Depth Of Surface Cracks Research Articles

Prediction of depth model for cracks in steel using infrared thermography

Nowadays thermography is used as Non-Destructive Testing (NDT) for the detection and characterization of several types of flaws and imperfections. Testing cracks in steel and, particularly in welds presents enormous importance due to the danger of the cracking process. For this reason, the measurements of cracks are important for the prediction and valuation of the type of failure and its consequences. Open to surface cracks can be measured in the surface plane and in the depth plane (plane perpendicular to surface), being the surface plane the one that describes the surface of the welding. Since thermographic imaging directly gives information on the surface plane, the objective of this paper is to optimize the use of infrared thermography for inspection by proposing a method to predict the depth of surface cracks generated by the welding process. The study is implemented based on the analysis of the relationship between infrared (IR) data acquired with an infrared camera and geometric data into the crack extracted by applying a novel 3D macro-photogrammetric procedure. The 3D geometrical model is segmented in different sections and the depth profiles are correlated with the different temperature values along the corresponding sections. With the proposed technique, obtaining a correlation between depth data and thermal surface data is possible. It will allow the design of a depth prediction model which enables the inspection of depth of cracks using the thermographic technique.

Impact of micromechanical parameters on wire sawing: a 3D discrete element analysis

Wire sawing is one of the most prominent technologies for producing solar wafers. In the following paper a numerical model for the simulation of the wire sawing process at microlevel using the discrete element method is presented. The abrasive particles are represented by convex polyhedra. Based on the contact forces on the ingot, local material removal rates are calculated. These local material removal rates are then used to update the shape of the ingot in a stepwise simulation. The model allows for detailed analysis of the influence of different parameters on the micromechanical processes during wire sawing. In particular the influence of wire speed, lapping pressure, particle concentration, particle size, particle shape and debris on the sawing process is investigated. In a post-processing macroscopic process characteristics like kerf width, depth of surface cracks or sawing rate are calculated. Thus, the processes at the microlevel are related to the macroscopic process characteristics, which are of interest when applying wire sawing in practice.

Non-destructive evaluation of depth of surface cracks using ultrasonic frequency analysis.

Ultrasonic is one of the most common uses of a non-destructive evaluation method for crack detection and characterization. The effectiveness of the acoustic-ultrasound Structural Health Monitoring (SHM) technique for the determination of the depth of the surface crack was presented. A method for ultrasonic sizing of surface cracks combined with the time domain and frequency spectrum was adopted. The ultrasonic frequency spectrum was obtained by Fourier transform technique. A series of test specimens with various depths of surface crack ranging from 1 mm to 8 mm was fabricated. The depth of the surface crack was evaluated using the pulse-echo technique. In this work, three different longitudinal waves with frequencies of 2.25 MHz, 5 MHz and 10 MHz were employed to investigate the effect of frequency on the sizing detection of surface cracks. Reasonable accuracies were achieved with measurement errors less than 7%.

Research on Depth Evaluation of Surface Crack in Laser Cladding Coating with Metal Magnetic Memory Technology

Depth of evaluation method of surface crack in laser cladding coating with metal magnetic memory was introduced in this paper. Laser cladding coating specimen were degaussed, placement direction of specimen and detection direction unchanged, detection speed and lift off value of probe were the constant. Results show that gradient value ofHp(y) signal corresponding to surface crack increases as tensile load increases under the same depth of surface crack, gradient value ofHp(y) signal corresponding to surface crack increases as depth of surface crack increases under the same tensile load. Orientation of internal magnetic domain changes as tensile load changes and magnetic leakage field caused by surface crack are seen as two main reasons for above results. Using fitting method with quadratic polynomial, depth of surface crack in laser cladding coating can be evaluated nondestructively in this paper.

Study on the Model of Surface Crack Depth in Ceramics Grinding

Based on "indentation fracture mechanics" model, this paper offers a model on the crack depth of surface in ceramics grinding. Through carrying out one-way trip grinding and surface crack depth measuring experiments on silicon nitride, a model for silicon nitride grinding surface crack depth is established. In this model, the parameters can be confirmed by the experiment. By the grinding experiment, the parameters of the model can be confirmed, and the controlled grinding surface quality for the ceramic materials can be expected.

Effect of electron beam irradiation on polymer electrolytes: Change in morphology, crystallinity, dielectric constant and AC conductivity with dose

Polymer electrolyte (PEO:Li2SO4) films were exposed to 8MeV electron beam (EB) with various doses to investigate the radiation effect on dielectric permittivity (real and imaginary) and AC conductivity by using PC based Impedance Analyzer in the frequency range of 40–1MHz at different temperatures. The change in chemical interaction, morphology, and thermal properties was analyzed with the help of Fourier Transform InfraRed (FT-IR), Scanning Electron Micrographs (SEM) and Differential Scanning Calorimeter (DSC) techniques respectively for before and after irradiation. The chemical change was confirmed from the FT-IR result which showed that peak intensities corresponding to C–H, C=C, and –C–O–C– bonds decrease with increase in EB dose clearly indicating that the degradation of polymer chain or segments (i.e., –CH2–CH2–). The DSC result showed that the melting temperature of unirradiated film is 69.42°C which reduced to 67.55°C for 30kGy dose suggesting an exothermic behaviour. The SEM images give that surface roughness and crack depths increase with increasing dose. The XRD result reveals a decreased ~30% crystallite size for 30kGy dose compared with unirradiated film. Further, it is seen that dielectric permittivity and frequency dependent conductivity were found to increase with increasing irradiation dose. The maximum AC conductivity was observed to be 1.88×10−4s/cm for 30kGy and the estimated change in charge carrier concentration also showed high for 30kGy dose. The AC conductivity obeys Power׳s law. The frequency exponent (s) parameter shows temperature dependent behaviour which decreases after irradiation.

Continuous casting slab surface crack depth measurement using sinusoidal phase grating method

With the development of hot charging and direct rolling technology in continuous slab casting, there are increasing demands for the surface quality of hot continuously cast slab evoked by modern metal material fabrication. In order to reduce noise, which is caused by scale, water film and oscillation marks, during on-line detection of surface defects, a sinusoidal phase grating projection method is presented to detect the depth and surface profile of surface cracks in continuous slab casting. This technology, based on a deformed projected grating pattern, which carries three-dimensional information of the measured surface of the slab, can provide an absolute measurement of the depth of the surface defect by using a temporal phase unwrapping algorithm. The main advantage is that objects containing depth discontinuities of the crack are profiled as easily as smooth ones. The experimental results show the method has a high signal to noise ratio, and good applicability for automatic crack depth testing in continuous casting.

Evaluating the depth of open cracks in concrete from parameters of electric response to elastic-impact excitation

We have studied the character of decay of the spectral components of electric response to elastic impact excitation of a concrete sample with artificial cracks of various depths. A criterion for determining the depth of surface cracks in concrete is proposed based on results of time-frequency analysis of the response signal.

Heat transfer modeling for surface crack depth evaluation

This paper presents a theoretical approach for the quantitative depth evaluation of linear opened surface cracks by using lock-in infrared thermography. In order to simulate heat flow near a crack, a three-dimensional simulation model has been developed by using finite element simulation. We show that, under a periodic local thermal excitation in the vicinity of the crack, the second spatial derivative of the amplitude image can provide information on this depth. The influence of the simulation parameters are discussed for the optimal characterization of defects.

Crack sizing by laser excited thermography

Active thermography is a nowadays widely used NDT method making use of thermal material properties for defect detection. Basically, the sample is heated and the resulting surface temperature is recorded by an IR camera. For laser thermography a laser is used to heat the sample locally. The resulting spherical heat flow allows the detection of voids in arbitrary orientation. In this work, a method is presented which is suitable for the quantitative characterization of depth and angle of surface cracks. The main idea is to evaluate the crack-caused asymmetries of the laser's thermal footprint. The heat is introduced at fixed reference positions relative to the crack. In this paper a data analysis procedure is presented which allows the crack depth and angle to be described by only two characteristic scalar parameters. By investigating artificial test specimens with spark eroded notches, the feasibility of this method is validated. Furthermore, the behavior of the characteristic parameters with variations of crack angle, depth and experimental conditions is studied systematically by FEM simulations, showing that these parameters are well behaved.

Creep fracture mechanics parameters for internal axial surface cracks in pressurized cylinders and creep crack growth analysis

In the present study, a low alloy Cr–Mo steel cylinder subjected to internal pressure at high temperature with a semi-elliptical crack located at the inner surface is considered. The creep crack driving force parameter C∗-integrals calculated by finite element (FE) method, are compared with results from previous studies, which indicates that empirical equations may be inaccurate under some conditions. A total of 96 cases for wide practical ranges of geometry and material parameters are performed to obtain systematic FE results of C∗-integral, which are tabulated and formulated in this paper. It is observed that the maximum C∗-integral may occur neither at the deepest point nor at the surface point when the aspect ratio is large enough and the value of C∗-integral is significantly sensitive to the crack depth ratio. Furthermore, based on the proposed equations for estimating C∗-integrals and a step-by-step analysis procedure, crack profile development, crack depth, crack length and remaining life prediction are obtained for surface cracks with various initial aspect ratios. It is found that when the crack depth ratio is increased, there is no obvious convergence of crack aspect ratio observed. The magnitude of half crack length increment is always minor compared with the crack depth increment. In addition, the remaining life is much more dependent on the surface crack depth than on the surface crack length.

Detection and measurement of surface cracks by the ultrasonic method for evaluating fatigue failure of metals

The problem of measuring the dimensions of safe cracks by the acoustic method was considered on the basis of the concept of safe cracks. The results of investigations are presented and the obtained data on the detection and measurement of the depth of surface cracks using Rayleigh waves at artificial reflectors of the surface-notch type and at real cracks and specimens, which are subjected to cyclic loads during the “growth” of fatigue cracks, are analyzed.

Numerical Study on Depth Gauging of Surface Breaking Defects Using Laser-Generated Surface Acoustic Waves

Laser-generated surface acoustic waves scattering from surface cracks of various depths and widths have been calculated by the finite element method, where a surface notch is introduced to represent a fatigue crack for the convenience of modeling. The bipolar Rayleigh waves have been captured clearly using this model, as the laser line source close to the surface crack. In addition, the numerical results demonstrate that there exist clear oscillation signals following the reflected Rayleigh waves, the temporal cycles of which are found to be dependent on only notch depth, the arrival time of which is related mainly to the width of the notch. Therefore, a new crack evaluation method based on the temporal characteristics of surface acoustic wave signals has been proposed and discussed in this paper, which is helpful for measuring the depth of surface cracks accurately.

Influence of crack length on crack depth measurement by an alternating current potential drop technique

An alternating current potential drop (ACPD) technique is used for sizing depth of surface cracks in metallic components. Crack depth estimations are prone to large deviations when ACPD measurements are made on very shallow and finite length cracks, especially in low conducting materials such as austenitic stainless steel (SS). Detailed studies have been carried out to investigate the influence of crack length and aspect ratio (length to depth) on depth estimation by performing measurements on electric discharge machined notches with the aspect ratio in the range of 1 to 40 in SS plates. In notches with finite length, an additional path for current to flow through the surface along the length is available causing the notch depths to be underestimated. The experimentally observed deviation in notch depth estimates is explained from a simple mathematical approach using the equivalent resistive circuit model based on the additional path available for the current to flow. A scheme is proposed to accurately measure the depth of cracks with finite lengths in SS components.

On-site measurement of delamination and surface crack in concrete structure by visualized NDT

On-site measurement in concrete piers of a highway structure was conducted by visualized non-destructive testing (NDT). First, the radar technique was applied to identify delaminated areas between pre-stressed concrete (PC) panels covered and original concrete piers. By applying the impact-echo method, Stack Imaging of spectral amplitudes Based on Impact-Echo (SIBIE) procedure is developed as an imaging technique, which can visually display a cross-sectional view based on the impact-echo data. In order to identify voids in delaminated areas and depths of surface cracks, then the impact-echo tests were conducted. From these results, a superior applicability of the SIBIE procedure to on-site measurement is demonstrated in existing concrete structures.

Confocal Examination of Subsurface Cracking in Ceramic Materials

The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM). Twenty (8 x 4 x 2 mm(3)) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles. Twenty- to 30-microm deep subsurface cracking appeared in SSL, with 8 to 10 microm in AC, and 7 microm close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-microm deep subsurface cracks were detected in SSL and 45 microm in AC after 80K cycles. Statistically, there was significant difference among the three materials (p < 0.05). Bonferroni multiple comparison of means test confirmed the ANOVA test and showed that there was no statistical difference (p > 0.05) in crack depth within the same ceramic material with different surface finishes. The ceramic materials with different microstructures showed different patterns of subsurface cracking.

Capacity of Fractographic Analysis for Load-Time History Reconstruction and Fatigue Crack Growth Rate Estimation for the 2024-T3 Aluminium Alloy

Capacity of Fractographic Analysis for Load-Time History Reconstruction and Fatigue Crack Growth Rate Estimation for the 2024-T3 Aluminium AlloyThe subject of the paper is the considerations for the feasibility of load time history reconstruction on the basis of microfracture analysis for a failed component made of 2024-T3 aluminium alloy that operates under variable amplitude loading. For this goal three different variable amplitude load sequences with single and multiple overloads and underloads were applied to investigate crack growth rate and to examine the images of fatigue striations on the fracture surface of a component. These loads are employed when simulating the fatigue crack behaviour in aeronautical alloys. Microfracture analysis was also used either for learning the interaction of variable amplitude loading for crack growth rate in 2024-T3 alloy or for establishing the relation between surface crack and crack depth growth.

Ｃｕ鋼の表面赤熱脆性に及ぼすショットピーニングの影響

The recycling of scrap steels is a global issue due to the environmental problem. Tramp elements such as Cu and Sn that they can contain cause surface cracking of steels during hot rolling process (i.e., the liquid embrittlement by Cu). This paper describes the influence of shot peening on the surface hot shortness of x% Cu (x50, 0.4 and 0.6) containing low carbon–Nb–V steel. These materials were shot peened by Al2O3 at room temperature and they were subjected to 1100°C oxidation in air or in water vapor contained atmosphere followed by tensile strain or compression strain. Surface hot shortness was assessed by measuring the number and depth of surface cracks occurring in the specimens. It was found that shot peening largely changed the oxidized scale structure such as Fe2O3/Fe3O4 and Fe3O4/FeO interfaces, the volume fraction of voids in the scale, and the distribution of Cu enriched alloy at the interface of scale/steel, thereby suppressing the hot shortness of Cu steels.The authors discussed this mechanism by macroscopically homogenous and microscopically heterogeneous oxidation due to the introduction of defects such as dislocations and lattice distortions into surface layer of Cu steels by shot peening. It was concluded that shot peening is high potentialities for suppressing the hot shortness of Cu containing steel as a new method other than using expensive nickel.

Characterization of surface crack depth and repair evaluation using Rayleigh waves

The issues of surface crack depth determination and the evaluation of repair effectiveness are not trivial for concrete engineers. In the present paper, surface waves are applied on concrete blocks with artificial slots to correlate wave parameters with crack depth. To simulate crack repair with an injected material, epoxy is applied to the slots in the laboratory and quantification of the filling percentage is attempted. Simultaneously, a frequency domain boundary element method is employed for the numerical simulation of transient pulses interacting with surface breaking cracks. Experimental results compare well with the numerical ones, showing that the repair effectiveness, which so far can be evaluated only by destructive techniques , is possible by simple surface wave measurements.

Reliability Calculation of Welded Pressure Pipe with Circumferential Crack Based on 3-D Elastic-Plastic SFEM

In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t&lt;0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.