A Convex Route to Thermomechanics: Learning Internal Energy and Dissipation

TL;DR

This paper introduces a neural network framework for discovering thermomechanical constitutive models using internal energy and dissipation potentials, ensuring thermodynamic consistency and convexity.

Contribution

It proposes a novel approach that avoids mixed convexity conditions by using input convex neural networks for internal energy and dissipation, enabling thermodynamically consistent modeling.

Findings

Accurately captures constitutive behavior in synthetic and experimental datasets.

Ensures thermodynamic admissibility through neural network architecture.

Successfully models coupled thermomechanical responses of soft tissues and rubbers.

Abstract

We present a physics-based neural network framework for the discovery of constitutive models in fully coupled thermomechanics. In contrast to classical formulations based on the Helmholtz energy, we adopt the internal energy and a dissipation potential as primary constitutive functions, expressed in terms of deformation and entropy. This choice avoids the need to enforce mixed convexity--concavity conditions and facilitates a consistent incorporation of thermodynamic principles. In this contribution, we focus on materials without preferred directions or internal variables. While the formulation is posed in terms of entropy, the temperature is treated as the independent observable, and the entropy is inferred internally through the constitutive relation, enabling thermodynamically consistent modeling without requiring entropy data. Thermodynamic admissibility of the networks is guaranteed by construction. The internal energy and dissipation potential are represented by input convex neural networks, ensuring convexity and compliance with the second law. Objectivity, material symmetry, and normalization are embedded directly into the architecture through invariant-based representations and zero-anchored formulations. We demonstrate the performance of the proposed framework on synthetic and experimental datasets, including purely thermal problems and fully coupled thermomechanical responses of soft tissues and filled rubbers. The results show that the learned models accurately capture the underlying constitutive behavior. All code, data, and trained models are made publicly available via https://doi.org/10.5281/zenodo.19248596.