Chapter 6 Grid strain analysis and its application in composite sheet forming

Defect formation during preforming of a bi-axial non-crimp fabric with a pillar stitch pattern

“…Grid strain analysis (GSA) [24] was used to determine the level of shear deformation in the formed hemispheres. As shown in Figure 7(b), the 3D coordinates of grid intersection points were digitised using a coordinate measuring machine (CMM), and the angles between the gridlines were calculated using GSA.…”

Sheet Forming Studies using Low-cost Composites

“…The sheet forming limit tests follow the procedure proposed by Martin et al [18]. It consists of setting a series of rectangular planar blanks with constant thickness and length, and variable width.…”

“…on the FLD the strain points are from pure shear, simple tension, plane strain, and biaxial tension as discussed by Avila and Jabbur [24]. The experiment performed by Martin et al [18] in unidirectional [0] 4 fiber glass/polypropylene composites has a clear plane strain nature, in other words, the points are concentrated around the major strain axis, which brings as a consequence small values for minor strains. They not only show the presence of low safe strains for the cross ply [0,90] 2s and angle ply [0,þ60,À60] 2s fiber glass/polypropylene, but they also mention that most of the safe strains are located on the FLD left side, which makes impossible the existence of a biaxial tensile stress field.…”

Profile forming of pre-pressed wood-strand preforms

“…These deformations can lead to instabilities in profile forming of continuous fiber reinforced thermoplastic (CFRT) composites. Excessive stretching often results in thinning instability [12], and thickening causes another type of instability: wrinkling or buckling [13]. Similar problems can occur while profile forming woodstrand preforms.…”