mechanics of materials


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mechanics of materials

  1. 1. Assignment # 1STRESS:Stress is a measure of the internal forces acting within a deformable body.Quantitatively, it is a measure of the average force per unit area of a surface withinthe body on which internal forces act. TYPES OF STRESSStresses occur in any material that is subject to a load or any applied force. Thereare many types of stresses, but they can all be generally classified in one of sixcategories1. Residual Stress: Residual stresses are due to the manufacturing processes that leave stresses in a material. Welding leaves residual stresses in the metals welded.2. Structural Stress: Structural stresses are stresses produced in structural members because of the weights they support. The weights provide the loadings. These stresses are found in building foundations and frameworks, as well as in machinery parts.3. Pressure Stress: Pressure stresses are stresses induced in vessels containing pressurized materials. The loading is provided by the same force producing the pressure4. Flow Stress: Flow stresses occur when a mass of flowing fluid induces a dynamic pressure on a conduit wall. The force of the fluid striking the wall acts as the load. Water hammer is an example of a transient flow stress5. Thermal Stress: Thermal stresses exist whenever temperature gradients are present in a material. Different temperatures produce different expansions and subject materials to internal stress. This type of stress is particularly noticeable in mechanisms operating at high temperatures that are cooled by a cold fluid.Mechanics of Materials Page1
  2. 2. Assignment # 16. Fatigue Stress: Fatigue stresses are due to cyclic application of a stress. The stresses could be due to vibration or thermal cycling.The importance of all stresses is increased when the materials supporting them areflawed. Flaws tend to add additional stress to a material. Also, when loadings arecyclic or unsteady, stresses can effect a material more severely. The additionalstresses associated with flaws and cyclic loading may exceed the stress necessaryfor a material to fail. Stress intensity within the body of a component is expressedas one of three basic types of internal load. They are known as tensile,compressive, and shear. Figure 1 illustrates the different types of stress.Mathematically, there are only two types of internal load because tensile andcompressive stress may be regarded as the positive and negative versions of thesame type of normal loading.As illustrated in Figure 1, the plane of a tensile or compressive stress liesperpendicular to the axis of operation of the force from which it originates. Theplane of a shear stress lies in the plane of the force system from which it originates.It is essential to keep these differences quite clear both in mind and mode ofexpression.Mechanics of Materials Page2
  3. 3. Assignment # 1a) Tensile Stress: Tensile stress is that type of stress in which the two sections of material on either side of a stress plane tend to pull apart or elongate as illustrated in Figure 1(a).b) Compressive Stress: Compressive stress is the reverse of tensile stress. Adjacent parts of the material tend to press against each other through a typical stress plane as illustrated in Figure 1(b).c) Shear Stress: Shear stress exists when two parts of a material tend to slide across each other in any typical plane of shear upon application of force parallel to that plane as illustrated in Figure 1(c).Assessment of mechanical properties is made by addressing the three basic stresstypes. Because tensile and compressive loads produce stresses that act across aplane, in a direction perpendicular (normal) to the plane, tensile and compressivestresses are called normal stresses. For tensile stresses: "+SN" (or "SN") or "s" (sigma) For compressive stresses: "-SN" or "-s" (minus sigma)The ability of a material to react to compressive stress or pressure is calledcompressibility. For example, metals and liquids are incompressible, but gases andvapors are compressible. The shear stress is equal to the force divided by the areaof the face parallel to the direction in which the force acts, as shown in Figure 1(c)above.Mechanics of Materials Page3
  4. 4. Assignment # 1 Stress strain curve for steelMechanics of Materials Page4
  5. 5. Assignment # 1 EQUIPMENTS USED IN MATERIAL TESTING LAB1. Computerized Universal Tester:Computerized Universal Tester to find out the following parameters1. Tensile strength2. Compression3. Elongation4. Fold-resisting5. Bending6. Flaking7. Shearing8. Adhesive2. Material Testing Machines: It has been specialy designed for testing metals and other materials under tension, compression bending, transverse and shear loads. It is equally suitable to carry out hardness test on metals.3. Mortar penetometer:It is used for finding out the rate of hardening ofmortars sieved from concrete mixtures, bymeans of penetraion needles of different cross-sectional areasMechanics of Materials Page5
  6. 6. Assignment # 14. Auto tensile tester: Auto tensile tester is applicable in tensile, peeling, tearing, heat seal and adhesivetest of plastic film, complex film, flexible packaging materials, adhesives, adhesive tapes, pressure sensitive tape, medical plasters, protective films, release paper, rubber and paper, etc5. Tensile Tester:It is used for Adhesives, Peel Testing, SealStrength, 180° Peel Strength, BondStrength.Determination of tensile strength, stretch atbreak and tensile energy absorption6. Impact Tester:The impact test is a method for evaluatingthe toughness and notch sensitivity ofengineering materials. It is usually used totest the toughness of metals, but similartests are used for polymers, ceramics andcompositesMechanics of Materials Page6
  7. 7. Assignment # 17. Nick Break and Weldability tester:The principle of this test is to break the sample through the weld metal in order toexamine the fractured surface8. Tensile bend compression flarring tester:A tensile test measures the resistance of a material to a static or slowly appliedforce.9. Bend:Bend testing is a procedure to determine the relative ductility of metal that is to beformed (usually sheet, strip, plate or wire) or to determine soundness andtoughness of metal10. Compression:Compression testing is a method for assessing theability of a material to withstand compressiveloads.11. Hardness Tester:This is a simple indentation test for determining thehardness of a wide variety of materials. The testconsists of applying a prescribed load, usuallybetween 500kg and 3000kgMechanics of Materials Page7