Size Of Surface Defects Research Articles

Effect of shot peening conditions on the surface defect size rendered which is harmless in carburized steel

Effect of shot peening conditions on the surface defect size rendered which is harmless in carburized steel

Effect of surface defects on damage and failure of dynamically driven cylindrical shells

In this work, expanding cylinder experiments are performed using a gas gun on the aluminum 6061 alloy to understand the dynamic deformation and failure behavior of this material in the presence of surface defects in the form of scratches. The experiments are then modeled with the modified Tepla (for tensile plasticity) model, which is equipped with the damage yield function of Gurson [“Continuum theory of ductile rupture by void nucleation and growth: Part I—Yield criteria and flow rules for porous ductile media,” (1977)] and Tvergaard and Needleman [Acta Metall. 32(1), 157–169 (1984)], over-stress viscosity [F. Addessio and J. Johnson, J. Appl. Phys. 74(3), 1640–1648 (1993)], and the underlying viscoplastic model of Preston et al. [J. Appl. Phys. 93(1), 211–220 (2003)] (Preston–Tonks–Wallace model) for the dense material. The Tepla model parameters were calibrated using the Bayesian approach against experimentally measured free-surface velocity data obtained from plate impact experiments on the aluminum 6061 alloy. The evolution of radial expansion and shapes of the deformed cylinder from the simulations on a pristine cylinder wall and a cylinder wall with a longitudinal surface defect shows excellent agreement with the corresponding experimental results. Finally, the role of surface defect size and cylinder wall geometry on the dynamic strength of the cylinder wall was also investigated through a series of simulations.

Advanced Eddy Current Testing of Carbon Composites

Carbon composites due to their specific properties find applications in various industries, especially in aerospace industry. Widely used carbon fibre reinforced polymers (CFRP) have already been applied even for the aircraft primary structures. The development of advanced diagnostic techniques that are able to easily detect and identify the degradation of the carbon fibre material is still a challenge for various NDT methods. This paper describes the possibility to apply eddy current (EC) for testing of carbon composite structures. Two types of eddy current probes were developed and tested with excellent results. The new conventional eddy current probes are able to reliably and easily detect surface and subsurface discontinuities such as delamination and thickness variation. The probe setting parameters are described for different types of carbon composites (type of matrix and reinforcement, layup). Precise settings are necessary for the successful eddy current testing. It was determined that reliable detection of a minimum surface defect size is Ø1.5 mm for specimens and that eddy currents are able to penetrate into a thickness up to approximately 4 mm depending on the type of carbon composite. Additionally, this paper describes the comparison of eddy current testing with ultrasonic phased array method (PAUT). Composite aircraft structures are very susceptible to impact damage usually detected using PAUT. Therefore, sensitivity and resolution analysis of impact damage detection was performed by means of these two methods. It was found out that the results are very similar to each other when standard pulse-echo technique of PAUT was used. This carbon composite eddy current testing could fully replace or complement other NDT methods such as visual or ultrasonic inspections. Also it could guarantee the product quality in production, aircraft maintenance and in the development of new aircraft structures.

Finite element analysis of fracture behavior in ceramics: Competition between artificial notch and internal defects under three-point bending

Evaluation of the nonlinear relationship between the surface defect size and fracture strength of ceramics is important for engineering applications. In this study, we aim to predict the apparent nonlinear relationship between the defect size and fracture strength of single-edge notched beams (SENBs) using the finite element method. Specifically, we applied the methodology for predicting fracture strength from microstructure distribution data (relative density, pore size, aspect ratio, and grain size) to a finite element analysis (FEA) model in which the shape and size of the initial defects are defined at notch locations. By reproducing the apparent nonlinearity caused by the competition between the surface and internal defects within the framework of linear elastic fracture mechanics, the effectiveness of the FEA methodology for the evaluation of strength scatter and allowable crack size in ceramics was demonstrated.

Surface Defect Segmentation and Detection of Printing Roller Based on Improved FT Algorithm

The method based on machine vision is one of the important ways of printing roller defect detection. It has the advantage of intuitively reflecting the surface state of printing roller, but the effect of detecting the position where the surface defect of printing roller is not obvious is not ideal. Aiming at the problems of different printing roller surface defects and large interference of background texture, a printing roller surface defect detection algorithm based on improved frequency tuning significance and threshold segmentation is proposed. Firstly, the nonlocal mean filter method is used to preprocess the image to solve the influence of noise on the image; Then, the saliency map is extracted by converting the lab color space of FT algorithm to HSV color space, normalizing and weighting each eigenvalue respectively; Finally, the salient image is binarized by iterative threshold segmentation to obtain the final defect image. The experimental results show that the accuracy of the algorithm is 97.1%, which is better than other similar algorithms. It can accurately detect the roller image with different size of surface defects and texture background interference, and the comprehensive performance is outstanding.

Finite Element Analysis of Fracture Strength of Ceramics Considering Both Surface and Internal Defects

Structural ceramics are being considered for use in a variety of fields due to their excellent properties. However, ceramics are very sensitive to defects and minute surface defects can affect fracture strength. In addition, the relationship between surface defects and fracture strength exhibits non-linearity, and thus, the conventional linear elastic fracture mechanics may not predict fracture strength. Therefore, there is a need for an accurate method to determine the effect of surface defects on the fracture strength of ceramics. In this study, we developed a method that extends the model proposed by the authors to incorporate fracture strength reduction due to surface defects. This method can reproduce the non-linearity of the relationship between surface defects and fracture strength of ceramics. Then, we discuss about the competing relationship between internal and surface defects. It can also estimate the allowable size of surface defects by combing with the Weibull distribution of fracture strength.

Influence of indentation size on the corrosion behaviour of a phosphate conversion coated AZ80 magnesium alloy

The service performance of magnesium alloy wheel hub was simulated by studying the effect of surface defect size on the corrosion resistance of a calcium phosphate conversion coated AZ80 magnesium alloy. The surface defects were produced with different sizes using a Film Impactor. The corrosion behaviour was studied using electrochemical, hydrogen evolution and immersion tests. The microstructures were characterized using a scanning electron microscope and a laser confocal microscope. Phases and the corrosion products were analyzed using XRD and XPS. The size of the surface defects influenced the corrosion resistance of the coating and the corrosion initiation area. The coating provided no protection for an indentation larger than 2.7 mm. The corrosion mechanism of the coating was also clarified.

Catalyst-free synthesis and mechanical characterization of TaC nanowires

TaC nanowires are expected to be an ideal reinforcing material in ultra-high-temperature ceramics. However, their growth mechanisms and mechanical properties remain unclear, and low-cost large-scale synthesis has not been realised. In this study, bulk synthesis of [100]-oriented TaC nanowires is accomplished by carbothermal synthesis through a direct vapor-solid mechanism. Thermal resonance test results show that the synthesized square TaC nanowires with cross-sectional side-lengths of 65 to 497 nm have a size-independent Young’s modulus of (510.6±12.6) GPa; very close to the corresponding values of their bulk counterparts, but differing considerably from previously published measurements. Molecular dynamics (MD) simulations show that TaC nanowires with side-lengths of above 15 nm have a constant Young’s modulus of 517 GPa, and size effects on the modulus values should only occur at side-lengths below 15 nm. During bending tests, the TaC nanowires fracture into several segments in a brittle mode, and exhibit an increasing fracture strain from 1.88% to 4.28% as their side-length decreases from 489 to 90 nm. Weibull statistics analyses and TEM observations indicate that the failure of the nanowires should be primarily dependent on the number and size of surface defects. MD simulations further reveal that the defect-free TaC nanowires fail brittlely at a theoretical strain up to 5.76%.

Optimisation of the wear resistance properties of laser cladded T-800 coatings

Taguchi design of experiments (DoE) was employed to determine appropriate laser cladding (LC) parameters for optimising microstructural and anti-wear properties of Tribaloy (T-800) coatings. The nature of wear mechanism was also explored with scanning electron microscopy (SEM). Statistical analysis established that both microhardness and wear rates were primarily dependent on powder feed rates and scanning speeds while coefficient of friction (COF) is significantly influenced by spot diameter. Variation in wear morphology, across the samples, could be explained by presence or absence of surface defects; sizes of surface defects, distance between the surface defects as well as the nature of evolving microstructure within the clad samples. Optimum samples were imparted with microhardness (900 HV), COF (0.0743) and specific wear rate (0.0071 mm3/N/m), and these compared favourably well with the predicted values. Samples fabricated with optimum LC parameters are suitable for wear application in mining industries.

Prediction of Fatigue Limit of Spring Steel Considering Surface Defect Size and Stress Ratio

Surface defects decrease the fatigue limit of metals. In this study, the effects of surface defects on the fatigue limit of high-strength spring steel specimens were investigated. Several equations to predict the fatigue limit of specimens with surface defects were evaluated. Specimens with a semicircular slit with depths ranging from 30 to 400 µm were prepared. The Vickers hardness of the specimen was approximately 470 HV. Bending fatigue tests were performed at stress ratios ranging from −2 to 0.4. The fatigue test results showed that the fatigue limit decreased with an increase in the slit depth. Moreover, the maximum defect size that resulted in a decrease in the fatigue limit was dependent on the stress ratio. On comparing the predicted fatigue limits with the experimental results, it was confirmed that the predictions made based on the modified El-Haddad model were in good agreement with the experimentally obtained data. Thus, this model can be used to evaluate the fatigue limit of high-strength steels containing small surface defects with different stress ratios.

Assessment of fatigue damage of fluoroorganic aircraft glass using digital holography methods

A digital holography method is proposed for determination of the depth and characteristic size of fatigue damage of fluoroorganic aircraft windows. The ability of this method to determine the characteristic lateral size of surface defects of the aircraft cabin window components with a measurement error of ±15µm and the longitudinal size (depth of the surface defect) with a measurement error of up to ±100µm (for defects with characteristic lateral sizes less than 60 µm) is demonstrated. The investigation and developed model of the digital holographic camera indicate the possibility of developing the method for testing the aircraft cabin window components for surface damage with the required accuracy and estimation of its effects on flight safety.

THEORETICAL DEFINITION OF OPTIMAL PARAMETERS OF FIELD PIPELINE HYDRAULIC TESTS

Background Accidents and shutdowns of field technical pipelines not only lead to the loss of gas, oil and oil products, but also require the cost of repair and restoration work, which entails large economic costs, estimated at billions of rubles annually. Aims and Objectives Calculation of oil field pipelines test pressure taking into account the ovality and curvature of pipes, the type of stress state, the size of surface defects, plastic properties of pipes. Results To determine the maximum test pressure, it seems reasonable to divide the pipeline into sections for hydraulic testing, indicate the sources of production and the place of discharge of water. For each site, it should be found the minimum radius of elastic bending and wall thickness. Trouble-free operation of the oil pipeline can be ensured by periodic hydraulic testing - approximately 1 time in 3 years or by periodically reducing the working pressure. Another way to ensure trouble-free operation of a heat conductor is to reduce the load cycling.

Notch-defect interaction in additively manufactured Inconel 718

Powder bed fusion based additively manufactured components are known to have poor surface quality, especially when building downward facing surfaces. These surfaces can contain defects, from which fatigue cracks can be initiated. In this work the notched fatigue behaviour of Inconel 718 specimens produced by selective laser melting is investigated. The main focus is set on the interaction between notch geometries and local defects due to the amount of overhang in the notch region. Four different geometries are considered, with different amount of notch acuities and degree of downward facing surfaces. A variation in failure sites, with respect to the notch bisector line, was fond in the specimens, and the position was found to be dependent on the amount of overhang and notch acuity. The fatigue life was found to be dependent on the size of surface defects measured in fracture surfaces. Further, the use of average strain energy density as a failure criteria in additively manufactured metals is discussed.

Multiscale Simulation of Surface Defects Influence Nanoindentation by a Quasi-Continuum Method

Microscopic properties of nanocrystal aluminum thin film have been investigated using the quasicontinuum method in order to study the influence of surface defects in nanoindentation. Various distances between the surface defect and indenter have been taken into account. The results show that as the distance between the pit and indenter increases, the nanohardness increases in a wave pattern associated with a cycle of three atoms, which is closely related to the crystal structure of periodic atoms arrangement on {1 1 1} atomic close-packed planes of face-centered cubic metal; when the adjacent distance between the pit and indenter is more than 16 atomic spacing, there is almost no effect on nanohardness. In addition, the theoretical formula for the necessary load for elastic-to-plastic transition of Al film has been modified with the initial surface defect size, which may contribute to the investigation of material property with surface defects.

Ultrasonic Defect Detection of Structural Plates Using Quasi-Rayleigh Waves

Abstract This article discusses the application of so-called ultrasonic quasi-Rayleigh waves to detect surface defects of mechanical constructions, namely plate structures. The application of quasi-Rayleigh waves allows the extension of the scope of detection using conventional ultrasonic methods that are based on bulk waves. This extension means larger distances as well as higher sensitivity of the detection of surface defects such as fatigue or corrosion cracks. An advantage of this method is the transfer of wave energy from one side of a plate to another, which helps to overcome one-sided obstacles (such as cross-pieces, reinforcement elements). The article describes characteristic properties of quasi-Rayleigh waves that are important for the proper (in terms of frequency in particular) design of the excitation of waves towards the structure. FEM simulation results then provide information regarding the sensitivity of the wave response to the presence and sizes of surface defects (perpendicular slots) in an isotropic material with the properties of steel. The theoretical knowledge is set against experimental measurements obtained with the use of a steel plate with cross-pieces welded to it.

A novel treatment of carbon fibers with improving tensile strength to synthesize evenly distributed carbon nanotubes on their surface

Well-dispersed iron oxide (Fe3O4) nanoparticles and evenly distributed carbon nanotubes (CNTs) were synthesized on the surface of carbon fibers pretreated by the concentrated HNO3 oxidation and subsequent KOH activation. Results showed that KOH activation provided an opportunity not only to fix a suitable content of oxygen-containing functional groups on carbon fiber surface thus preventing the absorption of large nanoparticles, but also contributed to the formation of numerous nanopores on the fiber surface by etching effect, which could limit the movement of the absorbed nanoparticles. The well-dispersed Fe3O4 nanoparticles had a uniform diameter of 122.01nm and density of 2.47×109cm−2. Tensile test demonstrated that the tensile strength of fiber bundles was increased by 30.88% due to the decrease of surface defect size. In addition, CNTs reached a homogenous distribution on the surface of KOH-treated carbon fibers while only CNTs clusters, short CNTs and large pyrocarbon particles were formed on the surface of oxidized carbon fibers. Our work provides a meaningful way to modify carbon fibers with improving the mechanical strength and synthesize well-dispersed Fe3O4 nanoparticles as well as evenly distributed CNTs on their surface.

The Next Generation of Germanium Substrates: ExpogerTM

Umicore has been the leading Germanium substrate manufacturer over the last 20 years. We are only able to maintain that position by constantly improving the quality of our product. In this work, Umicore wants to present how it will continue this tradition by adding even more value to its product.In the beginning of 2014 we proposed to our customers to help them in achieving their yield improvement goals. Two main concerns were expressed: the breakage rate in their production line and non-uniform epi-growth. After two years of development, Umicore has bundled these two improvements into a new product. The ExpoGerTM wafer combines a better mechanical yield with a uniform, epi-ready surface enabling a narrower distribution of the electrical performance.The breakage rate of the customers is related to the wafers that suffer from early failure. The percentage of early failures is related to its thickness. With the trend towards even thinner substrates, it is important to add features that reduce the percentage of early failures. Two features are crucial: the shape of the substrate edge and the stress relief etch, which influences the wafer strength.Just as for the strength, two distinctive aspects define the surface quality. On the one hand, there are the number and size of surface defects, which have an important influence on the metal-organic chemical vapour deposition (MOCVD) growth performed at Umicore’s customers. On the other hand, drying marks, which are invisible to the naked eye, may lead to a local, non-uniform growth and they can be a precursor to time dependent haze issues.Umicore is able to demonstrate the impact of the ExpoGerTM processes on the strength and surface quality of its wafers and thus on the production yield of its customers.

An approach to determine a critical size for rolling contact fatigue initiating from rail surface defects

ABSTRACTA methodology for the determination of a critical size of surface defects, above which RCF can initiate, has been developed and demonstrated with its application to the passive type of squats under typical Dutch railway loading conditions. Such a methodology is based on stress evaluation of transient rolling contact at the defects, for which a detailed 3D frictional rolling contact model is integrated in the vehicle–track interaction system. Through comparing the maximal von Mises stress at defects of different sizes with the tensile strength of the rail material, the critical size is derived for squats. Observations during a field monitoring test show a good validation of the determined critical size. In practice, the critical size can be used for distinguishing between light squats and trivial defects by visual inspection or by automatic image recognition, so that false statistics of squats can be reduced or prevented. With necessary modifications and improvements, the developed methodology may also be applied to RCF of other rolling contact pairs in general, such as bearings and gears.

Fatigue life equality of polished and electrical discharge machined WC-Co hard metal achieved solely by wet blasting

WC-Co hard metals are materials widely used in wear applications, metal machining and highly fatigue loaded tools. Shaping tools and components made of hard metals often requires electrical discharge machining (EDM) that is well-known to negatively influence the material's fatigue properties.The current work demonstrates that it is possible to achieve a fatigue limit of electrical discharge machined specimens equal to the one of finely ground and polished reference samples. This is achieved by the application of advanced wire EDM technology combined with a sole surface post-treatment step of abrasive blasting. Stress amplitude-life curves were determined in a four point bending test setup. Depth profiles of residual stress were determined by means of X-ray diffraction for electrical discharge machined samples prior to and after blasting. Surface defect size was documented in metallographic cross sections by scanning electron microscopy. The surface residual stress state was found to be crucially important regarding the observed fatigue behavior. If the applied EMD technology produces cracks shallow enough to allow for their removal by abrasive blasting and compressive residual stress is introduced as deep into the surface as damage reaches, the negative effect of EDM on the fatigue limit is neutralized.

Studies on structural defects in bare, PVP capped and TPPO capped copper oxide nanoparticles by positron annihilation lifetime spectroscopy and their impact on photocatalytic degradation of rhodamine B

Enhanced photocatalytic dye degradation by reducing sizes of surface defects.