A Reference Stress Approach to Creep Bending of Straight Tubes

Abstract

Reference-stress parameters, based on the Norton constitutive equation, are developed for creep bending of circular and elliptical tubes. The parameters are presented in the form of a design chart.

The reference stress methods apply also to other simple constitutive equations of the power law, exponential and hyperbolic sine forms, and also to two complex equations describing creep behaviour over the entire range from primary to tertiary. In these equations the functions of stress and time are not separable and reference stress techniques provide a convenient method of evaluating stationary stress distributions and investigating the variation of these stresses with time.

Aluminium alloy tubes were creep tested with cyclic uniform bending moments. Creep strains to fracture were measured by an end-rotation method.

The creep behaviour of the tubes was well predicted by reference-stress cyclic tensile creep tests.

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References

Marriott

D. L.

‘A review of reference stress methods for estimating creep deformation’, Creep in structures (edited by Hult

) 1972, 137–152 (Springer-Verlag, Berlin).

Penny

R. K.

Marriott

D. L.

Design for creep 1971 (McGraw-Hill, London).

Penny

R. K.

Marriott

D. L.

‘Creep buckling of boss-loaded spherical shells’, First Int. Conf. on Pressure Vessel Technology. Pt 2. Materials and Fabrication 1969, 861 (American Society of Mechanical Engineers).

Sim

R. G.

Penny

R. K.

‘Some results of testing simple structures under constant and variable loading during creep’, Exp. Mech. 1970 10, 152 (SESA).

Fairbairn

Mackie

W. W.

‘Creep of thick walled tubes subjected to internal pressure’, Creep in structures (edited by Hult

) 1972, 189–202 (Springer-Verlag, Berlin).

Mackenzie

A. C.

‘On the use of a single uniaxial test to estimate deformation rates in some structures undergoing creep’, Int. J. mech. Sci. 1968 10, 441–453.

Spence

‘Creep behavior of smooth curved pipes under bending’, First Int. Conf. on Pressure Vessel Technology. Pt 1. Design and Analysis 1969, 309–315 (American Society of Mechanical Engineers).

Spence

‘An upper bound analysis for the deformation of smooth pipe bends in creep’, Creep in structures (edited by Hult

) 1972, 234–246 (Springer-Verlag, Berlin).

Snedden

‘Primary creep of anisotropic RR58 aluminium alloy at 180°C’, NEL Report No. 531 1972 (National Engineering Laboratory).

10.

Graham

Walles

K. F. A.

‘Relationships between long- and short-time creep and tensile properties of a commercial alloy’, J. Iron Steel Inst. 1955 179, 105.

11.

Henderson

Snedden

J. D.

‘Creep fracture of anisotropic cylindrical bars under pure torque’, Creep in structures (edited by Hult

) 1972, 18–37 (Springer-Verlag, Berlin).