Solid State Phenomena Vol. 110

Abstract: This paper presents high cycle fatigue properties of a Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone. The thickness and width of the thin film of specimen are 1.1μm and 480.0μm, respectively. Tensile tests of five specimens are performed, from which the ultimate strength is found to be 144MPa. High cycle fatigue tests of six specimens are also performed, from which the fatigue strength coefficient and the fatigue strength exponent are found to be 336MPa and –0.1514, respectively.

Abstract: Austenitic stainless steel is a useful material for various industrial facilities such as the nuclear and steam power plant and the heavy chemical industry due to its good corrosion resistance and mechanical properties. However, it has also a large problem that austenitic stainless steel is sensitized in the welding process and its corrosion resistance and mechanical properties decreases by sensitization. Thus, in this paper, corrosion fatigue characteristics of artificially sensitized austenitic STS304 were investigated through corrosion fatigue test. From the results, corrosion fatigue strength of sensitized STS304 was remarkably reduced compare to non-sensitized ones. And it is expected that corrosion fatigue life of TMCP steel can be nondestructively predicted using the DCPD method.

Abstract: This paper presents a case history involving a failure of water pipeline due to a deep excavation. The case history was analyzed using both the simplified method and more sophisticated finite element modeling. Also presented are the fundamentals of damage assessment of buried pipelines associated with deep excavation-induced ground movements. A number of ground displacement profiles pertinent to the damage assessment are introduced. The results of the analysis indicated that the excessive ground movement was the major cause for the failure. These results were partly supported by the finite element analysis which takes the soil-pipe interaction effect account. It is demonstrated that although conservative, the simplified approach presented in this paper can be effectively used as a first-order method for excavation-induced pipeline damage.

Abstract: In ASME Sec. III ‘design by analysis’ approach, stresses are generally calculated by finite element method and compared to corresponding stress limits after categorizing those components. However, in order to obtain optimum results, time consuming and expensive manipulations are required owing to its mesh size dependency and complicate stress categorization. In this paper, a new approach based on structural stress is proposed to resolve the issues and applied to a heat exchanger motor operated valve. At first, the technical bases and specific features of structural stress approach are briefly discussed. Secondly a series of finite element analyses are carried out to show the limitations of current ASME approaches and to get basic data for the proposed approach. Finally, a structural stress concentration factor of motor operated valve is determined after comparison of local stresses and structural stresses, and utilized for fatigue life evaluation. Since the results show a promising applicability, it seems that the structural stress based approach can be utilized for fatigue life evaluation of components with complex geometries.

Abstract: Acoustic emission (AE) technique was applied as a non-destructive test method to detect and evaluate the localized damage at high temperature environment. The creep-fatigue crack growth tests were carried out with the acquisition of AE signal at 1000°F. Under trapezoidal waveform loadings, AE results showed different features according to each damage mode. During the creep period, low and steady emissions were shown, while emissions were burst and high counts rate was recorded during the fatigue loading. Based on these characteristics, damage contribution was expressed in terms of acoustic emission parameter as a part-time monitoring method. Comparisons of damage contribution with respect to lifetime showed the transient behavior from cycle-dependent to time-dependent process. In case of full-time monitoring, bilinear behavior between AE counts and life was represented. From both monitoring results, it was confirmed that creep and fatigue damage can be characterized by means of emission features and AE is possible way to evaluate the localized damage at elevated temperature.

Abstract: In order to simulate the growth of arbitrarily shaped three-dimensional cracks, the finite element alternating method is extended. As the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear is used. In the study, a crack is modeled as distribution of displacement discontinuities, and the governing equation is formulated as singularity-reduced integral equations. With the proposed method several example problems, such as a penny-shaped crack, an elliptical crack in an infinite solid and a semi-elliptical surface crack in an elbow are solved. And their growth under fatigue loading is also considered and the accuracy and efficiency of the method are demonstrated.

Abstract: Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.