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Purpose: This study aims to investigate the compression characteristics of the 3D-printed polylactic acid (PLA) samples at temperatures below the glass transition temperature (Tg) with varying strain rates and develop a thermo-mechanical viscoplastic constitutive model to predict the finite strain compression response using a single set of material parameters. Also, the micro-mechanical damage processes are linked to the global stress–strain response at varied strain rates and temperatures through scanning electron microscopy (SEM). Design/methodology/approach: Tg of PLA was determined using a dynamic mechanical analyzer. Compression experiments were conducted at strain rates of 2 × 10–3/s and 2 × 10–2/s at 25°C, 40°C and 50°C. The failure mechanisms were examined using SEM. A finite strain thermo-mechanical viscoplastic constitutive model was developed to analyze the deformations at the considered strain rates and temperatures. Findings: Tg of PLA was determined as 55°C. While the yield and post-yield stresses drop with increasing temperature, their trend reverses with an increased strain rate. SEM imaging indicated plasticizing effects at higher temperatures, while filament fragmentation and twisting at higher strain rates were identified as the dominant failure mechanisms. Using a non-linear regression analysis to predict the experimental data, an overall R2 value of 0.98 was achieved between experimental and model prediction, implying the robustness of the model's calibration. Originality/value: In this study, a viscoplastic constitutive model was developed that considers the combined effect of temperature and strain rate for FDM-printed PLA experiencing extensive compression. Using appropriate temperature-dependent modulus and flow rate properties, a single set of model parameters predicted the rise in the gap between yield stress and degree of softening as strain rates and temperatures increased. [ABSTRACT FROM AUTHOR]

Ball end magnetorheological finishing (BEMRF) is a process employed for precision finishing of flattened, intricate form complex 3D surfaces up to the nano level. Roughness of a surface determines the quality of results produced, which is usually measured by stylus-based instruments, with some optical methodologies also being adopted. These conventional methods when used for BEMRF tend to introduce errors in the part, which have to be removed from its fixture for measurement, and it is not feasible to remount it in the exactly same orientation again. Applications such as insular finishing (i.e., confined to a narrow region on the workpiece) demand the workpiece to be kept in the same orientation throughout, leading to requirement of measuring roughness in situ during the BEMRF process. A confocal sensor fits the requirement because of its confined design and lightweight capabilities. This work presents integration of a confocal sensor into the BEMRF setup for in situ roughness measurement. An initial Ra value of 352 nm was reduced to 289 nm just by insular finishing before finishing the full surface down to 78 nm in the case of a grinding error, from 420 nm to 342 nm by insular finishing, and finally down to 142 nm in the case of lapping error. [ABSTRACT FROM AUTHOR]