Evaluation of Single-Lap and Block Shear Test Methods in Adhesively Bonded Composite Joints

Alec Redmann,Pavana Prabhakar,Tim A Osswald,Felix Tischer,Vinay Damodaran

doi:10.3390/jcs5010027

Alec Redmann, Pavana Prabhakar + Show 3 more

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https://doi.org/10.3390/jcs5010027

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Abstract

Adhesive bonding is increasingly being used for composite structures, especially in aerospace and automotive industries. One common joint configuration used to test adhesive strength is the single-lap shear joint, which has been widely studied and shown to produce significant normal (peeling) stresses. When bonding composite structures, the normal stresses are capable of causing delamination before the adhesive bond fails, providing inconclusive engineering data regarding the bonding strength. An alternative test is the block shear joint, which uses a shorter sample geometry and a compressive-shear loading to reduce normal stresses. Analytical models proposed by Goland and Reissner and Hart-Smith are used to compare the edge-bending moment for the two joint configurations. The stress distributions along the bondline are also compared using finite element analysis. Experimental tests are conducted to evaluate these analyses and the failure modes of each configuration are recorded. Block shear samples demonstrate a joint strength over 100% higher than single-lap shear specimen bonded with the same adhesive material. The lower joint strength measured in single-lap shear is found to be potentially misleading due to delamination of the composite adherend.

Highlights

As designers and engineers continue to push the boundaries of high-performance design, fiber reinforced plastics (FRP) are increasingly finding use in structural applications due to their light weight and superior mechanical properties
The single-lap shear test is a widely used method to measure the performance of adhesives and surface treatments
A significant challenge with this method is acquiring consistent and reliable engineering data due to complex stress states caused by the sample geometry and loading condition

Summary

Introduction

As designers and engineers continue to push the boundaries of high-performance design, fiber reinforced plastics (FRP) are increasingly finding use in structural applications due to their light weight and superior mechanical properties. Many of these applications, especially in the aerospace and automotive industries, require geometrical complexity, multiple components, and multiple materials. Especially in the aerospace and automotive industries, require geometrical complexity, multiple components, and multiple materials These requirements lead to a need for assembly and joining elements during manufacturing—typically mechanical fasteners or adhesives. Adhesive bonding avoids a weight penalty that is incurred by mechanical fasteners, better supporting the goal of a lightweight design, and galvanic corrosion is minimized, which can be responsible for more than 20% of the maintenance costs in aerospace and automotive applications [3,4,5]

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