Jung-Hun Choi

Assessment of Local Wall Thinned Pipeline Under Combined Bending and Pressure

Failure of a pipeline due to local wall thinning is getting more attention in the nuclear power plant industry. Although guidelines such as ANSI/ASME B31G are still useful for assessing the integrity of a wall thinned pipeline, there are some limitations in these guidelines. For instance, these guidelines consider only pressure loading and thus neglect bending loading. However, most pipelines in nuclear power plants are subjected to internal pressure and bending moment due to dead-weight loads and seismic loads. Therefore, an assessment procedure for locally wall thinned pipeline subjected to combined loading is needed. In this paper, three-dimensional finite element (FE) analyses were performed to simulate full-scale pipe tests conducted for various shapes of wall thinned area under internal pressure and bending moment. Maximum moments based on true ultimate stress (σu,t) were obtain from FE results to predict the failure of the pipe. These results were compared with test results, which showed good agree...

Evaluation of Failure Strength of Woven CFRP Composite Plate Subject to Axial Load by Tan-Cheng Failure Criterion

Abstract In the manufacture of CFRP(Carbon Fiber Reinforced Polymer Composite) composite structures, various independent components join by bolts and pins. Holes for bolts and pins have an effect on the failure strength of such structures, because those act as notches in structures. The failure characteristic of such structures are different from those of plain plate subject to remote load. In this paper, tensile properties of woven CFRP composite plates with laminates of 0°, 30°and 45° were obtained according to ASTM D 3039. By using obtained tensile failure strength and Tan-Cheng failure criterion, tensile failure strength of CFRP laminate with arbitrary fiber angle were evaluated. Also, the degradation of tensile properties by center hole(φ10mm) with a remote load was evaluated and the failure strengths were applied to Tans failure criterion, similarly. [이 논문은 2008년도 재료 및 파괴부문 춘계학술대회(2008. 5. 29.-30., 충북대) 발표논문임] † 책임저자, 회원, 성균관대학교 기계공학부 E-mail : seok@skku.edu TEL : (031)290-7446 FAX : (031)290-7482 * 성균관대학교 대학원 기계공학부** 회원, 성균관대학교 기계공학부

FATIGUE CRACK PROPAGATION BEHAVIOR ACCORDING TOFIBER ARRAYING DIRECTION FOR LOAD DIRECTION INWOVEN CFRP COMPOSITE

The fatigue crack propagation of CFRP (carbon fiber reinforced composite material) laminates is of current interest, particularly with regard to their durability under fatigue loading. Recently, carbon fiber reinforced composite materials (Woven fabric) are widely used in various fields of engineering because of its advanced properties. Then, many researchers have studied woven fabric CFRP materials but fatigue crack propagation behaviors for composites have not been still standardized . It shows the different crack propagation behavior according to load and fiber direction. Therefore, there is a need to consider fatigue crack propagation behavior in conformity with fiber arraying direction to load direction at designing structure using woven CFRP materials. In this study, therefore, the fatigue crack propagation for plain woven CFRP composite materials was investigated under two different fiber array direction (fiber arraying direction to load : 0°, 45°). Fatigue crack propagation tests of the woven CFRP composite were conducted under sinusoidal wave-form with stress ratios of 0.3 at a frequency of 10Hz, respectively. As a result of test, fatigue crack propagation rates (da/dN) were plotted against the stress-intensity factor amplitude (ΔK) and other factor. Also we compared ΔK with other factor that considering in-plain anisotropy. All of tests of fatigue crack propagation were carried out under mode I opening loading by using compact tension specimens.

Evaluation of Fatigue Life Characteristic of a Real Waterwork Pipe Using the Probability Density Function

The fatigue characteristics of a material or a structure are generally derived from fatigue tests of standard specimens. However, test results of standard specimens are different from those of real structures or components. Therefore, to calculate more accurate fatigue life, the geometrical effect and surface condition must be considered by comparing test results of standard specimens with those of real structures or components. Thus the object of this paper is to evaluate the fatigue characteristics of a real waterwork pipe. Also, to evaluate fatigue characteristic based on life distribution, the statistical fatigue characteristics were analyzed by the normal distribution and related data of P-S-N curve.

Evaluation of Fatigue Crack Propagation Depending on Fiber Array Direction in Woven CFRP Composites

초록: 많은연구자들이평직탄소섬유강화플라스틱에대해서연구해왔지만피로균열진전에관한연구는아직도미지한상태이다. 그리고하중과섬유배열각도에따라균열진전양상이다름을알수있다. 본연구에서는서로다른두개의섬유배열각도(0°, 45°)에서평직탄소섬유강화플라스틱의피로균열진전에대해연구하였다. 평직탄소섬유강화플라스틱의피로균열진전테스를하중비0.1에10Hz로수행하였다. 그시험결과로써, 피로균열진전속도(da/dN)와에너지해방률(ΔG)과의그래프를도출하였고, 섬유배열각도에따른균열진전양상을0°의경우에는Mode I를적용하였고, 45°의경우에는Mixed Mode를적용하였다.Abstract: Many researchers have studied woven fabric carbon-fiber-reinforced composite (CFRP) materials but thestudy of fatigue crack propagation in composites has been insufficient. It has known that the crack propagationbehavior differs depending on the load and the fiber direction. In this study, the fatigue crack propagation alongtwo different fiber array directions (0°, 45°) in plain woven CFRP composite was investigated. Fatigue crackpropagation tests were conducted on the woven CFRP composite under a sinusoidal waveform load with stressratios of 0.1 at a frequency of 10 Hz. Once the results of the tests were obtained, fatigue crack propagation rates(da/dN) were plotted against the energy release rate amplitude (ΔG), and it was observed that either mode I crackpropagation or mixed mode crack propagation occurs depending on the fiber array direction.

A Study on Behavior of Mixed Mode Fatigue Crack Growth of Spiral Welding Part Under Bending Load

Manufacturing of large scale steel pipes in a nuclear power plant, offshore structures and a petroleum chemical plant, etc., a spiral welding method is mainly used. Such a welding part generally has several types of defect such as an undercut, a pit and a crack and in many cases, it finally reaches the failure by crack growth from these. The linear elastic fracture mechanics has been applied to a study on fatigue crack growth of welding parts, that is, as the weld, the heat affected zone (HAZ) and the base metal part in a large scale steel pipe by several reachers. However, since such studies are mainly the results by a standard specimen under uniaxial tensile load, they are different from the fatigue crack growth of a real large scale steel pipe under multiaxial load. In this study, we performed the evaluation for the characteristics of the mixed mode fatigue crack growth behavior of a spiral welding part in a real large scale steel pipe under bending load.Copyright

Calculation of the Crack Length for a Pipe Specimen using the Modified Load Ratio Method

The objective of this paper is to apply the load ratio method to the measurement of the crack length of the real scale pipe specimen. The load ratio method was modified and finite element analyses were performed to derive the relationship between the normalized compliance and the normalized crack length for the pipe specimen. In order to measure the crack length, the direct current potential drop method and the modified load ratio method were applied to the pipe test. The applicability of the modified load ratio method was confirmed by comparing the calculated crack length with the measured crack length from the pipe experiment.