Design for Static Strength

Robert B. Wilcox, P.E.

Course Outline

This course covers the design of parts for static strength. Safety factors, material properties, elementary heat treatment, stress concentrations, and ductile vs. brittle materials will be discussed. Various static failure theories will be presented, focusing on Von Mises-Hencky (distortion energy) theory for ductile materials, and the modified Mohr theory for brittle materials. Application of FEA results to static failure theories will be covered. The course is intended as either a review or a primer in the field of designing for static strength. It is assumed the student has a working knowledge of basic stress analysis. Fatigue and fracture mechanics will not be covered.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

• Obtain an understanding of the static tensile test;
• Understand the difference between ductile and static materials;
• Learn what a stress-strain curve is and recognize a brittle material curve vs. a ductile material curve;
• Have reviewed the concepts of mean, standard deviation and variance;
• Understand the normal distribution curve;
• Learn what a standardized variable is and how to apply it to a design situation;
• Understand some of the rudimentary heat treatment processes;
• Learn how to apply stress concentration factors to design;
• Learn how to adjust stress concentration factors for notch sensitivity of brittle materials;
• Be aware of how temperatures may affect materials;
• Learn about the major types of corrosion which can affect strength;
• Learn ways to reduce the effects of corrosion;
• Understand single safety factors in design;
• Learn how to apply multiple safety factors in design;
• Be aware of some of the different considerations when applying safety factors;
• Become familiar with the viable static failure theories;
• Understand the application of principle stresses in the failure theories;
• Learn which static failure theories to apply depending on material properties;
• Be able to apply distortion energy theory;
• Be able to apply the modified Mohr's theory; and
• See how FEA results may have to be modified, verified by hand, or adjusted depending on material properties.
  
  

Intended Audience

This course is intended for engineers or architects who want to review the basics of static design theory, and learn how to apply results from either manual or FEA in static failure theory.

Benefit to Attendees

The attendee will understand basic static strength design theory.


Course Introduction

Stress analysis methods have changed, but much of historical static design theory remains valid today. FEA results are frequently misapplied or judged to be overly conservative due to misunderstanding of stress concentration effects and static strength design theory. A solid understanding of the basic material constants and static design theory is essential for making sound design decisions based on modern computer based method of stress analysis. Understanding the differences between ductile and brittle materials and how they respond to stress concentrations is important in static design and is also frequently misunderstood. Manual stress calculation techniques are also essential for "reality checks" of computed results. This course helps tie together the stress analysis tools of today with basic manually applied classical static design theories.

Course Content

The course content is in a PDF file (500 KB) Design for Static Strength.

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Content

Prerequisites
Material Properties and Testing
Statistical Variations
Heat Treatment
Stress Concentrations
Temperature
Corrosion
Safety Factors and Allowable Stress
Combined Stress Failure Theories
Von Mises-Hencky (Distortion Energy) Theory
Maximum Shear Stress Theory
Mohr's Theory
Modified Mohr's Theory
Maximum Normal Stress Theory
Combined Stress Failure Theory Examples
Application of FEA Stresses
Bibliography

Course Summary

A concise treatment of elementary design for static strength concepts, which will assist designers in the task of designing parts and members for static applications.

Related Links

For additional technical information related to this subject, please visit the following websites or web pages:

Mohr's Circle Calculator: http://www.aoe.vt.edu/~jing/MohrCircle.html

Stress Concentration calculator: http://www.fatiguecalculator.com/finders/findkt.htm

Static failure theory and safety factor calculator (calculator is a script near the end of the page… http://www.mech.uwa.edu.au/DANotes/SSS/failure/theories.html

Good information on corrosion: http://www.corrosionsource.com/

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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