Study of deformations evolution in near-surface layers of adhesive joints (original) (raw)

This paper presents the study of the evolution in situ of distribution of local deformations in near-surface layers in pads made of carbon lamellas under strain deformation. The specimens were produced from two face-to-face docked steel pads 120×40×4 mm and two carbon lamellas FibARM Lamel 120×40×1,2 mm joint using the adhesion 'FibARM Resin Laminate+". The strain tests were performed using the "INSTRON 3386" test bed with a maximum tension of 100 кN (10,19 тs). Optical measurement system VIC-3D was used to identify the evolution of deformations distribution in the near-surface layers. The VIC-3D system allowed obtaining the images that reflect the evolution of distribution of relative deformations iso-fields under different loads. In situ experimental research was conducted focused on strain deformations in specimens made of a layered composite: metal/adhesive/carbon lamella. A crack in the specimen was modeled, which allowed determining that with a growth of the overall deformation there develops an evolution of special structural elements from chaotic (along the whole lamella area) to localized ones with higher deformation values in the crack region. It was established that at higher levels of overall deformation in the crack region on the carbon lamella surface, the maximum deformation region with one extremum is divided by a narrow line of low deformation into two parts along the joint of steel plates. A limit deformation is identified.

Through-thickness strain field measurement in a composite/aluminium adhesive joint

Composites Part A: Applied Science and Manufacturing, 2009

This paper presents an experimental procedure, which enables us to assess the shear strain field in an adhesive joint between composite and aluminium. In practice, this strain field is representative of the progressive stress transfer between a loaded structure and a composite patch used for reinforcement purposes. Digital image correlation (DIC) is used to measure the displacement field through the thickness of a patched specimen subjected to a tensile test. The shear strain field derives from the measured displacement field. The shear strain clearly decreases when the distance from the free edge of the adhesive increases, as predicted by numerical and analytical models of the joint. These measurements are used to estimate the in situ shear modulus of the adhesive. It is observed that the shear modulus decreases when the shear stress increases, thereby illustrating the non-linear response of the adhesive.

Deformation and damage evolution of a full-scale adhesive joint between a steel bracket and a sandwich panel for naval application

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2020

The increasing interest for the application of adhesive joints in naval superstructures motivates researchers to gain an in-depth understanding of the mechanical behaviour and failure mechanisms of these joints. This work reports on an experimental study of the deformation behaviour and damage evolution of a full-scale multi-material joint using different instrumentation techniques. Adhesively bonded joints of steel to sandwich panel components have been subjected to quasi-static tensile tests during which the global deformation of the joint and local strain distributions were monitored using digital image correlation (DIC). During one particular tensile test, fibre optic Bragg sensors (FBG) were also applied to the specimen’s surface at different locations in order to quantify the evolution of local strains. Additionally, acoustic emission (AE) sensors were installed in order to monitor damage initiation and evolution with increasing levels of imposed deformation. This test showcas...

Observation of deformation and damage at the tip of a crack in adhesive bonds loaded in shear and assessment of a criterion for fracture

Israel Society of Aeronautics and Astronautics 34th Israel Annual Conference on Aerospace Sciences, 1994

The evolution of damage at the tip of cracks in adhesive bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and a ductile epoxy resins were evaluated, with the bond thickness t being an experimental variable. An extensive zone of plastic deformation developed ahead of the crack tip prior to fracture. In the case of the brittle adhesive, for relatively thick bonds tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the interface, which led to a complete bond separation after interface cracks emanating from adjacent microcracks linked. In contrast, for the ductile adhesive the crack always grew from the tip. Strain gradients tended to develop there when the bond thickness was large. The adhesive shear strain was determined from fine lines scratched on the specimen edge. For both adhesives, the average crack tip shear strain at crack propagation rapidly decreased with increasing t. This effect was attributed to the changing sensitivity of the bond to the presence of flaws; thicker bonds can accommodate larger microcracks or microvoids which cause greater stress concentration. For a given bond thickness, the critical crack tip shear strain agreed well with the ultimate shear strain of the unflawed adhesive ?s previously determined using the napkin ring shear test 1-12]. This suggests that the ultimate shear strain is a key material property controlling crack growth. The critical distortional strain energy/unit area of the unflawed adhesive W~ was determined from the area under the stress-strain curve in the napkin ring test. Good agreement between W, and the adhesive mode II fracture energy was found for all joints tested except for relatively thick bonds. For the particular case of an elastic-perfectly plastic adhesive, the agreement above implies Gnc = W s =-tzy)~f.

Observation of deformation and damage at the tip of cracks in adhesive bonds loaded in shear and assessment of a criterion for fracture

The evolution of damage at the tip of cracks in adhesive bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and a ductile epoxy resins were evaluated, with the bond thickness t being an experimental variable. An extensive zone of plastic deformation developed ahead of the crack tip prior to fracture. In the case of the brittle adhesive, for relatively thick bonds tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the interface, which led to a complete bond separation after interface cracks emanating from adjacent microcracks linked. In contrast, for the ductile adhesive the crack always grew from the tip. Strain gradients tended to develop there when the bond thickness was large. The adhesive shear strain was determined from fine lines scratched on the specimen edge. For both adhesives, the average crack tip shear strain at crack propagation rapidly decreased with increasing t. This effect was attributed to the changing sensitivity of the bond to the presence of flaws; thicker bonds can accommodate larger microcracks or microvoids which cause greater stress concentration. For a given bond thickness, the critical crack tip shear strain agreed well with the ultimate shear strain of the unflawed adhesive ?s previously determined using the napkin ring shear test 1-12]. This suggests that the ultimate shear strain is a key material property controlling crack growth. The critical distortional strain energy/unit area of the unflawed adhesive W~ was determined from the area under the stress-strain curve in the napkin ring test. Good agreement between W, and the adhesive mode II fracture energy was found for all joints tested except for relatively thick bonds. For the particular case of an elastic-perfectly plastic adhesive, the agreement above implies Gnc = W s =-tzy)~f.

Study of the Impact of Surface Topography on Selected Mechanical Properties of Adhesive Joints

Coatings, 2024

Manufacturers of adhesives for industrial use determine the strength of adhesive joints during shear tests. Most often, components made of the same material are joined. In contrast, the roughness of the surfaces to be joined results from the use of a specific surface treatment technology. In adhesive manufacturers’ recommendations for metal-to-metal joints, surface technologies can be found without specifying numerical requirements for roughness. Modern techniques for shaping the geometric accuracy of components allow the formation of determined irregularities on the surface, which are characterised by their height and mutual distribution. Furthermore, regular irregularities can be obtained by using the appropriate tool and technological machining parameters. In this way, surfaces with similar load-bearing capacity, core volume, texture or expected hydrophobic properties can be produced by various methods. However, a basic prerequisite is the careful definition of the numerical requirements, both for the basic roughness indices and those of a complementary nature. As a rule, the strength of the adhesive joint is also lower than the strength of the adhesive itself. The strength of an adhesive joint depends on the ‘mechanical anchorage’ of the adhesive and the adhesion phenomenon on the surface. The research assumes that it is possible to induce an interaction between the geometric state of the surface and the properties of the adhesive, so as to guarantee the maximum strength of the adhesive joint. To verify this, a series of experimental tests were developed and carried out for two different adhesives characterised by different viscosities and offered bond strength. Based on the tests carried out, recommendations were made to the designers of adhesive joints, where, in addition to the height of the surface irregularities, the properties related to fluid retention and the shape of the irregularities in the valleys should be determined.

International Journal of Adhesion and Adhesives

This paper investigates fracture mechanics based design of the adhesively bonded Single Lap Joint (SLJ) made with curved Fibre Reinforced Plastic (FRP) composite adherends having pre-embedded adhesion failures and surface ply delaminations at either end of the lap portion. The propagation of pre-embedded through-the-width delaminations and adhesion failures in the SLJ under uniaxial tensile load has been characterized by computing the Strain Energy Release Rates (SERR) near the adhesion failure/delamination fronts. The Virtual Crack Closure Technique (VCCT) has been used for the computation of SERR. Three Dimensional (3-D) non-linear Finite Element (FE) analyses of the SLJ have been carried out for these defects existing either individually or simultaneously at different locations. The predominant modes of failure, the radial location from where these defects may start to grow have been identified. The propagations of adhesion failures have been studied at the interfaces of the adhesive and the adherends by pre-embedding them in the region of high-stress concentrations. Similarly, the propagations of the delaminations are investigated by pre-embedding them beneath the surface ply of both the adherends at the vicinities of the overlap ends. The vulnerabilities of these damage fronts are compared at different locations in the joint for the overall assessment of the structural integrity of the SLJ. The longitudinal shearing mode of adhesion failure is the dominant mode irrespective of their position. The adhesion failure in the lap adherend is more detrimental than the adhesion failure pre-embedded in a similar location at the interface of the strap adherend with the adhesive. The influence of the locations of delaminations when they grow in size on the structural integrity of the joint has also been analysed. The maximum values of SERRs and their radial locations in all the delamination fronts at several locations have been pointed out for structural design purposes. The dominating mode of failure in delamination fronts is highly sensitive to their locations. The growth rates are found to be significantly different in the lap and the strap adherends even for similar locations. It has been observed that the initially straight damage front will gradually tend to be curved in shape.

Analysis of crack propagation in an adhesive joint / M.D. Mohan Gift, J. Selvakumar, S. John Alexis

2016

Adhesive joints are widely used in industries because they have several advantages when compared to welded and riveted joints. One of the important factors is that they distribute the load and stresses uniformly over the entire bonded area providing good vibration resistance. Adhesive joints can readily bond dissimilar materials. The prediction of crack propagation validating the adhesive joint durability and toughness is a significant point which is addressed through various experimental methodologies based on the type of loading conditions. The analysis is hindered by the unpredictable substrate and adhesive behavior due to the loading conditions, the nature of crack propagation, and the geometry. The impact of hardener resin ratio alteration is a parameter which needs to be explored in validating the joint toughness. The Double Cantilever Beam tests which are used for analyzing the fracture toughness for mode-1 loading in adhesive joints focus on adhesive thickness variation exte...

Tensile fracture characterization of adhesive joints by standard and optical techniques

Engineering Fracture Mechanics, 2015

The use of adhesive joints has increased in recent decades due to its competitive features compared with traditional methods. This work aims to estimate the tensile critical strain energy release rate (G IC ) of adhesive joints by the Double-Cantilever Beam (DCB) test. The J-integral is used since it enables obtaining the tensile Cohesive Zone Model (CZM) law. An optical measuring method was developed for assessing the crack tip opening (d n ) and adherends rotation (h o ). The proposed CZM laws were best approximated by a triangular shape for the brittle adhesive and a trapezoidal shape for the two ductile adhesives.

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