Aspects of high strain rate industrial forging of Inconel 718

The major part of all material and microstructural data used for the modelling of nickel superalloy forgings is obtained from uniaxial laboratory tests with limited plastic strain and very simple thermo-mechanical history. At the same time, new challenges in near net shape industrial forging require a high level of reliability of modelling prediction of metal flow, for predicting the risk of defects and microstructural transformation. A few recently conducted benchmarking studies have shown that despite the availability of various material models (including microstructural ones) embedded in commercial FE software, in many cases, the level of prediction remains unsatisfactory. This is especially true for fast industrial forging processes (like screw press or hammer forgings). This paper suggests a methodology for processing the results from industrial forgings for obtaining robust data for calibration, validation, and improvement of material and microstructural models. This also can provide additional information on the material science behind the microstructural phenomena, which are problematic to capture and study using simple uniaxial tests

Modelling challenges for incremental bulk processes despite advances in simulation technology : example issues and approaches

Incremental bulk deformation processes have traditionally been difficult to simulate. This paper will argue that, despite advances in computation and software, they remain difficult to model. The main reason for this is the shortage of ideas on what is the real objective of FE modelling for such processes. Even a very detailed model and data obtained in simulation does not give answers to the main question - how to optimise the process parameters? High computational time and volume of information only aggravate the situation. All modern mathematical techniques of dimensionality reduction (such as POD/PGD) lose their power when the priorities and acceptable compromises of modelling are not clear. This paper tries to use a large volume of available experimental and modelling experience to illustrate this problem and look for possible break-through directions

Physical modelling for metal forming processes

Physical modelling has a long established history for the investigation of metal forming and other manufacturing processes. In recent times however its place and importance has diminished somewhat as a direct consequence of advances made in numerical modelling techniques. This paper re-examines the place of physical modelling and by means of selected examples demonstrates the benefits of the approach. Physical modelling often provides an indirect representation of the physics under consideration and may often involve scaling and the use of cheaper substitute materials. A question posed that has in some respects contributed to the diminution of physical modelling is whether the physical model is representative of the physics involved. Related to this question is a new approach to scaled experimentation that has appeared in the recent literature. The new approach is founded on the scaling of space itself and although the idea that space expands and distorts is not new to physics (e.g. cosmology and general relativity) its application to physical modelling is considered completely novel. The scaling concept enables the physics of processes to be projected into a scaled space and vice versa, thus providing quantification of the validity of any physical model. This aspect fortifies a particular weakness in the physical modelling approach making its reappraisal particularly timely. Selected numerical and experimental trials are being designed to showcase and reveal the benefits, validity and renewed importance of physical modelling

An approach for modeling the active transformation of microstructure of two-phase Alloys in FEM simulation of technological chains in superplastic forming (SPF)

Optimization and broadening of the technological regimes of superplastic forming require more accurate accounting of the transformation of microstructure during all stages of the forming process. On the one hand, it is very important to predict the resultant microstructure in different parts of the formed structure as it determines the operation properties, and on the other hand, active transformation of microstructure can lead to either hardening (grain coarsening) or softening (grain refinement) of the material. These changes in the mechanical behavior of a material can be quite significant and need to be taken into account in the FEM simulation of superplastic forming processes to achieve the required accuracy. One approach for modeling the microstructural transformation in an FEM simulation for a two-phase alloy is proposed herein. Constitutive model with internal variables is described. The questions of validity of macroscopic and microscopic equations are discussed. The approach for taking into account the transformation of metallographic texture is proposed

Mechanical behavior of titanium alloy Ti-6Al-4V with unprepared microstructure under jumpwise variations of the strain rate in the superplastic state

We present the results of extension tests with superplastic specimens made of structural titanium alloy with unprepared (coarse-grained) microstructure. The tests were performed at a constant temperature and constant or piecewise constant strain rate. It was shown that, in the case of a jumpwise decrease in the strain rate, the typical shape of the strain diagram depends on the test temperature. Some variations in the original microstructure are demonstrated