The main purpose of this paper is to introduce the five following papers on inverse problems, and to relate the field of inverse problems to measurements. Inverse techniques are an emerging suite of methods which, when fully embraced, promise to provide better experiments and improved understanding of physical processes. This paper provides an overview of the general procedure and concepts related to identification of parameters or functions by inverse techniques. A discussion of errors and their implication for an appropriate function for minimization in inverse procedures is presented, and two methods for achieving this minimization are discussed. Some sequential concepts for parameter estimation are presented, along with a discussion of residuals and confidence intervals. Experiment design and optimization are reviewed, and a discussion of residuals and their relation to model building is presented.

Work materials experience large strains, high strain rates, high temperatures, and complex loading histories in machining. The problem of how to accurately model dynamic material behavior, including the adiabatic effect is essential to understand a hard machining process. Several conventional constitutive models have often been used to approximate flow stress in machining analysis and simulations. The empirical or semiempirical conventional models lack mechanisms for incorporating isotropic/kinematic hardening, recovery, and loading history effects. In this study, the material constants of AISI 52100 steel (62 HRc) were determined for both the Internal State Variable (ISV) plasticity model and the conventional Johnson-Cook (JC) model. The material constants were obtained by fitting the ISV and JC models using nonlinear least square methods to same baseline test data at different strains, strain rates, and temperatures. Both models are capable of modeling strain hardening and thermal softening phenomena. However, the ISV model can also accommodate the adiabatic and recovery effects, while the JC model is isothermal. Based on the method of design of experiment, FEA simulations and corresponding cutting tests were performed using the cutting tool with a 20 deg chamfer angle. The predicted chip morphology using the ISV model is consistent with the measured chips, while the JC model is not. The predicted temperatures can be qualitatively verified by the subsurface microstructure. In addition, the ISV model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.

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