Tham khảo tài liệu 'mechanical properties of engineered materials 2008 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3 Basic Definitions of Stress and Strain INTRODUCTION The mechanical properties of materials describe their characteristic responses to applied loads and displacements. However most texts relate the mechanical properties of materials to stresses and strains. It is therefore important for the reader to become familiar with the basic definitions of stress and strain before proceeding on to the remaining chapters of this book. However the well-prepared reader may choose to skip skim this chapter and then move on to Chap. 4 in which the fundamentals of elasticity are introduced. The basic definitions of stress and strain are presented in this chapter along with experimental methods for the measurement and application of strain and stress. The chapter starts with the relationships between applied loads displacements and geometry that give rise to the basic definitions of strain and stress. Simple experimental methods for the measurement of strain and stress are then presented before describing the test machines that are often used for the application of strain and stress in the laboratory. BASIC DEFINITIONS OF STRESS The forces applied to the surface of a body may be resolved into components that are perpendicular or parallel to the surface Figs a c . In Copyright 2003 Marcel Dekker Inc. Figure Different types of stress a uniaxial tension b uniaxial compression c twisting moment. After Ashby and Jones 1996. Courtesy of Butterworth Heinemann. Copyright 2003 Marcel Dekker Inc. cases where uniform forces are applied in a direction that is perpendicular to the surface . along the direction normal to the surface Figs a and b we can define a uniaxial stress Ơ in terms of the normal axial load Pn divided by the cross-sectional area A. This gives _ Applied load normal to surface Pn cross-sectional area A It is also apparent from the above expression that stress has SI units of newtons per square meter N m2 or pascals Pa . Some older texts and
