Comparative Evaluation of Single-lap Joints Bonded with Different Adhesives by Cohesive Zone Modelling

Structures built from several components require some means of joining. In this context, bonding with adhesives has several advantagescompared to traditional joining methods, e.g. reduction of stress concentrations, reduced weight penalty and easy manufacturing. Adhesives can be strong and brittle (e.g., Araldite® AV138) or less strong and ductile (e.g., Araldite® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g., Sikaforce® 7888). In this work, the performance of the three above mentioned adhesives was tested in single-lap joints with varying values of overlap length (LO). The experimental work carried out is accompanied by a detailed numerical analysis by Finite Elements, based on Cohesive Zone Models (CZM). This procedure enabled detailing the performance of this predictive technique applied to bonded joints. Moreover, it was possible to evaluate which family of adhesives is more suited for each joint geometry. CZM revealed to be highly accurate, except for largely ductile adhesives, although this could be circumvented with a different cohesive law.info:eu-repo/semantics/publishedVersio

Design of a modular solution for an autonomous vehicle for cargo transport and handling

Due to the globalization of markets, the industrial competitiveness has increased significantly in the recent years. Within this scope, the transportation of products inside industrial parks acquires special relevancy. One of the solutions is the use of autonomous guided vehicles. This work presents the design of a modular autonomous vehicle, capable of carrying heavy loads, which will improve the performance of industrial parks. This is a compact vehicle with low associated costs and good transport speeds. A drive system was designed, which will be capable of transporting the proposed loads. This design was carried out using simulations of the transport with loads, either in plane ground or in an industrial park. A structural analysis to the vehicle was also undertaken by the Finite Element Method, showing the points of the structure that require reinforcement for the different load cases. Finally, the required corrections were implemented, giving to the structure the ability to carry the desired loads. The end result was an autonomous vehicle with capacity to safely transport the imposed loads in the most efficient possible manner.info:eu-repo/semantics/publishedVersio

Numerical Evaluation of the Direct Method for Cohesive Law Extraction in Shear by the End-Notched Flexure Test

With adhesive bonding, design can be oriented towards lighter structures, not only regarding the direct weight saving advantages of the joint over fastened or welded joints, but also because of flexibility to joint different materials. Cohesive Zone Models (CZM) are a powerful design tool, although the CZM laws of the adhesive bond in tension and shear are required as input in the models. This work evaluated the shear fracture toughness and CZM laws of bonded joints. The End-Notched Flexure (ENF) test geometry was used with this purpose. The experimental work consisted on the shear fracture characterization of the bond by conventional and the J-integral techniques. Additionally, by the J-integral technique, the precise shape of the cohesive law was defined. Numerical Finite Element (FE) simulations were carried out in Abaqus® to assess the accuracy of the obtained CZM laws in predicting the experimental behaviour of the ENF tests, with positive results. As output of this work, fracture data is provided in shear for the selected adhesive, allowing the subsequent strength prediction of bonded joints.info:eu-repo/semantics/publishedVersio

Comparative evaluation of adhesively-bonded single-lap and stepped-lap joints

Several adhesive joint configurations are available, namely butt joints, single-lap joints (SLJ), double-lap joints and scarf joints. Stepped-lap joints, which are not so studied, consist of a finite number of steps in the bonded area, possessing stress concentrations at all step edges instead of only at the bonded length edges. Stepped-lap joints increase the maximum load (Pm) over SLJ. The present study experimentally and numerically evaluates the static tensile strength of SLJ and stepped-lap joints bonded with the moderately ductile adhesive Araldite® 2015, considering varying values of overlap length (LO). A Finite Element Method (FEM) analysis was carried out to compare through-thickness normal (σy) and shear (τxy) stresses in the bondline between joint configurations. Additionally, a Cohesive Zone Modelling (CZM) analysis was considered to study the failure modes and to evaluate the CZM technique’s accuracy. Between SLJ and stepped-lap joints, the improved stress distributions of the stepped-lap joints resulted in higher joint performance, especially for higher LO. The CZM model revealed to be accurate in predicting Pm.info:eu-repo/semantics/publishedVersio

Design Concepts for Peel-Dominant Adhesive Joints in Aeronautic Applications

The adhesive bonding technique is employed from the aeronautical/aerospace industry to current house products. To comply with the requirements of distinct applications, different joint configurations are available to the designer. While single-lap joints (SLJ) are the most common in application and research, double-lap joints, scarf joints and T-joints find specific applications. T-joints are seldom studied in the literature, but these are used, for instance, in aircraft to bond the stiffener beams to the skin, or in the cars between the B-pillar and the rocker. Due to the high stress concentrations, T-joints often fail under average stresses much lower than the adhesive strengths, giving rise to the necessity for proper design and strength improvement methodologies. This work initially aims to validate the cohesive zone modelling (CZM) technique with experiments, and then use it to numerically evaluate and optimize the performance of T-joints subjected to peel loads. CZM is nowadays regarded as the most powerful strength prediction tool for adhesive joints, and can be a valuable tool to improve T-joints. Different features are addressed for a complete analysis: adhesive type, geometrical parameters, dual-adhesive technique for strength improvement, and composite joints. The evaluated geometrical parameters are the base adherend thickness (a), T-part thickness (t), overlap or bonding length (l) and curvature radius (r). As a result of this work, the model was successfully validated, and clear design guidelines were provided to define the ideal geometric and material (adhesive) conditions for best performance

Application of a Design for Excellence Methodology for a Wireless Charger Housing in Underwater Environments

A major effort is put into the production of green energy as a countermeasure to climatic changes and sustainability. Thus, the energy industry is currently betting on offshore wind energy, using wind turbines with fixed and floating platforms. This technology can benefit greatly from interventive autonomous underwater vehicles (AUVs) to assist in the maintenance and control of underwater structures. A wireless charger system can extend the time the AUV remains underwater, by allowing it to charge its batteries through a docking station. The present work details the development process of a housing component for a wireless charging system to be implemented in an AUV, addressed as wireless charger housing (WCH), from the concept stage to the final physical verification and operation stage. The wireless charger system prepared in this research aims to improve the longevity of the vehicle mission, without having to return to the surface, by enabling battery charging at a docking station. This product was designed following a design for excellence (DfX) and modular design philosophy, implementing visual scorecards to measure the success of certain design aspects. For an adequate choice of materials, the Ashby method was implemented. The structural performance of the prototypes was validated via a linear static finite element analysis (FEA). These prototypes were further physically verified in a hyperbaric chamber. Results showed that the application of FEA, together with well-defined design goals, enable the WCH optimisation while ensuring up to 75% power efficiency. This methodology produced a system capable of transmitting energy for underwater robotic applications.This work is funded by the European Commission under the European Union’s Horizon 2020—The EU Framework Programme for Research and Innovation 2014–2020, under grant agreement No. 871571 (ATLANTIS).info:eu-repo/semantics/publishedVersio

Fracture envelope estimation of a structural adhesive by dedicated fracture tests

Cohesive zone modelling (CZM) is widespread for the strength analysis of bonded joints. The fracture toughness (GC) is required to use CZM. A scarcely studied mixed-mode test is the Asymmetric Tapered Double-Cantilever Beam (ATDCB), which merges a Tapered Double-Cantilever Beam (TDCB) adherend with a Double-Cantilever Beam (DCB) adherend. This work addresses the ATDCB test to estimate the fracture envelope of a structural adhesive. TDCB and End-Notched Flexure (ENF) tests were also performed to acquire the tensile (GIC) and shear fracture toughness (GIIC), respectively. Numerically, mixed-mode CZM laws were constructed based on the obtained data, and the results were compared with experiments, to validate the CZM laws and the mixed mode propagation criterion. As a result, the best damage propagation criterion for mixed mode was estimated and validated.info:eu-repo/semantics/publishedVersio

Solving Quality Problems in Tyre Production Preparation Process: A Practical Approach

This work was carried out at Continental tyre factory in Portugal, regarding the APEX machines production process, with the main goal of improving of their performance and product quality rate. Main possible causes of defect generation were identified and proposals to enhance the functioning of the bead APEX production process were also carried out. By applying Six Sigma, variables that influence the quality of the production were identified. DMAIC cycle (Define, Measure, Analyse, Improve and Control) was applied in the process analysis, enabling a structured analysis and the identification of different causes that negatively affect the process studied and consequently allowed the identification of opportunities for improvement. With the help of the DMAIC method, a series of experiments were developed in order to achieve improvements in product quality rate and process control and stabilization.info:eu-repo/semantics/publishedVersio

Geometrical parameter study of adhesively-bonded T-joints by cohesive models

A wide variety of adhesive joints architectures is available, offering several options to the designers, although the most common are single-lap joints (SLJ), double-lap joints, and scarf joints. Additional designs, less used and studied are the stepped-lap, T-joints and tubular joints. T-joints find application in different types of industry, such as aircraft to bond stiffeners to skin and in the cars between the B-pillar and the rocker. This work numerically evaluates the performance of the structural adhesive Araldite® 2015 in an aluminum T-joint, after validation with experimental results. A cohesive zone modelling (CZM) numerical study is carried out to capture the behavior of different T-joints geometrical configurations when subjected to peel loads. The work includes a parametric study, considering maximum load (Pm) and dissipated energy at failure (U) prediction, considering four geometrical parameters: flat adherend thickness (a), T-element thickness (t), overlap length (l) and T-element radius (r). A significant effect on Pm was found for the tested parameters, and the CZM method revealed to be a precious method for studying T joints with precision and accuracy.info:eu-repo/semantics/publishedVersio

Comparison of different test configurations for the shear fracture toughness evaluation of a ductile adhesive

Cohesive zone modelling (CZM) is widely used for predicting the strength of adhesive joints. The key variable for crack path modelling is the critical strain energy release rate (GC), which can be separated into the tensile (GIC) and shear (GIIC) components. In shear, the End Notched Flexure (ENF) test is widespread. However, other test methods exist and could be a viable replacement. This work aims to make a numerical evaluation between the ENF and Four-Point End Notched Flexure (4ENF) tests to determine GIIC of a ductile adhesive (SikaForce® 7752) and to provide shear CZM laws for further application in design. An inverse technique was used to obtain the shear CZM laws of the adhesive. It was concluded that the GIIC values obtained by the ENF and 4ENF tests are in good agreement. The numerical analysis led to unique shear CZM laws for both tests, with similar results.info:eu-repo/semantics/publishedVersio