Olga I. Bylya

On the Behavior of Ti Alloys during Deforming in Near Superplastic Regimes

Traditionally, conditions under which superplastic deformation of poly crystalline material takes place include certain ranges of temperatures, strain rates and some limitations on the grain size. However neither exact criteria, nor mathematically formulated and determined domain of superplasticity are currently developed. In this article attempts are made to formulate the notion of the superplastic domain and its boundaries. To illustrate the behavior of the material near the boundary of the domain the results of the experiments on Ti‐6A1‐4V alloy with β‐annealed microstructure are presented.

Experimental Study of the Mechanical Behavior of Materials under Transient Regimes of Superplastic Deforming

Transient regimes of deforming are always present in any technological process and can be taken into account and used more widely if properly studied. The behavior of the materials under such regimes is becoming even more interesting if initial microstructure is coarse grained and undergoes transformation in the process of deforming. One of the transient processes which happen in any Superplastic deformation is the initial stage of loading, before steady superplastic flow starts. Initial parts of stress-strain curves during superplastic deformation are not frequently studied experimentally but provide very important information about mechanical properties of material. They are also necessary for development and verification of the constitutive equations. The results of experimental analysis of the behaviour of titanium alloys under superplastic conditions at the initial stages of loading and also under unloading are presented here. Another type of transient regimes of deforming is represented by the strain rate jumps. In such kind of experiments if the amplitudes of the jumps are big enough, the shifts of the corresponding parts of the stress-strain curves about the basic ones (hardening or softening) can be observed depending on the amplitude of the jump and microstructure of the material. Some experimental results related to this effect are discussed in this paper. The applicability of some constitutive equations for description of the observed results is discussed. The necessity of involving visco-elastic properties of material for proper description of its behavior in some regimes of deforming is also mentioned.

Development of a Variant of Scalar Constitutive Equations Suitable for Description of the near Super-Plastic Regimes of Deforming

When deformations are carried out with fine grained microstructure and within a narrow range of strain rates and temperature, metals and ceramics have been shown to exhibit superplastic behavior. Under these conditions the material demonstrates unusually high elongation with a relatively stable microstructure. But when the above mentioned parameters lie beyond a limit, near superplastic behavior is observed. The microstructure changes actively during the process of deformation and the response of the material becomes dependant on the history of loading. A model to describe the dependence on loading history by taking into account the change in microstructure is proposed. The model predicts the general trends observed and also provides possible explanation to some of the effects observed in the experimental data.

The mechanics of superplastic forming: how to incorporate and model superplastic and superplastic-like conditions

Much work has been carried out in understanding the mechanics of superplasticity (SP). Some of the present challenges in SP forming revolve around the use of lower forming temperatures and faster strain rates, which may involve pushing the process boundaries to incorporate “superplastic-like” forming – perhaps also in materials with non-optimized microstructures. For process optimization there is a requirement to be able to model both within the SP and superplastic-like processing window in an integrated way. From a mechanics point of view the presence of high rate sensitivity is often seen as the key factor in controlling SP response. However, changes in phase distribution and grain morphology, or the accumulation of damage (cavitation) may compromise this assumption. The paper will examine the range of validity of some SP constitutive models and how they may be adapted to take into account processing routes that may incorporate superplastic-like and more conventional SP deformation modes.

A Study on Variation of Microstructural Parameters in Titanium Alloys during near Superplastic Regime of Deformation

Deformation of Titanium alloys close to optimal superplastic condition i.e. near superplastic regime of deformation leads to significant change in microstructures.VT-9 titanium alloy was used in order to find out those parameters of microstructure which are varying significantly during near superplastic regime of deformation. Tensile tests were carried out at 930°C up to fracture with a constant strain rate of 5*10-4 s-1 and a jump wise varying strain rate of 1*10-4 s-1 & 5*10-4 s-1 .The microstructural parameters of both air-cooled and water quenched portion i.e. size of alpha phase, percentages of alpha phase and parameter of non-uniaxiality of alpha phase were found to change significantly during near superplastic regime of deformation. It has been found that in the near superplastic regime of deformation percentage of α-phase decreased from 90% to 13%. As the β-transus temperature of this alloy is 970°C, this significant change in percentage of α-phase is attributed to deformation induced phase transformation. Optical microscopes, micro Vickers hardness test, XRD, FESEM have been used to characterize the microstructure of the material.

Optimization of the Accuracy of Automotive Parking for the Car-Type Mobile Robot

The autonomous ability of the system, which enables it to park itself without any human interference, finds its application mostly in automobile industry. Though the basic algorithm of autonomous parking is relatively simple, the question of reliability and accuracy of parking can be quite complicated. The mathematical models developed theoretically and simulated numerically not always can in the same accurate way perform in a real vehicle. One of the main reasons for it is the interplay between the controlling system and mechanical structure of the vehicle. To investigate this problem the car-type robot simulating the specific features of the mechanical structure of the real car was developed. It was used for verification of few parking approaches proposed in the literature. A parking algorithm was proposed and programmed for a developed car-type robot. The experimental comparison between theoretically calculated and actually observed values of main parking parameters was done and analysed. The approach of optimization of parking strategy from the view point of minimization of positioning errors was proposed and tested.

Development and Optimization of Perimeter Traversing Robot

This paper presents the development and optimization of control parameters of an autonomous robot capable of traversing a planar surface without going beyond the surface boundary. Based on standard Lego® design, the proposed robot travels on surfaces with different geometrical shapes and collects data on the basis of which the perimeter can be redrawn using MATLAB. The remote detection capabilities of this robot can find its application in construction, defence surveillance operations, geological and space research and industry as an automated process of measurement, especially when the surface being measured is beyond human reach. The robot detects the edge using a color sensor which differentiates the color of the surface from its boundary. After detecting an edge point, the robot retracts and turns to detect an edge point in another direction. The length of the paths traversed by the robot from one edge point to another serves as the input data to the MATLAB program which computes this data and transforms it to a plot of the perimeter. Experiments conducted demonstrate the optimal values of parameters for control of motion of the robot to give satisfactory results with minimal power and time expenditure.