Ivan Kirkpatrick
User Rank
Threaded fasteners
Ivan Kirkpatrick   7/21/2011 11:13:29 AM

Many people don't fully realize how much of their environment is made up of threaded fasteners.  As a Design Engineer a significant fraction of my time was spent analyzing and reviewing threaded fastener designs.  

Good designs in this field are usually the result of very carefully engineered solutions and thorough application of stress analysis via finite element programs.

Good standards are required and must be carefully developed to insure the design goals are met.  this is especially true in the aerospace and defense industries.

Slight changes in the 1980's regarding Federal Standard H-28 were the cause of several major efforts in the design of the SEAWOLF class submarine.  The changes required additional analysis of thread engagement for tapped holes in critical fasteners in the submarine.  this also required additional inspection requirements to be added to drawings and of course the additional costs of performing the inspections.

As I recall almost every critical tapped hole on the ship was deeper and cost more to produce than the previous designs.

Proper torque and documentation are critical to the proper functioning of the design.  One example for a computer disk drive failure was the result of a slight error in calculating the installation torque on a fastener.  This resulted in many failures and loss of confidence in the manufacturers products. 

Threaded fasteners are ubiquitous in our daily life and proper design, inspection and application of advances in this field impact safety, manufacturing costs and design life.

Alexander Wolfe
User Rank
High-tech Implants
Alexander Wolfe   7/21/2011 3:05:31 PM
This is slightly off topic, but this piece reminded me of your excellent recent cover story, High-Tech Implants.  My question is, I'm wondering if there are a number of companies which have cutting-edge expertise in the type of joints and fasteners you're talking about here in the elbow story, yet they're not in the medical space. So are there partnering opportunities between medically focused engineering concerns and non-medical ones, which could result in innovative approaches and products? 

Beth Stackpole
User Rank
Re: High-tech Implants
Beth Stackpole   7/21/2011 3:37:56 PM
The testing process around these types of fasteners in medical applications must be quite arduous given the wear and tear they have to take over the course of regular activity in a life time. I wonder if they do any virtual simulation and testing--the notion of putting something through 100,000 cycles is mind boggling.

Dave Palmer
User Rank
Re: High-tech Implants
Dave Palmer   7/21/2011 6:08:04 PM
Beth, MTS makes a wide variety of test equipment which is used in medical applications, as does Instron, and probably several other companies.  I'm not in the medical field, but I've always been intrigued when I have seen this specialized equipment in catalogues.

Even in my field (recreational products), there's nothing unusual about putting a component through 100,000 cycles, 1,000,000 cycles, or more.  Because of the nature of the physical processes which govern phenomena like fatigue and wear, in many cases you simply can't extrapolate from what happens at a low number of cycles to what will happen at a high number of cycles.  The only solution is to do the test.

It's one thing to use simulation tools in the design stage, and this is certainly something which has proven incredibly valuable, but I can't imagine them ever replacing physical testing in the validation stage.  After all, how do you know your simulation results are accurate unless you test physical parts?

Beth Stackpole
User Rank
Re: High-tech Implants
Beth Stackpole   7/22/2011 7:35:31 AM
It's good to know there are tools out there that can facilitate the rigorous process of physical testing of designs. I guess when it comes down to it, simulation can only do so much and never completely mitigate the need for putting a physical prototype or early product design through its paces.



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