Behaviour of Iron and Steel Materials during Tensile Testing Aug28

Behaviour of Iron and Steel Materials during Tensile Testing...

Behaviour of Iron and Steel Materials during Tensile Testing The mechanical properties of iron and steels are often assessed through tensile testing. The testing technique is well standardized and can be conducted economically with a minimum of equipment. Since iron and steel materials are being utilized in structural applications, they are to have tensile properties which meet the requirements of the relevant codes and standards. These requirements in the code and standards are the minimum strength and ductility levels. Due to this, information available from tensile testing is often underutilized. However, direct examination of many of the metallurgical interactions which influence the results of tensile testing can considerably improve the usefulness of the testing data. Examination of these interactions, and correlation with metallurgical / material /application variables such as heat treatment, surface finish, test environment, stress state, and anticipated thermo-mechanical exposures, can lead to significant improvements in both the efficiency and the quality of utilization of iron and steel materials in the engineering applications. Tensile testing of iron and steel materials is done for many reasons. Tensile properties are normally included in material specification to ensure quality and are often used to predict the behaviour of these materials during different forms of loading other than uniaxial tension. The result of tensile testing is normally used in the selection of these materials for engineering uses. It provides a relatively easy and cheap technique for developing mechanical property data for the selection, qualification, and utilization of these materials in engineering applications. This data is generally used to establish the suitability of these materials for a particular application, and/or to provide a basis for comparison with other substitute materials. The elastic moduli of iron and steel materials are dependent on the rate at which the test sample...

Mechanical Properties of Steels...

Mechanical Properties of Steels The most important properties of steels which account for their widespread use are their mechanical properties. These properties include a combination of very high strength with the ability to bend rather than break. Different tests have been developed to describe the strength and ductility (a measure of bendability) of steels. A number of these tests which are used to describe the mechanical properties of steels are described below. Tensile testing Tensile testing of steel is a kind of a testing done for the evaluation of the strength of steels. A length of the steel material, usually a round cylindrical rod, is pulled apart in a machine that applies a known force, F. The machine has grips which are attached to the ends of the cylindrical steel rod, and the force is applied parallel to the axis of the rod, as shown schematically in Fig 1. As the force increases, the rod gets longer, and the change in length is represented as delta l (? l), where the symbol delta (?) means ‘a change in’ and the l refers to the original length of the rod. If a force of 50 kg is applied to two rods of the same steel material, where one is thin and the other thick then the thin rod elongate more. To compare their mechanical properties independent of rod diameter, the term ‘stress’ is used. Stress is simply the force divided by the cross-sectional area of the rod. When the same stress is applied to the thin and thick rods, they elongate the same amount, because the actual force applied to the thick rod is now larger than that applied to the thin rod by an amount proportional to its larger area. Because stress is force...

Chains and their Types...

Chains and their Types A chain is a series of connected links which are typically made of metal. A chain may consist of two or more links. Chains can be classified in many different ways. From a theoretical viewpoint, a chain is a continuous flexible rack engaging the teeth on a pair of gears. A sprocket, being a toothed wheel whose teeth are shaped to mesh with a chain, is a form of gear. From a viewpoint based on its history and development, chain is a mechanical belt running over sprockets that can be used to transmit power or convey materials. Chains have the following four basic functions. Transmit power. Convey objects or materials. Convert rotary motion to linear motion, or linear motion to rotary motion. Synchronize or to time motion Chains have the following general advantages over other equipment intended to do the same functions. Have controlled flexibility in only one plane. Have a positive action over sprockets, no slippage takes place. Carry very heavy loads with little stretch. Efficiency of a chain joint passing around a sprocket approaches 100 % because of the large internal mechanical advantages of links in flexure. Provide extended wear life because flexure takes place between bearing surfaces with high hardness designed specifically to resist wear. Can be operated satisfactorily in adverse environments, such as under high temperatures or where they are subject to moisture or foreign materials. Can be manufactured from special steels to resist specific environments. Have an unlimited shelf life. They do not deteriorate with age or with sun, oil, or grease. Types of chains From industry stand point, the major types of chains are (i) roller chains, (ii) leaf chains, (iii) silent chains, (iv) engineering steel chains, and (v) flat-top chains. (Fig 1) Fig 1 Types...

Properties of Steels

Properties of Steels When selecting a steel material for a particular application, user has to be confident that it will be suitable for the loading conditions and environmental challenges it will be subjected to while in service. Understanding and control of the properties of the steel material is therefore necessary. Further properties of steel can be controlled through different processes such as hot and cold working, heat treatment etc. There are many measurement systems used to define the properties of given steel. These measurement systems normally come under four categories. These are physical properties, chemical properties, microstructural properties and mechanical properties.  Physical properties of steels The physical properties of steel are related to the physics of the material, such as density, thermal conductivity, elastic modulus, Poison’s ratio etc. Typical physical properties of steels are given in Tab 1. Tab1 Physical properties of steels           Properties Carbon steels Alloy steels Stainless steels Tool steels Density (tons/Cum) 7.85 7.85 7.75-8.1 7.72-8.0 Elastic modulus (GPa) 190-210 190-210 190-210 190-210 Poisson’s ratio 0.27-0.3 0.27-0.3 0.27-0.3 0.27-0.3 Thermal expansion (10-6/K) 11-16.6 9.0-15 9.0-20.7 9.4-15.1 Melting point (deg C) 1371-1540 Thermal conductivity (W/m-K) 24.3-65.2 26-48.6 11.2-36.7 19.9-48.3 Specific heat (J/kg-K) 450-2081 452-1499 420-500   Electrical resistivity (10-9W-m) 130-1250 210-1251 75.7-1020   Chemical properties of steels Iron is the basic component of steel. When carbon (C), a nonmetal, is added to iron (Fe) in amounts up to 2.0 %, the result is an alloy known as steel. Composition of steel mainly consists of iron and other elements such as carbon, manganese, silicon, phosphorus, sulfur, and alloying elements. A large number of elements in wide ranging percentages are used for the purpose of alloying of steels. Variations in chemical composition of steels are responsible for a great variety...

Fire Resistant Steels...

Fire Resistant Steels Steel is inherently a noncombustible material. It loses strength when heated sufficiently.  Steel structural properties and its yield strength considerably decrease when it is heated to temperatures seen in a fire scenario. The critical temperature of a steel structural member is the temperature at which it cannot safely support its load. Building codes and structural engineering standard practice defines different critical temperatures depending on the structural element type, configuration, orientation, and loading characteristics. The critical temperature is often considered the temperature at which its yield stress has been reduced to 60 % of the room temperature yield stress. Fire is a chemical phenomenon that occurs as a result of thermal processes. When a steel section is exposed to a fire then the level of temperature increase on the face of steel section depends on thermal inertia, exposure of surface area and the protective coating. As the rate and amount of heat flow from the fire environment to steel section increase, the temperature, and thus the risk of failure for the steel section also increases. Since the steel has a very high thermal conductivity, exposed surface of the steel section easily transmits the conveyed heat from the fire source to the other members of the whole structure in a short period of time. Heat is transmitted in between the steel sections from high temperature sections to low temperature sections by way of conduction, radiation or convection modes. Steel sectional properties and its yield strength considerably reduce as it absorbs heat upon exposure to a high temperature level. A steel structural member may easily collapse during a fire if the temperature is allowed to reach a critical value. The fire resistance of the steel member is related to some important factors including the section size, the perimeter...