Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

Abstract

This study investigates the problem of material fracture in cross wedge rolling (CWR). It was found that this problem could be analysed by means of well-known phenomenological criteria of fracture that are implemented in commercial FEM (Finite Element Method) simulation programs for forming processes. The accuracy of predicting material fracture depends on the critical damage value that is determined by calibration tests in which the modelled and real stresses must be in good agreement. To improve this accuracy, a new calibration test is proposed. The test is based on the CWR process. Owing to the shape of the tools and test piece used in CWR, the forming conditions in this process deteriorate with the distance from the centre of the test piece, which at a certain moment leads to fracture initiation. Knowing the location of axial crack initiation in the specimen, it is possible to determine the critical value of material damage via numerical simulation. The new calibration test is used to determine the critical damage of 42CrMo4 steel subjected to forming in the temperature range of 900–1100 °C. In addition, 12 criteria of ductile fracture are employed in the study. The results show that the critical damage significantly increases with the temperature.

Modernisation of the drop forging process on the example of forming a bracket forging

“…Świadczy o tym rozkład funkcji zniszczenia obliczonej zgodnie ze znormalizowanym Największe wartości funkcja ta przyjmuje w stopniu o najmniejszej średnicy od strony stopnia centralnego, gdzie prawdopodobnie dochodzi do skręcania materiału na skutek różnych prędkości obrotowych poszczególnych stopni przedmiotu obrabianego. Maksymalna wartość funkcji zniszczenia nie przekracza wartości 2 i jest znacznie mniejsza od wartości krytycznej, która dla stali w gatunku 42CrMo4 przy temperaturze 1138,7°C przyjmuje wartość 3,587 [13].…”

New Methodology for Predicting the Cracking Phenomenon in the Radial Extrusion Process of Hollow Parts with a Flange

“…They are described by an integral from a certain function, the value of which depends on the state of stress and strain that occurs in the material. The mentioned criteria include: Cockroft-Latham [8], Freudenthal [9], Brozzo [10], Norris [11], Ayad [12], Rice-Teracey [13], Argon [14], Zhan [15], Oyan [16], Ko [17]. Application of the above relationships requires knowledge of the value of the limiting integral, which is determined experimentally in appropriate calibration tests.…”

Improving the Performance Properties of Eutectoid Steel Products by a Complex Effect

“…The growing demand for rolled metal products quality is continuously connected to the fail-safe operation of forming rolls [ 1 ]. The analysis of the related publications on improving mechanical properties of the products’ working layer shows that improvements are carried out in the following main directions: optimization of the used materials chemical composition and development of new materials [ 2 , 3 ]; effective heat treatment methods development [ 4 , 5 ]; and development of the reliable methods for the massive product’s working layer quality control without any destruction [ 6 , 7 , 8 ].…”