×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Mechanical engineering general discussion FAQ

## Structural Calculations

 How do I construct Free Body Diagrams? by GregLocock faq404-1785 Posted: 22 Sep 12 (Edited 24 Sep 12) /////DRAFT////// v0.03 Authors: Greg Locock zekeman 0) Assumption is that you are trying to solve a quasi static 2D system of forces moments and accelerations on one contiguous body, but the principle holds for 3D. For multiple bodies you will end up with multiple FBDs. 1) Identify the location and magnitude and direction of all forces and moments of interest. Usually these should only be the forces and moments acting ON the body. You could use just the forces the body is exerting on its constraints, but by convention we don't. The location of the point of application of a moment to a rigid body makes no difference. 2)Identify the accelerations of all 'large' inertias. Add D'Alembert pseudo forces (inertia * acceleration) to the centre of gravity in opposition to the accelerations. You may need to include pseudo moments due to rotational accelerations. 4)Sum all forces and pseudoforces in some obvious direction. Since the system is in equilibrium the total should be zero. 5)Sum all the forces and pseudoforces in some other direction that is not parallel to that in (4)(typically, but not necessarily, at right angles to it). Since the system is in equilibrium the total should be zero. 6)Take moments about a cunningly chosen location. Since the system is in equilibrium the total should be zero. //At this point, if your system is well mannered, you should have a solvable solution// If it is not fully defined you have to add additional constraints. Alternatively it may be over defined, for example, a car, sitting on four springs, is not solvable by the above, unless you know the profile of the road surface, and the lengths of the springs. That is called compatibility. See also http://en.wikipedia.org/wiki/Free_body_diagram //////DRAFT///// Back to Mechanical engineering general discussion FAQ Index Back to Mechanical engineering general discussion Forum

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!