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In an application, an Acme-threaded power screws is to be designed to raise a maximum load of 50 kN. (a) Select a satisfactory screw from the Table on the basis of tensile strength, limiting the tensile stress to 70 MPa (2 marks). (b) Then determine the required thickness of the nut that to limit the shear stress in the threads to 35 MPa (2 marks). (c) For the screw thus designed, check whether the condition of self-locking is satisfied (2 marks). A solid circular machined shaft of a mechanical system is designed to carry a fluctuating torque from 30 N. m to 65 N. m. The shaft is manufactured from AISI 4140 OQT 1000 with σ-| 160 MPa. Consider a stress concentration factor of 2.5 near the ends of the bar and a design factor of 2. a- Calculate the required design torque values and draw the torque cycle (due to scale) showing all values (4 marks) b- Calculate the actual endurance strength in sheer (4 marks) c- Determine the required diameter for a design factor of 2 (4 marks) d- Obtain the actual size factor and comment on its suitability

Answer 1

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