Determination of Theoretical Plastic Stress-Strain Relations for Variable Combined Stress Ratios

1952 ◽  
Vol 19 (4) ◽  
pp. 485-488
Author(s):  
L. W. Hu ◽  
Joseph Marin
Keyword(s):  
Graphical Methods ◽  
Stress Tests ◽  
Combined Stress ◽  
Stress Strain ◽  
Simple Tension ◽  
Stress Ratios ◽  
Theoretical Stress ◽  
Stress Invariant ◽  
Plastic Stress

Abstract To distinguish between the various theories of plastic flow defining plastic stress-strain relations under combined stresses, it is necessary to conduct combined stress tests in which the ratio of the stress components does not remain constant during the test. To compare these results with the flow theory of the second stress-invariant type, graphical methods have been used to determine the combined plastic stress-strain relations based upon the simple tension plastic stress-strain relations. This paper presents an analytical procedure for the determination of these theoretical stress-strain relations. For certain stress conditions the graphical methods have the disadvantage of yielding inaccurate results—an objection not present in the proposed method. Furthermore, the proposed analytical method is less time-consuming than the graphical methods.

Combined-Stress Tests on 24S-T Aluminum-Alloy Tubes

1947 ◽  
Vol 14 (2) ◽  
pp. A147-A153
Author(s):  
W. R. Osgood
Keyword(s):  
Aluminum Alloy ◽  
Hoop Stress ◽  
Axial Stress ◽  
Axial Strain ◽  
Maximum Deviation ◽  
Shearing Stress ◽  
Stress Tests ◽  
Combined Stress ◽  
Stress Strain ◽  
Shearing Strain

Abstract Combined-stress tests were made on five 24S-T aluminum-alloy tubes, 1 3/4 in. ID × 0.05 in. thick. The ratios of circumferential (hoop) stress to axial stress were 0, 1/2, 1, 2, and ∞. The tubes were tested to failure and sufficient measurements of circumferential strain and axial strain were taken to plot stress-strain curves almost up to rupture. The results are presented in the form of two sets of stress-strain curves for each ratio of stresses, namely, maximum shearing stress plotted against maximum shearing strain, and octahedral shearing stress plotted against octahedral shearing strain. In each plot the maximum deviation of the curves is about ± 5 per cent. A method of evaluating small octahedral shearing strains from the data is given which does not assume Poisson’s ratio to be 1/2.

Combined Stress Tests in Plasticity

1956 ◽  
Vol 23 (1) ◽  
pp. 43-48
Author(s):  
Aris Phillips ◽  
Lloyd Kaechele
Keyword(s):  
Uniaxial Tension ◽  
Plastic Region ◽  
Uniaxial Stress ◽  
Stress Tests ◽  
Combined Stress ◽  
Principal Stresses ◽  
Thin Walled ◽  
Stress Ratios

Abstract A substantial number of combined stress tests on thin-walled tubes of aluminum 2S-O are reported. In most of the tests the tubes have been subjected to combined tension and torsion with variable stress ratios. In the last six tests each tube has first been subjected to uniaxial tension until sufficiently deep in the plastic region and then this state of uniaxial stress has been rotated while the magnitude of the principal stresses remained constant. The purpose of the tests was to get information as to the validity of the incremental theories of plasticity. The results of these tests favor the incremental theories.

Plastic Biaxial Stress-Strain Relations for Alcoa 24S-T Subjected to Variable-Stress Ratios

1950 ◽  
Vol 17 (4) ◽  
pp. 372-376
Author(s):  
Joseph Marin ◽  
B. J. Kotalik
Keyword(s):  
Type Theory ◽  
Stress Ratio ◽  
Biaxial Stress ◽  
Test Results ◽  
Principal Stresses ◽  
Stress Strain ◽  
Axial Tension ◽  
Stress Ratios ◽  
Predicted Values ◽  
Plastic Stress

Abstract Usually plastic biaxial stress-strain relations for metals have been determined for tests in which the ratios of the principal stresses have been maintained essentially constant. This paper presents biaxial plastic stress-strain relations for both constant and variable-stress ratios. The purpose of conducting the variable-stress-ratio tests is to attempt to prove whether the flow- or deformation-type theory is the correct theory for predicting plastic stress-strain relations. The paper also gives a comparison between the actual and theoretically predicted values of the biaxial yield, ultimate and fracture strengths, and the biaxial ductility. Various ratios of biaxial tensile stresses were investigated by subjecting tubular specimens to axial tension and internal pressure. The test results showed that the yield-strength values agree best with the distortion-energy theory. For the prediction of the plastic stress-strain relations the deformation-type theory was found to be in approximate agreement with the test results for both the constant- and variable-stress-ratio tests.

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