Biaxial tension tests were carried out to study the tensile behavior of the flax fabric. The results showing the biaxial behavior of the fabric in the weft direction are pre­sented in Fig. 7.25 for different values of the parameter k. The parameter kt= ef є is defined as the ratio between the strain in the weft direction over the one in the

warp

warp direction. The results show that an increasing value of kt leads to higher strain in the weft tows. This means that the crimp effect decreases in this case. The crimp effect is the lowest in the case of the unidirectional test (k =e /e =0).

c warp weft

Figure 7.25 indicates that the maximum failure strain is obtained in the case of the uniaxial test. This phenomenon is normal and is due to the crimp effect. The maximum strain to failure is observed for the case of the uniaxial test (kC=0). For all the considered cases, the failure strain is lower than 4.5%. These values are much lower than the ones measured on the tetrahedron face (Figs. 20, and 21). It is there­fore probable that failure occurs in the tightest tows of the face during the process.

In a general way, the biaxial tensile behavior of the fabric is very similar to the ones observed on woven fabrics made from glass or carbon fibers.6773 Even if the tows are not constituted with continuous fibers, the entanglement between the fibers provides a sufficient continuity to the tow so that this one behaves like a homoge­neous entity.