上海交通大学：《工程学导论》课程教学资源（讲义）Technical knowledge_2Materials&ME

Introduction to Engineering-Materials Materials and Engineering Shanghai Jiao Tong University 1 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 1 Materials and Engineering

Introduction to Engineering-Materials Contents 1.Introduction 2.Material Properties 3.Selection of Materials Objectives Understand how material properties are used to qualify materials for engineering design Understand how traditional and composite materials are used in engineering design Shanghai Jiao Tong University 2 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 2 Contents 1. Introduction 2. Material Properties 3. Selection of Materials Objectives  Understand how material properties are used to qualify materials for engineering design  Understand how traditional and composite materials are used in engineering design

Introduction to Engineering-Materials 1.Introduction Materials The foundation and fabric of manufactured products Mechanical design is dependent on and limited by materials Properties of materials are usually the deciding factor in choosing materials for a particular application ■Material science: The study of the structure and properties of any material - Using this body of knowledge to create new types of materials To tailor the properties of a material for specific uses New materials and processes enable other new technologies to be commercially successful Shanghai Jiao Tong University 3 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 3 1. Introduction  Materials  The foundation and fabric of manufactured products  Mechanical design is dependent on and limited by materials  Properties of materials are usually the deciding factor in choosing materials for a particular application  Material science : – The study of the structure and properties of any material – Using this body of knowledge to create new types of materials – To tailor the properties of a material for specific uses  New materials and processes enable other new technologies to be commercially successful

Introduction to Engineering-Materials 2.Material Properties The principal properties of materials can be broadly divided into Mechanical Properties concerned mainly with strength Physical Properties such as melting temperature,density, etc Shanghai Jiao Tong University 4 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 4 2. Material Properties Mechanical Properties ( concerned mainly with strength ) Physical Properties ( such as melting temperature,density, etc ) The principal properties of materials can be broadly divided into :

Introduction to Engineering-Materials 2.1 Stress-Strain Curve ■Test specimen “dog bone?”specimen Materials Testing Machine ■Tensile test process A specimen is clamped by two jaws Jaws are gradually pulled apart during the test,placing the specimen in tension Shanghai Jiao Tong University 5 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 5 2.1 Stress-Strain Curve “dog bone” specimen  Test specimen  Materials Testing Machine  Tensile test process  A specimen is clamped by two jaws  Jaws are gradually pulled apart during the test, placing the specimen in tension

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. low￾carbon 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