On the yielding behaviour in magnetorheology using ultrasounds, shear and normal stresses, and optical microscopy. (16th October 2015)

• Record Type: Journal Article
• Authors: Rodríguez-López, Jaime; Blázquez, Pedro Castro; Elvira, Luis; de Espinosa, Francisco Montero; Ramírez, Javier; de Vicente, Juan
• Is Part Of: Journal of physics. Volume 48:Number 46(2015)
• Publication Date: 2015-10-16
• Subjects: ultrasounds -- magnetorheology -- magnetorheological fluids -- yield stress -- normal stress -- static yield stress -- dynamic yield stress; Physics -- Periodicals; 530
• DOI: 10.1088/0022-3727/48/46/465503
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: The yielding behaviour of magnetorheological fluids has been investigated by videomicroscopy, ultrasonic and rheometry techniques simultaneously. Particularly, the effect of different factors such as, the magnetic field strength, particle size, surface chemistry of the particles, particle concentration and carrier fluid viscosity has been studied. Special attention has been paid to correlate the yielding information obtained by acoustical, optical and mechanical techniques. As a general trend, independently of the particular field strength and suspension formulation, the steady shear flow curve exhibits three well differentiated regions. In the first region, at small stresses, field-induced structures remain quasistatic and all magnitudes remain constant. For larger stresses the number of aggregates decreases but their size increases. This is identified with the onset of flow, and corresponds to the classical static yield stress and a decrease in time-of-flight and normal stresses. For even larger stress values, the suspensions fully flow. This stress value corresponds to the classical dynamic yield stress and is associated to a minimum in the time-of-flight and normal stresses.