Load-elongation (L-E) curves of undrawn and drawn nylon 6 filaments were plotted on the same abscissa to investigate their drawing behaviors. The results are:
1. The elongation of drawn filaments at the primary yield point was almost the same as the draw ratio of the filament.
2. Filament drawn at slow extension rate had a higher effective draw ratio due to a higher degree of molecular orientation than drawn at high speed.
3. The longer the drawn filament relaxed at a given draw ratio, the higher the degree of molecular orientation and the larger the shifts of the primary yield point, as if the equivalent higher draw ratio were applied.

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The modified loop strength test when the bending angle, which is 180° in ordinary tests, is varied from 180° to 80° was carried out, together with the following theoretical analysis and discussion.
1. The theoretical equations expressing the relation between the bending angle and the loop strength are obtained on the following assumptions:
a. Some part of the linear region of a fiber is transfered by shear into the bending region, and the bending strain is reduced a little.
b. The rupture of a fiber in the loop test takes place when the sum of the bending strain and the stretching strain has reached the breaking strain in the simple stretching test of the fiber.
c. The change of the loop strength with the bending angle is dependent upon the degree of decrease of the above bending strain e, , giving the following equations: e_m; =Cδ., e_m; =e_mo; (1-2δ/φ), where δ is the quantity corresponding to the shear strain produced by the above transfer of the boundary; C a constant; and φ the bending angle.
2. The theoretical equations are as follows; α₁; =1-e_m; E₁; /f_B; (e_y; <e_B; -e_m; ), α₂; =1+(e_B; -e_y; )(E₂; -E₁; )/f_B; -e_m; E₂; /f_B; (e_y; >e_B; -e_m; ), where α₁; and α₂; are the ratios of the loops strengths to the strengths for simple stretching; E₂; and E₁; the slopes of the stress-strain curves before and after the yield point of the sample; f_B; and e_B; the ordinary breaking strength and strain; e_y; the yield strain.
3. The experimental results for polyethylene terephthalate filaments can be approximately explained by the above equations except the small bending angle. The bending strain at the bending angle of 180° is estimated roughly as 15%, for the breaking strain of 30%, and as 7% far the breaking strain of 11%.

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The equation of weft motion on an air jet loom which reserves the measured yarn by an air stream is derived. This and the one reported in the previous paper which treats the measuring drum system are used to evaluate various weaving factors. The results are: (i) From the point of the loom speed obtainable, there is little difference between such air reserving systems as blown on the whole of the measured yarn., or blow n on one leg of the loop or blown on many loops. (ii) Also little difference is shown between the measuring drum system and the air reserving system in point of the yarn velocity. (iii) However, the loom speed can considerably be enhanced if the initial jet velocity is increased, or if the yarn length blown up by air at start is lengthened. (iv) Fine yarn is superior for narrow fabric weaving. Wider weaving may be better for coarse yarn. (v) As the reed space is broadened, the weft consumption rate can be increased. (vi) The following velocities are recommended in case of cotton 20's: 60-70m/sec for the uniform sub-streams added along the shed, 20-30m/sec for yarn-reserving air.

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