[Page 13] E DIN 25201-4:2010-03 Annex B (normative) Test specification for demonstrating the resistance to self-loosening of secured bolted joints B.1 Purpose and methods of testing The purpose of the tests is to determine and facilitate a comparative assessment of the self-loosening behaviour of bolted joints subject to dynamic transverse stress under defined test conditions. […]
Fasteners in bolted joints subjected to transverse loading conditions will loosen, unless the correct torque, a locking element or both are applied. Understanding the self-loosening behavior of fasteners under vibration conditions is an essential element of the fastener and locking element product design process undertaken by fastener manufacturers. Downstream fastener users such as original equipment manufacturers (OEMs) require an understanding of how bolted joints will perform during actual service, which may include transverse loading conditions. Here Vibrationmaster CEO Morten Schiff uses an example to provide a step-by-step explanation and demonstration of how to perform a vibration test.
Producing fasteners that satisfy various standards is a “service qualifier” for fastener manufacturers. Every engineer in downstream original equipment manufacturer (OEM) end-users will assume that the fasteners they specify meet basic international standards. Increasingly, fastener manufacturers develop products to meet the specific performance characteristics laid down in their downstream customers’ standards and are creating their own benchmarks. Ensuring fastener manufacturers can deliver products meeting demanding ‘tested by me’ criteria requires innovative testing strategies and flexible, modular and affordable testing equipment to implement them.
Fasteners and bolted joints quite literally hold automotive designs, assemblies and the resulting completed vehicle together. So, a complete understanding of how they perform is essential to drive innovation, improve quality and safety and introduce production efficiencies in the automotive sector. Each of these aspects contributes to the competitive advantage of automotive original equipment manufacturers (OEMs). Fastener manufacturers who understand how their products can contribute to creating competitive advantage and can develop new fasteners to meet car makers’ needs can better serve their automotive OEM customers. Vibrationmaster’s Morten Schiff and REC solutions in fastening technology’s Bernhard Reck explain how automotive OEMs apply static and dynamic fastener and bolted joint testing methodologies to drive product, quality, safety and process improvements.
When a fastener or bolted joint fails, the results can be catastrophic and also sometimes tragic. The impact of the failure might be an isolated component malfunction, or an aircraft dropping from the sky. Whatever the impact, any fastener or bolted joint failure puts the pressure on the fastener manufacturer, the original equipment manufacturer (OEM), the operator and their insurers to determine the root cause and, ultimately, liability. Underpinning this process is the work of forensic engineers who apply fastener and bolted joint tests to find out what went wrong, so a solution can be developed to ensure it never happens again. Vibrationmaster’s Morten Schiff and Bolt Science’s Bill Eccles explain how forensic fastener and bolted joint testing methodologies can be used to determine failure modes.
A clear fastener testing strategy offers a wide range of benefits, from basic compliance to securing confidence from downstream original equipment manufacturer (OEM) customers. Astute fastener manufacturers can turn their investment in testing from being a cost to an opportunity to generate new sales and profits, particularly during periods when market demand for fasteners is depressed. An effective test strategy enables fastener manufacturers to continuously improve their products and to develop a source of competitive advantage. Key elements of a testing strategy are to identify and correctly brief a test laboratory on what tests to conduct, then interpreting the results to provide maximum return on investment.
No-one used to ask for the test reports on fasteners that had been vibration tested to determine their self-loosening behavior. They were simply never required. Vibrationmaster CEO Morten Schiff explains the new reporting requirements according to the DIN 25201, and how this new format can be used globally.
Testing plays a key role when developing new fastener and locking elements in response to customer requirements. The choice of testing enables fastener manufacturers’ Development Engineers to confirm that the new product performs according to specification. Downstream fastener consumers are constantly searching for innovative solutions to prevent self-loosening, a phenomenon first empirically investigated by Dr. Gerhard Junker in the 1960s. The result was the Junker test to determine self-loosening behavior, which has played a key role in the development of Unbrako’s new Durlok locking wedge washer.
The number of wind turbine-related accidents globally reached a record high of 160 in 2011, including 11 fatalities. Turbine failure can also have a serious impact on energy supply security. Studies into wind turbine reliability show that vibration fatigue is the third most common reason for wind turbine failure. When analysing the root causes of failures, the suitability of design methods and component standards has been called into question. Introducing standards such as DIN 25201 may prevent vibration-induced fastener self-loosening, thus cutting turbine failure rates and resulting in reduced accident numbers and fatalities, increased energy security and lower operation and maintenance costs.
Determining the self-loosening behavior of fasteners according to the new DIN 25201 has become a whole lot more complicated. But that means components and products will be a whole lot safer. Vibrationmaster CEO Morten Schiff describes new reference and verification testing requirements in this third in a series of four articles about the new DIN 25201.