Yield stress measurements
Notwithstanding the continuing debate over the very existence of a ‘true’ yield
stress, the concept of an apparent yield stress has been found to be an
extremely useful empiricism in many areas of science and engineering
[Hartnett and Hu, 1989] (see also Chapter 1). A recent comprehensive review
n,o[Barnes, 1999] has critically assessed the various issues raised in the definiti
. measurement and application of apparent yield stress behaviour
Any operational definition of apparent yield stress should take into account
both the inevitable rheometrical limitations in its determination, and the
lacharac-teristic time of the process to which it pertains. Such an operation
definition has been proposed for a true yield stress in the context of the
. [classical stress relaxation experiment [Spaans and Williams, 1995
Notwithstanding the inherent advantages of the controlled-stress technique
results in yield studies, it should be borne in mind that an interpretation of the
stress of creep-compliance measurements in terms of a ‘real’ yield stress (i.e. a
ehbelow which the sample exhibits Hookean elastic behaviour) is subject to t
ace-lusual experimental limitations of machine resolution (i.e. of angular disp
. ment) and the role of time-scale in the sample’s response to applied stress
Numerous workers have described the role of wall-slip effects on
nes,rmeasurements made with conventional smooth-walled geometries [Ba
ume fraction,l1995]. Slip can occur in suspensions at high (ca. 60%) solids vo
and can involve fluctuating torque in a rotational viscometer under steady
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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