Sheet forming of the multi-layered biaxial weft knitted fabric reinforcement. Part I: On hemispherical surfaces

The fibre bundle element model (FBEM) composed of geometric, microscopic and numerical submodels is proposed for the sheet forming of the multi-layered biaxial weft knitted (MBWK) fabric. The geometric submodel describes the kinematic forming behaviour. The microscopic one in the multi-scale analyses regards the internal friction as the mechanism of the “pseudo-plasticity”. The numerical one offers an improved mapping solution. Two forming criterions, i.e. yarn jamming and weft kinking rules are introduced and related to the geometric parameters. The horizontal and vertical forming tests are conducted and some important phenomena are revealed. The sliding of the elements cannot be neglected. The two main defects are shown in a field map. The FBEM agrees excellently with the experimental results and builds a sound basis for the usage of the MBWK fabric in composite manufacturing.