A Possibility for Quantitative Detection of Mechanically-Induced Invisible Damage by Thermal Property Measurement via Entropy Generation for a Polymer Material

Abstract

Entropy generation from a mechanical and thermal perspective are quantitatively compared via molecular dynamic (MD) simulations and mechanical and thermal experiments. The entropy generation values regarding mechanical tensile loading—which causes invisible damage—of the Polyamide 6 (PA6) material are discussed in this study. The entropy values measured mechanically and thermally in the MD simulation were similar. To verify this consistency, mechanical and thermal experiments for measuring entropy generation were conducted. The experimentally obtained mechanical entropy was slightly less than that calculated by MD simulation. The thermal capacity is estimated based on the specific heat capacity measured by differential scanning calorimetry (DSC), applying the assumed extrapolation methods. The estimated entropy generation was higher than the aforementioned values. There is a possibility that the entropy-estimating method used in this study was inappropriate, resulting in overestimations. In any case, it is verified that entropy increases with mechanical loading and material invisible damage can be qualitatively detected via thermal property measurements.

Molecular Dynamics Simulation of Cumulative Microscopic Damage in a Thermosetting Polymer under Cyclic Loading

“…We focus on the degradation of mechanical properties, entropy generation, and void content inside the system. Entropy is expected to serve as a physical quantity for quantitatively measuring the degradation of materials, such as the difficult-to-measure bond dissociation and void content in experiments [51][52][53][54]. Therefore, verifying the correlation between entropy and bond dissociation or void content is highly significant for assessing the remaining life of CFRP.…”

A Molecular Dynamics Simulation for Thermal Activation Process in Covalent Bond Dissociation of a Crosslinked Thermosetting Polymer

“…This study investigates the time evolutions of covalent bond dissociation and fracture behavior of a thermosetting polymer based on molecular dynamics (MD) simulation, which is essential for elucidating microscopic damage mechanisms of matrix crack and transverse crack in CFRPs. MD simulation has been applied to polymers [ 7 , 8 , 9 , 10 ], reinforcements [ 11 , 12 ], and their composites [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ], which have quantitatively reproduced thermomechanical properties near equilibrium state such as density, Young’s modulus, and glass transition temperature. Characteristics in the higher-strain region, where covalent bond dissociation is involved, remain challenging to simulate.…”

Durability Analysis of CFRP Adhesive Joints: A Study Based on Entropy Damage Modeling Using FEM

“…Additionally, the fatigue life estimation of CFRP was assessed by considering both confidence levels and reliability. Koyanagi et al [36][37][38][39][40] recently formulated a computational approach that integrates entropy damage to analyze the failure mechanism of a viscoelastic matrix and CFRP cross-ply laminates.…”