Size Of Internal Defects Research Articles

Ultrasonic Non-Destructive Testing and Evaluation of Stainless-Steel Resistance Spot Welding Based on Spiral C-Scan Technique.

In order to achieve the non-destructive testing and quality evaluation of stainless-steel resistance spot welding (RSW) joints, a portable ultrasonic spiral C-scan testing instrument was developed based on the principle of ultrasonic pulse reflection. A mathematical model for the quality evaluation of RSW joints was established, and the centroid of the ultrasonic C-scan image in the nugget zone of the RSW was determined based on the principle of static moment. The longest and shortest axes passing through the centroid in the image were extracted, and the ratio of the longest axis to the shortest axis (RLS) factor and the average of axis (AOA) factor were calculated, respectively, to evaluate the quality of the joint. To study the effectiveness of the detection results, tensile tests, and stereo analysis were conducted on the solder joints after sampling. The results indicate that this detection method can realize online detection and significantly improve the detection efficiency; the detection value of internal defect size is close to the true value with an error of 0.1 mm; the combination of RLS and AOA factors can be used to evaluate the mechanical properties of RSW joints. This technology can be used to solve the NDT, evaluate problems of RSW joints, and realize engineering applications.

Corrosion-Fatigue Performance of 3D-Printed (L-PBF) AlSi10Mg.

Additive manufacturing (AM) allows for optimized part design, reducing weight compared to conventional manufacturing. However, the microstructure, surface state, distribution, and size of internal defects (e.g., porosities) are very closely related to the AM fabrication process and post-treatment operations. All these parameters can have a strong impact on the corrosion and fatigue performance of the final component. Thus, the fatigue-corrosion behavior of the 3D-printed (L-PBF) AlSi10Mg aluminum alloy has been investigated. The influence of load sequence (sequential vs. combined) was explored using Wöhler diagrams. Surface roughness and defects in AM materials were examined, and surface treatment was applied to improve surface quality. The machined specimens showed the highest fatigue properties regardless of load sequence by improving both the roughness and removing the contour layer containing the highest density of defect. The impact of corrosion was more pronounced for as-printed specimens as slightly deeper pits were formed, which lowered the fatigue-corrosion life. As discussed, the corrosion, fatigue and fatigue-corrosion mechanisms were strongly related to the local microstructure and existing defects in the AM sample.

Influence of Combined Heat Treatment and Hot Isostatic Pressure (HT-HIP) on Titanium Aluminide Processed by L-PBF.

Postprocessing is essential for improving titanium aluminide (TiAl) microstructure and part quality after using the laser powder bed fusion (L-PBF) method. It has been reported that Ti-48Al-2Cr-2Nb (%at) processed by L-PBF has internal defects and low fracture toughness. Microstructure control by heat treatment (HT) showed a significant improvement in the ductility of the material. Alternatively, hot isostatic pressing (HIPing) could be applied to reduce the residual stresses and internal defects formed during the L-PBF. Combining the benefits of these two subsequent processes into a single predetermined process is appealing for Ti-48Al-2Cr-2Nb (%at) to minimize cost. This work presents a novel strategy to postprocess L-PBF TiAl by applying combined heat treatment and hot isostatic pressing in one process, namely HT-HIP. The process includes three cycles with different conditions (i.e., temperature, time, and pressure). These conditions were determined to achieve improved part quality and microstructure. The results show that the tensile residual stresses decreased from a peak of 249 MPa in the as-built sample to compressive stresses that peaked at -90 MPa after the HT-HIP process. The number and size of internal defects could be greatly reduced. The defects were transformed into a regular spherical shape, which is good in terms of fatigue strength. Additionally, a duplex microstructure with lamellar α2/γ colonies could be introduced for better ductility. Different levels of duplex microstructure could be achieved along with the process cycles. The grain structure using EBSD analysis showed refined equiaxed grains, which demonstrate better strength after the HT-HIP process. Twinning boundaries were also observed in the HT-HIP sample. The grain orientation tendency to the build direction significantly reduced after the HT-HIP process. The nanoindentation test was applied to evaluate the nanohardness of the as-built and HT-HIP samples. It could be demonstrated that the nanohardness is dependent on the formed phases and lamellar density inside the grains. The mean hardness value was 8.19 GPa for the as-built sample, while it was 5.48 GPa for the HT-HIP sample.

Numerical modeling for evaluation of the thermal resistance of reflective airspaces with and without defects

The thermal resistances (R-values) of airspaces depends on the emittance of all surfaces around an airspace, dimensions, heat-flow direction, and the temperatures of the bounding surfaces. Assessing the energy performance of building envelope components and fenestration systems requires accurate results for the R-values of any enclosed spaces. The evaluation of reflective insulation R-values has evolved to include use of computational fluid dynamics and surface-to-surface radiation to quantify convective and radiative contributions to the heat transfer across airspaces of all types. This paper compares an advanced and validated model for calculating enclosed airspace R-values with the widely-used ISO 6946 and airspace R-values in the ASHRAE Handbook-Fundamentals. The impact of construction and installation defects on the thermal performance of reflective insulation has not been previously evaluated. In this research, an advanced model was used to evaluate a construction defect and dimensional aspect ratios that one-dimensional methods do not address. Imperfect installation and defects that result in air movement into or through a reflective insulation assembly reduces the thermal resistance of the assembly. Additionally, the amount of thermal resistance reduction depends on the amount and temperature of invasive air or the size of internal defects that allows natural convection inside the reflective airspace. In this study, these performance issues are evaluated quantitatively using computer simulation techniques. The differences in results obtained using methods that are currently being used to evaluate the R-value and the advantages of the advanced method for evaluating the reflective insulation performance for different applications are discussed. For the case considered in this study, the results showed that the failure to achieve parallel surfaces results in less than a 5% decrease in thermal resistance. Also, the results showed that internal air gaps between airspaces result in negligible loss in R-value unless air gaps that allow circulation between airspaces are created.

Step heating thermography supported by machine learning and simulation for internal defect size measurement in additive manufacturing

A methodology based on step-heating thermography for predicting the length dimension of small defects in additive manufacturing from temperature data measured on thermal images is proposed. Regression learners were applied with different configurations to predict the length of the defects. These algorithms were trained using large datasets generated with Finite Element Method simulations. The different predictive methods obtained were optimized using Bayesian inference. Using predictive methods generated and based on intrinsic performance results, knowing the material characteristics, the defect length can be predicted from single temperature data in defect and non-defect zone. Thus, the developed algorithms were implemented in a laboratory set-up carried out on ad-hoc manufactured parts of Nylon and polylactic acid which include induced defects with different sizes and thicknesses. Using the trained algorithm, the deviation of the predicted results for the defect size varied between 13% and 37% for PLA and between 13% and 36% for Nylon.

Effect of Carburizing and Nitriding on Fatigue Properties of 18Cr2Ni4WA Steel in Very High Cycle Fatigue Regime

The work aims to study the influence of carburizing and nitriding on fatigue properties of 18Cr2Ni4WA high strength steel in very high cycle fatigue regime. Very high cycle fatigue tests were carried out on 18Cr2Ni4WA Steel after carburizing and nitriding respectively. The micro morphology of fatigue fracture was observed by scanning electron microscope, the failure mode and failure mechanism were discussed. The relationship between fatigue life and defect size, FGA size, fish eye size of fracture was analyzed. The characteristic size of defects is evaluated by Gumbel, Weibull and GEV distribution functions, and a modified Akiniwa fatigue life prediction model considering the relationship between FGA size and inclusion size was established. The results showed that, nitriding and carburizing treatment improve the surface fatigue limit of the steel. The fatigue life decreases with the increase of internal defect size and FGA size. After carburizing and nitriding treatment, the internal fatigue strength of the specimen decreases slightly. When the failure probability is 99%, the internal defect sizes of nitrided specimens calculated by Weibull, Gumbel and GEV distributions are 141.5 μm, 148.4 μm and 211.7 μm respectively. The calculated internal defect sizes of carburized specimens are 47 μm, 67.8 μm and 40 μm respectively. Compared with the experimental data, the fatigue strength predicted by GEV is the most appropriate. carburizing and nitriding treatment can improve the surface fatigue strength of 18Cr2Ni4WA steel, but slightly reduce the internal fatigue strength. The prediction result of the new model is conservative when the failure probability is 99%, which is suitable for engineering application.

A fundamental study on visualization of location and size of internal defect in concrete using radar images and GAN

A fundamental study on visualization of location and size of internal defect in concrete using radar images and GAN

Relationship between internal defect size and fatigue limit in selective laser melted Inconel 718

Relationship between internal defect size and fatigue limit in selective laser melted Inconel 718

An quantitative inspection method for internal defects based on laser ultrasonic technology

This article proposes the use of laser-generated Lr wave to quantitatively detect internal defects in materials. It analyzes the interaction between laser-generated Lr wave and internal defects in detail, considering that the scattered Lr wave generated at different positions of the internal defect reach different detection points, by analyzing the arrival times of the scattered Lr wave at different positions of the internal defect, it can effectively correct quantitative calculation of internal defects. The finite element simulation results show that this method can effectively quantitatively detect the size of internal defect, which provides an effective method for the quantitative detection of internal defects in materials.

Analysis of the effect of surface roughness on fatigue performance of powder bed fusion additive manufactured metals

An important advantage of AM is to create net-shaped components with no need for further surface machining since it is usually very difficult for complex geometries. The effect of surface roughness on fatigue performance of powder bed fusion additively manufactured metals was evaluated in this work. The intrinsic rough surface of metal AM parts that could act like existing surface cracks and significantly affect fatigue performance is investigated. The effect of processing and post-processing conditions on surface roughness of AM parts are reviewed and the effect of surface roughness on fatigue performance is analyzed. The synergistic effect of internal defects and surface roughness on fatigue performance is also evaluated. Arithmetic mean surface roughness parameter Ra is used here as a representation of surface roughness, since this parameter has been presented in most of the studies dealing with metal AM surface roughness. Surface roughness effect on fatigue performance is shown to be dominant even in the presence of relatively large internal defects and various microstructures. Ra decreases with an increase in power. This consequently increases fatigue limit, although scatter is observed due to the secondary effect of internal defects and microstructure. For similar microstructures, considering synergistic effect of Ra along with average critical internal defect size in combination with the stress amplitude, resulted in improved correlation of the S-N fatigue data.

Critical internal defect size for subsurface crack initiation in heavy haul car wheels

Rolling contact fatigue failure is one of the very common causes for the replacement of heavy haul car wheels. There are two crack initiation modes in rolling contact fatigue failures, which are surface and subsurface crack initiation modes. Internal defects such as voids and non–metallic inclusions are known to be the possible origins of subsurface cracks. In this study, torsion and axial fatigue tests are conducted on railway wheel steel with artificial defects, and finite element analyses of heavy haul car wheels are performed to study the subsurface crack initiation due to cyclic rolling contact. The fatigue limits of the wheel steel decrease with an increase in the artificial defect size. The shear and axial fatigue limits with different defect sizes agree well the El–Haddad formula. Based on the finite element analysis considering the multiaxial stress state, the critical defect size for subsurface crack initiation is estimated to be 1.1 mm. This indicates that subsurface cracks might be initiated in service conditions as the critical size is less than 1.6 mm, which is the maximum permissible size of an internal defect in the wheel rim as per Association of American Railroads specifications. Therefore, higher–cleanliness wheels would be required to prevent subsurface cracks.

Study on the cavity closure behavior of steel ingots during open die forging

The manufacturing of sound forgings from large steel ingots requires that internal cavity defects generated during the steel ingot solidification process be compressed by open die forging. The forging ratio that is generally recommended to remove internal defects in large forged products is 3S (threefold); however, the practice lacks a theoretical basis. In this study, a forging experiment and a finite element analysis were performed to investigate the correlation between the forging ratio for large steel ingots (3S) and the cavity closure behavior. First, a hot compression experiment was performed by varying the temperature and strain rate, and the flow stress data observed in the experiment was applied to the finite element analysis. In the experiment for the cogging process, the forging ratio was applied to an actual non-compressive defect material. The finite element analysis was performed using the same forging path as the forging experiment. In the cogging experiment, cavity closure was found by ultrasonic inspection at the forging ratio of 2.9S. The finite element analysis showed that the size of the cavity was significantly decreased at the forging ratio of 2.9S. A finite element analysis was also performed to investigate effective strain and hydrostatic stress at the forging ratio of 2.9S. Finally, this article provides the theoretical basis for the limitation of the internal defect size in initial materials, the threshold effective strain, and the limiting forging ratio of forged products to ensure the internal soundness of large forged products.

Quantitative detection of internal defects based on morphological opening, filling and binarizing operations on wrapped phase of out-of-plane deformation in digital speckle pattern interferometry

A novel method used for quantitative detection of internal defects with boundary of arbitrary shape is proposed in this paper for the first time. This method can be used to determine accurately the location and size of internal defects based on sequential morphological opening, filling and binarizing operations on the wrapped phase of out-of-plane deformation in phase-shifting digital speckle pattern interferometry. Because internal defects are detected directly from a wrapped phase rather than an unwrapped phase, the method proposed in this paper requires neither unwrapping of wrapped phase nor denoising of interference fringes when used for quantitative detection of internal defects. Theoretical analysis, numerical simulation, experimental verification and error calculation are presented in this paper.

Analysis of the effect of deviations in surface preparation technology on the size of internal defects in pulsed-arc welding

Investigations were carried out into the effect of the parameters of pulsed-arc welding on the formation of oxide inclusions when the quality of surface preparation (missing individual areas in grinding) is impaired. The length of the oxide inclusions was estimated on the basis of the ratio of the total length of the oxide films to the length of the welded joint (Σlf/Lw) and the dispersion was estimated by the deviation of the sum of the lengths of the oxide films to their number (Σlf/n). The results show that the largest length of the oxide inclusions was obtained at a gap of 1 mm, but the average length of the oxide films in the weld metal is maximum in the gap size range 1.7–2 mm. The increase of the welding speed reduces the total length of the oxide inclusions. The lowest value of the total length of the oxide inclusions in the weld metal and the smallest average dimensions of the films were recorded in pulsed-arc welding in the conditions with ‘hardness’ of the conditions of 0.7 (τpulse = 0.3 s, τoff = 0.21 s).

Incidence of Associated Brain and Ophthalmic Anomalies in Frontoethmoidal Encephalomeningocele Evaluated by Multidetector Computed Tomography Facial Bone Imaging.

Frontoethmoidal encephalomeningocele (FEEM) is a congenital disorder characterized by herniation of brain and meninges through an anterior skull defect. The main pathological changes are found internally at the foramen cecum and externally at the frontonaso-orbital region. The aim of this study was to determine the incidence of developmental anomalies found in FEEM using multidetector computed tomography images of the facial bone. A total of 78 patients who underwent multidetector computed tomography scan of the facial bone during the January 1, 2003 to June 31, 2012 study period were retrospectively reviewed. Demographic data, size of internal defect, and intracranial anomalies were recorded. Associated brain and ophthalmic anomalies were identified in 53 patients (67.9%), and all of those had brain anomalies. The most common brain anomalies were absent/undetermined septum pellucidum (75.5%), ventricular dilatation (71.7%), abnormal frontal horn (67.9%), and dysgenesis of the corpus callosum (58.5%). Eight patients (10.3%) had ophthalmic anomalies. Patients with brain and ophthalmic anomalies tended to have a higher incidence of large-size internal defects. The authors found a high prevalence of developmental anomalies in FEEM patients. Absent/undetermined septum pellucidum was the most commonly found anomaly in this study. Brain and ophthalmic anomalies tended to have a higher incidence of large-size internal bone defects. Consistent with the authors' acknowledged limitation, further studies using dedicated brain MRI and magnetic resonance angiography to evaluate parenchymal abnormalities and vascular anomalies may be beneficial for surgical planning, prognosis, and the identification of clinical correlations.

The depth measurement of internal defect based on laser speckle shearing interference

Speckle shearing interference has been widely used in non-destructive testing (NDT) as a useful NDT tool for its 阿advantages such as full-field, non-contacting measurement and so on. It reveals internal defect of an object by identifying defect-induced deformation anomalies. The location and size of internal defects are critical factors in determining the stability of the performance and the service life of the workpiece. This paper put forward a method of the depth measurement of internal defect based on laser speckle shearing interference. The measurement of defect depth is achieved by establishing the mechanical model which contains defect depth, out-of-plane displacement and load conditions, etc., and combining the relevant image information obtained from speckle pattern. The measurement error is less than 10%. The experiments demonstrate that it has a good consistency between the actual depth and the measurement result obtained by the method of this paper.

Quantitative detection of size and centroid of internal defect based on Radon transform and morphological operation in phase-shifting digital speckle pattern interferometry

This paper proposes a new method for detecting the size and centroid of an internal defect based on the Radon transform and morphological operation. This method proposed in the paper can be used in phase-shifting digital speckle pattern interferometry to measure quantitatively the size of the internal defect and to determine accurately the centroid of the internal defect. Theoretical analysis, experimental result, and error calculation are presented in this paper.

Proposed Simple Determination Method for Welding Condition of Joint from Fatigue Limit Characteristics (1st Report: Application to TIG-Butt-Joint of Non-combustible Mg Alloy)

The non-combustible Mg alloy is useful as a structural material because of its high specific strength and high ignition point, but its suitable welding conditions have not been established for manufacturing floors. In this study, a simple evaluation method for the fatigue limit characteristics of a welded joint was proposed using the edge shape of the welding bead geometry, the internal defect size and the material characteristics. Moreover, the welding condition parameter ranges to insure a stable fatigue limit for the TIG butt joint of a non-combustible Mg alloy were proposed using this method.

Estimation of internal defect size by means of radial deformations in pipes subjected to internal pressure

Metals like carbon steel are used extensively in pipeline industries due to simplicity and economy. However, flaws such as cracks, pitting, local wall thinning can be generated by corrosion, erosion, and environmental exposure to various substances. In this paper, an analysis of asymmetric radial deformation in pipe with local wall thinning under internal pressure is proposed. The deformation is asymmetric with respect to the axis and consists of a radial displacement of all points in the wall of the pipe. Here, only the vertical and horizontal displacements in pipe are taken into account and they are calculated by means of strain energy method based on the classical Castigliano's theorem. In order to validate the results, a commercially available finite element code is used. The agreement between the theoretical predictions and numerical results is very close. It is found that the internal defect sizes can be estimated knowing the horizontal and vertical displacements.

Axial fatigue of a gas‐nitrided quenched and tempered AISI 4140 steel: effect of nitriding depth

ABSTRACTFatigue testing under fully reversed axial loading (R=−1) and zero‐to‐tension axial loading (R= 0) was carried out on AISI 4140 gas‐nitrided smooth specimens. Three different treatment durations were investigated in order to assess the effect of nitriding depth on fatigue strength in high cycle fatigue. Complete specimens characterization, i.e., hardness and residual stresses profiles (including measurement of stabilized residual stresses) as well as metallographic and fractographic observations, was achieved to analyse fatigue behaviour. Fatigue of the nitrided steel is a competition between a surface crack growing in a compressive residual stress field and an internal crack or ‘fish‐eye’ crack growing in vacuum. Fatigue life increases with nitriding depth until surface cracking is slow enough for failure to occur from an internal crack. Unlike bending, in axial fatigue ‘fish‐eye’ cracks can initiate anywhere in the core volume under uniform stress. In these conditions, axial fatigue performance is lower than that obtained under bending and nitriding depth may have no more influence. In order to interpret the results, special attention was given to the effects of compressive residual stresses on the surface short crack growth (closure effect) as well as the effects of internal defect size on internal fatigue lives. A superimposed tensile mean stress reduces the internal fatigue strength of nitrided steel more than the surface fatigue strength of the base metal. Both cracking mechanisms are not equally sensitive to mean stress.