Effect of notch root radius on stress intensity in mode I and mode III loading
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Therefore, the displacement solution of any classical plasticity problem for which all specified forces are zero and which is subject to strain-rate sensitivity of the powerlaw type, Eq. [1], is independent of velocity and material strength. The force distribution for a different material strength or external velocity is a simple multiple of any other solution, as specified in Eq. [6]. An immediate consequence is that any isothermally displacement-controlled test subjected to Eq. [1] (e.g., a standard tensile test) will exhibit exactly the same strain distribution and necking behavior, independent of strength or displacement rate. This invariance has been observed under isothermal testing conditions of interstitial-free steel. 9,t~Any observed difference in necking, post-uniform elongation, and ductile failure strains must therefore be attributed to material variance from Eq. [1]. A common source of this variance, in addition to different forms of Eq. [ 1], may be deformation-induced heating, H,~2the magnitude of which depends on both stress and strain and which, therefore, does not follow the usual scaling of Eq. [1].
Effect of Notch Root Radius on Stress Intensity in Mode I and Mode !11 Loading R.E. SWANSON, A. W. THOMPSON, and I. M. BERNSTEIN It has been established I that hydrogen accumulates in regions of hydrostatic stress because the increase in local chemical potential enhances solubility in such regions. 2 Elastic analysis shows 3 that hydrostatic stress is a maximum ahead of a notch in Mode I loading, and ideally hydrostatic stress is zero for Mode III loading. Thus, observations of different susceptibilities to stress corrosion cracking (SCC) under Mode I and Mode III loadings should provide evidence to support a model involving hydrogen in the SCC process. If, however, the material tends to fail by anodic dissolution processes, then failure should occur at similar rates (for comparable applied loads or stress intensities) in both tension and torsion, since film fracture should ensue for both and stressed material will be exposed to the environment in both cases. The evaluation of test results4-12 typically involves comparison of the normalized stress or stress intensity values for the two loading modes. The normalized value is given as the ratio of the applied stress or stress intensity to the yield stress or fracture stress intensity for a similar specimen tested in air. An example is shown in Figure 113with the stress intensity ratio plotted against time to failure. In systems where hydrogen does not contribute to SCC, the lowest Mode III curve will be similar to that for Mode I. Where hydrogen embrittlement plays a dominant role in the SCC process, the Mode III curve will be much higher (top line). For systems where SCC occurs by a combination of hydrogen and dissolution effects, the Mode III curve should be in an intermediate position. I
This work is supported by the National Science Foundation through a Presidential Young Investigation Award (DMR-8352486) to the second author. B
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