Chang-Doo Jang

Determination of Inherent Strain Regions to Estimate Plate Deformation by Line Heating

The inherent strain method is known to be very effective in predicting the plate deformation by line heating. Traditionally the inherent strain regions have been determined from the temperature distribution and the phase transformation regions(Ac3) of welding experiments. Since the phenomena of line heating are similar to those of welding, the experimental results under the same welding conditions have been applied directly to line heating analysis. The results cannot, however, reflect the effect of heating pattern and plate thickness. Besides, water-cooling in the actual heating process can alter the steel`s phase to martensite and shear plastic deformation occurs during the transformation. In this study, the experimental measurement of temperature distribution was substituted with a transient heat transfer analysis using FEM so that we could obtain the temperature distribution according to heat flux models of the heating pass. In order to consider plastic strains occurring additionally under phase transformation, inherent strain regions were assumed to be limited to the eutectoid temperature(Ac1). Using the regions, plate deformations could be predicted to validate our method and the results were in good agreement with the experimental ones

Analysis of Post Weld Deformation at HAZ by External Forces Based on Inherent Strain

In case of welding, the inherent strains are generated, because a structure experiences the plastic yielding. The inherent strain is defined as the irrecoverable strain after removing structural restraints and loading. For the analysis method of welding distortion, equivalent loading method based on inherent strain is in general use due to its efficiency and effectiveness. However, it is generally difficult to know the final strain of the welded structure if additional loadings were applied after welding. for this reason, this study introduced the concept of the hardening and added the hardening term to the equivalent loading method based on inherent strain. Therefore, the purposes of this study are to develop the inherent strain formula considering the hardening effect and to calculate residual Stresses Using Proposed inherent Strain. Also, this Study Verified the availability Of proposed inherent strain method by loading-unloading experiment on welded plate.

Developed Inherent Strain Method Considering Phase Transformation of Mild Steel in Line Heating

The inherent strain method is known to be very efficient in predicting the deformation of steel plate by line heating. However, in the actual line heating process in shipyard, the rapid quenching changes the phase of steel. In this study, In order to consider additional effects under phase transformation, inherent strain regions were assumed to expand. Also, when calculating inherent strain, material properties of steel in heating and cooling are applied differently considering phase transformation. In this process, a new method which can reflect thermal volume expansion of martensite is suggested.8y the suggested method, it was possible to predict the plate deformations by line heating more precisely.Ā᐀會Ā᐀ﶖ⨀ᡰ쾴ഀĀ저會Ā저㡆ﶖ⨀쾴Ā᐀會Ā᐀遆ﶖ⨀碋쾴Ā᐀會Ā᐀ﶖ⨀쾴瀀ꀏ會Ā䁇ﶖ⨀끰쾴Ā᐀會Ā᐀顇ﶖ⨀䡱쾴Ā㰀會Ā㰀ﶖ⨀쾴Ā㈀會Ā㈀䡈ﶖ⨀硲쾴Ā᐀會Ā᐀ꁈﶖ⨀쾴Ā᐀會Ā᐀ﶖ⨀ꡳ쾴Ā저會Ā저偉ﶖ⨀偮쾴Ā저會Ā저ꡉﶖ⨀쾴Ā저會Ā저Jﶖ⨀聯쾴Ā저會Ā저塊ﶖ⨀ႌ쾴؀Ā؀會Ā؀끊ﶖ⨀衬쾴䤀Ā切會Ā切ࡋﶖ⨀롭쾴Ā搀

Numerical Analysis and Experimental Verification of Relaxation and Redistribution of Welding Residual Stresses

For the precise assessment of the effect of welding residual stresses on structural strength and fatigue crack growth behavior, new FE analysis algorithms for the estimation of residual stress relaxation due to external load and redistribution due to fatigue crack propagation were proposed in this paper. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis In the analysis of fatigue crack propagation, the applied SIF(Stress Intensity Factor) range was evaluated by -point displacement extrapolation method, and the effect of welding residual stresses on crack propagation was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

A study on the simulation of water cooling process for the prediction of plate deformation due to line heating

Abstract In a line heating process for hull forming, the phase of the steel transforms from austenite to martensite, bainite, ferrite, or pearlite depending on the actual speed of cooling following line heating. In order to simulate the water cooling process widely used in shipyards, a heat transfer analysis on the effects of impinging water jet, film boil-ing, and radiation was performed. From the above simulation it was possible to obtain the actual speed of cooling and volume percentage of each phase in the inherent strain region of a line heated steel plate. Based on the materi-al properties calculated from the volume percentage of each phase, it should be possible to predict the plate de-formations due to line heating with better precision. Compared to the line heating experimental results, the simu-lated water cooling process method was verified to improve the predictability of the plate deformation due to line heating. Keywords: Line Heating Process; Heat Transfer Analysis; Cooling Speed; Phase Transformation; Inherent Strain; Plate Defor -mation