The article discusses the mathematical representation of the multiaxial Bauschinger effect, a phenomenon where the elastic limit of a material changes after tensile loading, and vice versa, in compression. The authors, C.O. Frederick and P.J. Armstrong, were consultants and researchers at the Central Electricity Generating Board (CEGB) in the 1960s. They developed a model that accurately represents the Bauschinger effect and other inelastic behaviors of materials, which was later recognized and used by Jean-Louis Chaboche in his work on viscoplastic constitutive equations. The article highlights the importance of accurate constitutive models in predicting the behavior of materials under cyclic and multiaxial loads, particularly in high-temperature applications. The authors' model, based on the concept of internal microstress, was found to be more accurate than previous models and has been widely cited in the literature. The model's simplicity and effectiveness have made it a valuable tool in finite element analysis and other computational methods. The article also provides a historical context, detailing the development of the model within the CEGB and the subsequent career paths of Frederick and Armstrong. It mentions that the model was initially published internally but never officially in the open literature, and its significance was only recognized later by Chaboche, who independently discovered it and incorporated it into his own research. The article concludes by acknowledging the contributions of Frederick, Armstrong, and Chaboche, and by providing a detailed mathematical representation of the multiaxial Bauschinger effect, along with references to the original CEGB report.The article discusses the mathematical representation of the multiaxial Bauschinger effect, a phenomenon where the elastic limit of a material changes after tensile loading, and vice versa, in compression. The authors, C.O. Frederick and P.J. Armstrong, were consultants and researchers at the Central Electricity Generating Board (CEGB) in the 1960s. They developed a model that accurately represents the Bauschinger effect and other inelastic behaviors of materials, which was later recognized and used by Jean-Louis Chaboche in his work on viscoplastic constitutive equations. The article highlights the importance of accurate constitutive models in predicting the behavior of materials under cyclic and multiaxial loads, particularly in high-temperature applications. The authors' model, based on the concept of internal microstress, was found to be more accurate than previous models and has been widely cited in the literature. The model's simplicity and effectiveness have made it a valuable tool in finite element analysis and other computational methods. The article also provides a historical context, detailing the development of the model within the CEGB and the subsequent career paths of Frederick and Armstrong. It mentions that the model was initially published internally but never officially in the open literature, and its significance was only recognized later by Chaboche, who independently discovered it and incorporated it into his own research. The article concludes by acknowledging the contributions of Frederick, Armstrong, and Chaboche, and by providing a detailed mathematical representation of the multiaxial Bauschinger effect, along with references to the original CEGB report.