ARTICLES

Bolted Joints from End to End

Like most subjects, bolted joint development contains a number of important considerations, some of which are often overlooked. While estimating the bolt tension achieved for a given tightening strategy is certainly a common focus, the effect that load has on the joint components is less fully discussed and understood. One of the reasons threaded fasteners are so widely used is ...
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In Response to the 2015 Bolt Failure on the Lemnhult Wind Farm

On Christmas Eve 2015 a 390 ft. tall wind turbine located in the Lemnhult wind farm near Vetlanda Sweden collapsed when the bolts in the tower’s lowermost flange joint, containing one hundred M64 bolts, failed. The incident came into the news recently with the release of the Swedish Accident Investigation Authority’s final report. Based on a short summary that was ...
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Part 2: The Three Least Understood Truths in Bolted Joint Design

By: David Archer In Part 1 of this article, we discussed the tension of structural joints and external tensile loads applied to joints and the effect on bolt tension. The third least understood truth, sizing fasteners, will be revealed in this final installment. What follows is more of what you always wanted to know about bolted joints but were afraid ...
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Part 1: The Three Least Understood Truths in Bolted Joint Design

In fastening, as in most endeavors, the most common misconceptions relate to the most fundamental principles. These errors are commonly made simply because their universal nature provides the greatest opportunity for making them. For example, the reason that most auto accidents occur within a small radius of the driver’s home isn’t because those streets are the most dangerous, but because ...
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ASTM F16.96 Subcommittee on Bolting Technology

Special Meeting at IFI Headquarters In 1986, 17 engineers met at the United Engineering Center in New York for the purpose of establishing an expert group.  John Bickford, who organized the meeting, was concerned about the lack of real knowledge about how we use threaded fasteners in our designs.  The meeting resulted in the formation of the Bolting Technology Council ...
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Threaded Fastener Loosening

A common frustration of threaded fastener suppliers is their customers pointing to their fastener as the cause of their joint loosening problems. Even when the problem is failure from fastener fracture, in the vast majority of instances the fastener meets all specifications and the root cause of their problems is the joint design or assembly process. Furthermore, even when the ...
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Thinking About the Unthinkable

Recently, I was asked to serve as an expert witness in a case where a catastrophic bolted joint failure led to severe, debilitating injury. The discovery phase, where information is requested and where people are deposed under oath, is a sobering, expensive and time-consuming process for all on its receiving end. I came to realize that, if considered before it ...
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Know Your Customer, Know Your Competition

Every supplier has opinions of their customers and what seems to motivate them to buy. Success in meeting economic goals is always dependent on the accuracy of those views. Following is one view of what makes the product development engineer tick in 2006. Of course the first question is whether engineering or procurement is your real customer. Ultimately, it’s either ...
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Drive Features – How Low Can You Go?

Here in metro Detroit, a popular subject for editorials and panel debate is why it seems the passion America once held for the automobile is in decline. Does the legislation and message coming out of Washington promote the development of appliances on wheels? Are manufacturers too risk-adverse and infested with a “bean-counting” mentality to ignite a passion dormant only through ...
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Dissecting the Nut Factor

A Riddle, Wrapped In a Mystery, Inside an Enigma It is recognized that we measure torque when tightening threaded fasteners only because measuring bolt tension, the more important quantity, is much more difficult. The relationship between the torque applied to a fastener and the tension created from the resulting bolt elongation is most commonly described by T = F*K*D where ...
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Calibration Techniques for Ultrasonic Tension Measurement

The fundamentals of using ultrasonic pulse-echo technology for bolt strain measurement, detecting change in the time required for a pulse of energy to travel the length of the fastener after elongation, can be performed with very good resolution and repeatability. The challenge is utilizing this core capability in a manner such that the resulting calculation of boll tension is also ...
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Bolted Joint FAQs

Two of the most commonly asked questions about fasteners are "When should fine-thread fasteners be used?" and "is it preferable to apply torque to the nut rather than the bolt head?" Many different factors influence those decisions, but here are some basic answers to both questions. WHEN SHOULD FINE-THREADED FASTENERS BE USED? For a given fastener diameter, as thread pitch ...
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Use of Washers and Flange Heads

It is likely that most common answer to the question “What is the main benefit of flat washers or flange head nuts and bolts?” would be that the increased bearing area they provide distributes the bolt load over a greater area thus decreasing the potential for compressive yield. While true, during testing we were able to get visual evidence of ...
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Torque Control vs. Angle Control

In previous columns. I've explained why tightening fasteners to a particular torque does not mean the resulting bolt tension will be either accurate or repeatable. That's one of the biggest challenges of using bolted joints that depend on clamp load. However, another means of tightening that does not rely on the torque tension relationship is available to manufacturing engineers. This ...
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Problems Solved

Bolted joints are the vast majority of our consulting business. Our work is divided evenly between validating joints under development and troubleshooting problems with existing joints. Our troubleshooting experience led us to develop the matrix below to help engineers solve common problems with bolted joints. Distilling even the most common problems and solutions into the confines of this column requires ...
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Nine Common Bolting Boo-Boos

As with most endeavors where success can't be measured by keeping score, a good job of engineering is often defined by not doing a bad job. In other words, the most direct measurement of successful joint design and assembly is a lack of joint problems. As an independent test lab, we evaluate joint capabilities, failure modes and root causes of ...
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More Data, Less Knowledge?

Several times before. I have discussed the need for physical testing in the development and validation of bolted joints. However, just as both the quality of the joint and the quality of the joint designer's knowledge base will be limited by reliance on numerical analysis, the same limitations occur when experience and applied experimentation is all one has to draw ...
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