Introduction to Engineering-Materials 2.1 Stress-Strain Curve ● A sensor that measures force is attached to one of the jaws A second sensor,called an extensometer,is used to measure the elongation A computer records the force and elongation data during the measurement,and those values are then converted to stress and strain Shanghai Jiao Tong University 6 Introduction to Engineering H.Shao
Introduction to Engineering Introduction to Engineering —— Materials Materials Shanghai Jiao Tong University Shanghai Jiao Tong University Introduction to Engineering Introduction to Engineering H. Shao 6 A sensor that measures force is attached to one of the jaws A second sensor, called an extensometer, is used to measure the elongation A computer records the force and elongation data during the measurement, and those values are then converted to stress and strain 2.1 Stress-Strain Curve
Introduction to Engineering-Materials 2.1 Stress-Strain Curve Stress-strain curve An idealized stress-strain curve for a ductile material (e.g.low- carbon steel) Ductile:the ability of a material to withstand a significant amount of stretching before it breaks Ductile materials:hard to break E ·Aluminum,low carbon steel Brittle materials:easy to break cast iron,concrete, ceramics,and glass Strain,a Shanghai Jiao Tong University 7 Introduction to Engineering H.Shao
Introduction to Engineering Introduction to Engineering —— Materials Materials Shanghai Jiao Tong University Shanghai Jiao Tong University Introduction to Engineering Introduction to Engineering H. Shao 7 2.1 Stress-Strain Curve Strain,ε Stress, σ A B C D E Stress-strain curve An idealized stress-strain curve for a ductile material (e.g. lowcarbon steel) Ductile: the ability of a material to withstand a significant amount of stretching before it breaks Ductile materials: hard to break • Aluminum, low carbon steel Brittle materials: easy to break • cast iron, concrete, ceramics, and glass
Introduction to Engineering-Materials 2.1 Stress-Strain Curve Elastic and Plastic Regions The low-strain elastic region(no permanent deformation) The higher-strain plastic region(permanently elongated) ■ Most engineering designs tend to avoid the plastic E region Within the linear region ■All stresses in the structure or component must be below the yield Strain,a stress Elastic region Plastic region Shanghai Jiao Tong University 8 Introduction to Engineering H.Shao
Introduction to Engineering Introduction to Engineering —— Materials Materials Shanghai Jiao Tong University Shanghai Jiao Tong University Introduction to Engineering Introduction to Engineering H. Shao 8 2.1 Stress-Strain Curve Elastic and Plastic Regions The low-strain elastic region (no permanent deformation) The higher-strain plastic region (permanently elongated) Most engineering designs tend to avoid the plastic region Within the linear region All stresses in the structure or component must be below the yield stress Strain,ε Stress, σ A B C D E Elastic region Plastic region
Introduction to Engineering-Materials 2.1 Stress-Strain Curve Proportional Limit -When strains below the proportional limit A .Stress and strain are linearly related according to o=E8 .The quantity E is a material property. It is measured simply as the B slope of the stress-strain curve in E A its straight-line region Proportional limit Modulus,E Strain,a Shanghai Jiao Tong University 9 Introduction to Engineering H.Shao
Introduction to Engineering Introduction to Engineering —— Materials Materials Shanghai Jiao Tong University Shanghai Jiao Tong University Introduction to Engineering Introduction to Engineering H. Shao 9 2.1 Stress-Strain Curve Proportional Limit –When strains below the proportional limit A •Stress and strain are linearly related according to •The quantity E is a material property. • It is measured simply as the slope of the stress-strain curve in its straight-line region Strain,ε Stress, σ A B C D E Modulus, E Proportional limit E
Introduction to Engineering-Materials 2.1 Stress-Strain Curve Elastic Limit Point B is called the elastic limit. - For loading between points A and B,the material continues to behave elastically It will spring back upon removal of the force,but the stress and strain are no longer proportional D B E Elastic limit Strain.a Shanghai Jiao Tong University 10 Introduction to Engineering H.Shao
Introduction to Engineering Introduction to Engineering —— Materials Materials Shanghai Jiao Tong University Shanghai Jiao Tong University Introduction to Engineering Introduction to Engineering H. Shao 10 2.1 Stress-Strain Curve Elastic Limit – Point B is called the elastic limit. – For loading between points A and B, the material continues to behave elastically – It will spring back upon removal of the force, but the stress and strain are no longer proportional Strain,ε Stress, σ A B C D E Elastic limit