Knowles Lecture

Tuesday, February 3, 2026, 9:00am - 4:30pm
135 Gates•Thomas, Jim & Sandy Hall Auditorium

The 15th annual James K. Knowles Lectures and Caltech Solid Mechanics Symposium will be held on Tuesday, February 3, 2026, in the Jim & Sandy Hall Auditorium in Gates•Thomas. The James K. Knowles Lecture will be followed by the Solid Mechanics Symposium with presentations by current Caltech graduate students and postdocs.

The Lectures and Symposium are in memory of James K. Knowles, William J. Keenan, Jr. Professor of Applied Mechanics, Emeritus, who passed away on November 1, 2009. He is well known for his research contributions to the theory of nonlinear elasticity and the mathematical theories of materials and structures. Dr. Knowles inspired and influenced generations of students and scholars and authored over one hundred journal publications, as well as a textbook for graduate students entitled Linear Vector Spaces and Cartesian Tensors (Oxford University Press).

The Lectures and Symposium will be held annually and are made possible by the Division of Engineering and Applied Science and the support of family, friends and colleagues through donations to the James K. Knowles Memorial Fund.

James K. Knowles Lecture

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Laura De Lorenzis, Full Professor at the Department of Mechanical and Process Engineering, ETH Zürich

Variational phase-field modeling of fracture: toward second-generation models

Variational phase-field models of brittle fracture are powerful tools for studying Griffith-type crack propagation in complex scenarios. However, as approximations of Griffith's theory—which does not incorporate a strength criterion—these models lack flexibility in prescribing material-specific strength surfaces. Consequently, they struggle to accurately capture crack nucleation under multiaxial stress conditions. For this reason, many recently proposed models have given up the elegance and the theoretical and practical advantages of the variational setting to achieve greater flexibility in reproducing experimental observations.

In this presentation, we explore recent strategies developed in the group of the speaker to endow variational phase-field models with sufficient flexibility to overcome current limitations, potentially paving the way for a second generation of variational phase-field fracture models. For fracture under multiaxial stress states, we first illustrate the pros and cons of models based on the notion of energy decomposition and propose a new model of this type that controls the competition between nucleation under compressive and tensile stresses. Then, we illustrate a novel phase-field model of cohesive fracture that allows for an arbitrarily shaped convex strength surface, thereby reconciling fracture nucleation and propagation within a unified framework. Finally, we illustrate further recent results on phase-field modeling of cohesive fracture in anisotropic materials and under dynamic conditions.

Laura De Lorenzis received her Engineering degree and her PhD from the University of her hometown Lecce, in southern Italy, where she began her academic career. In 2013 she moved to the TU Braunschweig, Germany, as Professor and Director of the Institute of Applied Mechanics. Since 2020 she is Professor of Computational Mechanics at ETH Zürich. She was visiting scholar in several institutions, including Chalmers University of Technology, the Hong Kong Polytechnic University, MIT (with a Fulbright Fellowship), the University of Hannover (with an Alexander von Humboldt Fellowship), the University of Texas at Austin and the University of Cape Town. She is the recipient of several prizes, including the RILEM L'Hermite Medal 2011, the AIMETA Junior Prize 2011, the IIFC Young Investigator Award 2012, the Euromech Solid Mechanics Fellowship 2022, the IACM Fellowship 2024, two best paper awards and two student teaching prizes. In 2011 she was awarded a European Research Council Starting Researcher Grant. She has delivered over 30 plenary lectures at international conferences and authored or co-authored more than 160 papers on international journals on different topics of computational and applied mechanics. Since 2023 she is Editor of Computer Methods in Applied Mechanics and Engineering.