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.
The new Junker test to DIN 25201-4 involves more stringent reference testing, verification testing and reporting requirements than the original DIN 65151.
- Reference testing is conducted to determine the effective displacement at which the bolt starts to self-loosen, so that the performance of the securing element or locking mechanism can be effectively tested.
- Three subsequent reference tests are performed to ensure the effective displacement value is correct.
- Twelve Verification tests for each set of measurements are recorded from the Reference test. Data recorded includes the pre-stressing force, transverse displacement under load and the number of load cycles.
- The securing effect of the locking mechanism is considered adequate if a minimum of 80% preload remains from an initial 50% preload applied at the beginning of the test. The preload must be maintained for 2000 load cycles.
- The new DIN 25201 requirements provide customers with data about products they are purchasing and also allows researchers and test engineers to exchange data about locking device performance with much greater confidence.