An experimental investigation on the effect of adhesive distribution on strength of bonded joints

Abstract

Adhesive joints are widely used due to their higher strengths, lower weights, lesser expenses and ease of fabrication than other methods of joining. Hence, they are used extensively in aerospace and automobile industries. High quality bonds require the use of fixtures which are essential to ensure proper curing and to attain uniform thickness. Improper adhesive application and method of fixturing can cause irregularities in the distribution of the adhesive along the overlap which could affect the joint strength. This is especially critical for aerospace components as the replacement of parts can be costly and time consuming. This paper presents a nondestructive test (NDT) methodology to quantify the bonded joints where the adhesive does not completely cover the overlap area. Single lap adhesive joints with carbon fiber adherents were fabricated using a two-part epoxy based adhesive. The adhesive region was fabricated to have various shapes including elliptical and circular of different sizes and a joint with full coverage for comparison. Polytetrafluoroethylene (PTFE) cutouts were used to mask regions of adhesive to achieve the desired coverage pattern. After fabrication all samples were ultrasonically scanned with a 10 MHz spherically focused immersion transducer using pulse-echo ultrasonics to determine the actual as tested adhesive distribution shape. The scans were able to resolve the shape of adhesive distribution across the overlap region of 25.4 × 25.4 mm and were correlated with the actual adhesive distribution at the interface after lap shear tests. Lap shear tests were then performed on the samples fabricated and the samples were loaded to failure. It was found that the shape and the orientation of the adhesive shape relative to the loading direction had an effect on failure strength.

The potential of improving wood preservative penetration into glued wood products bonded with one-component polyurethane by discontinuous adhesive bondline design

“…If we exclude this uncovered area, then the results show that the difference in wood failure is not significant indicating that the adhesive application design does not have an effect on the adhesivewood interaction in the bondline. The effect of adhesive distribution in the bonded joints was also investigated on carbon fibre-epoxy composites (Pisharody et al 2019). In this paper, the results show that the shear strength significantly decreases by reducing the adhesive coverage area.…”

Defects and uncertainties of adhesively bonded composite joints

“…Poor and irregular adhesive filling and distribution can significantly affect an adhesively bonded joint's life expectancy due to fatigue, especially if the filling irregularity defect occurs in regions with high-stress concentration [40][41][42]. Additionally, poor filling can lead to gaps that increase local stresses in the surrounding adhesive area [42]. Hence, poor filling can inherently cause disbond and delamination as the joint is not adequately filled.…”

Nondestructive Inspection and Quantification of Select Interface Defects in Honeycomb Sandwich Panels

“…Blanford and Jack [ 34 ] used high-frequency ultrasonic to quantify the three-dimensional damage zone in a carbon fiber laminated composite from low-velocity impacts using immersion tank inspection. Blackman et al introduced a novel pulse–echo ultrasound technique for sizing foreign objects in carbon fiber laminates [ 35 ], and recently, a study by Pisharody et al [ 36 ] used immersion tank inspections to perform ultrasonic scanning to assess the damage zone around an adhesive joint.…”