# 5.2.1.3 Substrate Flexibility

> From: LOCTITE®X Digital Manual for Bonding (https://www.loctitex.com/en/manuals/bonding/5.2.1.3-substrate-flexibility/)

##### 5.2.1.3 Substrate Flexibility

In general, many adhesives will have properties relating to flexibility listed in the technical literature, such as TDS or material specification sheets. The flexibility of cured adhesives will usually be characterised by Young’s modulus (also referred to as the elastic modulus), elongation before break and Poisson’s ratio. In general, there is a trade-off between shear strength performance and elongation, as seen in Figure 127. Engineers must be aware of this relationship when they match the flexibility of the adhesive to the requirements of the surfaces being assembled. Just like solid materials, cured adhesives have flexibility and strength properties that vary by polymer chemistry. Generalised expected properties by chemistry are shown in Figure 127. In many cases, matching the flexibility of the adhesive to the substrate (Figure 128) is ideal. In other cases, a high-strength, rigid bond is required to provide the best structural integrity.

_Figure 127 Flexibility of adhesives_

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