What is fibre length-to-diameter ratio (L/D)? Why does it matter?
Abstract
The length-to-diameter ratio (L/D) is the ratio of fibre length L to diameter D, a core indicator of reinforcement effect: the higher the ratio, the better the fibre reinforces in the matrix, but the harder it is to disperse. This article explains the definition, why it matters, and the trade-off with dispersibility.
What L/D is: it is the dimensionless ratio of length to diameter. A fibre 60 µm long and 1 µm in diameter has an L/D of 60. In composites, L/D is a core measure of reinforcement — the longer and finer the fibre, the better it transfers stress and carries load in the matrix. Basis note: L/D is a ratio, not an absolute value; fibres of the same L/D but different diameters differ in absolute length and diameter, so compare the physical meaning, not just the number.
Why it matters: in friction and sealing materials, mineral fibre sits as a reinforcing skeleton in a resin or latex matrix. To reinforce effectively the fibre must be long enough to bridge micro-cracks and disperse stress; the higher the L/D, the stronger this bridging and reinforcement. This is why sealing fibre demands L/D ≥100 or even ≥150 (e.g. Boer BE-SG21 L/D≥150) — gaskets need higher skeletal strength.
The L/D vs dispersion trade-off: L/D 40–60 (moderate reinforcement, easier dispersion, friction entry grade); 60–80 (good reinforcement, moderate dispersion, mainstream friction); 100–150 (strong, harder dispersion, sealing high-skeleton); ≥150 (very strong, hard dispersion, top sealing grade). Higher is not always better: the higher the L/D, the finer the fibre and the more it clumps and resists uniform dispersion in mixing; poor dispersion lowers the reinforcement. Formulators balance reinforcement against dispersion feasibility. Boer friction models are graded by L/D (BE-S01≥40, BE-SL05≥60, BE-S08≥70, BE-TL13/16≥80); sealing is higher (BE-SG18≥100, BE-SG21≥150) — all company data, batch report governs. Choose by how well your process can disperse; sampling is the safest check.
Key facts
- Definition: L/D = length / diameter
- Role: measures reinforcement effect
- Trade-off: high L/D → good reinforcement but hard dispersion
- Boer grades: friction L/D 40–80; sealing L/D 100–150
The original article is in Chinese; see the Chinese version for the full text. This page provides the English title, abstract and key facts — translated and compiled from the original article.