The Junker vibration test meeting DIN 65151 (Dynamic testing of the locking characteristics of fasteners under transverse loading conditions - vibration test) standards is a common and reliable method for testing and comparing the security of bolted joints.
The" Junker's" transverse vibration-loosening test provides a simplified method for broad scale testing and inspection of the transverse vibration ( loosening) properties of fasteners. The test machine is able to generate relative motion in the clamped parts perpendicular to the axis of the fasteners.The Junkers method provides quantitative results relating the variables of clamp-load, number of cycles, and amplitude.
The Junkers test is considered a 'severe' test of the loosening characteristics of fasteners, particularly when compared to previously introduced test methods which rely on axial dynamic loading to induce loosening. Junker largely established the viability of the current method in a paper entitled, 'Investigations of the Mechanism of Self-Loosening and Optimal Locking of Bolted Connections'.
A comparison transverse vibration test is designed to expose two or more fastener sets to the same test parameters to determine the effects of the differences.The present research compared nut-bolt-washer assemblies with nut-bolt-DTl assemblies. To better understand vibration loosening, Junker's provides us with models of bolted joints under static conditions and under transverse vibration.
Results of transverse vibration-loosening tests are useful for deployment of bolting strategies which reduce or prevent the risk of vibration loosening in service, or mitigate its effects where it cannot be avoided entirely. According to Gerhard H. Junker, originator of this test, "It is well established that a dynamically loaded joint fails in most cases either by fatigue failure or by rotation loosening of the fastener. Even the fatigue failure is often initiated by partial loosening."
Results of the HEICO-LOCK® washer Junkers test:
Vibration loosening of the fasteners which did not include HEICO-LOCK® washers was clearly evident. Vibration loosening of the fasteners set with HEICO-LOCK® washers was noticeable less than those with other locking fasteners. The retained clamp load after cycling was higher with HEICO-LOCK® washers than with other fastening methods.
Under the conditions of the subject test, there was a significant difference in the loss of clamp load between fastener sets with and without HEICO-LOCK® wedge lock washers. Fasteners without HEICO-LOCK® washers lost a large percentage of their initial clamp force after cycling contrasted with a much smaller loss in the fasteners set with HEICO-LOCK® washers. Under the test parameters and conditions of the study, HEICO-LOCK® washers provide improved resistance to vibration-loosening.
As stated above, the test was conducted in accordance with DIN 65151. In addition, the exact test method and testing sequence was specified and will be added to DIN 25301 ( 'Design guide for railway vehicles and their components - Bolted joints - Part 2: Design - Mechanical applications'). These parameters were designed and verified in an industry promoted research project that was conducted by the Fachhochschule Koeln (University of Applies Science Cologne, Germany) and the IMA Research Institute, Dresden, Germany. This process will become part of DIN 25201 in an addendum named DIN 25201-4 /6/.
HEICO-LOCK® wedge lock washers were tested in accordance with the expanded version of DIN 25201-4/6/. The test diagram show an extensive improvement and advantage when compared with standard washers and commonly used locking devices.