Text b Wear
In material and components science, wear is the erosion of material from a solid surface by the action of another surface. It is related to surface interactions and more specifically the removal of material from a surface as a result of mechanical action. Wear can also be defined as a process in which interaction of the surfaces of a solid with its working environment results in dimensional loss of the solid, with or without loss of material. Aspects of the working environment which affect wear include loads (such as sliding, reciprocating, rolling, and impact loads), speed, temperature, type of counterbody (solid, liquid or gas), and type of contact.
The working life of an engineering component is over when dimensional losses exceed the specified tolerance limits. Wear, along with other aging processes such as fatigue, creep and fracture toughness, causes progressive degradation of materials with time, leading to failure of material.
The complex nature of wear has delayed its investigations. Up to now there has been no specific standard for testing or measuring a materials wear resistance although a number of wear tests have been developed in an attempt to standardize wear testing for specific applications.
There are at least five types of wear:
Adhesive wear is the most common form of wear and occurs when two bodies slides over each other, or are pressed into one another, which promote material transfer between the two surfaces. Adhesive wear can be described as plastic deformation of very small fragments within the surface layer when two surfaces slides against each other.
Abrasive wear occurs when a hard rough surface slides across a softer surface. Abrasive wear is commonly classified according to the type of contact and the contact environment. The type of contact determines the mode of abrasive wear. The two of abrasive wear are known as two-body and three-body abrasive wear.
Surface fatigue is a process by which the surface of a material is weakened by cyclic loading. Fatigue wear is produced when the wear particles are detached by cyclic crack growth of microcarcks on the suface. These microcaraks are either superficial cracks or subsurface cracks.
Fretting wear is the repeated cyclical rubbing between two surfaces over a period of time which will remove material from one or both surfaces in contact. It occurs typically in bearings, although most bearings have their surfaces hardened to resist the problem.
Erosive wear is caused by the impact of particles of solid or liquid against the surface of an object. The impacting particles gradually remove material from the surface through repeated deformations and cutting actions
Задания к тексту B:
I. Найдите в тексте английские эквиваленты следующим русским выражениям:
материаловедение; сложная природа износа; поверхностная усталость; срок службы технического компонента; поверхностное взаимодействие; абразивный износ; процесс старения; адгезионный износ; потеря размеров твердого тела; эрозивный износ; усталость, ползучесть и трещиностойкость; фреттинг-износ; до сих пор;
II. Сформулируйте в нескольких словах содержание каждого абзаца.
III. Напишите резюме к тексту.
IV. Ответьте на вопросы:
What is wear?
What is wear related to?
How can wear also be defined?
What do aspects of the working environment which affect wear include?
When is the working life of an engineering component over?
What causes progressive degradation of materials with time?
What has delayed the wear investigations?
There has been no specific standard for testing or measuring a materials wear resistance up to now, has there?
Have a number of wear tests been developed in an attempt to standardize wear testing or to minimize wear for specific applications?
How many types of wear do you know?
What are they?
V. Перескажите текст, используя в качестве плана вопросы предыдущего упражнения.