Приложение к билету для экзамена по сдаче кандидатского минимума. Mеchanical constitutive models for cast metals at high temperatures

МИНИСТЕРСТВО ОБРАЗОВАНИЯ РЕСПУБЛИКИ БЕЛАРУСЬ

ГОМЕЛЬСКИЙ ПОЛИТЕХНИЧЕСКИЙ ИНСТИТУТ им.П.О.СУХОГО

Кафедра белорусского и иностранного языков.

Приложение к билету для экзамена по сдаче кандидатского минимума.

английский язык

Вопрос 1 . Чтение и адекватный перевод оригинального текста по специальности аспиранта (соискателя).

Шифр: 05.16.04.

Mеchanical constitutive models for cast metals at high temperatures.

Basic principles

Solving of any problem related to stress calculations requires an assumption of a constitutive equation for the cast material. this being a relationship between stress and strain or strain rate. In other words, a constitutive equation describes the mechanical response of a material to an external load or deformation.

The constitutive equations for cast metals must take into account wide temperature ranges over which stresses and deformation occur, particularly the highest homologous temperature range. This implies some requirements for the equations, the most essential of which can be summarized as follows (l):

· the material should be treated as an elasto-visco-plastic body, i.e. time-dependent plastic behaviour cannot be ignored:

· temperature must be included, either directly or through a temperature dependence of material constants:

· the equations must include a dependence of stress on temperature and strain-rate deformation history, since deformations performed at different temperatures or strain rates produce different internal microstructures of the material.

The stress dependence of the non-elastic portion of strain is more complex. The visco-plastic properties of most metallic materials depend strongly on temperature (and on strein rate), because both the flow of the material (i.e. movement of dislocations) and the structural changes can be thermally activated processes. The recovery of strain-hardened structure, being a source of the stress dependence on deformation history, is thought to be the most important one and is usually included in constitutive equations ( I).

High-temperature behaviour of metals

The typical temperature-dependence of the mechanical properties of metallic alloys can be illustrated. for example, by curves of tensile flow stress obtained at a moderate strain rate. Guiding graphs for the main groups of alloys cast in metallic moulds are presented in Figure 2. In the high-temperature region (typically above 0.5 Т_m, where T_m, is the solidus temperature) the strong temperature dependence of the flow stress, due to themlally actilvated creep, can be observed, while at lower temperatures the so called 'athermal' behaviour, characterized by slopes of the stress-temperature curves equal to that resulting from the temperature dependence of the Young's modulus, is typical.

The temperatura dependence of the elastic moduli,for exampele the Young^,s modulus, requires a special attention. It is a common practice, that the values measured by static tensing, i.e. determined from the slopes of the initial, linear portions of the strain-stress curves obtained in tension or compression tests carried out at constant speed of the machine crosshead, are used for solving stress problems.

Ст. преподаватель___________________________Л.А.Хилькевич

Одобрено на заседании

кафедры 15.05.98

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