Lecture

2. Mechanical Engineering Design Utilizes Math Products Structures Devices Material Sciences Mechanical Sciences Thermal Fluids Electrical Phases Recognition of need Definition of the Problem Synthesis Analysis & optimization Evaluation Presentation Continuously

3. Design Considerations Strength Reliability Thermal Properties Corrosion Wear Processing Friction Utility Cost Safety Factor Weight Life Noise Styling Shape Size Flexibility Control Stiffness Surface Finish Lubrication Maintenance Volume Liability

4. Codes & Standards ASTM � testing

6. Stress Components

7. Mohr�s Circle

8. Problem A stress element has the following stresses Sx=80 MPa Txy=50 MPa CW Find principle stresses and directions, find max shear stress and corresponding normal stress.

9. Solution Assume unstated stresses are = 0 Plot A, D Compute C Compute AC Compute E, F Figure ACB Rotate � ACB CW for principle stresses Rotate � ACE to get max shear stress

10. Uniformly Distributed Stress Called �pure� or �simple� Assumptions Bar is straight, homogeneous material Line of action of the force taken thru centroid of section Section taken far from Load Discontinuities Abrupt changes in shape Special case for compression of long slender rods

11. Hooke�s Law Elastic, linear stress strain Where Therefore

12. Stresses in Beams Most beams have both bending stress and shear stress

13. Shear Stresses in Rect Sections

14. Max Bending Shear Stress Usually we are interested in max shear stress Common shapes (table) In all cases, shear at outer fibers/elements is = 0 Horizontal & vertical shear stress at a point are equal in magnitude

15. Torsion Shear Stress

16. Non-Uniform Stresses Non-uniform cross sections Cylinders Curved Members Bearings Stress concentrations Temperature gradients

17. Stresses in Cylinders

18. Stresses in Curved Members

19. Bearing Contact Stresses