Deformation Behavior of Polyurethane Adhesive in the Single-Lap Joint Based on the Microbeam X-ray Scattering Method

Abstract

Single-lap joint (SLJ) specimens were prepared using two stainless steel substrates as adherends and polyurethanes (PU) as an adhesive and then employed for adhesion testing. To investigate the internal structure of the PU adhesive during the shear deformation process, the in situ synchrotron radiation microbeam small-angle and wideangle X-ray scattering (SAXS and WAXS) measurements were carried out. A lab-made portable tensile tester was developed for the SAXS/WAXS measurement during lap shear deformation. The structure of adhesive bulk was also investigated during the simple uniaxial deformation for the comparison. An isotropic scattering ring�which was formed from the periodic structure of hard segment domains of the PU adhesive�was clearly observed in the SAXS pattern at the initial state. This isotropic ring changed to an ellipsoid shape whose minor and major axes were tilted from the stretching direction. The spacing of the hard segment domains of PU adhesives increased, and the tilt angle of the stress direction was merged with the stretching direction with an increase in the applied deformation. The orientation direction of the hard segment domains and molecular chain of the soft segment changed with a similar trend. Furthermore, the degree of change in these values was larger at the edge of the adhesive of the SLJ specimens, indicating the existence of spatial distribution of direction and the value of stress in the adhesive during lap shear deformation. These findings are expected to be quite useful for practical design of adhesives.

Characterization of Bending Strength in Similar and Dissimilar Carbon-Fiber-Reinforced Polymer/Aluminum Single-Lap Adhesive Joints

“…As can be seen from Figure 8, the fracture surface patterns are combinations of cohesive (a type of failure so that a layer of adhesive remains on both surfaces of the adherends) and adhesive (interfacial bond failure between the adhesive layer and the surfaces of the substrate) failures. These types of failures of the single-lap adhesive joints are also reported in many papers authored by different researchers [2,10,11].…”

“…As can be seen from Figure 8, the fracture surface patterns are combinations of cohesive (a type of failure so that a layer of adhesive remains on both surfaces of the adherends) and adhesive (interfacial bond failure between the adhesive layer and the surfaces of the substrate) failures. These types of failures of the single-lap adhesive joints are also reported in many papers authored by different researchers [2,10,11]. The deformed shape of the single-lap adhesive joint under three-point bending is depicted in Figure 9, which was described according to the principles of beam mechanics theory in bending loading conditions.…”

“…Adhesives can offer versatile applications throughout the car bodyshell, with these applications being influenced by factors such as adhesive stiffness, strength, and the specific placement of the adhesive within the bodyshell. For instance, certain nonstructural adhesives with lower strength (like polyurethanes [10,11]) are employed for purposes such as sealing or creating joints in regions of the vehicle that are not considered structural components. Conversely, other types of structural adhesives with greater strength, such as epoxy-based adhesives [9,12], find use in creating joints between structural elements such as chassis parts or metallic and non-metallic thin-walled critical components of a car's bodyshell.…”

Interfacial Structure Analyses of Single Carbon Fiber-Embedded Polymers by In Situ X-ray Scattering and Birefringence Measurements

“…Also, X-ray spectroscopy is useful for an opaque sample. Synchrotron radiation X-ray can be used to evaluate not only CFs but also the orientation of the polymer chains and craze formation during uniaxial elongation. − Furthermore, when the microbeam X-ray is used for this measurement, information on the interface between (CF/matrix polymer) may be obtained by mapping. − Schneider et al reported spatial distribution of failed interface and voids near the broken fiber edges in the epoxy matrix near the glass fibers in a stretched sample using microbeam small-angle X-ray scattering (SAXS) . Takahashi et al observed localized debonding and voiding in a single-CF epoxy resin using synchrotron radiation X-ray computed tomography upon applying stress or cyclic stress to the sample .…”