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ENGR-36_Lec-17_Frames.pptx 1 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Bruce Mayer, PE Licensed Electrical.

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Presentation on theme: "ENGR-36_Lec-17_Frames.pptx 1 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Bruce Mayer, PE Licensed Electrical."— Presentation transcript:

1 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 1 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Engineering 36 Chp 6: Machines

2 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 2 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Introduction: MultiPiece Structures For the equilibrium of structures made of several connected parts, the internal forces as well the external forces are considered. In the interaction between connected parts, Newton’s 3rd Law states that the forces of action and reaction between bodies in contact have the same magnitude, same line of action, and opposite sense. Three categories of engineering structures are considered: Frames: contain at least one multi-force member, i.e., a member acted upon by 3 or more forces. Trusses: formed from two-force members, i.e., straight members with end point connections Machines: structures containing moving parts designed to transmit and modify forces.

3 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 3 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Analysis of Machines Frames and Machines are structures with at least one multiforce member. Frames are designed to support loads and are usually stationary. Machines contain moving parts and are designed to transmit & modify forces. A free body diagram of the complete frame is used to determine the external forces acting on the frame. Internal forces are determined by dismembering the frame and creating free-body diagrams for each component. Forces between connected components are equal, have the same line of action, and opposite sense. Forces on two force members have known lines of action but unknown magnitude and sense. Forces on multiforce members have unknown magnitude and line of action. They must be represented with two unknown components.

4 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 4 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Pin Equilibrium  Consider Actions of Members AD & CF on Pin-C  Member CF Pulls Pin RIGHT Pushes Pin UP  Member AD Pulls Pin LEFT Pushes Pin Down  FBD

5 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 5 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Pin Equilibrium  Note that Pin-C is in Equilibrium By ΣF x = ΣF y = 0  The forces on the MEMBERS caused by the Pin are Equal and Opposite as Predicted by Newton’s 3 rd Law

6 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 6 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Machines Machines are structures designed to transmit and modify forces. Their main purpose is to transform input forces into output forces. Given the magnitude of P, determine the magnitude of Q. Create a free-body diagram of the complete machine, including the reaction that the wire exerts. The machine is a nonrigid structure. Use one of the components as a free-body. Taking moments about A,

7 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 7 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Example: CenterPull Brake  For the Center-Pull Bicycle Brake shown at right find Normal Force Exerted by the BrakePad on the Rim Neglect the brake- opening Spring Force

8 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 8 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Example: CenterPull Brake  There is a Single cable connecting Pts B, G, & C Thus T GB = T GC  The FBD for the Cable Connector  The Forces at the connector are CONCURRENT → Particle Applies  Take the ΣF y = 0 Note:

9 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 9 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Example: CenterPull Brake  The ΣF y = 0 at G  Use Trig & Geometry to find T BCG  The FBD for Brake Arm BAE

10 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 10 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Example: CenterPull Brake  Find F normal by ΣM A = 0 Note  Use F∙d to find Moments about A

11 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 11 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Example: CenterPull Brake 70 N

12 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 12 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics WhiteBoard Work Let’s Work This Nice Problem  For the Cutters with Applied Hand Force, P, Find the Force Applied to the Gripped Bolt Big Ol’ Bolt Cutter

13 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 13 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics

14 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 14 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Pliers (4-pc Structure)  AB is TWO-Force Member

15 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 15 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics

16 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 16 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics

17 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 17 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics

18 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 18 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics

19 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 19 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Double Toggle Machine

20 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 20 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Bruce Mayer, PE Registered Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Engineering 36 Appendix

21 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 21 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Friction-Filled Bearing  Consider Non- Frictionless Bearing  From the Diagram r ≡ Brg Radius F ≡ Brg Support Force as determined by Static Analysis  If the Brg has non- negligible Friction the Moment that OPPOSES rotation O r F

22 BMayer@ChabotCollege.edu ENGR-36_Lec-17_Frames.pptx 22 Bruce Mayer, PE Engineering-36: Engineering Mechanics - Statics Friction-Filled Bearing  The Rotation Resisting Moment:  Where µ ≡ the Bearing’s COEFFICIENT of FRICTION  µ Discussed in Detail in Chp08


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