Key Engineering Materials Vols. 340-341

Abstract: The Charpy V notch specimens of X70 pipeline steel with different notch orientation are tested under the static and dynamic conditions at different temperatures. By analyzing the load versus displacement curves and fracture appearances of specimens the relation of fracture behavior and loading rate is investigated. The maximum load increases and the displacement corresponding to maximum load reduces with test temperature decreasing. Both under the static conditions are larger than that under the dynamic conditions. The fracture sections of all test specimens are reduced in the thickness direction and quantity reduced depends on the load rate, notch orientation and test temperature. At the higher temperature, delamination cracks are found on the fracture surface both under the static and dynamic conditions, which are perpendicular to the thickness direction in T-L specimen and perpendicular to the main crack propagation direction in T-S specimen. Influence of loading rate on the delamination crack size and amount is obvious. The fracture initiation energy and total fracture energy increase with test temperature increasing. Influence of loading rate on the total fracture energy is unobvious at the higher temperature, but is obvious at the lower temperature. So the loading rate effects on total fracture energy are relevant to test temperature and notch orientation.

Abstract: In the recent years three-dimensional (3D) elastic-plastic analyses have been conducted extensively for the opening mode (mode I) fracture and the constraint effects are discussed in detail. However less work is focused on other modes as sliding mode (mode II), tearing mode (mode III) or the mixed mode fracture in three-dimensional. In this paper the thickness effect on pure mode II case is discussed by the finite element method (FEM). Modified Boundary Layer (MBL) model is used, which has the ability to take into account the combined effects of the in-plane constraint (T-stress) and the out-of-plane constraint (finite thickness). The result demonstrates the weak thickness dependence on the near tip stress and strain fields under mode II loading. And the size of the 3D zone at mode II loading is determined to range from 1.0 to 1.2 times the thickness. Two fracture parameters of J integral and crack tip sliding displacement (CTSD) are discussed, which are almost same at different thickness planes except those very near the surface. It is interesting to find that the relations between J and CTSD keep linear at different thickness planes. T-stress is symmetry on stress and strain distributions along the crack plane. However its effects indicate weak thickness dependent on the CTSD and J integral fracture parameter.

Abstract: The present study deals with the problem of interfacial cracks of antiplane sliding mode between a usual elastic material and a one-dimensional hexagonal quasicrystal. Based on the physical facts that balance of the phason stress field is foreign to the real force in or out of quasicrystal in physical space, and the quasicrystal is bonded to a usual elastic material without both phason displacement and stress fields, the problem is described by analytic functions and attributed to find solutions of the Riemann-Hilbert problem. It is found that the stress intensity factor is not related to phason strain field, and the phason stress field does not exist. The discontinuity of phonon displacement field across crack is related to the phason displacement field because of the coupling of phonon and phason strain fields. Although there is not the phason displacement on the bonded portion of interface, it exists on the crack’s surface. The energy release rate obtained from interfacial crack’s propagating is different from that of an interfacial crack between two different pure elastic materials.

Abstract: An adaptive finite element method for analyzing two-dimensional and axisymmetric nonlinear elastic fracture mechanics problems with cracks is presented. The J-integral is used as a parameter to characterize the severity of stresses and deformation near a crack tip. The domain integral technique is utilized as the J-integral solution scheme with the 9-node degenerated crack tip elements. The solution accuracy is further improved by incorporating an error estimation procedure to a remeshing algorithm with a solution mapping scheme to resume the analysis at a particular load level after the adaptive remeshing technique has been applied. Two benchmark problems are analyzed to evaluate the efficiency of the combined procedure.

Abstract: By controlled rolling and cooling process, a Mn-Ti high strength steel with yield strength on the order of 700MPa had been developed successfully. The microstructure consists of fine lath shaped bainite and ferrite. The strengthening factors of this steel are attributed to the tiny interlocked distribution of bainite lath and titanium carbide precipitation. When the amount of bainite is more than 70%, the yield strength of steel is higher than 700MPa, and good mechanical performances are obtained. As a result of presence of finely dispersed bainite slabs the plasticity of steel is improved, with the steel’s elongation being about 19%. Many tiny TiC precipitates are observed under transmission electron micrograph, and these particles result in precipitation strengthening.

Abstract: There are many problems in the common baiting methods, such as bad cross-section quality, low efficiency and so on. In order to overcome these disadvantages, a new bar cutting technology based on high speed and restrained state is put forward in the paper. The cutting process and cutting mechanics were analyzed. The stressing intensity factor and fracture toughness were introduced to analyze the influence of loading velocity on the cutting surface quality. By means of the dislocation theory, the influence of loading velocity on the fracture process was researched. Numerical simulation and experiments were carried out, and the results were conformed well with the theoretical ones.

Abstract: Fracture properties of softwood under mode I loading perpendicular to the grain are studied in this paper. The stress intensity factor KIC in the R and L directions is measured by the compact tension test using small several specimens. The shape and size of plastic zone in crack tip is determined by numerical simulations based on von Hill yield criterion. The results show that anisotropic material constants do not affect the length of plastic zone along crack direction and it only operates on the plastic zone with θcr≠ 0. Strength ratios α1, α2 and toughness ratios r1, r2, influencing on the plastic zone, are discussed. Comparative analysis shows that r1 and r2 work markedly on the shape and size of plastic zone, whereas α1, α2 do less.

Abstract: In this investigation, we evaluated diagnoses of a defect concerning coating of land-base gas turbine using infrared thermography camera. In this camera method has a strong point which is able to save time and costs compared with former method. Because it can be long field acquire temperature distribution by using non-contact method. But it has a week point that method applies thermal load about inspection sample. Presently, Method used widely in detection of crack is ultrasonic inspection. But this method, There is problem in application in place that uneven surface. In order to check cracks on a blade coating of a gas turbine, a part with cracks in a waste blade disposed after having been used in the field was extracted to produce a sample. So we apply the method by a infrared thermography camera to the produced sample, the sample was heated by means of a halogen lamp. In this paper, we want to describe production of land-base turbine sample, a method of applying thermal load at produced sample, infrared thermography camera technique, an analysis technique of thermography, a defect analysis of coating of land-base gas turbine blades.

Abstract: Pitting corrosion is a great concern when the integrity of ship's hull structures is considered. Corrosion pits with a conical shape are typically observed on coated hold frames in way of cargo holds of bulk carriers which exclusively carry coal and iron ore. Therefore, it is important to investigate the effect of pitting corrosion on local strength of hold frames of bulk carriers. In the present study, a series of 3-point bend tests with structural models which consist of web, shell and face plates has been conducted. In these tests, a concentrated load has been vertically applied at the center of simply supported models so that shear load would act on the web plate with artificial pits. In this testing condition, load increased even after shear buckling occurred. When there is artificial pitting, fracture of web plates occurs due to strain concentration at the pits. It has been revealed that the empirical formula, which was developed based on non-linear FE-analyses, overestimates the equivalent thickness for the shear ultimate strength obtained in the present experiment, because the effect of web fracture is not taken into account in the analyses.