摘要:

A Saint-Venant's principle associated with a one-dimensional dynamic coupled ther moelastic effective modulus theory for a microperiodic layered semispace is presented. In such a theory, the displacement u=u(x,t) and the temperaturetheta=theta(x,t) (x>=0,t>=0) are approximated by u(x,t)=U(x,t)+h(x)V(x,t) andtheta(x,t)=THETA(x,t)+ h(x)PHI(x,t), where U(x,t) andPHI(x,t) represent a macrodisplacement and a macrotemperature, respectively; V(x,t) andPHI(x,t)denote a displacement corrector and a temperature corrector, respectively; h=h(x) is a prescribed periodic microshape function; and the pairs (U,THETA) and (V,PHI) are found by solving an initial boundary value problem described by a system of linear partial differential equations with effective thermoelastic moduli subject to suitable initial and boundary conditions. It is shown that the thermoelastic energy associated with a solution to the problem and stored in the semi-space lying beyond a distance x from the loaded boundary x=0 over the time interval [0,t] decays exponentially as x toinfinityand its decay length L depends on the time t, an effective velocity of thermoelastic wave (c*l), an effective time (T*), and an effective thermoelastic coupling parameter (epsilon*). In particular, it is shown that for small (large) times the function L reveals behavior of the decay length for a pure thermal (elastic) energy of a semispace.

ISSN:0149-5739    

DOI:10.1080/014957300280533

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

This article presents an analytical approach for an axisymmetric double-layer annular cylinder subjected to hygrothermal loading for a small time. The coupled equations are first decoupled and divided into two general initial and boundary value problems for each layer. The boundary values at the interface are currently unknown and can be determined by the interfacial conditions. The Laplace transform method is implemented to solve these problems, and an asymptotic expansion for a large value of the transformed variable is used to obtain the transformed solutions. Generally, they can be numerically inverted to obtain the time domain response. However, analytical forms can be found from a table of inverse Laplace transforms for some special cases. The results are in agreement with the cases that have exact solutions or analytical solutions obtained by the alternative method. It is determined that the computing time required for the calculations is only about 1/5 compared with that by the alternative analytical approach for t*=0.02; and the shorter the time, the smaller the ratio of computing time. Moreover, the present method has a great advantage in obtaining the maximum stresses at the surfaces, which are very important for structural design.

ISSN:0149-5739    

DOI:10.1080/014957300280542

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

By means of a Gleeble machine, the flow stress at steady-state creep in an AA3103 aluminium alloy has been measured for temperatures and strain rates relevant for thermally induced deformations in DC casting. The strain rate has been determined by measuring the global radial strain rate at the specimen center by an extensometer, and the stress has been set equal to the force in the axial direction divided by the cross-section area. The parameters of Garofalo's equation have been fitted to the resulting steady-state stress and strain rate. Such a method is based upon the assumption of homogeneous stress and strain rate fields. In the Gleeble machine, the specimens are heated by the Joule effect leading to axial temperature gradients, and the specimen geometry is noncylindrical. The resulting inhomogeneities in the stress and strain rate fields are studied by finite element modeling, and it is shown that although they can be significant, the global radial strain rate and the axial force divided by the cross-section area at the specimen center can be relatively close to what the respective strain rate and stress values would have been if the conditions actually were homogeneous.

ISSN:0149-5739    

DOI:10.1080/014957300280551

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

In this article variants of rational choice of the functional optimization criteria are discussed. A generalization of energy criteria by introducing moment characteristics of local measures and by setting functions to take into account the local effect of stress-state changes in space and time domains is proposed. Calculations pertaining to exemplary tasks are presented.

ISSN:0149-5739    

DOI:10.1080/014957300280560

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

This article documents a series of physical direct chill casting simulations performed on specimens of an AA3103 alloy by means of a Gleeble machine. During the experiments the specimens are subjected to thermal and straining histories similar to those experienced by material points in an ingot during the casting process due to thermal stresses. The measured stress is compared to the stress given by a steady-state creep law for the measured temperature and strain rate versus time. The creep law gives a good fit for temperatures above 400oC but increasingly overestimates the stress level as the temperature decreases below this level because of the increasing importance of work hardening. Since thermally induced straining occurs in the entire temperature interval in the casting process, it is concluded that more sophisticated constitutive modeling than the creep law is needed.

ISSN:0149-5739    

DOI:10.1080/014957300280579

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor