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Title:Three-Dimensional Photoelastic Investigation of Simulated Weld Discontinuities
Author(s):Ottsen, Henning; Munse, W.H.
Abstract:The object of this investigation was to gain a better understanding of the fatigue behavior of welded joints with internal discontinuities. Since the existence of flaws in welds generally must be considered an accepted fact and since their presence is usually detrimental, means of determining the effect of such discontinuities on the behavior of the welded connections must be known. A review was made of previous investigations into the problem of the notch-sensitivity of metals in fatigue. On the basis of observations reported in several of the more successful approaches to this problem, a hypothesis for the prediction of the fatigue behavior of welded connections with discontinuities developed. This hypothesis suggests that the parameter best defining the notch-sensitivity of a material subjected to fatigue loadings is a characteristic volume of material around the notch tip over which the stress concentration can be averaged. The reduction in fatigue strength of a member due to the presence of a flaw is – according to the hypothesis – determined by the average elastic energy concentration induced by the flaw over the appropriate volume. In order to evaluate the applicability of the energy concentration hypothesis, two sets of information were sought: first, a suitable series of fatigue tests, which involved a sufficient number of test specimens containing a flaw type, the severity of which could be defined and varied in a relatively simple manner, and secondly, determinations of the elastic energy concentration induced by the selected flaws. A literature search produced reports of an investigation in which a substantial number of test specimens, containing partial penetration butt-welds of varying dimensions, had been subjected to repeated loadings. Due to the availability of this test information and the relative ease with which the lack of penetration flaws could be used in the e current study, this flaw type was adopted for the analysis of fatigue behavior in relation to flaw severity. Several geometries were then simulated in three-dimensional epoxy models and the stress distributions induced by the flaws and the loading determined using photoelastic techniques. The correlation of the photoelastic information with the data obtained from the fatigue tests indicates that the energy distributions are sensitive to variation in flaw severity. For the partial penetration butt-welds investigated, the proposed hypothesis ids proved to be well-suited for determining the fatigue strength reduction caused by the presence of the flaw. In order to further test the energy concentration hypothesis, it was applied to notched member radically different from the partial penetration butt-weld: a tension strip with a centrally located hole. It was found that, in this case also, the proposed hypothesis is well suited for predicting the fatigue behavior of the member. A detailed description of all phases of the photoelastic procedure is presented along with the definition and application of the proposed energy concentration hypothesis.
Issue Date:1970-03
Publisher:University of Illinois Engineering Experiment Station. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Civil Engineering Studies SRS-358
Genre:Technical Report
Sponsor:The State of Illinois, Division of Highways; The U.S. Department of Trsansportation, Bureau of Public Roads
Date Available in IDEALS:2009-11-24
Identifier in Online Catalog:6055646

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