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# rapor1 - Introduction and Theory Nearly all of the...

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Introduction and Theory: Nearly all of the materials that we deal with are subjected to force or loads when they are in service.To use these materials more conveniently,to design the new ones or to use them more safely; we have to know some mechanical and fundemantal properties of these materials under the action of forces or loads.To achieve our goal engineers have developed number of experimental techniques for mechanical testing of engineering materials subjected to different types of loading such as tension,compression,bending or torsion. Tensile Test is the most common type test used to measure the mechanical properties of a material. The tension test is widely used to provide a basic design information on the strength of materials and is an acceptance test for the specification of materials.At this point one can ask why we use this testing?Here are the corresponding answer:   Tensile tests are simple, relatively inexpensive, and fully standardized. By pulling on something, you will very quickly determine how the material will react to forces being applied in tension. Tension test will give a stress – strain relation of the tested material. The main parameters of the stress – strain relation are: - Tensile Strength ( UTS ) - Yield Strength ( y σ ) - Elastic Modulus ( E ) - Toughness - Resilience - Percent Elongation ( % L ) - Reduction in Area ( RA% ) - Poisson’s Ratio ( ν ) To understand the experiment more clearly we have to define some basic terms including some of the above expressions. Tensile Strength: It is the maximum load the specimen sustains during the test. UTS = Pmax/ A o Yield strength : The stress level at which plastic deformation starts. Ductility: It is extent to which a material can sustain plastic deformation without

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rupture.A material that experience very little or no plastic deformation is called brittle. Elongation and reduction of area are common indices of ductility. Reduction in area : %RA = ( Ao - Af)/Ao . 100% Percent Elongation : % l = (l f - l o) / l o . 100% The ductility of materials is important for at least two reasons. First, it indicates to a designer the degree to which a structure will deform plastically before fracture. Second, it specifies the degree of allowable deformation during fabrication operations. Toughness: It is the total area under the stres-strain curve , which measures the energy absorbed by the specimen in the process of breaking. For a material to be tough, it must display both strength and ductility; and often, ductile materials are tougher than brittle ones. Resilience: This is the capacity of a material to absorb energy when it is deformed elastically, namely it is the area of the elastic region. Also resilience can be defined ass property that enables a material to with stand impact without distortion. The associated property is the modulus of resilience, U r , which is the strain energy per unit volume required to stress a material from an unloaded state up to the point of yielding Yield Strength:Yield strength is the stress applied to the material at which plastic deformation starts to occur while the material is loaded. The point at which plastic
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rapor1 - Introduction and Theory Nearly all of the...

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