Biaxial Thermo–Mechanical Response of ABS Sheet Above T g Using DIC–Based Bubble Inflation Technique

Abstract

In this study, we examine the biaxial, large, and rapid deformation characteristics of heavy-gauge ABS sheets within the temperature range of 120°C to 160°C, relevant to the industrial forming process. A custom-built bubble inflation apparatus with a 300 mm diameter was designed for this purpose. Temperature uniformity across the sheet was verified using a thermal camera, while the temperature profile through the material's thickness was monitored during the heating using thermocouples near the top and bottom surfaces of the sheet. The bubble inflation test, combined with displacement, strain fields, and deformation rates at different locations, enables detailed characterization of the bubble's shape under large deformation. To address early-stage geometric instabilities due to sagging from thermal expansion, airflow was regulated with a precise flow control valve before inflation, while 3D-DIC monitored the real-time displacements to correct for sag deformation. The inflation pressure profile was recorded and synchronized with 3D-DIC strain evolution data for each test, allowing for analysis of the characteristic stress–strain curve at the pole. By evaluating the material's equi-biaxial properties at the pole and biaxial strain measurements away from the pole, the collected data provides a strong basis for future calibration of constitutive material models through an inverse approach, enabling accurate integration into process simulations.