Variation of Mechanical Properties of Structural Components of Hoisting-and-Conveying and Construction Machinery under Dynamic Stresses

Dynamic force (vibration and impulse force) modifies mechanical properties and flow behavior of solid bodies. Experiments in shearing of reinforcement bars with vibration (7.9 kHz) conducted by authors and S.A. Evtjukov at the Department of Construction Machinery of SPbGASU (Saint Petersburg State University of Architecture and Civil Engineering) revealed the reduction of the static part of the cutting force approximately 1.8-2.2 times less and with impulse force with 25 Hz frequency – 4-5 times less. In case of vibration, variation of mechanical properties and flow behavior of cut metal through vibroactivation was observed. Reflective effect and three focusing mechanisms stimulate these variations. The examined effect can be applied in metal treatment under pressure that enables to improve the quality of products, service life of instruments and processing machines. With the knowledge of presence of dynamic forces (impulse, in particular) it is possible to find engineering solutions decreasing or excluding influence of dynamic forces upon friction couples or constructional steelworks and therefore to boost their reliability and endurance, to exclude “unpredictable” accidents.