Crack Dimensions Research Articles

Effect of carbonate and phosphate conversion pretreatments and optimization on corrosion behaviour of subsequent electroless nickel coating on AZ91 alloy

The study reports a simple two steps chemical conversion treatment to enable electroless nickel (EN) coating on AZ91 alloy without using chromium or fluoride. The process involves calcium dihydrogen phosphate deployed in step 1 followed by the transformation into more insoluble product, for better corrosion and adhesion resistance, via alkali treatment in NaOH or Na2CO3 during step 2. The latter is attempted by varying the concentration in the range 0.25 to 2 M. The performance of conversion treatments is critically evaluated by the quality of the EN coating, deposited subsequently, with respect to morphology, corrosion, and adhesion resistance. The X-ray diffraction (XRD) and Raman analysis of the pretreated surface exhibits complete transformation to tri calcium phosphate or calcium carbonate after treated in NaOH or Na2CO3 solution respectively at an optimum 1 M concentration. The crack dimensions on the surface of thus pretreated AZ91 are largely suppressed, compared to those at <1 M or >1 M NaOH/Na2CO3 concentration, as revealed by scanning electron microscopy (SEM) and 3D profilometer. The EN coating on pretreated substrate at 1 M alkali concentration shows higher corrosion and scratch resistance than that at other concentrations. The 1 M Na2CO3 appears superior to NaOH pretreatment, as it imparts better corrosion and adhesion resistance of the subsequent EN coating. The electrochemical impedance spectroscopy (EIS) on EN coating after 1 M Na2CO3 treatment shows no coating deterioration up to 300 h of exposure to 0.5% NaCl solution as opposed to NaOH (for 100 h only).

Quantitative condition inspection and assessment of tunnel lining

Abstract To ensure the safety and the serviceability of underground structures, routine inspections and maintenance processes are essential for their optimal use. Presently, the practical inspection of tunnels depends on human-based methods, which has inherent limitations. This study proposed a quantitative system for the health inspection and assessment of the tunnel lining. The system is capable of acquiring and extracting cracks or other defects efficiently, drawing crack charts automatically and assessing the situation of tunnel lining with a much more accurate index. The consistency of the cracks automatically extracted by the proposed tunnel lining inspection system is verified with the investigation of two tunnels using different construction methods. For the health assessment of tunnel lining, a valid index is introduced to evaluate the lining status according to the fractal dimension of cracks. Results of the comparative tests and field tests indicate the validity of crack fractal dimension D. In addition, results of several real cases on field tests demonstrate its practicability. Such a system can achieve time-saving automated surveying solutions with fast data acquisition, identification and documentation of cracks as well as detection of structural changes. For an all-around assessment of the health situation for tunnel lining, the influence of strength characteristics of the tunnel lining due to its irregular shape should be taken into consideration in future research.

Bio-inspired fabrication, mechanical characterization and cutting performance evaluation of Al2O3/TiC micro-nano-composite ceramic with varying microscopic surfaces

Bio-inspired fabrication, mechanical characterization and intermittent cutting performance evaluation were conducted for Al2O3/TiC micro-nano-composite ceramic with varying microscopic surfaces. Functions and geometry features of the epidermis were analyzed for two biological species, namely, catharsius molossus and bullhead shark. The biomimetic microscopic texture on ceramic tool surface was designed and fabricated considering tool-chip contact area and chip flow direction. Varying combinations of laser beam angle and spacing were utilized in the fabrication of biomimetic microscopic texture. Microscopic hardness, fracture toughness and fractal dimension of the indentation-induced crack were analyzed and compared for the textured ceramics. A tool performance indicator CP was proposed. Ceramic tool stress in cutting process, mechanical features of the intrinsic microcrack and fractal dimension of the indentation-induced crack were reflected in the indicator. The indicator CP was employed to evaluate the intermittent cutting performance of ceramic tools with different biomimetic microscopic textures. The optimum combination of laser beam angle φ and spacing Ld was found to be 60° and 105 μm. The lowest CP and the lowest experimental tool wear VB appeared at this optimum combination. A proper balance between external loads, micromechanical properties and fracture resistance can be achieved for the textured ceramic tool by using the optimum combination of φ and Ld.

Apparatus for Identifying Microcracks on the Inner Surface of Glazed Pipes

Amethod of identifying cracks on the inner surface of a glazed coating on a pipe with aid of a flaw detector is examined. The technological scheme is presented and the principle of operation of the developed apparatus is presented. The electric resistance of cracks in the glazed coating of a pipe is determined in terms of the parameter readings of the apparatus. A calculation of the basic dimensions of cracks in coatings along the entire length of standard pipes is presented.

Three-dimensional Reconstruction and Growth Factor Model for Rock Cracks under Uniaxial Cyclic Loading/Unloading by X-ray CT

Abstract The spatial distribution and propagation of cracks are one of the key factors that can influence the initiation of rock failure. In this investigation, the technique of X-ray computed tomography (CT) scanning was used to survey the pattern of rock cracks during cyclic loading/unloading. The distribution and nonlinear development of rock cracks were explored by three-dimensional (3D) reconstruction for use to quantitatively describe their growth. An entropy model for rock mass and a crack growth factor model were established, which could help to reveal the relation between the crack propagation and the macroscopic destruction. The results showed that all disconnected cracks in two-dimensional (2D) images became connected with each other in 3D images. The fractal dimension of rock cracks was increasing first and then decreasing, which was the result of gradual transformation of rock cracks. The growth rate of cracks was decreased with the increase of the quantity of cracks, which was caused by the retardation. When the quantity of cracks grew to a maximal, the growth rate was reduced to zero.

Prediction of crack tip plasticity induced due to variation in solidification rate of weld pool and its effect on fatigue crack propagation rate (FCPR)

Effect of solidification rate on crack tip plastic zone size at various crack lengths was calculated analytically and numerically by simplified Sih’s and Irwin’s models, respectively. Influence of plastic zone size is explained in terms of COD and elastic stress intensity factor within valid range of small scale yielding approximation. Up to plastic zone size range of 4–5 mm, a good agreement between numerical and analytical plastic zone size and elastic stress intensity factor for all weldments was observed. For high loads and greater crack lengths, experimentally obtained COD values were found 15–19 % more than simulation ones due to rapidly induced plasticity at high crack dimensions. Solidification rate showed a significant influence on FCPR, for solidification rates 13.75 °C/s, 6.97 °C/s and 4.32 °C/s the obtained fatigue strength was 35.29 MPa, 36.26 MPa and 41.32 MPa, respectively.

Study on the Crack Morphology of Rock under Three Axis Stress

According to the three triaxial mechanics test of marble, granite and iron ore, the deformation characteristics of rock strength was analyzed, rock failure crack was acquisition by plastic casing, on the basis of box dimension theory, the relationship between rock crack dimension and rock confining pressure was analyzed. It was found that crack dimension decreases with the increasing of confining pressure, the crack dimension reversible analysis of rock stress state; based on stone weight on plastic casing, the concept of gravel coefficient was put forward, gravel and rock that confining pressure was positively correlated.

A two-dimensional fibre-reinforced mode-I crack problem under fractional order theory of thermoelasticity

ABSTRACTIn this work, we shall formulate the fibre-reinforced two-dimensional problem of thermoelasticity for an infinite space weakened by a finite linear opening mode-I crack. In the context of the fractional order theory of generalized thermoelasticity proposed by Sherief et al., we focus on investigating the dynamic response and the governing equations of the problem are formulated and solved by means of normal mode analysis. The distributions of the considered non-dimensional temperature, displacement and stress are obtained and illustrated graphically. The effects of fractional order parameter, rotation, crack dimension on the variations of the considered variables are investigated, and the results show that this parameter has significant influence on the variations of the considered variables.

A modified strain-controlled reference stress approach for submarine pipelines under large-scale plastic strain

The reel-lay approach is widely applied in submarine pipelines. During the process of reeling and unreeling, pipelines are subjected to nominal strain of 1–4%. In this study, various pipeline geometries and crack dimensions were calculated using a finite element analysis and analytical solution under strain-controlled boundary conditions. A modified reference stress approach was applied under strain-controlled boundary conditions using a derived implicit analytical solution of the nominal stress. The limit load solution was modified through a γ factor based on the finite element analysis under strain-controlled boundary conditions. A regression analysis of γ was conducted and an empirical formula was determined. The modified strain-controlled reference approach is in contrast to other ECA methods and proved to be closer to the finite element analysis results.

Pharmacology of BMN 250 administered via intracerebroventricular infusion once every 2 weeks for twenty-six weeks or longer in a canine model of mucopolysaccharidosis type IIIB

An analytical method for determination of dimensions of longitudinal crack in monolithic beams, based on frequency measurements, has been extended to model L and inverted T cracks. Such cracks including longitudinal crack arise in beams made of layered isotropic or composite materials. A new formulation for modelling cracks in bi-material beams is presented. Longitudinal crack segment sizes, for L and inverted T cracks, varying from 2.7% to 13.6% of length of Euler-Bernoulli beams are considered. Both forward and inverse problems have been examined. In the forward problems, the analytical results are compared with finite element (FE) solutions. In the inverse problems, the accuracy of prediction of crack dimensions is verified using FE results as input for virtual testing. The analytical results show good agreement with the actual crack dimensions. Further, experimental studies have been done to verify the accuracy of the analytical method for prediction of dimensions of three types of crack in isotropic and bi-material beams. The results show that the proposed formulation is reliable and can be employed for crack detection in slender beam like structures in practice.

Array Waveguide Probe Loaded With Split-Ring Resonators for Sizing the Cracks in Metal Surface

Microwave nondestructive testing (NDT) technology developed rapidly, but crack detection in metal surface is facing many troubles, such as hard quantitation and low sensitivity. To solve these problems, this letter proposes a two-cell array waveguide microwave NDT probe with an array of split-ring resonators which operates at 12.5 GHz. It detects quantitatively tiny crack (as low as 0.5 mm) in metal surface. Maximum difference between simulation and experimental results is just 9%. Result shows that the peak distance of $S_{21}$ has a sensitive and quantitative link with the width and depth of crack. It is shown that the probe is capable of determining the location and dimension of surface cracks of a few millimeter depths and widths.

Thinking on the Integrity Education of College Students Under the New Situation

Honesty education for college students can cultivate and cultivate students' honesty and honest character, but the current college education has some problems, restricting the honesty education of college students, starting from the multi dimension of crack the reality plight of integrity education of College students.

Optimization of Composite Layering Effect Based on Measured Formation Fracture Height to Length Ratios

This study achieves two main goals. First, it develops a method that uses the Composite Layering Effect (CLE) Equation to predict the behavior of potential fractures in conventional and unconventional reservoirs from core samples. The second goal of this study is to determine how different mineralogical and elemental components affect the behavior of fractures predicted using the CLE equation. After the samples are fractured, X-ray Powder Diffraction (XRD) and X-ray Fluorescence (XRF) techniques are executed to measure the mineralogical and elemental compositions of the core samples respectively. In this method, core samples are first obtained from the formation. Next, X-Ray Computed Tomography (CT) is used to determine if core samples have preexisting fractures. The samples are then fractured slightly using Uniaxial Compressive Strength (UCS), in which a compressive-strength machine initiates fractures by applying uniaxial load and stopping automatically upon reaching a predetermined load. CT then confirms the existence of the new fractures, and Image J interprets the height–length ratio of each fracture. These results are used in calculating the CLE. The results of these experiments revealed the relationship between the mineral and elemental compositions of the rocks and the crack dimensions. It was seen that the presence of quartz and clay minerals had the strongest influence on the CLE value due to the brittle behavior of the quartz and ductile behavior of the clay minerals (nacrite). The highest CLE value was recorded for the shale sample that had a preexisting fracture. The fracture patterns developed in the shale samples were mainly parallel to one another. In contrast, the fracture patterns developed in sandstones started out parallel and later merged together to form a connected fracture network.

Localized Liquation and Resultant Pitting Corrosion Behavior of Welding Coarse-Grained Heat-Affected Zone in Niobium-Stabilized Austenitic Stainless Steel

Effect of localized liquation on pitting corrosion behavior of Nb-stabilized austenitic stainless steels was investigated by potentiodynamic and potentiostatic polarization tests on the welding coarse-grained heat-affected zone (CGHAZ) samples simulated using finite-element software SYSWELD and Gleeble simulator. Results indicated that localized liquation gave rise to Nb-rich liquation bands along grain boundary, inhibiting metastable pit initiation and growth, but resulted in liquation cracks that facilitated the occurrence of stable pitting. Moreover, the large scatter in pitting potential and passive current density observed in CGHAZ samples was attributed to the heterogeneities in the distribution, geometry and dimensions of liquation cracks.

Study of the reinforcement of structure members by polypropylene fibres waste

The valorisation of industrial waste in the field of construction became a very interesting axis of research from scientific, economic and environmental point of view. We have conducted this work to study the effect of the addition of polypropylene fibres waste on the mechanical behaviour of reinforced concrete beams subjected to a simple flexural loading, with and without transversal reinforcement. The used fibres are coming from the waste of the fabrication of domestic brushes and sweeps; they have an average diameter of 0.47 mm and a length between 40 and 60 mm. Two weight dosages of fibres are used, 0.25 and 0.5 %. The experimental results showed that the incorporation of polypropylene fibres waste into the concrete affects negatively its workability, but its flexural and compressive strength are improved. The fibers have presented a significant contribution on the shear behavior and the cracking of beams, particularly in absence of transversal bars. The waste used in this work as fibrous reinforcement has not only increased the ductility of reinforced concrete beams, but it have also provided a perfect cracking distribution on the concrete surface and it has participated in a considerable way in the reduction of cracks number and dimensions, which allows to ensure the material durability and then the structure longevity. The reinforcement of concrete beams with 0.5 % of polypropylene fibers waste with a minimal steel bars can ensure an excellent mechanical behavior in shear, as in flexion.

Study of the reinforcement of structure members by polypropylene fibres waste

The valorisation of industrial waste in the field of construction became a very interesting axis of research from scientific, economic and environmental point of view. We have conducted this work to study the effect of the addition of polypropylene fibres waste on the mechanical behaviour of reinforced concrete beams subjected to a simple flexural loading, with and without transversal reinforcement. The used fibres are coming from the waste of the fabrication of domestic brushes and sweeps; they have an average diameter of 0.47 mm and a length between 40 and 60 mm. Two weight dosages of fibres are used, 0.25 and 0.5 %. The experimental results showed that the incorporation of polypropylene fibres waste into the concrete affects negatively its workability, but its flexural and compressive strength are improved. The fibers have presented a significant contribution on the shear behavior and the cracking of beams, particularly in absence of transversal bars. The waste used in this work as fibrous reinforcement has not only increased the ductility of reinforced concrete beams, but it have also provided a perfect cracking distribution on the concrete surface and it has participated in a considerable way in the reduction of cracks number and dimensions, which allows to ensure the material durability and then the structure longevity. The reinforcement of concrete beams with 0.5 % of polypropylene fibers waste with a minimal steel bars can ensure an excellent mechanical behavior in shear, as in flexion.

Damage to shallow tunnels in different geomaterials under static and dynamic loading

In the present study, an attempt is made to understand the behavior and pattern of tunnel damage subjected to the static and dynamic loading conditions, through the simulation of natural as well as artificial stress states such as loads due to overburden, building, earthquake and blast. The analysis is carried out by using FEM based numerical tool i.e. ABAQUS for different geo-materials. The Mohr-Coulomb plasticity model is used for modeling the rock mass and Johnson–Cook plasticity model have been used for the simulation of stress–strain response of drop hammer. The results of the analysis are studied for stresses, deformation and safety zones in surrounding rock. The displacement of the crown along the axis of tunnel is quantified. It is observed that the strength properties play a crucial role in quantifying the yielded zone in rock mass under both static and impact loading. The effect of weathering is investigated and the deformations for different weathering stages is measured. The crack dimensions reduce as the brittleness of the material increases. Different zones of influence are investigated for all the materials. It is noticed that the zone is significantly crushed in the case of dynamic loading, due to the high velocity of impact and the length of crack is large in the case of static loading as compared to the dynamic loading.

Identification of overheating of an industrial fluidized catalytic cracking regenerator

Considerable overheating can be observed on the outer surface of the fluidized catalytic cracking regenerator. The maximum temperature values and the location of overheating areas change over time. Considering the long times between overhauls (of up to 5 years), it is difficult to pinpoint the factors that cause overheating. An examination of the insulation layer during renovation works does not reveal any obvious damage that could have been responsible for the phenomenon. In order to explain the observed overheating process, a thermal and strength analysis of the fluid catalytic cracking regenerator was conducted. A new algorithm is formulated for identification of the refractory lining state and the heat transfer coefficient between the FCC zeolite catalyst particles and the regenerator walls. The heat transfer coefficient on the regenerator inner surface is estimated after its repair, when no overheating areas are visible. The heat transfer coefficients due to radiation and natural and forced convection are determined based on measured values of the regenerator shell and air temperatures, wind velocity and air pressure. The regenerator outer steel surface temperature is measured using an infrared camera.The presented numerical model of the catalytic cracking regenerator wall enables identification of the wall overheating process. The numerical simulation shows how cracks can open and close in the insulation layer depending on atmospheric conditions. This paper puts forward a new method of identifying heat transfer coefficients and cracks in the refractory lining. The unknown heat transfer coefficient on the regenerator inner surface and the crack dimensions will be calculated by means of the inverse method. A least squares objective function is defined to select parameters such that the computed temperatures will agree within certain limits with the temperature values measured experimentally.The information about the crack size can be used for an on-line assessment of the refractory lining, during the lining modification, and also to estimate the remnant life of steel pressure elements. The method accuracy is presented during real measurements performed by means of an infrared camera using the Gaussian error propagation rule.

Novel insight into swept frequency eddy-current non-destructive evaluation of material defects

Swept frequency eddy-current non-destructive evaluation of defects is concerned in this paper. Possibility of evaluation of detected crack dimensions from response signals is experimentally studied. Two plate specimens having electro-discharge machined slits of various dimensions are inspected using an eddy-current probe. The probe is fixed at a certain position above a specimen during entire inspection of one slit. Frequency of the exciting signal is changed in a wide range in order to acquire frequency response characteristics. The frequency range is adjusted in such a way that the electrical resonance is clearly visible from the acquired characteristics. The characteristics are further processed for exploring their variations in respect to size of inspected slits. Presented results clearly show that the resonance frequency depends on dimensions of a slit. These unique results thus bring new insight into possible utilization of fixed eddy-current sensors driven with swept frequency signal for non-destructive evaluation of cracks.

Fatigue tests of welded connections between longitudinal stringer and deck plate in railway bridge orthotropic steel decks

This research presented the fatigue tests of longitudinal stringer-to-deck (SD) welded connections, which have been identified as the locations most sensitive to fatigue damage in the orthotropic steel decks (OSDs) of railway bridges. Four full-scale SD connections were fabricated, and two loading patches were considered. Static loading was first carried out to obtain the structural hot spot stresses at weld toes as well as stress concentration factors (SCFs), by which the hot spots providing the highest stresses were identified. Cyclic loading was then implemented next to the static loading, and the behaviors including fatigue crack initiation and propagation process, fatigue failure mode, characteristic fatigue life, as well as degradation of vertical rigidity, were all obtained from the test. The crack growing process can be totally divided into four stages, and the fatigue lives after the crack arrived at the deck edge were very short. Variations of crack dimensions were also obtained, and the simplified formulae of crack growth rate were numerically fitted so that the crack propagation lives can be predicted by using the crack dimensions. Comparisons also show that the FAT 100 curve in IIW fatigue design recommendation could overestimate the fatigue resistance of such connections where double-sided fillet welds were used to connect the stringer web and the deck plate, and therefore double-sided groove welds with partial or full penetrations are recommended for the stringer-to-deck connections in railway bridge decks.