摘要:

Results of uniaxial stress relaxation experiments under finite strain are presented. Relaxation functions appearing in an approximate nonlinear constitutive equation are evaluated for a polyurethane material. The accuracy of these functions is checked by a strip biaxial test in which predicted response is compared with measured response. In addition, based on relaxation tests of ethylene propylene, a second approximate constitutive equation is proposed.

ISSN:0148-6055    

DOI:10.1122/1.549061

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

The phenomenon of stress relaxation, the time decrease of internal stress due to localized flow in a solid under constant uniaxial strain, is viewed in terms of present kinetic theories and available data for metals. Rate equations for shear flow, derived from molecular models of liquids and gases, are reviewed briefly. Combined with the theory of elasticity, these equations are shown to be identical to the classical Maxwell model and to the empirical logarithmic form in limiting cases for stress relaxation in solids. Without reference to the specific details of the localized flow, the general equations are found to correlate uniaxial data for many types of steels, copper, aluminum, magnesium, and lead for various temperatures and stress levels. In all of the data, one characteristic controlling reaction is found, and in some cases a secondary reaction dependent upon the level of the uniaxial prestress is also found. For nonaging metals, the data fit equations in which the relaxation stress approaches zero asymptotically in time. A simple modification of the rate equations is made so that an age‐hardening metal can approach a nonzero stress during relaxation. Prestress is used as a controlling variable in correlating data for uniaxial stress relaxation. Apparent heats and entropies of activation are calculated for Inconel and copper at elevated temperatures. For nearly all metals, the apparent free energy of activation for the controlling reaction in the relaxation process decreases slightly as the prestress is increased.

ISSN:0148-6055    

DOI:10.1122/1.549052

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

A temperature‐reduced form of the Powell‐Eyring equation is shown to represent the flow properties as a function of temperature for relatively dilute aqueous carboxymethylcelullose and carboxypolymethylene dispensions, Paraplex G40, and blood over moderate temperature ranges. Convenient methods for determining the activation energy and the equation constants from experimental flow data are presented.

ISSN:0148-6055    

DOI:10.1122/1.549062

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549069

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549053

出版商:The Society of Rheology    

年代:1966

数据来源: AIP