Engr 270 LA -- Materials Science Experiment # 5a -- Tensile Properties of Materials: The Stress-Strain Diagram Objective: 1. To obtain an understanding of the tensile test for engineering materials. 2. To understand the significance of some of the primary plastic and elastic properties of engineering materials as derived from the tensile test. 3. To learn the procedure to operate a tensile testing machine using standard tensile samples. 4. To understand the construction of stress-strain diagrams and the determination of mechanical properties from such diagrams. Background: Many commercial specifications, insofar as they are concerned with the mechanical properties of a material, are based on the tensile test. A simple tensile test consists of slowly applying an axial force or load to a standard specimen by means of a suitable testing machine, and measuring dimensional changes that are produced at the various loads. The stretching in the direction of the load is of particular interest. The deformation per standard unit of length is called the (longitudinal) strain, ε. The normal stress, σ, is the force per unit area, where the area is based on the original cross-sectional area of the specimen perpendicular to the applied force. When a specimen is pulled to failure in a tensile testing machine, the stress-strain diagram may be obtained by plotting the values of stress as ordinates and the corresponding strains as abscissas. A proper analysis of this diagram will give the necessary information for the determination of the desired mechanical properties. The properties commonly considered are the ultimate strength, the yield strength (or yield point), and the degree of ductility as indicated by % elongation ε(+) and the % reduction-of-area AR. For a more complete understanding of the mechanical properties of the specimen, the Young’s Modulus of elasticity, E, the elastic limit or the proportional limit should be considered as well. In the most general way, we may define the mechanical strength of engineering materials as their ability to withstand loads without excessive distortion or failure. The simplest type of mechanical loading to analyze is static tension, and it is also commonly encountered in engineering structures. An understanding of the tensile properties of materials also helps predict the response of the material to other types of loading. We therefore begin our study of mechanical properties of materials with the static tension test. Elastic Behavior Elastic deformation is said to have occurred when a material, which has been deformed under load, returns to its original shape and dimensions when the load is removed. Elastic deformation in metals and ceramics occurs as a result of temporary extension of interatomic bonds during the application of the load. In other materials such as polymers, elastic deformation may involve the stretching and deformation of long chain molecules, or more complex phenomena. In the elastic range of metals, the strain occurs essentially in linear proportion to the applied stress. The constant of proportionality between stress and strain is the Young’s modulus of elasticity, E. 1
Engr 270 LA -- Materials Science Experiment # 5a -- Tensile Properties of Materials: The Stress-Strain Diagram
Jun 24, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
