Advanced mechanical design analysis Essay Example | Topics and Well Written Essays - 1750 words

Advanced mechanical design analysis - Essay Example The structure given for analysis is simply supported using the rollers at both the ends.The beam element consists of three separate pieces.Two pieces of longer span both connected to the end portions while the middle piece the smaller one, connects both the longer pieces using an assembly of pin joints. The loads to which the beam is subjected consist of three concentrated loads, one having a magnitude of 26 KN acting at the centre while the loads of magnitude 18 KN and 20 KN acting at 0.9 m and 1.1 m from both the ends. The connection provided in the members undertakes the roles of transfer of loads from one member to the other besides acting as means of support. As the connections are specified as pinned the members are given the freedom to rotate. The pinned connections are provided to facilitate the large deflection possible in the bridge element. In case stiff connection like welded connections are provided it would create additional stress in the body due to the induced rigidit y of the connections. As the rigidity in the pinned connections are every low the members wouldn't experience any stress concentrations created by rotational effects or reaction forces.The objective of the problem is to determine the stresses in the four different beam cross sections and also the deflection caused when different beam cross sections are used. The beam theory is adopted whenever the structural analysis is required on a member characterized by significant span, L, comparable depth, D, and width, W. Thus the bending theory says that M/I = f /y= E/R. Where M is the maximum bending moment, I is the moment of Inertia, f is the maximum fibre stress, y is the depth to the outermost fibre from the neutral axis, E is the modulus of elasticity and R is the radius of gyration. The stresses and the deflection caused in the beam from the external loads depend on length of the beam or span and the depth of the beam. Also, the stresses and the deflections in the beam shall be expres sed as the functions of shear force and bending moment. Thus it is very necessary to obtain the shear force and bending moment diagram. For the given problem the shear force and bending moment diagram shall be determined, it is shown separately as the hand calculations. The finite element analysis was undertaken using the MYSTRO AND LUSAS finite element software where the FEA models were formed using the command files than CAD interface systems. This approach even though was a little tedious and complex was described by separate set of commands. The success of FEA technique lies in the planning and preparation of suitable mesh arrangement for the problem to be addressed. The objective is to identify the most optimum mesh size arrangement that gives the most accurate stress distribution with in reasonable time for analysis. The region of high stress in the beam could be meshed very fine and those outside the region could be discretised using coarse mesh. The elements used for the discretisation is arrived based of variety of trial models. The elements that are used in the final analysis is three dimensional hexahedral elements which has eight nodes with each node having three degrees of freedom. These elements are geometrically linear and has an assu med internal strain field. They are sued to model the beam flanges and connecting plates. The beam webs are modelled using the three or four noded elements having 5 degrees of freedom and the connections are also modelled using hexahedral elements. The material used is assumed to behavior in the linear field. The modulus of elasticity and poisons ratio given in the problem could be used for the analysis. The beam is restrained to move in the vertical direction. The roller supports provided would give the model a free movement along it longitudinal direction. Three dimensional beam element refers to the element that have two nodes and each node having six degrees of freedom. Three translation motion and three rotational motion are the