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Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.


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TL;DR: In this paper, the fracture toughness of bainitic RPV steels with similar chemical compositions but different manufacturing processes was examined in view of cleavage fracture stress at crack-tip.
Abstract: The fracture behaviors in the ductile–brittle transition region of reactor pressure vessel (RPV) steels with similar chemical compositions but different manufacturing processes were examined in view of cleavage fracture stress at crack-tip. The steels typically had a variation in grain size and carbide size distribution through the different manufacturing processes. Fracture toughness was evaluated by using a statistical method in accordance to the ASTM standard E1921. From the fractography of the tested specimens, it was found that fracture toughness of the steels increased with increasing distance from the crack-tip to the cleavage initiating location, namely cleavage initiation distance (CID, X f ) and its statistical mean value ( K JC(med) ) was proportional to the cleavage fracture stress ( σ f ) determined from finite-element (FE) calculation at cleavage initiating location. On the other hand, σ f could also be calculated by applying the size of microstructural parameters, such as carbide, grain and bainite packet, into the Griffith’s theory for brittle fracture. Among the parameters, the σ f obtained from the mean diameter of the carbides above 1% of the total population was in good agreement with the σ f value from the FE calculation for the five different steels. The results suggest that the fracture toughness of bainitic RPV steels in the transition region is mostly influenced by only some 1% of total carbides and the critical step for cleavage fracture of the RPV steels should be the propagation of this carbide size crack to the adjacent ferrite matrix.

36 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the tensile and creep properties of both the Ti-6Al-4V alloy and the composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP).
Abstract: Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the matrix alloy at the strain rates ranging from approximately 10−5 to 10−3 s−1. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which was followed by the ductile fracture of the matrix.

36 citations

Journal ArticleDOI
TL;DR: In this paper, a static thermal tensioning (STT) was used to improve fatigue performance in AA 5083 metal inert gas (MIG) welded joints by cooling the weld zone and its adjacent area during welding whereas both sides away from the weld were heated at various temperatures of 100, 200 and 300 to generate thermal gradient.

36 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the cyclic deformation response of DZ125 base metal and the brazed joint in two aspects, i.e. fatigue life and fatigue fracture behavior, with a comparative method.
Abstract: a b s t r a c t Due to the different low cycle fatigue (LCF) properties and fatigue fracture behavior between DZ125 base metal and the brazed joint, the LCF tests are carried out systematically using tension cycling under stress amplitude control conditions (stress ratio R = 0) at elevated temperature in laboratory air. The present paper sets out to investigate the cyclic deformation response of DZ125 base metal and the brazed joint in two aspects, i.e. fatigue life and fatigue fracture behavior, with the comparative method. Furthermore, the comparative method on the typical fatigue fracture surface features (including fatigue source zone, crack propagation zone and fatigue fracture zone) of DZ125 base metal and the brazed joint cycled to failure is conducted in detail. Based on both the macro mechanical behavior and macro and micro fracture observations, experimental results show that: (1) for the brazed joint, the softening is not obvious at lower stress ranges. But from 640 to 720 MPa, it is very significant; (2) under the same test condition, the brazed joint shows lower fatigue life compared with DZ125 base metal and all brazed joints are fractured in the brazing seam observed by the Scanning Electron Microscope (SEM); and (3) there are many distinctive differences of the fracture phenomena between DZ125 base metal and the brazed joint as follows: (1) the crack initiation mode; (2) the crack propagation behavior; and (3) the morphology of dimple pattern at the fatigue fracture zone.

36 citations

Journal ArticleDOI
TL;DR: In this article, a recently developed synchrotron X-ray diffraction technique was used to detect the onset and progression of abnormal grain growth during stress-controlled fatigue loading.
Abstract: Conventional structural metals suffer from fatigue-crack initiation through dislocation activity which forms persistent slip bands leading to notch-like extrusions and intrusions. Ultrafine-grained and nanocrystalline metals can potentially exhibit superior fatigue-crack initiation resistance by suppressing these cumulative dislocation activities. Prior studies on these metals have confirmed improved high-cycle fatigue performance. In the case of nano-grained metals, analyses of subsurface crack initiation sites have indicated that the crack nucleation is associated with abnormally large grains. However, these post-mortem analyses have led to only speculation about when abnormal grain growth occurs (e.g., during fatigue, after crack initiation, or during crack growth). In this study, a recently developed synchrotron X-ray diffraction technique was used to detect the onset and progression of abnormal grain growth during stress-controlled fatigue loading. This study provides the first direct evidence that the grain coarsening is cyclically induced and occurs well before final fatigue failure—our results indicate that the first half of the fatigue life was spent prior to the detectable onset of abnormal grain growth, while the second half was spent coarsening the nanocrystalline structure and cyclically deforming the abnormally large grains until crack initiation. Post-mortem fractography, coupled with cycle-dependent diffraction data, provides the first details regarding the kinetics of this abnormal grain growth process during high-cycle fatigue testing. Precession electron diffraction images collected in a transmission electron microscope after the in situ fatigue experiment also confirm the X-ray evidence that the abnormally large grains contain substantial misorientation gradients and sub-grain boundaries.

36 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023120
2022254
2021229
2020206
2019205
2018176