The comparisons of the results for other force ratios are shown
in Figs. 9 and 10. The repetition of tests results obtained for the
warp and small divergence of tests results for the weft can be observed
very well. The reason for this fact is that the warp direction has been assumed as basic for specimens cut. The weft direction is
not always perpendicular to the warp direction (very small
changes in the virgin fabric can be observed). Therefore not always
is there the same number of complete threads in the weft direction
in the cross arm. Following, it should be noted that for the weft and
warp for load ratio 1:2, 2:1, 4:1 results are very similar to those obtained
for 1:1 stress ratio. The calculated coefficients of determina tion R2 are given in Table 3. All curves for different load ratios have
been compared to mean stress–strain curves of 1:1 load ratio. Only
for the load ratio 1:8 for the warp and for load ratio 8:1 for the weft
significant differences to 1:1 stress ratio results can be observed.
For the load ratio 1:8 it can be noticed (Fig. 9) that strains for the
warp have negative values. In this type of fabrics when the weft
threads are subjected to high loading in comparison to the warp,
the weft threads straighten and the warp threads become folded.
Therefore, it can be concluded that in the engineering applications,
for this type of fabric, 1:1 stress ratio is representative, as 8:1 stress
ratio (rwarp:rweft) is seldom applied in hanging roof constructions.
Finally, comparison of biaxial stress–strain curves with uniaxial
tensile test results is given, see Fig. 11. It can be ascertain that uniaxial
tensile tests results give a good approximation of the biaxial
stress state for 1:1 load ratio. Therefore finally, for the investigated
type of coated fabric, it can be concluded that uniaxial tensile tests
give a good outlook on its mechanical properties.