The paper deals with a study intended to modify the DWT (drop weight tear) tests performed on full thickness specimens taken from pipelines. The objective is to arrange the test so that the stress field in the region, where the crack develops, maintains its value as it occurs on pipelines. From this point of view, it is shown that the slope angle of the supports must reach values as high as 75° to induce a persistent stress that is comparable with the hoop stress, experienced by the pipe, when a longitudinal crack propagates. A new experimental set-up for drop weight tear tests is proposed. Its principal characteristic is the adoption of inclined supports driving die hinges connected to the specimen. This choice accomplishes the need that the specimen was subjected to a persistent stress field in the ligament, thus approaching the stress field experienced by a crack propagating in a pipeline. This set-up requires a proper processing of the data that is accurately explained in the paper. The tests are conducted under a quasi-static loading but the method has been designed to apply in dynamic tests. The method takes advantage of image identification and processing of some markers applied on the system components; thus, the frame sequence allows to monitorize the fracture mechanism. Standard DWT specimens have been used; this was made possible through the application of two extensions on the specimen itself. The adoption of the extensions allows to reduce the compression plasticity under the hammer, which generally affects the significance of the results. However, the extensions could be eliminated if non-standard specimens (longer) are extracted and flattened from the pipe. The advantages of this new set-up are widely discussed in the paper, where the analytical derivation of all quantities presented is shown. The final objective is a tool able to compute several parameters such as nominal stresses, loads, energies and kinematical variables. The tests were accurately discussed on a X100 steel, but the same tool applied on X60 steel confirmed the accuracy of the measurement set-up. When introducing inclined sliding planes, it is advisable to represents the DWT test results in terms of bending moment - relative rotation instead of simple load - displacement. By this point of view, all data originating by different support slopes can be joined together. In this paper the method is applied on quasi-static tests; dynamic DWTT (drop weight tear test) of course behaves differently. Here, the interest is pointed out on the overall method and the check of it instead than on experimental results: all die equilibriums and energy balances are well satisfied. The same strategy could be applied to dynamic tests thus performing DWTT under crack propagation conditions that result closer to pipeline fracture propagation. In a simpler way, the deep static analysis conducted in this paper could open the way to modify the standard instrumented DWT test by the adoption of inclined supports, even excluding the image-processing procedure.


    Access

    Access via TIB

    Check availability in my library

    Order at Subito €


    Export, share and cite



    Title :

    New experimental set-up to approach pipeline fracture behaviour by three-point bending specimens


    Additional title:

    Neuer experimenteller Ansatz zur Untersuchung des Pipeline-Bruchverhaltens mittels drei-Punkt-Biegeversuchen


    Contributors:
    Minotti, M. (author) / Salvini, P. (author)


    Publication date :

    2012


    Size :

    22 Seiten, 23 Bilder, 25 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English