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- Adhesively-bonded repair proposal for wood members damaged by horizontal shear using carbon-epoxy patchesPublication . Campilho, Raul; Moura, M. F. S. F. de; Ramantani, Dimitra A.; Morais, J. J. L.; Barreto, A. M. J. P.; Domingues, J. J. M. S.In this work, a repair technique with adhesively bonded carbon-epoxy patches is proposed for wood members damaged by horizontal shear and under bending loads. This damage is characterized by horizontal crack growth near the neutral plane of the wood beam, normally originating from checks and shakes. The repair consists of adhesively bonded carbon-epoxy patches on the vertical side faces of the beam at the cracked region to block sliding between the beam arms. An experimental and numerical parametric analysis was performed on the patch length. The numerical analysis used the finite element method (FEM) and cohesive zone models (CZMs), with an inverse modelling technique for the characterization of the adhesive layer. Trapezoidal cohesive laws in each pure mode were used to account for the ductility of the adhesive used. To fully reproduce the tests, horizontal damage propagation within the wood beam was also simulated. A good correlation with the experiments was found. Regarding the effectiveness of the repair, for the conditions selected for this work, a full strength recovery was achieved for the bigger value of patch length tested.
- Evaluation of T-joints in aluminium structures under different geometriesPublication . Moreira, F.J.P.; Campilho, R.D.S.G.; Cardoso, M.G.; Silva, Francisco J. G.The adhesive bonding technique is nowadays very popular in industrial applications, and is gradually replacing other more traditional bonding methods (fastened, welded and riveted joints) due to some advantages. However, its application supposes accurate methods for strength prediction. As a result, the techniques to predict the strength of adhesive joints has highly evolved. The eXtended Finite Element Method (XFEM) is a recent innovation implemented over the (Finite Element Method) FEM that enables crack growth to be modelled. However, its application to adhesive joints is still scarce. This work consists of an experimental and XFEM analysis of aluminium alloy T-joints, adhesively-bonded with three adhesive types. A parametric study is undertaken regarding the curved adherends’ thickness (tP2), with values between 1 and 4 mm. The adhesives Araldite® AV138 (strong but brittle), Araldite® 2015 (less strong but moderately ductile) and the Sikaforce® 7752 (with the smallest strength but highly ductile) were tested. A comparative analysis between the different joints conditions was undertaken by plotting peel (σу) and shear (τxy) stresses. The XFEM predictive capabilities were tested with different damage initiation criteria. It was found that, provided that the modelling conditions are properly set, accurate numerical results can be found.
- Numerical analysis of the dynamic behaviour of adhesive joints: A reviewPublication . Ramalho, L.D.C.; Sánchez-Arce, Isidro J.; Gonçalves, Diogo C.; Belinha, Jorge; Campilho, R.D.S.G.Adhesive joints are being increasingly used in various industries, including the automotive or the wind turbines industries. Such increasing interest is a direct result of its high structural efficiency and also the product of its related scientific research. Therefore, the state-of-the-art on adhesive joints is significantly expanding. The current work aims to discuss the most recent works dedicated to the numerical analysis of the dynamic behaviour of adhesive joints. Dynamic behaviour was divided into three separate fields: fatigue, variable strain rate and impact, and modal analysis. It was found that Cohesive Zone Models are a popular approach to study fatigue, variable strain rates and impact. Additionally, the available literature focused on fatigue and impact is more extensive than the one focused on modal analysis. Overall, it was found that the available research on the numerical analysis of the dynamic behaviour of adhesive joints is increasing at a solid rate, and many geometrical and material variations have been tested numerically. With this review designers and researchers of adhesive joints should be able to choose the most suitable numerical technique for their specific dynamic analysis.
- Improving the Efficiency of the Bowden Cable Terminal Injection Process for the Automotive IndustryPublication . Pereira, José L. T. A.; Campilho, Raul; Silva, Francisco J. G.; Sánchez-Arce, Isidro J.; Prakash, Chander; Buddhi, DharamControl cables transfer force between two separate locations by a flexible mean, and hence, they are important in the automotive industry and many others; their terminals interact with both moving and moved mechanisms, so they must be strong. Cable terminals are commonly made of ZAMAK and are created by injection molding. However, such a production method requires leaving extra material to allow the correct molding, also known as sprues, which are removed later in the process. In this case, the sprues were separating from the terminals in an uncontrolled way. In this work, the cause of sprues separating prematurely from the terminals in a production line is addressed. The whole process was analyzed, and each possible solution was evaluated using process improvement techniques and the Finite Element Method, leading to the best solutions. Molds, mold structures, and auxiliary equipment were improved, resulting in a minimally invasive intervention and remaining compatible with other equipment. Cost analyses were done, indicating an investment return in less than a year. The modification led to a reduction of 62.6% in the sprue mass, while porosity was reduced by 10.2% and 55.9%, corresponding to two terminal models. In conclusion, the interventions fulfilled the requirements and improved the operation of the line.
- Numerical Evaluation of the Direct Method for Cohesive Law Extraction in Shear by the End-Notched Flexure TestPublication . Fernandes, R.L.; Campilho, R.D.S.G.; Leitão, A.C.C.; Azevedo, J.C.S.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.
- How to Become a Manufacturing Cell Fully-Automated Without Robots: Case-Study in the Automotive Components IndustryPublication . Silva, F.J.G.; Pinto, Gustavo Filipe; Baptista, Andresa; Campilho, R.D.S.G.; Araújo, WProductivity is a key factor for companies manufacturing parts and sets to the automotive industry. Automation plays an important role in this matter, allowing development of entire manufacturing cells without the direct need of workers. Even in countries where the labour cost is relatively low, it becomes necessary to improve the level of automation applied to manufacture cells and reduce the dependence of the human labour unpredictability, also increasing the quality and reducing the costs. This case study was developed based on an industrial request in order to improve a semi-automatic cell devoted to seat suspension mat manufacturing. The original cell allows several automatic operations but it needs two workers for two specific operations not considered in the initial design. Thus, new concepts of wire feeding and manipulation were developed in order to allow a better material flow throughout the cell. The new cell was designed and built with success, allowing obtain a fully-automated system, which leads to a better productivity and reliability of the manufacturing process.
- Fracture propagation based on meshless method and energy release rate criterion extended to the Double Cantilever Beam adhesive joint testPublication . Gonçalves, D.C.; Sánchez-Arce, I.J.; Ramalho, L.D.C.; Campilho, R.D.S.G.; Belinha, JorgeIn this work, a numerical methodology based on a meshless technique is proposed to predict the fracture propagation in Double Cantilever Beam (DCB) adhesive joints. The Radial Point Interpolation Method (RPIM) is used to approximate the field variable at each crack increment step. The meshless method permits a flexible discretization of the problem domain in a set of unstructured field nodes and eases the implementation of the geometric crack propagation algorithm. Regarding the fracture propagation algorithm, a recent adaptative remeshing technique is used combined with the RPIM. The crack tip is explicitly propagated by locally remeshing the field nodes and triangular integration cells in the crack tip vicinity. To predict the crack initiation, a fracture mechanics criterion based on the energy release rate in DCB is implemented. The proposed numerical methodology is validated with experimental data.
- Substrate geometry effect on the strength of repaired plates: Combined XFEM and CZM approachPublication . Djebbar, S. Ch.; Madani, K.; El Ajrami, M.; Houari, A.; Kaddouri, N.; Mokhtari, M.; Feaugas, X.; Campilho, R.D.S.G.Aluminum alloys are commonly used in aeronautical applications because of their specific strength and improved corrosion resistance. These structures, during their service, are exposed to various loading cycles, eventually leading to failure at the loci of geometric discontinuities. Repairing by metal or composite patch bonding is widespread to extend the structures’ life by limiting stress concentrations and delaying crack initiation. This work consists of a numerical study, validated by experimental test data, to assess the effect of a central circular notch in an aluminum plate, either reinforced or not by an adhesively bonded composite patch, on the global tensile response of the structure. The constitutive law of the aluminum and adhesive is assumed nonlinear and follows Von Mises equivalent stress flow theory with a hardening variable in incremental form. Damage initiation in the aluminum alloy is modeled by the XFEM (eXtended Finite Element Method), using the maximum principal stress criterion (MAXPS) for damage initiation prediction. Damage evolution is based on the energy approach. The adhesive layer was modeled by CZM (Cohesive Zone Model). A good agreement was found between the experimental results of the tensile curves of the repaired and unrepaired plates with those resulting from numerical modeling. Once the numerical model was validated, several parameters werenumerically studied, namely the shape of the composite patch, the size of the notch, the nature of the adhesive and repair mode by single and double patch, to reduce maximum stress of the damaged area and provide maximum repair efficiency.
- Feasibility Analysis of Machining Cobalt-Chromium Alloy (Stellite-6) Using TiN Coated Binary InsertsPublication . Shah, Saurabh; Joshi, Anand; Chauhan, Kamlesh; Oza, Ankit; Prakash, Chander; Campilho, Raul; Kumar, SandeepThe objective of the study was to check the feasibility of machining Stellite 6, a cobalt–chromium superalloy, using TiN-coated carbide inserts in an end milling operation. The inserts were coated using the magnetron sputtering process. The sputtering power and gas flow rate were considered as the variables during the coating process. The performance of the coated binary carbide insert was checked during the end milling of Stellite 6 (~45 HRC) through an experiment with a Taguchi design. Experimental runs based on an orthogonal array were executed for each insert type to check the feasibility of machining this cobalt-based alloy. Adequate precision and the optimum parametric conditions were determined and are reported in this study. Analysis of variance (ANOVA) with a two-factor interaction model was also undertaken to forecast the key elements influencing surface roughness. Based on the ANOVA model, the depth of the cut, combined with the insert type, was the factor that had the greatest influence on surface roughness, followed by the cutting feed, whereas the cutting velocity had the least significance based on the tests. Moreover, the regression analysis demonstrated that the created model can be used to accurately forecast surface roughness in end milling of Stellite 6 with confidence intervals of 95%.
- Experimental and numerical evaluation of composite repairs on wood beams damaged by cross-grainingPublication . Campilho, Raul; Moura, M. F. S. F. de; Barreto, A. M. J. P.; Morais, J. J. L.; Domingues, J. J. M. S.An experimental and Finite Element study was performed on the bending behaviour of wood beams of the Pinus Pinaster species repaired with adhesively-bonded carbon–epoxy patches, after sustaining damage by cross-grain failure. This damage is characterized by crack growth at a small angle to the beams longitudinal axis, due to misalignment between the wood fibres and the beam axis. Cross-grain failure can occur in large-scale in a wood member when trees that have grown spirally or with a pronounced taper are cut for lumber. Three patch lengths were tested. The simulations include the possibility of cohesive fracture of the adhesive layer, failure within the wood beam in two propagation planes and patch interlaminar failure, by the use of cohesive zone modelling. The respective cohesive properties were estimated either by an inverse method or from the literature. The comparison with the tests allowed the validation of the proposed methodology, opening a good perspective for the reduction of costs in the design stages of these repairs due to extensive experimentation.