Crushed Core Research Articles

Study of Ultrasonic-Guided Wave Interaction With Core Crush Damage for Nondestructive Evaluation of a Honeycomb Composite Sandwich Panel

AbstractHoneycomb composite sandwich structures are extensively used for the manufacturing of many different components of aerospace, automobiles, wind turbine blades, and marine ship hull structures. Despite its widespread use and advantages, the honeycomb core is frequently damaged during production and operation, even if the damage is not visible on the face-sheet. In this study, an ultrasonic-guided wave (GW) propagation technique is utilized for robust and reliable nondestructive evaluation of a honeycomb composite sandwich panel (HCSP) in the presence of core crush damage. A 2D semi-analytical model was developed to understand the dispersion characteristics in the HCSP and to identify various modes of GW propagation in the signals. Extensive numerical simulations are carried out using abaqus to study the guided wave interaction with core crush damage. For this purpose, two numerical models were considered (a realistic model with both crushed core and cavity, and a simplified model that only comprises the cavity) and experimentally validated using a contact-type transducer. The presence of core crush damage in an HCSP increases the amplitude and group velocity of the primary antisymmetric mode, and this characteristic has been used for localization of the core crush region in the HCSP. Finally, a damage detection algorithm using signal difference coefficient is presented for successful localization of the core crush region within a square monitoring area. Unlike other studies reported in the literature, we demonstrate the utility of the simplified numerical model for studying GW interactions with core crush defect and experimentally validate the nondestructive evaluation (NDE) technique to localize core crush defect on an HCSP.

Extra-Heavy Oil Aquathermolysis Using Nickel-Based Catalyst: Some Aspects of In-Situ Transformation of Catalyst Precursor

In the present work, we studied the catalytic performance of an oil-soluble nickel-based catalyst during aquathermolysis of oil-saturated crushed cores from Boca de Jaruco extra-heavy oil field. The decomposition of nickel tallate and some aspects of in-situ transformation of the given catalyst precursor under the steam injection conditions were investigated in a high-pressure batch reactor using XRD and SEM analysis methods. The changes in physical and chemical properties of core extracts after the catalytic aquathermolysis process with various duration were studied using gas chromatography for analyzing gas products, SARA analysis, GC-MS of saturated and aromatic fractions, FT-IR spectrometer, elemental analysis, and matrix-activated laser desorption/ionization (MALDI). The results showed that nickel tallate in the presence of oil-saturated crushed core under the injection of steam at 300 °C transforms mainly into nonstoichiometric forms of nickel sulfide. According to the SEM images, the size of nickel sulfide particles was in the range of 80–100 nm. The behavior of main catalytic aquathermolysis gas products such as CH4, CO2, H2S, and H2 depending on the duration of the process was analyzed. The catalytic upgrading at 300 °C provided decrease in the content of resins and asphaltenes, and increase in saturated hydrocarbon content. Moreover, the content of low-molecular alkanes, which were not detected before the catalytic aquathermolysis process, dramatically increased in saturates fraction after catalytic aquathermolysis reactions. In addition, the aromatics hydrocarbons saturated with high molecular weight polycyclic aromatic compounds—isomers of benzo(a)fluorine, which were initially concentrated in resins and asphaltenes. Nickel sulfide showed a good performance in desulfurization of high-molecular components of extra-heavy oil. The cracking of the weak C–S bonds, which mainly concentrated in resins and asphaltenes, ring-opening reactions, detachment of alkyl substitutes from asphaltenes and inhibition of polymerization reactions in the presence of catalytic complex reduced the average molecular mass of resins (from 871.7 to 523.3 a.m.u.) and asphaltenes (from 1572.7 to 1072.3 a.m.u.). Thus, nickel tallate is a promising catalyst to promote the in-situ upgrading of extra-heavy oil during steam injection techniques.

Some Aspects to Develop Method for Determining the Open Porosity of Ultralow-Permeability Rocks on Crushed Core

Laboratory studies of shale formations face serious challenges, one of which is the development of methods to determine the porosity of ultralow-permeability rocks. As the object of study, more than 100 ultra-permeability different lithological composition core samples of the Bazhenov Formation were used. The paper presents the results of determining the open porosity of ultralow-permeability rocks of the Bazhenov Formation using two methods adapted for crushed core. This is a gas-volumetric method and a modified liquid saturation method. The paper shows the legitimacy of using the proposed methods to determine open porosity in sandstones by comparing the results on cylindrical samples and on crushed core. According to the results of the study, a methodology to determine the bulk density and grain density of ultralow-permeability rocks of the Bazhenov Formation was been completed. Also, a systematic error in determining the open porosity of ultralow-permeability rocks of the Bazhenov Formation by the standard method on plugs was also shown.

The Effect of Clay Content in the Adsorption of Surfactant by Reservoir Rock in the Enhanced Oil Recovery Process

Surfactant flooding aims at lowering the interfacial tensions between the oil and water phases to improve the displacement efficiency during oil recovery. However, high adsorption of surfactant by reservoir core is undesirable since it could decrease the ability of surfactant to reduce the interfacial tension between oil and brine which makes injection ineffective. This study was done to get better understanding of the effect of clay content on oil displacement. The procedures of adsorption process are as follows: crushed core were put into flasks wich filled with surfactant and heated up at different temperature for three days operation. The clean solution was then measured its absorbance using UV spectrophotometer. The result of adsorption experiments show that the adsorption decreasedup to 25 % when temperature was increased from 25 to 70oC. The experimental for studying the effect of clay content on the adsorption also shows the right behavior. The experimental results also show that adsorption of surfactant is higher in the clean core than in the core filled with oil. This phenomenon is true since the contact area between surfactant and core is much higher when the core is clean. The oil displacement experiments show that the oil recovery also depends on type of reservoir rock used in the process.

Experimental investigation and development of correlation for static and dynamic polymer adsorption in porous media

Part of the injected polymer during polymer flooding is lost in porous media by adsorption, mechanical entrapment, and hydrodynamic retention. Therefore, having a clear understanding of polymer losses/retention is very important for designing a technically and economically successful polymer flooding project. Polymer losses are traditionally modeled using Langmuir Isotherms, requiring costly and time-consuming dynamic corefloods to obtain fitting parameters. This research suggests a faster and low-cost method for first-order approximation of polymer adsorption in porous media without conducting corefloods. The proposed technique uses the results of polymer adsorption on the crushed core in the static test that can be used in a lookup table in the simulator instead of Langmuir Isotherms Equation. Mercury injection (MICP) was used to find a cut-off molecular size based on the hydrodynamic size of the polymer calculated using the Flory-Fox equation. Brunauer-Emmett-Teller (BET) tests are used to measure the specific surface area of the crushed core. These three tests determine the equivalent weight of crushed core to be used for static adsorption tests that would represent the specific surface area of the core. Seven high permeability Bentheimer core plugs from outcrops were used to perform polymer corefloods to determine polymer adsorption, followed by seven static adsorption tests performed at similar conditions to compare the results. Polymer adsorption tests showed that 1-h residence time, 0.5 solid-to-liquid ratio, and pre-saturating crushed core with brine before starting static adsorption were important to map static to dynamic polymer adsorption. Other important observations were the increase in polymer adsorption with increasing polymer molecular weight, polymer concentration, and NaCl salinity in order of descending significance of the effect. The proposed method gave a reasonable statistical correlation between static and dynamic polymer adsorption with a coefficient of determination (R2) of 0.97, and Pearson's correlation coefficient (r) of 0.98. The maximum deviation between static and dynamic result was 34% for cores of similar flow zones, and 48% for cores of dissimilar flow zones.

Residual dent in locally loaded foam core sandwich structures – Analysis and use for NDI

This paper addresses the residual denting in the face sheet and corresponding core damage in a locally loaded flat sandwich structure with foam core. The problem is analytically considered in the context of elastic bending of the face sheet accompanied by non-linear deformation of the crushed foam core. The plane and axisymmetric formulations are studied. The obtained solutions allow for the estimation of the magnitude of the residual face dent through the size of the crushed core zone (or vice versa). Thus, the analytical background is proposed for a non-destructive inspection of locally indented/impacted sandwich structures. The solutions are verified experimentally.

Fatigue Behavior of Foam Core Sandwich Beams with Sub-Interface Impact Damage

The fatigue life of impact-damaged foam core sandwich beams with GFRP faces is investigated for constant load-amplitude cyclic loading. The damage produced by the low velocity/energy impact is characterised as a sub-interface cavity with surrounding crushed core whereas the face sheet is undamaged. The effect of bridging owing to the crushed core in the peripheral regions of impact damage, revealed in the preceding static study Shipsha et al. [1,2] is assessed under cyclic loading. The fatigue test results are analysed in a stress-life S-N diagram and compared with published data from undamaged beams. The effect of two load ratios R = 0.1 and -1 is investigated. The fatigue threshold load levels are experimentally quantified from the S-N curves. Furthermore, a modified point-stress criterion based on the threshold stress intensity factor, Kth, is proposed to estimate the “no-crack growth” limit loads. The results show good agreement with performed experiments.

Failure Mechanisms and Modelling of Impact Damage in Sandwich Beams - A 2D Approach: Part II - Analysis and Modelling

This study addresses the effect of low velocity impact damage on the post-impact residual strength and failure mechanisms of sandwich beams with Rohacell WF51 foam core. The considered impact damage has a form of a subinterface cavity surrounded by crushed core while the face sheet remains virtually undamaged. Part I of this study deals with experimental investigation of impact-damaged beams tested in transverse shear, bending and edgewise compression. It is shown that the crushed core and the bridging condition in the peripheral regions of the impact damage exert a significant effect on the post-impact critical loads and failure mechanisms. In this paper, parameterised finite element (FE) models of impact damage with implemented crushed core properties are developed for numerical analyses of post-impact failure. In the analysis of the shear case, a model for II bridging condition in the peripheral regions of impact damage is introduced. A point-stress criterion is applied for predictions of failure loads and crack kink angle. Geometrically nonlinear FE analysis is employed for evaluation of critical loads for local buckling in the beams with impact damage. The FE analyses demonstrate good agreement with experimental results.