of the thermal resistances of the complicated network obtained for bolted joints. The analytical models for material, contact and radiation resistances, developed by the authors and available in the literature, are used. Thermal resistances and resistance paths are compared among themselves. The resistances found irrelevant are excluded from the circuit and a simplified thermal circuit is obtained. A sensitivity analysis of the parameters used in the formulation of the overall thermal resistance of the simplified network is performed. This study points out the important parameters, which should be precisely determined. The comparison of the present model with the experimental data and with the literature correlations shows the accuracy of the simplified thermal circuit. Large variations of the parameters used to calculate the contact resistance do not modify significantly the overall thermal resistance of the bolted joint. Therefore, the precise determination of the contact conductance may not be relevant for many bolted joint configurations used in practical applications.

The so-called Green Engine architectures are deeply investigated by the scientific community with the aim of reducing fuel consumption and noise emissions by 50%, and pollutants by 80%, environmental targets established by the Advisory Council for Aeronautical Research in Europe to be achieved by 2020. Low pressure turbine improvements will be important to increase the efficiency of the two most innovative propulsive architectures, the Geared Turbofan and the Open Rotor Engine. The low pressure turbine is released from the fan and can rotate at higher speed values, implying a reduction in fuel consumption. Due to a higher rotational speed, low pressure turbine disks design needs careful considerations due to their higher stress level and reduced burst limit. This paper presents a multi-objective hybrid optimization methodology designed to study high speed low pressure turbine disks. The presented study falls within the preliminary design phase, thus a code based on finite differences was used to perform an optimization study of high speed low pressure turbine disks. The objective functions of the constrained multi-objective optimization were the minimization of the disks weight and the maximization of the burst speed, and a hybrid approach was pursued to better investigate the design space and find the optimum. Then a surrogate-model-based hybrid optimization was conducted to reduce computational time while ensuring the analysis accuracy. A trade-off of most common approximation strategies was conducted. Distributed computing was used involving three national research centers, and parallel computing was adopted to spread the calculation tasks on local workstations. Numeric and Finite-Element-Methodology-based validations followed. This study provides an innovative approach to design such critical components by reducing disks weight by 15% and computational time by 30% if compared to traditional design methodologies. Furthermore, a good match between optimal solutions was found, thus justifying a surrogate-model-based-approach that led to further gains in computational time.

Proper orthogonal decomposition of the dynamics in bolted joints

The design process of new air- and rotorcraft is commonly separated into three different consecutive phases. In the conceptual design phase, the viability of different designs is investigated with respect to customer requirements and/or the market situation. It usually ends with the identification of a basic aircraft lay-out. In the subsequent preliminary design stage the various disciplines are introduced, thus redefining the design process as a multidisciplinary optimization (MDO) task. The objective of this design stage is to enhance the initial aircraft configuration by establishing an advanced design comprising a loft provided with primary structure. This updated aircraft configuration represents a global optimum solution for the specified requirements which will then be optimized on a local level in the concluding detailed design phase with particular regard to manufacturing aspects. The investigations in the preliminary design phase comprise the generation of numerous similar but still different analytical and finite element (FE) models. Even though computational power is constantly increasing the model generation process is still a time-consuming task. Moreover, it is also a potential source of errors which — in the worst case — may lead to time- and cost-intensive redesign activities during the detailed design. As the preliminary design stage, therefore, is of particular importance during the overall design process the model generation process benefits from parametric models and automated process chains. The presented paper overviews the tools used for the automated generation of FE models developed and used at the Institute of Structures and Design (BT) of the German Aerospace Center (DLR) for the subsequent use in numerical simulations. Furthermore, basic requirements for the effective use of parametrization and automation like a common data format and infrastructure will be introduced. Exemplary models and applications will be presented to illustrate the positive impact on efficiency in aircraft design. Concluding, future development steps and possible applications will be discussed.

Seismic performance of bolted double-web T-stub connections with T-shaped steel column