The strength of fiber is usually measured in bundle form because there is better correlation between fiber bundle strength and \(\underline{\hspace{2cm}}\)
Step 1: Clarify the query. The question focuses on why staple fiber strength (e.g., cotton) is tested in bundles (e.g., using a Stelometer or HVI) instead of individually. The rationale provided is the bundle strength's strong correlation with another crucial characteristic.
Step 2: Examine staple yarn composition. Staple yarn strength stems from the twisting of numerous individual fibers. Yarn strength relies on individual fiber strength, fiber arrangement, length, fineness, and fiber-to-fiber grip.
Step 3: Contrast single fiber and bundle strength tests. Single fiber testing is slow and yields inconsistent results. Bundle testing averages multiple fiber properties, simulating fiber interaction within a yarn. Research and practical application confirm that bundle strength accurately predicts the strength of the resultant spun yarn.
Conclusion: Fiber bundle strength is measured due to its strong, dependable correlation with final yarn strength.
Match Fibre with Application.\[\begin{array}{|l|l|} \hline \textbf{LIST I} & \textbf{LIST II} \\ \textbf{Fibre} & \textbf{Application} \\ \hline \hline \text{A. Silk fibre} & \text{I. Fire retardant} \\ \hline \text{B. Wool fibre} & \text{II. Directional lustre} \\ \hline \text{C. Nomex fibre} & \text{III. Bulletproof} \\ \hline \text{D. Kevlar fibre} & \text{IV. Thermal insulation} \\ \hline \end{array}\]