Don’t Come Unstuck Designing Structural Adhesive Bonds

This guest contribution on Innovation Intelligence is written by Jo Hussey, Sales & Marketing at Componeering Inc. ESAComp software by Componeering is used for design and analysis of composite structures. ESAComp is available through the Altair Partner Alliance.

From the earliest known adhesive – a tar made from birch bark – used in the Stone Age to help haft stone tools to wooden handles, man has looked to exploit the benefits offered by bonded joints.

Natural adhesives, such as rubber, and adhesives derived from fish, casein (Latin for “cheese”) and animal hides appeared in the late 1600s and were patented in Europe and the United States. The first synthetic adhesive resin, phenolic, followed the invention of Bakelite by Belgian Leo Baekeland (US Patent US942699 in 1909).

Both World Wars brought technological leaps in many sectors including; development, production and new materials such as plastics and resins with a variety of properties. Adhesives were needed to join these new materials together and to established materials like metals and glass. Wartime restrictions on metals (notably aluminum and steel) spurred innovative uses of wood, particularly in the aircraft sector.

Today, synthetic adhesives, with their variety of chemical compounds, provide an enormous range of commercial products to meet needs within all industry sectors worldwide. Synthetic adhesives have many uses from the bonding of hip replacements into bones to the assembly of fuselages or spacecraft destined for life in orbit.

The success of a bonded joint relies on its ability to resist a combination of mechanical and environmental factors. By the application of proper design principles coupled with manufacturing best practices, the bond itself can be even stronger than the materials it joins.

Structural joint design for composites

Much has been written on the design approach for bonded joints and the mechanisms occurring within them, of which the works of L.J. Hart-Smith are considered the reference. Without such understanding, applications for composites would have been hindered by an inability to join them by any means other than mechanically with bolts, screws and rivets which require holes to be drilled thus weakening the composite parts in the regions where they are joined.

Composite structures all have joints, so their design and analysis is paramount to determining their overall performance. Therefore, ESAComp has comprehensive capabilities for both bonded and mechanical joints which are very efficient in the preliminary design of various joint configurations.

Here, we take a quick look at the preliminary design of a wing spar bonded joint, which follows the study described in DOT/FAA/AR-01/7 (April 2001) “Stress Analysis of In-Plane, Shear-Loaded, Adhesively Bonded Composite Joints and Assemblies”.

In this example, we consider a tip loaded wing of a small aircraft or wind turbine blade. The wing spar carries a constant in-plane shear (Nxy), which needs to be transferred from the joint laminates to the shear web.

A parameterized double lap joint allows efficient examination of how the parameters of the joint (laminate selection, joint overlap length, selection of the adhesive material and its thickness) influence the performance of the joint.

The joint can be loaded with a combination of in-plane tension/compression, in-plane shear, out-of-plane shear, and the bending moment.

In-plane shear stress resultant induced out-of-plane shear stresses τyz have been studied for various overlap lengths (10/25/50mm). The ESAComp results shown here correspond with those given in DOT/FAA/AR-01/7 (April 2001).

ESAComp is a stand-alone tool but also interfaces with commercial FE packages, such as HyperWorks. A typical FE approach for modelling wing structures is based on shell elements. The study of the discontinuity needs special methodology and it is often neglected. From the FE solution, resultant forces and moments can be extracted and used as an input for the specific bonded joint analysis tools. This approach provides flexibility to choose the best solution at different phases of the design process.

ESAComp also allows going beyond the elastic limit of the adhesive. The non-linear (bi-linear) adhesive model is solved using a concept called effective stress/strain. The non-linear failure analysis provides two margins of safety (MoS) values. One with respect to the yield strength, the other with respect to final failure.

Contact Componeering to learn more about the capabilities of the adhesive bond analysis module.

Meet Componeering at:

JEC World 2017, booth N68 in Hall 5A, March 14-16 in Paris, France

ATC Europe 2017, June 26-28, in Frankenthal, Germany




Note: Image of Spruce Goose courtesy of D.P. Bashford

Altair Partner Alliance
Altair Partner Alliance

About Altair Partner Alliance

The Altair Partner Alliance (APA) provides access to a broad spectrum of complementary software products, through the use of HyperWorks Units (HWUs) at no additional cost. Their continuously expanding list of partner software, across a broad range of disciplines, serves the needs of hundreds of companies ranging from automotive, aerospace, and defense to consumer products, biomedical and heavy equipment. The APA curates a diverse collection of blog posts written by its many partners to keep readers informed on a variety of trending engineering topics.