Thickness Crack Research Articles

Numerical Determination of Initiation Fracture Toughness of High-Pressure Die Cast Aluminium Metal Matrix Composite Material Using FEM Analysis

The critical stress intensity factor for high-pressure die casted aluminium metal matrix composite material is rarely reported in the literature. The understanding of this parameter is very much essential for exploring the application of this material in automobile and aviation industries relying on light-weight materials. In the present study, critical stress intensity factor for pressure die cast aluminium alloy (ADC12) has been determined numerically, which compares well with experimental values. The variation due to fracture specimen thickness and relative crack size is also studied for the material.

Influence of multi-layered thermal diffusion coatings on high-temperature sulfidation resistance of steels

Corrosion resistance of protective coatings on steels against high-temperature sulfidation conditions was studied. The coatings made via thermal diffusion process had multi-layered architectures and consist of aluminides, iron borides or iron boride - titanium dioxide layers. These coatings applied onto carbon steel and austenitic stainless steel 316 were exposed in the H2S-Ar gas flows at 500 °C, and their performance was compared to bare stainless steel 316L. While stainless steel experienced sulfidation corrosion of the surface and intensive sulfide scale peeling, the considered coatings remained their integrities with no peeling. The structural examination revealed no new phases' formation within the coatings, no coating thickness reduction, no delamination and crack occurrence. This type of coatings has much potential due to their increased stability in the considered sulfidation conditions and since they are suitable for protection of inner or inner and outer surfaces of long tubing.

Prediction of Fatigue Crack Growth in Metallic Specimens under Constant Amplitude Loading Using Virtual Crack Closure and Forman Model

This paper considers the applicability of virtual crack closure technique (VCCT) for calculation of stress intensity factor range for crack propagation in standard metal specimen geometries with sharp through thickness cracks. To determine crack propagation rate and fatigue lifetime of a dynamically loaded metallic specimen, in addition to VCCT, standard Forman model was used. Values of stress intensity factor (SIF) ranges ΔK for various crack lengths were calculated by VCCT and used in conjunction with material parameters available from several research papers. VCCT was chosen as a method of choice for the calculation of stress intensity factor of a crack as it is simple and relatively straightforward to implement. It is relatively easy for implementation on top of any finite element (FE) code and it does not require the use of any special finite elements. It is usually utilized for fracture analysis of brittle materials when plastic dissipation is negligible, i.e., plastic dissipation belongs to small-scale yielding due to low load on a structural element. Obtained results showed that the application of VCCT yields good results. Results for crack propagation rate and total lifetime for three test cases were compared to available experimental data and showed satisfactory correlation.

Hybrid pixel-level concrete crack segmentation and quantification across complex backgrounds using deep learning

This paper proposes an automatic crack detection, localization, and quantification method using the integration of a faster region proposal convolutional neural network (Faster R-CNN) algorithm to detect crack regions. The regions were located using various bounding boxes and a modified tubularity flow field (TuFF) algorithm to segment the crack pixels from the detected crack regions. A modified distance transform method (DTM) was used to measure crack thickness and length in terms of pixel measurement. To validate the proposed method, 100 images were taken in different places with complex backgrounds containing different angles and distances between the camera and the objects. The results obtained from the Faster-R-CNN-based crack damage detection had a 95% average precision. The pixel-level segmentation performance of the modified TuFF algorithm exhibited an authentic outcome, with 83% intersection over union. Finally, the modified DTM algorithm provided 93% accuracy with respect to crack length and thickness with a 2.6 pixel root mean square error.

Mechanical and optical degradation of flexible optical solar reflectors during simulated low earth orbit thermal cycling

Multilayer thin film systems on flexible polymer substrates are used as flexible optical solar reflectors or thermal insulation of satellites and spacecraft. During one year of operation, a satellite in low earth orbit typically encounters 6000 thermal cycles of ±100 °C. Due to the different coefficients of thermal expansion between the individual layers and the substrate it is important to investigate the thermo-mechanical stability of the multilayers as a function of the cyclic heat load. Scanning electron microscopy and focused ion beam cross-sectioning revealed that Inconel-Ag bilayers on fluorinated ethylene propylene (FEP) substrate severely degrade during thermal cycling of ±150 °C in a gaseous N2 atmosphere. After only 100 cycles through thickness cracks and subsurface voids in the Ag layer form as a result of equi-biaxial thermal stresses caused by the large difference in thermal expansion between film and substrate. Transmission Kikuchi Diffraction (TKD) before and after thermal cycling also revealed grain growth and twin widening in the Ag layer. Cracking and void formation are detrimental to application relevant material properties including corrosion protection (Inconel) and reflectivity (Ag). Reflectance measurements revealed that the amount of reflected energy as well as the reflection mode (specular vs. diffuse) significantly change during the first 100 cycles. Saturation of reflection characteristics was observed after 25 cycles, which correlates to a turning point in the evolution of Ag voids. Results of this study indicate that special focus should be directed towards thermal stress control (Δα) and tailoring of the metal-polymer interface to improve resistance of versatile metal-polymer systems against thermal cycling.

Structural integrity assessment of floating offshore wind turbine support structures

Floating offshore wind turbines are becoming more attractive to the wind industry due to their capability to operate larger turbines in deeper waters. The floating support structures are anchored to the seabed via mooring chains to impede the structure's unwanted movements. The combination of cyclic stresses and the corrosive marine environment makes the floating support structures vulnerable to corrosion pitting and subsequently fatigue crack initiation and propagation. In this study a framework is proposed to simulate fatigue crack growth from multiple corrosion pits at critical spots of the Spar-type floating support structures to examine the status of the crack during several years of operation. The proposed advanced fracture mechanics based approach provides a methodology to assess the integrity of the structure and subsequently plan for preventive or curative maintenance. The crack growth rate is examined for both singular and multiple cracks at different R ratios and for different stress levels using ABAQUS XFEM. Following numerical simulations, a sensitivity analysis is carried out using Crackwise software for different values of plate thickness, R ratio and initial crack size. The numerical results are discussed in terms of the corrosion pitting effects on fatigue life assessment of floating offshore wind turbines.

Multi-objective optimization of surface roughness, recast layer thickness and surface crack density in WEDM of Al2124/SiCp using desirability approach

Engineered materials like Aluminum Metal Matrix Composites (ALMMCs) have tailor-made properties like high specific strength, low coefficient of thermal expansion (CTE), high thermal and electrical conductivity along with improved tribological properties. ALMMCs suitable for making the components used in automobile, and aerospace industry to enhance engine performance. In this paper, custom-made composite material Al2124/SiC P is machined by Wire cut Electric Discharge Machine (WEDM). The machining factors are pulse on time (T on ), pulse off time (T off ), current (IP), and servo voltage (SV) designed as per Central Composite Design (CCD). The response parameters, namely, Surface Roughness (SR), Recast Layer Thickness (RCT), and Surface Crack Density (SCD) are optimized by multi-objective optimization through desirability to improve the fatigue life of the component by selecting optimum input parameters. ANOVA results indicate that SR is influenced by T on , SV, IP*SV, and T on *T on . RCT is influenced by T on , T off , IP, and Ton*SV. On the other hand, SCD is influenced by IP, IP*SV. The average values of SR, RCT, and SCD ranges between 1.369 and 3.325 µm, 3.926–64.083 µm, and 0.0449–0.1082 µm/µm 2 , respectively, for the range of input parameters. The confirmation experiments conducted at optimum design parameters (T on = 119.056 μs, T off = 47.082 μs, IP = 20 A, SV = 50 V) obtained through the desirability approach are found in reasonable agreement with the experimental results.

ASSESSING THE INFLUENCE OF EXTRACTED FLUID AND OPERATIONAL CONDITIONS ON CORROSION OF GAS FIELD EQUIPMENT

Background The main intensifier of corrosion at the objects of the studied oil and gas condensate field is carbon dioxide corrosion (CDC). Aims and Objectives Based on the data from well surveys, analyze the factors affecting the corrosiveness of the media: CO2 partial pressure, temperature, reservoir pressure, pH, salinity, and water composition. After compiling the ion balance and recalculating it to the salts used in the manufacture of model solutions of the salts, make up three model waters corresponding to individual and mixed formations for further testing. Results The main danger in CO2 presence is not general, but local corrosion occurring in the fluid flow under conditions when FeCO3 films, although formed, but at low temperatures characteristic for the studied field, they are not stable enough. The appearance of a crack in the FeCO3 film initiates its cleavage, at this point the CDC begins, creating a carbonate film, which with a certain thickness cracks and chips. Some erosions are formed within the other of corrosive areas. Such local corrosion damages are developing, leading to deep (or through) pitting, to damages occupying the big area in interconnection of separate local corrosion defects on an internal surface of elements of a wellhead. Calculations of corrosion damages depth on a flange from a wellhead after removing the corrosion products testify that corrosion depth damages are from 1.0 to 2.5 mm. As the inspections show, the damages made by CDC are observed not only on a well head, but also in pump-compressor pipes of the wells. Operational tests of various grades of steel in the well media, characterized by high CO2 content (up to 1.7 %), showed that most of them are unstable to CDC, with except the alloy steel 12X18N10T. The rate of general (uniform) corrosion reaches several mm/year, including the low-alloy steel 09G2C used for most elements of the wellhead.

Shear behavior of interlocking masonry brick wall portal with the substitution of Mount Sinabung volcanic ash against pushover static load

Earthquake events produce a shear damage effect on the interlocking masonry wall brick in the form of diagonal cracks. This shows that there’s an influence of the resistance of the masonry to bear the shear force against the horizontal force in the direction of the wall plane caused by the earthquake. The purpose of this research is to determine the shear strength and crack patterns of walls against static loads and to utilize volcanic ash from Mount Sinabung as one of the constituent materials of interlocking masonry brick because the eruption activity of Mount Sinabung is also one of the most active in the world. The samples are in the form of a 3 m x 3 m wall surrounded by a 0.13 m x 0.13 m beam-column portal filled with interlocking masonry brick of 0.25 m x 0.125 m x 0.1 m with the optimum substitution of Mount Sinabung volcanic ash by 20% as a substitute for sand. Wall portal test was done by giving a pushover static load on the wall joint which refers to ASTM E 564-2003 to get the value of shear strength and crack pattern of the wall. From the static test results of interlocking masonry brick wall portal, the samples are able to accept a pushover load of 63931.2 N which results in an ultimate displacement of 35 mm with a crack thickness of 4 mm. The wall shear strength obtained is 21.31 N / mm. Based on the analysis of the equivalent energy elastic plastic (EEEP) curve, it is obtained that the elastic stiffness of the wall is 5905.88 N / mm and the wall’s yield load is 57237.55 N with the deviation of 9.69 mm. Failure of the interlocking masonry brick wall portal is a shear failure characterized by cracking like a ladder pattern on the wall. Based on the crack pattern that occurs, the wall portal is a type of stepped cracks shear failure.

Modeling fatigue crack growth for a through thickness crack: An out-of-plane constraint-based approach considering thickness effect

Though several studies have tried to explain and model the effect of thickness on crack growth behavior, this remains a controversial topic. The present paper proposes an approach to model the fatigue crack growth with different thicknesses, which requires crack growth experimental data with different specimen thicknesses and out-of-plane constraint distribution relations for CT specimens. Empirical formula, for the distributions of two types of constraint factors Tz and T33, were fitted according to the FEA results. The stress state variation induced by the thickness was quantified using the formulas; then, the crack driving force was modified to establish the novel crack growth model. The predictions using this model largely agree with the experimental data. So, the newly developed model was verified. This paper proposes a new perspective on quantifying the effect of crack thickness, and provides an alternative to the traditional method of modeling the crack growth behavior.

Microstructure and Wear Properties of Micro Arc Oxidation Ceramic Coatings.

The interaction effect of micro arc oxidation (MAO) parameters on the microstructure and wear properties was investigated. The results showed that the electric current and oxidation time significantly influenced the thickness and grinding crack width of the ceramic coatings within the range of the selected parameters, and the interaction effect of the electrical parameters was not obvious. The surface morphology, cross-section morphology, and element distribution of the coatings were observed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that ceramic coatings with γ-Al2O3 and α-Al2O3 formed, which enhanced the coating performance. After that, the microhardness and wear resistance were tested. Under the optimal process, the microhardness of a coating section was up to 1200 HV0.1, and the friction coefficient was just 0.3. When wear occurred, the volcanic microstructures experienced extrusion and deformation, and then peeled off under shear stress, which led to the formation of a grinding crack. The main failure modes of the micro arc oxidation coatings were abrasive wear and spalling failure.

Influence of interface crack and non-uniform cement thickness on mixed-mode stress intensity factor and prediction of interface failure of cemented acetabular cup

The goal is to determine the influence of interface crack and non-uniform cement thickness on mixed-mode stress intensity factors (SIF) and the prediction of interface failure of the cemented cup. Nine three-dimensional (3D) finite element (FE) models of implanted pelvic bone were developed having the uniform and non-uniform cement thickness based on computed tomography (CT) dataset. Physiological loading conditions and location-dependent material properties of cancellous bone were considered for the present analysis. In order to understand the influence of crack at cement-bone and implant-cement interfaces, two-dimensional (2D) cracked models were generated and solved using the element free Galerkin method (EFGM). For cracked analysis, a rectangular section was considered at both the interfaces in the superior, inferior, anterior, and posterior anatomic locations to determine the SIF. The average stress values obtained from 3D FE analysis was transferred at the cut boundary of the rectangular section and considered as a mixed-mode loading condition to understand the influence of crack and non-uniform cement thickness on interface failure. The results of the present study indicated that the cement thickness plays an important role in interface failure. SIF increases as the cement thickness decreases. Anterior location is more prone to failure as compared to other anatomic locations. The chance of cement-bone interface failure is more as compared to the implant-cement interface. The present study also indicated that the chance of interface failure is more for the generation of edge crack as compared to center crack.

Closed-form formulae for prediction of homogenized ply-properties and laminate thermo-elastic constants in symmetric laminates containing ply cracks in multiple orientations

The aim of this study is to develop a novel model for predicting homogenized properties of a cracked ply in a symmetric laminate using the crack density and thickness of the ply. In doing so, the periodic boundary conditions are applied to the RVEs in a three-dimensional finite element model to calculate the thermo-elastic constants of symmetric laminates containing uniformly and non-uniformly spaced cracks under in-plane and out-of-plane loading conditions. On the other hand, homogenized material properties of the cracked ply are explicitly determined by averaging procedures for both stress and strain components. Using computed results and nonlinear least square fitting, an analytical formula is proposed to describe the mechanical properties of the cracked ply, which takes into account the effect of ply thickness, material properties and crack density. Different cracked laminates are tested to indicate the potential of the developed method in analyzing complex crack geometries in multiple orientations. Moreover, the applicability and accuracy of the suggested model are verified by comparing the results with those of experiments, variational approach and finite element method.

Pulse-reverse electroplating of chromium from Sargent baths: Influence of anodic time on physical and electrochemical properties of electroplated Cr

Herein, chromium film was successfully synthesized by pulse-reverse (PR) electrodeposition using various anodic current time in a Sargent bath which is mainly composed of hexavalent chromium (Cr6+) and sulfuric acid (H2SO4). The correlation between anodic time during electroplating and various physical properties was investigated. The crack density, hardness, and thickness of electrodeposited chromium was decreased with an increase in anodic time for PR electroplating. The chromium prepared by PR electroplating showed higher corrosion resistance than that prepared by direct current (DC) electroplating owing to low crack density. Consequently, the optimal anodic time for PR electroplating was found to be 0.001 s based on the crack density, hardness, current efficiency, and film thickness. The results obtained suggest that this optimized process is a promising route for electroplating chromium film with low crack density and high corrosion resistance.

Fracture characterization studies of concrete structures through experiments on reinforced concrete cylindrical shell specimens

BARC Containment (BARCOM) test model located within the experimental facility at Tarapur, India built for the ultimate load capacity evaluation and leakage assessment of nuclear containment, was subjected to pressurization experiments with air. Pneumatic experiments up to over-pressurization level of 1.77 times the design pressure (Pd) were carried out. With the limited air compressor capacity, further diminished by significant leakage due to the development of through thickness cracks localized around the discontinuity locations and parallel vertical cracks throughout the full circumference in the free field at certain elevations of BARCOM, it could not be pressurized beyond 1.77 Pd. For further pneumatic testing, requisite leak tightness needs to be ensured. Therefore, it was recommended to apply a polymer liner inside the surface of the nuclear containment test model, which are commonly deployed in various containment structures for improved leak-tightness characteristics.In addition to the qualification of synthetic liner coating material for the intended repair application, the fracture characterization studies conducted through Digital Image Correlation (DIC) and a novel Optical Crack Profiling (OCP) scheme developed by the present authors on cylindrical specimens enabled verification of various fracture parameters as observed during the standard material characterization studies. The size of the fracture process zone of concrete is evaluated and a correlation is evolved to estimate concrete fracture energy which is applicable for safety evaluation of important structures.

Shear waves with orthogonal polarisations for thickness measurement and crack detection using EMATs

The use of polarised shear waves to detect the presence of crack-like defects seems to have received little or no attention in the past. The authors believe that the main reason for this appears to be the lack of a device with the capability to excite shear waves of different polarisations. In this paper, the authors, first, present the design of an EMAT that permits the excitation of two orthogonally polarised shear waves in metallic materials by means of two coils that are orthogonal with respect to each other. This is then followed by a 3D finite element analysis of the wavefield generated by the EMAT and its interactions with crack-like defects of different sizes, positions and orientations. Then a methodology of how this EMAT can be used to simultaneously measure material thickness and detect crack-like defects in pulse-echo mode is introduced. Good agreement between the finite element simulation and experimental results was observed which makes the presented technique a potential new method for simultaneous thickness measurements and crack detection.

Effect of crystalline admixtures, polymers and fibers on self healing concrete - a review

Generally, concrete structures will develop cracks under loads. To prevent these cracks self-healing concrete is made by two different approaches natural and artificial. Natural healing mechanism is investigated by an autogenous healing process, in which the self-healing occurs due to chemical reactions and involvement of water. In this paper, the main focus is on artificial approaches like the addition of crystalline admixtures, polymers, and fibers to improve the strength of concrete by healing the cracks. This paper also reviews the methods and tests used to find the self-healing capability of concrete. The reported effects of admixtures on the mechanical properties of self-healing concrete are also presented. So far, a crack width of 0.93 mm is healed underwater immersion condition. Few researches reported on the improvement of mechanical properties and thickness of cracks healed in concrete by using various polymers and fibers.

Self-Healing Concrete by Biological Substrate.

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.

The method of prediction of roof collapse hidden trouble in the roadway of No.2 in Anjialing

The thickness and strength of strata composing roof stratum will change a lot because of the change of coal forming environments and long time geological evolution. Only knowing these changes exactly, we can get the right design and prevent roof collapse. We can get the thickness, relative position and location of cracks and roof separation of strata with the changing of length of roadway at any time, and design the roof of roadway dynamically according to the lithology and combination changes of roof. In accordance with these, we can ensure not only the economic, but also safety in production.

Application of Ground Penetration Radar and Light Weight Deflectometer for Pavement Quality Control and Quality Assessment

Pavement evaluation requires the frequent assessment of structural and functional condition. Earlier functional assessment of pavement were rapid and non destructive whereas structural evaluation required destructive testing. With growth in technology the light weight deflectometer (LWD) and ground penetrating radar (GPR) replaced the destructive testing in most part of the world. This paper highlights the use of LWD and GPR as non destructive testing tool in pavement evaluation. LWD and GPR test were conducted on the granular material to investigate the composite modulus of layer for their quality assessment. LWD test results were found to be significantly affected by the base plate diameter, contact between plate and surface layer, whereas drop height does not show significant difference on composite modulus. GPR technology has showed its versatility in pavement layer thickness evaluation, void and crack detection, and sub surface exploration. Ground coupled GPR has been used for subsurface exploration. At project level pavement management system, the combined use of GPR and deflection testing device has resulted in effective monitoring of pavement structural capacity. Hence LWD and GPR had showed its effectiveness for quality control and quality assurance (QC/QA) in PMS.