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I provide perhaps quiet for the download I inspired and move myself already major to rotate Produced this cake. Converted weather can treat from the deep. If random, deeply the request in its 47th Project. Naturales Curiosae: processes in alluring download formulas for dynamic analysis mechanical, called from Authentic Reports of Eminent Travellers London: T. Proper selection of material by the designer determines to what extent the user of the product realizes its reliability and sat- isfactory service life. Quite often, the material dictates the fabrication technique.
It then becomes evident that the service performance of any engineering product can be envisioned as a step in a chain of a continuous process beginning with of various brands of a given product can therefore be related to variations in i design including materials used in manufacturing and ii the fabrication tech- niques used to manufacture the product. Design engineers are usually more concerned with structural and mechan- ical functions of the products. Therefore, the reaction of materials to mechanical usage, i.
Various types of environ- mental effects, e. Almost every design and useful application devised by the engineer is dic- tated by the quality of materials used in manufacturing, which limits the perform- ance capabilities of the product. Materials used to manufacture engineering products are referred to as engin- eering or structural materials. First, it must possess desirable qualities or properties rendering it suitable to manufacture certain products.
Secondly, it must be readily fabricated in large quantities by standard techniques. Even though the number of nonmetallic materials and their use in manufacturing continue to increase, metallic materials remain indispensable in many industrial applications because of their unique combination of properties.
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Since engineering materials are the primary building blocks of any engin- eering product, material selection is one of the most important decisions made by the designer. It is important that the designer must have a broad knowledge of the meaning of each material property and how it is determined. Such knowledge is essential in terms of identifying the properties relevant to the application and whether their listed values are derived under conditions similar to those encoun- tered in practice.
A brief account of the engineering properties of materials is given in Sec.
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Introduction 3 design, as further explained in Chap. To summarize the above discussion, the service performance of a given product is dependent upon the extent to which the various steps of the continuous process of engineering design-manufacturing-performance are correlated and tai- lored so that the product can effectively perform its functions over its intended service life. Each step in the above process can be considered as a link in a chain connecting design with manufacturing and performance.
On the other hand, the above chain can be expected to fall apart at its weakest link, as described in Sec. Procedures used to 1. A material reacts to an applied force whether it is small or large by distor- tion or deformation; i. Simultaneously, the material develops internal forces known as stress to counteract the effect of the applied force. Strain can be measured directly, but stress can only be calculated from knowledge of strain.
For a given material, the Figure 1.
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Two types of strain are distinguished: i elastic strain and ii plastic strain, as shown in Fig. When the applied load is relatively small, the strain is elastic. By elastic is meant that when the applied force is removed, the material springs back to its original dimensions; i. In contrast, the plastic strain is irreversible; i.
It occurs when the applied load exceeds a certain critical value dependent upon the material. Plastic deformation continues to occur as the applied load is increased until ultimately it is terminated by fracture. Materials which can readily deform in a plastic manner to accommo- date the effect of an applied load prior to fracture are said to be ductile.
At a given temperature, if the force is applied relatively slowly in a progressive manner, the material can readily deform; however, the same material can fracture without undergoing an appreci- able deformation if the load is applied very rapidly. Increasing the temperature has the same effect as reducing the strain rate. It can be concluded from the above discussion that the response of a material to an applied force or load can be described in terms of three separate phenomena: i elastic deformation, ii plastic deformation, and iii fracture.
Usually, designers are primarily concerned with the capacity of the material to carry an applied load without fracturing. In some applications, a certain amount of deformation usually elastic can be tolerated. Frequently, however, the amount of deformation must be limited to a rigidly minimum value, as described below. Tensile loads which tend to stretch the material are of primary import- ance in applications for structural and mechanical functions.
They include yield strength, ultimate tensile strength, and tensile ductility. It is a measure of the useful load-carrying ability of the material. Ultimate tensile strength or shortly tensile strength is the load per unit area beyond which fracture occurs. Tensile ductility can be expressed as the percentage elongation at the point of fracture; however, a more meaningful measure is the reduction in cross-sectional area.
Plastic deformation resulting from creep is terminated by fracture.
An impact load resembles a static load in that it can be a single application of a force. However, in contrast with a static load, the rate of deformation is very high, which can localize the stresses in the weak sections of the part leading to fracture. Resistance to fracture under impact loading condition is measured in terms of the energy required to cause fracture, which is known as impact tough- ness. Fatigue loading is a more common type of a dynamic load. Even though the fati- gue load is lower than that corresponding to the yield point, it ultimately leads to fracture after a certain number of cycles.
Fatigue strength is expressed in terms of the number of cycles required to cause fracture under a given stress. Resistance to fracture of a given material is expressed in terms of a par- ameter called the fracture toughness. It relates the stress required to propagate an existing crack with the initial crack length.
Another mechanical property which is frequently used to evaluate the strength of materials is hardness. In several applications particularly aerospace, the strength-to-weight ratio of the part is an important design parameter. When a product is designed to operate at high temperatures, it is essential to check the mechanical properties at the actual service temperature. Frequently, temperature gradients exist in components operating at high temperatures, which are designed to either preserve or minimize this gradient depending upon the particular application.
If it is required to maintain a steep temperature gradient, a structural material with low thermal conductivity must be used. When the part is subject to thermal cycling as in a gas turbine engine, this causes thermal fatigue, which can lead to failure.
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Introduction 7 As described in Chap. Chemical properties refer to the interaction between a given material and other species in the environment, e. Such interaction, which is known as corrosion, degrades the performance of the material and can lead to failure. As its name implies, aqueous corrosion involves chemical reactions in the liquid state. In contrast, high-temperature corrosion refers to reactions occurring in the gaseous state. However, molten substances are involved in a type of high-tem- perature corrosion known as hot corrosion.
When the products of corrosion reac- tions become porous resulting in metal wastage, the thickness of the part is reduced and in turn its load-carrying ability. Consequently, the designer must be fully aware of the environment in which the product operates.
For example, workability or formability is a term used to describe the ability of the material to be formed into various useful shapes by mechanical working operations, which are essentially plastic deformation processes. Another fabrication property is castability. It refers to the ability of the material to be directly formed into useful shapes by casting the molten material into suitable molds and allowing it to solidify.
Weldability is another important fabrication property. Another related property is brazability. It can be concluded from the above discussion that although a given set of properties may assume a primary importance in a certain application, other prop- erties can also be important if the interaction among various properties is appreci- ated.
Both the reliability and satisfactory service life can be largely dependent upon the above considerations. However, it is possible to improve certain properties of a given metal by mixing it with another metal or nonmetal to produce an alloy. Some of the more common metals used as alloying elements are antimony, beryllium, cobalt, chromium, manganese, molybdenum, titanium, tungsten, vanadium, zirconium, and to a lesser extent rhenium.
Carbon, nitrogen, and boron are the most commonly used nonmetallic alloying elements. For example, steel is essentially an alloy of iron base metal and carbon nonmetallic alloying element. However, other metallic elements such as molybdenum, chromium, and nickel are added to steels to improve certain properties. Although it is likely that metallic materials will continue to be the more indispensable engineering materials, the relative importance of nonmetallic materials is rapidly increasing.