the neutral axis shifted toward outside surface a little bit more when it was reloaded for both samples with and without nodes. Even though the neutral axis shifted in different manner for load and re-load condition, at the end, the axis tended to shift to same location. It was noted that the sample with nodes became stiffer when load over 165N. Plotted in Fig. 10.8 were the distributions of horizontal normal strain along the thickness direction at the center of the beam. Shown in the figure, the strain distribution was linear when load was low and in linear range. It suggest the plane assumption—“the plane cross sections remain plane after bending” is still valid for this heterogeneous material. When the load was increased to nonlinear range (large then 88N), non-linear strain has developed in the high porosity side of the beam. In contract, the strain distributions were still appearing in linear manner in the high fiber density side. If carefully examining the location of zero strain (the location of the neutral axis), it was found that neutral axis tended to stay in initial location in linear range of the load, but the axis started to shift towards to high fiber density when the load increased above 88N. Shown in Fig. 10.9 was the profile of Poisson’s ratio on the cross section at the center of the beam, when the load was 88N. It was noticed the Poisson’s ration was not constant on the cross section. Its profile looked like a reciprocal Fig. 10.8 Horizontal strain distributions on cross section at different load steps Fig. 10.9 Poisson’s ratio distribution along beam thickness at the end of the linear loading range 72 S. Xu et al.
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