An automated manufacturing line crane has suffered a fatigue failure of its lifting arm after three years of operation. The shop manager does not want to buy a new crane but wants to design a new arm to replace the broken one. Your team has been hired to do the fatigue calculations for the new arm. The crane has a 6-ft arm, oriented and attached in the concrete wall as shown in the figure below. The attachment is sturdy enough to be considered rigid. The arm should be manufactured from steel channels in Table A-7 on page 1026[1018 — v10] of the text book. You are allowed to design the arm by either using a single channel or by welding different channels together. The beam of the arm should be straight and prismatic with axis of symmetry in the plane of bending. The shop manager requires that you must design the lightest arm possible. The crane will lift a 1000 lbf load periodically and the arm of the crane must be designed for infinite fatigue life. Base your calculations assuming the channels are made of Cold Drawn AISI 1006 steel. Assume the tensile and compressive strengths are the same. For life calculations include endurance limit modifying factors ka and kb. In order to design the crane’s arm, do the following analysis and include them in your report. 1) Force analyses of the crane arm identifying and numerically determining all forces acting on the arm. 2) Calculate all bending moments acting at the connection to the shop wall. 3) Identify the highest stress location on the arm and calculate the stress due to all forces and moments at that location. 4) Do the fatigue analysis and size the beam for infinite life.
Use English units only in your selection of material and calculations.
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