Investigating optimal cutting configurations for the contour method of weld residual stress measurement

The present work examines optimal cutting configurations for the measurement of weld residual stresses (WRS) using the contour method. The accuracy of a conventional, single-cut configuration that employs rigid clamping is compared with novel, double-embedded cutting configurations that rely on specimen self-constraint during cutting. Numerical analyses examine the redistribution of WRS and the development of cutting-induced plasticity (CIP) in a three-pass austenitic slot weld (NeT TG4) during the cutting procedure for each configuration. Stress intensity factor (SIF) analyses are first used as a screening tool; these analyses characterise lower stress intensities near the cutting surface when double-embedded cutting configurations are used, relative to SIF profiles from a single-cut process. The lower stress intensities indicate the development of CIP – which will ultimately affect back-calculated WRS – is less likely to occur when using an embedded configuration. The improvements observed for embedded cutting approaches are confirmed using three-dimensional finite element (FE) cutting simulations. The simulations reveal significant localised plasticity that forms in the material ligaments located between the pilot holes and the outer edges of the specimen. This plasticity is caused by WRS redistribution during the cutting process. The compressive plasticity in these material ligaments is shown to reduce the overall tensile WRS near the weld region before this region is sectioned, thereby significantly reducing the amount of CIP when cutting through the weld region at a later stage of the cutting procedure. Further improvements to the embedded cutting configuration are observed when the equilibrating compressive stresses in material ligaments are removed entirely (via sectioning) prior to sectioning of the high WRS region in the vicinity of the weld. All numerical results are validated against a series of WRS measurements performed using the contour method on a set of NeT TG4 benchmark weld specimens

Numerical analysis of the effect of weld-induced residual stress and plastic damage on the ballistic performance of welded steel plate

The current paper presents numerical analyses that elucidate the effects of post-weld residual stress and associated plastic damage on the ballistic performance of 316L austenitic steel plate. Impact simulations of an 18 mm thick plate with a centreline three-pass slot weld by hemispherical-nosed and flat-nosed projectiles are performed, with initial velocities in the range of 300-800 m/s. The numerical framework consists of three interdependent stages: (i) a weld model was developed in Abaqus/Standard and validated using two independent experimental data sets; (ii) a Johnson-Cook material model is calibrated and validated along with the shear failure fracture criterion available in Abaqus/Explicit for impact models; and (iii) the weld modelling results were transferred to an impact model built in Abaqus/Explicit, which employs the validated material and fracture models to predict the ballistic performance of welded plate. It is shown that the associated plastic strain damage accumulated during the welding process - and its distribution - has an adverse effect on the ballistic performance. It has also been determined that a fracture criterion that accounts for pre-existing damage in the weldment must be used for accurate impact analyses of welded structures. Crown Copyright (C) 2012 Published by Elsevier B.V

Life assessment methodologies for high temperature branch pieces.

Branch pieces in high temperature steam circuits are a common feature of power generating plants both conventional and nuclear. A simple inverse code methodology based on BS1113 [1-3] exists for estimating base rupture life in cylinder to cylinder configurations (branches) under constant pressure and temperature. This does not cover the complex issue of estimating the mixed creep-fatigue effects of cycling which can have a significant influence on damage especially under the current practice of multi-shifting as utilities follow fluctuating energy markets. The current work is primarily aimed at extending the inverse code methodology for base rupture to include cycled loading due to startups and shutdowns. This is achieved under the guidelines of the R5 assessment code by the use of an analytical expression for metastable thermal stresses [4,5] and mapped thermal stress response. System loads are not considered in this work other than by the simple method suggested using the inverse code method. Only 90° non protruding branches are considered in the current work. Examples of 90° branches are examined showing the significance of cyclic loading on a variety of branch configurations. It was observed that base rupture dominates most configurations up to a "cliff edge" in thermal ramp rate followed by rapid accumulation of creep-fatigue damage at higher rates. The results are a useful aid when assessing the optimal operating conditions for individual power stations. © 2009, Australian Institute for Non-Destructive Testing (AINDT

Alpine, 27 December 1978 [picture] /

Part of: Kosciusko Huts Association photograph collection.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.pic-vn3259552