Papers by Keyword: Structural Stress

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Authors: Myung Hyun Kim, Chung In Ha, Sung Won Kang, Jeong Hwan Kim, Jae Myung Lee
Abstract: Fatigue strength assessments with two types of load carrying fillet weldment under out-of-plane bending load have been carried out by using both hot spot stress and structural stress methods. Basis for the derivation of structural stress method is discussed in detail. Finite element analyses using shell elements models have been performed for the fatigue strength assessment of weldments. As a result of the fatigue strength evaluation for load carrying transverse fillet weldment, hot spot stress method is found to be consistent with structural stress method as well as measurement. Hot spot stress, however, estimated for the load carrying longitudinal fillet weldment exhibit large variation with respect to mesh size and element type while the calculated structural stress for the longitudinal fillet weldment is relatively independent of mesh size. The fatigue life estimation according to structural stress has been introduced with the master S-N curve.
995
Authors: Myung Hyun Kim, Sung Won Kang, Jeong Hwan Kim, Jae Myung Lee, Hyoung Rae Kim
Abstract: In this study, a methodology for the assessment of fatigue failure modes of weldments due to partial penetration weld has been carried out by using structural stress method. Structural stress calculation procedure, using shell element based on equilibrium consideration using nodal forces and moments, is employed. It is important to note that the structural stress calculation procedures for partial penetration welds can be used to determine a minimum weld leg length, beyond which, weld root failure modes can be effectively suppressed. An example study, with respect to a fillet weld leg length design, is compared with a design criterion, and they are found to be in agreement.
601
Authors: C.M. Sonsino, D. Radaj, W. Fricke
Abstract: Some recently developed variants of local concepts for assessing the fatigue strength and structural durability of welded joints are reviewed. These comprise structural stress, notch stress or strain and fracture mechanics concepts. New variants of the structural stress concept are Dong’s gradient stress approach and Xiao-Yamada’s ‘one millimetre stress’ approach. FE meshing rules have been developed for welded joints in thin sheet structures. The concept of fictitious notch rounding is now better substantiated for aluminium alloys. The small-size notch concept is applicable to thin sheet lap joints. The new notch stress intensity factor concept is based on the singular stresses at the sharp weld toe notch. Advanced fracture mechanics concepts combine crack initiation at the seam weld root or nugget edge and crack propagation over the plate thickness resulting in endurable FK values as function of cycles per unit thickness, N/t.
565
Authors: Kwang Seok Kim, Joong Kyoo Kang, Joo Ho Heo, Sung Geun Lee
Abstract: The structural stress (SS) method developed by BATTELLE has been studied based on small or mid-size scale specimens. In order to apply the new method, such as SS, on an actual project, it should have application results on actual project. However, SS method didn’t have a lot of application data compared to class procedure using hot spot stress (HSS). In order to find out whether the SS method, for the evaluation of fatigue life, can give reasonable results when it is applied under the same loading suggested by classification societies, it was compared with fatigue lives derived by class. ABS & DNV’s simplified fatigue analysis method were adopted to check the validity of SS method. Before applying complicated loading of class, static loading case was applied, since the class method has their own correlation factor for wave loading. And then, simplified fatigue analysis was performed with more complicated loading cases. From the results of fatigue life calculation, it can be said that SS shows reasonable fatigue lives with respect to HSS or notch stress based fatigue lives.
633
Authors: Li Gong Sun, Chao Meng, Qing Duan Meng
Abstract: Based on viscoplastic Anand’s model, the structural stress of 8×8 InSb array detector with underfill dependent on indium bump sizes is systemically researched by finite element method. Simulation results show that as the diameters of indium bump decrease from 36μm to 20μm in step of 2μm, the maximum stress existing in InSb chip first reduces sharply, then increases flatly, and reaches minimum with indium bump diameter 32μm. The maximum stress in Si readout integrated circuit (ROIC) fluctuates at 320MPa with amplitude less than 50MPa, almost half stress in InSb chip. Yet the maximum stress in the indium bump array is almost unchangeable and keeps at 16.3MPa. When the height of indium bump increases from 9μm to 21μm in step of 6μm, the maximal stress in InSb chip first reduces sharply from 800MPa to 500MPa, then almost retains constant. With indium bump diameter 32μm and height 21μm, the maximum stresses in whole 8×8 InSb array detector reaches minimum 458MPa, besides, the stress distribution at the contacts areas is uniform and concentrated, the stress value is smallest and this structure is promising to avoid device invalidation.
2289
Authors: Myung Hyun Kim, Sung Won Kang, Jae Myung Lee, Wha Soo Kim
Abstract: In order to strengthen or repair the welded structural members or fatigue damaged areas, various surface treatment methods such as grinding, shot peening and/or hammer peening are commonly employed among other methods available. While the weld toe grinding method is known to give 3~4 times of fatigue strength improvement, this improvement may significantly vary according to weld bead shapes and loading modes. In this context, a series of fatigue tests is carried out for three types of test specimens that are typically found in ship structures. Weld burr grinding is carried out using an electric grinder in order to remove surface defects and improve weld bead profiles. The test results are compared with the same type of test specimen without applying the fatigue improvement technique in order to obtain a quantitative measure of the fatigue strength improvement. Moreover, structural stress method is employed to evaluate the effectiveness of the method in evaluating the fatigue strength improvement of welded structures.
1079
Authors: Jong Sung Kim, Tae Eun Jin
Abstract: In the paper, the validity of the modified mesh-insensitive SS (structural stress) procedure to apply to the welded joints with local thickness variation is identified via the comparison of SCFs (stress concentration factors) calculated for various FE (finite element) models. FCI (fatigue crac kinitiation) cycles are determined by using the SS/EPFM (elasto-plastic fracture mechanics) approach and the various fatigue crack growth models. Fatigue test is performed to identify the validity of the fatigue analysis results. Finally, as a result of comparison among test and various analysis results, it is found that the SS/FM (fracture mechanics) approach agrees well with the fatigue test results over all cycle regions and the SS/EPFM approach is more reliable than the SS/LEFM (linear elastic fracture mechanics) approach.
774
Authors: Myung Hyun Kim, Sung Won Kang, Chung In Ha, Jae Myung Lee, Jeong Hwan Kim, Sung Soo Na
Abstract: Two types of load carrying fillet weldment, which are typical weld joints in ship structures, were examined under out-of-plane bending load by using structural stress approach. Finite element analyses using both solid and shell elements models have been performed for the assessment of fatigue strength. Basis for the derivation of structural stress method is discussed in detail. The calculated structural stress values for the fatigue strength evaluation of load carrying fillet weldments are independent of mesh size. In this study, drawbacks and doubts associated with applying the structural method such as the guidance of virtual node method and the application of three-dimensional equilibrium condition for solid model have been discussed accompanied by various case studies. In order to solve the problem of the solid model, the alternative method for solid model by using the equilibrium condition of the nodal force has been introduced.
2069
Authors: Li Wen Zhang, Ming Shao, Qiang Yu, Peng Fei Li
Abstract: Based on finite element analysis, the structural stress of 8×8 InSb Infrared Focal Plane Array integrating with microlens arrays dependent on indium bump sizes is systemically researched. Simulation results show that as the diameters of indium bump increase from 16μm to 38μm in step of 2μm, the maximum stress existing in InSb chip first reduces, then increases, and reaches minimum with indium bump diameter 32μm. Yet the maximum stress in the indium bump array is almost unchangeable and keeps at 16.5MPa. The maximum stress in Si readout integrated circuit almost half stress in InSb chip. Besides, the stress appearing on those regions situating just on microlens array is much smaller than its surrounding regions, and the stress distribution is uniform at contacting areas between InSb chip and indium bump.
162
Authors: Qing Duan Meng, Qing Song Lin, Xiao Lei Zhang, Wei Guo Sun
Abstract: Two-step method is used to research stress and its distribution in 64×64 InSb infrared focal plane array (IRFPA) employing finite element method. First, a small 8×8 InSb IRFPA is studied by changing indium bump diameters from 24μm to 36μm, with indium bump thickness 20μm and InSb thickness 10μm, the simulated results show that von Mises stress in InSb chip is dependent on indium bump diameters, the varying tendency is just like the letter V, here when indium bump diameters is set to 30μm, the smallest von Mises stress is achieved and its distribution in InSb chip is uniform at contacting areas. Then, InSb IRFPA array scale is doubled once again from 8×8 to 64×64 to learn the effect from array size, thus, the stress and its distribution of 64×64 InSb IRFPA is obtained in a short time. Simulation results show that von Mises stress maximum in InSb chip and Si readout integrated circuit almost do not increases with array scale, and the largest von Mises stress is located in InSb chips. Besides, stress distribution on the bottom surface of InSb chip is radiating, and decreases from core to four corners, and stress value at contacting area is smaller than those on its surrounding areas, contrary to stress distribution on top surface of InSb chip.
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