The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform

J W Martin - One of the best experts on this subject based on the ideXlab platform.

  • mixed mode Crack Mouth reflection in time resolved acoustic microscopy of short fatigue Cracks in single crystal aluminium
    Journal of Physics D, 1994
    Co-Authors: T Zhai, D Knauss, G A D Briggs, J W Martin
    Abstract:

    An Al single crystal with the axial direction of (452) was fatigued in air, at a constant resolved shear stress amplitude (4 MPa), a frequency of 20 Hz and at room temperature. Time-resolved measurements were then carried out on short Cracks in persistent slip bands (PSBS) on the top surface, which has the largest slip steps, using the acoustic signal from the Crack, when the acoustic lens was scanned over the Crack sending convergent acoustic beams down the specimen, was detected and interpreted quantitatively. The signal results from the reflections of a mixed mode surface wave (Rayleigh longitudinal lateral wave) from the Crack Mouth. At 1.2*106 cycles, two short Cracks in the PSB were measured to be 17 and 27 mu m in depth. The angle with the specimen surface was observed to be about 54 degrees , compared with a value of 51 degrees determined by an X-ray method.

B Sobha - One of the best experts on this subject based on the ideXlab platform.

  • estimation of Crack Mouth opening displacement in concrete using optical fiber sensors
    Optometry: Open Access, 2018
    Co-Authors: B Sobha, K Samrajyam
    Abstract:

    Concrete is a multi-phase composite material and used widely in construction industry because of high compressive strength and low cost. Its limited tensile strength makes it prone to Cracking. Important parameters like characteristic length, fracture energy Gf critical Crack width WC are used to understand Cracks in concrete. The Crack width is estimated either as Crack Mouth opening displacement (CMOD/COD) or as Crack tip opening displacement (CTOD). Several optical and non-optical methods can provide information about Crack presence but do not provide information on Crack opening and Crack width which are important from considerations of durability. To this end we present our research results in three point bend tests on pre-notched concrete samples (M-20 composition) using (a) Intensity based plastic optic fiber (POF) using phase difference measurement method (b) Fiber Bragg grating (FBG) method. The CMOD estimation and relative sensitivity of these methods will be presented.

  • FIBER Bragg Grating (FBG) sensor for estimation of Crack Mouth Opening Displacement (CMOD) in concrete
    Journal of Optics, 2015
    Co-Authors: K Samrajyam, R. L. N. Sai Prasad, T. D. Gunneswara Rao, B Sobha
    Abstract:

    Crack Mouth opening displacement (CMOD) is one of the important parameters for characterizing the fracture properties in concrete. Amongst various optical fiber senors, Fiber Bragg gratings are (FBG) being used for structural health monitoring in the recent times. Very few reports exist in literature for use of CMOD estimation using FBG sensors. We report here, the use of FBG based sensor for the estimation of CMOD in plain concrete beams prepared as per recommendations of Reunion Internationale des Laboratoires et Experts des Materiaux, Systems de Construction et Ouvrages (RILEM) and subjected to three point bend test in a digitally controlled Universal Testing Machine (UTM). The results are compared with Linear Variable Differential Transformer (LVDT) and a good agreement is found. The FBG sensor's resolution is better than LVDT beyond the peak stress.

Hanna Johansson - One of the best experts on this subject based on the ideXlab platform.

  • Microstructures of oxide films formed in alloy 182 bwr core shroud support leg Cracks
    The Minerals Metals & Materials Series, 2017
    Co-Authors: Jiaxin Chen, Daniel Jädernäs, Ffredrik Lindberg, Henrik Pettersson, Martin Bjurman, Kwadwo Kese, Anders Jenssen, Massimo Cocco, Hanna Johansson
    Abstract:

    This paper contributes to a TEM examination on the oxide films formed at three locations along a Crack path in Alloy 182 weld from a BWR core shroud support leg, namely, the Crack Mouth, the midway ...

  • Microstructures of oxide films formed in alloy 182 BWR core shroud support leg Cracks
    The Minerals Metals & Materials Series, 2017
    Co-Authors: Jiaxin Chen, Daniel Jädernäs, Ffredrik Lindberg, Henrik Pettersson, Martin Bjurman, Kwadwo Kese, Anders Jenssen, Massimo Cocco, Hanna Johansson
    Abstract:

    This paper contributes to a TEM examination on the oxide films formed at three locations along a Crack path in Alloy 182 weld from a BWR core shroud support leg, namely, the Crack Mouth, the midway between the Mouth and the Crack tip, and the Crack tip. In the Crack Mouth the oxide film was approximately 1.6 μm in thickness and consisted of relatively pure NiO. The midway oxide film was mainly a nickel chromium oxide with a film thickness of 0.3 μm. At the Crack tip the oxide film was a nickel chromium iron oxide with a film thickness of 30 nm. In all studied locations the main oxides had the similar rocksalt structure and the Cracks were much wider than the thicknesses of the oxide films. It probably suggests that the corroded metal was largely dissolved into the coolant. The different dissolution rates of nickel, chromium and iron cations in the oxide films are clearly displayed with the compositions of the residual oxides. The oxide stability under different redox potentials along the Crack path is briefly discussed.

Robert H. Dodds - One of the best experts on this subject based on the ideXlab platform.

  • Crack Mouth opening displacement based η factors for se b specimens
    Journal of Testing and Evaluation, 2009
    Co-Authors: M R Mitchell, R E Link, J P Petti, Robert H. Dodds
    Abstract:

    Three-dimensional finite element analysis of SE(B) fracture toughness specimens with Crack sizes ranging from a/W=0.1–0.6 were performed to develop ηCMOD values for estimating Jpl in fracture toughness tests. The analyses included specimens with smooth sides and 20 % sidegrooves. The results for ηCMOD were 4–9 % lower than previously published results based on two-dimensional plane strain analysis. A simple linear expression for ηCMOD(a/W) was proposed for introduction into ASTM E1820 for calculating Jpl in SE(B) specimens with 0.05≤a/W≤0.7.

  • J and CTOD Estimation Equations for Shallow Cracks in Single Edge Notch Bend Specimens
    Shallow Crack Fracture Mechanics Toughness Tests and Applications, 1993
    Co-Authors: Mark T. Kirk, Robert H. Dodds
    Abstract:

    Fracture toughness values determined using shallow Cracked single edge notch bend, SE(B), specimens of structural thickness are useful for structural integrity assessments. However, testing standards have not yet incorporated formulas that permit evaluation of J and CTOD for shallow Cracks from experimentally measured quantities (i.e. load, Crack Mouth opening displacement (CMOD), and load line displacement (LLD)). Results from two dimensional plane strain finite - element analyses are used to develop J and CTOD estimation strategies appropriate for application to both shallow and deep Crack SE(B) specimens. Crack depth to specimen width ( a/W ) ratios between 0.05 and 0.70 are modelled using Ramberg Osgood strain hardening exponents ( n ) between 4 and 50. The estimation formulas divide J and CTOD into small scale yielding ( SSY ) and large scale yielding ( LSY ) components. For each case, the SSY component is determined by the linear elastic stress intensity factor, K I . The formulas differ in evaluation of the LSY component. The techniques considered include: estimating J or CTOD from plastic work based on load line displacement ( A pl | LLD ), from plastic work based on Crack Mouth opening displacement ( A pl | CMOD ), and from the plastic component of Crack Mouth opening displacement (CMOD pl ). A pl | CMOD provides the most accurate J estimation possible. The finite - element results for all conditions investigated fall within 9% of the following formula:

David Cameron Wright - One of the best experts on this subject based on the ideXlab platform.

  • Vibro-enhanced fluorescent penetrant inspection (FPI)
    Insight, 2009
    Co-Authors: K. Milne, Peter Cawley, A. Dunhill, David Cameron Wright
    Abstract:

    The potential of vibration as a means of encouraging liquid penetrant to fill and bleed out of Cracks, by changing the Crack Mouth opening or the surface energy of the liquid-solid interface, was investigated. An image-processing algorithm was used to automatically detect Crack indications. Tests were carried out with both static and dynamic loading; the change in Crack Mouth opening with static load was measured optically. The probability of detection of the penetrant process was observed to increase if the Crack was loaded either statically or dynamically. The cross-Crack strain required to observe an improvement was the same for static and dynamic loading (>500 μe). Therefore, there is no advantage in loading the Crack with this mode of vibration. Also, the dynamic strains approached the fatigue threshold for Crack propagation and so would be unacceptable from a structural integrity point of view.

  • VIBRO‐ENHANCED FLUORESCENT PENETRANT INSPECTION (FPI)
    AIP Conference Proceedings, 2008
    Co-Authors: K. Milne, Peter Cawley, A. Dunhill, David Cameron Wright
    Abstract:

    The potential of vibration as a means of encouraging liquid penetrant to fill and bleed‐out of Cracks, by changing the Crack closure or the surface energy of the liquid‐solid interface, was investigated. An image‐processing algorithm was used to automatically detect Crack indications. The change in Crack Mouth opening with static load was measured optically. An improvement was observed if the Crack was loaded either statically or dynamically to cross‐Crack strains greater than 500 μe.