Kazuki Ikushima

Development of in situ measurement system for welding deformation using digital cameras

Abstract A three-dimensional (3D) deformation (in plane and out of plane deformations) measurement method is developed using digital cameras, which require no special equipment. This method is a non-contact method, and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when the deformation to be measured is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. In this study, the proposed method is applied to the sequential measurement of displacement under strong lighting levels in arc welding. Through the comparison of the results measured by a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper, the quantitative validity of the proposed method is also verified.

Large-scale non-linear analysis of residual stresses in multi-pass pipe welds by idealized explicit FEM

In this research, idealized explicit FEM (IEFEM), which can analyze residual stress of the practical structures in practical time, was applied to large-scale residual stress problem of X groove multi-pass pipe welding. The analysis model has 3,376,074 degrees of freedom and 108 welding passes. In the analysis, all the welding passes and welding pass grouping technique were considered to investigate the influence of welding pass grouping on residual stress distribution. As a result, it was found that the residual stress distribution can be different if pass grouping technique is used. In addition, to investigate the influence of the welding pass sequence on residual stress distribution, analyses which consider another in-layer welding sequence and build-up sequence were carried out. As a result, it was found that the influence of the welding sequence on residual stress distribution is small. The computing time was practical even though all the welding passes are modeled in a full pass model.

Numerical analysis of residual stress distribution on peening process

Various peening techniques are employed to prevent stress corrosion cracking or to extend the fatigue life of structures. In this study, to investigate the effect of shot peening on operation, an analysis method that predicts the stress distribution due to shot peening was proposed. Using the proposed method, the load distribution from the shot collisions was modeled, and it was integrated with a dynamic analysis method based on the idealized explicit FEM (IEFEM). The accuracy of the proposed method was confirmed by comparing the stress distribution from the collision of a single shot with the results analyzed using ABAQUS. A thermal elastic-plastic analysis method using IEFEM was applied to the analysis of the residual stress distribution of a multi-pass-welded pipe joint. The calculated residual stress distribution was compared with the measured residual stress distribution measured using X-ray diffraction (XRD). The results showed that the two welding residual distributions were in good agreement. Considering the calculated welding residual stress distribution, the modification of the stress distribution due to shot peening was predicted using the proposed method. A similar stress distribution was obtained using XRD for the case where a large number of collisions were considered.

Development of Ultra Large Scale Computation for Transient Welding Deformation and Stress Using Idealized Explicit FEM Accelerated by GPU

Numerical simulations such as Finite Element Method (FEM) are widely used as tool of structural analyses in both design and production. However, in the application of FEM to welding problems, the simulation scale is usually limited to the welding joint level. Only a few large-scale welding analyses are performed on existing research because welding problems are transient and show strong nonlinearity. In such cases, it is necessary to use static implicit FEM to achieve an accurate analysis, but the larger analysis scale requires larger memory consumption and computing time. Thus, we previously proposed idealized explicit FEM (IEFEM) to achieve shorter computing time and lower memory consumption.Since IEFEM is based on dynamic explicit FEM, it is not needed to solve the stiffness matrix of the whole system and it is possible to analyze by only performing the calculation for each degree of freedom (DOF) and element. Such characteristic indicates that IEFEM is suitable for parallelization. Then, in this study, we developed parallelized IEFEM using a graphics processing unit (GPU). The usefulness and validity of the developed method are considered by analyzing a 3-dimensional multi-pass moving heat source problem, which is very difficult to analyze with commercial FEM software because of its analytical scale. As a result, it is found that parallelized IEFEM accelerated by a GPU can analyze a large-scale problem having over 1,000,000 DOFs on a single PC.Copyright

Prediction of Residual Stress in Multi-Pass Welded Joint Using Idealized Explicit FEM

Heavy thick steel plate is used for pipes and also ship structures, and multi-pass welding is usually adopted for the welding. Because of the heavy thickness, residual stress plays an important role, particularly in crack propagation. Implicit Finite Element Method (FEM) is often used as a welding analysis method to examine the residual stress of the welded plate, but it is not easily applied to multi-pass welding problems with tens of thousands of degrees of freedom, because of the huge computational time and memory consumption. Alternatively, it is possible to simulate the residual stress in shorter time with lower memory consumption by using Idealized Explicit Finite Element Method developed by the authors. Moreover, the computational time can be shortened by using Idealized Explicit FEM using a Graphics Processing Unit (GPU). In this research, Idealized Explicit FEM parallelized using a GPU is applied to the analysis of the residual stresses of the multi-pass welding joint of a pipe structure made of heavy thick steel plate.As the result, the residual stress simulated by the Idealized Explicit FEM corresponds to the measured residual stress. Furthermore, it is found that the grouping method may affect to the residual stress distribution.Copyright

Study on residual stress in multi-pass welded joint using idealized explicit FEM

Heavy thick steel plate is used for pipes and also ship structures, and multi-pass welding is usually adopted for the welding. Because of the heavy thickness, residual stress plays an important role, particularly in crack propagation. Implicit Finite Element Method (FEM) is often used as a welding analysis method to examine the residual stress of the welded plate, but it is not easily applied to multi-pass welding problems with tens of thousands of degrees of freedom, because of the huge computational time and memory consumption. Alternatively, it is possible to simulate the residual stress in shorter time with lower memory consumption by using Idealized Explicit Finite Element Method developed by the authors. Moreover, the computational time can be shortened by using Idealized Explicit FEM using a Graphics Processing Unit (GPU). In this research, Idealized Explicit FEM parallelized using a GPU is applied to the analysis of the residual stresses of the multi-pass welding joint of a pipe structure made of heavy thick steel plate. As the result, the residual stress simulated by the Idealized Explicit FEM corresponds to the measured residual stress. Furthermore, it is found that the grouping method may affect to the residual stress distribution.

Three-dimensional in situ measurement system for welding deformation using digital cameras

A 3-dimensional deformation (in-plane and out-of-plane deformation) measurement method is developed using digital cameras, which require no special equipment. This method is a non-contact method and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when measuring deformation is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. In this study, proposed method is applied to the sequential measurement of displacement under the strong lighting levels in arc welding. Through the comparison of the results measured by a 3-dimensional shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper, quantitative validity of the proposed method is also verified.

Development of three-dimensional welding deformation measurement based on stereo imaging technique

Due to the rapid improvement of digital cameras, especially the pixel resolution, digital image correlation (DIC) has been introduced to measure the deformation and strain of structures. Using digital cameras for the DIC technique is an easy and fast method for obtaining structural information, represented as all the pixel points in a photo. Because a wide range of structural deformation can be obtained with high accuracy, this method has the potential to be very useful. Currently, DIC can execute a measurement with high accuracy only when the out-of-plane displacement is small. When the out-of-plane displacement is large, the deformation causes the measurement error. Therefore, a stereo imaging method using two digital cameras is proposed in this study. The proposed method can measure not only in-plane deformation but also out-of-plane deformation with high accuracy without calibration of the errors caused by the out-of-plane displacement. In this paper, the measurement accuracy of the proposed method for in-plane deformation and out-of-plane deformation is discussed through the application of a bead-on-plate welding test. The proposed method can measure transverse shrinkage and angular distortion with high accuracy. In contrast to the vernier caliper and laser distance metre measurement methods, which can measure only a few points at a time, the proposed method using two digital cameras can measure the full field in a short time. These results confirm that the proposed method is more advantageous than other methods.