The paper by Hans Ziegler, titled "A Modification of Prager's Hardening Rule," discusses the response of rigid-work-hardening materials, focusing on the yield condition, flow rule, and hardening rule. The initial yield condition is represented as a surface in stress space, and the flow rule connects the plastic strain increment with stress and stress increment. Prager's hardening rule, which assumes a rigid yield surface that translates in the direction of the strain increment, accounts for the Bauschinger effect but is not invariant under dimension reductions. Ziegler proposes a modified hardening rule that retains the translation but in the direction of the vector connecting the center of the yield surface with the stress point. This modification simplifies certain applications, particularly in subspaces, and allows for the adjustment of the hardening rule to arbitrary non-linear laws in simple tension and compression. However, it introduces indeterminacy in the strain increment at corners or vertices of the yield surface, similar to perfectly plastic materials. The paper compares the modified rule with Prager's rule, noting that while the modified rule is easier to handle in some applications, it may not be physically as satisfactory.The paper by Hans Ziegler, titled "A Modification of Prager's Hardening Rule," discusses the response of rigid-work-hardening materials, focusing on the yield condition, flow rule, and hardening rule. The initial yield condition is represented as a surface in stress space, and the flow rule connects the plastic strain increment with stress and stress increment. Prager's hardening rule, which assumes a rigid yield surface that translates in the direction of the strain increment, accounts for the Bauschinger effect but is not invariant under dimension reductions. Ziegler proposes a modified hardening rule that retains the translation but in the direction of the vector connecting the center of the yield surface with the stress point. This modification simplifies certain applications, particularly in subspaces, and allows for the adjustment of the hardening rule to arbitrary non-linear laws in simple tension and compression. However, it introduces indeterminacy in the strain increment at corners or vertices of the yield surface, similar to perfectly plastic materials. The paper compares the modified rule with Prager's rule, noting that while the modified rule is easier to handle in some applications, it may not be physically as satisfactory.