1. Structural Safety Review of the ESS Battery Pack Snap-fit Joint

The topic we will cover today is "Snap-fit Fastening" of structures.

Cross-sectional photograph of thin-film defects

The term Snap-fit may sound very unfamiliar. However, it is one of the most commonly seen fastening methods in our everyday surroundings. It is widely used in many places, from the casings of electronic devices to the caps of marker pens.

Example of a vacuum gauge

Snap-fit fastening is similar in form to a cantilever, repeatedly bending and then snapping into engagement.
Because permanent deformation or fracture can occur depending on the material, entry angle, and cantilever geometry, optimized design through numerical analysis is critically important.

2. Why is a review of Snap-fit fastening structures necessary?

The ESS battery pack covered in this topic is a stacked structure assembled via Snap-fit fastening. Snap-fit is the simplest form of fastening device; its ease of assembly and disassembly helps reduce the assembly cost of manufactured products. It is also widely used because it offers the advantage of allowing a high separation force while keeping the engagement force low, and enabling repeated fastening and separation by utilizing the elasticity of the Snap-fit.

The most familiar example of Snap-fit fastening in everyday life is the cap of a marker pen. Looking closely at the inside, there is a slight protrusion: when force is applied to close it, the cap snaps past the protrusion and locks in place, and when pulled with force again, the cap comes off. Snap-fit is also extensively used in many plastic electronic devices such as mobile phones and laptops.

03. How can the analytical verification of a Snap-fit joint be performed?

The Snap-fit geometry is generally described as a cantilever form. The cantilever-type wing with high elongation undergoes bending deformation depending on the entry angle, reaches an open space to engage, and then performs the reverse process for disengagement — repeating this behavior cyclically.

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