Papers by Keyword: Crack Tip Opening Displacement (CTOD)

Abstract: The fracture toughness of different zones of X100 SAWL pipe was studied by three-point bend test method under different temperature. At the same temperature, the crack propagation resistance and tear modulus of X100 SAWL pipe distributed as: base metal>HAZ>weld bead, and the distribution of the CTOD value of X100 SAWL pipe is :base metal >weld bead >HAZ. Further investigation was conducted to analyze the decrease of fracture toughness (especially low temperature fracture toughness) and the occurrence of local unstable phenomenon in HAZ specimens.

Abstract: Fully-welded ball valves are widely used in the crude oil/natural gas transmission pipelines, and their quality has a direct bearing on the transportation safety of national energy. Two paralleled and symmetrical circular welds are used in the main welds of valve body, and the narrow-gap submerged arc welding (NG/SAW) is used in the welding groove. Because of conditional restrictions, it is impossible for the value to be post-weld heat treatment (PWHT). Therefore, the welds must have high impact toughness and strength. In order to study the welding performance of the base metal, SAW is used in the welding of proving rings of steel LF2 fully-welded ball valves. CTOD tests are applied to welding joints, and the result suggests that the minimum CTOD value of the valve’s welds and heat affected zone (HAZ) is more than 0.15mm. According to the criterion DNV-OS-C401, the welds in the fully-welded ball valve are safe enough without PWHT.

Abstract: First, tensile creep curve and creep propagation tests are conducted for austenitic stainless steel 0Cr18Ni9, i.e. 304 stainless steel at 550°C. The corresponding time hardening creep law is given for stresses ranging from 240 to 320 Mpa and the creep crack propagation length under a tension load of 10kN is measured by using QUESTAR long focus microscope system. Second, with the commercial finite element (FE) code ANSYS, the critical crack tip opening displacement (CTOD) is considered as crack propagation criterion to simulate the creep crack growth in the standard compact tension (CT) specimen. The FE predictions of the creep crack length in the primary and secondary stages are found to agree reasonably with the experimental results. The maximum computational error between the predictions and the experiment results is within 10%. Hence, the critical CTOD is a feasible criterion for crack growth simulations at elevated temperatures.

Abstract: This document demonstrates CTOD (crack tip opening displacement) tests at0°Cof welded joint in X80 marine drilling riser in accordance with the BS 7448 standard. The three point bending specimens are made in the weld center line and heat affected zone for the butt-welded joint in Φ533×25.4mm X80 marine drilling riser respectively according to the requirement of the standard. The CTOD testing results are discussed in detail, which can provide the basic to evaluate and optimize the welding and heat treatment technology of marine drilling riser.

Abstract: The ratio of J-conversion CTOD to CMOD-based CTOD was experimentally evaluated and analytically estimated in shallow crack specimens. It was demonstrated that the low strain hardening exponent in the Ramberg-Osgood relation reduced the CTOD ratio. A CTOD transformation equation, which was proposed by the authors, can transform CMOD-based CTOD into J-conversion CTOD with reasonable accuracy for 0.15≤a/W≤0.5.

Abstract: The tension, Charpy notch impact and fracture toughness tests on structural steels Q235B and Q345 were carried out under different prestrains. Ductile to brittle transition curves are investigated using Charpy impact tests. The results indicate that the prestrain decreases the impact toughness of both base metal (BM) and weld metal (WM); and increases the ductile-brittle transition temperature as well as the risk of fracture. The prestrain is also found to have a more significant effect in a less ductile material. River marking, the characteristic of cleavage fracture, is observed in the Q235B WM specimens 10% prestrain conditions at 0°C. The fracture surfaces of Q345 WM specimens are characterized by dimple-like structures. The depth of these dimples is decreased under prestrain applied before welding. The CTOD-prestrain curves are obtained using Boltzmann relation.

Abstract: This paper studied the assessment method for welding residual stress effects and constraint loss effects on brittle fracture of structural component subjected to membrane stress. The methodology of CTOD fracture toughness correction for welded joints is proposed from lower to upper ductile-brittle transition temperature region. The methodology is based on the tensile plastic zone size criterion and the equivalent CTOD ratio derived from the Weibull stress criterion. It has been found that the proposed methodology has given the reasonable fracture assessment results.

Abstract: There have been two different CTOD calculations, geometric CTOD calculation in BS7448 and J-based conversion in ASTM E1290 since the ASTM International revised E1290 in 2002, and it is useful to transform one CTOD into the other CTOD. In this study, analytical and experimental investigations into the ratio of ASTM E1290-CTOD to BS7448-CTOD were carried out, and two ratios of ASTM-CTOD to BS-CTOD, R1 and R2, were characterised in terms of cleavage cracking. These two characteristic CTOD ratios are helpful in simply transforming one critical CTOD to the other.

Abstract: A numerical analysis by means of the ANSYS code was performed in order to identify the ratio of both stress intensity factors and crack tip opening displacements for a cylindrical specimen with circumferential V-notch loaded by remote pure shear stress. This kind of loading produces pure mode II and III loading in four points on the circumferential crack front while the mix mode II+III exists in all other crack front points. In the linear-elastic range, the ratio of maximum values of mode III and mode II stress intensity factors was found to be . On the other hand, the ratio of crack tip opening displacements in the elastoplastic range approaches . These results can be used for the construction of fatigue crack growth rate curves in austenitic and ferritic steels measured in the near-threshold and near-fracture regions by means of a special testing device.

Abstract: A simple and reliable method has been proposed for determining fracture toughness of thin sheets. The principle of the method considers that critical crack opening displacement (c) corresponds to a specific amount of load drop during fracture toughness tests. The suggested technique yields c value for an interstitial free (IF) steel as 2.04 mm in excellent correspondence with an indirect estimate of 1.97 mm from the popular energy extrapolation technique. The magnitude of c for IF steel sheets is found to decrease with decreasing thickness in agreement with the expected variation of this criterion with specimen thickness in gross yielding fracture mechanics (GYFM) regime.