The Challenge of Attaching Dissimilar Materials - Structural Interfaces and Attachments in Biology - page 3

Although the mechanics of attachment for dissimilar materials can be studied
using many standard engineering methodologies, biological systems present addi-
tional challenges (e.g., biocompatibility requirements for total joint replacements).
On the other hand, in contrast to numerous engineering applications, biological
systems typically operate in a well-defined environment where the range of tem-
perature, hydration, and pH is tightly regulated. The effects of these variations can
therefore be neglected in most analyses of biologic attachments.
The goal of this introductory chapter is to illustrate examples of representative
attachments of dissimilar materials in engineering and biology, and to place into
context the deeper treatments of the mechanics and physiology of material
attachments studied throughout the rest of the topic. While we do not attempt to
present a comprehensive list of such attachments, the chosen examples demonstrate
typical cases and problems associated with such joints. We include as well a brief
discussion of the relevant fracture problem that should be addressed when design-
ing or analyzing attachments of dissimilar materials.
1.2 Examples of Attachments of Dissimilar Materials
1.2.1 Engineering
Attachments of dissimilar materials in engineering are usually adhesively bonded
or bolted, and have presented challenges to generations of engineers. Beginning in
the 1950s, a series of rigorous treatments of the mechanical responses of such
attachments have been developed. These have increased in sophistication in recent
years, so that estimating the toughness of simple engineering materials is now
possible. This is in stark contrast to frameworks for understanding biological
attachment. Chap. 3 presents an overview of some of the established models for
understanding the bonded attachment of engineering materials, and places the
attachment of tendon to bone into the context of these models.
Adhesively bonded attachments possess a number of advantages, such as sealing
against corrosion, damage tolerance, and reasonably good fatigue behavior. On the
other hand, these attachments are characterized by high residual stresses, they
cannot be disassembled or easily inspected, and they are sensitive to peeling and
transverse shear stresses that lead to debonding. Bolted connections are less sensi-
tive to peeling and transverse shear stresses and they can easily be inspected or
disassembled. However, bolted assemblies also introduce stress concentrations and
a degree of compliance, and their fatigue behavior is generally inferior to adhe-
sively bonded attachments. We concentrate here on several examples of bonded
attachments.