In hot rolling, the quantities rolling load, torque, and power consumption are important measurable process parameters. For the determination of rolling loads in hot flat rolling processes, like heavy plate rolling, Sims's model1 is a well‐known approach represented by an analytical formula. The solution of Sims's equation leads to the multiplier Q, which is a function of the roll gap geometry. The rolling load is then computed by applying the width of the plate, the contact length, the multiplier, and an average material flow stress called kfm. This flow stress is commonly recalculated from process data as a function of temperature, pass strain, and a mean strain rate, applying the Sims model itself. One question arises from this method: Are the recalculated flow stresses physically based values or in other words, what is the (physical) meaning or interpretation of these values? The present paper tries to give an answer to this question by determining the influence of the roll gap geometry alternatively by means of a simple 2D FEM model which gives a corresponding multiplier referred to as QFE. Flow stresses are recalculated from a set of process data using both factors. The results are compared to experimental flow stress data from hot compression tests. It is shown, that the recalculated flow stresses using QFE are in better agreement with the laboratory data than the recalculated values using Sims's Q.
The time-dependent inhomogeneous temperature distribution during the cooling of steel plates gives rise to thermal strains which, in turn, generate plastification and thus residual stresses. Moreover, transformation from the parent austenite phase into a product phase typically entails not only metallurgical strains but also accounts for transformation induced plasticity (TRIP), which again generates transformation related residual stresses. It is the goal of this paper to build a unified model that takes into account all relevant contributions to the total strain rate, i.e., elastic, plastic, thermal, metallurgical and TRIP strain contributions. The material parameters relevant for TRIP are determined by means of dilatometric tests as well as by purely numerical means. For the evolution of the product phase a kinetic relationship will be presented that allows differentiating between different local cooling rates. It is set up with an Avrami-like approach, specially designed for complex cooling histories. The material model is implemented into the commercial finite element package ABAQUS, which allows to simulate the evolution of the residual stresses in heavy steel plates after complete cool-down to room temperature.
The influence of a residual stress field on the fatigue crack growth was investigated by a numerical simulation for an inclined elliptically shaped subsurface crack in a half space. The necessary opening mode stress intensity factors Kl caused by the resulting stress field were calculated by means of the singular integral equation method. The crack growth analyses were conducted by the application of linear elastic fracture mechanics using the Paris law relationship between Kl and da/dN.
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