Adherend thickness effect on the tensile fracture toughness of a structural adhesive using an optical data acquisition method

Abstract

Adhesive bonding is nowadays a serious candidate to replace methods such as fastening or riveting, because of attractive mechanical properties. 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. This work studies the tensile behaviour of adhesive joints between aluminium adherends considering different values of adherend thickness (h) and the double-cantilever beam (DCB) test. The experimental work consists of the definition of the tensile fracture toughness (GIC) for the different joint configurations. A conventional fracture character-ization method was used, together with a J-integral approach, that take into account the plasticity effects occurring in the adhesive layer. An optical measurement method is used for the evaluation of crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab s sub-routine for the automated extraction of these quantities. As output of this work, a comparative evaluation between bonded systems with different values of adherend thickness is carried out and complete fracture data is provided in tension for the subsequent strength prediction of joints with identical conditions.

Effect of the size reduction on the bulk tensile and double cantilever beam specimens used in cohesive zone models

“…9 Some work has been done on the study of how specific geometric parameters influence the resulting fracture toughness (G IC ). An increasing trend of G IC with adherend thickness was found, 10 which is relevant to our study on DCB size reduction. This behaviour was considered to be due to an increasing degree of adherend restraining for bigger thickness values, as a larger region is loaded ahead of the crack tip.…”

“…All these geometric parameters may have an effect on the values of fracture toughness, because it has been suggested that G IC is not a material parameter, but a geometry-dependent quantity instead. 10 Furthermore, all these parameters are used in the CBBM data reduction scheme, suggesting they influence the end values. 17 Initial crack length.…”

Analysis of the metal adhesively bonded double cantilever beam specimen

“…In spite of the above questions regarding the meaningfulness of the mode I fracture energy, the DCB specimen has been increasingly used to evaluate the traction-separation law of the adhesive [17][18][19][20][21][22][23][24][25]. The method employed, often designated as "direct", reqAccurate methods to compute J I , which may in turn require measurements of load-point crack-tip rotations [19,20,25], or simply application of beam theory based data reduction schemes [21][22][23][24] similar to those used for delamination of composites [16,26,27].…”

“…The method employed, often designated as "direct", reqAccurate methods to compute J I , which may in turn require measurements of load-point crack-tip rotations [19,20,25], or simply application of beam theory based data reduction schemes [21][22][23][24] similar to those used for delamination of composites [16,26,27].…”

Influence of the temperature on the fracture energy of a methacrylate adhesive for mining applications

“…Campilho et al studied the influence of adherend thickness on the measured value of G Ic of a ductile adhesive through DCB tests. Regardless of the data reduction methods, a growing trend of G IC regarding the thickness has been found, suggesting that the G Ic is not a material parameter, but it is a parameter dependent on the geometry used [13]. Moreover, in thin-layer adhesive joints, cracks are forced to follow the defined path through the middle area, since in general the adhesive is weaker and more adaptable than the substrates, which usually causes a cohesive failure of the adhesive [14].…”