Abstract
Adhesive bonding has become more efficient in the last few decades due to the adhesives developments, granting higher strength and ductility. As a result, adhesives are being increasingly used in industries such as the automotive, aerospace and construction. Thus, it is highly important to predict the strength of bonded joints to assess the feasibility of joining during the fabrication process of components (e.g. due to complex geometries) or for repairing purposes. When using the Finite Element Method with advanced propagation laws, the tensile (Gnc) and shear (Gsc) fracture toughness of adhesive joints must be determined with accuracy. Several conventional methods to obtain Gnc and Gsc exist in the literature, mainly based on Linear Elastic Fracture Mechanics (LEFM). The J-integral technique is accurate to measure these parameters for adhesives with high ductility. In this work, the J-integral is used to obtain Gnc by the Double-Cantilever Beam (DCB) test. An optical measurement method is developed for the evaluation of the crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab® sub-routine for the automated extraction of these quantities. As output of this work, an optical method that allows an easier and quicker extraction of the parameters to obtain Gnc than the available methods is proposed (by the J-integral technique) and some results are presented regarding joints with different geometry and adherend material.
Highlights
The developments in adhesives technology made possible the use of adhesive bonding in many fields of engineering, such as automotive and aeronautical [1]
The rotation of the adherends was measured by an incremental shaft encoder and the crack tip opening by two Linear Variable Differential Transducers (LVDT)
The complete tensile Cohesive Zone Models (CZM) law of the adhesive was derived by the direct method in some cases, on account of the available Gn- n curve that was differentiated to provide the tn- n law
Summary
The developments in adhesives technology made possible the use of adhesive bonding in many fields of engineering, such as automotive and aeronautical [1]. More recent numerical techniques, such as Cohesive Zone Models (CZM), combine stress criteria to account for damage initiation with energetic, e.g. fracture toughness, data to estimate damage propagation [8] This allows to consider the distinct ductility of adhesives and to gain accuracy in the predictions. CZM in particular can accurately predict damage growth if the fracture laws are correctly estimated [9] These laws are based on the values of cohesive strength in tension and shear, tn0 and ts0, respectively, and Gnc and Gsc. These laws are based on the values of cohesive strength in tension and shear, tn0 and ts0, respectively, and Gnc and Gsc These parameters that cannot be directly related with the material properties measured as bulk, since they account for constraint effects (for adhesive joints, caused by the adherends). The data analysis is automated to ease the data reduction process
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