Post-Forming Mechanical Properties of a Polymer Sheet Processed by Incremental Sheet Forming: Insights into Effects of Plastic Strain, and Orientation and Size of Specimen

Abstract

The innovative Incremental Sheet Forming (ISF) process affects the post-forming properties of thermoplastic polymers. However, the effects of degree of plastic strain, and the orientation and size of specimen on the mechanical properties are still unknown. In the present study, therefore, the ISF process is performed on a polymer sheet by varying the plastic strain ranging from 6% to 108%. The corresponding effects on the properties and associated polymer structure are quantified by conducting a variety of mechanical and structural tests. The results reveal that the post-ISF tensile properties like yield stress, ultimate stress, drawing stress, elastic modulus and elongation decrease from 26.6 to 10 MPa, 30.5 to 15.4 MPa, 18.9 to 9.9 MPa, 916 to 300 MPa and 1107% to 457%, respectively, as the strain increases in the investigated range. The value of post-ISF relaxation properties, contrary to the tensile properties, increases with increasing strain up to 62%. Particularly, reductions in stress, strain and modulus increase from 41% to 202%, 37% to 51%, and 41% to 202%. As regard the orientation effect, the sheet in the feed direction shows greater strength than the transverse direction (up to 142% in yield stress and 72% in ultimate stress). Moreover, the smaller sample offers greater strength than the larger one (up to 158% in yield stress and 109% in ultimate stress). The analysis of the post-ISF tensile properties and structural results lead us to conclude that the drop in the tensile properties due to increasing strain occurs due to corresponding increase in the voids area fraction (1.25% to 31%) and a reduction in the crystallinity (38% to 31%).

Novel Biobased Polyamide Thermoplastic Elastomer with Medium Hardness

“…[ 13 ] The curve is not smooth, which might be because of the slippage in chain entanglements during stretching. [ 22,23 ] Similar tensile curves were previously reported for some other polyamides, PA6,14, PA6,16, and PA6,20. [ 24 ] PA36,9 has a tensile strength of 36.70 ± 2.27 MPa, Young's modulus of 20.21 ± 3.57 MPa, elongation at break of 1220 ± 88%, and energy at break of 211.18 ± 25.20 MJ m −3 .…”

Minimizing the Main Strains and Thickness Reduction in the Single Point Incremental Forming Process of Polyamide and High-Density Polyethylene Sheets

“…Wei et al correlated the plastic strain induced in polypropylene parts processed by SPIF to the different post-forming tensile properties [ 43 ]. The elasticity modulus, elongation, yield stress, ultimate stress and drawing stress were analyzed.…”

A Research on The Formability of PVC Sheet in Single Point Incremental Forming (SPIF) Technology

“…Two Point Incremental Forming (TPIF) [2] At the beginning, this method is applied for forming metal sheets, but with the bloom of plastic or PVC based materials there are also researches of ISF for PVC material. In paper [3], the authors research the post-forming properties of thermoplastic polymer. Their results show that the post-ISF-process tensile properties is decreased, and the strain is increased in their experiment ranges.…”