PSI - Issue 44

Ivan Marenda et al. / Procedia Structural Integrity 44 (2023) 2152–2157 Ivan Marenda et al./ Structural Integrity Procedia 00 (2022) 000–000

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higher values can be obtained by including one or more lead cores. High damping rubber devices have a pronounced Mullins effect. The Mullins effect is defined as a permanent or semi-permanent variation in the response of the rubber during repeated cycles. As a result, a smaller amount of energy is requested to reach the same deformation in subsequent cycles. Furthermore, the model of these devices shall consider the variation of the main characteristics (Q d , k d ) with temperature, aging, shear strain, production etc. Therefore, standards define the modification factors to consider these phenomena. The FPDs are based on the functional principle of a pendulum . During motion, the device increases its potential energy and dissipates energy by means of friction between the sliding surface and special polymeric materials. It is important to control and limit the roughness of the sliding surface and to know the characteristics of the system. Therefore, the knowledge of the variation of the friction coefficient during the load history is fundamental to predict the dynamic behaviour of the structure. Friction is closely linked to several parameters like the roughness of the surfaces of the joint and to the physical and chemical characteristics of the materials in contact. It is necessary to precisely define the static and dynamic friction coefficient. It is fundamental to highlight that the behaviour of the polymeric material both in mechanical and thermal terms is closely related to the real contact area of the joint. The aim of this article is to summarize the main results obtained from Hirun International studies on the special HI-M sliding material used in the HFs. After a brief background on the mechanical modelling of the joint, the results obtained by numerous tests on pendulums will be shown. Nomenclature D displacement (m) T q total height of the elastomer (m)

HDRB High Damping Rubber Bearing (-) LDRB Low Damping Rubber Bearing (-) LRB Lead Rubber Bearing (-) FPD Friction Pendulum Device (-) HF Hirun Friction pendulum device (-) HI-M HIrun special sliding Material (-) A r real area of contact (m2) A a apparent area of contact (m2) p apparent contact pressure (Pa) H mic microhardness (Pa) s rms surface roughness (m) m mean absolute surface slope (-) n s number of contacts (-) a radius of contact (m) t y maximum yield shear strass (Pa) µ friction coefficient (-) µ HV friction coefficient at high velocity (-) µ LV friction coefficient at low velocity (-) a

parameter which accounts for the variations of velocity (s/m)

N

axial load (kN) velocity (m/s)

v

2. Background Friction and wear are phenomena dependent on the characteristics of the surfaces in contact. The complex nature of these systems reflects the difficulty in interpreting and predicting the friction and wear of the surfaces. The interaction between two surfaces in contact is both mechanical and physical. The former creates a system of stress strain, while the latter creates physical or chemical bonds between surfaces. The contact can be schematized by means of an axial and a tangential behavior.